EyeLink 临床和动眼神经眼球追踪出版物
EyeLink clinical and oculomotor research publications up until 2023 (with some early 2024s) are listed below by year. You can search the publications using keywords such as Saccadic Adaptation, Schizophrenia, Nystagmus, etc. You can also search for individual author names, and limit searches by year (choose the year then click the search button). If we missed any EyeLink clinical or oculomotor articles, please email us!
2011 |
Gerald Pfeffer; Mathias Abegg; A. Talia Vertinsky; Isabella Ceccherini; Francesco Caroli; Jason J. S. Barton The ocular motor features of adult-onset alexander disease: A case and review of the literature Journal Article In: Journal of Neuro-Ophthalmology, vol. 31, no. 2, pp. 155–159, 2011. @article{Pfeffer2011, A 51-year-old Chinese man presented with gaze-evoked nystagmus, impaired smooth pursuit and vestibular ocular reflex cancellation, and saccadic dysmetria, along with a family history suggestive of late-onset autosomal dominant parkinsonism. MRI revealed abnormalities of the medulla and cervical spinal cord typical of adult-onset Alexander disease, and genetic testing showed homozygosity for the p.D295N polymorphic allele in the gene encoding the glial fibrillary acidic protein. A review of the literature shows that ocular signs are frequent in adult-onset Alexander disease, most commonly gaze-evoked nystagmus, pendular nystagmus, and/or oculopalatal myoclonus, and less commonly ptosis, miosis, and saccadic dysmetria. These signs are consistent with the propensity of adult-onset Alexander disease to cause medullary abnormalities on neuroimaging. |
L. Pisella; N. Alahyane; A. Blangero; F. Thery; S. Blanc; Denis Pelisson Right-hemispheric dominance for visual remapping in humans Journal Article In: Philosophical Transactions of the Royal Society B: Biological Sciences, vol. 366, pp. 572–585, 2011. @article{Pisella2011, We review evidence showing a right-hemispheric dominance for visuo-spatial processing and representation in humans. Accordingly, visual disorganization symptoms (intuitively related to remapping impairments) are observed in both neglect and constructional apraxia. More specifically, we review findings from the intervening saccade paradigm in humans–and present additional original data–which suggest a specific role of the asymmetrical network at the temporo-parietal junction (TPJ) in the right hemisphere in visual remapping: following damage to the right dorsal posterior parietal cortex (PPC) as well as part of the corpus callosum connecting the PPC to the frontal lobes, patient OK in a double-step saccadic task exhibited an impairment when the second saccade had to be directed rightward. This singular and lateralized deficit cannot result solely from the patient's cortical lesion and, therefore, we propose that it is due to his callosal lesion that may specifically interrupt the interhemispheric transfer of information necessary to execute accurate rightward saccades towards a remapped target location. This suggests a specialized right-hemispheric network for visuo-spatial remapping that subsequently transfers target location information to downstream planning regions, which are symmetrically organized. |
Brian A. Richardson; Anusha Ratneswaran; James Lyons; Ramesh Balasubramaniam The time course of online trajectory corrections in memory-guided saccades Journal Article In: Experimental Brain Research, vol. 212, no. 3, pp. 457–469, 2011. @article{Richardson2011, Recent investigations have revealed the kinematics of horizontal saccades are less variable near the end of the trajectory than during the course of execution. Converging evidence indicates that oculomotor networks use online sensorimotor feedback to correct for initial trajectory errors. It is also known that oculomotor networks express saccadic corrections with decreased efficiency when responses are made toward memorized locations. The present research investigated whether repetitive motor timekeeping influences online feedback-based corrections in predictive saccades. Predictive saccades are a subclass of memory-guided saccades and are observed when one makes series of timed saccades. We hypothesized that cueing predictive saccades in a sequence would facilitate the expression of trajectory corrections. Seven participants produced a number of single unpaced, visually guided saccades, and also sequences of timed predictive saccades. Kinematic and trajectory variability were used to measure the expression of online saccadic corrections at a number of time indices in saccade trajectories. In particular, we estimated the minimum time required to implement feedback-based corrections, which was consistently 37 ms. Our observations demonstrate that motor commands in predictive memory-guided saccades can be parameterized by spatial working memory and retain the accuracy of online trajectory corrections typically associated with visually guided behavior. In contrast, untimed memory-guided saccades exhibited diminished kinematic evidence for online corrections. We conclude that motor timekeeping and sequencing contributed to efficient saccadic corrections. These results contribute to an evolving view of the interactions between motor planning and spatial working memory, as they relate to oculomotor control. |
Fabian Schnier; Markus Lappe Differences in inter-saccadic adaptation transfer between inward and outward adaptation Journal Article In: Journal of Neurophysiology, vol. 106, no. 3, pp. 1399–1410, 2011. @article{Schnier2011, Saccadic adaptation is a mechanism to increase or decrease the ampli- tude gain of subsequent saccades, if a saccade is not on target. Recent research has shown that the mechanism of gain increasing, or outward adaptation, and the mechanism of gain decreasing, or inward adapta- tion, rely on partly different processes. We investigate how outward and inward adaptation of reactive saccades transfer to other types of saccades, namely scanning, overlap, memory-guided, and gap sac- cades. Previous research has shown that inward adaptation of reactive saccades transfers only partially to these other saccade types, suggest- ing differences in the control mechanisms between these saccade categories. We show that outward adaptation transfers stronger to scanning and overlap saccades than inward adaptation, and that the strength of transfer depends on the duration for which the saccade target is visible before saccade onset. Furthermore, we show that this transfer is mainly driven by an increase in saccade duration, which is apparent for all saccade categories. Inward adaptation, in contrast, is accompanied by a decrease in duration and in peak velocity, but only the peak velocity decrease transfers from reactive saccades to other saccade categories, i.e., saccadic duration remains constant or even increases for test saccades of the other categories. Our results, there- fore, show that duration and peak velocity are independent parameters of saccadic adaptation and that they are differently involved in the transfer of adaptation between saccade categories. Furthermore, our results add evidence that inward and outward adaptation are different processes. |
Laetitia Cirilli; Philippe Timary; Philippe Lefèvre; Marcus Missal Individual differences in impulsivity predict anticipatory eye movements Journal Article In: PLoS ONE, vol. 6, no. 10, pp. e26699, 2011. @article{Cirilli2011, Impulsivity is the tendency to act without forethought. It is a personality trait commonly used in the diagnosis of many psychiatric diseases. In clinical practice, impulsivity is estimated using written questionnaires. However, answers to questions might be subject to personal biases and misinterpretations. In order to alleviate this problem, eye movements could be used to study differences in decision processes related to impulsivity. Therefore, we investigated correlations between impulsivity scores obtained with a questionnaire in healthy subjects and characteristics of their anticipatory eye movements in a simple smooth pursuit task. Healthy subjects were asked to answer the UPPS questionnaire (Urgency Premeditation Perseverance and Sensation seeking Impulsive Behavior scale), which distinguishes four independent dimensions of impulsivity: Urgency, lack of Premeditation, lack of Perseverance, and Sensation seeking. The same subjects took part in an oculomotor task that consisted of pursuing a target that moved in a predictable direction. This task reliably evoked anticipatory saccades and smooth eye movements. We found that eye movement characteristics such as latency and velocity were significantly correlated with UPPS scores. The specific correlations between distinct UPPS factors and oculomotor anticipation parameters support the validity of the UPPS construct and corroborate neurobiological explanations for impulsivity. We suggest that the oculomotor approach of impulsivity put forth in the present study could help bridge the gap between psychiatry and physiology. |
R. Contreras; Jamshid Ghajar; S. Bahar; M. Suh Effect of cognitive load on eye-target synchronization during smooth pursuit eye movement Journal Article In: Brain Research, vol. 1398, pp. 55–63, 2011. @article{Contreras2011, In mild traumatic brain injury (mTBI), the fiber tracts that connect the frontal cortex with the cerebellum may suffer shear damage, leading to attention deficits and performance variability. This damage also disrupts the enhancement of eye-target synchronization that can be affected by cognitive load when subjects are tested using a concurrent eye-tracking test and word-recall test. We investigated the effect of cognitive load on eye-target synchronization in normal and mTBI patients using the nonlinear dynamical technique of stochastic phase synchronization. Results demonstrate that eye-target synchronization was negatively affected by cognitive load in mTBI subjects. In contrast, eye-target synchronization improved under intermediate cognitive load in young (≤ 40 years old) normal subjects. |
J. Rhys Davies; Tom C. A. Freeman Simultaneous adaptation to non-collinear retinal motion and smooth pursuit eye movement Journal Article In: Vision Research, vol. 51, no. 14, pp. 1637–1647, 2011. @article{Davies2011, Simultaneously adapting to retinal motion and non-collinear pursuit eye movement produces a motion aftereffect (MAE) that moves in a different direction to either of the individual adapting motions. Mack, Hill and Kahn (1989, Perception, 18, 649-655) suggested that the MAE was determined by the perceived motion experienced during adaptation. We tested the perceived-motion hypothesis by having observers report perceived direction during simultaneous adaptation. For both central and peripheral retinal motion adaptation, perceived direction did not predict the direction of subsequent MAE. To explain the findings we propose that the MAE is based on the vector sum of two components, one corresponding to a retinal MAE opposite to the adapting retinal motion and the other corresponding to an extra-retina MAE opposite to the eye movement. A vector model of this component hypothesis showed that the MAE directions reported in our experiments were the result of an extra-retinal component that was substantially larger in magnitude than the retinal component when the adapting retinal motion was positioned centrally. However, when retinal adaptation was peripheral, the model suggested the magnitude of the components should be about the same. These predictions were tested in a final experiment that used a magnitude estimation technique. Contrary to the predictions, the results showed no interaction between type of adaptation (retinal or pursuit) and the location of adapting retinal motion. Possible reasons for the failure of component hypothesis to fully explain the data are discussed. |
Alexis D. J. Makin; Rochelle Ackerley; Kelly S. Wild; Ellen Poliakoff; Emma Gowen; Wael El-Deredy Coherent illusory contours reduce microsaccade frequency Journal Article In: Neuropsychologia, vol. 49, no. 9, pp. 2798–2801, 2011. @article{Makin2011, Synchronized high-frequency gamma band oscillations (30-100. Hz) are thought to mediate the binding of single visual features into whole-object representations. For example, induced gamma band oscillations (iGBRs) have been recorded ∼280. ms after the onset of a coherent Kanizsa triangle, but not after an incoherent equivalent shape. However, several recent studies have provided evidence that the EEG-recorded iGBR may be a by-product of small saccadic eye movements (microsaccades). Considering these two previous findings, one would hypothesis that there should be more microsaccades following the onset of a coherent Kanizsa triangle. However, we found that microsaccade rebound rate was significantly higher after an incoherent triangle was presented. This result suggests that microsaccades are not a reliable indicator of perceptual binding, and, more importantly, implies that iGBR cannot be universally produced by ocular artefacts. |
Krista E. Overvliet; E. Azañón; S. Soto-Faraco Somatosensory saccades reveal the timing of tactile spatial remapping Journal Article In: Neuropsychologia, vol. 49, no. 11, pp. 3046–3052, 2011. @article{Overvliet2011, Remapping tactile events from skin to external space is an essential process for human behaviour. It allows us to refer tactile sensations to their actual externally based location, by combining anatomically based somatosensory information with proprioceptive information about the current body posture. We examined the time course of tactile remapping by recording speeded saccadic responses to somatosensory stimuli delivered to the hands. We conducted two experiments in which arm posture varied (crossed or uncrossed), so that anatomical and external frames of reference were either put in spatial conflict or were aligned. The data showed that saccade onset latencies in the crossed hands conditions were slower than in the uncrossed hands condition, suggesting that, in the crossed hands condition, remapping had to be completed before a correct saccade could be executed. Saccades to tactile stimuli when the hands were crossed were sometimes initiated to the wrong direction and then corrected in-flight, resulting in a turn-around saccade. These turn-around saccades were more likely to occur in short-latency responses, compared to onset latencies of saccades that went straight to target. The latter suggests that participants were postponing their saccade until the time the tactile event was represented according to the current body posture. We propose that the difference between saccade onset latencies of crossed and uncrossed hand postures, and between the onset of a turn-around saccade and a straight saccade in the crossed hand posture, reveal the timing of tactile spatial remapping. |
Steffen Klingenhoefer; F. Bremmer Saccadic suppression of displacement in face of saccade adaptation Journal Article In: Vision Research, vol. 51, pp. 881–889, 2011. @article{Klingenhoefer2011, Saccades challenge visual perception since they induce large shifts of the image on the retina. Nevertheless, we perceive the outer world as being stable. The saccadic system also can rapidly adapt to changes in the environment (saccadic adaptation). In such case, a dissociation is introduced between a driving visual signal (the original saccade target) and a motor output (the adapted saccade vector). The question arises, how saccadic adaptation interferes with perceptual visual stability. In order to answer this question, we engaged human subjects in a saccade adaptation paradigm and interspersed trials in which the saccade target was displaced perisaccadically to a random position. In these trials subjects had to report on their perception of displacements of the saccade target. Subjects were tested in two conditions. In the 'blank' condition, the saccade target was briefly blanked after the end of the saccade. In the 'no-blank' condition the target was permanently visible. Confirming previous findings, the visual system was rather insensitive to displacements of the saccade target in an unadapted state, an effect termed saccadic suppression of displacement (SSD). In all adaptation conditions, we found spatial perception to correlate with the adaptive changes in saccade landing site. In contrast, small changes in saccade amplitude that occurred on a trial by trial basis did not correlate with perception. In the 'no-blank' condition we observed a prominent increase in suppression strength during backward adaptation. We discuss our findings in the context of existing theories on transsaccadic perceptual stability and its neural basis. |
Stephan Koenig; Harald Lachnit Curved saccade trajectories reveal conflicting predictions in associative learning Journal Article In: Journal of Experimental Psychology: Learning, Memory, and Cognition, vol. 37, no. 5, pp. 1164–1177, 2011. @article{Koenig2011, We report how the trajectories of saccadic eye movements are affected by memory interference acquired during associative learning. Human participants learned to perform saccadic choice responses based on the presentation of arbitrary central cues A, B, AC, BC, AX, BY, X, and Y that were trained to predict the appearance of a peripheral target stimulus at 1 of 3 possible locations, right (R), mid (M), or left (L), in the upper hemifield. We analyzed as measures of associative learning the frequency, latency, and curvature of saccades elicited by the cues and directed at the trained locations in anticipation of the targets. Participants were trained on two concurrent discrimination problems A+R, AC+R, AX+M, X+M and B+L, BC+L, BY+M, Y+M. From a connectionist perspective, cues were predicted to acquire associative links connecting the cues to the trained outcomes in memory. Model simulations based on the learning rule of the Rescorla and Wagner (1972) model revealed that for some cues, the prediction of the correct target location was challenged by the interfering prediction of an incorrect location. We observed that saccades directed at the correct location in anticipation of the target curved away from the location that was predicted by the interfering association. Furthermore, changes in curvature during training corresponded to predicted changes in associative memory. We propose that this curvature was caused by the inhibition of the incorrect prediction, as previously has been suggested with the concept of distractor inhibition (Sheliga, Riggio, & Rizzolatti, 1994; Tipper, Howard, & Houghton, 2000). The paradigm provides a new method to examine memory interference during associative learning. |
Lianne C. Krab; Arja Goede-Bolder; Femke K. Aarsen; Henriëtte A. Moll; Chris I. De Zeeuw; Ype Elgersma; Josef N. Geest Motor learning in children with Neurofibromatosis Type I Journal Article In: Cerebellum, vol. 10, no. 1, pp. 14–21, 2011. @article{Krab2011, The aim of this study was to quantify the frequently observed problems in motor control in Neurofibromatosis type 1 (NF1) using three tasks on motor performance and motor learning. A group of 70 children with NF1 was compared to age-matched controls. As expected, NF1 children showed substantial problems in visuo-motor integration (Beery VMI). Prism-induced hand movement adaptation seemed to be mildly affected. However, no significant impairments in the accuracy of simple eye or hand movements were observed. Also, saccadic eye movement adaptation, a cerebellum dependent task, appeared normal. These results suggest that the motor problems of children with NF1 in daily life are unlikely to originate solely from impairments in motor learning. Our findings, therefore, do not support a general dysfunction of the cerebellum in children with NF1. |
Louisa Lavergne; Dorine Vergilino-Perez; Christelle Lemoine; Thérèse Collins; Karine Doré-Mazars Exploring and targeting saccades dissociated by saccadic adaptation Journal Article In: Brain Research, vol. 1415, pp. 47–55, 2011. @article{Lavergne2011, Saccadic adaptation maintains saccade accuracy and has been studied with targeting saccades, i.e. saccades that bring the gaze to a target, with the classical intra-saccadic step procedure in which the target systematically jumps to a new position during saccade execution. Post-saccadic visual feedback about the error between target position and the saccade landing position is crucial to establish and maintain adaptation. However, recent research focusing on two-saccade sequences has shown that exploring saccades, i.e. saccades that explore an object, resists this classical intra-saccadic step procedure but can be adapted by systematically changing the main parameter used for their coding: stimulus size. Here, we adapted an exploring saccade and a targeting saccade in two separate experiments, using the appropriate adaptation procedure, and we tested whether the adaptation induced on one saccade type transferred to the other. We showed that whereas classical targeting saccade adaptation does not transfer to exploring saccades, the reciprocal transfer (i.e., from exploring to targeting saccades) occurred when targeting saccades aimed for a spatially extended stimulus, but not when they aimed for an isolated target. These results show that, in addition to position errors, size errors can drive adaptation, and confirm that exploring vs. targeting a stimulus leads to two different motor planning modes. |
Katharina Havermann; Eckart Zimmermann; Markus Lappe Eye position effects in saccadic adaptation Journal Article In: Journal of Neurophysiology, vol. 106, no. 5, pp. 2536–2545, 2011. @article{Havermann2011, Saccades are used by the visual system to explore visual space with the high accuracy of the fovea. The visual error after the saccade is used to adapt the control of subsequent eye movements of the same amplitude and direction in order to keep saccades accurate. Saccadic adaptation is thus specific to saccade amplitude and direction. In the present study we show that saccadic adaptation is also specific to the initial position of the eye in the orbit. This is useful, because saccades are normally accompanied by head movements and the control of combined head and eye movements depends on eye position. Many parts of the saccadic system contain eye position information. Using the intrasaccadic target step paradigm, we adaptively reduced the amplitude of reactive saccades to a suddenly appearing target at a selective position of the eyes in the orbitae and tested the resulting amplitude changes for the same saccade vector at other starting positions. For central adaptation positions the saccade amplitude reduction transferred completely to eccentric starting positions. However, for adaptation at eccentric starting positions, there was a reduced transfer to saccades from central starting positions or from eccentric starting positions in the opposite hemifield. Thus eye position information modifies the transfer of saccadic amplitude changes in the adaptation of reactive saccades. A gain field mechanism may explain the eye position dependence found. |
Stephen J. Heinen; Z. Jin; Scott N. J. Watamaniuk Flexibility of foveal attention during ocular pursuit Journal Article In: Journal of Vision, vol. 11, no. 2, pp. 1–12, 2011. @article{Heinen2011, Smooth pursuit of natural objects requires flexible allocation of attention to inspect features. However, it has been reported that attention is focused at the fovea during pursuit. We ask here if foveal attention is obligatory during pursuit, or if it can be disengaged. Observers tracked a stimulus composed of a central dot surrounded by four others and identified one of the dots when it dimmed. Extinguishing the center dot before the dimming improved task performance, suggesting that attention was released from it. To determine if the center dot automatically usurped attention, we provided the pursuit system with an alternative sensory signal by adding peripheral motion that moved with the stimulus. This also improved identification performance, evidence that a central target does not necessarily require attention during pursuit. Identification performance at the central dot also improved, suggesting that the spatial extent of the background did not attract attention to the periphery; instead, peripheral motion freed pursuit attention from the central dot, affording better identification performance. The results show that attention can be flexibly allocated during pursuit and imply that attention resources for pursuit of small and large objects come from different sources. |
Stephanie Jainta The pupil reflects motor preparation for saccades – even before the eye starts to move Journal Article In: Frontiers in Human Neuroscience, vol. 5, pp. 97, 2011. @article{Jainta2011, The eye produces saccadic eye movements whose reaction times are perhaps the shortest in humans. Saccade latencies reflect ongoing cortical processing and, generally, shorter latencies are supposed to reflect advanced motor preparation. The dilation of the eye's pupil is reported to reflect cortical processing as well. Eight participants made saccades in a gap and overlap paradigm (in pure and mixed blocks), which we used in order to produce a variety of different saccade latencies. Saccades and pupil size were measured with the EyeLink II. The pattern in pupil dilation resembled that of a gap effect: for gap blocks, pupil dilations were larger compared to overlap blocks; mixing gap and overlap trials reduced the pupil dilation for gap trials thereby inducing a switching cost. Furthermore, saccade latencies across all tasks predicted the magnitude of pupil dilations post hoc: the longer the saccade latency the smaller the pupil dilation before the eye actually began to move. In accordance with observations for manual responses, we conclude that pupil dilations prior to saccade execution reflect advanced motor preparations and therefore provide valid indicator qualities for ongoing cortical processes. |
Stephanie Jainta; Anne Dehnert; Sven P. Heinrich; Wolfgang Jaschinski Binocular coordination during reading of blurred and nonblurred text Journal Article In: Investigative Ophthalmology & Visual Science, vol. 52, no. 13, pp. 9416–9424, 2011. @article{Jainta2011a, PURPOSE: Reading a text requires vergence angle adjustments, so that the images in the two eyes fall on corresponding retinal areas. Vergence adjustments bring the two retinal images into Panum's fusional area and therefore, small remaining errors or regulations do not lead to double vision. The present study evaluated dynamic and static aspects of the binocular coordination when upcoming text was blurred. METHODS: Binocular eye movements and accommodation responses were simultaneously measured for 20 participants while reading single, nonblurred sentences and while the text was blurred as if it were seen by a person in whom the combination of refraction and accommodation deviated from the stimulus plane by 0.5 D. RESULTS: Text comprehension did not change, even though fixation times increased for reading blurred sentences. The disconjugacy during saccades was also not affected by blurred text presentations, but the vergence adjustment during fixations was reduced. Further, for blurred text, the overall vergence angle shifted in the exo direction, and this shift correlated with the individual heterophoria. Accommodation measures showed that the lag of accommodation was slightly larger for reading blurred sentences and that the shift in vergence angle was larger when the individual lag of accommodation was also larger. CONCLUSIONS: The results suggest that reading comprehension is robust against changes in binocular coordination that result from moderate text degradation; nevertheless, these changes are likely to be linked to the development of fatigue and visual strain in near reading conditions. |
Peter J. Etchells; Christopher P. Benton; Casimir J. H. Ludwig; Iain D. Gilchrist Testing a simplified method for measuring velocity integration in saccades using a manipulation of target contrast Journal Article In: Frontiers in Psychology, vol. 2, pp. 115, 2011. @article{Etchells2011, A growing number of studies in vision research employ analyses of how perturbations in visual stimuli influence behavior on single trials. Recently, we have developed a method along such lines to assess the time course over which object velocity information is extracted on a trial-by-trial basis in order to produce an accurate intercepting saccade to a moving target. Here, we present a simplified version of this methodology, and use it to investigate how changes in stimulus contrast affect the temporal velocity integration window used when generating saccades to moving targets. Observers generated saccades to one of two moving targets which were presented at high (80%) or low (7.5%) contrast. In 50% of trials, target velocity stepped up or down after a variable interval after the saccadic go signal. The extent to which the saccade endpoint can be accounted for as a weighted combination of the pre- or post-step velocities allows for identification of the temporal velocity integration window. Our results show that the temporal integration window takes longer to peak in the low when compared to high contrast condition. By enabling the assessment of how information such as changes in velocity can be used in the programming of a saccadic eye movement on single trials, this study describes and tests a novel methodology with which to look at the internal processing mechanisms that transform sensory visual inputs into oculomotor outputs. |
Peggy Gerardin; Valérie Gaveau; Denis Pélisson; Claude Prablanc Integration of visual information for saccade production Journal Article In: Human Movement Science, vol. 30, no. 6, pp. 1009–1021, 2011. @article{Gerardin2011, To foveate a visual target, subjects usually execute a primary hypometric saccade (S1) bringing the target in perifoveal vision, followed by a corrective saccade (S2) or by more than one S2. It is still debated to what extent these S2 are pre-programmed or dependent only on post-saccadic retinal error. To answer this question, we used a visually-triggered saccade task in which target position and target visibility were manipulated. In one-third of the trials, the target was slightly displaced at S1 onset (so-called double step paradigm) and was maintained until the end of S1, until the start of the first S2 or until the end of the trial. Experiments took place in two visual environments: in the dark and in a dimly lit room with a visible random square background. The results showed that S2 were less accurate for shortest target durations. The duration of post-saccadic visual integration thus appears as the main factor responsible for corrective saccade accuracy. We also found that the visual context modulates primary saccade accuracy, especially for the most hypometric subjects. These findings suggest that the saccadic system is sensitive to the visual properties of the environment and uses different strategies to maintain final gaze accuracy. |
Colas N. Authié; Daniel R. Mestre Optokinetic nystagmus is elicited by curvilinear optic flow during high speed curve driving Journal Article In: Vision Research, vol. 51, no. 16, pp. 1791–1800, 2011. @article{Authie2011, When analyzing gaze behavior during curve driving, it is commonly accepted that gaze is mostly located in the vicinity of the tangent point, being the point where gaze direction tangents the curve inside edge. This approach neglects the fact that the tangent point is actually motionless only in the limit case when the trajectory precisely follows the curve's geometry. In this study, we measured gaze behavior during curve driving, with the general hypothesis that gaze is not static, when exposed to a global optical flow due to self-motion. In order to study spatio-temporal aspects of gaze during curve driving, we used a driving simulator coupled to a gaze recording system. Ten participants drove seven runs on a track composed of eight curves of various radii (50, 100, 200 and 500. m), with each radius appearing in both right and left directions. Results showed that average gaze position was, as previously described, located in the vicinity of the tangent point. However, analysis also revealed the presence of a systematic optokinetic nystagmus (OKN) around the tangent point position. The OKN slow phase direction does not match the local optic flow direction, while slow phase speed is about half of the local speed. Higher directional gains are observed when averaging the entire optical flow projected on the simulation display, whereas the best speed gain is obtained for a 2° optic flow area, centered on the instantaneous gaze location. The present study confirms that the tangent point is a privileged feature in the dynamic visual scene during curve driving, and underlines a contribution of the global optical flow to gaze behavior during active self-motion. |
Artem V. Belopolsky; Jan Theeuwes Selection within visual memory representations activates the oculomotor system Journal Article In: Neuropsychologia, vol. 49, no. 6, pp. 1605–1610, 2011. @article{Belopolsky2011, Humans tend to create and maintain internal representations of the environment that help guiding actions during the everyday activities. Previous studies have shown that the oculomotor system is involved in coding and maintenance of locations in visual-spatial working memory. In these studies selection of the relevant location for maintenance in working memory took place on the screen (selecting the location of a dot presented on the screen). The present study extended these findings by showing that the oculomotor system also codes selection of location from an internal memory representation. Participants first memorized two locations and after a retention interval selected one location for further maintenance. The results show that saccade trajectories deviated away from the ultimately remembered location. Furthermore, selection of the location from the memorized representation produced sustained oculomotor preparation to it. The results show that oculomotor system is very flexible and plays an active role for coding and maintaining information selected within internal memory representations. |
Chang-Mao Chao; Philip Tseng; Tzu-Yu Hsu; Jia-Han Su; Ovid J. L. Tzeng; Daisy L. Hung; Neil G. Muggleton; Chi-Hung Juan Predictability of saccadic behaviors is modified by transcranial magnetic stimulation over human posterior parietal cortex Journal Article In: Human Brain Mapping, vol. 32, no. 11, pp. 1961–1972, 2011. @article{Chao2011, Predictability in the visual environment provides a powerful cue for efficient processing of scenes and objects. Recently, studies have suggested that the directionality and magnitude of saccade curvature can be informative as to how the visual system processes predictive information. The pres-ent study investigated the role of the right posterior parietal cortex (rPPC) in shaping saccade curva-tures in the context of predictive and non-predictive visual cues. We used an orienting paradigm that incorporated manipulation of target location predictability and delivered transcranial magnetic stimulation (TMS) over rPPC. Participants were presented with either an informative or uninforma-tive cue to upcoming target locations. Our results showed that rPPC TMS generally increased sac-cade latency and saccade error rates. Intriguingly, rPPC TMS increased curvatures away from the distractor only when the target location was unpredictable and decreased saccadic errors towards the distractor. These effects on curvature and accuracy were not present when the target location was predictable. These results dissociate the strong contingency between saccade latency and saccade curvature and also indicate that rPPC plays an important role in allocating and suppressing attention to distractors when the target demands visual disambiguation. Furthermore, the present study sug-gests that, like the frontal eye fields, rPPC is critically involved in determining saccade curvature and the generation of saccadic behaviors under conditions of differing target predictability. |
Pierre Morel; Sophie Deneve; Pierre Baraduc Optimal and suboptimal use of postsaccadic vision in sequences of saccades Journal Article In: Journal of Neuroscience, vol. 31, no. 27, pp. 10039–10049, 2011. @article{Morel2011, Saccades are imprecise, due to sensory and motor noise. To avoid an accumulation of errors during sequences of saccades, a prediction derived from the efference copy can be combined with the reafferent visual feedback to adjust the following eye movement. By varying the information quantity of the visual feedback, we investigated how the reliability of the visual information affects the postsaccadic update in humans. Two elements of the visual scene were manipulated, the saccade target or the background, presented either together or in isolation. We determined the weight of the postsaccadic visual information by measuring the effect of intrasaccadic visual shifts on the following saccade. We confirmed that the weight of visual information evolves with information quantity as predicted for a statistically optimal system. In particular, we found that the visual background alone can guide the postsaccadic update, and that information from target and background are optimally combined. Moreover, these visual weights are adjusted dynamically and on a trial-to-trial basis to the level of visual noise determined by target eccentricity and reaction time. In contrast, we uncovered a dissociation between the visual signals used to update the next planned saccade (main saccade) and those used to generate an involuntary corrective saccade. The latter was exclusively based on visual information about the target, and discarded all information about the background: a suboptimal use of visual evidence. |
Nicole Naue; Daniel Strüber; Ingo Fründ; Jeanette Schadow; Daniel Lenz; Stefan Rach; Ursula Körner; Christoph S. Herrmann Gamma in motion: Pattern reversal elicits stronger gamma-band responses than motion Journal Article In: NeuroImage, vol. 55, no. 2, pp. 808–817, 2011. @article{Naue2011, Previous studies showed higher gamma-band responses (GBRs, ≈ 40. Hz) of the electroencephalogram (EEG) for moving compared to stationary stimuli. However, it is unclear whether this modulation by motion reflects a special responsiveness of the GBR to the stimulus feature ''motion,'' or whether GBR enhancements of similar magnitude can be elicited also by a salient change within a static stimulus that does not include motion.Therefore, we measured the EEG of healthy subjects watching stationary square wave gratings of high contrast that either started to move or reversed their black and white pattern shortly after their onset. The strong contrast change of the pattern reversal represented a salient but motionless change within the grating that was compared to the onset of the stationary grating and the motion onset. Induced and evoked GBRs were analyzed for all three display conditions. In order to assess the influenceof fixational eye movements on the induced GBRs, we also examined the time courses of microsaccade rates during the three display conditions. Amplitudes of both evoked and induced GBRs were stronger for pattern reversal than for motion onset. There was no significant amplitude difference between the onsets of the stationary and moving gratings. However, mean frequencies of the induced GBR were ~10. Hz higher in response to the onsets of moving compared to stationary gratings. Furthermore, the modulations of the induced GBR did not parallel the modulations of microsaccade rate, indicating that our induced GBRs reflect neuronal processes. These results suggest that, within the gamma-band range, the encoding of moving gratings in early visual cortex is primarily based on an upward frequency shift, whereas contrast changes within static gratings are reflected by amplitude enhancement. |
Sven Ohl; Stephan A. Brandt; Reinhold Kliegl Secondary (micro-)saccades: The influence of primary saccade end point and target eccentricity on the process of postsaccadic fixation Journal Article In: Vision Research, vol. 51, no. 23-24, pp. 2340–2347, 2011. @article{Ohl2011, We examine how the size of saccadic under-/overshoot and target eccentricity influence the latency, amplitude and orientation of secondary (micro-)saccades. In our experiment, a target appeared at an eccentricity of either 6° or 14° of visual angle. Subjects were instructed to direct their gaze as quickly as possible to the target and hold fixation at the new location until the end of the trial. Typically, increasing saccadic error is associated with faster and larger secondary saccades. We show that secondary saccades at distant in contrast to close targets have in a specific error range a shorter latency, larger amplitude, and follow more often the direction of the primary saccade. Finally, we demonstrate that an undershooting primary saccade is followed almost exclusively by secondary saccades into the same direction while overshooting primary saccades are followed by secondary saccades into both directions. This supports the notion that under- and overshooting imply different consequences for postsaccadic oculomotor processing. Results are discussed using a model, introduced by Rolfs, Kliegl, and Engbert (2008), to account for the generation of microsaccades. We argue that the dynamic interplay of target eccentricity and the magnitude of the saccadic under-/overshoot can be explained by a different strength of activation in the two hemispheres of the saccadic motor map in this model. |
Samantha C. Otero; Brendan S. Weekes; Samuel B. Hutton Pupil size changes during recognition memory Journal Article In: Psychophysiology, vol. 48, no. 10, pp. 1346–1353, 2011. @article{Otero2011, Pupils dilate to a greater extent when participants view old compared to new items during recognition memory tests. We report three experiments investigating the cognitive processes associated with this pupil old/new effect. Using a remember/know procedure, we found that the effect occurred for old items that were both remembered and known at recognition, although it was attenuated for known compared to remembered items. In Experiment 2, the pupil old/new effect was observed when items were presented acoustically, suggesting the effect does not depend on low-level visual processes. The pupil old/new effect was also greater for items encoded under deep compared to shallow orienting instructions, suggesting it may reflect the strength of the underlying memory trace. Finally, the pupil old/new effect was also found when participants falsely recognized items as being old. We propose that pupils respond to a strength-of-memory signal and suggest that pupillometry provides a useful technique for exploring the underlying mechanisms of recognition memory. |
Jorge Otero-Millan; Alessandro Serra; R. John Leigh; Xoana G. Troncoso; Stephen L. Macknik; Susana Martinez-Conde Distinctive features of saccadic intrusions and microsaccades in progressive supranuclear palsy Journal Article In: Journal of Neuroscience, vol. 31, no. 12, pp. 4379–4387, 2011. @article{OteroMillan2011a, The eyes do not stay perfectly still during attempted fixation; fixational eye movements and saccadic intrusions (SIs) continuously change the position of gaze. The most common type of SI, square-wave jerks (SWJs), consists of saccade pairs that appear purely horizontal on clinical inspection: the first saccade moves the eye away from the fixation target, and after a short interval, the second saccade brings it back toward the target. SWJs are prevalent in certain neurological disorders, including progressive supranuclear palsy (PSP). Here, we developed an objective method to identify SWJs. We found that SWJs are more frequent, larger, and more markedly horizontal in PSP patients than in healthy human subjects. Furthermore, the loss of a vertical component in fixational saccades and SWJs was the eye movement feature that best distinguished PSP patients from controls. We moreover determined that, in PSP patients and controls, the larger the saccade the more likely it was part of a SWJ. Furthermore, saccades produced by PSP patients had equivalent properties whether they were part of a SWJ or not, suggesting that normal fixational saccades (microsaccades) are rare in PSP. We propose that fixational saccades and SIs are generated by the same neural circuit and that, both in PSP patients and in controls, SWJs result from a coupling mechanism that generates a second corrective saccade shortly after a large fixation saccade. Because of brainstem and/or cerebellum impairment, fixational saccades in PSP are abnormally large and thus more likely to trigger a corrective saccade, giving rise to SWJs. |
2010 |
Konstantin Mergenthaler; Ralf Engbert Microsaccades are different from saccades in scene perception Journal Article In: Experimental Brain Research, vol. 203, no. 4, pp. 753–757, 2010. @article{Mergenthaler2010, Eye-fixation durations are among the best and most widely used measures of ongoing cognition in visual tasks, e.g., reading, visual search or scene perception. However, fixations are characterized by ongoing motor activity (or fixational eye movements) with microsaccades as their most pronounced components. Recent work demonstrated the similarities of microsaccades and inspection saccades. Here, we show that distinct properties of micro-saccades and inspection saccades can be found in a scene perception task, based on descriptive measures (e.g., a bimodal amplitude distribution) as well as functional characteristics (e.g., inter saccadic-event intervals and generating processes). Besides these specific diverences, microsaccade rates produced by individual participants in a fixation paradigm are correlated with microsaccade rates extracted from fixations in scene perception, indicating a common neurophysiological basis. Finally, we observed that slow fixational eye movements, called drift, are significantly reduced during long Wxations in scene viewing, which informs about the control of eye movements in scene viewing. |
Manon Mulckhuyse; Jan Theeuwes Unconscious cueing effects in saccadic eye movements - Facilitation and inhibition in temporal and nasal hemifield Journal Article In: Vision Research, vol. 50, no. 6, pp. 606–613, 2010. @article{Mulckhuyse2010, The current study investigated whether subliminal spatial cues can affect the oculomotor system. In addition, we performed the experiment under monocular viewing conditions. By limiting participants to monocular viewing conditions, we can examine behavioral temporal-nasal hemifield asymmetries. These behavioral asymmetries may arise from an anatomical asymmetry in the retinotectal pathway. The results show that even though our spatial cues were not consciously perceived they did affect the oculomotor system: relative to the neutral condition, saccade latencies to the validly cued location were shorter and saccade latencies to the invalidly cued location were longer. Although we did not observe an overall inhibition of return effect, there was a reliable effect of hemifield on IOR for those observers who showed an overall IOR effect. More specifically, consistent with the notion that processing via the retinotectal pathway is stronger in the temporal hemifield than in the nasal hemifield we found an IOR effect for cues presented in the temporal hemifield but not for cues presented in the nasal hemifield. We conclude that unconsciously processed spatial cues can affect the oculomotor system. In addition, the observed behavioral temporal-nasal hemifield asymmetry is consistent with retinotectal mediation. |
Emer O'Connor; Tom H. Margrain; Tom C. A. Freeman Age, eye movement and motion discrimination Journal Article In: Vision Research, vol. 50, no. 23, pp. 2588–2599, 2010. @article{OConnor2010, Age is known to affect sensitivity to retinal motion. However, little is known about how age might affect sensitivity to motion during pursuit. We therefore investigated direction discrimination and speed discrimination when moving stimuli were either fixated or pursued. Our experiments showed: (1) age influences direction discrimination at slow speeds but has little affect on speed discrimination; (2) the faster eye movements made in the pursuit conditions produced poorer direction discrimination at slower speeds, and poorer speed discrimination at all speeds; (3) regardless of eye-movement condition, observers always combined retinal and extra-retinal motion signals to make their judgements. Our results support the idea that performance in these tasks is limited by the internal noise associated with retinal and extra-retinal motion signals, both of which feed into a stage responsible for estimating head-centred motion. Imprecise eye movement, or later noise introduced at the combination stage, could not explain the results. |
Naseem Al-Aidroos; Jay Pratt Top-down control in time and space: Evidence from saccadic latencies and trajectories Journal Article In: Visual Cognition, vol. 18, no. 1, pp. 26–49, 2010. @article{AlAidroos2010, Visual distractors disrupt the production of saccadic eye movements temporally, by increasing saccade latency, and spatially, by biasing the trajectory of the movement. The present research investigated the extent to which top-down control can be exerted over these two forms of oculomotor capture. In two experiments, people were instructed to make target directed saccades in the presence of distractors, and temporal and spatial capture were assessed simultaneously by measuring saccade latency and saccade trajectory curvature, respectively. In Experiment 1, an attentional control set manipulation was employed, resulting in the elimination of temporal capture, but only an attenuation of spatial capture. In Experiment 2, foreknowledge of the target location caused an attenuation of temporal capture but an enhancement of spatial capture. These results suggest that, whereas temporal capture is contingent on top-down control, the spatial component of capture is stimulus-driven. |
Zoï Kapoula; Q. Yang; M. Vernet; P. Bonfils; Alain Londero Eye movement abnormalities in somatic tinnitus: Fixation, smooth pursuit and optokinetic nystagmus Journal Article In: Auris Nasus Larynx, vol. 37, no. 3, pp. 314–321, 2010. @article{Kapoula2010a, Objective: Smooth pursuit (SP), optokinetic nystagmus (OKN) and fixation were investigated in five subjects with somatic tinnitus modulated by eye movements, jaw or neck. Methods: Eye movements were recorded with the EyeLink II video system. Results: (1) Fixation was characterized by high frequency and amplitude of saccade intrusions; (2) SP had low gain particularly in the vertical direction, and it was characterized by high frequency of catch-up saccades with high amplitude, including predictive saccades; (3) OKN also had low gain particularly in the vertical direction. Each subject showed abnormality for more than one type of eye movement, and for specific directions. Conclusions and significance: The results suggest mild dysfunction of cortical-subcortical and cerebellar structures involved in the control of these eye movements. Particularly deficits for vertical pursuit eye movements and fixation instability in line with cerebellar signs. Further studies of more patients with or without modulated tinnitus are in progress. |
Zoï Kapoula; Qing Yang; Audrey Bonnet; Pauline Bourtoire; Jean Sandretto EMDR effects on pursuit eye movements Journal Article In: PLoS ONE, vol. 5, no. 5, pp. e10762, 2010. @article{Kapoula2010b, This study aimed to objectivize the quality of smooth pursuit eye movements in a standard laboratory task before and after an Eye Movement Desensitization and Reprocessing (EMDR) session run on seven healthy volunteers. EMDR was applied on autobiographic worries causing moderate distress. The EMDR session was complete in 5 out of the 7 cases; distress measured by SUDS (Subjective Units of Discomfort Scale) decreased to a near zero value. Smooth pursuit eye movements were recorded by an Eyelink II video system before and after EMDR. For the five complete sessions, pursuit eye movement improved after their EMDR session. Notably, the number of saccade intrusions-catch-up saccades (CUS)-decreased and, reciprocally, there was an increase in the smooth components of the pursuit. Such an increase in the smoothness of the pursuit presumably reflects an improvement in the use of visual attention needed to follow the target accurately. Perhaps EMDR reduces distress thereby activating a cholinergic effect known to improve ocular pursuit. |
Zoï Kapoula; Qing Yang; Marine Vernet; Benedicte Dieudonné; Sandrine Greffard; Marc Verny Spread deficits in initiation, speed and accuracy of horizontal and vertical automatic saccades in dementia with Lewy bodies Journal Article In: Frontiers in Neurology, vol. 1, pp. 138, 2010. @article{Kapoula2010, BACKGROUND: Mosimann et al. (2005) reported prolongation of saccade latency of prosaccades in dementia with Lewy body (DLB). The goal of this study is to go further examining all parameters, such as rates of express latency, but also accuracy and velocity of saccades, and their variability. METHODS: We examined horizontal and vertical saccades in 10 healthy elderly subjects and 10 patients with DLB. Two tasks were used: the gap (fixation target extinguishes prior to target onset) and the overlap (fixation stays on after target onset). Eye movements were recorded with the Eyelink II eye tracker. RESULTS: The main findings were: (1) as for healthy, latencies were shorter in the gap than in the overlap task (a gap effect); (2) for both tasks latency of saccades was longer for DLB patients and for all directions; (3) express latency in the gap task was absent for large majority of DLB patients while such saccades occurred frequency for controls; (4) accuracy and peak velocity were lower in DLB patients; (5) variability of all parameters was abnormally high in DLB patients.$backslash$ CONCLUSIONS: Abnormalities of all parameters, latency, accuracy and peak velocity reflect spread deficits in cortical-subcortical circuits involved in the triggering and execution of saccades. |
Dirk Kerzel; Sabine Born; David Souto Inhibition of steady-state smooth pursuit and catch-up saccades by abrupt visual and auditory Onsets Journal Article In: Journal of Neurophysiology, vol. 104, no. 5, pp. 2573–2585, 2010. @article{Kerzel2010, It is known that visual transients prolong saccadic latency and reduce saccadic frequency. The latter effect was attributed to subcortical structures because it occurred only 60-70 ms after stimulus onset. We examined the effects of large task-irrelevant transients on steady-state pursuit and the generation of catch-up saccades. Two screen-wide stripes of equal contrast (4, 20, or 100%) were briefly flashed at equal eccentricities (3, 6, or 12 degrees ) from the pursuit target. About 100 ms after flash onset, we observed that pursuit gain dropped by 6-12% and catch-up saccades were entirely suppressed. The relatively long latency of the inhibition suggests that it results from cortical mechanisms that may act by promoting fixation or the deployment of attention over the visual field. In addition, we show that a loud irrelevant sound is able to generate the same inhibition of saccades as visual transients, whereas it only induces a weak modulation of pursuit gain, indicating a privileged access of acoustic information to the saccadic system. Finally, irrelevant changes in motion direction orthogonal to pursuit had a smaller and later inhibitory effect. |
Kerstin Königs; Frank Bremmer Localization of visual and auditory stimuli during smooth pursuit eye movements Journal Article In: Journal of Vision, vol. 10, no. 8, pp. 1–14, 2010. @article{Koenigs2010, Humans move their eyes more often than their heart beats. Although these eye movements induce large retinal image shifts, we perceive our world as stable. Yet, this perceptual stability is not complete. A number of studies have shown that visual targets which are briefly presented during such eye movements are mislocalized in a characteristic manner. It is largely unknown, however, if auditory stimuli are also mislocalized, i.e. whether or not perception generalizes across senses and space is represented supramodally. In our current study subjects were asked to localize brief visual and auditory stimuli that were presented during smooth pursuit in the dark. In addition, we measured auditory and visual detection thresholds. Confirming previous studies, perceived visual positions were shifted in direction of the pursuit. This shift was stronger for the hemifield the eye was heading towards (foveopetal). Perceptual auditory space was compressed towards the pursuit target (ventriloquism effect). This perceptual error was slightly reduced during pursuit as compared to fixation and differed clearly from the mislocalization of visual targets. While we found an influence of pursuit on localization, we found no such effect on the detection of visual and auditory stimuli. Taken together, our results do not provide evidence for the hypothesis of a supramodal representation of space during active oculomotor behavior. |
Kaitlin E. W. Laidlaw; Alan Kingstone The time course of vertical, horizontal and oblique saccade trajectories: Evidence for greater distractor interference during vertical saccades Journal Article In: Vision Research, vol. 50, no. 9, pp. 829–837, 2010. @article{Laidlaw2010, The present study aimed to characterize the effect of a nearby distractor on vertical, horizontal, and oblique saccade curvature under normal saccade preparation times. Consistent with previous findings, longer-latency vertical saccades showed greater curvature away from a distractor than did oblique or horizontal saccades. At short latencies, vertical saccades also showed greater curvature towards the distractor. A neural explanation for why vertical saccades show greater interference from a distractor is theorized. |
Maren Lappe-Osthege; Silke Talamo; Christoph Helmchen; Andreas Sprenger Overestimation of saccadic peak velocity recorded by electro-oculography compared to video-oculography and scleral search coil Journal Article In: Clinical Neurophysiology, vol. 121, no. 10, pp. 1786–1787, 2010. @article{LappeOsthege2010, Peak velocity of saccadic eye movements is a crucial motor parameter in clinical neurology and oculomotor research. It may help to assign patients' lesions to even very small brain regions which are not (yet) recognizable with magnetic resonance imaging (MRI). Horizontal slowing of saccades is associated with pontine lesions of the paramedian pontine reticular formation while saccades in cerebellar or cortical lesions are usually not slowed. Accordingly, saccade velocity helps to classify and distinguish neurodegenerative and genetic movement disorders, e.g. Parkinson's disease or spinocerebellar ataxias. However, related studies are often not easily comparable as different recording techniques (e.g. electro-oculography, video-oculography, and scleral search coil) and different paradigms (e.g., reflexive, self-paced saccades) are used irrespective of their influence on saccade velocity. Therefore, we intraindividually compared saccadic peak velocities using electro-oculography (EOG), video-oculography (VOG) and scleral search coil (SSC) in a variety of saccade types and conditions to assess the comparability of these methods. |
Jochen Laubrock; Reinhold Kliegl; Martin Rolfs; Ralf Engbert When do microsaccades follow spatial attention? Journal Article In: Attention, Perception, and Psychophysics, vol. 72, no. 3, pp. 683–694, 2010. @article{Laubrock2010, Following up on an exchange about the relation between microsaccades and spatial attention (Horowitz, Fenc- sik, Fine, Yurgenson, & Wolfe, 2007; Horowitz, Fine, Fencsik, Yurgenson, & Wolfe, 2007; Laubrock, Engbert, Rolfs, & Kliegl, 2007), we examine the effects of selection criteria and response modality. We show that for Posner cuing with saccadic responses, microsaccades go with attention in at least 75% of cases (almost 90% if probability matching is assumed) when they are first (or only) microsaccades in the cue–target interval and when they occur between 200 and 400 msec after the cue. The relation between spatial attention and the direction of microsaccades drops to chance level for unselected microsaccades collected during manual-response conditions. Analyses of data from four cross-modal cuing experiments demonstrate an above-chance, intermediate link for visual cues, but no systematic relation for auditory cues. Thus, the link between spatial attention and direction of microsaccades depends on the experimental condition and time of occurrence, but it can be very strong. |
Thérèse Collins Extraretinal signal metrics in multiple-saccade sequences Journal Article In: Journal of Vision, vol. 10, no. 14, pp. 1–14, 2010. @article{Collins2010a, Executing sequences of memory-guided movements requires combining sensory information with information about previously made movements. In the oculomotor system, extraretinal information must be combined with stored visual information about target location. The use of extraretinal signals in oculomotor planning can be probed in the double-step task. Using this task and a multiple-step version, the present study examined whether an extraretinal signal was used on every trial, whether its metrics represented desired or actual eye displacement, and whether it was best characterized as a direct estimate of orbital eye position or a vector representation of eye displacement. The results show that accurate information, including saccadic adaptation, about the first saccade is used to plan the second saccade. Furthermore, with multiple saccades, endpoint variability increases with the number of saccades. Controls ruled out that this was due to the perceptual or memory requirements of storing several target locations. Instead, each memory-guided movement depends on an internal copy of an executed movement, which may present a small discrepancy with the actual movement. Increasing the number of estimates increases the variability because this small discrepancy accumulates over several saccades. Such accumulation is compatible with a corollary discharge signal carrying metric information about saccade vectors. |
Thérèse Collins; Tobias Heed; Brigitte Röder Eye-movement driven changes in the perception of auditory space Journal Article In: Attention, Perception, and Psychophysics, vol. 72, no. 3, pp. 736–746, 2010. @article{Collins2010c, The perceptual localization of sensory stimuli often depends on body position, and, when action is required, sensory coordinates must be transformed into a motor reference frame. We investigated the role of such a refer- ence frame change on visual and auditory spatial cognition. Participants had to make a saccade to a visual or auditory target and subsequently compare the location of a visual or auditory probe to the remembered location of the target. Neither visual nor auditory localization depended on trial-by-trial variability in saccade endpoint, suggesting that target locations are remapped across saccades in a manner allowing for oculomotor noise. We also compared visual and auditory localization performance before and after the systematic modification of saccade metrics by saccadic adaptation. Adaptation introduced systematic biases into transsaccadic visual and auditory localization behavior. These results show that information about eye movements is taken into account in both visual and auditory spatial cognition. We propose that auditory stimuli are remapped across saccades and that this eye-centered representation contributes to normal auditory localization. |
Sébastien Coppe; Jean-Jacques Orban de Xivry; Marcus Missal; Philippe Lefèvre Biological motion influences the visuomotor transformation for smooth pursuit eye movements Journal Article In: Vision Research, vol. 50, no. 24, pp. 2721–2728, 2010. @article{Coppe2010, Humans are very sensitive to the presence of other living persons or animals in their surrounding. Human actions can readily be perceived, even in a noisy environment. We recently demonstrated that biological motion, which schematically represents human motion, influences smooth pursuit eye movements during the initiation period (Orban de Xivry, Coppe, Lef??vre, & Missal, 2010). This smooth pursuit response is driven both by a visuomotor pathway, which transforms retinal inputs into motor commands, and by a memory pathway, which is directly related to the predictive properties of smooth pursuit. To date, it is unknown which of these pathways is influenced by biological motion. In the present study, we first use a theoretical model to demonstrate that an influence of biological motion on the visuomotor and memory pathways might both explain its influence on smooth pursuit initiation. In light of this model, we made theoretical predictions of the possible influence of biological motion on smooth pursuit during and after the transient blanking of the stimulus. These qualitative predictions were then compared with recordings of eye movements acquired before, during and after the transient blanking of the stimulus. The absence of difference in smooth pursuit eye movements during blanking of the stimuli and the stronger visually guided smooth pursuit reacceleration after reappearance of the biological motion stimuli in comparison with control stimuli suggests that biological motion influences the visuomotor pathway but not the memory pathway. |
C. Hemptinne; G. R. Barnes; Marcus Missal Influence of previous target motion on anticipatory pursuit deceleration Journal Article In: Experimental Brain Research, vol. 207, no. 3-4, pp. 173–184, 2010. @article{Hemptinne2010, During visual pursuit of a moving target, expected changes in its trajectory often evoke anticipatory smooth pursuit responses. In the present study, we investigated characteristics of anticipatory smooth pursuit decelerations before a change or the end of a target trajectory. Healthy humans had to pursue with the eyes a target moving along a circular path that predictably or unpredictably reversed direction and then retraced its movement back to the starting position. We found that anticipatory eye decelerations were often evoked in temporal expectation of target reversal and of the end of the trajectory. The latency of anticipatory decelerations initiated before target reversal was variable, had poor temporal accuracy and depended on the history of previous trials. Anticipations of the end of the trajectory were more accurate, more precise and were not influenced by previous trials. In this case, subjects probably based their estimate of the end of the trajectory on the duration just experienced before target motion reversal. These results suggest that anticipatory eye decelerations are based on the characteristics of the current or preceding trials depending on the most reliable information available. |
Kurt Debono; Alexander C. Schütz; Miriam Spering; Karl R. Gegenfurtner Receptive fields for smooth pursuit eye movements and motion perception Journal Article In: Vision Research, vol. 50, no. 24, pp. 2729–2739, 2010. @article{Debono2010, Humans use smooth pursuit eye movements to track moving objects of interest. In order to track an object accurately, motion signals from the target have to be integrated and segmented from motion signals in the visual context. Most studies on pursuit eye movements used small visual targets against a featureless background, disregarding the requirements of our natural visual environment. Here, we tested the ability of the pursuit and the perceptual system to integrate motion signals across larger areas of the visual field. Stimuli were random-dot kinematograms containing a horizontal motion signal, which was perturbed by a spatially localized, peripheral motion signal. Perturbations appeared in a gaze-contingent coordinate system and had a different direction than the main motion including a vertical component. We measured pursuit and perceptual direction discrimination decisions and found that both steady-state pursuit and perception were influenced most by perturbation angles close to that of the main motion signal and only in regions close to the center of gaze. The narrow direction bandwidth (26 angular degrees full width at half height) and small spatial extent (8 degrees of visual angle standard deviation) correspond closely to tuning parameters of neurons in the middle temporal area (MT). |
Jacob Duijnhouwer; Bart Krekelberg; Albert V. Berg; Richard J. A. Wezel Temporal integration of focus position signal during compensation for pursuit in optic flow. Journal Article In: Journal of Vision, vol. 10, no. 14, pp. 1–15, 2010. @article{Duijnhouwer2010, Observer translation results in optic flow that specifies heading. Concurrent smooth pursuit causes distortion of the retinal flow pattern for which the visual system compensates. The distortion and its perceptual compensation are usually modeled in terms of instantaneous velocities. However, apart from adding a velocity to the flow field, pursuit also incrementally changes the direction of gaze. The effect of gaze displacement on optic flow perception has received little attention. Here we separated the effects of velocity and gaze displacement by measuring the perceived two-dimensional focus position of rotating flow patterns during pursuit. Such stimuli are useful in the current context because the two effects work in orthogonal directions. As expected, the instantaneous pursuit velocity shifted the perceived focus orthogonally to the pursuit direction. Additionally, the focus was mislocalized in the direction of the pursuit. Experiments that manipulated the presentation duration, flow speed, and uncertainty of the focus location supported the idea that the latter component of mislocalization resulted from temporal integration of the retinal trajectory of the focus. Finally, a comparison of the shift magnitudes obtained in conditions with and without pursuit (but with similar retinal stimulation) suggested that the compensation for both effects uses extraretinal information. |
Kevin J. MacKenzie; David M. Hoffman; Simon J. Watt Accommodation to multiple-focal-plane displays: Implications for improving stereoscopic displays and for accommodation control Journal Article In: Journal of Vision, vol. 10, no. 8, pp. 1–22, 2010. @article{MacKenzie2010, Most stereoscopic displays present images at a single focal plane, resulting in "conflicts" between the stimuli to vergence and accommodation. Minimizing these conflicts is beneficial because they can cause distorted depth percepts, visual fatigue, and reduced stereoscopic performance. One proposed solution is to present a sum of images at multiple focal planes and to vary focal depth continuously by distributing image intensity across planes-a technique referred to as depth filtering. We evaluated this digital approximation to real-world variations in focal depth by measuring accommodation responses to depth-filtered stimuli at various simulated distances. Specifically, we determined the maximum image-plane separation that supported accurate and reliable accommodation. We used an analysis of retinal-image formation to predict when responses might be inaccurate. Accommodation to depth-filtered images was accurate and precise for image-plane separations up to ∼1 diopter, suggesting that depth filtering can be used to precisely match accommodation and vergence demands in a practical display. At larger plane separations, responses broke down in a manner consistent with our analysis. We develop this approach to consider how different spatial frequencies contribute to accommodation control. The results suggest that higher spatial frequencies contribute less to the accommodation response than has previously been thought. |
Jun Maruta; Minah Suh; Sumit N. Niogi; Pratik Mukherjee; Jamshid Ghajar Visual tracking synchronization as a metric for concussion screening Journal Article In: Journal of Head Trauma Rehabilitation, vol. 25, no. 4, pp. 293–305, 2010. @article{Maruta2010, Our goal was to determine whether performance variability during predictive visual tracking can provide a screening measure for mild traumatic brain injury (mTBI). Seventeen subjects with chronic postconcussive syndrome and 9 healthy control subjects were included in this study. Eye movements were recorded with video-oculography as the subject visually tracked a target that moved through a circular trajectory. We compared the variability of gaze positional errors relative to the target with the microstructural integrity of white matter tracts as measured by the fractional anisotropy (FA) parameter of diffusion tensor imaging. Gaze error variability was significantly correlated with the mean FA values of the right anterior corona radiata (ACR) and the left superior cerebellar peduncle, tracts that support spatial processing and sustenance of attention, and the genu of the corpus callosum. Because the ACR and the genu are among the most frequently damaged white matter tracts in mTBI, the correlations imply that gaze error variability during visual tracking may provide a useful screening tool for mTBI. Gaze error variability was also significantly correlated with attention and working memory measures in neurocognitive testing; thus, measurement of visual tracking performance is promising as a fast and practical screening tool for mTBI. |
Eugene McSorley; Alice G. Cruickshank Evidence that indirect inhibition of saccade initiation improves saccade accuracy Journal Article In: i-Perception, vol. 1, no. 2, pp. 73–82, 2010. @article{McSorley2010, Saccadic eye-movements to a visual target are less accurate if there are distracters close to its location (local distracters). The addition of more distracters, remote from the target location (remote distracters), invokes an involuntary increase in the response latency of the saccade and attenuates the effect of local distracters on accuracy. This may be due to the target and distracters directly competing (direct route) or to the remote distracters acting to impair the ability to disengage from fixation (indirect route). To distinguish between these we examined the development of saccade competition by recording saccade latency and accuracy responses made to a target and local distracter compared with those made with an addition of a remote distracter. The direct route would predict that the remote distracter impacts on the developing competition between target and local distracter, while the indirect route would predict no change as the accuracy benefit here derives from accessing the same competitive process but at a later stage. We found that the presence of the remote distracter did not change the pattern of accuracy improvement. This suggests that the remote distracter was acting along an indirect route that inhibits disengagement from fixation, slows saccade initiation, and enables more accurate saccades to be made. |
Mario Bettenbühl; Claudia Paladini; Konstantin Mergenthaler; Reinhold Kliegl; Ralf Engbert; Matthias Holschneider Microsaccade characterization using the continuous wavelet transform and principal component analysis Journal Article In: Journal of Eye Movement Research, vol. 3, no. 5, pp. 1–14, 2010. @article{Bettenbuehl2010, During visual fixation on a target, humans perform miniature (or fixational) eye movements consisting of three components, i.e., tremor, drift, and microsaccades. Microsaccades are high velocity components with small amplitudes within fixa- tional eye movements. However, microsaccade shapes and statistical properties vary between individual observers. Here we show that microsaccades can be formally represented with two significant shapes which we identfied using the mathematical definition of singularities for the detection of the former in real data with the continuous wavelet transform. For characterization and model selection, we carried out a principal component analysis, which identified a step shape with an overshoot as first and a bump which regulates the overshoot as second component. We conclude that microsaccades are singular events with an overshoot component which can be detected by the continuous wavelet transform. |
Marius Blanke; Ludwig Harsch; Jonas Knöll; Frank Bremmer Spatial perception during pursuit initiation Journal Article In: Vision Research, vol. 50, no. 24, pp. 2714–2720, 2010. @article{Blanke2010, Spatial perception is modulated by eye movements. During smooth pursuit, perceived locations are shifted in the direction of the eye movement. During active fixation, visual space is perceptually compressed towards the fovea. In our present study, we were interested to determine the time course of spatial localization during pursuit initiation, i.e. the transition period from fixation to steady-state pursuit. Human observers had to localize briefly flashed targets around the time of pursuit initiation. Our data clearly show that pursuit-like mislocalization starts well before the onset of the eye movement. Our results point towards corollary-discharge as neural source for the observed perceptual effect. |
Yoram S. Bonneh; Tobias H. Donner; Dov Sagi; Moshe Fried; Alexander Cooperman; Amos Arieli Motion-induced blindness and microsaccades: Cause and effect Journal Article In: Journal of Vision, vol. 10, no. 14, pp. 1–15, 2010. @article{Bonneh2010, It has been suggested that subjective disappearance of visual stimuli results from a spontaneous reduction of microsaccade rate causing image stabilization, enhanced adaptation, and a consequent fading. In motion-induced blindness (MIB), salient visual targets disappear intermittently when surrounded by a moving pattern. We investigated whether changes in microsaccade rate can account for MIB. We first determined that the moving mask does not affect microsaccade metrics (rate, magnitude, and temporal distribution). We then compared the dynamics of microsaccades during reported illusory disappearance (MIB) and physical disappearance (Replay) of a salient peripheral target. We found large modulations of microsaccade rate following perceptual transitions, whether illusory (MIB) or real (Replay). For MIB, the rate also decreased prior to disappearance and increased prior to reappearance. Importantly, MIB persisted in the presence of microsaccades although sustained microsaccade rate was lower during invisible than visible periods. These results suggest that the microsaccade system reacts to changes in visibility, but microsaccades also modulate MIB. The latter modulation is well described by a Poisson model of the perceptual transitions assuming that the probability for reappearance and disappearance is modulated following a microsaccade. Our results show that microsaccades counteract disappearance but are neither necessary nor sufficient to account for MIB. |
Doris I. Braun; Alexander C. Schütz; Karl R. Gegenfurtner Localization of speed differences of context stimuli during fixation and smooth pursuit eye movements Journal Article In: Vision Research, vol. 50, no. 24, pp. 2740–2749, 2010. @article{Braun2010, The visual system can detect speed changes of moving objects only by means of alterations of retinal image motion, which is also subject to changes induced by head or eye movements. Here we investigated whether smooth pursuit eye movements affect the ability to localize short speed perturbations of large context stimuli. Psychophysical thresholds for localization, discrimination and detection of speed perturbations in one of two context stimuli were measured under two main conditions: in fixation trials subjects fixated a central stationary spot, in pursuit trials they followed a horizontally moving target with their eyes. Context stimuli were vertically oriented sine wave gratings moving simultaneously above and below the fixation or pursuit target for one second in the same direction at the same or a different speed as the pursuit target. During the movement one of the gratings suddenly changed its speed for 500. ms and returned to its original speed. Observers were asked to discern the location of the speed change (two-alternative spatial forced choice task). While detection (two-interval forced choice) and discrimination thresholds for the kind of speed perturbation were in the normal range of Weber fractions of 10-15%, thresholds for the location of the speed perturbation were dramatically increased to 30-50%. Localization thresholds were particularly high when the retinal motion was mainly due to the context movements as during fixation or slow pursuit and significantly reduced when the retinal motion was mainly due to pursuit. This result indicates that the origin of retinal motion, whether it is caused by object motion or by voluntary pursuit is important. We conclude that the localization of speed perturbations affecting one of two peripheral moving objects is exceedingly complicated for the visual system probably due to the dominance of relative motion. During smooth pursuit the ability to localize speed perturbations of non-foveated objects seems to be improved by additional information gained from pursuit such as corollary discharge. |
Rebecca A. Champion; Tom C. A. Freeman Discrimination contours for the perception of head-centered velocity Journal Article In: Journal of Vision, vol. 10, no. 6, pp. 1–9, 2010. @article{Champion2010, There is little direct psychophysical evidence that the visual system contains mechanisms tuned to head-centered velocity when observers make a smooth pursuit eye movement. Much of the evidence is implicit, relying on measurements of bias (e.g., matching and nulling). We therefore measured discrimination contours in a space dimensioned by pursuit target motion and relative motion between target and background. Within this space, lines of constant head-centered motion are parallel to the main negative diagonal, so judgments dominated by mechanisms that combine individual components should produce contours with a similar orientation. Conversely, contours oriented parallel to the cardinal axes of the space indicate judgments based on individual components. The results provided evidence for mechanisms tuned to head-centered velocity-discrimination ellipses were significantly oriented away from the cardinal axes, toward the main negative diagonal. However, ellipse orientation was considerably less steep than predicted by a pure combination of components. This suggests that observers used a mixture of two strategies across trials, one based on individual components and another based on their sum. We provide a model that simulates this type of behavior and is able to reproduce the ellipse orientations we found. |
Katharina Havermann; Markus Lappe The influence of the consistency of postsaccadic visual errors on saccadic adaptation Journal Article In: Journal of Neurophysiology, vol. 103, no. 6, pp. 3302–3310, 2010. @article{Havermann2010, The saccadic system is a prime example of motor control without continuous visual feedback. These systems suffer from a strong vulnerability against disturbances. The mechanism of saccadic adaptation allows adjustment of saccades to alterations arising not only from anatomical changes but also from external changes. The weighting of errors according to their reliability provides a strong benefit for an optimized control system. Thus the consistency of visual error should influence the characteristics of adaptation. In the typical adaptation paradigm a visual error is introduced by stepping the target during the saccade by a given amount. In this paradigm, the retinal error varies with the accuracy of the saccade and the step size. To study the influence of error consistency we use a variant of the adaptation paradigm which allows to specify a constant error size. Intrasaccadic target step sizes were calculated with respect to the predicted landing position of each individual saccade. The consistency of the visual error was varied by introducing different levels of noise to the intrasaccadic target step. Different mean intrasaccadic target step sizes were examined: positive target step, negative target step, and a condition in which the mean of the error distribution was clamped to the fovea. In all three conditions saccadic adaptation was strongest when the error was consistent and became weaker as the error became more variable. These results show that saccadic adaptation takes not only the average error but also the consistency of the error into account. |
Stephen J. Heinen; Aarlenne Zein Khan; Philippe Lefevre; G. Blohm The default allocation of attention is broadly ahead of smooth pursuit Journal Article In: Journal of Vision, vol. 10, no. 13, pp. 1–17, 2010. @article{Heinen2010, When moving through our environment, it is vital to preferentially process positions on our future path in order to react quickly to critical situations. During smooth pursuit, attention may be directed ahead with either a focused locus or a broad bias. We examined the 2D spatial extent of attention during a smooth pursuit task using both saccade (SRT) and manual (MRT) reaction times as measures of attentional allocation. Targets were flashed at various locations around current eye position while subjects pursued a moving target. Subjects made a saccade or pressed a button as soon as they perceived the target. Both SRTs and MRTs were shortest to targets flashed ahead of compared to behind the direction of pursuit across half of the visual field ahead of pursuit direction. Furthermore, we found an increase specific to SRTs at small target eccentricities directly ahead of pursuit, which may be related to an additional saccade trigger strategy; small saccades take longer to execute if smooth pursuit brings the eyes close to the target. In summary, both SRTs and MRTs revealed that attention is by default broadly allocated in the visual hemi-field ahead of the line of sight during smooth pursuit eye movements. This attentional bias may serve a predictive purpose for facilitating the processing of upcoming events. |
Frouke Hermens; Petroc Sumner; Robin Walker Inhibition of masked primes as revealed by saccade curvature Journal Article In: Vision Research, vol. 50, no. 1, pp. 46–56, 2010. @article{Hermens2010c, In masked priming, responses are often speeded when primes are similar to targets ('positive compatibility effect'). However, sometimes similarity of prime and target impairs responses ('negative compatibility effect'). A similar distinction has been found for the curvature of saccade trajectories. Here, we test whether the same inhibition processes are involved in the two phenomena, by directly comparing response times and saccade curvature within the same masked priming paradigm. Interestingly, we found a dissociation between the directions of masked priming and saccade curvature, which could indicate that multiple types of inhibition are involved in the suppression of unwanted responses. |
Frouke Hermens; Robin Walker What determines the direction of microsaccades? Journal Article In: Journal of Eye Movement Research, vol. 3, no. 4, pp. 1–20, 2010. @article{Hermens2010, During visual fixation, our eyes are not entirely still. Instead, small eye movements, such as microsaccades, can be observed. We here investigate what determines the direction and frequency of these microsaccades, as this information might help to clarifywhat purpose they serve. The relative contribution of three possible factorswas examined: (1) the orienting of covert attention, (2) the spatial distribution of possible target locations, and (3) whether monocular or binocular microsaccades are considered. The orienting of covert attention and the distribution of possible target locations had a relatively weak effect on microsaccade rates and directions. In contrast, the classification of microsaccades as binocular (occurring in both eyes simultaneously) or monocular (observed in one eye only) strongly affected both the rate and the direction of microsaccades. The results are discussed in the context of existing findings. |
Frouke Hermens; Robin Walker The Influence of Onsets and Offsets on Saccade Programming Journal Article In: i-Perception, vol. 1, no. 2, pp. 83–94, 2010. @article{Hermens2010a, When making a saccadic eye movement to a peripheral target, a simultaneous stimulus onset at central fixation generally increases saccadic latency, while offsets reduce latency (‘gap effect'). Visual onsets remote from fixation also increase latency (‘remote distractor effect'); however, the influence of remote visual offsets is less clear. Previous studies, which used a search task, found that remote offsets either facilitated, inhibited, or did nothing to saccade latencies towards a peripheral target. It cannot be excluded, however, that the target selection process in such search tasks influenced the results. We therefore simplified the task and asked participants to make eye movements to a predictable target. Simultaneously with target onset, either one or multiple remote stimulus onsets and offsets were presented. It was found that peripheral onsets increased saccade latencies, but offsets did not influence the initiation of a saccade to the target. Moreover, the number of onsets and offsets did not affect the results. These results suggest that earlier effects of remote stimulus offsets and of the number of remote distractor onsets reside in the target identification process of the visual search task rather than the competition between possible saccade goals. The results are discussed in the context of models of saccade target selection. |
Frouke Hermens; Robin Walker Gaze and arrow distractors influence saccade trajectories similarly Journal Article In: Quarterly Journal of Experimental Psychology, vol. 63, no. 11, pp. 2120–2140, 2010. @article{Hermens2010b, Perceiving someone's averted eye-gaze is thought to result in an automatic shift of attention and in the preparation of an oculomotor response in the direction of perceived gaze. Although gaze cues have been regarded as being special in this respect, recent studies have found evidence for automatic attention shifts with nonsocial stimuli, such as arrow cues. Here, we directly compared the effects of social and nonsocial cues on eye movement preparation by examining the modulation of saccade trajectories made in the presence of eye-gaze, arrows, or peripheral distractors. At a short stimulus onset asynchrony (SOA) between the distractor and the target, saccades deviated towards the direction of centrally presented arrow distractors, but away from the peripheral distractors. No significant trajectory deviations were found for gaze distractors. At the longer SOA, saccades deviated away from the direction of the distractor for all three distractor types, but deviations were smaller for the centrally presented gaze and arrow distractors. These effects were independent of whether line-drawings or photos of faces were used and could not be explained by differences in the spatial properties of the peripheral distractor. The results suggest that all three types of distractors (gaze, arrow, peripheral) can induce the automatic programming of an eye movement. Moreover, the findings suggest that gaze and arrow distractors affect oculomotor preparation similarly, whereas peripheral distractors, which are classically regarded as eliciting an automatic shift of attention and an oculomotor response, induce a stronger and faster acting influence on response preparation and the corresponding inhibition of that response. |
Frouke Hermens; Johannes M. Zanker; Robin Walker Microsaccades and preparatory set: A comparison between delayed and immediate, exogenous and endogenous pro- and anti-saccades Journal Article In: Experimental Brain Research, vol. 201, no. 3, pp. 489–498, 2010. @article{Hermens2010d, When we fixate an object, our eyes are not entirely still, but undergo small displacements such as microsaccades. Here, we investigate whether these microsaccades are sensitive to the preparatory processes involved in programming a saccade. We show that the frequency of microsaccades depends in a specific manner on the intention where to move the eyes (towards a target location or away from it), when to move (immediately after the onset of the target or after a delay), and what type of cue is followed (a peripheral onset or a centrally presented symbolic cue). In particular, in the preparatory interval before and early after target onset, more microsaccades were found when a delayed saccade towards a peripheral target was prepared than when a saccade away was programmed. However, no such difference in the frequency of microsaccades was observed when saccades were initiated immediately after the onset of the target or when the saccades were programmed on the basis of a centrally presented arrow cue. The results are discussed in the context of the neural correlates of response preparation, known as preparatory set. |
Po-Jang Hsieh; Peter U. Tse BOLD signal in both ipsilateral and contralateral retinotopic cortex modulates with perceptual fading Journal Article In: PLoS ONE, vol. 5, no. 3, pp. e9638, 2010. @article{Hsieh2010, Under conditions of visual fixation, perceptual fading occurs when a stationary object, though present in the world and continually casting light upon the retina, vanishes from visual consciousness. The neural correlates of the consciousness of such an object will presumably modulate in activity with the onset and cessation of perceptual fading. METHOD: In order to localize the neural correlates of perceptual fading, a green disk that had been individually set to be equiluminant with the orange background, was presented in one of the four visual quadrants; Subjects indicated with a button press whether or not the disk was subjectively visible as it perceptually faded in and out. RESULTS: Blood oxygen-level dependent (BOLD) signal in V1 and ventral retinotopic areas V2v and V3v decreases when the disk subjectively disappears, and increases when it subjectively reappears. This effect occurs in early visual areas both ipsilaterally and contralaterally to the fading figure. That is, it occurs regardless of whether the fading stimulus is presented inside or outside of the corresponding portion of visual field. In addition, we find that the microsaccade rate rises before and after perceptual transitions from not seeing to seeing the disk, and decreases before perceptual transitions from seeing to not seeing the disk. These BOLD signal changes could be driven by a global process that operates across contralateral and ipsilateral visual cortex or by a confounding factor, such as microsaccade rate. |
Stephanie Jainta; Jörg Hoormann; Wilhelm Bernhard Kloke; Wolfgang Jaschinski Binocularity during reading fixations: Properties of the minimum fixation disparity Journal Article In: Vision Research, vol. 50, no. 18, pp. 1775–1785, 2010. @article{Jainta2010b, The present study was based on the physiologically reasonable assumption that the binocular system aims for a reduction of fixation disparity during fixation and that the minimum amount of fixation disparity reflects the optimal binocular status. We measured eye movements (EyeLink II) of 18 participants, while they read 60 sentences from the Potsdam-Sentence-Corpus (PSC) at a viewing distance of 60. cm. The minimum fixation disparity was frequently reached directly after the post-saccadic drift, sometimes at the end of fixation and sometimes somewhere in between. Minimum fixation disparity was strongly influenced only by fixation position (within the sentence) while the amplitude of incoming saccade had a negligible effect. Moreover, the effect of fixation position on minimum fixation disparity was correlated with the individual ability to compensate for binocular disconjugacy (due to saccades) while fixating during reading. Generally, we found fixation disparity to be correlated between conditions of reading and fixating single targets, while the reading fixation disparity tended to be more crossed (eso). |
Stephanie Jainta; Jaschin; Arnold J. Wilkins Periodic letter strokes within a word affect fixation disparity during reading Journal Article In: Journal of Vision, vol. 10, no. 13, pp. 1–11, 2010. @article{Jainta2010, We investigated the way in which binocular coordination in reading is affected by the spatial structure of text. Vergence eye movements were measured (EyeLink II) in 32 observers while they read 120 single German sentences (Potsdam Sentence Corpus) silently for comprehension. The similarity in shape between the neighboring strokes of component letters, as measured by the first peak in the horizontal auto-correlation of the images of the words, was found to be associated with (i) a smaller minimum fixation disparity (i.e. vergence error) during fixation; (ii) a longer time to reach this minimum disparity and (iii) a longer overall fixation duration. The results were obtained only for binocular reading: no effects of auto-correlation could be observed for monocular reading. The findings help to explain the longer reading times reported for words and fonts with high auto-correlation and may also begin to provide a causal link between poor binocular control and reading difficulties. |
Stephanie Jainta; Wolfgang Jaschinski “Trait” and “state” aspects of fixation disparity during reading Journal Article In: Journal of Eye Movement Research, vol. 3, no. 3, pp. 1–13, 2010. @article{Jainta2010a, In our study, 14 subjects read 60 sentences from the Potsdam Sentence Corpus twice (viewing distance: 60 cm), while eye movements were measured with the EyeLink II. We analyzed fixation disparities for complete sentence replications (N=388). After subtracting the average fixation disparity of each sentence from each observation (which gave the “state” fixation disparity), 99% of all remaining fixation disparities were aligned, i.e. smaller than one character width (20 min arc) – depending mostly on incoming saccade amplitude and fixation position. Additionally, we measured the heterophoria for each subject during calibration and found a qualitative relationship between average, individual measures of fixation disparity (“trait” fixation disparity) and heterophoria, after dividing the sample in 3 groups of esophore, exophore and orthophore subjects. We showed that the magnitude of “trait” fixation disparity was biased by the direction of heterophoria: the more eso the heterophoria, the more eso the average sentence fixation disparity. In sum, despite a large “trait” fixation disparity (in the range of -6.6 to +33.6 min arc), “state” fixation disparities within a sentence were on average -0.9 (± 8.7) min arc and, thus, as precise as needed, i.e. within the expected extent of Panum's area. |
Wolfgang Jaschinski; Stephanie Jainta; Wilhelm Bernhard Kloke Objective vs subjective measures of fixation disparity for short and long fixation periods Journal Article In: Ophthalmic and Physiological Optics, vol. 30, no. 4, pp. 379–390, 2010. @article{Jaschinski2010, Purpose: Fixation disparity, i.e. the vergence error for stationary fusion stimuli, can be measured objectively with eye trackers and subjectively with nonius lines. Between these two measures, previous studies found differences that tended to be proportional to the amount of forced vergence, i.e. the discrepancy between vergence and accommodative stimulus. We investigate whether objective and subjective fixation disparity might be similar without forced vergence. Method: We simultaneously measured fixation disparity with the EyeLink II system and with flashed dichoptic nonius lines in 17 subjects who observed targets at a vergence stimulus of 6 deg in an haploscope with 60 cm viewing distance. Results: We found individual differences in objective fixation disparity in a range of about 20 (eso) to )60 (exo) min arc which was considerably larger than the range of subjective fixation disparity. Results were similar for long fixation periods (about 15 s) and short fixation periods (about 1.5 s) between 5 deg saccadic gaze shifts. Further, objective fixation disparity was correlated with objective heterophoria, i.e. the vergence state without a fusion stimulus (r = 0.8, p < 0.001). Conclusion: Subjective fixation disparity explained only about 25% of the inter-individual variability in objective fixation disparity. The discrepancy between these two measures might be explained by sensory shifts in retinal correspondence, also in the present condition without forced vergence. |
Ralf Engbert; André Krügel Readers use bayesian estimation for eye movement control Journal Article In: Psychological Science, vol. 21, no. 3, pp. 366–371, 2010. @article{Engbert2010, During reading, saccadic landing positions within words show a pronounced peak close to the word center, with an additional systematic error that is modulated by the distance from the launch site and the length of the target word. Here we show that the systematic variation of fixation positions within words, the saccadic range error, can be derived from Bayesian decision theory. We present the first mathematical model for the saccadic range error; this model makes explicit assumptions regarding underlying visual and oculomotor processes. Analyzing a corpus of eye movement recordings, we obtained results that are consistent with the view that readers use Bayesian estimation for saccade planning. Furthermore, we show that alternative models fail to reproduce the experimental data. |
Peter J. Etchells; Christopher P. Benton; Casimir J. H. Ludwig; Iain D. Gilchrist The target velocity integration function for saccades Journal Article In: Journal of Vision, vol. 10, no. 6, pp. 1–14, 2010. @article{Etchells2010, Interacting with a dynamic environment calls for close coordination between the timing and direction of motor behaviors. Accurate motor behavior requires the system to predict where the target for action will be, both when action planning is complete and when the action is executed. In the current study, we investigate the time course of velocity information accrual in the period leading up to a saccade toward a moving object. In two experiments, observers were asked to generate saccades to one of two moving targets. Experiment 1 looks at the accuracy of saccades to targets that have trial-by-trial variations in velocity. We show that the pattern of errors in saccade landing position is best explained by proposing that trial-by-trial target velocity is taken into account in saccade planning. In Experiment 2, target velocity stepped up or down after a variable interval after the movement cue. The extent to which the movement endpoint reflects pre- or post-step velocity can be used to identify the temporal velocity integration window; we show that the system takes a temporally blurred snapshot of target velocity centered ∼200 ms before saccade onset. This estimate is used to generate a dynamically updated prediction of the target's likely future location. |
Simon Farrell; Casimir J. H. Ludwig; Lucy A. Ellis; Iain D. Gilchrist Influence of environmental statistics on inhibition of saccadic return Journal Article In: Proceedings of the National Academy of Sciences, vol. 107, no. 2, pp. 929–934, 2010. @article{Farrell2010, Initiating an eye movement is slowed if the saccade is directed to a location that has been fixated in the recent past. We show that this inhibitory effect is modulated by the temporal statistics of the environment: If a return location is likely to become behaviorally relevant, inhibition of return is absent. By fitting an accumulator model of saccadic decision-making, we show that the inhibitory effect and the sensitivity to local statistics can be dissociated in their effects on the rate of accumulation of evidence, and the threshold controlling the amount of evidence needed to generate a saccade. |
Tom C. A. Freeman; Rebecca A. Champion; Paul A. Warren A Bayesian model of perceived head-centered Velocity during smooth pursuit eye movement Journal Article In: Current Biology, vol. 20, no. 8, pp. 757–762, 2010. @article{Freeman2010, During smooth pursuit eye movement, observers often misperceive velocity. Pursued stimuli appear slower (Aubert-Fleishl phenomenon [1, 2]), stationary objects appear to move (Filehne illusion [3]), the perceived direction of moving objects is distorted (trajectory misperception [4]), and self-motion veers away from its true path (e.g., the slalom illusion [5]). Each illusion demonstrates that eye speed is underestimated with respect to image speed, a finding that has been taken as evidence of early sensory signals that differ in accuracy [4, 6-11]. Here we present an alternative Bayesian account, based on the idea that perceptual estimates are increasingly influenced by prior expectations as signals become more uncertain [12-15]. We show that the speeds of pursued stimuli are more difficult to discriminate than fixated stimuli. Observers are therefore less certain about motion signals encoding the speed of pursued stimuli, a finding we use to quantify the Aubert-Fleischl phenomenon based on the assumption that the prior for motion is centered on zero [16-20]. In doing so, we reveal an important property currently overlooked by Bayesian models of motion perception. Two Bayes estimates are needed at a relatively early stage in processing, one for pursued targets and one for image motion. |
Cheryl Frenck-Mestre; Nathalie Zardan; Annie Colas; Alain Ghio Eye-movement patterns of readers with down syndrome during sentence-processing: An exploratory study Journal Article In: American Journal on Intellectual and Developmental Disabilities, vol. 115, no. 3, pp. 193–206, 2010. @article{FrenckMestre2010, Eye movements were examined to determine how readers with Down syndrome process sentences online. Participants were 9 individuals with Down syndrome ranging in reading level from Grades 1 to 3 and a reading-level-matched control group. For syntactically simple sentences, the pattern of reading times was similar for the two groups, with longer reading times found at sentence end. This "wrap-up" effect was also found in the first reading of more complex sentences for the control group, whereas it only emerged later for the readers with Down syndrome. Our results provide evidence that eye movements can be used to investigate reading in individuals with Down syndrome and underline the need for future studies. |
Shai Gabay; Avishai Henik; Libe Gradstein Ocular motor ability and covert attention in patients with Duane Retraction Syndrome Journal Article In: Neuropsychologia, vol. 48, no. 10, pp. 3102–3109, 2010. @article{Gabay2010, Is orienting of spatial attention dependent on normal functioning of the ocular motor system? We investigated the role of motor pathways in covert orienting (attentional orienting without performing eye movements) by studying three patients suffering from Duane Retraction Syndrome-a congenital impairment in executing horizontal eye movements restricted to specific gaze directions. Patients showed a typical exogenous (reflexive) attention effect when the target was presented in visual fields to which they could perform an eye movement. This effect was not present when the target was presented in the visual field to which they could not perform eye movements. These findings stress the link between eye movements and attention. Specifically, they bring out the importance of the ability to execute appropriate eye movements for attentional orienting. We suggest that the relevant information about eye movement ability is provided by feedback from lower motor structures to higher attentional areas. |
Amanda L. Gamble; Ronald M. Rapee The time-course of attention to emotional faces in social phobia Journal Article In: Journal of Behavior Therapy and Experimental Psychiatry, vol. 41, no. 1, pp. 39–44, 2010. @article{Gamble2010, This study investigated the time-course of attentional bias in socially phobic (SP) and non-phobic (NP) adults. Participants viewed angry and happy faces paired with neutral faces (i.e., face-face pairs) and angry, happy and neutral faces paired with household objects (i.e., face-object pairs) for 5000 ms. Eye movement (EM) was measured throughout to assess biases in early and sustained attention. Attentional bias occurred only for face-face pairs. SP adults were vigilant for angry faces relative to neutral faces in the first 500 ms of the 5000 ms exposure, relative to NP adults. SP adults were also vigilant for happy faces over 500 ms, although there were no group-based differences in attention to happy-neutral face pairs. There were no group differences in attention to faces throughout the remainder of the exposure. Results suggest that social phobia is characterised by early vigilance for social cues with no bias in subsequent processing. |
C. Ellie Wilson; J. Brock; Romina Palermo Attention to social stimuli and facial identity recognition skills in autism spectrum disorder Journal Article In: Journal of Intellectual Disability Research, vol. 54, no. 12, pp. 1104–1115, 2010. @article{Wilson2010, Background Previous research suggests that indi- viduals with autism spectrum disorder (ASD) have a reduced preference for viewing social stimuli in the environment and impaired facial identity recognition. Methods Here, we directly tested a link between these two phenomena in 13 ASD children and 13 age-matched typically developing (TD) controls. Eye movements were recorded while participants passively viewed visual scenes containing people and objects. Participants also completed indepen- dent matching tasks for faces and objects. Results and Conclusions Behavioural data showed that participants with ASD were impaired on both face- and object-matching tasks relative to TD con- trols. Eye-tracking data revealed that both groups showed a strong bias to orient towards people.TD children spent proportionally more time looking at people than objects; however, there was no differ- ence in viewing times between people and objects in the ASD group. In the ASD group, an individu- al's preference for looking first at the people in scenes was associated with level of face recognition ability. Further research is required to determine whether a causal relationship exists between these factors. |
Jonathan B. Jacobs; Louis F. Dell'Osso Extending the eXpanded Nystagmus Acuity Function for vertical and multiplanar data Journal Article In: Vision Research, vol. 50, no. 3, pp. 271–278, 2010. @article{Jacobs2010, We updated and extended the functionality of the eXpanded Nystagmus Acuity Function (NAFX), for application under more diverse circumstances, improving its clinical predictive value. The original NAFX "τ-surface" of minimum-necessary-foveation times had been individually calculated for each combination of position and velocity limits. We have replaced it with an idealized mathematical function that repairs the irregularities in its surface due to idiosyncrasies in the subject data used for the initial calculations. To extend applicability to multiplanar data, we combine horizontal and vertical eye-movement data into a single waveform using vector summation. Torsional eye movements have little effect on visual acuity and are ignored. Age-related visual acuity relationships, derived from population data, more accurately relate the NAFX value to acuity for individual patients. Using the same patient fixation data that established the original NAF and NAFX functions, we verified that the updated NAFX yielded equivalent results for uniplanar data. For biplanar data, the results were also comparable to those of uniplanar data of the same magnitude. The updated NAFX yields greater accuracy in prediction of potential visual acuity for subjects of all ages, for uniplanar and multiplanar nystagmus, extending the objective, direct measure of post-therapy waveform improvement, allowing selection of the best therapy for a wider range of nystagmus patients. |
Evgenia Kanonidou; Frank A. Proudlock; Irene Gottlob Reading strategies in mild to moderate strabismic amblyopia: An eye movement investigation Journal Article In: Investigative Ophthalmology & Visual Science, vol. 51, no. 7, pp. 3502–3508, 2010. @article{Kanonidou2010, PURPOSE. To investigate oculomotor strategies in strabismic amblyopia and evaluate abnormalities during monocular and binocular reading. METHODS. Eye movements were recorded with a head-mounted infrared video eye-tracker (250 Hz, <0.01 degrees resolution) in 20 strabismic amblyopes (mean age, 44.9 +/- 10.7 years) and 20 normal control subjects (mean age, 42.8 +/- 10.9 years) while they silently read paragraphs of text. Monocular reading comparisons were made between the amblyopic eye and the nondominant eye of control subjects and the nonamblyopic eye and the dominant eye of the control subjects. Binocular reading between the amblyopic and control subjects was also compared. RESULTS. Mean reading speed, number of progressive and regressive saccades per line, saccadic amplitude (of progressive saccades), and fixation duration were estimated. Inter- and intrasubject statistical comparisons were made. Reading speed was significantly slower in amblyopes than in control subjects during monocular reading with amblyopic (13.094 characters/s vs. 22.188 characters/s; P < 0.0001) and nonamblyopic eyes (16.241 characters/s vs. 22.349 characters/s, P < 0.0001), and binocularly (15.698 characters/s vs. 23.425 characters/s, P < 0.0001). In amblyopes, reading was significantly slower with the amblyopic eye than with the nonamblyopic eye in binocular viewing (P < 0.05). These differences were associated with significantly more regressive saccades and longer fixation durations, but not with changes in saccadic amplitudes. CONCLUSIONS. In strabismic amblyopia, reading is impaired, not only during monocular viewing with the amblyopic eye, but also with the nonamblyopic eye and binocularly, even though normal visual acuity pertains to the latter two conditions. The impaired reading performance is associated with differences in both the saccadic and fixational patterns, most likely as adaptation strategies to abnormal sensory experiences such as crowding and suppression. |
Jason Rupp; Tanya Blekher; Jacqueline Gray Jackson; Xabier Beristain; Jeanine Marshall; Siu L. Hui; Joanne Wojcieszek; Tatiana M. Foroud Progression in prediagnostic Huntington disease Journal Article In: Journal of Neurology, Neurosurgery and Psychiatry, vol. 81, no. 4, pp. 379–384, 2010. @article{Rupp2010, OBJECTIVE: To examine rates of decline in individuals at risk for Huntington disease (HD). METHODS: 106 individuals at risk for HD completed a battery of neurocognitive, psychomotor and oculomotor tasks at two visits, approximately 2.5 years apart. Participants were classified as: (1) without the CAG expansion (normal controls, NC; n=68) or (2) with the CAG expansion (CAG+; n=38). The CAG+ group was further subdivided into those near to (near; n=19) or far from (far; n=19) their estimated age of onset. Longitudinal performance in the CAG+ group was evaluated with a repeated measures model with two main effects (time to onset, visit) and their interaction. Analysis of covariance was employed to detect differences in longitudinal performance in the three groups (NC, near and far). RESULTS: In the CAG+, the interaction term was significant (p < or = 0.02) for four measures (movement time, alternate button tapping, variability of latency for a memory guided task and percentage of errors for a more complex memory guided task), suggesting the rate of decline was more rapid as subjects approached onset. Longitudinal progression in the three groups differed for several variables (p<0.05). In most, the near group had significantly faster progression than NC; however, comparisons of the NC and far groups were less consistent. CONCLUSIONS: Different patterns of progression were observed during the prediagnostic period. For some measures, CAG+ subjects closer to estimated onset showed a more rapid decline while for other measures the CAG+ group had a constant rate of decline throughout the prediagnostic period that was more rapid than in NC. |
Kerstin I. Schattka; Ralph Radach; Walter Huber Eye movement correlates of acquired central dyslexia Journal Article In: Neuropsychologia, vol. 48, no. 10, pp. 2959–2973, 2010. @article{Schattka2010, Based on recent progress in theory and measurement techniques, the analysis of eye movements has become one of the major methodological tools in experimental reading research. Our work uses this approach to advance the understanding of impaired information processing in acquired central dyslexia of stroke patients with aphasia. Up to now there has been no research attempting to analyze both word-based viewing time measures and local fixation patterns in dyslexic readers. The goal of the study was to find out whether specific eye movement parameters reflect pathologically preferred segmental reading in contrast to lexical reading.We compared oral reading of single words of normal controls (n=11) with six aphasic participants (two cases of deep, surface and residual dyslexia each). Participants were asked to read aloud lines of target words differing in length and frequency. Segmental reading was characterized by deviant spatial distribution of saccadic landing positions with initial fixations located mainly at the beginning of the word, while lexical readers showed the normative 'preferred landing positions' left to the center of the words. Contrary to expectation, word length did not distinguish between segmental and lexical readers, while word frequency showed the expected effect for lexical readers only. Their mean fixation duration was already prolonged during first pass reading reflecting their attempts of immediate access to lexical information. After first pass reading, re-reading time was significantly increased in all participants with acquired central dyslexia due to their exceedingly higher monitoring demands for oral reading. |
Michael Scheel; Mathias Abegg; Linda J. Lanyon; Andre Mattman; Jason J. S. Barton Eye movement and diffusion tensor imaging analysis of treatment effects in a Niemann-Pick Type C patient Journal Article In: Molecular Genetics and Metabolism, vol. 99, no. 3, pp. 291–295, 2010. @article{Scheel2010, New treatment options for Niemann-Pick Type C (NPC) have recently become available. To assess the efficiency and efficacy of these new treatment markers for disease status and progression are needed. Both the diagnosis and the monitoring of disease progression are challenging and mostly rely on clinical impression and functional testing of horizontal eye movements. Diffusion tensor imaging (DTI) provides information about the microintegrity especially of white matter. We show here in a case report how DTI and measures derived from this imaging method can serve as adjunct quantitative markers for disease management in Niemann-Pick Type C. Two approaches are taken - first, we compare the fractional anisotropy (FA) in the white matter globally between a 29-year-old NPC patient and 18 healthy age-matched controls and show the remarkable difference in FA relatively early in the course of the disease. Second, a voxelwise comparison of FA values reveals where white matter integrity is compromised locally and demonstrate an individualized analysis of FA changes before and after 1 year of treatment with Miglustat. This method might be useful in future treatment trials for NPC to assess treatment effects. |
Christopher R. Sears; Charmaine L. Thomas; Jessica M. Lehuquet; Jeremy C. S. Johnson Attentional biases in dysphoria: An eye-tracking study of the allocation and disengagement of attention Journal Article In: Cognition and Emotion, vol. 24, no. 8, pp. 1349–1368, 2010. @article{Sears2010, This study looked for evidence of biases in the allocation and disengagement of attention in dysphoric individuals. Participants studied images for a recognition memory test while their eye fixations were tracked and recorded. Four image types were presented (depression-related, anxiety- related, positive, neutral) in each of two study conditions. For the simultaneous study condition, four images (one of each type) were presented simultaneously for 10 seconds, and the number of fixations and the total fixation time to each image was measured, similar to the procedure used by Eizenman et al. (2003) and Kellough, Beevers, Ellis, and Wells (2008). For the sequential study condition, four images (one of each type) were presented consecutively, each for 4 seconds; to measure disengagement of attention an endogenous cuing procedure was used (Posner, 1980). Dysphoric individuals spent significantly less time attending to positive images than non-dysphoric individuals, but there were no group differences in attention to depression-related images. There was also no evidence of a dysphoria-related bias in initial shifts of attention. With respect to the disengagement of attention, dysphoric individuals were slower to disengage their attention from depression-related images. The recognition memory data showed that dysphoric individuals had poorer memory for emotional images, but there was no evidence of a conventional mood-congruent memory bias. Differences in the attentional and memory biases observed in depressed and dysphoric individuals are discussed. |
B. Machner; C. Klein; Andreas Sprenger; P. Baumbach; P. P. Pramstaller; Christoph Helmchen; Wolfgang Heide Eye movement disorders are different in Parkin-linked and idiopathic early-onset PD Journal Article In: Neurology, vol. 75, pp. 125–128, 2010. @article{Machner2010, OBJECTIVES Parkin gene mutations are the most common cause of early-onset parkinsonism. Patients with Parkin mutations may be clinically indistinguishable from patients with idiopathic early-onset Parkinson disease (EOPD) without Parkin mutations. Eye movement disorders have been shown to differentiate parkinsonian syndromes, but have never been systematically studied in Parkin mutation carriers. METHODS Eye movements were recorded in symptomatic (n = 9) and asymptomatic Parkin mutation carriers (n = 13), patients with idiopathic EOPD (n = 14), and age-matched control subjects (n = 27) during established oculomotor tasks. RESULTS Both patients with EOPD and symptomatic Parkin mutation carriers showed hypometric prosaccades toward visual stimuli, as well as deficits in suppressing reflexive saccades toward unintended targets (antisaccade task). When directing gaze toward memorized target positions, patients with EOPD exhibited hypometric saccades, whereas symptomatic Parkin mutation carriers showed normal saccades. In contrast to patients with EOPD, the symptomatic Parkin mutation carriers showed impaired tracking of a moving target (reduced smooth pursuit gain). The asymptomatic Parkin mutation carriers did not differ from healthy control subjects in any of the tasks. CONCLUSIONS Although clinically similarly affected, symptomatic Parkin mutation carriers and patients with idiopathic EOPD differed in several oculomotor tasks. This finding may point to distinct anatomic structures underlying either condition: dysfunctions of cortical areas involved in smooth pursuit (V5, frontal eye field) in Parkin-linked parkinsonism vs greater impairment of basal ganglia circuits in idiopathic Parkinson disease. |
Anna L. Telling; Antje S. Meyer; Glyn W. Humphreys Distracted by relatives: Effects of frontal lobe damage on semantic distraction Journal Article In: Brain and Cognition, vol. 73, no. 3, pp. 203–214, 2010. @article{Telling2010, When young adults carry out visual search, distractors that are semantically related, rather than unrelated, to targets can disrupt target selection (see Belke, Humphreys, Watson, Meyer, & Telling, 2008; Moores, Laiti, & Chelazzi, 2003). This effect is apparent on the first eye movements in search, suggesting that attention is sometimes captured by related distractors. Here we assessed effects of semantically related distractors on search in patients with frontal-lobe lesions and compared them to the effects in age-matched controls. Compared with the controls, the patients were less likely to make a first saccade to the target and they were more likely to saccade to distractors (whether related or unrelated to the target). This suggests a deficit in a first stage of selecting a potential target for attention. In addition, the patients made more errors by responding to semantically related distractors on target-absent trials. This indicates a problem at a second stage of target verification, after items have been attended. The data suggest that frontal lobe damage disrupts both the ability to use peripheral information to guide attention, and the ability to keep separate the target of search from the related items, on occasions when related items achieve selection. |
Matthew J. Thurtell; Louis F. Dell'Osso; R. John Leigh; Marcelo Mattar; Jonathan B. Jacobs; Robert L. Tomsak Effects of acetazolamide on infantile nystagmus syndrome waveforms: comparisons to contact lenses and convergence in a well-studied subject. Journal Article In: The Open Ophthalmology Journal, vol. 4, pp. 42–51, 2010. @article{Thurtell2010, AIM: To determine if acetazolamide, an effective treatment for certain inherited channelopathies, has therapeutic effects on infantile nystagmus syndrome (INS) in a well-studied subject, compare them to other therapies in the same subject and to tenotomy and reattachment (T&R) in other subjects. METHODS: Eye-movement data were taken using a high-speed digital video recording system. Nystagmus waveforms were analyzed by applying an eXpanded Nystagmus Acuity Function (NAFX) at different gaze angles and determining the Longest Foveation Domain (LFD). RESULTS: Acetazolamide improved foveation by both a 59.7% increase in the peak value of the NAFX function (from 0.395 to 0.580) and a 70% broadening of the NAFX vs Gaze Angle curve (the LFD increased from 20° to 34°). The resulting U-shaped improvement in the percent NAFX vs Gaze Angle curve, varied from ~60% near the NAFX peak to over 1000% laterally. The therapeutic improvements in NAFX from acetazolamide (similar to T&R) were intermediate between those of soft contact lenses and convergence, the latter was best; for LFD improvements, acetazolamide and contact lenses were equivalent and less effective than convergence. Computer simulations suggested that damping the central oscillation driving INS was insufficient to produce the foveation improvements and increased NAFX values. CONCLUSION: Acetazolamide resulted in improved-foveation INS waveforms over a broadened range of gaze angles, probably acting at more than one site. This raises the question of whether hereditary INS involves an inherited channelopathy, and whether other agents with known effects on ion channels should be investigated as therapy for this condition. |
Goedele Van Belle; Philippe Lefèvre; Renaud Laguesse; Thomas Busigny; Peter Graef; Karl Verfaillie; Bruno Rossion Feature-based processing of personally familiar faces in prosopagnosia: Evidence from eye-gaze contingency Journal Article In: Behavioural Neurology, vol. 23, no. 4, pp. 255–257, 2010. @article{VanBelle2010b, How familiar and unfamiliar faces are perceived remains largely unknown. Two views have dominated this field of research. On the one hand, recordings of eye fixations on faces and response classification experiments suggest that a face is processed in terms of its individual components, or facial features (mouth, eyes, nose,...), a strategy called analytical processing. On the other hand, there is strong behavioral evidence for interdependence in the processing of different features of a face, rather supporting holistic processing of the face. According to the latter holistic view, facial features are simultaneously perceived and integrated into a single representation, so that the perceptual field is that of the whole face. To shed light on this issue, in two recent studies, we recorded eye movements in a neurological patient suffering from a selective impairment in face recognition (acquired prosopagnosia). Previously, we showed that (1) PS fixates exactly on each of the main features of the face (mouth, left eye, right eye), contrary to normal observers who fixate mainly centrally on the top of the nose, around the geometric centre of the face. Moreover (2), an original gaze-contingent stimulus presentation method applied to an unfamiliar face discrimination task led us to demonstrate that, contrary to normal observers, PS' perceptual field appears to be limited to one central feature fixated at a time. These observations indicate that prosopagnosia prevents processing the multiple elements of a whole face simultaneously, and thus that this ability is a key aspect in human face recognition expertise. Here, we extend these observations by testing the same patient with eye gaze contingency while she attempts to identify a large set of personally familiar individuals from their face. |
Stefan Van der Stigchel; I. Arend; M. Koningsbruggen; Robert D. Rafal Oculomotor integration in patients with a pulvinar lesion Journal Article In: Neuropsychologia, vol. 48, no. 12, pp. 3497–3504, 2010. @article{VanderStigchel2010, The pulvinar nucleus of the thalamus, with its connections to visual areas and to frontal and parietal oculomotor cortex, might serve as a nexus for integrating cortical control of voluntary eye movements with reflexive eye movements generated by the superior colliculus. To investigate this hypothesis, we tested five patients with a unilateral lesion of the pulvinar on the oculomotor capture paradigm. In this task, participants have to ignore a distractor item and make a saccade to a target in a visual search display. Results showed that the interference of the distractor was stronger when it was presented contralateral to their lesion compared to when it was presented in the ipsilesional visual field. These findings were confirmed by an additional single case experiment in which we measured saccade trajectory deviations as evoked by a single distractor. These results show that the pulvinar is involved in the successful influence of higher order signals (like our goals and intentions) on the guidance of our eye movements. |
Signe Vangkilde; Thomas Habekost Finding Wally: Prism adaptation improves visual search in chronic neglect Journal Article In: Neuropsychologia, vol. 48, no. 7, pp. 1994–2004, 2010. @article{Vangkilde2010, Several studies have found that visuo-motor adaptation to rightward deviating prismatic goggles (prism adaptation) can alleviate symptoms of neglect after brain damage, but the long-term effect and clinical relevance of this rehabilitation approach have been questioned. In particular, the effect on visual search performance is controversial. In the present study 6 patients with chronic spatial neglect due to rightsided focal brain damage were given 20 sessions of prism adaptation over a period of two weeks. These patients, as well as a matched control group of neglect patients (n=5), were tested using a variety of effect measures with special emphasis on visual search at baseline, shortly after training, and five weeks later. A positive and very consistent long-term effect of prism adaptation was found across clinical tests of neglect, lateral bias of eye movements, and measures of everyday function, including subjective reports. The results show that prism adaptation can provide durable and clinically significant alleviation of neglect symptoms, even in the stable phase of recovery. |
Gillian Porter; Ute Leonards; Gordon Wilcock; Judy Haworth; Tom Troscianko; Andrea Tales New insights into feature and conjunction search: II. Evidence from Alzheimer's disease Journal Article In: Cortex, vol. 46, no. 5, pp. 637–649, 2010. @article{Porter2010, Deficits in inefficient visual search task performance in Alzheimer's disease (AD) have been linked both to a general depletion of attentional resources and to a specific difficulty in performing conjunction discriminations. It has been difficult to examine the latter proposal because the uniqueness of conjunction search as compared to other visual search tasks has remained a matter of debate. We explored both these claims by measuring pupil dilation, as a measure of resource application, while patients with AD performed a conjunction search task and two single-feature search tasks of similar difficulty in healthy individuals. Maximum pupil dilation in the AD group was greater during performance of the conjunction than the feature search tasks, although pupil response was indistinguishable for the three tasks in healthy controls. This, together with patients' false positive errors for the conjunction task, indicates an AD-specific deficit impacting upon the ability to combine information on multiple dimensions. In addition, maximum pupil dilation was no less for patients than the control group during task performance, which tends to oppose the concept of general resource depletion in AD. However, eye movement patterns in the patient group indicated that they were less able than controls to use organised strategies to assist with task performance. The data are therefore in keeping with a loss of access to resource-saving strategies, rather than a loss of resources per se, in AD. Moreover they demonstrate an additional processing mechanism in performing conjunction search compared with inefficient single-feature search. |
Melanie A. Porter; Tracey A. Shaw; Pamela J. Marsh An unusual attraction to the eyes in Williams-Beuren syndrome: A manipulation of facial affect while measuring face scanpaths Journal Article In: Cognitive Neuropsychiatry, vol. 15, no. 6, pp. 505–530, 2010. @article{Porter2010b, INTRODUCTION: This study aimed to investigate face scanpaths and emotion recognition in Williams-Beuren syndrome (WBS) and whether: (1) the eyes capture the attention of WBS individuals faster than typically developing mental age-matched controls; (2) WBS patients spend abnormally prolonged periods of time viewing the eye region; and (3) emotion recognition skills or eye gaze patterns change depending on the emotional valance of the face. METHODS: Visual scanpaths were recorded while 16 WBS patients and 16 controls passively viewed happy, angry, fearful, and neutral faces. Emotion recognition was subsequently measured. RESULTS: The eyes did not capture the attention of WBS patients faster than controls, but once WBS patients attended to the eyes, they spent significantly more time looking at this region. Unexpectedly, WBS patients showed an impaired ability to recognise angry faces, but face scanpaths were similar across the different facial expressions. CONCLUSIONS: Findings suggest that face processing is atypical in WBS and that emotion recognition and eye gaze abnormalities in WBS are likely to be more complex than previously thought. Findings highlight the need to develop remediation programmes to teach WBS patients how to explore all facial features, enhancing their emotion recognition skills and "normalising" their social interactions. |
A. E. Ritchie; P. G. Griffiths; P. F. Chinnery; A. W. Davidson Eye movement recordings to investigate a supranuclear component in chronic progressive external ophthalmoplegia: A cross-sectional study Journal Article In: British Journal of Ophthalmology, vol. 94, no. 9, pp. 1165–1168, 2010. @article{Ritchie2010, BACKGROUND: It has been postulated that eye movement disorders in chronic progressive external ophthalmoplegia (CPEO) have a neurological as well as a myopathic component to them. AIM: To investigate whether there is a supranuclear component to eye movement disorders in CPEO using eye movement recordings. METHODS: Saccade and smooth pursuit (SP) characteristics together with vestibulo-ocular reflex (VOR) gain and VOR suppression (VORS) gain in 18 patients with CPEO and 34 normal patients were measured using Eyelink II video-oculography. RESULTS: The asymptotic values of the peak velocity main sequence curves were reduced in the CPEO group compared to those of normal patients, with a mean of 161 degrees/s (95% CI 126 degrees/s to 197 degrees/s) compared with 453 degrees/s (95% CI 430 to 475 degrees/s), respectively. Saccadic latency was longer in CPEO (263 ms; 95% CI 250 to 278), compared to controls (185 ms; 95% CI 181 to 189). Smooth pursuit and VOR gains were impaired in CPEO, although this could be explained by non-supranuclear causes. VORS gain was identical in the two groups. CONCLUSIONS: This study does not support a supranuclear component to the ophthalmoplegia of CPEO, although the increased latencies observed may warrant further investigation. |
Alexander Pastukhov; Jochen Braun Rare but precious: Microsaccades are highly informative about attentional allocation Journal Article In: Vision Research, vol. 50, no. 12, pp. 1173–1184, 2010. @article{Pastukhov2010, To clarify the relation between attention and microsaccades, we monitored microsaccades while observers performed tasks with different attentional demand. In four high-demand conditions, observers shifted attention covertly to a peripheral location, or focused attention at fixation. Three corresponding low-demand conditions on physically identical displays provided a basis for comparison. Our results revealed two distinct effects of attentional load: higher loads were associated consistently with lower microsaccade rates, but also with increased directional selectivity (up to 98% congruent). In short, when microsaccades were most rare, the direction of microsaccades proved most informative about the location of the attention focus. The detailed time-courses of the two effects differed, however, suggesting that they may reflect independent processes. |
Brian A. Richardson; Ramesh Balasubramaniam The effect of entrainment on the timing of periodic eye movements Journal Article In: Neuroscience Letters, vol. 469, no. 1, pp. 117–121, 2010. @article{Richardson2010, We performed an experiment in which eight healthy individuals made periodic eye movements at five pacing interval conditions (500 ms, 750 ms, 1000 ms, 1250 ms, and 1500 ms). Three methods of entrainment were used in the synchronization phase: saccade, continuous pursuit and discontinuous pursuit. The stimulus train was extinguished and in the continuation phase, subjects made saccadic eye movements at the entrained movement frequencies between two static targets. Using the Wing-Kristofferson model, clock and motor variance were extracted from the time series of continuation trials for all three entrainment conditions. Our results revealed a main effect of time interval on total variance clock variance (as predicted by Weber's law) and on motor variance. We also report that the pursuit entrainment conditions resulted in and mean duration and variance to the saccade entrainment. These results suggest that the neural networks recruited to support a periodic motor timing task depend on the method used to establish the temporal reference. |
Martin Rolfs; Tomas Knapen; Patrick Cavanagh Global saccadic adaptation Journal Article In: Vision Research, vol. 50, no. 18, pp. 1882–1890, 2010. @article{Rolfs2010, Our actions need constant calibration to arrive accurately at locations of their intended goals; errors in execution must drive rapid adjustments. As an example, saccadic eye movements are vital for bringing objects of interest into the high-acuity center of vision and they must be continually tuned to compensate for ongoing changes in body, muscle strength and neural variability. This adaptation of eye movement responses can be induced artificially by systematically displacing the saccade targets by a constant proportion during each saccade. Observers do not notice these shifts and yet the oculomotor system does, rapidly compensating for the landing error until the saccades finally land close to the artificially displaced target. This recalibration has been described as spatially selective, dropping off with distance in direction and amplitude from the adapted saccade vector. However, we now report that this local adaptation property is a consequence of adapting to only one direction at a time, the method generally used in previous studies. When we induced adaptation in all directions, using a quasi-random walk where each target was displaced 25% back toward to the previous fixation, we found strong, spatially generalized adaptation that could not be accounted for by an accumulation of many vector-specific adaptations. This global adaptation is a plausible strategy for calibration given the absence of any obvious growth changes or muscle deficits that would lead to vector specific losses and it provides a robust model for testing motor calibration. |
Fabian Schnier; Eckart Zimmermann; Markus Lappe Adaptation and mislocalization fields for saccadic outward adaptation in humans Journal Article In: Journal of Eye Movement Research, vol. 3, no. 3, pp. 1–18, 2010. @article{Schnier2010, Adaptive shortening of a saccade influences the metrics of other saccades within a spatial window around the adapted target. Within this adaptation field visual stimuli presented before an adapted saccade are mislocalized in proportion to the change of the saccade metric. We investigated the saccadic adaptation field and associated localization changes for saccade lengthening, or outward adaptation. We measured the adaptation field for two different saccade adaptations (14 deg to 20 deg and 20 deg to 26 deg) by testing transfer to 34 different target positions. We measured localization judgements by asking subjects to localize a probe flashed before saccade onset. The amount of adaptation transfer differed for different target locations. It increased with increases of the horizontal component of the saccade and remained largely constant with deviation of the vertical component of the saccade. Mislocalization of probes inside the adaptation field was correlated with the amount of adaptation of saccades to the probe location. These findings are consistent with the assumption that oculomotor space and perceptual space are linked to each other. |
Alexander C. Schütz; Doris I. Braun; J. Anthony Movshon; Karl R. Gegenfurtner Does the noise matter? Effects of different kinematogram types on smooth pursuit eye movements and perception Journal Article In: Journal of Vision, vol. 10, no. 13, pp. 1–22, 2010. @article{Schuetz2010a, We investigated how the human visual system and the pursuit system react to visual motion noise. We presented three different types of random-dot kinematograms at five different coherence levels. For transparent motion, the signal and noise labels on each dot were preserved throughout each trial, and noise dots moved with the same speed as the signal dots but in fixed random directions. For white noise motion, every 20 ms the signal and noise labels were randomly assigned to each dot and noise dots appeared at random positions. For Brownian motion, signal and noise labels were also randomly assigned, but the noise dots moved at the signal speed in a direction that varied randomly from moment to moment. Neither pursuit latency nor early eye acceleration differed among the different types of kinematograms. Late acceleration, pursuit gain, and perceived speed all depended on kinematogram type, with good agreement between pursuit gain and perceived speed. For transparent motion, pursuit gain and perceived speed were independent of coherence level. For white and Brownian motions, pursuit gain and perceived speed increased with coherence but were higher for white than for Brownian motion. This suggests that under our conditions, the pursuit system integrates across all directions of motion but not across all speeds. |
Alexander C. Schütz; M. Concetta Morrone Compression of time during smooth pursuit eye movements Journal Article In: Vision Research, vol. 50, no. 24, pp. 2702–2713, 2010. @article{Schuetz2010, Humans have a clear sense for the passage of time, but while implicit motor timing is quite accurate, explicit timing is prone to distortions particularly during action (Wenke & Haggard, 2009) and saccadic eye movements (Morrone, Ross, & Burr, 2005). Here, we investigated whether perceived duration is also affected by the execution of smooth pursuit eye movements, showing a compression of apparent duration similar to that observed during saccades. To this end, we presented two brief bars that marked intervals between 100 and 300 ms and asked subjects to judge their duration during fixation and pursuit. We found a compression of perceived duration for bars modulated in luminance contrast of about 32% and for bars modulated in chromatic contrast of 14% during pursuit compared to fixation. Interestingly, Weber ratios were similar for fixation and pursuit, if they are expressed as ratio between JND and perceived duration. This compression was constant for pursuit speeds from 7 to 14 deg/s and did not occur for intervals marked by auditory events. These results argue for a modality-specific component in the processing of temporal information. |
Reza Shadmehr; Jean-Jacques Orban de Xivry; Minnan Xu-Wilson; Ting-Yu Shih Temporal discounting of reward and the cost of time in motor control Journal Article In: Journal of Neuroscience, vol. 30, no. 31, pp. 10507–10516, 2010. @article{Shadmehr2010, Why do movements take a characteristic amount of time, and why do diseases that affect the reward system alter control of movements? Suppose that the purpose of any movement is to position our body in a more rewarding state. People and other animals discount future reward as a hyperbolic function of time. Here, we show that across populations of people and monkeys there is a correlation between discounting of reward and control of movements. We consider saccadic eye movements and hypothesize that duration of a movement is equivalent to a delay of reward. The hyperbolic cost of this delay not only accounts for kinematics of saccades in adults, it also accounts for the faster saccades of children, who temporally discount reward more steeply. Our theory explains why saccade velocities increase when reward is elevated, and why disorders in the encoding of reward, for example in Parkinson's disease and schizophrenia, produce changes in saccade. We show that delay of reward elevates the cost of saccades, reducing velocities. Finally, we consider coordinated movements that include motion of eyes and head and find that their kinematics is also consistent with a hyperbolic, reward-dependent cost of time. Therefore, each voluntary movement carries a cost because its duration delays acquisition of reward. The cost depends on the value that the brain assigns to stimuli, and the rate at which it discounts this value in time. The motor commands that move our eyes reflect this cost of time. |
John F. Soechting; Hrishikesh M. Rao; John Z. Juveli Incorporating prediction in models for two-dimensional smooth pursuit Journal Article In: PLoS ONE, vol. 5, no. 9, pp. e12574, 2010. @article{Soechting2010, A predictive component can contribute to the command signal for smooth pursuit. This is readily demonstrated by the fact that low frequency sinusoidal target motion can be tracked with zero time delay or even with a small lead. The objective of this study was to characterize the predictive contributions to pursuit tracking more precisely by developing analytical models for predictive smooth pursuit. Subjects tracked a small target moving in two dimensions. In the simplest case, the periodic target motion was composed of the sums of two sinusoidal motions (SS), along both the horizontal and the vertical axes. Motions following the same or similar paths, but having a richer spectral composition, were produced by having the target follow the same path but at a constant speed (CS), and by combining the horizontal SS velocity with the vertical CS velocity and vice versa. Several different quantitative models were evaluated. The predictive contribution to the eye tracking command signal could be modeled as a low-pass filtered target acceleration signal with a time delay. This predictive signal, when combined with retinal image velocity at the same time delay, as in classical models for the initiation of pursuit, gave a good fit to the data. The weighting of the predictive acceleration component was different in different experimental conditions, being largest when target motion was simplest, following the SS velocity profiles. |
Riju Srimal; Clayton E. Curtis Secondary adaptation of memory-guided saccades Journal Article In: Experimental Brain Research, vol. 206, no. 1, pp. 35–46, 2010. @article{Srimal2010, Adaptation of saccade gains in response to errors keeps vision and action co-registered in the absence of awareness or effort. Timing is key, as the visual error must be available shortly after the saccade is generated or adaptation does not occur. Here, we tested the hypothesis that when feedback is delayed, learning still occurs, but does so through small secondary corrective saccades. Using a memory-guided saccade task, we gave feedback about the accuracy of saccades that was falsely displaced by a consistent amount, but only after long delays. Despite the delayed feedback, over time subjects improved in accuracy toward the false feedback. They did so not by adjusting their primary saccades, but via directed corrective saccades made before feedback was given. We propose that saccade learning may be driven by different types of feedback teaching signals. One teaching signal relies upon a tight temporal relation with the saccade and contributes to obligatory learning independent of awareness. When this signal is ineffective due to delayed error feedback, a second compensatory teaching signal enables flexible adjustments to the spatial goal of saccades and helps maintain sensorimotor accuracy. |
Masahiko Terao; Junji Watanabe; Akihiro Yagi; Shin'ya Nishida Smooth pursuit eye movements improve temporal resolution for color perception Journal Article In: PLoS ONE, vol. 5, no. 6, pp. e11214, 2010. @article{Terao2010, Human observers see a single mixed color (yellow) when different colors (red and green) rapidly alternate. Accumulating evidence suggests that the critical temporal frequency beyond which chromatic fusion occurs does not simply reflect the temporal limit of peripheral encoding. However, it remains poorly understood how the central processing controls the fusion frequency. Here we show that the fusion frequency can be elevated by extra-retinal signals during smooth pursuit. This eye movement can keep the image of a moving target in the fovea, but it also introduces a backward retinal sweep of the stationary background pattern. We found that the fusion frequency was higher when retinal color changes were generated by pursuit-induced background motions than when the same retinal color changes were generated by object motions during eye fixation. This temporal improvement cannot be ascribed to a general increase in contrast gain of specific neural mechanisms during pursuit, since the improvement was not observed with a pattern flickering without changing position on the retina or with a pattern moving in the direction opposite to the background motion during pursuit. Our findings indicate that chromatic fusion is controlled by a cortical mechanism that suppresses motion blur. A plausible mechanism is that eye-movement signals change spatiotemporal trajectories along which color signals are integrated so as to reduce chromatic integration at the same locations (i.e., along stationary trajectories) on the retina that normally causes retinal blur during fixation. |
Douwe P. Bergsma; G. J. Wildt Visual training of cerebral blindness patients gradually enlarges the visual field Journal Article In: British Journal of Ophthalmology, vol. 94, no. 1, pp. 88–96, 2010. @article{Bergsma2010, BACKGROUND: Multiple studies on recovery of hemianopsia after cerebrovascular accident report visual-field enlargements after stimulation of the visual-field border area. These enlargements are made evident by the difference between pre- and post-training measurements of the visual field. Until now, it was not known how the visual-field enlargement develops. AIM: To study how the enlargement develops as a function of time. METHODS: 11 subjects were trained by stimulating the border area of their visual-field defect using a Goldmann perimeter. The visual-field border location was assessed using dynamic Goldmann perimetry before, after and during training (after each 10th training session). To monitor eye fixation, a video-based eye-tracker was used during each complete perimetry session. RESULTS: It was found that visual-field enlargement during training is actually a gradual shift of the visual-field border, which was independent of the type of stimulus-set used during training. The shift could be observed while eye fixation was accurate. CONCLUSION: Visual-detection training leads to a decrease in detection thresholds in the affected visual-field areas and to visual-field enlargement. Training effects can be generalised to important daily-life activities like reading. |
Jens Blechert; Ulrich Ansorge; Brunna Tuschen-Caffier A body-related dot-probe task reveals distinct attentional patterns for bulimia nervosa and anorexia nervosa Journal Article In: Journal of Abnormal Psychology, vol. 119, no. 3, pp. 575–585, 2010. @article{Blechert2010, We investigated body-related attentional biases in eating disorders by testing whether individuals with anorexia nervosa (AN |