EyeLink Eye Trackers in Clinical and Oculomotor Publications

@article{Kloke2009,

title = {Microsaccades under monocular viewing conditions},

author = {Wilhelm Bernhard Kloke and Wolfgang Jaschinski and Stephanie Jainta},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Eye Movement Research},

volume = {3},

number = {1},

pages = {1–7},

abstract = {Among the eye movements during fixation, the function of small saccades occuring quite commonly at fixation is still unclear. It has been reported that a substantial number of these microsaccades seem to occur in only one of the eyes. The aim of the present study is to investigate microsaccades in monocular stimulation conditions. Although this is an artificial test condition which does not occur in natural vision, this monocular presentation paradigm allows for a critical test of a presumptive monoc- ular mechanism of saccade generation. Results in these conditions can be compared with the normal binocular stimulation mode. We checked the statistical properties of microsaccades under monocular stimulation conditions and found no indication for specific interactions for monocularly detected small saccades, which might be present if they were based on a monocular physiological activation mechanism.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Knapp2009,

title = {Effect of distance upon horizontal and vertical look and stare OKN},

author = {Christopher M. Knapp and Irene Gottlob and Rebecca J. McLean and Suzzane Rafelt and Frank A. Proudlock},

doi = {10.1167/9.12.23},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Vision},

volume = {9},

number = {12},

pages = {1–9},

abstract = {Previous reports suggest that distance influences horizontal stare OKN gains; however, the effect of distance on vertical OKN and look OKN is unknown. Horizontal and vertical look and stare OKN gains were recorded in 16 healthy volunteers (velocity 38.4 degrees /s) at three distances (0.3 m, 1 m, and 2.5 m) and two different stimulus sizes. Asymmetry of responses and correlation of gains in different directions were compared. Measurements at near were compared with and without glasses. Distance did not significantly affect horizontal look and stare OKN or vertical look OKN, however, downward stare OKN gains were reduced at greater distances (p = 0.002). Mean downward stare OKN gains recorded in each individual were strongly correlated to leftward and rightward gains but not upward gains. In contrast, upward OKN gains were not correlated to gains in leftward, rightward, or downward directions. Downward stare OKN responses are significantly sensitive to the effects of distance, whereas stare OKN in other directions and look OKN responses in all directions are not. Individual mean downward stare OKN gains are more closely related to horizontal responses rather than upward responses. This suggests that the downward OKN system is more functionally related to the horizontal system rather than the upward OKN system.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ludwig2009a,

title = {The mechanism underlying inhibition of saccadic return},

author = {Casimir J. H. Ludwig and Simon Farrell and Lucy A. Ellis and Iain D. Gilchrist},

doi = {10.1016/j.cogpsych.2009.04.002},

year  = {2009},

date = {2009-01-01},

journal = {Cognitive Psychology},

volume = {59},

number = {2},

pages = {180–202},

publisher = {Elsevier Inc.},

abstract = {Human observers take longer to re-direct gaze to a previously fixated location. Although there has been some exploration of the characteristics of inhibition of saccadic return (ISR), the exact mechanisms by which ISR operates are currently unknown. In the framework of accumulation models of response times, in which evidence is integrated over time to a response threshold, ISR could reflect a reduction in the rate of accumulation for saccades to return locations or an increase in the effective criterion for response. In two experiments, participants generated sequences of three saccades, in response to a peripheral or a central cue. ISR occurred across these manipulations: saccade latency was consistently increased for movements to the immediately previously fixated location. Latency distributions from individual observers were fit with a Linear Ballistic Accumulator model. ISR was best accounted for as a change in the accumulation rate. We suggest this parameter represents the overall desirability of a particular course of action, the evidence for which may be derived from a variety of sensory and non-sensory sources.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{McKyton2009,

title = {Pattern matching is assessed in retinotopic coordinates},

author = {Ayelet McKyton and Yoni Pertzov and Ehud Zohary},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Vision},

volume = {9},

number = {13},

pages = {1–10},

abstract = {We typically examine scenes by performing multiple saccades to different objects of interest within the image. Therefore, an extra-retinotopic representation, invariant to the changes in the retinal image caused by eye movements, might be useful for high-level visual processing. We investigate here, using a matching task, whether the representation of complex natural images is retinotopic or screen-based. Subjects observed two simultaneously presented images, made a saccadic eye movement to a new fixation point, and viewed a third image. Their task was to judge whether the third image was identical to one of the two earlier images or different. Identical images could appear either in the same retinotopic position, in the same screen position, or in totally different locations. Performance was best when the identical images appeared in the same retinotopic position and worst when they appeared in the opposite hemifield. Counter to commonplace intuition, no advantage was conferred from presenting the identical images in the same screen position. This, together with performance sensitivity for image translation of a few degrees, suggests that image matching, which can often be judged without overall recognition of the scene, is mostly determined by neuronal activity in earlier brain areas containing a strictly retinotopic representation and small receptive fields.},

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pubstate = {published},

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}

@article{McSorley2009b,

title = {The development of the spatial extent of oculomotor inhibition},

author = {Eugene McSorley and Alice G. Cruickshank and Laura A. Inman},

doi = {10.1016/j.brainres.2009.08.081},

year  = {2009},

date = {2009-01-01},

journal = {Brain Research},

volume = {1298},

pages = {92–98},

publisher = {Elsevier B.V.},

abstract = {Inhibition is intimately involved in the ability to select a target for a goal-directed movement. The effect of distracters on the deviation of oculomotor trajectories and landing positions provides evidence of such inhibition. Individual saccade trajectories and landing positions may deviate initially either towards, or away from, a competing distracter-the direction and extent of this deviation depends upon saccade latency and the target to distracter separation. However, the underlying commonality of the sources of oculomotor inhibition has not been investigated. Here we report the relationship between distracter-related deviation of saccade trajectory, landing position and saccade latency. Observers saccaded to a target which could be accompanied by a distracter shown at various distances from very close (10 angular degrees) to far away (120 angular degrees). A fixation-gap paradigm was used to manipulate latency independently of the influence of competing distracters. When distracters were close to the target, saccade trajectory and landing position deviated toward the distracter position, while at greater separations landing position was always accurate but trajectories deviated away from the distracters. Different spatial patterns of deviations across latency were found. This pattern of results is consistent with the metrics of the saccade reflecting coarse pooling of the ongoing activity at the distracter location: saccade trajectory reflects activity at saccade initiation while landing position reveals activity at saccade end.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{McSorley2009,

title = {The spatial and temporal shape of oculomotor inhibition},

author = {Eugene McSorley and Patrick Haggard and Robin Walker},

doi = {10.1016/j.visres.2009.01.015},

year  = {2009},

date = {2009-01-01},

journal = {Vision Research},

volume = {49},

number = {6},

pages = {608–614},

publisher = {Elsevier Ltd},

abstract = {Selecting a stimulus as the target for a goal-directed movement involves inhibiting other competing possible responses. Inhibition has generally proved hard to study behaviorally, because it results in no measurable output. The effect of distractors on the shape of oculomotor and manual trajectories provide evidence of such inhibition. Individual saccades may deviate initially either towards, or away from, a competing distractor - the direction and extent of this deviation depends upon saccade latency, target predictability and the target to distractor separation. The experiment reported here used these effects to show how inhibition of distractor locations develops over time. Distractors could be presented at various distances from unpredictable and predictable targets in two separate experiments. The deviation of saccade trajectories was compared between trials with and without distractors. Inhibition was measured by saccade trajectory deviation. Inhibition was found to increase as the distractor distance from target decreased but was found to increase with saccade latency at all distractor distances (albeit to different peaks). Surprisingly, no differences were found between unpredictable and predictable targets perhaps because our saccade latencies were generally long (∼260-280 ms.). We conclude that oculomotor inhibition of saccades to possible target objects involves the same mechanisms for all distractor distances and target types.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Montagnini2009,

title = {Dynamic interaction between "Go" and "Stop" signals in the saccadic eye movement system: New evidence against the functional independence of the underlying neural mechanisms},

author = {Anna Montagnini and Leonardo Chelazzi},

doi = {10.1016/j.visres.2008.07.018},

year  = {2009},

date = {2009-01-01},

journal = {Vision Research},

volume = {49},

number = {10},

pages = {1316–1328},

publisher = {Elsevier Ltd},

abstract = {We investigated human oculomotor behaviour in a Go-NoGo saccadic task in which the saccadic response to a peripheral visual target was to be inhibited in a minority of trials (NoGo trials). Different from classical experimental paradigms on the inhibitory control of intended actions, in our task the inhibitory cue was identical to the saccadic target (used in Go trials) in timing, location and shape-the only difference being its colour. By analysing the latency and the metrics of saccades erroneously executed after a NoGo instruction (NoGo-escapes), we observed a characteristic pattern of performance: first, we observed a decrease in the amplitude of NoGo-escapes with increasing latency; second, we revealed a consistent population of long-latency small saccades opposite in direction to the NoGo cue; finally, we found a strong side-specific inhibitory effect in terms of saccadic reaction times, on trials immediately following a NoGo trial. In addition, we manipulated the readiness to initiate a saccade towards the visual target, by introducing a probability bias in the random sequence of target locations. We found that the capacity to inhibit the impending saccade was improved for the most likely target location, i.e. the condition corresponding to the increased readiness for movement execution. Overall, our results challenge the notion of a central inhibitory mechanism independent from movement preparation. More precisely, they indicate that the two mechanisms (action preparation and action inhibition) interact dynamically, possibly sharing spatially-specific mechanisms, and are similarly affected by particular contextual manipulations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Morvan2009,

title = {The nonlinear structure of motion perception during smooth eye movements},

author = {Camille Morvan and Mark Wexler},

doi = {10.1167/9.7.1},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Vision},

volume = {9},

number = {7},

pages = {1–13},

abstract = {To perceive object motion when the eyes themselves undergo smooth movement, we can either perceive motion directly-by extracting motion relative to a background presumed to be fixed-or through compensation, by correcting retinal motion by information about eye movement. To isolate compensation, we created stimuli in which, while the eye undergoes smooth movement due to inertia, only one object is visible-and the motion of this stimulus is decoupled from that of the eye. Using a wide variety of stimulus speeds and directions, we rule out a linear model of compensation, in which stimulus velocity is estimated as a linear combination of retinal and eye velocities multiplied by a constant gain. In fact, we find that when the stimulus moves in the same direction as the eyes, there is little compensation, but when movement is in the opposite direction, compensation grows in a nonlinear way with speed. We conclude that eye movement is estimated from a combination of extraretinal and retinal signals, the latter based on an assumption of stimulus stationarity. Two simple models, in which the direction of eye movement is computed from the extraretinal signal and the speed from the retinal signal, account well for our results.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mulckhuyse2009,

title = {Early and late modulation of saccade deviations by target distractor similarity},

author = {Mulckhuyse Mulckhuyse and Stefan Van der Stigchel and Jan Theeuwes},

doi = {10.1152/jn.00068.2009},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Neurophysiology},

volume = {102},

number = {3},

pages = {1451–1458},

abstract = {In this study, we investigated the time course of oculomotor competition between bottom-up and top-down selection processes using saccade trajectory deviations as a dependent measure. We used a paradigm in which we manipulated saccade latency by offsetting the fixation point at different time points relative to target onset. In experiment 1, observers made a saccade to a filled colored circle while another irrelevant distractor circle was presented. The distractor was either similar (i.e., identical) or dissimilar to the target. Results showed that the strength of saccade deviation was modulated by target distractor similarity for short saccade latencies. To rule out the possibility that the similar distractor affected the saccade trajectory merely because it was identical to the target, the distractor in experiment 2 was a square shape of which only the color was similar or dissimilar to the target. The results showed that deviations for both short and long latencies were modulated by target distractor similarity. When saccade latencies were short, we found less saccade deviation away from a similar than from a dissimilar distractor. When saccade latencies were long, the opposite pattern was found: more saccade deviation away from a similar than from a dissimilar distractor. In contrast to previous findings, our study shows that task-relevant information can already influence the early processes of oculomotor control. We conclude that competition between saccadic goals is subject to two different processes with different time courses: one fast activating process signaling the saliency and task relevance of a location and one slower inhibitory process suppressing that location.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Munuera2009,

title = {Optimal sensorimotor control in eye movement sequences},

author = {Jérôme Munuera and Pierre Morel and Jean-Rene Duhamel and Sophie Deneve},

doi = {10.1523/JNEUROSCI.1169-08.2009},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Neuroscience},

volume = {29},

number = {10},

pages = {3026–3035},

abstract = {Fast and accurate motor behavior requires combining noisy and delayed sensory information with knowledge of self-generated body motion; much evidence indicates that humans do this in a near-optimal manner during arm movements. However, it is unclear whether this principle applies to eye movements. We measured the relative contributions of visual sensory feedback and the motor efference copy (and/or proprioceptive feedback) when humans perform two saccades in rapid succession, the first saccade to a visual target and the second to a memorized target. Unbeknownst to the subject, we introduced an artificial motor error by randomly "jumping" the visual target during the first saccade. The correction of the memory-guided saccade allowed us to measure the relative contributions of visual feedback and efferent copy (and/or proprioceptive feedback) to motor-plan updating. In a control experiment, we extinguished the target during the saccade rather than changing its location to measure the relative contribution of motor noise and target localization error to saccade variability without any visual feedback. The motor noise contribution increased with saccade amplitude, but remained <30% of the total variability. Subjects adjusted the gain of their visual feedback for different saccade amplitudes as a function of its reliability. Even during trials where subjects performed a corrective saccade to compensate for the target-jump, the correction by the visual feedback, while stronger, remained far below 100%. In all conditions, an optimal controller predicted the visual feedback gain well, suggesting that humans combine optimally their efferent copy and sensory feedback when performing eye movements.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nummenmaa2009,

title = {Emotional scene content drives the saccade generation system reflexively},

author = {Lauri Nummenmaa and Jukka Hyönä and Manuel G. Calvo},

doi = {10.1037/a0013626},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Experimental Psychology: Human Perception and Performance},

volume = {35},

number = {2},

pages = {305–323},

abstract = {The authors assessed whether parafoveal perception of emotional content influences saccade programming. In Experiment 1, paired emotional and neutral scenes were presented to parafoveal vision. Participants performed voluntary saccades toward either of the scenes according to an imperative signal (color cue). Saccadic reaction times were faster when the cue pointed toward the emotional picture rather than toward the neutral picture. Experiment 2 replicated these findings with a reflexive saccade task, in which abrupt luminosity changes were used as exogenous saccade cues. In Experiment 3, participants performed vertical reflexive saccades that were orthogonal to the emotional-neutral picture locations. Saccade endpoints and trajectories deviated away from the visual field in which the emotional scenes were presented. Experiment 4 showed that computationally modeled visual saliency does not vary as a function of scene content and that inversion abolishes the rapid orienting toward the emotional scenes. Visual confounds cannot thus explain the results. The authors conclude that early saccade target selection and execution processes are automatically influenced by emotional picture content. This reveals processing of meaningful scene content prior to overt attention to the stimulus.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nuthmann2009a,

title = {An examination of binocular reading fixations based on sentence corpus data},

author = {Antje Nuthmann and Reinhold Kliegl},

doi = {10.1167/9.5.31},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Vision},

volume = {9},

number = {5},

pages = {31–31},

abstract = {Binocular eye movements of normal adult readers were examined as they read single sentences. Analyses of horizontal and vertical fixation disparities indicated that the most prevalent type of disparate fixation is crossed (i.e., the left eye is located further to the right than the right eye) while the left eye frequently fixates somewhat above the right eye. The Gaussian distribution of the binocular fixation point peaked 2.6 cm in front of the plane of text, reflecting the prevalence of horizontally crossed fixations. Fixation disparity accumulates during the course of successive saccades and fixations within a line of text, but only to an extent that does not compromise single binocular vision. In reading, the version and vergence system interact in a way that is qualitatively similar to what has been observed in simple nonreading tasks. Finally, results presented here render it unlikely that vergence movements in reading aim at realigning the eyes at a given saccade target word.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Panouilleres2009,

title = {Behavioural evidence of separate adaptation mechanisms controlling saccade amplitude lengthening and shortening},

author = {Muriel T. N. Panouillères and Tiffany Weiss and Christian Urquizar and Roméo Salemme and Douglas P. Munoz and Denis Pélisson},

doi = {10.1152/jn.90988.2008},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Neurophysiology},

volume = {101},

number = {3},

pages = {1550–1559},

abstract = {The accuracy of saccadic eye movements is maintained over the long term by adaptation mechanisms that decrease or increase saccade amplitude. It is still unknown whether these opposite adaptive changes rely on common mechanisms. Here, a double-step target paradigm was used to adaptively decrease (backward second target step) or increase (forward step) the amplitude of reactive saccades in one direction only. To test which sensorimotor transformation stages are subjected to these adaptive changes, we measured their transfer to antisaccades in which sensory and motor vectors are spatially dissociated. In the backward adaptation condition, all subjects showed a significant amplitude decrease for adapted prosaccades and a significant transfer of adaptation to antisaccades performed in the adapted direction, but not to oppositely directed antisaccades elicited by a target jump in the adapted direction. In the forward adaptation condition, only 14 of 19 subjects showed a significant amplitude increase for prosaccades and no significant adaptation transfer to antisaccades was detected in either the adapted or nonadapted direction. These findings suggest that, whereas the level(s) of forward adaptation cannot be resolved, the mechanisms involved in backward adaptation of reactive saccades take place at a sensorimotor level downstream from the vector inversion process of antisaccades and differ markedly from those involved in forward adaptation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Roth2009,

title = {Comparing explorative saccade and flicker training in hemianopia: A randomized controlled study},

author = {T. Roth and Alexander N. Sokolov and A. Messias and P. Roth and M. Weller and Susanne Trauzettel-Klosinski},

year  = {2009},

date = {2009-01-01},

journal = {Neurology},

volume = {72},

pages = {324–331},

abstract = {Objective: Patients with homonymous hemianopia are disabled on everyday exploratory activities. We examined whether explorative saccade training (EST), compared with flicker-stimulation training (FT), would selectively improve saccadic behavior on the patients' blind side and benefit performance on natural exploratory tasks. Methods: Twenty-eight hemianopic patients were randomly assigned to distinct groups performing for 6 weeks either EST (a digit-search task) or FT (blind-hemifield stimulation by flickering letters). Outcome variables (response times [RTs] during natural search, number of fixations during natural scene exploration, fixation stability, visual fields, and quality-of-life scores) were collected before, directly after, and 6 weeks after training. Results: EST yielded a reduced (post/pre, 47%) digit-search RT for the blind side. Natural search RT decreased (post/pre, 23%) on the blind side but not on the seeing side. After FT, both sides' RT remained unchanged. Only with EST did the number of fixations during natural scene exploration increase toward the blind and decrease on the seeing side (follow-up/pre difference, 238%). Even with the target located on the seeing side, after EST more fixations occurred toward the blind side. The EST group showed decreased (post/pre, 43%) fixation stability and increased (post/pre, 482%) asymmetry of fixations toward the blind side. Visual field size remained constant after both treatments. EST patients reported improvements in social domain. Conclusions: Explorative saccade training selectively improves saccadic behavior, natural search, and scene exploration on the blind side. Flicker-stimulation training does not improve saccadic behavior or visual fields. The findings show substantial benefits of compensatory exploration training, including subjective improvements in mastering daily-life activities, in a randomized controlled trial.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{sbg09,

title = {Object recognition during foveating eye movements},

author = {Alexander C. Schütz and Doris I. Braun and Karl R. Gegenfurtner},

doi = {10.1016/j.visres.2009.05.022},

year  = {2009},

date = {2009-01-01},

journal = {Vision Research},

volume = {49},

number = {18},

pages = {2241–2253},

publisher = {Elsevier Ltd},

abstract = {We studied how saccadic and smooth pursuit eye movements affect the recognition of briefly presented letters appearing within the eye movement target. First we compared the recognition performance during steady-state pursuit and during fixation. Single letters were presented for seven different durations ranging from 10 to 400 ms and four contrast levels ranging from 5% to 40%. For both types of eye movements the recognition rates increased with duration and contrast, but they were on average 11% lower during pursuit. In daily life humans use a combination of saccadic and smooth pursuit eye movements to foveate a peripheral moving object. To investigate this more natural situation, we presented a peripheral target that was either stationary or moving horizontally, above or below the fixation spot. Participants were asked to saccade to the target and to keep it foveated. The letters were presented at different times relative to the first target directed saccade. As would be expected from retinal masking and motion blur during saccades, the discrimination performance increased with increasing post-saccadic delay. If the target moved and the saccade was followed by pursuit, letter recognition performance was on average 16% lower than if the target was stationary and the saccade was followed by fixation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Schutz2009,

title = {Chromatic contrast sensitivity during optokinetic nystagmus, visually enhanced vestibulo-ocular reflex, and smooth pursuit eye movements},

author = {Alexander C. Schütz and Doris I. Braun and Karl R. Gegenfurtner},

doi = {10.1152/jn.91248.2008},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Neurophysiology},

volume = {101},

number = {5},

pages = {2317–2327},

abstract = {Recently we showed that sensitivity for chromatic- and high-spatial frequency luminance stimuli is enhanced during smooth-pursuit eye movements (SPEMs). Here we investigated whether this enhancement is a general property of slow eye movements. Besides SPEM there are two other classes of eye movements that operate in a similar range of eye velocities: the optokinetic nystagmus (OKN) is a reflexive pattern of alternating fast and slow eye movements elicited by wide-field visual motion and the vestibulo-ocular reflex (VOR) stabilizes the gaze during head movements. In a natural environment all three classes of eye movements act synergistically to allow clear central vision during self- and object motion. To test whether the same improvement of chromatic sensitivity occurs during all of these eye movements, we measured human detection performance of chromatic and luminance line stimuli during OKN and contrast sensitivity during VOR and SPEM at comparable velocities. For comparison, performance in the same tasks was tested during fixation. During the slow phase of OKN we found a similar enhancement of chromatic detection rate like that during SPEM, whereas no enhancement was observable during VOR. This result indicates similarities between slow-phase OKN and SPEM, which are distinct from VOR.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{sbkg08,

title = {Improved visual sensitivity during smooth pursuit eye movements: Temporal and spatial characteristics},

author = {Alexander C. Schütz and Doris I. Braun and Karl R. Gegenfurtner and Alexander C. Schu},

doi = {10.1017/S0952523809990083},

year  = {2009},

date = {2009-01-01},

journal = {Visual Neuroscience},

volume = {26},

number = {3},

pages = {329–340},

abstract = {Recently, we showed that contrast sensitivity for color and high–spatial frequency luminance stimuli is enhanced during smooth pursuit eye movements (Schütz et al., 2008). In this study, we investigated the enhancement over a wide range of temporal and spatial frequencies. In Experiment 1, we measured the temporal impulse response function (TIRF) for colored stimuli. The TIRF for pursuit and fixation differed mostly with respect to the gain but not with respect to the natural temporal frequency. Hence, the sensitivity enhancement seems to be rather independent of the temporal frequency of the stimuli. In Experiment 2, we measured the spatial contrast sensitivity function for luminance-defined Gabor patches with spatial frequencies ranging from 0.2 to 7 cpd. We found a sensitivity improvement during pursuit for spatial frequencies above 2–3 cpd. Between 0.5 and 3 cpd, sensitivity was impaired by smooth pursuit eye movements, but no consistent difference was observed below 0.5 cpd. The results of both experiments are consistent with an increased contrast gain of the parvocellular retinogeniculate pathway.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{sk09,

title = {Involuntary cueing effects during smooth pursuit: Facilitation and inhibition of return in oculocentric coordinates},

author = {David Souto and Dirk Kerzel},

doi = {10.1007/s00221-008-1555-x},

year  = {2009},

date = {2009-01-01},

journal = {Experimental Brain Research},

volume = {192},

number = {1},

pages = {25–31},

abstract = {Peripheral cues induce facilitation with short cue-target intervals and inhibition of return (IOR) with long cue-target intervals. Modulations of facilitation and IOR by continuous displacements of the eye or the cued stimuli are poorly understood. Previously, the retinal coordinates of the cued location were changed by saccadic or smooth pursuit eye movements during the cue-target interval. In contrast, we probed the relevant coordinates for facilitation and IOR by orthogonally varying object motion (stationary, moving) and eye movement (fixation, smooth pursuit). In the pursuit conditions, cue and target were presented during the ongoing eye movement and observers made a saccade to the target. Importantly, we found facilitation and IOR of similar size during smooth pursuit and fixation. The results suggest that involuntary orienting is possible even when attention has to be allocated to the moving target during smooth pursuit. Comparison of conditions with stabilized and moving objects suggest an oculocentric basis for facilitation as well as inhibition. Facilitation and IOR were reduced with objects that moved on the retina both with smooth pursuit and eye fixation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Souto2009,

title = {Evidence for an attentional component in saccadic inhibition of return},

author = {David Souto and Dirk Kerzel},

doi = {10.1007/s00221-009-1824-3},

year  = {2009},

date = {2009-01-01},

journal = {Experimental Brain Research},

volume = {195},

number = {4},

pages = {531–540},

abstract = {After presentation of a peripheral cue, facilitation at the cued location is followed by inhibition of return (IOR). It has been recently proposed that IOR may originate at different processing stages for manual and ocular responses, with manual IOR resulting from inhibited attentional orienting, and ocular IOR resulting form inhibited motor preparation. Contrary to this interpretation, we found an effect of target contrast on saccadic IOR. The effect of contrast decreased with increasing reaction times (RTs) for saccades, but not for manual key-press responses. This may have masked the effect of contrast on IOR with saccades in previous studies (Hunt and Kingstone in J Exp Psychol Hum Percept Perform 29:1068-1074, 2003) because only mean RTs were considered. We also found that background luminance strongly influenced the effects of gap and target contrast on IOR.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Starzynski2009,

title = {Noise-enhanced target discrimination under the influence of fixational eye movements and external noise},

author = {Christian Starzynski and Ralf Engbert},

doi = {10.1063/1.3098950},

year  = {2009},

date = {2009-01-01},

journal = {Chaos},

volume = {19},

number = {1},

pages = {1–7},

abstract = {Active motor processes are present in many sensory systems to enhance perception. In the human visual system, miniature eye movements are produced involuntarily and unconsciously when we fixate a stationary target. These fixational eye movements represent self-generated noise which serves important perceptual functions. Here we investigate fixational eye movements under the influence of external noise. In a two-choice discrimination task, the target stimulus performed a random walk with varying noise intensity. We observe noise-enhanced discrimination of the target stimulus characterized by a U-shaped curve of manual response times as a function of the diffusion constant of the stimulus. Based on the experiments, we develop a stochastic information-accumulator model for stimulus discrimination in a noisy environment. Our results provide a new explanation for the constructive role of fixational eye movements in visual perception.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Stritzke2009,

title = {Effects of salience and reward information during saccadic decisions under risk},

author = {Martin Stritzke and Julia Trommershäuser and Karl R. Gegenfurtner},

doi = {10.1364/JOSAA.26.0000B1},

year  = {2009},

date = {2009-01-01},

journal = {Journal of the Optical Society of America A},

volume = {26},

number = {11},

pages = {B1–B13},

abstract = {Previous work has demonstrated that humans select visuomotor strategies maximizing expected gain during speeded hand movements under risk; see, e.g., [Trends Cogn. Sci. 12, 291 (2008)]; [Glimcher, eds., Neuroeconomics: Decision Making and the Brain (Elsevier, 2008), p. 95]. Here we report a similar study in which we recorded saccadic eye movements in a saccadic decision task in which monetary rewards and losses were associated with the final position of the eye movement. Saccades into a color-coded target region won points; saccades into a partially overlapping or abutting penalty region could yield a loss. The points won during the experiment were converted into a small monetary bonus at the end of the experiment. We compared participants' winnings to the score of an optimal observer maximizing expected gain that was calculated based on each participant's saccadic endpoint variability, similar to a recent model of optimal movement planning under risk [J. Opt. Soc. Am. A 20, 1419 (2003)]; [Spatial Vis. 16, 255 (2003)]. We used three different experimental paradigms with different interstimulus intervals (Gap, No Gap, and Overlap) to manipulate saccadic latencies and a fourth experiment (Memory) with a prolonged 500 ms delay period. Our results show that our subjects took the reward information, as specified by the different penalties, into account when making saccades and fixated onto or very close to the target region and less into the penalty region. However, the selected strategies differed significantly from optimal strategies maximizing expected gain in conditions when the magnitude of reward or penalty was changed. Furthermore, scores were notably affected by stimulus saliency. They were higher when the target region was filled and the penalty region outlined by a thin line, as compared to conditions in which the target was indicated by a less salient stimulus. Scores were particularly poor in trials with the shortest latencies (120-140 ms) mostly obtained in the Gap paradigm. At longer latencies scores improved considerably for latencies longer than 160 ms. This was in line with an improvement in accuracy for single targets up to 160 ms. Our results indicate that processing both of reward information and of stimulus saliency affect the programming of saccades, with a dominating contribution of stimulus saliency for eye movements with faster latencies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tavassoli2009,

title = {Dynamics of smooth pursuit maintenance},

author = {Abtine Tavassoli and Dario L. Ringach},

doi = {10.1152/jn.91320.2008},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Neurophysiology},

volume = {102},

number = {1},

pages = {110–118},

abstract = {Smooth pursuit eye movements allow the approximate stabilization of a moving visual target on the retina. To study the dynamics of smooth pursuit, we measured eye velocity during the visual tracking of a Gabor target moving at a constant velocity plus a noisy perturbation term. The optimal linear filter linking fluctuations in target velocity to evoked fluctuations in eye velocity was computed. These filters predicted eye velocity to novel stimuli in the 0- to 15-Hz band with good accuracy, showing that pursuit maintenance is approximately linear under these conditions. The shape of the filters were indicative of fast dynamics, with pure delays of merely approximately 67 ms, times-to-peak of approximately 115 ms, and effective integration times of approximately 45 ms. The gain of the system, reflected in the amplitude of the filters, was inversely proportional to the size of the velocity fluctuations and independent of the target mean speed. A modest slow-down of the dynamics was observed as the contrast of the target decreased. Finally, the temporal filters recovered during fixation and pursuit were similar in shape, supporting the notion that they might share a common underlying circuitry. These findings show that the visual tracking of moving objects by the human eye includes a reflexive-like pathway with high contrast sensitivity and fast dynamics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Valsecchi2009,

title = {Microsaccadic responses in a bimodal oddball task},

author = {Matteo Valsecchi and Massimo Turatto},

doi = {10.1007/s00426-008-0142-x},

year  = {2009},

date = {2009-01-01},

journal = {Psychological Research},

volume = {73},

number = {1},

pages = {23–33},

abstract = {In a visual oddball task the presentation of rare targets induces a prolonged microsaccadic inhibition as compared to standards. Here, we replicated this effect also in the auditory modality. In addition, although auditory standards induced a more limited modulation of microsaccadic frequency as compared to visual standards, auditory oddballs induced a prolonged microsaccadic inhibition. With bimodal standard stimuli the microsaccadic response was determined by the attended modality, resembling that produced by attended unimodal stimuli. The present findings support the idea that the microsaccadic response to oddball and standard stimuli is partly driven by cognitive mechanisms common to both the visual and the auditory modality, and that microsaccades can be used as an implicit behavioral measure of ongoing cognitive processes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{VanderStigchel2009,

title = {Eye cannot see it: The interference of subliminal distractors on saccade metrics},

author = {Stefan Van der Stigchel and Manon Mulckhuyse and Jan Theeuwes},

doi = {10.1016/j.visres.2009.05.018},

year  = {2009},

date = {2009-01-01},

journal = {Vision Research},

volume = {49},

number = {16},

pages = {2104–2109},

publisher = {Elsevier Ltd},

abstract = {The present study investigated whether subliminal (unconsciously perceived) visual information influences eye movement metrics, like saccade trajectories and endpoints. Participants made eye movements upwards and downwards while a subliminal distractor was presented in the periphery. Results showed that the subliminal distractor interfered with the execution of an eye movement, although the effects were smaller compared to a control experiment in which the distractor was presented supraliminal. Because saccade metrics are mediated by low level brain areas, this indicates that subliminal visual information evokes competition at a very low level in the oculomotor system.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vernet2009,

title = {Binocular motor coordination during saccades and fixations while reading: A magnitude and time analysis},

author = {Marine Vernet},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Vision},

volume = {9},

number = {2009},

pages = {1–13},

abstract = {Reading involves saccades and fixations. Misalignment of the eyes should be small enough to allow sensory fusion. Recent studies reported disparity of the eyes during fixations. This study examines disconjugacy, i.e. change in disparity over time, both during saccades and fixations. Text reading saccades and saccades to single targets of similar sizes (2.5-) are compared. Young subjects were screened to avoid problems of binocular vision and oculomotor vergence. The results show high quality of motor binocular coordination in both tasks: the amplitude difference between the saccade of the eyes was approximately 0.16-; during the fixation period, the drift difference was only 0.13-. The disconjugate drift occurred mainly during the first 48 ms of fixation, was equally distributed to the eyes and was often reducing the saccade disconjugacy. Quality of coordination regardless of the task is indicative of robust physiological mechanisms. We suggest the existence of active binocular control mechanisms in which vergence signals may have a central role. Even computation of saccades may be based on continuous interaction between saccade and vergence.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vernet2009a,

title = {Switching between gap and overlap pro-saccades: Cost or benefit?},

author = {Marine Vernet and Qing Yang and Marie Gruselle and Mareike Trams and Zoï Kapoula},

doi = {10.1007/s00221-009-1887-1},

year  = {2009},

date = {2009-01-01},

journal = {Experimental Brain Research},

volume = {197},

number = {1},

pages = {49–58},

abstract = {Triggering of saccades depends on the task: in the gap task, fixation point switches off and target appears after a gap period; in the overlap task, target appears while fixation point is still on. Saccade latencies are shorter in the gap task, due to fixation disengagement and advanced movement preparation during the gap. The two modes of initiation are also hypothesized to be subtended by different cortical-subcortical circuits. This study tested whether interleaving the two tasks modifies latencies, due to switching between different modes of triggering. Two groups of healthy participants (21-29 vs. 39-55 years) made horizontal and vertical saccades in gap, overlap, and mixed tasks; saccades were recorded with the Eyelink. Both groups showed shorter latencies in the gap task, i.e. a robust gap effect and systematic differences between directions. For young adults, interleaving tasks made the latencies shorter or longer depending on direction, while for middle-age adults, latencies became longer for all directions. Our observations can be explained in the context of models such as that of Brown et al. (Neural Netw 17:471-510, 2004), which proposed that different combinations of frontal eye field (FEF) layers, interacting with cortico-subcortical areas, control saccade triggering in gap and overlap trials. Moreover, we suggest that in early adulthood, the FEF is functioning optimally; frequent changes of activity in the FEF can be beneficial, leading to shorter latencies, at least for some directions. However, for middle-age adults, frequent changes of activity of a less optimally functioning FEF can be time consuming. Studying the alternation of gap and overlap tasks provides a fine tool to explore development, aging and disease.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Wagner2009,

title = {Vergence in reverspective: Percept-driven versus data-driven eye movement control},

author = {Michael Wagner and Walter H. Ehrenstein and Thomas V. Papathomas},

doi = {10.1016/j.neulet.2008.10.093},

year  = {2009},

date = {2009-01-01},

journal = {Neuroscience Letters},

volume = {449},

number = {2},

pages = {142–146},

abstract = {'Reverspectives' (by artist Patrick Hughes) consist of truncated pyramids with their small faces closer to the viewer, allowing realistic scenes to be painted on them. Because their pictorial perspective reverses the physical depth arrangement, reverspectives provide a bistable paradigm of two radically different, competing depth percepts, even when viewed binocularly: points that are physically further are perceived to be closer and vice versa. The key question addressed here is whether vergence is governed by the physical and/or the perceived depth of fixated targets. Vergence eye movements were recorded using the EyeLink II system under conditions optimized to obtain both the veridical and illusory depth percepts of a reverspective. Six gaze locations were signaled by LEDs placed at strategically selected depths on the stimulus surface. We obtained strong evidence that stable vergence fixations were governed by the percept: for the same LED position, eyes converged under veridical depth percepts and diverged under illusory percepts, thus rendering pictorial cues to be as effective as physical cues in vergence control. These results, obtained with stable fixations, do not disagree with earlier studies that found rapid fixational eye movements to be governed by physical depth cues. Together, these results allow us to speculate on the existence of at least two eye movement systems: an automatic, data-driven system for rapid successions of fixations; and a deliberate schema-driven vergence system that accounts for stable fixations based on the perceptual state of the observer.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Wang2009,

title = {Factors influencing pursuit ability in infantile nystagmus syndrome: Target timing and foveation capability.},

author = {Z. I. Wang and Louis F. Dell'Osso},

doi = {10.1016/j.visres.2008.10.007},

year  = {2009},

date = {2009-01-01},

journal = {Vision Research},

volume = {49},

number = {2},

pages = {182–189},

publisher = {Elsevier Ltd},

abstract = {We wished to determine the influential factors for Infantile Nystagmus Syndrome (INS) subjects' ability to acquire and pursue moving targets using predictions from the behavioral Ocular Motor System (OMS) model and data from INS subjects. Ocular motor simulations using a behavioral OMS model were performed in MATLAB Simulink. Eye-movement recordings were performed using a high-speed digital video system. We studied five INS subjects who pursued a 10°/s ramp target to both left and right. We measured their target-acquisition times based on position criteria. The following parameters were studied: Lt (measured from the target-ramp initiation to the first on-target foveation period), target pursuit direction, and foveation-period pursuit gain. Analyses and simulations were performed in MATLAB environment using OMLAB software (OMtools, download from http://www.omlab.org). Ramp-target timing influenced target-acquisition time; the closer to the intrinsic saccades in the waveform the ramp stimuli started, the longer was Lt. However, arriving at the target position may not guarantee its foveation. Foveation-period pursuit gains vs. target or slow-phase direction had an idiosyncratic relationship for each subject. Adjustments to the model's Fixation subsystem reproduced the idiosyncratic foveation-period pursuit gains; the gain of the Smooth Pursuit subsystem was maintained at its normal value. The model output predicted a steady-state error when target initiation occurred during intrinsic saccades, consistent with human data. We conclude that INS subjects acquire ramp targets with longer latency for target initiations during or near the intrinsic saccades, consistent with the findings in our step-stimuli timing study. This effect might be due to the interaction between the saccadic and pursuit systems. The combined effects of target timing and Fixation-subsystem gain determined how fast and how well the INS subjects pursued ramp stimuli during their foveations periods (i.e., their foveation-period pursuit gain). The OMS model again demonstrated its behavioral characteristics and prediction capabilities (e.g., steady-state error) and revealed an important interaction between the Fixation and Smooth Pursuit subsystems.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{West2009,

title = {Saccadic trajectories receive online correction: Evidence for a feedback-based system of oculomotor control},

author = {Gregory L. West and Timothy N. Welsh and Jay Pratt},

doi = {10.3200/JMBR.41.2.117-127},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Motor Behavior},

volume = {41},

number = {2},

pages = {117–126},

abstract = {Although a considerable amount of research has investigated the planning and production of saccadic eye movements, it remains unclear whether (a) central planning processes prior to movement onset largely determine these eye movements or (b) they receive online correction during the actual trajectory. To investigate this issue, the authors measured the spatial position of the eye at specific kinematic markers during saccadic movements (i.e., peak acceleration, peak velocity, peak deceleration, saccade endpoint). In 2 experiments, the authors examined saccades ranging in amplitude from 4 to 20 degrees and computed the variability profiles (SD) of eye position at each kinematic marker and the proportion of explained variance (R2) between each kinematic marker and the saccade endpoint. In Experiment 1, the authors examined differences in the kinematic signature of saccadic online control between eye movements made in gap or overlap conditions. In Experiment 2, the authors examined the online control of saccades made from stored target information after delays of 500, 1,500, and 3,500 ms. Findings evince a robust and consistent feedback-based system of online oculomotor control during saccadic eye movements.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Wismeijer2009,

title = {The effect of changing size on vergence is mediated by changing disparity},

author = {Dagmar A. Wismeijer and Casper J. Erkelens},

doi = {10.1167/9.13.12},

year  = {2009},

date = {2009-01-01},

journal = {Journal of vision},

volume = {9},

number = {13},

pages = {12 1–10},

abstract = {In this study, we investigated the effect of changing size on vergence. Erkelens and Regan (1986) proposed that this cue to motion in depth affects vergence in a similar way as it affects perception. The measured effect on vergence was small and we wondered why the vergence system would use changing size as an additional cue to changing disparity. To elucidate the effect of changing size on vergence, we used an annulus carrying both changing size and changing disparity signals to motion in depth. The cues were either congruent or signaled a different depth. The results showed that vergence was affected by changing size, however in an opposite way than that perception was affected. These results were incongruent with those reported by Erkelens and Regan (1986). We therefore additionally measured the effects on vergence of the individual parameters associated with changing size, i.e., stimulus area, retinal eccentricity, and luminance. Stimulus (retinal) eccentricity was inversely related to vergence gain. Luminance, on the other hand, had a smaller but positive relation to vergence gain. Thus, changing size affected the disparity signal two-fold: it changed the retinal location of the disparity signal and it changed the strength of the disparity signal (luminance change). These effects of changing size on disparity can explain both our results (change in retinal location of the disparity signal) and those of Erkelens and Regan (1986; change in luminance). We thus conclude that changing size did not in itself contribute to vergence, rather its effect on vergence was mediated by disparity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zimmermann2009,

title = {Mislocalization of flashed and stationary visual stimuli after adaptation of reactive and scanning saccades},

author = {Eckart Zimmermann and Markus Lappe},

doi = {10.1523/JNEUROSCI.1604-09.2009},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Neuroscience},

volume = {29},

number = {35},

pages = {11055–11064},

abstract = {When we look around and register the location of visual objects, our oculomotor system continuously prepares targets for saccadic eye movements. The preparation of saccade targets may be directly involved in the perception of object location because modification of saccade amplitude by saccade adaptation leads to a distortion of the visual localization of briefly flashed spatial probes. Here, we investigated effects of adaptation on the localization of continuously visible objects. We compared adaptation-induced mislocalization of probes that were present for 20 ms during the saccade preparation period and of probes that were present for >1 s before saccade initiation. We studied the mislocalization of these probes for two different saccade types, reactive saccades to a suddenly appearing target and scanning saccades in the self-paced viewing of a stationary scene. Adaptation of reactive saccades induced mislocalization of flashed probes. Adaptation of scanning saccades induced in addition also mislocalization of stationary objects. The mislocalization occurred in the absence of visual landmarks and must therefore originate from the change in saccade motor parameters. After adaptation of one type of saccade, the saccade amplitude change and the mislocalization transferred only weakly to the other saccade type. Mislocalization of flashed and stationary probes thus followed the selectivity of saccade adaptation. Since the generation and adaptation of reactive and scanning saccades are known to involve partially different brain mechanisms, our results suggest that visual localization of objects in space is linked to saccade targeting at multiple sites in the brain.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bate2009,

title = {Covert face recognition relies on affective valence in congenital prosopagnosia},

author = {Sarah Bate and Catherine Haslam and Ashok Jansari and Timothy L. Hodgson},

doi = {10.1080/02643290903175004},

year  = {2009},

date = {2009-01-01},

journal = {Cognitive Neuropsychology},

volume = {26},

number = {4},

pages = {391–411},

abstract = {Dominant accounts of covert recognition in prosopagnosia assume subthreshold activation of face representations created prior to onset of the disorder. Yet, such accounts cannot explain covert recognition in congenital prosopagnosia, where the impairment is present from birth. Alternatively, covert recognition may rely on affective valence, yet no study has explored this possibility. The current study addressed this issue in 3 individuals with congenital prosopagnosia, using measures of the scanpath to indicate recognition. Participants were asked to memorize 30 faces paired with descriptions of aggressive, nice, or neutral behaviours. In a later recognition test, eye movements were monitored while participants discriminated studied from novel faces. Sampling was reduced for studied–nice compared to studied–aggressive faces, and performance for studied–neutral and novel faces fell between these two conditions. This pattern of findings suggests that (a) positive emotion can facilitate processing in prosopagnosia, and (b) covert recognition may rely on emotional valence rather than familiarity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Blekher2009,

title = {Test-retest reliability of saccadic measures in subjects at risk for Huntington disease},

author = {Tanya Blekher and Marjorie R. Weaver and Xueya Cai and Siu L. Hui and Jeanine Marshall and Jacqueline Gray Jackson and Joanne Wojcieszek and Robert D. Yee and Tatiana M. Foroud},

doi = {10.1167/iovs.09-3538},

year  = {2009},

date = {2009-01-01},

journal = {Investigative Ophthalmology & Visual Science},

volume = {50},

number = {12},

pages = {5707–5711},

abstract = {PURPOSE Abnormalities in saccades appear to be sensitive and specific biomarkers in the prediagnostic stages of Huntington disease (HD). The goal of this study was to evaluate test-retest reliability of saccadic measures in prediagnostic carriers of the HD gene expansion (PDHD) and normal controls (NC). METHODS The study sample included 9 PDHD and 12 NC who completed two study visits within an approximate 1-month interval. At the first visit, all participants completed a uniform clinical evaluation. A high-resolution, video-based system was used to record eye movements during completion of a battery of visually guided, antisaccade, and memory-guided tasks. Latency, velocity, gain, and percentage of errors were quantified. Test-retest reliability was estimated by calculating the intraclass correlation (ICC) of the saccade measures collected at the first and second visits. In addition, an equality test based on Fisher's z-transformation was used to evaluate the effects of group (PDHD and NC) and the subject's sex on ICC. RESULTS The percentage of errors showed moderate to high reliability in the antisaccade and memory-guided tasks (ICC = 0.64-0.93). The latency of the saccades also demonstrated moderate to high reliability (ICC = 0.55-0.87) across all tasks. The velocity and gain of the saccades showed moderate reliability. The ICC was similar in the PDHD and NC groups. There was no significant effect of sex on the ICC. CONCLUSIONS Good reliability of saccadic latency and percentage of errors in both antisaccade and memory-guided tasks suggests that these measures could serve as biomarkers to evaluate progression in HD.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Blekher2009a,

title = {Visual scanning and cognitive performance in prediagnostic and early-stage Huntington's disease},

author = {Tanya Blekher and Marjorie R. Weaver and Jeanine Marshall and Siu L. Hui and Jacqueline Gray Jackson and Julie C. Stout and Xabier Beristain and Joanne Wojcieszek and Robert D. Yee and Tatiana M. Foroud},

doi = {10.1002/mds.22329},

year  = {2009},

date = {2009-01-01},

journal = {Movement Disorders},

volume = {24},

number = {4},

pages = {533–540},

abstract = {The objective of this study was to evaluate visual scanning strategies in carriers of the Huntington disease (HD) gene expansion and to test whether there is an association between measures of visual scanning and cognitive performance. The study sample included control (NC},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Blekher2009b,

title = {Multiple step pattern as a biomarker in Parkinson disease},

author = {Tanya Blekher and Marjorie R. Weaver and Jason Rupp and William C. Nichols and Siu L. Hui and Jacqueline Gray and Robert D. Yee and Joanne Wojcieszek and Tatiana M. Foroud},

doi = {10.1016/j.parkreldis.2009.01.002},

year  = {2009},

date = {2009-01-01},

journal = {Parkinsonism and Related Disorders},

volume = {15},

number = {7},

pages = {506–510},

publisher = {Elsevier Ltd},

abstract = {Objective: To evaluate quantitative measures of saccades as possible biomarkers in early stages of Parkinson disease (PD) and in a population at-risk for PD. Methods: The study sample (n = 68) included mildly to moderately affected PD patients, their unaffected siblings, and control individuals. All participants completed a clinical evaluation by a movement disorder neurologist. Genotyping of the G2019S mutation in the LRRK2 gene was performed in the PD patients and their unaffected siblings. A high resolution, video-based eye tracking system was employed to record eye positions during a battery of visually guided, anti-saccadic (AS), and two memory-guided (MG) tasks. Saccade measures (latency, velocity, gain, error rate, and multiple step pattern) were quantified. Results: PD patients and a subgroup of their unaffected siblings had an abnormally high incidence of multiple step patterns (MSP) and reduced gain of saccades as compared with controls. The abnormalities were most pronounced in the more challenging version of the MG task. For this task, the MSP measure demonstrated good sensitivity (87%) and excellent specificity (96%) in the ability to discriminate PD patients from controls. PD patients and their siblings also made more errors in the AS task. Conclusions: Abnormalities in eye movement measures appear to be sensitive and specific measures in PD patients as well as a subset of those at-risk for PD. The inclusion of quantitative laboratory testing of saccadic movements may increase the sensitivity of the neurological examination to identify individuals who are at greater risk for PD.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Cronin2009,

title = {Spectral domain optical coherence tomography for detection of foveal morphology in patients with nystagmus},

author = {Tara H. Cronin and Richard W. Hertle and Hiroshi Ishikawa and Joel S. Schuman},

doi = {10.1016/j.jaapos.2009.09.019},

year  = {2009},

date = {2009-01-01},

journal = {Journal of AAPOS},

volume = {13},

number = {6},

pages = {563–566},

publisher = {American Association for Pediatric Ophthalmology and Strabismus},

abstract = {Purpose: To evaluate the feasibility of spectral domain optical coherence tomography (SD-OCT) macular scanning as a means of studying the afferent visual system in nystagmus patients. Methods: Nystagmus patients who underwent SD-OCT, clinical evaluation, and eye movement recordings were recruited for this prospective, single-center, noncomparative study. Three SD-OCT macular three-dimensional cube scans per eye (200 × 200 × 1024 samplings in a 6 × 6 mm region) were obtained for qualitative retinal morphology analysis. Results: Nineteen patients (6-68 years; average, 19 years) were analyzed. Of these, 17 patients had infantile nystagmus syndrome, and 2 had fusion maldevelopment nystagmus; 17 patients (89%) had associated sensory system abnormalities, including 9 (47%) with albinism. Macular images were successfully obtained in all but 1 patient (95%). Of the 8 successfully imaged oculocutaneous patients, 7 patients demonstrated "fovea plana," and all demonstrated abnormal morphology. Conclusion: SD-OCT reliably provides detailed structural imaging of the fovea in nystagmus patients.A figure is presentedA figure is presented. © 2009 American Association for Pediatric Ophthalmology and Strabismus.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dalrymple2009,

title = {Global perception in simultanagnosia is not as simple as a game of connect-the-dots},

author = {Kirsten A. Dalrymple and Walter F. Bischof and David Cameron and Jason J. S. Barton and Alan Kingstone},

doi = {10.1016/j.visres.2009.05.002},

year  = {2009},

date = {2009-01-01},

journal = {Vision Research},

volume = {49},

number = {14},

pages = {1901–1908},

publisher = {Elsevier Ltd},

abstract = {Simultanagnosia is a neuropsychological disorder characterized by a restriction of visuospatial attention. In addition, patients are able to identify local elements of a scene, but not the global whole. This may be due to a failure to scan and assemble local elements into a global whole (i.e. connect-the-dots). We monitored the eye movements of a simultanagnosic patient while she identified local and global elements of hierarchical letters. Scanning each local element was not necessary, nor sufficient, for successful global level identification. Our results argue against a connect-the-dots strategy of global identification and suggest that residual global processing may be occurring.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Foulsham2009,

title = {Fixation and saliency during search of natural scenes: The case of visual agnosia},

author = {Tom Foulsham and Jason J. S. Barton and Alan Kingstone and Richard Dewhurst and Geoffrey Underwood},

doi = {10.1016/j.neuropsychologia.2009.03.013},

year  = {2009},

date = {2009-01-01},

journal = {Neuropsychologia},

volume = {47},

number = {8-9},

pages = {1994–2003},

abstract = {Models of eye movement control in natural scenes often distinguish between stimulus-driven processes (which guide the eyes to visually salient regions) and those based on task and object knowledge (which depend on expectations or identification of objects and scene gist). In the present investigation, the eye movements of a patient with visual agnosia were recorded while she searched for objects within photographs of natural scenes and compared to those made by students and age-matched controls. Agnosia is assumed to disrupt the top-down knowledge available in this task, and so may increase the reliance on bottom-up cues. The patient's deficit in object recognition was seen in poor search performance and inefficient scanning. The low-level saliency of target objects had an effect on responses in visual agnosia, and the most salient region in the scene was more likely to be fixated by the patient than by controls. An analysis of model-predicted saliency at fixation locations indicated a closer match between fixations and low-level saliency in agnosia than in controls. These findings are discussed in relation to saliency-map models and the balance between high and low-level factors in eye guidance.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Halliday2009,

title = {No Lewy pathology in monkeys with over 10 years of severe MPTP Parkinsonism},

author = {Glenda Halliday and Maria Trinidad Herrero and Karen Murphy and Heather McCann and Francisco Ros-Bernal and Carlos Barcia and Hideo Mori and Francisco J. Blesa and Jose A. Obeso},

doi = {10.1002/mds.22481},

year  = {2009},

date = {2009-01-01},

journal = {Movement Disorders},

volume = {24},

number = {10},

pages = {1519–1545},

abstract = {The recent knowledge that 10 years after trans- plantation surviving human fetal neurons adopt the histopathology of Parkinson's disease suggests that Lewy body formation takes a decade to achieve. To determine whether similar histopathology occurs in 1-methyl-4- phenyl-1,2,3,6-tetrahydropyridine (MPTP)-primate models over a similar timeframe, the brains of two adult monkeys made parkinsonian in their youth with intermittent injections of MPTP were studied. Despite substantial nigral degeneration and increased α-synuclein immunoreactivity within surviving neurons, there was no evidence of Lewy body formation. This suggests that MPTP-induced oxidative stress and inflammation per se are not sufficient for Lewy body formation, or Lewy bodies are human specific},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hertel2009,

title = {Different saccadic abnormalities in PINK1 mutation carriers and in patients with non-genetic Parkinson's disease},

author = {Susanne Hertel and Andreas Sprenger and Christine Klein and Detlef Kömpf and Christoph Helmchen and Hubert Kimmig},

doi = {10.1007/s00415-009-5092-8},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Neurology},

volume = {256},

number = {7},

pages = {1192–1194},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hertle2009,

title = {Eye muscle surgery for infantile nystagmus syndrome in the first two years of life},

author = {Richard W. Hertle and Joost Felius and Dongsheng Yang and Matthew Kaufman},

doi = {10.2147/OPTH.S7541},

year  = {2009},

date = {2009-01-01},

journal = {Clinical Ophthalmology},

volume = {3},

number = {1},

pages = {615–624},

abstract = {PURPOSE: To report visual and elctrophysioloigcal effects of eye muscle surgery in young patients with infantile nystagmus syndrome (INS). METHODS: Prospective, interventional case cohort of 19 patients aged under 24 months who were operated on for combinations of strabismus, an anomalous head posture, and nystagmus. All patients were followed at least nine months. Outcome measures, part of an institutionally approved study, included Teller acuity, head position, strabismic deviation, and eye movement recordings, from which waveform types and a nystagmus optimal foveation fraction (NOFF). Computerized parametric and nonparametric statistical analysis of data were perfomed using standard software on both individual and group data. RESULTS: Age averaged 17.7 months (13.1-month follow-up). Thirteen (68%) patients had associated optic nerve or retinal disease. 42% had amblyopia, 68% had refractive errors. Group means in binocular Teller acuity (P < 0.05), strabismic deviation (P < 0.05), head posture (P < 0.001), and the NOFF measures (P < 0.01) from eye movement recordings improved in all patients. There was a change in null zone waveforms to more favorable jerk types. There were no reoperations or surgical complications. CONCLUSIONS: Surgery on the extraocular muscles in patients aged less than two years with INS results in improvements in multiple aspects of ocular motor and visual function.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hochstadt2009,

title = {Set-shifting and the on-line processing of relative clauses in Parkinson's disease: Results from a novel eye-tracking method},

author = {Jesse Hochstadt},

doi = {10.1016/j.cortex.2009.03.010},

year  = {2009},

date = {2009-01-01},

journal = {Cortex},

volume = {45},

number = {8},

pages = {991–1011},

publisher = {Elsevier Srl},

abstract = {Past research indicates that in Parkinson's disease (PD), set-shifting deficits cause impaired comprehension of sentences containing restrictive relative clauses (RCs). Some research also suggests that verbal working memory deficits impair comprehension of long-distance (LD) dependencies in sentences with center-embedded RCs. To test whether these deficits impair comprehension by affecting on-line processing, we tracked patients' eye movements as they matched pictures with sentences with final- or center-embedded RCs (e.g., The queen was kicking the cook who was fat, The queen who was kicking the cook was thin) and active or passive verbs. Decreases in looks to distracters ruled out at the transitive verb (e.g., a cook kicking a queen) and the adjective (a fat queen kicking a thin cook) reflected how effective processing was at those points. Though patients showed greater difficulty comprehending center-embedded and passive sentences, set-shifting errors correlated with comprehension of all sentences. Consistent with this, patients with poorer comprehension exhibited impaired on-line processing of both center-embedded and final RCs (for which comprehension was better due to their grammatical simplicity), and these effects correlated with set-shifting errors. We consider two possible explanations for this apparently general RC-processing deficit. First, because RCs are infrequent, set-shifting may be needed to override the processor's expectations for higher-frequency structures. Second, because restrictive RCs typically refer to information already in the discourse context, set-shifting may be needed to redirect attention from linguistic foreground to background information. Eye-tracking data indicated no difficulty processing LD dependencies; correlations of verbal working memory with comprehension of passive and center-embedded sentences may reflect off-line use of memory. In trials with passive verbs, patients looked toward the verb distracter before even processing the verb. This effect was larger than that previously seen for young participants, suggesting that PD may amplify a normal bias to assume the subject noun is the agent.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hong2009,

title = {Is motion perception deficit in Schizophrenia a consequence of eye-tracking abnormality?},

author = {L. Elliot Hong and Kathleen A. Turano and Hugh B. O'Neill and Lei Hao and Ikwunga Wonodi and Robert P. McMahon and Gunvant K. Thaker},

doi = {10.1016/j.biopsych.2008.10.021},

year  = {2009},

date = {2009-01-01},

journal = {Biological Psychiatry},

volume = {65},

number = {12},

pages = {1079–1085},

publisher = {Society of Biological Psychiatry},

abstract = {Background: Studies have shown that schizophrenia patients have motion perception deficit, which was thought to cause eye-tracking abnormality in schizophrenia. However, eye movement closely interacts with motion perception. The known eye-tracking difficulties in schizophrenia patients may interact with their motion perception. Methods: Two speed discrimination experiments were conducted in a within-subject design. In experiment 1, the stimulus duration was 150 msec to minimize the chance of eye-tracking occurrence. In experiment 2, the duration was increased to 300 msec, increasing the possibility of eye movement intrusion. Regular eye-tracking performance was evaluated in a third experiment. Results: At 150 msec, speed discrimination thresholds did not differ between schizophrenia patients (n = 38) and control subjects (n = 33). At 300 msec, patients had significantly higher thresholds than control subjects (p = .03). Furthermore, frequencies of eye tracking during the 300 msec stimulus were significantly correlated with speed discrimination in control subjects (p = .01) but not in patients, suggesting that eye-tracking initiation may benefit control subjects but not patients. The frequency of eye tracking during speed discrimination was not significantly related to regular eye-tracking performance. Conclusions: Speed discrimination, per se, is not impaired in schizophrenia patients. The observed abnormality appears to be a consequence of impairment in generating or integrating the feedback information from eye movements. This study introduces a novel approach to motion perception studies and highlights the importance of concurrently measuring eye movements to understand interactions between these two systems; the results argue for a conceptual revision regarding motion perception abnormality in schizophrenia.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jacobs2009,

title = {Using the NAFX to measure the effectiveness over time of gene therapy in canine LCA},

author = {Jonathan B. Jacobs and Louis F. Dell'Osso and Zhong I. Wang and Gregory M. Acland and Jean Bennett},

doi = {10.1167/iovs.09-3387},

year  = {2009},

date = {2009-01-01},

journal = {Investigative Ophthalmology & Visual Science},

volume = {50},

number = {10},

pages = {4685–4692},

abstract = {PURPOSE: To use ocular motility recordings to determine the changes over time of infantile nystagmus syndrome (INS) in RPE65-deficient canines with Leber Congenital Amaurosis (LCA) and assess the time course of the recalibration of the ocular motor system (OMS). METHODS: Nine dogs were treated bilaterally with AAV-RPE65. A second cohort of four dogs was treated with AAV2.RPE65, an optimized vector. Their fixation eye movements were recorded before treatment and at 4-week intervals for 3 months, by using high-speed (500 Hz) digital videography. The dogs were suspended in a sling and encouraged to fixate on distant (57 inches) targets at gaze angles varying between +/-15 degrees horizontally and +/-10 degrees vertically. The records for each eye were examined for qualitative changes in waveform and for quantitative changes in centralisation with the expanded nystagmus acuity function (NAFX) and compared with ERG results for restoration of receptor function. RESULTS: First group: Before treatment, five of the dogs had clinically apparent INS with jerk, pendular, or both waveforms and with peak-to-peak amplitudes as great as 15 degrees . One dog had intermittent nystagmus. At the 1- and 2-month examinations, no change in nystagmus waveform or NAFX was observed in any of the initial dogs, while at 10 weeks, one dog treated bilaterally with the standard dosage showed reduced nystagmus in only one eye. The other eye did not respond to treatment, as confirmed by ERG. This result was unexpected since it was previously documented that unilateral treatment leads to bilateral reduction of INS. The other dog treated with the standard dosage showed no reduction of its small-amplitude, high-frequency pendular nystagmus despite positive ERG responses. Second group: Only one dog of the four had clinically detectable INS, similar in characteristics to that seen in the affected dogs of the first group. Unlike any previous dog studied, this one showed a damping of the nystagmus within the first 4 weeks after treatment. CONCLUSIONS: In all but one of the cases in which OMS recalibration occurred, as measured by the clinical appearance of nystagmus and by quantitative measurement using the NAFX, the improvement was apparent no sooner than 10 weeks after treatment. Longer term, dose-related studies are needed to determine the minimum necessary degree of restored receptor functionality, the duration after rescue for recalibration of the OMS, and the conditions under which recalibration information can successfully affect the contralateral eye.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kumar2009,

title = {Asperger syndrome associated with idiopathic infantile nystagmus-A report of 2 cases},

author = {Anil Kumar and Nagini Sarvananthan and Frank A. Proudlock and Mervyn G. Thomas and Eryl O. Roberts and Irene Gottlob},

doi = {10.1080/09273970902829154},

year  = {2009},

date = {2009-01-01},

journal = {Strabismus},

volume = {17},

number = {2},

pages = {63–65},

abstract = {Asperger syndrome is a severe and chronic developmental disorder. It is closely associated with autism and is grouped under autism spectrum disorder (ASD). Various eye movement abnormalities in AS have been reported in literature such as increased errors and latencies on the antisaccadic task implicating dysfunction of the prefrontal cortex, impairment of the pursuit especially for targets presented in the right visual hemisphere, suggesting disturbance in the left extrastraite cortex. There are no reports in the literature of association between idiopathic infantile nystagmus (IIN) and AS. We report 2 cases of Asperger syndrome associated with idiopathic infantile nystagmus.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kumar2009a,

title = {Treatment of acquired periodic alternating nystagmus with memantine: A case report},

author = {Anil Kumar and Shery Thomas and Rebecca J. McLean and Frank A. Proudlock and Eryl O. Roberts and Mike Boggild and Irene Gottlob},

doi = {10.1097/WNF.0b013e3181873697},

year  = {2009},

date = {2009-01-01},

journal = {Clinical Neuropharmacology},

volume = {32},

number = {2},

pages = {109–110},

abstract = {We report a case of acquired periodic alternating nystagmus associated with common variable immunodeficiency and cutaneous sarcoid. The patient was initially treated with baclofen with minimal subjective improvement. We found a significant improvement in the patient's symptoms and nystagmus intensity after treatment with memantine.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lamontagne2009,

title = {Gaze and postural reorientation in the control of locomotor steering after stroke},

author = {Anouk Lamontagne and Joyce Fung},

doi = {10.1177/1545968308324549},

year  = {2009},

date = {2009-01-01},

journal = {Neurorehabilitation and Neural Repair},

volume = {23},

number = {3},

pages = {256–266},

abstract = {BACKGROUND: Steering of locomotion is a complex task involving stabilizing and anticipatory orienting behavior essential for the maintenance of balance and for establishing a stable frame of reference for future motor and sensory events. How these mechanisms are affected by stroke remains unknown. OBJECTIVES: To compare locomotor steering behavior between stroke and healthy individuals and to determine whether steering abilities are influenced by walking speed, turning direction and walking capacity in stroke individuals. METHODS: Gaze and body kinematics were recorded in 8 stroke and 7 healthy individuals while walking and turning in response to a visual cue. Horizontal orientation of gaze, head, thorax, pelvis, and feet with respect to spatial and heading coordinates were examined. RESULTS: Temporal and spatial coordination of gaze and body movements revealed stabilizing and anticipatory orienting mechanisms in the healthy individuals. Changing walking speed affected the onset time but not the sequencing of segment reorientation. In the individuals with stroke, abnormally large and uncoordinated head and gaze motion were observed. The sequence of gaze, head, thorax and pelvis horizontal reorientation also was also disrupted. Alterations in orienting behaviors were more pronounced at the slowest walking speeds and turning to the nonparetic side in 3 of the most severely disabled individuals. CONCLUSION: The results in this convenience sample of slow and faster walkers suggest that stroke alters the stabilizing and orienting behavior during steering of locomotion. Such alterations are not caused by the inherently slow walking speed, but rather by a combination of biomechanical factors and defective sensorimotor integration, including altered vestibulo-ocular reflexes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Li2009,

title = {Picture perception in Chinese dyslexic children: An eye-movement study},

author = {Xiu-Hong Li and Jin Jing and Xiao-Bing Zou and Xu Huang and Yu Jin and Qing-Xiong Wang and Xue-Bin Chen and Bin-Rang Yang and Si-Yuan Yang},

year  = {2009},

date = {2009-01-01},

journal = {Chinese Medical Journal},

volume = {122},

number = {3},

pages = {267–271},

abstract = {BACKGROUND: Currently, whether or not there is visuospatial impairments in Chinese dyslexic children is still a matter of discussion. The relatively recent application of an eye-tracking paradigm may offer an opportunity to address this issue. In China, in comparison with reading studies, there have not been nearly as many eye movement studies dealing with nonreading tasks such as picture identification and whether Chinese children with dyslexia have a picture processing deficit is not clear. The purposes of the present study were to determine whether or not there is visuospatial impairments in Chinese dyslexic children. Moreover, we attempted to discuss whether or not the abnormal eye movement pattern that dyslexic subjects show during reading of text appropriate for their age is a consequence of their linguistic difficulties. METHODS: An eye-link II High-Speed Eye Tracker was used to track the series of eye-movement of 19 Chinese dyslexic children and 19 Chinese normal children. All of the subjects were presented with three pictures for this eye-tracking task and 6 relative eye-movement parameters, first fixation duration, average fixation duration, average saccade amplitude, mean saccade distance, fixation frequency and saccade frequency were recorded for analysis. RESULTS: Analyzing the relative parameter among three pictures, except for the fixation frequency and the saccade frequency, other eye-movement parameters were significantly different among the three pictures (P<0.05). Among the three pictures, the first fixation duration was longer, and the average fixation duration, the average saccade amplitude and the mean saccade distance were shorter from picture 2 to picture 3. Comparing all eye-movement parameter between the two groups, the scores of average saccade amplitude (P=0.017) and the mean saccade distance (P=0.02) were less in the dyslexia group than in the normal group (P<0.05), other parameters were the same in the two different groups (P>0.05). CONCLUSIONS: The characteristics of the pictures can significantly influence the visuospatial cognitive processing capability of the Chinese children. There is a detectable disability for the Chinese dyslexic children in the visuospatial cognitive processing: their saccade amplitude and mean saccade distance are shorter, which may be interpreted as specific for their reading disability.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ludwig2009,

title = {Modelling contralesional movement slowing after unilateral brain damage},

author = {Casimir J. H. Ludwig and Stephen H. Butler and Stéphanie Rossit and Monika Harvey and Iain D. Gilchrist},

doi = {10.1016/j.neulet.2009.01.033},

year  = {2009},

date = {2009-01-01},

journal = {Neuroscience Letters},

volume = {452},

number = {1},

pages = {1–4},

abstract = {Effective interaction with the world requires the brain to signal behaviourally relevant events and organise an appropriate and timely motor response to such events. Unilateral brain lesion typically results in a reduction and slowing of motor behaviour directed to contralesional space. Accumulator models of choice and reaction time can distinguish between two possible functional causes of this deficit: slowed extraction of evidence in favour of a motor response or an increase in the required amount of evidence for response generation. Three patients with unilateral damage to the right hemisphere were tested on a visually guided saccade task. All three patients showed a dramatic increase in the latency of their responses to targets in the contralesional visual field. We fit their saccade latency distributions with a number of competing accumulator models that embody the alternative functional causes of this deficit. The latency difference between the two hemifields was best accounted for as an increase in the amount of evidence required for a contralesional response.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Moeller2009,

title = {Basic number processing deficits in developmental dyscalculia: Evidence from eye tracking},

author = {Korbinian Moeller and S. Neuburger and L. Kaufmann and K. Landerl and Hans-Christoph Nuerk},

doi = {10.1016/j.cogdev.2009.09.007},

year  = {2009},

date = {2009-01-01},

journal = {Cognitive Development},

volume = {24},

number = {4},

pages = {371–386},

abstract = {Recent research suggests that developmental dyscalculia is associated with a subitizing deficit (i.e., the inability to quickly enumerate small sets of up to 3 objects). However, the nature of this deficit has not previously been investigated. In the present study the eye-tracking methodology was employed to clarify whether (a) the subitizing deficit of two boys with dyscalculia resulted from a general slowing in the access to magnitude representation, or (b) children with dyscalculia resort to a back-up counting strategy even for small object sets. In a dot-counting task, a standard problem size effect for the number of fixations required to encode the presented numerosity within the subitizing range was observed. Together with the finding that problem size had no impact on the average fixation duration, this result suggested that children with dyscalculia may indeed have to count, while typically developing controls are able to enumerate the number of dots in parallel, i.e., subitize. Implications for the understanding of developmental dyscalculia are considered.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mueri2009,

title = {Visual exploration pattern in hemineglect},

author = {René M. Müri and D. Cazzoli and Thomas Nyffeler and Tobias Pflugshaupt},

doi = {10.1007/s00426-008-0204-0},

year  = {2009},

date = {2009-01-01},

journal = {Psychological Research},

volume = {73},

number = {2},

pages = {147–157},

abstract = {The analysis of eye movement parameters in visual neglect such as cumulative fixation duration, saccade amplitude, or the numbers of saccades has been used to probe attention deficits in neglect patients, since the pattern of exploratory eye movements has been taken as a strong index of attention distribution. The current overview of the literature of visual neglect has its emphasis on studies dealing with eye movement and exploration analysis. We present our own results in 15 neglect patients. The free exploration behavior was analyzed in these patients presenting 32 naturalistic color photographs of everyday scenes. Cumulative fixation duration, spatial distribution of fixations in the horizontal and vertical plane, the number and amplitude of exploratory saccades was analyzed and compared with the results of an age-matched control group. A main result of our study was that in neglect patients, fixation distribution of free exploration of natural scenes is not only influenced by the left-right bias in the horizontal direction but also by the vertical direction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pflugshaupt2009,

title = {About the role of visual field defects in pure alexia},

author = {Tobias Pflugshaupt and Klemens Gutbrod and Pascal Wurtz and Roman Von Wartburg and Thomas Nyffeler and Bianca De Haan and Hans-Otto Karnath and René M. Mueri},

doi = {10.1093/brain/awp141},

year  = {2009},

date = {2009-01-01},

journal = {Brain},

volume = {132},

number = {7},

pages = {1907–1917},

abstract = {Pure alexia is an acquired reading disorder characterized by a disproportionate prolongation of reading time as a function of word length. Although the vast majority of cases reported in the literature show a right-sided visual defect, little is known about the contribution of this low-level visual impairment to their reading difficulties. The present study was aimed at investigating this issue by comparing eye movement patterns during text reading in six patients with pure alexia with those of six patients with hemianopic dyslexia showing similar right-sided visual field defects. We found that the role of the field defect in the reading difficulties of pure alexics was highly deficit-specific. While the amplitude of rightward saccades during text reading seems largely determined by the restricted visual field, other visuo-motor impairments—particularly the pronounced increases in fixation frequency and viewing time as a function of word length—may have little to do with their visual field defect. In addition, subtracting the lesions of the hemianopic dyslexics from those found in pure alexics revealed the largest group differences in posterior parts of the left fusiform gyrus, occipito-temporal sulcus and inferior temporal gyrus. These regions included the coordinate assigned to the centre of the visual word form area in healthy adults, which provides further evidence for a relation between pure alexia and a damaged visual word form area. Finally, we propose a list of three criteria that may improve the differential diagnosis of pure alexia and allow appropriate therapy recommendations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pflugshaupt2009a,

title = {Linking physiology with behaviour: Functional specialisation of the visual field is reflected in gaze patterns during visual search},

author = {Tobias Pflugshaupt and Roman Wartburg and Pascal Wurtz and Silvia Chaves and Anouk Déruaz and Thomas Nyffeler and Sebastian Arx and Mathias Luethi and Dario Cazzoli and René M. Mueri},

doi = {10.1016/j.visres.2008.10.021},

year  = {2009},

date = {2009-01-01},

journal = {Vision Research},

volume = {49},

number = {2},

pages = {237–248},

publisher = {Elsevier Ltd},

abstract = {Based on neurophysiological findings and a grid to score binocular visual field function, two hypotheses concerning the spatial distribution of fixations during visual search were tested and confirmed in healthy participants and patients with homonymous visual field defects. Both groups showed significant biases of fixations and viewing time towards the centre of the screen and the upper screen half. Patients displayed a third bias towards the side of their field defect, which represents oculomotor compensation. Moreover, significant correlations between the extent of these three biases and search performance were found. Our findings suggest a new, more dynamic view of how functional specialisation of the visual field influences behaviour.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pinkhardt2009,

title = {Comparison of smooth pursuit eye movement deficits in multiple system atrophy and Parkinson's disease},

author = {Elmar H. Pinkhardt and Jan Kassubek and Sigurd Süssmuth and Albert C. Ludolph and Wolfgang Becker and Reinhart Jürgens},

doi = {10.1007/s00415-009-5131-5},

year  = {2009},

date = {2009-01-01},

journal = {Journal of Neurology},

volume = {256},

number = {9},

pages = {1438–1446},

abstract = {Because of the large overlap and quantitative similarity of eye movement alterations in Parkinson's disease (PD) and multiple system atrophy (MSA), a measurement of eye movement is generally not considered helpful for the differential diagnosis. However, in view of the pathophysiological differences between MSA and PD as well as between the cerebellar (MSA-C) and Parkinsonian (MSA-P) subtypes of MSA, we wondered whether a detailed investigation of oculomotor performance would unravel parameters that could help to differentiate between these entities. We recorded eye movements during sinusoidal pursuit tracking by means of video-oculography in 11 cases of MSA-P, 8 cases of MSA-C and 27 cases of PD and compared them to 23 healthy controls (CTL). The gain of the smooth pursuit eye movement (SPEM) component exhibited significant group differences between each of the three subject groups (MSA, PD, controls) but not between MSA-P and MSA-C. The similarity of pursuit impairment in MSA-P and in MSA-C suggests a commencement of cerebellar pathology in MSA-P despite the lack of clinical signs. Otherwise, SPEM gain was of little use for differential diagnosis between MSA and PD because of wide overlap. However, inspection of the saccadic component of pursuit tracking revealed that in MSA saccades typically correct for position errors accumulated during SPEM epochs ("catch-up saccades"), whereas in PD, saccades were often directed toward future target positions ("anticipatory saccades"). The differences in pursuit tracking between PD and MSA were large enough to warrant their use as ancillary diagnostic criteria for the distinction between these disorders.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rubin2009,

title = {The role of eye movements during reading in patients with age-related macular degeneration (AMD)},

author = {Gary S. Rubin and Mary P. Feely},

doi = {10.1080/01658100902998732},

year  = {2009},

date = {2009-01-01},

journal = {Neuro-Ophthalmology},

volume = {33},

number = {3},

pages = {120–126},

abstract = {AMD patients often have particular difficulty reading, even when the text is magnified to compensate for reduced visual acuity. This study explores whether reading performance can be explained by eye movement factors. Forty patients with advanced AMD were tested with a high-speed video eye tracker to evaluate fixation stability and saccadic eye movements. Reading speed was measured for standardized texts viewed at the critical print size. Visual acuity and contrast sensitivity were unrelated to reading speed, but fixation stability, proportion of regressive saccades and size of forward saccades were all significantly associated with reading performance, accounting for 74% of the variance. The implications of these findings for low-vision training programmes are discussed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tsuchiya2009,

title = {Intact rapid detection of fearful faces in the absence of the amygdala},

author = {Naotsugu Tsuchiya and Farshad Moradi and Csilla Felsen and Madoka Yamazaki and Ralph Adolphs},

doi = {10.1038/nn.2380},

year  = {2009},

date = {2009-01-01},

journal = {Nature Neuroscience},

volume = {12},

number = {10},

pages = {1224–1225},

abstract = {The amygdala is thought to process fear-related stimuli rapidly and nonconsciously. We found that an individual with complete bilateral amygdala lesions, who cannot recognize fear from faces, nonetheless showed normal rapid detection and nonconscious processing of those same fearful faces. We conclude that the amygdala is not essential for early stages of fear processing but, instead, modulates recognition and social judgment.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Alahyane2008,

title = {Separate neural substrates in the human cerebellum for sensory-motor adaptation of reactive and of scanning voluntary saccades},

author = {N. Alahyane and V. Fonteille and C. Urquizar and Roméo Salemme and Norbert Nighoghossian and Denis Pelisson and C. Tilikete},

doi = {10.1007/s12311-008-0065-5},

year  = {2008},

date = {2008-01-01},

journal = {Cerebellum},

volume = {7},

number = {4},

pages = {595–601},

abstract = {Sensory-motor adaptation processes are critically involved in maintaining accurate motor behavior throughout life. Yet their underlying neural substrates and task-dependency bases are still poorly understood. We address these issues here by studying adaptation of saccadic eye movements, a well-established model of sensory-motor plasticity. The cerebellum plays a major role in saccadic adaptation but it has not yet been investigated whether this role can account for the known specificity of adaptation to the saccade type (e.g., reactive versus voluntary). Two patients with focal lesions in different parts of the cerebellum were tested using the double-step target paradigm. Each patient was submitted to two separate sessions: one for reactive saccades (RS) triggered by the sudden appearance of a visual target and the second for scanning voluntary saccades (SVS) performed when exploring a more complex scene. We found that a medial cerebellar lesion impaired adaptation of reactive-but not of voluntary-saccades, whereas a lateral lesion affected adaptation of scanning voluntary saccades, but not of reactive saccades. These findings provide the first evidence of an involvement of the lateral cerebellum in saccadic adaptation, and extend the demonstrated role of the cerebellum in RS adaptation to adaptation of SVS. The double dissociation of adaptive abilities is also consistent with our previous hypothesis of the involvement in saccadic adaptation of partially separated cerebellar areas specific to the reactive or voluntary task (Alahyane et al. Brain Res 1135:107-121 (2007)).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Alahyane2008a,

title = {Spatial transfer of adaptation of scanning voluntary saccades in humans},

author = {Nadia Alahyane and Anne-Dominique Devauchelle and Roméo Salemme and Denis Pélisson},

doi = {10.1097/WNR.0b013e3282f2a5f2},

year  = {2008},

date = {2008-01-01},

journal = {Neuroreport},

volume = {19},

number = {1},

pages = {37–41},

abstract = {The properties and neural substrates of the adaptive mechanisms that maintain over time the accuracy of voluntary, internally triggered saccades are still poorly understood. Here, we used transfer tests to evaluate the spatial properties of adaptation of scanning voluntary saccades. We found that an adaptive reduction of the size of a horizontal rightward 7 degrees saccade transferred to other saccades of a wide range of amplitudes and directions. This transfer decreased as tested saccades increasingly differed in amplitude or direction from the trained saccade, being null for vertical and leftward saccades. Voluntary saccade adaptation thus presents bounded, but large adaptation fields, suggesting that at least part of the underlying neural substrate encodes saccades as vectors.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Alaidroos2008,

title = {Structured perceptual arrays and the modulation of Fitts's Law: Examining saccadic eye movements},

author = {Naseem Al-aidroos and Jos J. Adam and Martin H. Fischer and Jay Pratt},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Motor Behavior},

volume = {40},

number = {2},

pages = {155–164},

abstract = {On the basis of recent observations of a modulation of Fitts's law for manual pointing movements in structured visual arrays (J. J. Adam, R. Mol, J. Pratt, & M. H. Fischer, 2006; J. Pratt, J. J. Adam, & M. H. Fischer, 2007), the authors examined whether a similar modulation occurs for saccadic eye move- ments. Healthy participants (N = 19) made horizontal saccades to targets that appeared randomly in 1 of 4 positions, either on an empty background or within 1 of 4 placeholder boxes. Whereas in previous studies, placeholders caused a decrease in movement time (MT) without the normal decrease in movement accuracy predicted by Fitts's law, placeholders in the present experiment increased saccadic accuracy (decreased endpoint variability) with- out an increase in MT. The present results extend the findings of J. J. Adam et al. of a modulation of Fitts's law from the temporal domain to the spatial domain and from manual movements to eye movements.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Badler2008,

title = {Anticipatory pursuit is influenced by a concurrent timing task},

author = {Jeremy B. Badler and Philippe Lefèvre and Marcus Missal},

doi = {10.1167/8.6.672},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {16},

pages = {1–9},

abstract = {The ability to predict upcoming events is important to compensate for relatively long sensory-motor delays. When stimuli are temporally regular, their prediction depends on a representation of elapsed time. However, it is well known that the allocation of attention to the timing of an upcoming event alters this representation. The role of attention on the temporal processing component of prediction was investigated in a visual smooth pursuit task that was performed either in isolation or concurrently with a manual response task. Subjects used smooth pursuit eye movements to accurately track a moving target after a constant-duration delay interval. In the manual response task, subjects had to estimate the instant of target motion onset by pressing a button. The onset of anticipatory pursuit eye movements was used to quantify the subject's estimate of elapsed time. We found that onset times were delayed significantly in the presence of the concurrent manual task relative to the pursuit task in isolation. There was also a correlation between the oculomotor and manual response latencies. In the framework of Scalar Timing Theory, the results are consistent with a centralized attentional gating mechanism that allocates clock resources between smooth pursuit preparation and the parallel timing task.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Buonocore2008,

title = {Saccadic inhibition underlies the remote distractor effect},

author = {Antimo Buonocore and Robert D. McIntosh},

doi = {10.1007/s00221-008-1558-7},

year  = {2008},

date = {2008-01-01},

journal = {Experimental Brain Research},

volume = {191},

number = {1},

pages = {117–122},

abstract = {The remote distractor effect is a robust finding whereby a saccade to a lateralised visual target is delayed by the simultaneous, or near simultaneous, onset of a distractor in the opposite hemifield. Saccadic inhibition is a more recently discovered phenomenon whereby a transient change to the scene during a visual task induces a depression in saccadic frequency beginning within 70 ms, and maximal around 90-100 ms. We assessed whether saccadic inhibition is responsible for the increase in saccadic latency induced by remote distractors. Participants performed a simple saccadic task in which the delay between target and distractor was varied between 0, 25, 50, 100 and 150 ms. Examination of the distributions of saccadic latencies showed that each distractor produced a discrete dip in saccadic frequency, time-locked to distractor onset, conforming closely to the character of saccadic inhibition. We conclude that saccadic inhibition underlies the remote distractor effect.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Contreras2008,

title = {Eye-target synchronization in mild traumatic brain-injured patients},

author = {R. Contreras and Rachel Kolster and Henning U. Voss and Jamshid Ghajar and M. Suh and S. Bahar},

doi = {10.1007/s10867-008-9092-1},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Biological Physics},

volume = {34},

number = {3-4},

pages = {381–392},

abstract = {Eye-target synchronization is critical for effective smooth pursuit of a moving visual target. We apply the nonlinear dynamical technique of stochastic-phase synchronization to human visual pursuit of a moving target, in both normal and mild traumatic brain-injured (mTBI) patients. We observe significant fatigue effects in all subject populations, in which subjects synchronize better with the target during the first half of the trial than in the second half. The fatigue effect differed, however, between the normal and the mTBI populations and between old and young subpopulations of each group. In some cases, the younger (</=40 years old) normal subjects performed better than mTBI subjects and also better than older (>40 years old) normal subjects. Our results, however, suggest that further studies will be necessary before a standard of "normal" smooth pursuit synchronization can be developed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Diederich2008,

title = {Crossmodal interaction in saccadic reaction time: Separating multisensory from warning effects in the time window of integration model},

author = {Adele Diederich and Hans Colonius},

doi = {10.1007/s00221-007-1197-4},

year  = {2008},

date = {2008-01-01},

journal = {Experimental Brain Research},

volume = {186},

number = {1},

pages = {1–22},

abstract = {In a focused attention task saccadic reaction time (SRT) to a visual target stimulus (LED) was measured with an auditory (white noise burst) or tactile (vibration applied to palm) non-target presented in ipsi- or contralateral position to the target. Crossmodal facilitation of SRT was observed under all configurations and stimulus onset asynchrony (SOA) values ranging from -500 (non-target prior to target) to 0 ms, but the effect was larger for ipsi- than for contralateral presentation within an SOA range from -200 ms to 0. The time-window-of-integration (TWIN) model (Colonius and Diederich in J Cogn Neurosci 16:1000, 2004) is extended here to separate the effect of a spatially unspecific warning effect of the non-target from a spatially specific and genuine multisensory integration effect.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Diederich2008a,

title = {When a high-intensity "distractor" is better then a low-intensity one: Modeling the effect of an auditory or tactile nontarget stimulus on visual saccadic reaction time},

author = {Adele Diederich and Hans Colonius and Adele Diederich},

doi = {10.1016/j.brainres.2008.05.081},

year  = {2008},

date = {2008-01-01},

journal = {Brain Research},

volume = {1242},

pages = {219–230},

publisher = {Elsevier B.V.},

abstract = {In a focused attention task saccadic reaction time (SRT) to a visual target stimulus (LED) was measured with an auditory (white noise burst) or tactile (vibration applied to palm) nontarget presented in ipsi- or contralateral position to the target. Crossmodal facilitation of SRT was observed under all configurations and stimulus onset asynchrony (SOA) values ranging from - 250 ms (nontarget prior to target) to 50 ms. This study specifically addressed the effect of varying nontarget intensity. While facilitation effects for auditory nontargets are somewhat more pronounced than for tactile ones, decreasing intensity slightly reduced facilitation for both types of nontargets. The time course of crossmodal mean SRT over SOA and the pattern of facilitation observed here suggest the existence of two distinct underlying mechanisms: (a) a spatially unspecific crossmodal warning triggered by the nontarget being detected early enough before the arrival of the target plus (b) a spatially specific multisensory integration mechanism triggered by the target processing time terminating within the time window of integration. It is shown that the time window of integration (TWIN) model introduced by the authors gives a reasonable quantitative account of the data relating observed SRT to the unobservable probability of integration and crossmodal warning for each SOA value under a high and low intensity level of the nontarget.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Garaas2008a,

title = {A gaze-contingent paradigm for studying continuous saccadic adaptation},

author = {Tyler W. Garaas and Tyson Nieuwenhuis and Marc Pomplun},

doi = {10.1016/j.jneumeth.2007.10.022},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Neuroscience Methods},

volume = {168},

number = {2},

pages = {334–340},

abstract = {Saccadic eye movements are used to quickly and accurately orient our fovea within our visual field to obtain detailed information from various locations. The accuracy of these eye movements is maintained throughout life despite constant pressure on oculomotor muscles and neuronal structures by growth and aging; this maintenance appears to be a product of an adaptive mechanism that continuously accounts for consistent post-saccadic visual error, and is referred to as saccadic adaptation. In this paper, we present a new paradigm to test saccadic adaptation under circumstances that more closely resemble natural visual error in everyday vision, whereas previous saccadic adaptation paradigms study adaptation in a largely restricted form. The paradigm achieves this by positioning a stimulus panel atop an identically colored background relative to the gaze position of the participant. We demonstrate the paradigm by successfully decreasing participants' saccadic amplitudes during a common visual search task by shifting the stimulus panel in the opposite direction of the saccade by 50% of the saccadic amplitude. Participants' adaptation reached approximately 60% of the 50% back-shift during the adaptation phase, and was uniformly distributed across saccadic direction. The adaptation time-course found using the new paradigm is consistent with that achieved using previous paradigms. Task-performance results and the manner in which eye movements changed during adaptation were also analyzed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gaveau2008,

title = {Saccade control and eye-hand coordination in optic ataxia},

author = {Valérie Gaveau and Denis Pélisson and Annabelle Blangero and Christian Urquizar and Claude Prablanc and Alain Vighetto and Laure Pisella},

doi = {10.1016/j.neuropsychologia.2007.08.028},

year  = {2008},

date = {2008-01-01},

journal = {Neuropsychologia},

volume = {46},

number = {2},

pages = {475–486},

abstract = {The aim of this work was to investigate ocular control in patients with optic ataxia (OA). Following a lesion in the posterior parietal cortex (PPC), these patients exhibit a deficit for fast visuo-motor control of reach-to-grasp movements. Here, we assessed the fast visuo-motor control of saccades as well as spontaneous eye-hand coordination in two bilateral OA patients and five neurologically intact controls in an ecological "look and point" paradigm. To test fast saccadic control, trials with unexpected target-jumps synchronised with saccade onset were randomly intermixed with stationary target trials. Results confirmed that control subjects achieved visual capture (foveation) of the displaced targets with the same timing as stationary targets (fast saccadic control) and began their hand movement systematically at the end of the primary saccade. In contrast, the two bilateral OA patients exhibited a delayed visual capture, especially of displaced targets, resulting from an impairment of fast saccadic control. They also exhibited a peculiar eye-hand coordination pattern, spontaneously delaying their hand movement onset until the execution of a final corrective saccade, which allowed target foveation. To test whether this pathological behaviour results from a delay in updating visual target location, we had subjects perform a second experiment in the same control subjects in which the target-jump was synchronised with saccade offset. With less time for target location updating, the control subjects exhibited the same lack of fast saccadic control as the OA patients. We propose that OA corresponds to an impairment of fast updating of target location, therefore affecting both eye and hand movements.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gordon2008,

title = {Object continuity and the transsaccadic representation of form},

author = {Robert D. Gordon and Sarah D. Vollmer and Megan L. Frankl},

year  = {2008},

date = {2008-01-01},

journal = {Perception and Psychophysics},

volume = {70},

number = {4},

pages = {667–679},

abstract = {Transsaccadic object file representations were investigated in three experiments. Subjects moved their eyes from a central fixation cross to a location between two peripheral objects. During the saccade, this preview display was replaced with a target display containing a single object to be named. On trials on which the target identity matched one of the preview objects, its orientation either matched or did not match the previewed orientation. The results of Experiments 1 and 2 revealed that orientation changes disrupt perceptual continuity for objects located near fixation, but not for objects located further from fixation. The results of Experiment 3 confirmed that orientation changes do not disrupt continuity for distant objects, while showing that subjects nevertheless maintain an object-specific representation of the orientation of such objects. Together, the results suggest that object files represent orientation but that whether or not orientation plays a role in the processes that determine continuity depends on the quality of the perceptual representation. While},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hernandez2008,

title = {How does saccade adaptation affect visual perception?},

author = {Teresa D. Hernandez and Carmel A. Levitan and Martin S. Banks and Clifton M. Schor},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {8},

pages = {1–16},

abstract = {Three signals are used to visually localize targets and stimulate saccades: (1) retinal location signals for intended saccade amplitude, (2) sensory-motor transform (SMT) of retinal signals to extra-ocular muscle innervation, and (3) estimates of eye position from extra-retinal signals. We investigated effects of adapting saccade amplitude to a double-step change in target location on perceived direction. In a flashed-pointing task, subjects pointed an unseen hand at a briefly displayed eccentric target without making a saccade. In a sustained-pointing task, subjects made a horizontal saccade to a double-step target. One second after the second step, they pointed an unseen hand at the final target position. After saccade-shortening adaptation, there was little change in hand-pointing azimuth toward the flashed target suggesting that most saccade adaptation was caused by changes in the SMT. After saccade-lengthening adaptation, there were small changes in hand-pointing azimuth to flashed targets, indicating that 1/3 of saccade adaptation was caused by changes in estimated retinal location signals and 2/3 by changes in the SMT. The sustained hand-pointing task indicated that estimates of eye position adapted inversely with changes of the SMT. Changes in perceived direction resulting from saccade adaptation are mainly influenced by extra-retinal factors with a small retinal component in the lengthening condition.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hong2008,

title = {Refining the predictive pursuit endophenotype in schizophrenia.},

author = {L. Elliot Hong and Kathleen A. Turano and Hugh B. O'Neill and Lei Hao and Ikwunga Wonodi and Robert P. McMahon and Amie Elliott and Gunvant K. Thaker},

doi = {10.1016/j.biopsych.2007.06.004},

year  = {2008},

date = {2008-01-01},

journal = {Biological Psychiatry},

volume = {63},

number = {5},

pages = {458–464},

abstract = {Background: To utilize fully a schizophrenia endophenotype in gene search and subsequent neurobiological studies, it is critical that the precise underlying physiologic deficit is identified. Abnormality in smooth pursuit eye movements is one of the endophenotypes of schizophrenia. The precise nature of the abnormality is unknown. Previous work has shown a reduced predictive pursuit response to a briefly masked (i.e., invisible) moving object in schizophrenia. However, the overt awareness of target removal can confound the measurement. Methods: This study employed a novel method that covertly stabilized the moving target image onto the fovea. The foveal stabilization was implemented after the target on a monitor had oscillated at least for one cycle and near the change of direction when the eye velocity momentarily reached zero. Thus, the subsequent pursuit eye movements were completely predictive and internally driven. Eye velocity during this foveally stabilized smooth pursuit was compared among schizophrenia patients (n = 45), their unaffected first-degree relatives (n = 42), and healthy comparison subjects (n = 22). Results: Schizophrenia patients and their unaffected relatives performed similarly and both had substantially reduced predictive pursuit acceleration and velocity under the foveally stabilized condition. Conclusions: These findings show that inability to maintain internal representation of the target motion or integration of such information into a predictive response may be the specific brain deficit indexed by the smooth pursuit endophenotype in schizophrenia. Similar performance between patients and unaffected relatives suggests that the refined predictive pursuit measure may index a less complex genetic origin of the eye-tracking deficits in schizophrenia families.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hoormann2008,

title = {The effect of calibration errors on the accuracy of the eye movement recordings},

author = {Jörg Hoormann and Stephanie Jainta and Wolfgang Jaschinski},

doi = {10.16910/jemr.1.2.3},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Eye Movement Research},

volume = {1},

number = {2},

pages = {1–7},

abstract = {For calibrating eye movement recordings, a regression between spatially defined calibration points and corresponding measured raw data is performed. Based on this regression, a confidence interval (CI) of the actually measured eye position can be calculated in order to$backslash$nquantify the measurement error introduced by inaccurate calibration coefficients. For calculating this CI, a standard deviation (SD) - depending on the calibration quality and the$backslash$ndesign of the calibration procedure - is needed.$backslash$nExamples of binocular recordings with separate monocular calibrations illustrate that the SD is almost independent of the number and spatial separation between the calibration points – even though the later was expected from theoretical simulation. Our simulations and recordings demonstrate that the SD depends critically on residuals at certain calibration points, thus robust regressions are suggested.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jaschinski2008,

title = {Comparison of shutter glasses and mirror stereoscope for measuring dynamic and static vergence},

author = {Wolfgang Jaschinski and Stephanie Jainta and Jörg Hoormann},

doi = {10.16910/jemr.1.2.5},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Eye Movement Research},

volume = {1},

number = {2},

pages = {1–7},

abstract = {Vergence eye movement recordings in response to disparity step stimuli require to present different stimuli to the two eyes. The traditional method is a mirror stereoscope. Shutter glasses are more convenient, but have disadvantages as limited repetition rate, residual cross task, and reduced luminance. Therefore, we compared both techniques measuring (1) dynamic disparity step responses for stimuli of 1 and 3 deg and (2) fixation disparity, the static vergence error. Shutter glasses and mirror stereoscope gave very similar dynamic responses with correlations of about 0.95 for the objectively measured vergence velocity and for the response amplitude reached 400 ms after the step stimulus (measured objectively with eye movement recordings and subjectively with dichoptic nonius lines). Both techniques also provided similar amounts of fixation disparity, tested with dichoptic nonius lines.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kaminiarz2008,

title = {Expansion of visual space during optokinetic afternystagmus (OKAN)},

author = {Andre Kaminiarz and Bart Krekelberg and Frank Bremmer},

doi = {10.1152/jn.00017.2008},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Neurophysiology},

volume = {99},

number = {5},

pages = {2470–2478},

abstract = {The mechanisms underlying visual perceptual stability are usually investigated using voluntary eye movements. In such studies, errors in perceptual stability during saccades and pursuit are commonly interpreted as mismatches between actual eye position and eye-position signals in the brain. The generality of this interpretation could in principle be tested by investigating spatial localization during reflexive eye movements whose kinematics are very similar to those of voluntary eye movements. Accordingly, in this study, we determined mislocalization of flashed visual targets during optokinetic afternystagmus (OKAN). These eye movements are quite unique in that they occur in complete darkness and are generated by subcortical control mechanisms. We found that during horizontal OKAN slow phases, subjects mislocalize targets away from the fovea in the horizontal direction. This corresponds to a perceived expansion of visual space and is unlike mislocalization found for any other voluntary or reflexive eye movement. Around the OKAN fast phases, we found a bias in the direction of the fast phase prior to its onset and opposite to the fast-phase direction thereafter. Such a biphasic modulation has also been reported in the temporal vicinity of saccades and during optokinetic nystagmus (OKN). A direct comparison, however, showed that the modulation during OKAN was much larger and occurred earlier relative to fast-phase onset than during OKN. A simple mismatch between the current eye position and the eye-position signal in the brain is unlikely to explain such disparate results across similar eye movements. Instead, these data support the view that mislocalization arises from errors in eye-centered position information.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kerzel2008,

title = {Local motion inside an object affects pointing less than smooth pursuit},

author = {Dirk Kerzel and Angélique Gauch and Blandine Ulmann},

doi = {10.1007/s00221-008-1514-6},

year  = {2008},

date = {2008-01-01},

journal = {Experimental Brain Research},

volume = {191},

number = {2},

pages = {187–195},

abstract = {During smooth pursuit eye movements, briefly presented objects are mislocalized in the direction of motion. It has been proposed that the localization error is the sum of the pursuit signal and the retinal motion signal in a ~200 ms interval after flash onset. To evaluate contributions of retinal motion signals produced by the entire object (global motion) and elements within the object (local motion), we asked observers to reach to flashed Gabor patches (Gaussian-windowed sine-wave gratings). Global motion was manipulated by varying the duration of a stationary flash, and local motion was manipulated by varying the motion of the sine-wave. Our results confirm that global retinal motion reduces the localization error. The effect of local retinal motion on object localization was far smaller, even though local and global motion had equal effects on eye velocity. Thus, local retinal motion has differential access to manual and oculomotor control circuits. Further, we observed moderate correlations between smooth pursuit gain and localization error.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kerzel2008a,

title = {Effects of attention shifts to stationary objects during steady-state smooth pursuit eye movements},

author = {Dirk Kerzel and David Souto and Nathalie E. Ziegler},

doi = {10.1016/j.visres.2008.01.015},

year  = {2008},

date = {2008-01-01},

journal = {Vision Research},

volume = {48},

number = {7},

pages = {958–969},

abstract = {A number of studies have shown that stationary backgrounds compromise smooth pursuit eye movements. It has been suggested that poor attentional selection of the pursuit target was responsible for reductions of pursuit gain. To quantify the detrimental effects of attention, we instructed observers to either pay attention to background objects or to ignore them. The to-be-attended object was indicated by peripheral or central cues. Strong reductions of pursuit gain occurred when the following conditions were met: (a) the subject payed attention to the object (b) a salient event was present, for instance the onset of the target or cue and (c) the attended target produced retinal motion. Removing any of the three conditions resulted in no or far smaller decreases of pursuit gain. Further, decreases in pursuit gain were present with perceptual discrimination and simple manual detection.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Knapp2008,

title = {Horizontal and vertical look and stare optokinetic nystagmus symmetry in healthy adult volunteers},

author = {Christopher M. Knapp and Irene Gottlob and Rebecca J. McLean and Frank A. Proudlock},

doi = {10.1167/iovs.07-0773},

year  = {2008},

date = {2008-01-01},

journal = {Investigative Ophthalmology & Visual Science},

volume = {49},

number = {2},

pages = {581–588},

abstract = {PURPOSE: Look optokinetic nystagmus (OKN) consists of voluntary tracking of details in a moving visual field, whereas stare OKN is reflexive and consists of shorter slow phases of lower gain. Horizontal OKN is symmetrical in healthy adults, whereas symmetry of vertical OKN is controversial. Horizontal and vertical look and stare OKN symmetry was measured, and the consistency of individual asymmetries and the effect of varying stimulus conditions were investigated.METHODS: Horizontal and vertical look and stare OKN gains were recorded in 15 healthy volunteers (40 degrees /s) using new methods to delineate look and stare OKN. Responses with right and left eye viewing were compared to investigate consistency of individual OKN asymmetry. In a second experiment, the symmetry of stare OKN was measured in nine volunteers varying velocity (20 degrees /s and 40 degrees /s), contrast (50% and 100%), grating contrast profile (square or sine wave), and stimulus shape (full screen or circular vignetted).RESULTS: There was no horizontal or vertical asymmetry in look or stare OKN gain for all volunteers grouped together. However, individual vertical asymmetries were strongly correlated for left and right eye viewing (look: r = 0.77},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Matheron2008,

title = {Effects of ocular dominance on the vertical vergence induced by a 2-diopter vertical prism during standing},

author = {Eric Matheron and Qing Yang and Thanh Thuan Lê and Zoï Kapoula},

doi = {10.1016/j.neulet.2008.08.025},

year  = {2008},

date = {2008-01-01},

journal = {Neuroscience Letters},

volume = {444},

number = {2},

pages = {176–180},

abstract = {This study examined the eye movement responses to vertical disparity induced by a 2-diopter vertical prism base down while in standing position. Vertical vergence movements are known to be small requiring accurate measurement with the head stabilized, and was done with the EyeLink 2. The 2-diopter vertical prism, base down, was inserted in front of either the non-dominant eye (NDE) or dominant eye (DE) at 40 and 200 cm. The results showed that vertical vergence was stronger and excessive relative to the required value (i.e. 1.14°) when the prism was on the NDE for both distances, but more appropriate when the prism was on the DE. The results suggest that sensory disparity process and vertical vergence responses are modulated by eye dominance.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Moshel2008,

title = {Persistence and phase synchronisation properties of fixational eye movements},

author = {S. Moshel and Ari Z. Zivotofsky and L. Jin-Rong and Ralf Engbert and Jürgen Kurths and Reinhold Kliegl and Shlomo Havlin},

doi = {10.1140/epjst/e2008-00762-3},

year  = {2008},

date = {2008-01-01},

journal = {The European Physical Journal Special Topics},

volume = {161},

pages = {207–223},

abstract = {When we fixate our gaze on a stable object, our eyes move continuously with extremely small involuntary and autonomic movements, that even we are unaware of during their occurrence. One of the roles of these fixational eye movements is to prevent the adaptation of the visual system to continuous illumination and inhibit fading of the image. These random, small movements are restricted at long time scales so as to keep the target at the centre of the field of view. In addition, the synchronisation properties between both eyes are related to binocular coordination in order to provide stereopsis. We investigated the roles of different time scale behaviours, especially how they are expressed in the different spatial directions (vertical versus horizontal). We also tested the synchronisation between both eyes. Results show different scaling behaviour between horizontal and vertical movements. When the small ballistic movements, i.e., microsaccades, are removed, the scaling behaviour in both axes becomes similar. Our findings suggest that microsaccades enhance the persistence at short time scales mostly in the horizontal component and much less in the vertical component. We also applied the phase synchronisation decay method to study the synchronisation between six combinations of binocular fixational eye movement components. We found that the vertical-vertical components of right and left eyes are significantly more synchronised than the horizontal-horizontal components. These differences may be due to the need for continuously moving the eyes in the horizontal plane in order to match the stereoscopic image for different viewing distances.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nefs2008,

title = {Induced motion in depth and the effects of vergence eye movements},

author = {Harold T. Nefs and J. M. Harris},

doi = {10.1167/8.3.8},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {3},

pages = {1–16},

abstract = {Induced motion is the false impression that physically stationary objects move when in the presence of other objects that really move. In this study, we investigated this motion illusion in the depth dimension. We raised three related questions, as follows: (1) What cues in the stimulus are responsible for this motion illusion in depth? (2) Is the size of this illusion affected by vergence eye movements? And (3) are the effects of eye movements different for motion in depth and for motion in the frontoparallel plane? To answer these questions, we measured the point of subjective stationarity. Observers viewed an inducer target that oscillated in depth and a test target that was located directly above it. The test target moved in phase or out of phase with the inducer, but with a smaller amplitude. Observers had to indicate whether the test target and the inducer target moved in phase or out of phase with one another. They were asked to keep their eyes either on the test target or on the inducer. For motion in depth, created by binocular disparity and retinal size change or by binocular disparity alone, we found that when the eyes followed the inducer, subjective stationarity occurred at approximately 40-45% of the inducer's amplitude. When the eyes were kept fixated on the test target, the bias decreased tenfold to around 4%. When size change was the only cue to motion in depth, there was no illusory motion. When the eyes were kept on an inducer moving in the frontoparallel plane, induced motion was of the same order as for induced motion in depth, namely, approximately 44%. When the induced motion was in the frontoparallel plane, we found that perceived stationarity occurred at approximately 23% of inducer's amplitude when the eyes were kept on the test target.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{OteroMillan2008,

title = {Saccades and microsaccades during visual fixation, exploration, and search: Foundations for a common saccadic generator},

author = {Jorge Otero-Millan and Xoana G. Troncoso and Stephen L. Macknik and Ignacio Serrano-Pedraza and Susana Martinez-Conde},

doi = {10.1167/9.8.447},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {14},

pages = {1–18},

abstract = {Microsaccades are known to occur during prolonged visual fixation, but it is a matter of controversy whether they also happen during free-viewing. Here we set out to determine: 1) whether microsaccades occur during free visual exploration and visual search, 2) whether microsaccade dynamics vary as a function of visual stimulation and viewing task, and 3) whether saccades and microsaccades share characteristics that might argue in favor of a common saccade-microsaccade oculomotor generator. Human subjects viewed naturalistic stimuli while performing various viewing tasks, including visual exploration, visual search, and prolonged visual fixation. Their eye movements were simultaneously recorded with high precision. Our results show that microsaccades are produced during the fixation periods that occur during visual exploration and visual search. Microsaccade dynamics during free-viewing moreover varied as a function of visual stimulation and viewing task, with increasingly demanding tasks resulting in increased microsaccade production. Moreover, saccades and microsaccades had comparable spatiotemporal characteristics, including the presence of equivalent refractory periods between all pair-wise combinations of saccades and microsaccades. Thus our results indicate a microsaccade-saccade continuum and support the hypothesis of a common oculomotor generator for saccades and microsaccades.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Reeve2008,

title = {Convergent flash localization near saccades without equivalent "compression" of perceived separation},

author = {Paul Reeve and James J. Clark and J. Kevin O'Regan},

doi = {10.1167/8.13.5},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {13},

pages = {1–19},

abstract = {Visual space is sometimes said to be "compressed" before saccadic eye movements. The most central evidence for this hypothesis is a converging pattern of localization errors on single flashes presented close to saccade time under certain conditions. An intuitive version of the compression hypothesis predicts that the reported distance between simultaneous, spatially separated presaccadic flashes should contract in the same way as their individual locations. In our experiment we tested this prediction by having subjects perform one of two tasks on stimuli made up of two bars simultaneously flashed near saccade time: either localizing one of the bars or judging the separation between the two. Localization judgments showed the previously observed converging pattern over the 50-100 ms before saccades. Contractions in perceived separation between the two bars were not accurately predicted by this pattern: they occurred mainly during saccades and were much weaker than convergence in localization. Different forms of spatial information about flashed stimuli can be differentially modulated before, during, and after saccades. Structural alterations in the perceptual field around saccades may explain these different effects, but alternative hypotheses based on decision making under uncertainty and on the influence of other perisaccadic mechanisms are also consistent with this and other evidence.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rey2008,

title = {Saccades horizontal or vertical at near or at far do not deteriorate postural control},

author = {Frédéric P. Rey and Thanh Thuan Lê and René Bertin and Zoï Kapoula},

doi = {10.1016/j.anl.2007.07.001},

year  = {2008},

date = {2008-01-01},

journal = {Auris Nasus Larynx},

volume = {35},

number = {2},

pages = {185–191},

abstract = {Objective: There is a discrepancy about the effect of saccades on postural control: some studies reported a stabilization effect, other studies the opposite. Perturbation of posture by saccades could be related to loss of vision during saccades (saccades suppression) due to high velocity retinal slip. On the other hand, efferent and afferent proprioceptive signals related to saccades can be used for obtaining spatial stability over saccades and maintaining good postural control. In natural conditions saccades can be horizontal, vertical and made at different distance. The present study examines all these parameters to provide a more complete view on the role of saccade on postural control in quiet stance. Methods: Horizontal or vertical saccades of 30° were made at 1 Hz and at two distances, 40 and 200 cm. Eye movements were recorded with video-oculograhpy (EyeLink II). Posturography was recorded with the TechnoConcept platform. The results from "saccade" conditions are compared to "fixation control" condition (at far and near). Results: The video oculography results show that subjects performed the fixation or the saccade task correctly. Execution of saccades (horizontal or vertical at near or at far distance) had no significant effect on the surface of center of pressure (CoP), neither on the standard deviation of the lateral body sway, nor on the variance of speed of the CoP. Moreover, whatever the distance, execution of saccades decreased significantly the standard deviation of the antero-posterior sway. Conclusion: We conclude that saccades, of either the direction and at either the distance, do not deteriorate postural control; rather they could reduce sway. Efferent and proprioceptive oculomotor signals as well as attention could contribute to maintain or improve postural stability while making saccades.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{rke08,

title = {Toward a model of microsaccade generation: The case of microsaccadic inhibition},

author = {Martin Rolfs and Reinhold Kliegl and Ralf Engbert},

doi = {10.1167/8.11.5},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {11},

pages = {1–23},

abstract = {Microsaccades are one component of the small eye movements that constitute fixation. Their implementation in the oculomotor system is unknown. To better understand the physiological and mechanistic processes underlying microsaccade generation, we studied microsaccadic inhibition, a transient drop of microsaccade rate, in response to irrelevant visual and auditory stimuli. Quantitative descriptions of the time course and strength of inhibition revealed a strong dependence of microsaccadic inhibition on stimulus characteristics. In Experiment 1, microsaccadic inhibition occurred sooner after auditory than after visual stimuli and after luminance-contrast than after color-contrast visual stimuli. Moreover, microsaccade amplitude strongly decreased during microsaccadic inhibition. In Experiment 2, the latency of microsaccadic inhibition increased with decreasing luminance contrast. We develop a conceptual model of microsaccade generation in which microsaccades result from fixation-related activity in a motor map coding for both fixation and saccades. In this map, fixation is represented at the central site. Saccades are generated by activity in the periphery, their amplitude increasing with eccentricity. The activity at the central, fixation-related site of the map predicts the rate of microsaccades as well as their amplitude and direction distributions. This model represents a framework for understanding the dynamics of microsaccade behavior in a broad range of tasks.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rolfs2008,

title = {Microsaccade-induced prolongation of saccadic latencies depends on microsaccade amplitude},

author = {Martin Rolfs and Jochen Laubrock and Reinhold Kliegl},

doi = {10.16910/jemr.1.3.1},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Eye Movement Research},

volume = {1},

number = {3},

pages = {1–8},

abstract = {Fixations consist of small movements including microsaccades, i.e., rapid flicks in eye position that replace the retinal image by up to 1 degree of visual angle. Recently, we showed in a delayed-saccade task (1) that the rate of microsaccades decreased in the course of saccade preparation and (2) that microsaccades occurring around the time of a go signal were associated with prolonged saccade latencies (Rolfs et al., 2006). A re-analysis of the same data set revealed a strong dependence of these findings on microsaccade amplitude. First, microsaccade amplitude dropped to a minimum just before the generation of a saccade. Second, the delay of response saccades was a function of microsaccade amplitude: Microsaccades with larger amplitudes were followed by longer response latencies. These finding were predicted by a recently proposed model that attributes microsaccade generation to fixation-related activity in a saccadic motor map that is in competition with the generation of large saccades (Rolfs et al., 2008). We propose, therefore, that microsaccade statistics provide a behavioral correlate of fixation-related activity in the oculomotor system.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{sdbkg07,

title = {Improved visual sensitivity during smooth pursuit eye movements},

author = {Alexander C. Schütz and Doris I. Braun and Dirk Kerzel and Karl R. Gegenfurtner},

doi = {10.1038/nn.2194},

year  = {2008},

date = {2008-01-01},

journal = {Nature Neuroscience},

volume = {11},

number = {10},

pages = {1211–1216},

abstract = {When we view the world around us, we constantly move our eyes. This brings objects of interest into the fovea and keeps them there, but visual sensitivity has been shown to deteriorate while the eyes are moving. Here we show that human sensitivity for some visual stimuli is improved during smooth pursuit eye movements. Detection thresholds for briefly flashed, colored stimuli were 16% lower during pursuit than during fixation. Similarly, detection thresholds for luminance-defined stimuli of high spatial frequency were lowered. These findings suggest that the pursuit-induced sensitivity increase may have its neuronal origin in the parvocellular retino-thalamic system. This implies that the visual system not only uses feedback connections to improve processing for locations and objects being attended to, but that a whole processing subsystem can be boosted. During pursuit, facilitation of the parvocellular system may reduce motion blur for stationary objects and increase sensitivity to speed changes of the tracked object.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{sf08b,

title = {Motion perception during sinusoidal smooth pursuit eye movements: Signal latencies and non-linearities},

author = {Jan L. Souman and Tom C. A. Freeman},

doi = {10.1167/8.14.10r/8/14/10/ [pii]},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {14},

pages = {1–14},

abstract = {Smooth pursuit eye movements add motion to the retinal image. To compensate, the visual system can combine estimates of pursuit velocity and retinal motion to recover motion with respect to the head. Little attention has been paid to the temporal characteristics of this compensation process. Here, we describe how the latency difference between the eye movement signal and the retinal signal can be measured for motion perception during sinusoidal pursuit. In two experiments, observers compared the peak velocity of a motion stimulus presented in pursuit and fixation intervals. Both the pursuit target and the motion stimulus moved with a sinusoidal profile. The phase and amplitude of the motion stimulus were varied systematically in different conditions, along with the amplitude of pursuit. The latency difference between the eye movement signal and the retinal signal was measured by fitting the standard linear model and a non-linear variant to the observed velocity matches. We found that the eye movement signal lagged the retinal signal by a small amount. The non-linear model fitted the velocity matches better than the linear one and this difference increased with pursuit amplitude. The results support previous claims that the visual system estimates eye movement velocity and retinal velocity in a non-linear fashion and that the latency difference between the two signals is small.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{sk08,

title = {Dynamics of attention during the initiation of smooth pursuit eye movements},

author = {David Souto and Dirk Kerzel},

doi = {10.1167/8.14.3},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {14},

pages = {3–1–16},

abstract = {Many studies indicate that saccades are necessarily preceded by a shift of attention to the target location. There is no direct evidence for the same coupling during smooth pursuit. If smooth pursuit and attention were coupled, pursuit onset should be delayed whenever attention is focused on a stationary, non-target location. To test this hypothesis, observers were instructed to shift their attention to a peripheral location according to a location cue (Experiments 1 and 2) or a symbolic cue (Experiment 3) around the time of smooth pursuit initiation. Attending to static targets had only negligible effects on smooth pursuit latencies and the early open-loop response but lowered pursuit velocity substantially about the onset of closed-loop pursuit. Around this time, eye velocity reflected the competition between the to-be-tracked and to-be-attended object motion, entailing a reduction of eye velocity by 50% compared to the single task condition. The precise time course of attentional modulation of smooth pursuit initiation was at odds with the idea that an attention shift must precede any voluntary eye movement. Finally, the initial catch-up saccades were strongly delayed with attention diverted from the pursuit target. Implications for models of target selection for pursuit and saccades are discussed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{smg08,

title = {Competition between color and luminance for target selection in smooth pursuit and saccadic eye movements},

author = {Miriam Spering and Anna Montagnini and Karl R. Gegenfurtner},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {15},

pages = {1–19},

abstract = {Visual processing of color and luminance for smooth pursuit and saccadic eye movements was investigated using a target selection paradigm. In two experiments, stimuli were varied along the dimensions color and luminance, and selection of the more salient target was compared in pursuit and saccades. Initial pursuit was biased in the direction of the luminance component whereas saccades showed a relative preference for color. An early pursuit response toward luminance was often reversed to color by a later saccade. Observers' perceptual judgments of stimulus salience, obtained in two control experiments, were clearly biased toward luminance. This choice bias in perceptual data implies that the initial short-latency pursuit response agrees with perceptual judgments. In contrast, saccades, which have a longer latency than pursuit, do not seem to follow the perceptual judgment of salience but instead show a stronger relative preference for color. These substantial differences in target selection imply that target selection processes for pursuit and saccadic eye movements use distinctly different weights for color and luminance stimuli.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Steenken2008a,

title = {Time course of auditory masker effects: Tapping the locus of audiovisual integration?},

author = {Rike Steenken and Adele Diederich and Hans Colonius},

doi = {10.1016/j.neulet.2008.02.017},

year  = {2008},

date = {2008-01-01},

journal = {Neuroscience Letters},

volume = {435},

number = {1},

pages = {78–83},

abstract = {In a focused attention paradigm, saccadic reaction time (SRT) to a visual target tends to be shorter when an auditory accessory stimulus is presented in close temporal and spatial proximity. Observed SRT reductions typically diminish as spatial disparity between the stimuli increases. Here a visual target LED (500 ms duration) was presented above or below the fixation point and a simultaneously presented auditory accessory (2 ms duration) could appear at the same or the opposite vertical position. SRT enhancement was about 35 ms in the coincident and 10 ms in the disparate condition. In order to further probe the audiovisual integration mechanism, in addition to the auditory non-target an auditory masker (200 ms duration) was presented before, simultaneous to, or after the accessory stimulus. In all interstimulus interval (ISI) conditions, SRT enhancement went down both in the coincident and disparate configuration, but this decrement was fairly stable across the ISI values. If multisensory integration solely relied on a feed-forward process, one would expect a monotonic decrease of the masker effect with increasing ISI in the backward masking condition. It is therefore conceivable that the relatively high-energetic masker causes a broad excitatory response of SC neurons. During this state, the spatial audio-visual information from multisensory association areas is fed back and merged with the spatially unspecific excitation pattern induced by the masker. Assuming that a certain threshold of activation has to be achieved in order to generate a saccade in the correct direction, the blurred joint output of noise and spatial audio-visual information needs more time to reach this threshold prolonging SRT to an audio-visual object.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Teichert2008,

title = {Depth perception during saccades},

author = {T. Teichert and Steffen Klingenhoefer and T. Wachtler and Frank Bremmer},

doi = {10.1167/8.14.27},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {14},

pages = {1–13},

abstract = {A number of studies have investigated the localization of briefly flashed targets during saccades to understand how the brain perceptually compensates for changes in gaze direction. Typical version saccades, i.e., saccades between two points of the horopter, are not only associated with changes in gaze direction, but also with large transient changes of ocular vergence. These transient changes in vergence have to be compensated for just as changes in gaze direction. We investigated depth judgments of perisaccadically flashed stimuli relative to continuously present references and report several novel findings. First, disparity thresholds increased around saccade onset. Second, for horizontal saccades, depth judgments were prone to systematic errors: Stimuli flashed around saccade onset were perceived in a closer depth plane than persistently shown references with the same retinal disparity. Briefly before and after this period, flashed stimuli tended to be perceived in a farther depth plane. Third, depth judgments for upward and downward saccades differed substantially: For upward, but not for downward saccades we observed the same pattern of mislocalization as for horizontal saccades. Finally, unlike localization in the fronto-parallel plane, depth judgments did not critically depend on the presence of visual references. Current models fail to account for the observed pattern of mislocalization in depth.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Troncoso2008,

title = {Microsaccades counteract perceptual filling-in},

author = {Xoana G. Troncoso and Stephen L. Macknik and Susana Martinez-conde},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Vision},

volume = {8},

number = {14},

pages = {1–9},

abstract = {Artificial scotomas positioned within peripheral dynamic noise fade perceptually during visual fixation (that is, the surrounding dynamic noise appears to fill-in the scotoma). Because the scotomas' edges are continuously refreshed by the dynamic noise background, this filling-in effect cannot be explained by low-level adaptation mechanisms (such as those that may underlie classical Troxler fading). We recently showed that microsaccades counteract Troxler fading and drive first-order visibility during fixation (S. Martinez-Conde, S. L. Macknik, X. G. Troncoso, & T. A. Dyar, 2006). Here we set out to determine whether microsaccades may counteract the perceptual filling-in of artificial scotomas and thus drive second-order visibility. If so, microsaccades may not only counteract low-level adaptation but also play a role in higher perceptual processes. We asked subjects to indicate, via button press/release, whether an artificial scotoma presented on a dynamic noise background was visible or invisible at any given time. The subjects' eye movements were simultaneously measured with a high precision video system. We found that increases in microsaccade production counteracted the perception of filling-in, driving the visibility of the artificial scotoma. Conversely, decreased microsaccades allowed perceptual filling-in to take place. Our results show that microsaccades do not solely overcome low-level adaptation mechanisms but they also contribute to maintaining second-order visibility during fixation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Troncoso2008b,

title = {Microsaccades drive illusory motion in the Enigma illusion},

author = {Xoana G. Troncoso and Stephen L. Macknik and Jorge Otero-Millan and Susana Martinez-Conde},

doi = {10.1073/pnas.0709389105},

year  = {2008},

date = {2008-01-01},

journal = {Proceedings of the National Academy of Sciences},

volume = {105},

number = {41},

pages = {16033–16038},

abstract = {Visual images consisting of repetitive patterns can elicit striking illusory motion percepts. For almost 200 years, artists, psychologists, and neuroscientists have debated whether this type of illusion originates in the eye or in the brain. For more than a decade, the controversy has centered on the powerful illusory motion perceived in the painting Enigma, created by op-artist Isia Leviant. However, no previous study has directly correlated the Enigma illusion to any specific physiological mechanism, and so the debate rages on. Here, we show that microsaccades, a type of miniature eye movement produced during visual fixation, can drive illusory motion in Enigma. We asked subjects to indicate when illusory motion sped up or slowed down during the observation of Enigma while we simultaneously recorded their eye movements with high precision. Before "faster" motion periods, the rate of microsaccades increased. Before "slower/no" motion periods, the rate of microsaccades decreased. These results reveal a direct link between microsaccade production and the perception of illusory motion in Enigma and rule out the hypothesis that the origin of the illusion is purely cortical.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{VanderStigchel2008a,

title = {The influence of "blind" distractors on eye movement trajectories in visual hemifield defects},

author = {Stefan Van der Stigchel and Wieske Zoest and Jan Theeuwes and Jason J. S. Barton},

doi = {10.1162/jocn.2008.20145},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Cognitive Neuroscience},

volume = {20},

number = {11},

pages = {2025–2036},

abstract = {There is evidence that some visual information in blind regions may still be processed in patients with hemifield defects after cerebral lesions ("blindsight"). We tested the hypothesis that, in the absence of retinogeniculostriate processing, residual retinotectal processing may still be detected as modifications of saccades to seen targets by irrelevant distractors in the blind hemifield. Six patients were presented with distractors in the blind and intact portions of their visual field and participants were instructed to make eye movements to targets in the intact field. Eye movements were recorded to determine if blind-field distractors caused deviation in saccadic trajectories. No deviation was found in one patient with an optic chiasm lesion, which affect both retinotectal and retinogeniculostriate pathways. In five patients with lesions of the optic radiations or the striate cortex, the results were mixed, with two of the five patients showing significant deviations of saccadic trajectory away from the "blind" distractor. In a second experiment, two of the five patients were tested with the target and the distractor more closely aligned. Both patients showed a "global effect," in that saccades deviated toward the distractor, but the effect was stronger in the patient who also showed significant trajectory deviation in the first experiment. Although our study confirms that distractor effects on saccadic trajectory can occur in patients with damage to the retinogeniculostriate visual pathway but preserved retinotectal projections, there remain questions regarding what additional factors are required for these effects to manifest themselves in a given patient.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{VanPelt2008,

title = {Updating target distance across eye movements in depth},

author = {Stan Van Pelt and W. Pieter Medendorp},

doi = {10.1152/jn.01281.2007},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Neurophysiology},

volume = {99},

number = {5},

pages = {2281–2290},

abstract = {We tested between two coding mechanisms that the brain may use to retain distance information about a target for a reaching movement across vergence eye movements. If the brain was to encode a retinal disparity representation (retinal model), i.e., target depth relative to the plane of fixation, each vergence eye movement would require an active update of this representation to preserve depth constancy. Alternatively, if the brain was to store an egocentric distance representation of the target by integrating retinal disparity and vergence signals at the moment of target presentation, this representation should remain stable across subsequent vergence shifts (nonretinal model). We tested between these schemes by measuring errors of human reaching movements (n = 14 subjects) to remembered targets, briefly presented before a vergence eye movement. For comparison, we also tested their directional accuracy across version eye movements. With intervening vergence shifts, the memory-guided reaches showed an error pattern that was based on the new eye position and on the depth of the remembered target relative to that position. This suggests that target depth is recomputed after the gaze shift, supporting the retinal model. Our results also confirm earlier literature showing retinal updating of target direction. Furthermore, regression analyses revealed updating gains close to one for both target depth and direction, suggesting that the errors arise after the updating stage during the subsequent reference frame transformations that are involved in reaching.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vernet2008b,

title = {Divergence influences triggering of both vertical and horizontal saccades},

author = {Marine Vernet and Qing Yang and Gintautas Daunys and Christophe Orssaud and Zoï Kapoula},

doi = {10.1097/OPX.0b013e3181647196},

year  = {2008},

date = {2008-01-01},

journal = {Optometry and Vision Science},

volume = {85},

number = {3},

pages = {187–195},

abstract = {Purpose. In real life, divergence is frequently combined with vertical saccades. The purpose of this study was to examine the initiation of vertical and horizontal saccades, pure or combined with divergence. Methods. We used a gap paradigm to elicit vertical or horizontal saccades (10 degrees), pure or combined with a predictable divergence (10 degrees). Eye movements from 12 subjects were recorded with EyeLink II. Results. The major results were (i) when combined with divergence, the latency of horizontal saccades increased but not the latency of vertical saccades; (ii) for both vertical and horizontal saccades, a tight correlation between the latency of saccade and divergence was found; (iii) when the divergence was anticipated, the saccade was delayed. Conclusion. We conclude that the initiation of both components of combined movements is interdependent.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Walker2008,

title = {The influence of distractors on saccade target selection: Saccade trajectory effects},

author = {Robin Walker and Eugene McSorley},

doi = {10.16910/jemr.2.3.7},

year  = {2008},

date = {2008-01-01},

journal = {Journal of Eye Movement Research},

volume = {2},

number = {3},

pages = {1–13},

abstract = {It has long been known that the path (trajectory) taken by the eye to land on a target is rarely straight (Yarbus, 1967). Furthermore, the magnitude and direction of this natural tendency for curvature can be modulated by the presence of a competing distractor stimulus presented along with the saccade target. The distractorrelated modulation of saccade trajectories provides a subtle measure of the underlying competitive processes involved in saccade target selection. Here we review some of our own studies into the effects distractors have on saccade trajectories, which can be regarded as a way of probing the competitive balance between target and distractor salience.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{White2008,

title = {Saccadic facilitation in natural backgrounds},

author = {Brian J. White and Martin Stritzke and Karl R. Gegenfurtner},

doi = {10.1016/j.cub.2007.12.027},

year  = {2008},

date = {2008-01-01},

journal = {Current Biology},

volume = {18},

number = {2},

pages = {124–128},

abstract = {In visual systems with a fovea, only a small portion of the visual field can be analyzed with high accuracy. Saccadic eye movements shift that center of gaze around several times a second. Saccades have been characterized in great detail and depend critically on a number of visual properties of the stimuli [1-5]. However, typical experiments have used bright spots on dark backgrounds, while our natural environment has a highly characteristic rich spatial structure [6, 7]. Here we show that the saccadic system, unlike the perceptual system, is able to compensate for the masking caused by structured backgrounds. Consequently, saccadic latencies in the context of natural backgrounds are much faster than unstructured backgrounds at equal levels of visibility. The results suggest that whenever a structured background acts to mask the visibility of the saccade target, it simultaneously preactivates saccadic circuitry and thus ensures a fast reaction to potentially critical stimuli that are difficult to detect in our environment. © 2008 Elsevier Ltd. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Wismeijer2008,

title = {Depth cues, rather than perceived depth, govern vergence},

author = {D. A. Wismeijer and Raymond Van Ee and Casper J. Erkelens},

doi = {10.1007/s00221-007-1081-2},

year  = {2008},

date = {2008-01-01},

journal = {Experimental Brain Research},

volume = {184},

number = {1},

pages = {61–70},

abstract = {We studied the influence of perceived surface orientation on vergence accompanying a saccade while viewing an ambiguous stimulus. We used the slant rivalry stimulus, in which perspective foreshortening and disparity specified opposite surface orientations. This rivalrous configuration induces alternations of perceived surface orientation, while the slant cues remain constant. Subjects were able to voluntarily control their perceptual state while viewing the ambiguous stimulus. They were asked to make a saccade across the perceived slanted surface. Our data show that vergence responses closely approximated the vergence response predicted by the disparity cue, irrespective of voluntarily controlled perceived orientation. However, comparing the data obtained while viewing the ambiguous stimulus with data from an unambiguous stimulus condition (when disparity and perspective specified similar surface orientations) revealed an effect of perspective cues on vergence. Collectively our results show that depth cues rather than perceived depth govern vergence.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Abel2008,

title = {Wavelet analysis in infantile nystagmus syndrome: Limitations and abilities},

author = {Larry Allen Abel and Zhong I. Wang and Louis F. Dell'Osso},

doi = {10.1167/iovs.08-1710},

year  = {2008},

date = {2008-01-01},

journal = {Investigative Ophthalmology & Visual Science},

volume = {49},

number = {8},

pages = {3413–3423},

abstract = {PURPOSE: To investigate the proper usage of wavelet analysis in infantile nystagmus syndrome (INS) and determine its limitations and abilities. METHODS: Data were analyzed from accurate eye-movement recordings of INS patients. Wavelet analysis was performed to examine the foveation characteristics, morphologic characteristics and time variation in different INS waveforms. Also compared were the wavelet analysis and the expanded nystagmus acuity function (NAFX) analysis on sections of pre- and post-tenotomy data. RESULTS: Wavelet spectra showed some sensitivity to different features of INS waveforms and reflected their variations across time. However, wavelet analysis was not effective in detecting foveation periods, especially in a complicated INS waveform. NAFX, on the other hand, was a much more direct way of evaluating waveform changes after nystagmus treatments. CONCLUSIONS: Wavelet analysis is a tool that performs, with difficulty, some things that can be done faster and better by directly operating on the nystagmus waveform itself. It appears, however, to be insensitive to the subtle but visually important improvements brought about by INS therapies. Wavelet analysis may have a role in developing automated waveform classifiers where its time-dependent characterization of the waveform can be used. The limitations of wavelet analysis outweighed its abilities in INS waveform-characteristic examination.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bate2008,

title = {Evidence of an eye movement-based memory effect in congenital prosopagnosia},

author = {Sarah Bate and Catherine Haslam and Jeremy J. Tree and Timothy L. Hodgson},

doi = {10.1016/j.cortex.2007.02.004},

year  = {2008},

date = {2008-01-01},

journal = {Cortex},

volume = {44},

number = {7},

pages = {806–819},

abstract = {While extensive work has examined the role of covert recognition in acquired prosopagnosia, little attention has been directed to this process in the congenital form of the disorder. Indeed, evidence of covert recognition has only been demonstrated in one congenital case in which autonomic measures provided evidence of recognition (Jones and Tranel, 2001), whereas two investigations using behavioural indicators failed to demonstrate the effect (de Haan and Campbell, 1991; Bentin et al., 1999). In this paper, we use a behavioural indicator, an "eye movement-based memory effect" (Althoff and Cohen, 1999), to provide evidence of covert recognition in congenital prosopagnosia. In an initial experiment, we examined viewing strategies elicited to famous and novel faces in control participants, and found fewer fixations and reduced regional sampling for famous compared to novel faces. In a second experiment, we examined the same processes in a patient with congenital prosopagnosia (AA), and found some evidence of an eye movement-based memory effect regardless of his recognition accuracy. Finally, we examined whether a difference in scanning strategy was evident for those famous faces AA failed to explicitly recognise, and again found evidence of reduced sampling for famous faces. We use these findings to (a) provide evidence of intact structural representations in a case of congenital prosopagnosia, and (b) to suggest that covert recognition can be demonstrated using behavioural indicators in this disorder.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Davis2008,

title = {Modeling Uhthoff's phenomenon in MS patients with internuclear ophthalmoparesis},

author = {Scott L. Davis and Teresa C. Frohman and C. J. Crandall and M. J. Brown and D. A. Mills and Phillip D. Kramer and O. Stuve and Elliot M. Frohman},

doi = {10.1212/01.wnl.0000291009.69226.4d},

year  = {2008},

date = {2008-01-01},

journal = {Neurology},

volume = {70},

pages = {1098–1106},

abstract = {Objective: The goal of this investigation was to demonstrate that internuclear ophthalmoparesis (INO) can be utilized to model the effects of body temperature-induced changes on the fidelity of axonal conduction in multiple sclerosis (Uhthoff's phenomenon). Methods: Ocular motor function was measured using infrared oculography at 10-minute intervals in patients with multiple sclerosis (MS) with INO (MS-INO; n=8), patients with MS without INO (MS-CON; n=8), and matched healthy controls (CON; n=8) at normothermic baseline, during whole-body heating (increase in core temperature 0.8°C as measured by an ingestible temperature probe and transabdominal telemetry), and after whole-body cooling. The versional disconjugacy index (velocity-VDI), the ratio of abducting/adducting eye movements for velocity, was calculated to assess changes in interocular disconjugacy. The first pass amplitude (FPA), the position of the adducting eye when the abducting eye achieves a centrifugal fixation target, was also computed. Results: Velocity-VDI and FPA in MS-INO patients was elevated (p<0.001) following whole body heating with respect to baseline measures, confirming a compromise in axonal electrical impulse transmission properties. Velocity-VDI and FPA in MS-INO patients was then restored to baseline values following whole-body cooling, confirming the reversible and stereotyped nature of this characteristic feature of demyelination. Conclusions: We have developed a neurophysiologic model for objectively understanding temperature-related reversible changes in axonal conduction in multiple sclerosis. Our observations corroborate the hypothesis that changes in core body temperature (heating and cooling) are associated with stereotypic decay and restoration in axonal conduction mechanisms.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}