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Caroline Paquette; J. Fung
Temporal facilitation of gaze in the presence of postural reactions triggered by sudden surface perturbations Journal Article
In: Neuroscience, vol. 145, no. 2, pp. 505–519, 2007.
Saccadic reaction times can be shortened by an additional sensory modality (e.g. auditory, tactile) presented in temporal proximity to the triggering cue. Whereas somatosensory cues given by sudden perturbations of the support surface can trigger appropriate postural adjustments to maintain upright stance, it is not known how gaze executions are affected by the dual task of maintaining upright balance while redirecting gaze. It was hypothesized that the onset latency of gaze movements toward visual targets will be shortened by sudden surface perturbations following visual target shifts to prompt a stable visual anchor for postural stabilization. Eight subjects stood on a movable platform with gaze fixated on a central target 2 m directly in front, and were instructed to shift their gaze to lateral targets located along a 63° arc to the right and left. The trials began with the central target lit followed randomly by either the right, left or center target. Fifty or 250 ms following this target shift, balance was perturbed by a sudden yaw movement of the support surface (15.5° over 210 ms at 130°/s), with no stepping or large arm reactions observed. The latency of the gaze shifts was significantly shortened (by ∼72 ms) when executed simultaneously with a surface perturbation. A decrease in excitation latency was also observed in the cervical paraspinals and sternocleidomastoid muscles. Postural responses in the ankle and knee muscles were not affected by gaze shifts. Pelvic horizontal angular motion closely followed surface motion whereas head motion was influenced by gaze shifts. During the combined gaze shift and surface motion conditions, thorax movement excursion was larger and not correlated with either the surface motion or visual target shift. In conclusion, postural adjustments in response to sudden surface yaws facilitate voluntary gaze shift execution and this enhancement may result from the sensory fusion of somatosensory and visual information.
Frank A. Proudlock; Irene Gottlob
Physiology and pathology of eye-head coordination Journal Article
In: Progress in Retinal and Eye Research, vol. 26, no. 5, pp. 486–515, 2007.
Human head movement control can be considered as part of the oculomotor system since the control of gaze involves coordination of the eyes and head. Humans show a remarkable degree of flexibility in eye-head coordination strategies, nonetheless an individual will often demonstrate stereotypical patterns of eye-head behaviour for a given visual task. This review examines eye-head coordination in laboratory-based visual tasks, such as saccadic gaze shifts and combined eye-head pursuit, and in common tasks in daily life, such as reading. The effect of the aging process on eye-head coordination is then reviewed from infancy through to senescence. Consideration is also given to how pathology can affect eye-head coordination from the lowest through to the highest levels of oculomotor control, comparing conditions as diverse as eye movement restrictions and schizophrenia. Given the adaptability of the eye-head system we postulate that this flexible system is under the control of the frontal cortical regions, which assist in planning, coordinating and executing behaviour. We provide evidence for this based on changes in eye-head coordination dependant on the context and expectation of presented visual stimuli, as well as from changes in eye-head coordination caused by frontal lobe dysfunction.
On the limited role of target onset in the gap task: Support for the motor-preparation hypothesis Journal Article
In: Journal of Vision, vol. 7, no. 10, pp. 1–20, 2007.
Saccade latency is reduced when the fixation stimulus is removed shortly before a saccade target appears (gap task) as compared to when the fixation stimulus remains present (overlap task). To test the assumption that this gap effect benefits from advanced motor preparation (M. Paré & D. P. Munoz, 1996), we manipulated target onset independently of the signal to launch a saccade (peripheral offset at the mirror location). In Experiment 1, we showed that, when the target appears at one of only two possible locations, target onset strongly improves performance (lower latency, higher accuracy) in the overlap task but not in the gap task. In Experiment 2, we found that the lack of an effect of target onset in the gap task was not due to inhibition of a reflexive response to the transient associated with the offset (go signal) in our task. In Experiment 3, we manipulated target onset and target uncertainty (two, four, or eight potential target locations) in gap and overlap tasks. As target uncertainty increased, the gap effect decreased, and the effect of target onset on saccade latency in the gap condition became greater. Overall, our results suggest, in line with the motor-preparation hypothesis, that saccade metrics in a gap task are computed before the target is actually displayed and that advanced motor preparation is enhanced when the location of the target is predictable. Analyses of anticipations and regular-latency errors corroborated this view.
Alexander C. Schütz; Doris I. Braun; Karl R. Gegenfurtner
Contrast sensitivity during the initiation of smooth pursuit eye movements Journal Article
In: Vision Research, vol. 47, no. 21, pp. 2767–2777, 2007.
Eye movements challenge the perception of a stable world by inducing retinal image displacement. During saccadic eye movements visual stability is accompanied by a remapping of visual receptive fields, a compression of visual space and perceptual suppression. Here we explore whether a similar suppression changes the perception of briefly presented low contrast targets during the initiation of smooth pursuit eye movements. In a 2AFC design we investigated the contrast sensitivity for threshold-level stimuli during the initiation of smooth pursuit and during saccades. Pursuit was elicited by horizontal step-ramp and ramp stimuli. At any time from 200 ms before to 500 ms after pursuit stimulus onset, a blurred 0.3 deg wide horizontal line with low contrast just above detection threshold appeared for 10 ms either 2 deg above or below the pursuit trajectory. Observers had to pursue the moving stimulus and to indicate whether the target line appeared above or below the pursuit trajectory. In contrast to perceptual suppression effects during saccades, no pronounced suppression was found at pursuit onset for step-ramp motion. When pursuit was elicited by a ramp stimulus, pursuit initiation was accompanied by catch-up saccades, which caused saccadic suppression. Additionally, contrast sensitivity was attenuated at the time of pursuit or saccade stimulus onset. This attenuation might be due to an attentional deficit, because the stimulus required the focus of attention during the programming of the following eye movement.
Alexander C. Schütz; Elias Delipetkos; Doris I. Braun; Dirk Kerzel; Karl R. Gegenfurtner
Temporal contrast sensitivity during smooth pursuit eye movements Journal Article
In: Journal of Vision, vol. 7, no. 13, pp. 1–15, 2007.
During smooth pursuit eye movements, stimuli other than the pursuit target move across the retina, and this might affect their detectability. We measured detection thresholds for vertically oriented Gabor stimuli with different temporal frequencies (1, 4, 8, 12, 16, 20, and 24 Hz) of the sinusoids. Observers kept fixation on a small target spot that was either stationary or moved horizontally at a speed of 8 deg/s. The sinusoid of the Gabor stimuli moved either in the same or in the opposite direction as the pursuit target. Observers had to indicate whether the Gabor stimuli were displayed 4- above or below the target spot. Results show that contrast sensitivity was mainly determined by retinal-image motion but was slightly reduced during smooth pursuit eye movements. Moreover, sensitivity for motion opposite to pursuit direction was reduced in comparison to motion in pursuit direction. The loss in sensitivity for peripheral targets during pursuit can be interpreted in terms of space-based attention to the pursuit target. The loss of sensitivity for motion opposite to pursuit direction can be interpreted as feature-based attention to the pursuit direction.
Konstantin Mergenthaler; Ralf Engbert
Modeling the control of fixational eye movements with neurophysiological delays Journal Article
In: Physical Review Letters, vol. 98, no. 13, pp. 1–4, 2007.
We propose a model for the control of fixational eye movements using time-delayed random walks. Fixational eye movements produce random displacements of the retinal image to prevent perceptual fading. First, we demonstrate that a transition from persistent to antipersistent correlations occurs in data recorded from a visual fixation task. Second, we propose and investigate a delayed random-walk model and get, by comparison of the transition points, an estimate of the neurophysiological delay. Differences between horizontal and vertical components of eye movements are found which can be explained neurophysiologically. Finally, we compare our numerical results with analytic approximations.
David M. Milstein; Michael C. Dorris
The influence of expected value on saccadic preparation Journal Article
In: Journal of Neuroscience, vol. 27, no. 18, pp. 4810–4818, 2007.
Basing higher-order decisions on expected value (reward probability x reward magnitude) maximizes an agent's accruement of reward over time. The goal of this study was to determine whether the advanced preparation of simple actions reflected the expected value of the potential outcomes. Human subjects were required to direct a saccadic eye movement to a visual target that was presented either to the left or right of a central fixation point on each trial. Expected value was manipulated by adjusting the probability of presenting each target and their associated magnitude of monetary reward across 15 blocks of trials. We found that saccadic reaction times (SRTs) were negatively correlated to the relative expected value of the targets. Occasionally, an irrelevant visual distractor was presented before the target to probe the spatial allocation of saccadic preparation. Distractor-directed errors (oculomotor captures) varied as a function of the relative expected value of, and the distance of distractors from, the potential valued targets. SRTs and oculomotor captures were better correlated to the relative expected value of actions than to reward probability, reward magnitude, or overall motivation. Together, our results suggest that the level and spatial distribution of competitive dynamic neural fields representing saccadic preparation reflect the relative expected value of the potential actions.
Harold T. Nefs; Julie M. Harris
Vergence effects on the perception of motion-in-depth Journal Article
In: Experimental Brain Research, vol. 183, no. 3, pp. 313–322, 2007.
When the eyes follow a target that is moving directly towards the head they make a vergence eye movement. Accurate perception of the target's motion requires adequate compensation for the movements of the eyes. The experiments in this paper address the issue of how well the visual system compensates for vergence eye movements when viewing moving targets. We show that there are small but consistent biases across observers: When the eyes follow a target that is moving in depth, it is typically perceived as slower than when the eyes are kept stationary. We also analysed the eye movements that were made by observers. We found that there are considerable differences between observers and between trials, but we did not find evidence that the gains and phase lags of the eye movements were related to psychophysical performance.
Yasuki Noguchi; Shinsuke Shimojo; Ryusuke Kakigi; Minoru Hoshiyama
Spatial contexts can inhibit a mislocalization of visual stimuli during smooth pursuit Journal Article
In: Journal of Vision, vol. 7, no. 13, pp. 1–15, 2007.
The position of a flash presented during pursuit is mislocalized in the direction of the pursuit. Although this has been explained by a temporal mismatch between the slow visual processing of flash and fast efferent signals on eye positions, here we show that spatial contexts also play an important role in determining the flash position. We put various continuously lit objects (walls) between veridical and to-be-mislocalized positions of flash. Consequently, these walls significantly reduced the mislocalization of flash, preventing the flash from being mislocalized beyond the wall (Experiment 1). When the wall was shortened or had a hole in its center, the shape of the mislocalized flash was vertically shortened as if cutoff or funneled by the wall (Experiment 2). The wall also induced color interactions; a red wall made a green flash appear yellowish if it was in the path of mislocalization (Experiment 3). Finally, those flash-wall interactions could be induced even when the walls were presented after the disappearance of flash (Experiment 4). These results indicate that various features (position, shape, and color) of flash during pursuit are determined with an integration window that is spatially and temporally broad, providing a new insight for generating mechanisms of eye-movement mislocalizations.
G. A. Spitzyna; Richard J. S. Wise; Scott A. McDonald; G. T. Plant; D. Kidd; H. Crewes; Alexander P. Leff
Optokinetic therapy improves text reading in patients with hemianopic alexia: A controlled trial Journal Article
In: Neurology, vol. 68, no. 22, pp. 1922–1930, 2007.
OBJECTIVE: An acquired right-sided homonymous hemianopia can result in slowed left-to-right text reading, called hemianopic alexia (HA). Patients with HA lack essential visual information to help guide ensuing reading fixations. We tested two hypotheses: first, that practice with a visual rehabilitation method that induced small-field optokinetic nystagmus (OKN) would improve reading speeds in patients with HA when compared to a sham visual rehabilitation therapy; second, that this therapy would preferentially affect reading saccades into the blind field. METHODS: Nineteen patients with HA were entered into a two-armed study with two therapy blocks in each arm: one group practiced reading moving text (MT) that scrolled from right to left daily for two 4-week blocks (Group1), while the other had sham therapy (spot the difference) for the first block and then crossed over to MT for the second. RESULTS: Group 1 showed significant improvements in static text reading speed over both therapy blocks (18% improvement), while Group 2 did not significantly improve over the first block (5% improvement) but did when they crossed over to the MT block (23% improvement). MT therapy was associated with a direction-specific effect on saccadic amplitude for rightward but not leftward reading saccades. CONCLUSION: Optokinetic nystagmus inducing therapy preferentially affects reading saccades in the direction of the induced (involuntary) saccadic component. This is the first study to demonstrate the effectiveness of a specific eye movement based therapy in patients with hemianopic alexia (HA) in the context of a therapy-controlled trial. A free Web-based version of the therapy used in this study is available online to suitable patients with HA.
James T. Todd; Karl R. Gegenfurtner; Lore Thaler; James T. Todd; Miriam Spering; Karl R. Gegenfurtner
Illusory bending of a rigidly moving line segment: Effects of image motion and smooth pursuit eye movements. Journal Article
In: Journal of Vision, vol. 7, no. 6, pp. 1–13, 2007.
Four experiments in which observers judged the apparent "rubberiness" of a line segment undergoing different types of rigid motion are reported. The results reveal that observers perceive illusory bending when the motion involves certain combinations of translational and rotational components and that the illusion is maximized when these components are presented at a frequency of approximately 3 Hz with a relative phase angle of approximately 120 degrees . Smooth pursuit eye movements can amplify or attenuate the illusion, which is consistent with other results reported in the literature that show effects of eye movements on perceived image motion. The illusion is unaffected by background motion that is in counterphase with the motion of the line segment but is significantly attenuated by background motion that is in-phase. This is consistent with the idea that human observers integrate motion signals within a local frame of reference, and it provides strong evidence that visual persistency cannot be the sole cause of the illusion as was suggested by J. R. Pomerantz (1983). An analysis of the motion patterns suggests that the illusory bending motion may be due to an inability of observers to accurately track the motions of features whose image displacements undergo rapid simultaneous changes in both space and time. A measure of these changes is presented, which is highly correlated with observers' numerical ratings of rubberiness.
Massimo Turatto; Matteo Valsecchi; Luigi Tamè; Elena Betta
Microsaccades distinguish between global and local visual processing Journal Article
In: NeuroReport, vol. 18, no. 10, pp. 1015–1018, 2007.
Much is known about the functional mechanisms involved in visual search. Yet, the fundamental question of whether the visual system can perform different types of visual analysis at different spatial resolutions still remains unsettled. In the visual-attention literature, the distinction between different spatial scales of visual processing corresponds to the distinction between distributed and focused attention. Some authors have argued that singleton detection can be performed in distributed attention, whereas others suggest that even such a simple visual operation involves focused attention. Here we showed that microsaccades were spatially biased during singleton discrimination but not during singleton detection. The results provide support to the hypothesis that some coarse visual analysis can be performed in a distributed attention mode.
Matteo Valsecchi; Elena Betta; Massimo Turatto
Visual oddballs induce prolonged microsaccadic inhibition Journal Article
In: Experimental Brain Research, vol. 177, no. 2, pp. 196–208, 2007.
Eyes never stop moving. Even when asked to maintain the eyes at fixation, the oculomotor system produces small and rapid eye movements called microsaccades, at a frequency of about 1.5-2 s(-1). The frequency of microsaccades changes when a stimulus is presented in the visual field, showing a stereotyped response pattern consisting of an early inhibition of microsaccades followed by a rebound, before the baseline is reached again. Although this pattern of response has generally been considered as a sort of oculomotor reflex, directional biases in microsaccades have been recently linked to the orienting of spatial attention. In the present study, we show for the first time that regardless of any spatial bias, the pattern of absolute microsaccadic frequency is different for oddball stimuli compared to that elicited by standard stimuli. In a visual-oddball task, the oddball stimuli caused an initial prolonged inhibition of microsaccades, particularly when oddballs had to be explicitly recognized and remembered. The present findings suggest that high-order cognitive processes, other than spatial attention, can influence the frequency of microsaccades. Finally, we also introduce a new method for exploring the visual system response to oddball stimuli.
Matteo Valsecchi; Massimo Turatto
Microsaccadic response to visual events that are invisible to the superior colliculus Journal Article
In: Behavioral Neuroscience, vol. 121, no. 4, pp. 786–793, 2007.
Even when people think their eyes are still, tiny fixational eye movements, called microsaccades, occur at a rate of -1 Hz. Whenever a new (and potentially dangerous) event takes place in the visual field, the microsaccadic frequency is at first inhibited and then is followed by a rebound before the frequency returns to baseline. It has been suggested that this inhibition-rebound response is a type of oculomotor reflex mediated by the superior colliculus (SC), a midbrain structure involved in saccade programming. The present study investigated microsaccadic responses to visual events that were invisible to the SC; the authors recorded microsaccadic responses to visual oddballs when the latter were equiluminant with respect to the standard stimuli and when both oddballs and standards were equiluminant with respect to the background. Results showed that microsaccadic responses to oddballs and to standards were virtually identical both when the stimuli were visible to the SC and when they were invisible to it. Although the SC may be the generator of microsaccades, this research suggests that the specific fixational oculomotor activity in response to visual events can be controlled by other brain centers.
Robert J. Beers
The sources of variability in saccadic eye movements Journal Article
In: Journal of Neuroscience, vol. 27, no. 33, pp. 8757–8770, 2007.
Our movements are variable, but the origin of this variability is poorly understood. We examined the sources of variability in human saccadic eye movements. In two experiments, we measured the spatiotemporal variability in saccade trajectories as a function of movement direction and amplitude. One of our new observations is that the variability in movement direction is smaller for purely horizontal and vertical saccades than for saccades in oblique directions. We also found that saccade amplitude, duration, and peak velocity are all correlated with one another. To determine the origin of the observed variability, we estimated the noise in motor commands from the observed spatiotemporal variability, while taking into account the variability resulting from uncertainty in localization of the target. This analysis revealed that uncertainty in target localization is the major source of variability in saccade endpoints, whereas noise in the magnitude of the motor commands explains a slightly smaller fraction. In addition, there is temporal variability such that saccades with a longer than average duration have a smaller than average peak velocity. This noise model has a large generality because it correctly predicts the variability in other data sets, which contain saccades starting from very different initial locations. Because the temporal noise most likely originates in movement planning, and the motor command noise in movement execution, we conclude that uncertainty in sensory signals and noise in movement planning and execution all contribute to the variability in saccade trajectories. These results are important for understanding how the brain controls movement.
Henning U. Voss; Bruce D. McCandliss; Jamshid Ghajar; Minah Suh
A quantitative synchronization model for smooth pursuit target tracking Journal Article
In: Biological Cybernetics, vol. 96, no. 3, pp. 309–322, 2007.
We propose a quantitative model for human smooth pursuit tracking of a continuously moving visual target which is based on synchronization of an internal expectancy model of the target position coupled to the retinal target signal. The model predictions are tested in a smooth circular pursuit eye tracking experiment with transient target blanking of variable duration. In subjects with a high tracking accuracy, the model accounts for smooth pursuit and repeatedly reproduces quantitatively characteristic patterns of the eye dynamics during target blanking. In its simplest form, the model has only one free parameter, a coupling constant. An extended model with a second parameter, a time delay or memory term, accounts for predictive smooth pursuit eye movements which advance the target. The model constitutes an example of synchronization of a complex biological system with perceived sensory signals.
Jeremy B. Wilmer; Ken Nakayama
Two distinct visual motion mechanisms for smooth pursuit: evidence from individual differences Journal Article
In: Neuron, vol. 54, no. 6, pp. 987–1000, 2007.
Smooth-pursuit eye velocity to a moving target is more accurate after an initial catch-up saccade than before, an enhancement that is poorly understood. We present an individual-differences-based method for identifying mechanisms underlying a physiological response and use it to test whether visual motion signals driving pursuit differ pre- and postsaccade. Correlating moment-to-moment measurements of pursuit over time with two psychophysical measures of speed estimation during fixation, we find two independent associations across individuals. Presaccadic pursuit acceleration is predicted by the precision of low-level (motion-energy-based) speed estimation, and postsaccadic pursuit precision is predicted by the precision of high-level (position-tracking) speed estimation. These results provide evidence that a low-level motion signal influences presaccadic acceleration and an independent high-level motion signal influences postsaccadic precision, thus presenting a plausible mechanism for postsaccadic enhancement of pursuit. textcopyright 2007 Elsevier Inc. All rights reserved.
Andre Kaminiarz; Bart Krekelberg; Frank Bremmer
Localization of visual targets during optokinetic eye movements Journal Article
In: Vision Research, vol. 47, no. 6, pp. 869–878, 2007.
We investigated localization of brief visual targets during reflexive eye movements (optokinetic nystagmus). Subjects mislocalized these targets in the direction of the slow eye movement. This error decreased shortly before a saccade and temporarily increased afterwards. The pattern of mislocalization differs markedly from mislocalization during voluntary eye movements in the presence of visual references, but (spatially) resembles mislocalization during voluntary eye movements in darkness. Because neither reflexive eye movements nor voluntary eye movements in darkness have explicit (visual) goals, these data support the view that visual goals support perceptual stability as an important link between pre- and post-saccadic scenes.
Stephen J. Kerrigan; John F. Soechting
Anisotropies in the gain of smooth pursuit during two-dimensional tracking as probed by brief perturbations Journal Article
In: Experimental Brain Research, vol. 180, no. 3, pp. 435–448, 2007.
Previous investigations suggest the gain of smooth pursuit is directionally anisotropic and is regulated in a task-dependent manner. Smooth pursuit is also known to be influenced by expectations concerning the target's motion, but the role of such expectations in modulating feedback gain is not known. In the present work, the gain of smooth pursuit was probed by applying brief perturbations to quasi-predictable two-dimensional target motion at multiple time points. The target initially moved in a straight line, then followed the circumference of a circle for distances ranging between 180 degrees and 270 degrees . Finally, the path reverted to linear motion. Perturbations consisted of a pulse of velocity 50 or 100 ms in duration, applied in one of eight possible directions. They were applied at the onset of the curve or after the target had traversed an arc of 45 degrees or 90 degrees . Pursuit gain was measured by computing the average amplitude of the response in smooth pursuit velocity over a 100 ms interval. To do so we used a coordinate system defined by the motion of the target at the onset of the perturbation, with directions tangential and normal to the path. Responses to the perturbations had two components: one that was modulated with the direction of the perturbation and one that was directionally nonspecific. For the directional response, on average the gain in the normal direction was slightly larger than the gain in the tangential direction, with a ratio ranging from 1.0 to 1.3. The directionally nonspecific response, which was more prominent for perturbations at curve onset or at 90 degrees , consisted of a transient decrease in pursuit speed. Perturbations applied at curve onset also delayed the tracking of the curved target motion.
K. Konigs; J. Knoll; Frank Bremmer
Localisation of auditory targets during optokinetic nystagmus Journal Article
In: Perception, vol. 36, pp. 1507–1513, 2007.
Previous studies have shown that the perceived location of visual stimuli briefly flashed during smooth pursuit, saccades, or optokinetic nystagmus (OKN) is not veridical. We investigated whether these mislocalisations can also be observed for brief auditory stimuli presented during OKN. Experiments were carried out in a lightproof sound-attenuated chamber. Participants performed eye movements elicited by visual stimuli. An auditory target (white noise) was presented for 5 ms. Our data clearly indicate that auditory targets are mislocalised during reflexive eye movements. OKN induces a shift of perceived location in the direction of the slow eye movement and is modulated in the temporal vicinity of the fast phase. The mislocalisation is stronger for look- as compared to stare-nystagmus. The size and temporal pattern of the observed mislocalisation are different from that found for visual targets. This suggests that different neural mechanisms are at play to integrate oculomotor signals and information on the spatial location of visual as well as auditory stimuli.
J. Hübner; Andreas Sprenger; C. Klein; J. Hagenah; Holger Rambold; C. Zuhlke; D. Kompf; A. Rolfs; H. Kimmig; Christoph Helmchen
Eye movement abnormalities in spinocerebellar ataxia type 17 (SCA17) Journal Article
In: Neurology, vol. 69, no. 11, pp. 1160–1168, 2007.
BACKGROUND: Spinocerebellar ataxia type 17 (SCA17) is associated with an expansion of CAG/CAA trinucleotide repeats in the gene encoding the TATA-binding protein. In this quantitative characterization of eye movements in SCA17 mutation carriers, we investigated whether eye movement abnormalities originate from multiple lesion sites as suggested by their phenotypic heterogeneity. METHODS: Eye movements (saccades, smooth pursuit) of 15 SCA17 mutation carriers (mean age 36.9 years, range 20 to 54 years; mean disease duration 7.3 years, range 0 to 20 years; 2 clinically unaffected, 13 affected) were compared with 15 age-matched control subjects using the video-based two-dimensional EYELINK II system. RESULTS: Smooth pursuit initiation (step-ramp paradigm) and maintenance were strongly impaired, i.e., pursuit latency was increased and acceleration decreased, whereas latency and position error of the first catch-up saccade were normal. Visually guided saccades were hypometric but had normal velocities. Gaze-evoked nystagmus was found in one-third of the mutation carriers, including downbeat and rebound nystagmus. There was a pathologic increase in error rates of antisaccades (52%) and memory-guided saccades (42%). Oculomotor disorders were not correlated with repeat length. Smooth pursuit impairment and saccadic disorders increased with disease duration. CONCLUSIONS: Several oculomotor deficits of spinocerebellar ataxia type 17 (SCA17) mutation carriers are compatible with cerebellar degeneration. This is consistent with histopathologic and imaging (morphometric) data. In contrast, increased error rates in antisaccades and memory-guided saccades point to a deficient frontal inhibition of reflexive movements, which is probably best explained by cortical dysfunction and may be related to other phenotypic SCA17 signs, e.g., dementia and parkinsonism.
Vyv C. Huddy; Timothy L. Hodgson; Masuma Kapasi; Stanley H. Mutsatsa; Isobel Harrison; Thomas R. E. Barnes; Eileen M. Joyce
Gaze strategies during planning in first-episode psychosis Journal Article
In: Journal of Abnormal Psychology, vol. 116, no. 3, pp. 589–598, 2007.
Eye movements were measured during the performance of a computerized Tower of London task to specify the source of planning abnormalities in patients with 1st-episode schizophrenia or schizoaffective disorder. Subjects viewed 2 arrays of colored balls in the upper and lower parts of the screen. They were asked to plan the shortest sequence of moves required to rearrange the balls in the lower screen to match the upper arrangement. Compared with healthy controls, patients made more planning errors, and decision times were longer. However, the patients showed the same gaze biases as controls prior to making a response, indicating that they understood the requirements of the task, approached the task in a strategic manner by identifying the nature of the problem, and used appropriate fixation strategies to plan and elaborate solutions. The patients showed increased duration of long-gaze periods toward both parts of the screen. This suggests that the patients had difficulty in encoding the essential features of the stimulus array. This finding is compatible with slowing of working memory consolidation.
Rebecca L. Johnson; Keith Rayner
Top-down and bottom-up effects in pure alexia: Evidence from eye movements Journal Article
In: Neuropsychologia, vol. 45, no. 10, pp. 2246–2257, 2007.
The eye movements of a patient with pure alexia, GJ, were recorded as he read sentences in order to explore the roles of top-down and bottom-up information during letter-by-letter reading. Specifically, the effects of word frequency and word predictability were examined. Additional analyses examined the interaction of these effects with the lower level influences of word length and letter confusability. The results indicate that GJ is sensitive to all four of these variables in sentence reading. These findings support an interactive account of reading where letter-by-letter readers use both bottom-up and top-down information to decode words. Due to the disrupted bottom-up processes caused by damage to the Visual Word Form Area or the input connections to it, pure alexic patients rely more heavily on intact top-down information in reading.
Philip J. Benson; Ute Leonards; Robert M. Lothian; David M. St. Clair; Marco C. G. Merlo
Visual scan paths in first-episode schizophrenia and cannabis-induced psychosis Journal Article
In: Journal of Psychiatry and Neuroscience, vol. 32, no. 4, pp. 267–274, 2007.
OBJECTIVE: Patterns of successive saccades and fixations (scan paths) that are made while viewing images are often spatially restricted in schizophrenia, but the relation with cannabis-induced psychosis has not been examined. We used higher-order statistical methods to examine spatiotemporal characteristics of scan paths to determine whether viewing behaviour was distinguishable on a continuum. METHODS: Patients with early acute first-episode paranoid schizophrenia (SCH; n = 11), cannabis-induced psychosis (CIP; n = 6) and unaffected control subjects (n = 22) undertook a task requiring free viewing of facial, fractal and landscape images for 5 seconds while their eye movements were recorded. Frequencies and distributions of saccades and fixations were calculated in relation to image regions examined during each trial. RESULTS: Findings were independent of image category, indicating generalized scanning deficits. Compared with control subjects, patients with SCH and CIP made fewer saccades and fewer fixations of longer duration. In turn, the spatial distribution of fixations in CIP patients was more clustered than in SCH and control subjects. The diversity of features fixated in subjects with CIP was also lower than in SCH patients and control subjects. CONCLUSION: A continuous approach to characterizing scan path changes in different phenotypes suggests that CIP shares some of the abnormalities of SCH but can be distinguished with measures that are sensitive to cognitive strategies active or inhibited during visual exploration.
Christoph Helmchen; Stefan Gottschalk; Thurid Sander; Peter Trillenberg; Holger Rambold; Andreas Sprenger
Beneficial effects of 3,4-diaminopyridine on positioning downbeat nystagmus in a circumscribed uvulo-nodular lesion  Journal Article
In: Journal of Neurology, vol. 254, no. 8, pp. 1126–1128, 2007.
Central positioning downbeat nystagmus (pDBN) presents with transient nystagmus in supine or the head hanging position in the absence of DBN in the head erect position. In contrast to central positional downbeat nystagmus, pDBN requires rapid head posi- tioning manoeuvres to be elicited. The pathomechanism and therapy of central pDBN is not yet known and circumscribed lesions are missing so far [1, 2]. We examined the effect of 3,4-diaminopyridine (DAP) [3, 4] on the oculomotor behavior of a patient with pDBN.
Timothy L. Hodgson; Marcia Chamberlain; Benjamin A. Parris; Martin James; Nicholas Gutowski; Masud Husain; Christopher Kennard
The role of the ventrolateral frontal cortex in inhibitory oculomotor control Journal Article
In: Brain, vol. 130, no. 6, pp. 1525–1537, 2007.
It has been proposed that the inferior/ventrolateral frontal cortex plays a critical role in the inhibitory control of action during cognitive tasks. However, the contribution of this region to the control of eye movements has not been clearly established. Here, we describe the performance of a group of 23 frontal lobe damaged patients in an oculomotor rule switching task for which the association between a centrally presented visual cue and the direction of a saccade could change from trial to trial. A subset of 16 patients also completed the standard antisaccade task. Ventrolateral damage was found to be a significant predictor of errors in both tasks. Analysis of the rate at which patients corrected errors in the rule switching task also revealed an important dissociation between left and right hemisphere damaged patients. Whilst patients with left ventrolateral damage usually corrected response errors with secondary saccades, those with right hemisphere lesions often failed to do so. The results suggest that the inferior frontal cortex forms part of a wider frontal network mediating inhibitory control over stimulus elicited eye movements. The critical role played by the right ventrolateral region in cognitive tasks may arise due to an additional functional specialization for the monitoring and updating of task rules.
Anouk Lamontagne; Caroline Paquette; Joyce Fung
Stroke affects the coordination of gaze and posture during preplanned turns while walking Miscellaneous
BACKGROUND: In healthy subjects, the act of walking and turning is accomplished by a sequential horizontal reorientation of gaze, head, and body toward the direction of the turn. Subjects with stroke, however, have difficulty altering their walking direction and present with loss of balance when performing a head turn or whole body rotation. OBJECTIVE: To study, in a pilot case study, the spatial and temporal coordination of gaze and posture during preplanned turns executed while walking in severely disabled and mildly disabled subjects with stroke as compared to a healthy control walking at slow speed. METHODS: Horizontal plane orientations of gaze, head, thorax, pelvis, and feet as well as the body's center of mass (CoM) trajectory were analyzed as subjects were walking straight or executing a 90-deg turn. RESULTS: Subjects with stroke revealed altered orientation and sequencing of gaze body segments. These alterations were more pronounced in the most severely disabled subject with stroke, especially when turning to the nonparetic side as compared to the paretic side. CONCLUSIONS: These findings suggest an altered coordination of gaze and posture during steering of locomotion in subjects with stroke. This altered coordination is likely due to a complex interaction of motor, sensory, and biomechanical factors that may explain the poor balance and poor control of heading direction during walking and turning in stroke.
Mark F. Lenzenweger; Geoff McLachlan; Donald B. Rubin
Resolving the latent structure of schizophrenia endophenotypes using expectation-maximization-based finite mixture modeling Journal Article
In: Journal of Abnormal Psychology, vol. 116, no. 1, pp. 16–29, 2007.
Prior research has focused on the latent structure of endophenotypic markers of schizophrenia liability, or schizotypy. The work supports the existence of 2 relatively distinct latent classes and derives largely from the taxometric analysis of psychometric values. The present study used finite mixture modeling as a technique for discerning latent structure and the laboratory-measured endophenotypes of sustained attention deficits and eye-tracking dysfunction as endophenotype indexes. In a large adult community sample (N=311), finite mixture analysis of the sustained attention index d' and 2 eye-tracking indexes (gain and catch-up saccade rate) revealed evidence for 2 latent components. A putative schizotypy class accounted for 27% of the sample. A supplementary maximum covariance taxometric analysis yielded highly consistent results. Subjects in the schizotypy component displayed higher rates of schizotypal personality features and an increased rate of treated schizophrenia in their 1st-degree biological relatives compared with subjects in the other component. Implications of these results are examined in light of major theories of schizophrenia liability, and methodological advantages of finite mixture modeling for psychopathology research, with particular emphasis on genomic issues, are discussed.
Rebecca J. McLean; Frank A. Proudlock; Shery Thomas; Christopher Degg; Irene Gottlob
Congenital nystagmus: Randomized, controlled, double-masked trial of memantine/gabapentin Journal Article
In: Annals of Neurology, vol. 61, no. 2, pp. 130–138, 2007.
OBJECTIVE: Nystagmus consists of involuntary to and fro movements of the eyes. Although studies have shown that memantine and gabapentin can reduce acquired nystagmus, no drug treatment has been systematically investigated in congenital nystagmus. METHODS: We performed a randomized, double-masked, placebo-controlled study investigating the effects of memantine and gabapentin on congenital nystagmus over a period of 56 days. The primary outcome measure was logarithmic minimum angle of resolution (logMAR) visual acuity; the secondary outcome measures were nystagmus intensity and foveation, subjective questionnaires about visual function (VF-14) and social function. Analyses were by intention to treat. RESULTS: Forty-eight patients were included in the study. One patient in the placebo group dropped out. Patients were randomized into either a memantine group (n=16), gabapentin group (n=16), or placebo group (n=15). Mean visual acuity improvements showed a significant effect between treatment groups (F=6.2; p=0.004, analysis of variance) with improvement in both memantine and gabapentin groups. Participants with afferent visual defects showed poorer improvements in visual acuity to medication than those with apparently normal visual systems. However, eye movement recordings showed that both nystagmus forms improved in nystagmus intensity (F=7.7; p=0.001) and foveation (F=8.7; p=0.0007). Participants subjectively reported an improvement in vision after memantine and gabapentin treatment more often than in the placebo group (p=0.03). However, there were no significant differences between the treatment groups with visual function (VF-14) or social function questionnaires because all groups reported improvements. INTERPRETATION: Our findings show that pharmacological agents such as memantine and gabapentin can improve visual acuity, reduce nystagmus intensity, and improve foveation in congenital nystagmus.
Z. I. Wang; Louis F. Dell'Osso
Being "slow to see" is a dynamic visual function consequence of infantile nystagmus syndrome: Model predictions and patient data identify stimulus timing as its cause Journal Article
In: Vision Research, vol. 47, no. 11, pp. 1550–1560, 2007.
The objective of this study was to investigate the dynamic properties of infantile nystagmus syndrome (INS) that affect visual function; i.e., which factors influence latency of the initial reflexive saccade (Ls) and latency to target acquisition (Lt). We used our behavioral ocular motor system (OMS) model to simulate saccadic responses (in the presence of INS) to target jumps at different times within a single INS cycle and at random times during multiple cycles. We then studied the responses of 4 INS subjects with different waveforms to test the model's predictions. Infrared reflection was used for 1 INS subject, high-speed digital video for 3. We recorded and analyzed human responses to large and small target-step stimuli. We evaluated the following factors: stimulus time within the cycle (Tc), normalized Tc (Tc%), initial orbital position (Po), saccade amplitude, initial retinal error (ei), and final retinal error (ef). The ocular motor simulations were performed in MATLAB Simulink environment and the analysis was performed in MATLAB environment using OMLAB software. Both the OMS model and OMtools software are available from http://http:www.omlab.org. Our data analysis showed that for each subject, Ls was a fixed value that is typically higher than the normal saccadic latency. Although saccadic latency appears somewhat lengthened in INS, the amount is insufficient to cause the "slow-to-see" impression. For Lt, Tc% was the most influential factor for each waveform type. The main refixation strategies employed by INS subjects made use of slow and fast phases and catch-up saccades, or combinations of them. These strategies helped the subjects to foveate effectively after target movement, sometimes at the cost of increased target acquisition time. Foveating or braking saccades intrinsic to the nystagmus waveforms seemed to disrupt the OMS' ability to accurately calculate reflexive saccades' amplitude and refoveate. Our OMS model simulations demonstrated this emergent behavior and predicted the lengthy target acquisition times found in the patient data.
Zhong I. Wang; Louis F. Dell'Osso; Robert L. Tomsak; Jonathan B. Jacobs
Combining recessions (nystagmus and strabismus) with tenotomy improved visual function and decreased oscillopsia and diplopia in acquired downbeat nystagmus and in horizontal infantile nystagmus syndrome Journal Article
In: Journal of AAPOS, vol. 11, no. 2, pp. 135–141, 2007.
Purpose: To investigate the effects of combined tenotomy and recession procedures on both acquired downbeat nystagmus and horizontal infantile nystagmus. Methods: Patient 1 had downbeat nystagmus with a chin-down (upgaze) position, oscillopsia, strabismus, and diplopia. Asymmetric superior rectus recessions and inferior rectus tenotomies reduced right hypertropia and rotated both eyes downward. Patient 2 had horizontal infantile nystagmus, a 20° left-eye exotropia, and alternating (abducting-eye) fixation. Lateral rectus recessions and medial rectus tenotomies were performed. Horizontal and vertical eye movements were recorded pre- and postsurgically using high-speed digital video. The eXpanded Nystagmus Acuity Function (NAFX) and nystagmus amplitudes and frequencies were measured. Results: Patient 1: The NAFX peak moved from 10° up to primary position where NAFX values improved 17% and visual acuity increased 25%. Vertical NAFX increased across the -10° to +5° vertical range. Primary-position right hypertropia decreased ∼50%; foveation time per cycle increased 102%; vertical amplitude, oscillopsia, and diplopia were reduced, and frequency was unchanged. Patient 2: Two lateral, narrow high-NAFX regions (due to alternating fixation) became one broad region with a 43% increase in primary position (acuity increased ∼92.3%). Diplopia amplitude decreased; convergence and gaze holding were improved. Primary-position right exotropia was reduced; foveation time per cycle increased 257%; horizontal-component amplitude decreased 45.7%, and frequency remained unchanged. Conclusions: Combining tenotomy with nystagmus or strabismus recession procedures increased NAFX and visual acuities and reduced diplopia and oscillopsia in downbeat nystagmus and infantile nystagmus.
Nadia Alahyane; Roméo Salemme; Christian Urquizar; Julien Cotti; Alain Guillaume; Jean-Louis Vercher; Denis Pélisson
Oculomotor plasticity: Are mechanisms of adaptation for reactive and voluntary saccades separate? Journal Article
In: Brain Research, vol. 1135, no. 1, pp. 107–121, 2007.
Saccadic eye movements are permanently controlled and their accuracy maintained by adaptive mechanisms that compensate for physiological or pathological perturbations. In contrast to the adaptation of reactive saccades (RS) which are automatically triggered by the sudden appearance of a single target, little is known about the adaptation of voluntary saccades which allow us to intentionally scan our environment in nearly all our daily activities. In this study, we addressed this issue in human subjects by determining the properties of adaptation of scanning voluntary saccades (SVS) and comparing these features to those of RS. We also tested the reciprocal transfers of adaptation between the two saccade types. Our results revealed that SVS and RS adaptations disclosed similar adaptation fields, time course and recovery levels, with only a slightly lower after-effect for SVS. Moreover, RS and SVS main sequences both remained unaffected after adaptation. Finally and quite unexpectedly, the pattern of adaptation transfers was asymmetrical, with a much stronger transfer from SVS to RS (79%) than in the reverse direction (22%). These data demonstrate that adaptations of RS and SVS share several behavioural properties but at the same time rely on partially distinct processes. Based on these findings, it is proposed that adaptations of RS and SVS may involve a neural network including both a common site and two separate sites specifically recruited for each saccade type.
Paul Sauleau; Pierre Pollak; Paul Krack; Denis Pélisson; Alain Vighetto; Alim Louis Benabid; Caroline Tilikete
Contraversive eye deviation during stimulation of the subthalamic region Journal Article
In: Movement Disorders, vol. 22, no. 12, pp. 1810–1813, 2007.
Contraversive eye deviation (CED) is most often observed intraoperatively during subthalamic nucleus implantation for Parkinson's disease and considered to result from wrong electrode positioning. We report on a woman, bilaterally implanted in the subthalamic nucleus for severe Parkinson's disease disclosing long-lasting CED only when the stimulators were activated separately. Clinical examination and eye movements recording in this patient showed that CED occurred when stimulation was applied at the site and at similar intensity used for the best antiparkinsonian effect. These results suggest that the subthalamic area may be involved in orienting movements, either through the subthalamic nucleus itself or the fibers from the Frontal Eye Fields. Interestingly, this report shows that CED may be corrected by bilateral stimulation and that CED may not necessarily implicate electrode repositioning.
Daniel Smilek; Kelly A. Malcolmson; Jonathan S. A. Carriere; Meghan Eller; Donna Kwan; Michael G. Reynolds
When "3" is a jerk and "E" is a king: Personifying inanimate objects in synesthesia Journal Article
In: Journal of Cognitive Neuroscience, vol. 19, no. 6, pp. 981–992, 2007.
We report a case study of an individual (TE) for whom inanimate objects, such as letters, numbers, simple shapes, and even furniture, are experienced as having rich and detailed personalities. TE reports that her object-personality pairings are stable over time, occur independent of her intentions, and have been there for as long as she can remember. In these respects, her experiences are indicative of synesthesia. Here we show that TE's object-personality pairings are very consistent across test-retest, even for novel objects. A qualitative analysis of TE's personality descriptions revealed that her personifications are extremely detailed and multi-dimensional, and that her personifications of familiar and novel objects differ in specific ways. We also found that TE's eye movements can be biased by the emotional associations she has with letters and numbers. These findings demonstrate that synesthesia can involve complex semantic personifications, which can influence visual attention. Finally, we propose a neural model of normal personification and the unusual personifications that accompany object-personality synesthesia.
Michael L. Spezio; Ralph Adolphs; Robert S. Hurley; Joseph Piven
Abnormal use of facial information in high-functioning autism Journal Article
In: Journal of Autism and Developmental Disorders, vol. 37, no. 5, pp. 929–939, 2007.
Altered visual exploration of faces likely contributes to social cognition deficits seen in autism. To investigate the relationship between face gaze and social cognition in autism, we measured both face gaze and how facial regions were actually used during emotion judgments from faces. Compared to IQ-matched healthy controls, nine high-functioning adults with autism failed to make use of information from the eye region of faces, instead relying primarily on information from the mouth. Face gaze accounted for the increased reliance on the mouth, and partially accounted for the deficit in using information from the eyes. These findings provide a novel quantitative assessment of how people with autism utilize information in faces when making social judgments.
Michael L. Spezio; Ralph Adolphs; Robert S. Hurley; Joseph Piven
Analysis of face gaze in autism using Journal Article
In: Neuropsychologia, vol. 45, no. 1, pp. 144–151, 2007.
One of the components of abnormal social functioning in autism is an impaired ability to direct eye gaze onto other people's faces in social situations. Here, we investigated the relationship between gaze onto the eye and mouth regions of faces, and the visual information that was present within those regions. We used the "Bubbles" method to vary the facial information available on any given trial by revealing only small parts of the face, and measured the eye movements made as participants viewed these stimuli. Compared to ten IQ- and age-matched healthy controls, eight participants with autism showed less fixation specificity to the eyes and mouth, a greater tendency to saccade away from the eyes when information was present in those regions, and abnormal directionality of saccades. The findings provide novel detail to the abnormal way in which people with autism look at faces, an impairment that likely influences all subsequent face processing.
Bert Steenbergen; Julius Verrel; Andrew M. Gordon
Motor planning in congenital hemiplegia Journal Article
In: Disability and Rehabilitation, vol. 29, no. 1, pp. 13–23, 2007.
PURPOSE: Cerebral Palsy (CP) is a broad definition of a neurological condition in which disorders in movement execution and postural control limit the performance of activities of daily living. In this paper, we first review studies on motor planning in hemiplegic CP. Second, preliminary data of a recent study on eye-hand coordination in participants with hemiplegic CP are presented. Here, the potential role of vision for online and prospective control of action was examined. METHOD: Review and presentation of preliminary data of an eye- and hand movement registration experiment in hemiplegic CP. RESULTS: Deficits in motor planning in hemiplegic CP contribute to limitations of activities of daily living. In the second part, exemplary plots of eye-hand coordination are presented for the affected and unaffected hand in one participant with hemiplegic CP, and for the preferred hand in controls, both as an illustration of the research methodology and to give an impression of the observed gaze patterns. CONCLUSION: Research on CP should not solely focus on low-level aspects of action execution, but also take into account the more high-level aspects of motor control, such as planning. Possible deviations therein may be sought in altered gaze patterns as illustrated in the paper.
Elena Betta; Giovanni Galfano; Massimo Turatto
Microsaccadic response during inhibition of return in a target-target paradigm Journal Article
In: Vision Research, vol. 47, no. 3, pp. 428–436, 2007.
This study examined the relationship between inhibition of return (IOR) in covert orienting and microsaccade statistics. Unlike a previous study [Galfano, G., Betta, E., & Turatto, M. (2004)], IOR was assessed by means of a target-target paradigm, and microsaccade dynamics were monitored as a function of both the first and the second visual event. In line with what has been reported with a cue-target paradigm, a significant directional modulation was observed opposite to the first visual event. Because participants were to respond to any stimulus, this rules out the possibility that the modulation resulted from a generic motor inhibition, showing instead that it is peculiarly coupled to the oculomotor system. Importantly, after the second visual event, a different response was observed in microsaccade orientation, whose direction critically depended of whether the second visual event appeared at the same location as the first visual event. The results are consistent with the notion that IOR is composed of both attentional and oculomotor components, and challenge the view that covert orienting paradigms engage the attentional component in isolation.
François Bonnetblanc; Pierre Baraduc
Saccadic adaptation without retinal postsaccadic error Journal Article
In: NeuroReport, vol. 18, no. 13, pp. 1399–1402, 2007.
Primary saccades undershoot their target. Corrective saccades are then triggered by retinal postsaccadic information. We tested whether primary saccades still undershoot when no postsaccadic visual information is available. Participants saccaded to five targets (10-34 degrees) that were either constantly illuminated (ON) or extinguished at saccade onset (OFF(Onset)). In OFF(Onset), few corrective saccades were observed. The saccadic gain increased over trials for the furthest (34 degrees) target. Terminal eye position after glissades or microsaccades progressively converged to the values observed in ON (targets over 16 degrees). Target extinction during the saccade only did not elicit any change. The results show that (i) postsaccadic retinal signals stabilize the saccadic gain and (ii) adaptive changes that reduce terminal error can take place without visual information.
C. R. Camalier; A. Gotler; A. Murthy; K. G. Thompson; Gordon D. Logan; T. J. Palmeri; Jeffrey D. Schall
Dynamics of saccade target selection: Race model analysis of double step and search step saccade production in human and macaque Journal Article
In: Vision Research, vol. 47, no. 16, pp. 2187–2211, 2007.
We investigated how saccade target selection by humans and macaque monkeys reacts to unexpected changes of the image. This was explored using double step and search step tasks in which a target, presented alone or as a singleton in a visual search array, steps to a different location on infrequent, random trials. We report that human and macaque monkey performance are qualitatively indistinguishable. Performance is stochastic with the probability of producing a compensated saccade to the final target location decreasing with the delay of the step. Compensated saccades to the final target location are produced with latencies relative to the step that are comparable to or less than the average latency of saccades on trials with no target step. Noncompensated errors to the initial target location are produced with latencies less than the average latency of saccades on trials with no target step. Noncompensated saccades to the initial target location are followed by corrective saccades to the final target location following an intersaccade interval that decreases with the interval between the target step and the initiation of the noncompensated saccade. We show that this pattern of results cannot be accounted for by a race between two stochastically independent processes producing the saccade to the initial target location and another process producing the saccade to the final target location. However, performance can be accounted for by a race between three stochastically independent processes-a GO process producing the saccade to the initial target location, a STOP process interrupting that GO process, and another GO process producing the saccade to the final target location. Furthermore, if the STOP process and second GO process start at the same time, then the model can account for the incidence and latency of mid-flight corrections and rapid corrective saccades. This model provides a computational account of saccade production when the image changes unexpectedly.
C. S. Chapman; Amelia R. Hunt; Alan Kingstone
Squeezing uncertainty from saccadic compression Journal Article
In: Journal of Eye Movement Research, vol. 1, no. 1, pp. 1–5, 2007.
Brief visual stimuli presented before and during a saccade are often mislocalized due to spatial compression. This saccadic compression effect is thought to have a perceptual basis, and results in visual objects being squeezed together and their number underestimated. Here we show that observers are also uncertain about their visual experiences just before and during a saccade. It is known that responses tend to be biased away from extreme values under conditions of uncertainty. Thus, a plausible alternative explanation of compression is that it reflects the uncertainty-bias to underestimate the number of items that were presented. We test this hypothesis and find that saccadic compression is independent of certainty, and is significantly modulated by orientation, with larger effects for stimuli oriented horizontally, in the direction of the saccade. These findings confirm that saccadic compression is a perceptual phenomenon that may enable seamless perceptual continuity across saccades.
Thérèse Collins; Karine Doré-Mazars; Markus Lappe
Motor space structures perceptual space: Evidence from human saccadic adaptation Journal Article
In: Brain Research, vol. 1172, no. 1, pp. 32–39, 2007.
Saccadic adaptation is the progressive correction of systematic saccade targeting errors. When a saccade to a particular target is adapted, saccades within a spatial window around the target, the adaptation field, are affected as a function of their distance from the adapted target. Furthermore, previous studies suggest that saccadic adaptation might modify the perceptual localization of objects in space. We investigated the localization of visual probes before and after saccadic adaptation, and examined whether the spatial layout of the observed mislocalizations was structurally similar to the saccadic adaptation field. We adapted a horizontal saccade directed towards a target 12° to the right. Thirty-eight saccades towards the right visual hemifield were then used to measure the adaptation field. The adaptation field was asymmetric: transfer of adaptation to saccades larger than the adapted saccade was greater than transfer to smaller saccades. Subjects judged the localization of 39 visual probes both within and outside the adaptation field. The perceived localization of a probe at a given position was proportional to the amount of transfer from the adapted saccade to the saccade towards that position. This similar effect of saccadic adaptation on both the action and perception representations of space suggests that the system providing saccade metrics also contributes to the metric used for the perception of space.
Amelia R. Hunt; Adrian Mühlenen; Alan Kingstone
The time course of attentional and oculomotor capture reveals a common cause Journal Article
In: Journal of Experimental Psychology: Human Perception and Performance, vol. 33, no. 2, pp. 271–284, 2007.
Eye movements are often misdirected toward a distractor when it appears abruptly, an effect known as oculomotor capture. Fundamental differences between eye movements and attention have led to questions about the relationship of oculomotor capture to the more general effect of sudden onsets on performance, known as attentional capture. This study explores that issue by examining the time course of eye movements and manual localization responses to targets in the presence of sudden-onset distractors. The results demonstrate that for both response types, the proportion of trials on which responses are erroneously directed to sudden onsets reflects the quality of information about the visual display at a given point in time. Oculomotor capture appears to be a specific instance of a more general attentional capture effect. Differences and similarities between the two types of capture can be explained by the critical idea that the quality of information about a visual display changes over time and that different response systems tend to access this information at different moments in time.
Samuel B. Hutton; Brendan S. Weekes
Low frequency rTMS over posterior parietal cortex impairs smooth pursuit eye tracking Journal Article
In: Experimental Brain Research, vol. 183, no. 2, pp. 195–200, 2007.
The role of the posterior parietal cortex in smooth pursuit eye movements remains unclear. We used low frequency repetitive transcranial magnetic stimulation (rTMS) to study the cognitive and neural systems involved in the control of smooth pursuit eye movements. Eighteen participants were tested on two separate occasions. On each occasion we measured smooth pursuit eye tracking before and after 6 min of 1 Hz rTMS delivered at 90% of motor threshold. Low frequency rTMS over the posterior parietal cortex led to a significant reduction in smooth pursuit velocity gain, whereas rTMS over the motor cortex had no effect on gain. We conclude that low frequency offline rTMS is a potentially useful tool with which to explore the cortical systems involved in oculomotor control.
Stephanie Jainta; Jörg Hoormann; W. Jaschinski
Objective and subjective measures of vergence step responses Journal Article
In: Vision Research, vol. 47, no. 26, pp. 3238–3246, 2007.
Dichoptic nonius lines are used for subjectively (psychophysically) measuring vergence states, but they have been questioned as valid indicators of vergence eye position. In a mirror-stereoscope, we presented convergent and divergent step-stimuli and estimated the vergence response with nonius lines flashed at fixed delays after the disparity step stimulus. For each delay, an adaptive psychophysical procedure was run to determine the physical nonius offset required for subjective alignment; these vergence states were compared with objective eye movement recordings. Between both measures of initial vergence, we calculated the maximal cross-correlation coefficient: the median in our sample was about 0.9 for convergence and divergence, suggesting a good agreement. Relative to the objective measures, the subjective method revealed a smaller vergence velocity and a larger vergence response in the final phase of the response, but both measures were well correlated. The dynamic nonius test is therefore considered to be useful to relatively evaluate a subject's ability in disparity vergence.
Wolfgang Jaschinski; Stephanie Jainta; Jörg Hoormann; Nina Walper
Objective vs subjective measurements of dark vergence Journal Article
In: Ophthalmic and Physiological Optics, vol. 27, no. 1, pp. 85–92, 2007.
Dark vergence is a resting position of vergence (tonic vergence), measured in a dark visual field to eliminate fusional, accommodative, and proximal stimuli. The vergence resting position is relevant for measures of phoria and fixation disparity. Dark vergence differs reliably among subjects: the average subject converges at a viewing distance of about 1 m, while the inter-individual range is from infinity to about 40 cm. In previous research, dark vergence was measured subjectively, i.e. observers adjusted the horizontal offset of dichoptically presented nonius targets to perceived alignment. Results of such subjective vergence tests do not necessarily agree with those of the objective measurements of eye position with eye trackers. Therefore, we made simultaneous subjective and objective measurements of dark vergence and found similar results with both methods in repeated tests in two sessions. Thus, the nonius test is sufficient for a subjective estimation of dark vergence.
Tobias Pflugshaupt; Urs P. Mosimann; Wolfgang J. Schmitt; Roman Wartburg; Pascal Wurtz; Mathias Lüthi; Thomas Nyffeler; Christian W. Hess; René M. Müri
To look or not to look at threat? Scanpath differences within a group of spider phobics Journal Article
In: Journal of Anxiety Disorders, vol. 21, no. 3, pp. 353–366, 2007.
Predicting the behavior of phobic patients in a confrontational situation is challenging. While avoidance as a major clinical component of phobias suggests that patients orient away from threat, findings based on cognitive paradigms indicate an attentional bias towards threat. Here we present eye movement data from 21 spider phobics and 21 control subjects, based on 3 basic oculomotor tasks and a visual exploration task that included close-up views of spiders. Relative to the control group, patients showed accelerated reflexive saccades in one of the basic oculomotor tasks, while the fear-relevant exploration task evoked a general slowing in their scanning behavior and pronounced oculomotor avoidance. However, this avoidance strongly varied within the patient group and was not associated with the scores from spider avoidance-sensitive questionnaire scales. We suggest that variation of oculomotor avoidance between phobics reflects different strategies of how they cope with threat in confrontational situations.
Tobias Pflugshaupt; Thomas Nyffeler; Roman Wartburg; Pascal Wurtz; Mathias Lüthi; Daniela Hubl; Klemens Gutbrod; Freimut D. Juengling; Christian W. Hess; René M. Müri
When left becomes right and vice versa: Mirrored vision after cerebral hypoxia Journal Article
In: Neuropsychologia, vol. 45, no. 9, pp. 2078–2091, 2007.
The combination of acquired mirror writing and reading is an extremely rare neurological disorder. It is encountered when brain damaged patients prefer horizontally mirrored over normal script in writing and reading. Previous theories have related this pathology to a disinhibition of mirrored engrams in the non-dominant hemisphere, possibly accompanied by a reversal of the preferred scanning direction. Here, we report the experimental investigation of PR, a patient who developed pronounced mirror writing and reading following septic shock that caused hypoxic brain damage. A series of five oculomotor experiments revealed that the patient's preferred scanning direction was indeed reversed. However, PR showed striking scanpath abnormalities and mirror reversals that cannot be explained by previous theories. Considered together with mirror phenomena she displayed in neuropsychological tasks and everyday activities, our findings suggest a horizontal reversal of visual information on a perceptual level. In addition, a systematic manipulation of visual variables within two further experiments had dramatic effects on her mirror phenomena. When confronted with moving, flickering or briefly presented stimuli, PR showed hardly any left-right reversals. Not only do these findings underline the perceptual nature of her disorder, but also allow interpretation of the pathology in terms of a dissociation between visual subsystems. We speculate that early visual cortices are crucially involved in this dissociation. More generally, her mirrored vision may represent an extreme clinical manifestation of the relative instability of the horizontal axis in spatial vision.
Julien Cotti; Alain Guillaume; Nadia Alahyane; Denis Pelisson; Jean-Louis Vercher
Adaptation of voluntary saccades, but not of reactive saccades, transfers to hand pointing movements Journal Article
In: Journal of Neurophysiology, vol. 98, no. 2, pp. 602–612, 2007.
Studying the transfer of visuomotor adaptation from a given effector (e.g., the eye) to another (e.g., the hand) allows us to question whether sensorimotor processes influenced by adaptation are common to both effector control systems and thus to address the level where adaptation takes place. Previous studies have shown only very weak transfer of the amplitude adaptation of reactive saccades--i.e., produced automatically in response to the sudden appearance of visual targets--to hand pointing movements. Here we compared the amplitude of hand pointing movements recorded before and after adaptation of either reactive or voluntary saccades, produced either in a saccade sequence task or in a single saccade task. No transfer to hand pointing movements was found after adaptation of reactive saccades. In contrast, a substantial transfer to the hand was obtained following adaptation of voluntary saccades produced in sequence. Large amounts of transfer between the two saccade types were also found. These results demonstrate that the visuomotor processes influenced by saccadic adaptation depend on the type of saccades and that, in the case of voluntary saccades, they are shared by hand pointing movements. Implications for the neurophysiological substrates of the adaptation of reactive and voluntary saccades are discussed.
Adele Diederich; Hans Colonius
Modeling spatial effects in visual-tactile saccadic reaction time Journal Article
In: Perception and Psychophysics, vol. 69, no. 1, pp. 56–67, 2007.
Saccadic reaction time (SRT) to visual targets tends to be shorter when nonvisual stimuli are presented in close temporal or spatial proximity, even when subjects are instructed to ignore the accessory input. Here, we investigate visual-tactile interaction effects on SRT under varying spatial configurations. SRT to bimodal stimuli was reduced by up to 30 msec, in comparison with responses to unimodal visual targets. In contrast to previous findings, the amount of multisensory facilitation did not decrease with increases in the physical distance between the target and the nontarget but depended on (1) whether the target and the nontarget were presented in the same hemifield (ipsilateral) or in different hemifields (contralateral), (2) the eccentricity of the stimuli, and (3) the frequency of the vibrotactile nontarget. The time-window-of-integration (TWIN) model for SRT (Colonius & Diederich, 2004) is shown to yield an explicit characterization of the observed multisensory spatial interaction effects through the removal of the peripheral-processing effects of stimulus location and tactile frequency.
Adele Diederich; Hans Colonius
Why two "Distractors" are better than one: Modeling the effect of non-target auditory and tactile stimuli on visual saccadic reaction time Journal Article
In: Experimental Brain Research, vol. 179, no. 1, pp. 43–54, 2007.
Saccadic reaction time (SRT) was measured in a focused attention task with a visual target stimulus (LED) and auditory (white noise burst) and tactile (vibration applied to palm) stimuli presented as non-targets at five different onset times (SOAs) with respect to the target. Mean SRT was reduced (i) when the number of non-targets was increased and (ii) when target and non-targets were all presented in the same hemifield; (iii) this facilitation first increases and then decreases as the time point of presenting the non-targets is shifted from early to late relative to the target presentation. These results are consistent with the time-window-of-integration (TWIN) model (Colonius and Diederich in J Cogn Neurosci 16:1000-1009, 2004) which distinguishes a peripheral stage of independent sensory channels racing against each other from a second stage of neural integration of the input and preparation of an oculomotor response. Cross-modal interaction manifests itself in an increase or decrease of second stage processing time. For the first time, without making specific distributional assumptions on the processing times, TWIN is shown to yield numerical estimates for the facilitative effects of the number of non-targets and of the spatial configuration of target and non-targets. More generally, the TWIN model framework suggests that multisensory integration is a function of unimodal stimulus properties, like intensity, in the first stage and of cross-modal stimulus properties, like spatial disparity, in the second stage.
Jay A. Edelman; Árni Kristjánsson; Ken Nakayama
The influence of object-relative visuomotor set on express saccades Journal Article
In: Journal of Vision, vol. 7, no. 6, pp. 1–13, 2007.
Express saccades are considered to have the shortest latency (70-110 ms) of all saccadic eye movements. The influence of visuomotor set, preparatory processes that spatially affect a sensorimotor response, on express saccades was examined by instructing human subjects to make a saccade to one of two simultaneously appearing spots defined by its position relative to the other. A temporal gap between fixation point disappearance and target appearance was used to facilitate the production of express saccades. For all subjects, the instruction influenced the vector of express saccades without increasing saccade latency. The effect on express saccades was only slightly weaker than that for longer latency saccades. Saccade curvature was minimal and did not depend strongly on task. Further experiments demonstrated that the effect of instruction on express saccade vector was much weaker when saccades were instructed to be made to one side of a single small spot, that the effect of instruction was equally strong when directing saccades to the less salient of two stimuli, and that an instruction could not only determine the direction of the effect but also modulate the effect's magnitude. The effect of instruction on saccade vector was no higher when blocked than when varied across trials. These results suggest that express saccades are influenced by object-relative spatial preparatory processes without increasing their reaction time and, thus, that high-level cognitive processes can influence the most reflexive of saccadic eye movements.
J. M. Hagen; Josef N. Geest; R. S. Giessen; Gerardina C. Lagers-van Haselen; H. J. F. M. M. Eussen; J. J. P. Gille; L. C. P. Govaerts; C. H. Wouters; I. F. M. Coo; C. C. Hoogenraad; Sebastiaan K. E. Koekkoek; Maarten A. Frens; N. Camp; A. Linden; M. C. E. Jansweijer; S. S. Thorgeirsson; Chris I. De Zeeuw
Contribution of CYLN2 and GTF2IRD1 to neurological and cognitive symptoms in Williams Syndrome Journal Article
In: Neurobiology of Disease, vol. 26, no. 1, pp. 112–124, 2007.
Williams Syndrome (WS, [MIM 194050]) is a disorder caused by a hemizygous deletion of 25-30 genes on chromosome 7q11.23. Several of these genes including those encoding cytoplasmic linker protein-115 (CYLN2) and general transcription factors (GTF2I and GTF2IRD1) are expressed in the brain and may contribute to the distinct neurological and cognitive deficits in WS patients. Recent studies of patients with partial deletions indicate that hemizygosity of GTF2I probably contributes to mental retardation in WS. Here we investigate whether CYLN2 and GTF2IRD1 contribute to the motoric and cognitive deficits in WS. Behavioral assessment of a new patient in which STX1A and LIMK1, but not CYLN2 and GTF2IRD1, are deleted showed that his cognitive and motor coordination functions were significantly better than in typical WS patients. Comparative analyses of gene specific CYLN2 and GTF2IRD1 knockout mice showed that a reduced size of the corpus callosum as well as deficits in motor coordination and hippocampal memory formation may be attributed to a deletion of CYLN2, while increased ventricle volume can be attributed to both CYLN2 and GTF2IRD1. We conclude that the motor and cognitive deficits in Williams Syndrome are caused by a variety of genes and that heterozygous deletion of CYLN2 is one of the major causes responsible for such dysfunctions.
Caroline Tilikete; Ansgar Koene; Norbert Nighoghossian; Alain Vighetto; Denis Pélisson
Saccadic lateropulsion in Wallenberg syndrome: A window to access cerebellar control of saccades? Journal Article
In: Experimental Brain Research, vol. 174, no. 3, pp. 555–565, 2006.
Saccadic lateropulsion is characterized by an undershoot of contralaterally directed saccades, an overshoot of ipsilaterally directed saccades and an ipsilateral deviation of vertical saccades. In Wallenberg syndrome, it is thought to result from altered signals in the olivo-cerebellar pathway to the oculomotor cerebellar network. In the current study we aimed to determine whether saccadic lateropulsion results from a cerebellar impairment of motor related signals or visuo-spatial related signals. We studied the trajectory, the accuracy, the direction and the amplitude of a variety of vertical and oblique saccades produced by five patients and nine control subjects. Some results are consistent with previous data suggesting altered motor related signals. Indeed, the horizontal error of contralesional saccades in patients increased with the desired horizontal saccade size. Furthermore, the initial directional error measured during the saccadic acceleration phase was smaller than the global directional error, suggesting that the eye trajectory curved progressively. However, some other results suggest that the processes that specify the horizontal spatial goal of the saccades might be impaired in the patients. Indeed, the horizontal error of ipsilesional saccades in patients did not change significantly with the desired horizontal saccade size. In addition, when comparing saccades with similar intended direction, it was found that the directional error was inversely related to the vertical saccade amplitude. Thus we conclude that the cerebellum might be involved both in controlling the motor execution of saccades and in determining the visuo-spatial information about their goal.
Elena Betta; Massimo Turatto
Are you ready? I can tell by looking at your microsaccades Journal Article
In: NeuroReport, vol. 17, no. 10, pp. 1001–1004, 2006.
The direction of microsaccades has been shown to be biased by the allocation of spatial attention. Here, we investigated whether the cognitive processes involved in preparing to respond to an upcoming target can modulate the microsaccadic response. Specifically, we found that optimal manual response preparation, reflected by faster response times, was associated with a reduction in the absolute frequency of microsaccades. The present results are consistent with previous studies suggesting a relationship between oculomotor activity and different sorts of motor responses. Our findings, however, surprisingly demonstrate that the effect of preparation and stimulus expectation extends to an automatic and unconscious oculomotor activity such as microsaccade execution.
Z. Wang; Louis F. Dell'Osso; Z. Zhang; R. John Leigh; Jonathan B. Jacobs
Tenotomy does not affect saccadic velocities: Support for the "small-signal" gain hypothesis Journal Article
In: Vision Research, vol. 46, no. 14, pp. 2259–2267, 2006.
We investigated the effects of four-muscle tenotomy on saccadic characteristics in infantile nystagmus syndrome (INS) and acquired pendular nystagmus (APN). Eye movements of 10 subjects with INS and one with APN were recorded using infrared reflection, magnetic search coil, or high-speed digital video. The expanded nystagmus acuity function (NAFX) quantified tenotomy-induced foveation changes in the INS. Saccadic characteristics and peak-to-peak nystagmus amplitudes were measured. Novel statistical tests were performed on the saccadic data. Six out of the 10 INS subjects showed no changes in saccadic duration, peak velocity, acceleration, or trajectory. In the other four, the differences were less than in peak-to-peak amplitudes (from 14.6% to 39.5%) and NAFX (from 22.2% to 162.4%). The APN subject also showed no changes despite a 50% decrease in peak-to-peak amplitude and a 34% increase in NAFX. The "small-signal" changes (peak-to-peak nystagmus amplitude and NAFX) were found to far exceed any "large-signal" changes (saccadic). Tenotomy successfully reduced INS and APN, enabling higher visual acuity without adversely affecting saccadic characteristics. These findings support the peripheral, small-signal gain reduction (via proprioceptive tension control) hypothesis. Current linear plant models, limited to normal steady-state muscle tension levels, cannot explain the effects of the tenotomy.
Zhong Wang; Louis F. Dell'Osso; Jonathan B. Jacobs; Robert A. Burnstine; Robert L. Tomsak
Effects of tenotomy on patients with infantile nystagmus syndrome: Foveation improvement over a broadened visual field Journal Article
In: Journal of AAPOS, vol. 10, no. 6, pp. 552–560, 2006.
Purpose: To investigate the effects of four-muscle tenotomy on visual function and gaze angle in patients with infantile nystagmus syndrome (INS). Methods: Eye movements of nine patients with infantile nystagmus were recorded using infrared reflection or high-speed digital video techniques. Experimental protocols were designed to record the patients' eye-movement waveforms, pre- and post-tenotomy, at different gaze angles. We used the eXpanded Nystagmus Acuity Function (NAFX) to measure tenotomy-induced changes in the nystagmus at primary position and various gaze angles. The longest foveation domains (LFD) were measured from fitted curves. Peak-to-peak nystagmus amplitudes and foveation-period durations were also measured. All measurements were made unmasked. Results: All seven patients with narrow, high-NAFX, gaze-angle regions showed broadening of these regions of higher visual function. Three patients showed moderate NAFX improvement (13.9-32.6%) at primary position, five showed large improvement (39.9-162.4%), and one showed no NAFX change (due to his high pretenotomy NAFX). Primary position measured acuities improved in six patients. All patients had reductions in nystagmus amplitudes ranging from 14.6 to 37%. The duration of the foveation period increased in all nine patients (11.2-200%). The percentage improvements in both the NAFX and the LFD decreased with higher pretenotomy values. Conclusions: In addition to elevating primary position NAFX, tenotomy also broadens the high-NAFX regions. This broadening effect is more prominent in patients who had sharp pretenotomy NAFX peaks. Four-muscle tenotomy produces higher primary position NAFX increases in infantile nystagmus patients whose pretenotomy values are relatively low, with the improvement decreasing at higher pretenotomy values. The tenotomy procedure improves visual function beyond primary position acuity. This extends the utility of surgical therapy to several different classes of patients with INS for whom other procedures are contraindicated. The pretenotomy NAFX can now be used to predict both primary position acuity improvements and broadening of a patient's high-NAFX range of gaze angles. textcopyright 2006 American Association for Pediatric Ophthalmology and Strabismus.
Nagini Sarvananthan; Frank A. Proudlock; I. Choudhuri; H. Dua; Irene Gottlob
Pharmacologic treatment of congenital nystagmus Journal Article
In: Archives of Ophthalmology, vol. 124, pp. 916–917, 2006.
Pharmacologic treatment has been used in acquired nystagmus with mixed success. Treatments have included baclofen, sodium valproate, gabapentin, and memantine. However, in congenital nystagmus, little is known about the effect of drugs. We describe a patient with congenital nystagmus and corneal dystrophy who improved dramati- cally with gabapentin treatment.
T. Shery; Frank A. Proudlock; N. Sarvananthan; Rebecca J. McLean; Irene Gottlob
The effects of gabapentin and memantine in acquired and congenital nystagmus: A retrospective study Journal Article
In: British Journal of Ophthalmology, vol. 90, no. 7, pp. 839–843, 2006.
Background: Pharmacological treatment has been successful in some forms of acquired neurological nystagmus. However, drugs are not known to be effective in idiopathic infantile nystagmus or nystagmus associated with ocular diseases. Methods: The authors retrospectively analysed Snellen visual acuity (VA), subjective visual function, and eye movement recordings of 23 patients with nystagmus (13 secondary to multiple sclerosis, three associated with other neurological diseases, two idiopathic infantile, and five with associated ocular diseases) treated with gabapentin or memantine. Results: With gabapentin, 10 of 13 patients with nystagmus secondary to multiple sclerosis (MS) showed some improvement. Memantine improved the VA in all three patients with MS who did not improve on gabapentin. There was no change of nystagmus in other neurological disorders. Patients with congenital nystagmus showed reduction of nystagmus and their VA changes depended on the ocular pathology. Conclusion: Gabapentin and memantine may be effective in acquired nystagmus secondary to MS. To the authors' knowledge this is the first series of patients showing that gabapentin is effective in improving nystagmus in congenital nystagmus/nystagmus associated with ocular pathology. Memantine may be useful as an alternative drug in treating patients with nystagmus.
Ibrahim Dahlstrom-Hakki; Alexander Pollatsek
Limits on integrating motion information across saccades Journal Article
In: Perception and Psychophysics, vol. 68, no. 1, pp. 43–54, 2006.
In two experiments, we investigated whether people could detect changes in the rotary motion of a cube. A rendering of a cube rotating at a constant angular velocity was presented on a video monitor and, at a key point in the trial, a cross was presented to one side of the cube as a cue for a saccade. On some trials, a change in the rotation occurred either about 100 msec before the saccade or during the saccade; on other trials, there was no change. The change consisted of moving the cube to a new position in the "rotation sequence," after which it continued to rotate at the same angular velocity as before. There was also a control on all trials to ensure that change detection was not due to the detection of low-level motion. Although detection of the change was well above chance when it occurred during the fixation, it was at chance when it occurred during the saccade, except in the case of one participant (who was in both experiments). This chance performance also occurred in Experiment 2 for (1) a slower rotation speed and (2) an axis of rotation that made the rotation planar. The participant who had above chance performance (and as good as that when the change occurred during a fixation) reported using a "strategy" that did not track the path of the cube. It thus appears that there is no natural way in which the visual system tracks this rotary motion, and that detection of change requires some sort of recoding. This finding raises the question of whether good performance in other, apparently similar, motion-detection tasks is a result of similar recoding.
Ralf Engbert; Konstantin Mergenthaler
Microsaccades are triggered by low retinal image slip Journal Article
In: Proceedings of the National Academy of Sciences, vol. 103, no. 18, pp. 7192–7197, 2006.
Even during visual fixation of a stationary target, our eyes perform rather erratic miniature movements, which represent a random walk. These "fixational" eye movements counteract perceptual fading, a consequence of fast adaptation of the retinal receptor systems to constant input. The most important contribution to fixational eye movements is produced by microsaccades; however, a specific function of microsaccades only recently has been found. Here we show that the occurrence of microsaccades is correlated with low retinal image slip approximately 200 ms before microsaccade onset. This result suggests that microsaccades are triggered dynamically, in contrast to the current view that microsaccades are randomly distributed in time characterized by their rate-of-occurrence of 1 to 2 per second. As a result of the dynamic triggering mechanism, individual microsaccade rate can be predicted by the fractal dimension of trajectories. Finally, we propose a minimal computational model for the dynamic triggering of microsaccades.
Casper J. Erkelens
Coordination of smooth pursuit and saccades Journal Article
In: Vision Research, vol. 46, no. 1-2, pp. 163–170, 2006.
Smooth pursuit and saccades are two components of tracking eye movements. Their coordination has usually been studied by investigating latencies of pursuit onset in response to a moving target appearing simultaneously with the disappearance of the stationary fixation target. The general finding from such studies has been that latencies of saccades and pursuit are different and reflect independent processes. We discuss several limitations of the used targets. In this paper, we study latencies of saccades and smooth pursuit in response to a moving target that overlaps in time with a pursued moving target. We find that saccades and pursuit changes are synchronized. Furthermore, pursuit changes are made fast. Directional changes occur almost entirely within the accompanying saccade. To explain the results we hypothesize a two-stage mechanism for the coordinated generation of saccades and pursuit.
Kai Essig; Marc Pomplun; Helge Ritter
A neural network for 3D gaze recording with binocular eye trackers Journal Article
In: International Journal of Parallel, Emergent and Distributed Systems, vol. 21, no. 2, pp. 79–95, 2006.
Using eye tracking for the investigation of visual attention has become increasingly popular during the last few decades. Nevertheless, only a small number of eye tracking studies have employed 3D displays, although such displays would closely resemble our natural visual environment. Besides higher cost and effort for the experimental setup, the main reason for the avoidance of 3D displays is the problem of computing a subject's current 3D gaze position based on the measured binocular gaze angles. The geometrical approaches to this problem that have been studied so far involved substantial error in the measurement of 3D gaze trajectories. In order to tackle this problem, we developed an anaglyph-based 3D calibration procedure and used a well-suited type of artificial neural network—a parametrized self-organizing map (PSOM)—to estimate the 3D gaze point from a subject's binocular eye-position data. We report an experiment in which the accuracy of the PSOM gaze-point estimation is compared to a geometrical solution. The results show that the neural network approach produces more accurate results than the geometrical method, especially for the depth axis and for distant stimuli.
Transcranial magnetic stimulation of frontal oculomotor regions during smooth pursuit Journal Article
In: Journal of Neuroscience, vol. 26, no. 2, pp. 458–466, 2006.
Both the frontal eye fields (FEFs) and supplementary eye fields (SEFs) are known to be involved in smooth pursuit eye movements. It has been shown recently that stimulation of the smooth-pursuit area of the FEF [frontal pursuit area (FPA)] in monkey increases the pursuit response to unexpected changes in target motion during pursuit. In the current study, we applied transcranial magnetic stimulation (TMS) to the FPA and SEF in humans during sinusoidal pursuit to assess its effects on the pursuit response to predictable, rather than unexpected, changes in target motion. For the FPA, we found that TMS applied immediately before the target reversed direction increased eye velocity in the new direction, whereas TMS applied in mid-cycle, immediately before the target began to slow, decreased eye velocity. For the SEF, TMS applied at target reversal increased eye velocity in the new direction but had no effect on eye velocity when applied at mid-cycle. TMS of the control region (leg region of the somatosensory cortex) did not affect eye velocity at either point. Previous stimulation studies of FPA during pursuit have suggested that this region is involved in controlling the gain of the transformation of visual signals into pursuit motor commands. The current results suggest that the gain of the transformation of predictive signals into motor commands is also controlled by the FPA. The effect of stimulation of the SEF is distinct from that of the FPA and suggests that its role in sinusoidal pursuit is primarily at the target direction reversal.
Waheeda Rahman; Frank A. Proudlock; Irene Gottlob
Oral gabapentin treatment for symptomatic Heimann-Bielschowsky Pphenomenon Journal Article
In: American Journal of Ophthalmology, vol. 141, pp. 221–222, 2006.
PURPOSE: To describe a patient with symptomatic Heimann-Bielschowsky phenomenon (HBP) treated suc- cessfully with oral gabapentin. DESIGN: Interventional case report. METHODS: A 57-year-old patient with retinitis pigmentosa had a 12-month history of vertical oscillopsia. The right visual acuity was 20/200 and the left visual acuity was 20/60 with glasses. He had a coarse, slow, pendular, vertical movement of the right eye consistent with Heimann- Bielschowsky phenomenon. His treatment commenced with oral gabapentin with gradual increase in dose to 2400 mg/d. Eye movement recordings were performed before and after treatment. RESULTS: He became considerably less symptomatic on gabapentin. The right visual acuity improved to 20/80 with glasses. Eye movement recordings confirmed mark- edly reduced vertical oscillations of the right eye. The patient continues on gabapentin with no side effects and sustained effect. CONCLUSIONS: The vertical nystagmoid movement in HBP can be considerably reduced and symptoms remarkably improved when treated with oral gabapentin.
Dirk Kerzel; M. Pilar Aivar; Nathalie E. Ziegler; Eli Brenner
Mislocalization of flashes during smooth pursuit hardly depends on the lighting conditions Journal Article
In: Vision Research, vol. 46, no. 6-7, pp. 1145–1154, 2006.
Targets that are briefly flashed during smooth pursuit eye movements are mislocalized in the direction of motion (forward shift) and away from the fovea (spatial expansion). Hansen [Hansen, R. M. (1979). Spatial localization during pursuit eye movements. Vision Research 19(11), 1213-1221] reported that these errors are not present for fast motor responses in the dark, whereas Rotman et al. [Rotman, G., Brenner, E., Smeets, J. B. (2004). Quickly tapping targets that are flashed during smooth pursuit reveals perceptual mislocalizations. Experimental Brain Research 156(4), 409-414] reported that they are present for fast motor responses in the light. To evaluate whether the lighting conditions are the critical factor, we asked observers to point to the positions of flashed objects during smooth pursuit either in the dark or with the room lights on. In a first experiment, the flash, which could appear at 1 of 15 different positions, was always shown when the eye had reached a certain spatial position. We found a forward bias and spatial expansion that were independent of the target and ambient luminance. In a second experiment, the flash was always shown at the same retinal position, but the spatial position of the eye at the moment of flash presentation was varied. In this case we found differences between the luminance conditions, in terms of how the errors depended on the velocity and position on the trajectory. We also found specific conditions in which people did not mislocalize the target in the direction of pursuit at all. These findings may account for the above-mentioned discrepancy. We conclude that although the lighting conditions do influence the localization errors under some circumstances, it is certainly not so that such errors are absent whenever the experiment is conducted in the dark.
Mark F. Lenzenweger; Gillian A. O'Driscoll
Smooth pursuit eye movement and schizotypy in the community Journal Article
In: Journal of Abnormal Psychology, vol. 115, no. 4, pp. 779–786, 2006.
Deficits in smooth pursuit eye movements are well documented in schizophrenia and schizotypic psychopathology. The status of eye tracking dysfunction (ETD) as an endophenotype for schizophrenia liability is relatively robust. However, the relation of ETD to schizophrenia-related deviance in the general population has not been confirmed. This study examined smooth pursuit eye tracking and schizotypal personality features in the general population. Smooth pursuit eye movement and schizotypal features were measured in 300 adult community subjects. The sample included both sexes, subjects with a wide age and educational range, and subjects with no prior history of psychosis. Primary outcome measures were peak gain (eye velocity/target velocity), catch-up saccade rate, and schizotypal feature scores. Total schizotypal features were significantly associated with decreased peak gain and were associated at the trend level with increased catch-up saccade rate. These associations were essentially unchanged after controlling for age, sex, and intellectual level effects. These data confirm a hypothesized association between schizotypal features and poorer eye tracking performance (principally, peak gain) in the general population as well as support the conceptualization of ETD as an endophenotype for schizophrenia liability.
Jan L. Souman; Ignace T. C. Hooge; Alexander H. Wertheim
Localization and motion perception during smooth pursuit eye movements Journal Article
In: Experimental Brain Research, vol. 171, no. 4, pp. 448–458, 2006.
We investigated the relationship between compensation for the effects of smooth pursuit eye movements in localization and motion perception. Participants had to indicate the perceived motion direction, the starting point and the end point of a vertically moving stimulus dot presented during horizontal smooth pursuit. The presentation duration of the stimulus was varied. From the indicated starting and end points, the motion direction was predicted and compared with the actual indicated directions. Both the directions predicted from localization and the indicated directions deviated from the physical directions, but the errors in the predicted directions were larger than those in the indicated directions. The results of a control experiment, in which the same tasks were performed during fixation, suggest that this difference reflects different transformations from a retinocentric to a head-centric frame of reference. This difference appears to be mainly due to an asymmetry in the effect of retinal image motion direction on localization during smooth pursuit.
Jan L. Souman; Ignace T. C. Hooge; Alexander H. Wertheim
Frame of reference transformations in motion perception during smooth pursuit eye movements Journal Article
In: Journal of Computational Neuroscience, vol. 20, no. 1, pp. 61–76, 2006.
Smooth pursuit eye movements change the retinal image velocity of objects in the visual field. In order to change from a retinocentric frame of reference into a head-centric one, the visual system has to take the eye movements into account. Studies on motion perception during smooth pursuit eye movements have measured either perceived speed or perceived direction during smooth pursuit to investigate this frame of reference transformation, but never both at the same time. We devised a new velocity matching task, in which participants matched both perceived speed and direction during fixation to that during pursuit. In Experiment 1, the velocity matches were determined for a range of stimulus directions, with the head-centric stimulus speed kept constant. In Experiment 2, the retinal stimulus speed was kept approximately constant, with the same range of stimulus directions. In both experiments, the velocity matches for all directions were shifted against the pursuit direction, suggesting an incomplete transformation of the frame of reference. The degree of compensation was approximately constant across stimulus direction. We fitted the classical linear model, the model of Turano and Massof (2001) and that of Freeman (2001) to the velocity matches. The model of Turano and Massof fitted the velocity matches best, but the differences between de model fits were quite small. Evaluation of the models and comparison to a few alternatives suggests that further specification of the potential effect of retinal image characteristics on the eye movement signal is needed.
Miriam Spering; Karl R. Gegenfurtner; Dirk Kerzel
Distractor interference during smooth pursuit eye movements Journal Article
In: Journal of Experimental Psychology: Human Perception and Performance, vol. 32, no. 5, pp. 1136–1154, 2006.
When 2 targets for pursuit eye movements move in different directions, the eye velocity follows the vector average (S. G. Lisberger & V. P. Ferrera, 1997). The present study investigates the mechanisms of target selection when observers are instructed to follow a predefined horizontal target and to ignore a moving distractor stimulus. Results show that at 140 ms after distractor onset, horizontal eye velocity is decreased by about 25%. Vertical eye velocity increases or decreases by 1 degrees /s in the direction opposite from the distractor. This deviation varies in size with distractor direction, velocity, and contrast. The effect was present during the initiation and steady-state tracking phase of pursuit but only when the observer had prior information about target motion. Neither vector averaging nor winner-take-all models could predict the response to a moving to-be-ignored distractor during steady-state tracking of a predefined target. The contributions of perceptual mislocalization and spatial attention to the vertical deviation in pursuit are discussed.
Minah Suh; Sambrita Basu; Rachel Kolster; Ranjeeta Sarkar; Bruce D. McCandliss; Jamshid Ghajar
Increased oculomotor deficits during target blanking as an indicator of mild traumatic brain injury Journal Article
In: Neuroscience Letters, vol. 410, no. 3, pp. 203–207, 2006.
Given the susceptibility of cerebellar-cortical tracts to shearing injury from traumatic brain injury (TBI), we investigated impairment in the generation of predictive eye movements and its relationship to cognitive deficits in mild TBI patients using a smooth pursuit target-blanking paradigm. Compared to a target-tracking paradigm without blanking, this paradigm more greatly necessitates the generation of predictive eye movements, which are subserved by brain regions involved in cognitive processing. Mild TBI patients showed impaired prediction of target trajectories during target blanking, demonstrated by generation of saccades at earlier and more variable time points, as well as greater and more variable oculomotor error compared to controls. In addition, California Verbal Learning Test (CVLT-II) scores related to working memory, learning, and executive function were more highly correlated with oculomotor variability during target blanking than during target tracking. Our results suggest that a disruption of cerebellar-cortical connections in TBI may account for both oculomotor and cognitive impairment, and that measures of predictive eye movements during target blanking may be a sensitive metric of cognitive deficits after mild TBI.
Minah Suh; Rachel Kolster; Ranjeeta Sarkar; Bruce D. McCandliss; Jamshid Ghajar
Deficits in predictive smooth pursuit after mild traumatic brain injury Journal Article
In: Neuroscience Letters, vol. 401, no. 1-2, pp. 108–113, 2006.
Given that even mild traumatic brain injury (TBI) may produce extensive diffuse axonal injury (DAI), we hypothesized that mild TBI patients would show deficits in predictive smooth pursuit eye movements (SPEM), associated with impaired cognitive functions, as these processes are dependent on common white matter connectivity between multiple cerebral and cerebellar regions. The ability to predict target trajectories during SPEM was investigated in 21 mild TBI patients using a periodic sinusoidal paradigm. Compared to 26 control subjects, TBI patients demonstrated decreased target prediction. TBI patients also showed increased eye position error and variability of eye position, which correlated with decreased target prediction. In all subjects, average target prediction, eye position error and eye position variability correlated with scores related to attention and executive function on the California Verbal Learning Test (CVLT-II). However, there were no differences between TBI and control groups in average eye gain or intra-individual eye gain variability, or in performance on the Wechsler Abbreviated Scale of Intelligence (WASI), suggesting that the observed deficits did not result from general oculomotor impairment or reduced IQ. The correlation between SPEM performance and CVLT-II scores suggests that predictive SPEM may be a sensitive assay of cognitive functioning, including attention and executive function. This is the first report to our knowledge that TBI patients show impaired predictive SPEM and eye position variability, and that these impairments correlate with cognitive deficits.
Benjamin W. Tatler; Roland J. Baddeley; Benjamin T. Vincent
The long and the short of it: Spatial statistics at fixation vary with saccade amplitude and task Journal Article
In: Vision Research, vol. 46, no. 12, pp. 1857–1862, 2006.
We recorded over 90,000 saccades while observers viewed a diverse collection of natural images and measured low level visual features at fixation. The features that discriminated between where observers fixated and where they did not varied considerably with task, and the length of the preceding saccade. Short saccades (<8°) are image feature dependent, long are less so. For free viewing, short saccades target high frequency information, long saccades are scale-invariant. When searching for luminance targets, saccades of all lengths are scale-invariant. We argue that models of saccade behaviour must account not only for task but also for saccade length and that long and short saccades are targeted differently.
P. U. Tse; G. P. Caplovitz; P. -J. Hsieh
Microsaccade directions do not predict directionality of illusory brightness changes of overlapping transparent surfaces Journal Article
In: Vision Research, vol. 46, no. 22, pp. 3823–3830, 2006.
Tse (2005) recently introduced a new class of illusory brightness changes where shifts of attention lead to shifts in perceived brightness across overlapping, transparent figures, under conditions of visual fixation. In the absence of endogenous attentional shifts, illusory brightness changes appear to shift from figure to figure spontaneously, much as occurs in other multistable phenomena. The goal of the present research is to determine whether fixational microsaccades are correlated with perceived brightness changes. It has recently been demonstrated that microsaccades can reveal the direction of covert attentional shifts either toward (Engbert, R. & Kliegl, R. (2003). Microsaccades uncover the orientation of covert attention. Vision Research, 43, 1035-1045; Hafed, Z. M. & Clark, J. J. (2002). Microsaccades as an overt measure of covert attention shifts. Vision Research, 42(22), 2533-2545) or away from (Rolfs, M., Engbert, R., & Kliegl, R. (2004). Microsaccade orientation supports attentional enhancement opposite a peripheral cue: commentary on Tse, Sheinberg, and Logothetis (2003). Psychological Science, 15(10), 705-707) a peripheral cue under certain circumstances. Others (Horwitz, G. D. & Albright, T. D. (2003). Short-latency fixational saccades induced by luminance increments. Journal of Neurophysiology, 90(2), 1333-1339; Tse, P. U., Sheinberg, D. L., & Logothetis, N. K. (2002). Fixational eye movements are not affected by abrupt onsets that capture attention. Vision Research, 42, 1663-1669; Tse, P. U., Sheinberg, D. L., & Logothetis, N. K. (2004). The distribution of microsaccade directions need not reveal the location of attention. Psychological Science, 15(10), 708-710) found no change in the distribution of microsaccade directions as a function of where attention is allocated, although changes in the rate of microsaccades were observed in all of these studies in response to the onset of attentional reallocation. It is therefore possible that the distribution of microsaccade directions will change as a function of which figure is perceived to darken, or that changes in this distribution predict which figure will subsequently darken. We find no correlation between this distribution and which figure undergoes the effect, and therefore conclude that microsaccade directionality is not influenced by and does not influence which figure undergoes the effect. Moreover, the directions of microsaccades that occur immediately prior to a perceptual switch are not correlated with the perceived position of the figure that undergoes the effect. However, we do find that the rate of microsaccades decreases upon a perceptual switch, signifying an attentional shift coincident with the perceptual shift. We conclude that microsaccade directionality does not determine, predict, or cause which figure will subsequently be perceived to undergo an illusory brightness change.
Massimo Turatto; Elena Betta
Redundant visual signals boost saccade execution Journal Article
In: Psychonomic Bulletin & Review, vol. 13, no. 5, pp. 928–932, 2006.
The redundant signal effect (RSE) refers to the fact that human beings react more quickly to a pair of stimuli than to only one stimulus. In previous studies of the RSE in the oculomotor system, bimodal signals have been used as the goal of the saccade. In consistency with studies using manual response times (RTs), saccadic RTs have been shown to be shorter for redundant multimodal stimuli than for single unimodal stimuli. In the present experiments, we extended these findings by demonstrating an RSE in the saccadic system elicited only by unimodal visual stimuli. In addition, we found that shorter saccadic RTs were accompanied by an increased saccadic peak velocity. The present results are of relevance for neurophysiological models of saccade execution, since the boost of saccades was elicited by two visual transients (acting as a "go" signal) that were presented not at the goal of the saccade but at various other locations.
Josef N. Geest; Gerardina C. Lagers-van Haselen; Maarten A. Frens
Saccade adaptation in Williams-Beuren syndrome Journal Article
In: Investigative Ophthalmology & Visual Science, vol. 47, no. 4, pp. 1464–1468, 2006.
PURPOSE: To investigate the capacity for rapid saccade adaptation in Williams-Beuren Syndrome (WBS), a genetic neurodevelopmental disorder, in which it has been observed that saccadic accuracy is severely reduced. METHODS: Saccade amplitude modification was elicited by backward steps (30% of target eccentricity) during the primary saccade in a classic saccade-adaptation paradigm. RESULTS: Patients with WBS showed a significant decrease in saccade amplitude. Furthermore, we observed that higher saccade accuracy before adaptation was related to more adaptation. CONCLUSIONS: The increased variability in motor performance does not abolish the ability for saccadic adaptation in subjects with WBS. Our results are congruent with the notion that part of the behavioral deficits observed in WBS may have a cerebellar origin.
Wieske Zoest; Mieke Donk
Saccadic target selection as a function of time Journal Article
In: Spatial Vision, vol. 19, no. 1, pp. 61–76, 2006.
Recent evidence indicates that stimulus-driven and goal-directed control of visual selection operate independently and in different time windows (van Zoest et al., 2004). The present study further investigates how eye movements are affected by stimulus-driven and goal-directed control. Observers were presented with search displays consisting of one target, multiple non-targets and one distractor element. The task of observers was to make a fast eye movement to a target immediately following the offset of a central fixation point, an event that either co-occurred with or soon followed the presentation of the search display. Distractor saliency and target-distractor similarity were independently manipulated. The results demonstrated that the effect of distractor saliency was transient and only present for the fastest eye movements, whereas the effect of target-distractor similarity was sustained and present in all but the fastest eye movements. The results support an independent timing account of visual selection.
Martin Rolfs; Jochen Laubrock; Reinhold Kliegl
Shortening and prolongation of saccade latencies following microsaccades Journal Article
In: Experimental Brain Research, vol. 169, no. 3, pp. 369–376, 2006.
When the eyes fixate at a point in a visual scene, small saccades rapidly shift the image on the retina. The effect of these microsaccades on the latency of subsequent large-scale saccades may be twofold. First, microsaccades are associated with an enhancement of visual perception. Their occurrence during saccade target perception could, thus, decrease saccade latencies. Second, microsaccades are likely to indicate activity in fixation-related oculomotor neurons. These represent competitors to saccade-related cells in the interplay of gaze holding and shifting. Consequently, an increase in saccade latencies would be expected after microsaccades. Here, we present evidence for both aspects of microsaccadic impact on saccade latency. In a delayed response task, participants made saccades to visible or memorized targets. First, microsaccade occurrence up to 50 ms before target disappearance correlated with 18 ms (or 8%) faster saccades to memorized targets. Second, if microsaccades occurred shortly (i.e., <150 ms) before a saccade was required, mean saccadic reaction time in visual and memory trials was increased by about 40 ms (or 16%). Hence, microsaccades can have opposite consequences for saccade latencies, pointing at a differential role of these fixational eye movements in the preparation of saccade motor programs.
Susana Martinez-Conde; Stephen L. Macknik; Xoana G. Troncoso; Thomas A. Dyar
Microsaccades counteract visual fading during fixation Journal Article
In: Neuron, vol. 49, no. 2, pp. 297–305, 2006.
Our eyes move continually, even while we fixate our gaze on an object. If fixational eye movements are counteracted, our perception of stationary objects fades completely, due to neural adaptation. Some studies have suggested that fixational microsaccades refresh retinal images, thereby preventing adaptation and fading. However, other studies disagree, and so the role of microsaccades remains unclear. Here, we correlate visibility during fixation to the occurrence of microsaccades. We asked subjects to indicate when Troxler fading of a peripheral target occurs, while simultaneously recording their eye movements with high precision. We found that before a fading period, the probability, rate, and magnitude of microsaccades decreased. Before transitions toward visibility, the probability, rate, and magnitude of microsaccades increased. These results reveal a direct link between suppression of microsaccades and fading and suggest a causal relationship between microsaccade production and target visibility during fixation.
Time course of oculomotor inhibition revealed by saccade trajectory modulation Journal Article
In: Journal of Neurophysiology, vol. 96, no. 3, pp. 1420–1424, 2006.
Selecting a stimulus as the target for a goal-directed movement involves inhibiting other competing possible responses. Both target and distractor stimuli activate populations of neurons in topographic oculomotor maps such as the superior colliculus. Local inhibitory interconnections between these populations ensure only one saccade target is selected. Suppress-ing saccades to distractors may additionally involve inhibiting corre-sponding map regions to bias the local competition. Behavioral evidence of these inhibitory processes comes from the effects of distractors on oculomotor and manual trajectories. Individual saccades may initially deviate either toward or away from a distractor, but the source of this variability has not been investigated. Here we investi-gate the relation between distractor-related deviation of trajectory and saccade latency. Targets were presented with, or without, distractors, and the deviation of saccade trajectories arising from the presence of distractors was measured. A fixation gap paradigm was used to manipulate latency independently of the influence of competing dis-tractors. Shorter-latency saccades deviated toward distractors and longer-latency saccades deviated away from distractors. The transition between deviation toward or away from distractors occurred at a saccade latency of around 200 ms. This shows that the time course of the inhibitory process involved in distractor related suppression is relatively slow.
F. Møller; M. L. Laursen; A. K. Sjølie
Fixation topography in normal test persons Journal Article
In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 244, pp. 577–582, 2006.
BACKGROUND: The eye is moved so that the object of interest falls on the central fovea, where the spatial resolution is highest. In the present study we quantified eye movements of normal test persons during steady fixation and characterized the fixation using a 3D fixation plot (X horizontal eye position, Y vertical eye position, Z time in each eye position). METHOD: Fixation eye movements were quantified binocularly in ten normal test persons during a 40-s fixation task using an infrared recording technique. RESULTS: The fixation plot was characterized by a single preferred fixation locus in 17 eyes. One eye had two distinctly separated preferred fixation locations and in two eyes the configuration of fixation plot was flat with no single identifiable locus of fixation. The fixation plots were elliptical along the horizontal meridian in 9 eyes, elliptical along the vertical meridian in 8 eyes, and round in 3 eyes. The fixation area (RAF95) ranged between 1418 and 14182 arcmin(2), and a significant positive correlation was found between RAF95 and the mean microsaccadic amplitude (p<0.001). CONCLUSION: The fixation plots are often characterized by a single preferred fixation locus but may also be almost flat with no identifiable location of fixation. The individual fixations patterns resembles the cone density contour plots as found in histological studies, and it may be speculated, that the shape of the fixation plot is determined by the cone density topography.
F. Møller; M. L. Laursen; A. K. Sjølie
The contribution of microsaccades and drifts in the maintenance of binocular steady fixation Journal Article
In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 244, no. 4, pp. 465–471, 2006.
BACKGROUND: The eye performs three types of eye movements during fixation: fast microsaccades are interrupted by slow drift movements, and tremor is superimposed on the drifts. The contribution of the microsaccades and drifts in maintaining fixation has been discussed since the late 1950s. Initially, microsaccades were thought to correct the misalignment from the optimal fixation locus induced by the drift movements, a theory still postulated in more recent work. The present study aimed to uncover to what extent each fixation movement contributes to maintain steady binocular fixation. METHOD: Binocular fixation during a 40-s fixation task was recorded using an infrared recording technique for ten normal test persons. Start and end point of each microsaccade and drift were superimposed on a fixation map, and the distance to the preferred retinal location of fixation (PRL) was measured. RESULTS: It was found that 32.6% of the microsaccades corrected the previous drift movement towards the PRL, whereas 53.1% of the drifts corrected the endpoint of the previous microsaccade towards the PRL. The overall mean post-microsaccadic and mean post-drift distance to the PRL for the ten normal test persons were 0.46 degrees and 0.41 degrees , respectively; the difference was not statistically significant. Interindividually, the mean post-microsaccadic distance to the PRL ranged between 0.21 degrees and 0.91 degrees and the mean post-drift distance to the PRL ranged between 0.20 degrees and 0.72 degrees . CONCLUSION: Neither the endpoints of the microsaccades nor the drifts bring the visual line to coincide with the centre of the PRL. Consequently, it must be the eye movements performed during the drifts ("slow control") that keep the visual line in the centre of the foveola.
Leigh A. Mrotek; Martha Flanders; John F. Soechting
Oculomotor responses to gradual changes in target direction Journal Article
In: Experimental Brain Research, vol. 172, no. 2, pp. 175–192, 2006.
Smooth pursuit tracking of targets moving linearly (in one dimension) is well characterized by a model where retinal image motion drives eye acceleration. However, previous findings suggest that this model cannot be simply extended to two-dimensional (2D) tracking. To examine 2D pursuit, in the present study, human subjects tracked a target that moved linearly and then followed the arc of a circle. The subjects' gaze angular velocity accurately matched target angular velocity, but the direction of smooth pursuit always lagged behind the current target direction. Pursuit speed slowly declined after the onset of the curve (for about 500 ms), even though the target speed was constant. In a second experiment, brief perturbations were presented immediately prior to the beginning of the change in direction. The subjects' responses to these perturbations consisted of two components: (1) a response specific to the parameters of the perturbation and (2) a nonspecific response that always consisted of a transient decrease in gaze velocity. With the exception of this nonspecific response, pursuit behavior in response to the gradual changes in direction and to the perturbations could be explained by using retinal slip (image velocity) as the input signal. The retinal slip was parallel and perpendicular to the instantaneous direction of pursuit ultimately resulted in changes in gaze velocity (via gaze acceleration). Perhaps due to the subjects' expectations that the target will curve, the sensitivity to the image motion in the direction of pursuit was not as strong as the sensitivity to image motion perpendicular to gaze velocity.
Lauri Nummenmaa; Jari K. Hietanen
Gaze distractors influence saccadic curvature: Evidence for the role of the oculomotor system in gaze-cued orienting Journal Article
In: Vision Research, vol. 46, no. 21, pp. 3674–3680, 2006.
We examined the role of the oculomotor system in gaze-triggered orienting of attention by measuring whether perceiving of task-irrelevant gaze distractors and peripheral spatial distractors influence saccadic curvature similarly. Participants performed reflexive, vertical saccades to designated target areas while their eye movements were recorded. Schematic faces with averted gaze or peripheral boxes were presented before or simultaneously (-100 ms/0 ms SOAs) with the imperative signal. Gaze distractors caused the saccades to curve away from the distractor direction at both SOAs and peripheral distractors only at the 0-ms SOA. The results imply that gaze-cued shifts of visual attention involve both cortical attention orienting systems and subcortical oculomotor systems.
Robin Walker; Eugene McSorley
The parallel programming of voluntary and reflexive saccades Journal Article
In: Vision Research, vol. 46, no. 13, pp. 2082–2093, 2006.
A novel two-step paradigm was used to investigate the parallel programming of consecutive, stimulus-elicited ('reflexive') and endogenous ('voluntary') saccades. The mean latency of voluntary saccades, made following the first reflexive saccades in two-step conditions, was significantly reduced compared to that of voluntary saccades made in the single-step control trials. The latency of the first reflexive saccades was modulated by the requirement to make a second saccade: first saccade latency increased when a second voluntary saccade was required in the opposite direction to the first saccade, and decreased when a second saccade was required in the same direction as the first reflexive saccade. A second experiment confirmed the basic effect and also showed that a second reflexive saccade may be programmed in parallel with a first voluntary saccade. The results support the view that voluntary and reflexive saccades can be programmed in parallel on a common motor map.
Robin Walker; Eugene Mcsorley; Patrick Haggard
The control of saccade trajectories : Direction of curvature depends on prior knowledge of target location and saccade latency Journal Article
In: Perception and Psychophysics, vol. 68, no. 1, pp. 129–138, 2006.
Recent reports have shown that saccades can deviate either toward or away from distractors. However, the specific conditions responsible for the change in initial saccade direction are not known. One possibility, examined here, is that the direction of curvature (toward or away from distractors) reflects preparatory tuning of the oculomotor system when the location of the target and distractor are known in advance. This was investigated by examining saccade trajectories under predictable and unpredictable target conditions. In Experiment 1, the targets and the distractors appeared unpredictably, whereas in Experiment 2 an arrow cue presented at fixation indicated the location of the forthcoming target prior to stimulus onset. Saccades were made to targets on the horizontal, vertical, and principal oblique axis, and distractors appeared simultaneously at an adjacent location (a separation of +/- 45 degrees of visual angle). On average, saccade trajectories curved toward distractors when target locations were unpredictable and curved away from distractors when target locations were known in advance. There was no overall difference in mean saccade latencies between the two experiments. The magnitude of the distractor modulation of saccade trajectory (either toward or away from) was comparable across the different saccade directions (horizontal, vertical, and oblique). These results are interpreted in terms of the time course of competitive interactions operating in the neural structures involved in the suppression of distractors and the selection of a saccade target. A relatively slow mechanism that inhibits movements to distractors produces curvature away from the distractor. This mechanism has more time to operate when target location is predictable, increasing the likelihood that the saccade trajectory will deviate away from the distractor.
The temporal and spatial limits of compensation for fixational eye movements Journal Article
In: Vision Research, vol. 46, no. 18, pp. 2848–2858, 2006.
High-fidelity eye tracking is combined with a perceptual grouping task to provide insight into the likely mechanisms underlying the compensation of retinal image motion caused by movement of the eyes. The experiments describe the covert detection of minute temporal and spatial offsets incorporated into a test stimulus. Analysis of eye motion on individual trials indicates that the temporal offset sensitivity is actually due to motion of the eye inducing artificial spatial offsets in the briefly presented stimuli. The results have strong implications for two popular models of compensation for fixational eye movements, namely efference copy and image-based models. If an efference copy model is assumed, the results place constraints on the spatial accuracy and source of compensation. If an image-based model is assumed then limitations are placed on the integration time window over which motion estimates are calculated.
Brian J. White; Dirk Kerzel; Karl R. Gegenfurtner
The spatio-temporal tuning of the mechanisms in the control of saccadic eye movements Journal Article
In: Vision Research, vol. 46, no. 22, pp. 3886–3897, 2006.
We compared the spatio-temporal tuning of perception to the mechanisms that drive saccadic eye movements. Detection thresholds were measured for Gabor-targets presented left or right of fixation (4 or 8 deg eccentricity), at one of four spatial frequencies (1, 2, 4 or 8 cpd) oscillating at one of three temporal frequencies (1, 8 or 16 Hz). We then measured saccade latency to each target presented at various multiples of detection threshold. Consistent with previous research, latency decreased as a function of contrast. However, at equal detection performance, we found no systematic difference in saccadic latency and no difference in average oculometric performance (% correct saccade direction) across the different target spatio-temporal frequencies. Furthermore, position error remained fairly constant across all conditions. The results are consistent with the idea that the spatio-temporal signals used for perception are the same as those used by the mechanisms driving saccadic eye movements.
Jonathan B. Jacobs; Louis F. Dell'Osso; Richard W. Hertle; Gregory M. Acland; Jean Bennett
Eye movement recordings as an effectiveness indicator of gene therapy in RPE65-deficient canines: Implications for the ocular motor system Journal Article
In: Investigative Ophthalmology & Visual Science, vol. 47, no. 7, pp. 2865–2875, 2006.
PURPOSE: To perform ocular motility recordings of infantile nystagmus (IN) in RPE65-deficient canines and determine whether they can be used as a motor indicator of restored retinal function to investigate the effects of gene therapy. METHODS: Treated and untreated canines were comfortably suspended in a custom-built sling and encouraged to fixate on distant targets at gaze angles varying between +/-15 degrees horizontally and +/-10 degrees vertically. Ocular motility recordings were made, using two distinct methods-infrared reflection and high-speed video. The resultant recordings from three untreated, four treated, and three pre- and post-treatment dogs were analyzed for using the eXpanded Nystagmus Acuity Function (NAFX), which yields an objective assessment of best potential visual acuity, based on the duration and repeatable accuracy of foveation and centralisation. RESULTS: During fixation, the untreated dogs exhibited large-amplitude, classic IN waveforms, including pendular and jerk in both the horizontal and vertical planes, which prevented them from keeping the targets within the area centralis (the region of highest receptor density, spanning +/-3 degrees horizontally by +/-1.5 degrees vertically, analogous to the fovea). Some untreated dogs also had small-amplitude (0.5-1 degrees), high-frequency (6-9 Hz) oscillations. Under the same conditions, successfully treated canines no longer exhibited clinically detectable IN. Their IN was converted to waveforms with very low amplitudes that yielded higher NAFX values and allowed target images to remain well within the area centralis. Of note, uniocular treatment appeared to damp the IN in both eyes. Behaviorally, the treated dogs were able to successfully navigate through obstacles more easily without inadvertent contact, a task beyond the untreated dogs' ability. CONCLUSIONS: Gene therapy that successfully restored retinal function also reduced the accompanying IN to such a great extent that it was not clinically detectable approximately 90% of the time in many of the dogs. IN improvement, as quantified by the NAFX, is an objective motor indicator of visual improvement due to gene therapy.
Stamatina A. Kabanarou; Michael D. Crossland; Caren Bellmann; Angela Rees; Louise E. Culham; Gary S. Rubin
Gaze changes with binocular versus monocular viewing in age-related macular degeneration Journal Article
In: Ophthalmology, vol. 113, no. 12, pp. 2251–2258, 2006.
Purpose: To determine and explain gaze changes during binocular versus monocular viewing in patients with age-related macular degeneration (AMD). Design: Cross-sectional study. Participants: Twenty-nine patients with bilateral late-stage AMD. Methods: Distance acuity and fundus pathologic features were evaluated. Eye position was recorded while viewing a circular fixation target under monocular and binocular viewing conditions using an infrared eye tracker (SMI Gazetracker, SensoMotoric, Germany; Eyelink Software 2.04). Gaze changes were quantified by calculating the mean x-coordinate and y-coordinate eye position of the center of the bivariate contour ellipse area for a 30-second fixation task under both viewing conditions. Retinal loci used for monocular fixation for each eye were determined using the scanning laser ophthalmoscope (SLO; SLO 101, Rodenstock, Munich, Germany). Main Outcome Measure: Gaze position. Results: Nine patients showed no shift in gaze position from monocular to binocular viewing. Three patients demonstrated a shift in both eyes, and 17 patients demonstrated a shift in only 1 eye. The mean shift was 4.7±5° (standard deviation). The shift in gaze position in the worse eye was predictive of the distance between the 2 monocular preferred retinal loci (PRLs; better and worse eye; r2= 0.59; P<0.0001), whereas there was no association between the shift in gaze position in the better eye and distance (r2= 0.00; P = 0.91). Conclusions: Most AMD patients shift gaze position in 1 or both eyes when viewing binocularly compared with monocularly. These changes suggest that different retinal locations are used for fixation under the 2 viewing conditions. The SLO data showed that these patients are likely to demonstrate monocular PRLs that fall on noncorresponding areas. These results may have implications for the effective development of eccentric viewing and binocular behavior of AMD patients.
Stephen H. Butler; Iain D. Gilchrist; Casimir J. H. Ludwig; Keith Muir; Monika Harvey
Impairments of oculomotor control in a patient with a right temporo-parietal lesion Journal Article
In: Cognitive Neuropsychology, vol. 23, no. 6, pp. 990–999, 2006.
Goal-driven control over saccade target selection requires the inhibition of task-irrelevant, stimulus-driven saccades. A widely held assumption is that frontal structures are of critical importance for this function. Here we report the oculomotor capture behaviour of a patient with a right temporo-parietal lesion, which challenges this view. T.H. was asked to search for a target among distractors and to signal its location with a saccade. A task-irrelevant, additional distractor appeared with or without abrupt onset, and it was either similar or dissimilar in its colour to the target. Compared to controls, T.H. showed an elevated level of capture overall. He also showed spatial extinction, which was partially overridden by an abrupt onset distractor. These results support the view that effective oculomotor control depends on an intact network of frontal and posterior brain regions. We argue that stimulus-driven and goal-driven signals are computed at different stages, but are ultimately combined in a common functional salience map.
Inger Montfoort; Willem P. A. Kelders; Josef N. Geest; Inger B. Schipper; Louw Feenstra; Chris I. De Zeeuw; Maarten A. Frens
Interaction between ocular stabilization reflexes in patients with whiplash injury Journal Article
In: Investigative Ophthalmology & Visual Science, vol. 47, no. 7, pp. 2881–2884, 2006.
PURPOSE: In the past few decades, the automobile has become an increasingly more popular means of transport, which has led to an increasing number of rear-end collisions and consequently has resulted in more patients with whiplash-associated disorders (WADs). Recently, it was found that the gain of one of the ocular stabilization reflexes-the cervico-ocular reflex (COR)-is elevated in patients with whiplash injury. The COR responds to proprioceptive signals from the neck and acts in conjunction with the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) to preserve stable vision on the retina during head motion. Therefore, an investigation was conducted to determine whether the reported elevation of the COR in WADs is accompanied by changes in VOR or OKR. METHODS: Eye movements of 13 patients and 18 age-matched healthy controls were recorded with an infrared eye-tracking device. RESULTS: Analysis confirmed a significant increase in COR gain in whiplash patients. Meanwhile the VOR and OKR gains remained the same. No correlation was found between the gains of the reflexes in individual patients. This is in contrast to earlier observations in elderly subjects and subjects with labyrinthine defects, who showed increases in COR gain and decreases in VOR gain. CONCLUSIONS: Impaired neck motion, altered proprioception of the neck, or disorganization in the process of VOR plasticity could explain the lack of change in VOR gain.
Dirk Neumann; Michael L. Spezio; Joseph Piven; Ralph Adolphs
Looking you in the mouth: Abnormal gaze in autism resulting from impaired top-down modulation of visual attention Journal Article
In: Social Cognitive and Affective Neuroscience, vol. 1, no. 3, pp. 194–202, 2006.
People with autism are impaired in their social behavior, including their eye contact with others, but the processes that underlie this impairment remain elusive. We combined high-resolution eye tracking with computational modeling in a group of 10 high-functioning individuals with autism to address this issue. The group fixated the location of the mouth in facial expressions more than did matched controls, even when the mouth was not shown, even in faces that were inverted and most noticeably at latencies of 200-400 ms. Comparisons with a computational model of visual saliency argue that the abnormal bias for fixating the mouth in autism is not driven by an exaggerated sensitivity to the bottom-up saliency of the features, but rather by an abnormal top-down strategy for allocating visual attention.
Helena Ojanpää; Risto Näsänen; Juha Päällysaho; Ritva Akila; Kiti Müller; Ari Kaukiainen; Markku Sainio
Visual search and eye movements in patients with chronic solvent-induced toxic encephalopathy Journal Article
In: Neurotoxicology, vol. 27, no. 6, pp. 1013–1023, 2006.
Various aspects of visual perception have been found to be impaired in patients with occupational chronic solvent-induced toxic encephalopathy (CSE). The purpose of the study was to characterise the changes in eye movements and visual search performance in CSE patients. We measured eye movements of 13 CSE patients and 22 healthy controls during dynamic visual search task by using a fast video eye tracker. The task was to search for and identify a target letter among numerals presented in a rectangular stimulus matrix (3 × 3-10 × 10 items). Threshold search time, i.e. the duration of stimulus presentation required for identifying the target with a given probability was determined by using a psychophysical staircase method. The visual search times of the CSE patients were clearly longer, and they needed considerably more eye fixations than healthy controls to find the target. Thus, their reduced performance in this task was mainly related to the reduction in the number of items which could be processed during a single eye fixation (perceptual span). This reduction probably reflects a limited capacity of visual attention, since visual acuity, contrast sensitivity, and the oculomotor saccade velocity were found to be normal. The results suggest that motor slowness or low-level visual factors do not explain the poor performance of CSE patients in visual search tasks. The results are also discussed with respect to the effects of education, and compared to the performance in the widely used neuropsychological Trail Making Test, which uses similar stimuli and requires visual search. textcopyright 2006 Elsevier Inc. All rights reserved.
Charlotte Golding; C. Danchaivijitr; Timothy L. Hodgson; Sarah J. Tabrizi; Christopher Kennard
Identification of an oculomotor biomarker of preclinical Huntington disease Journal Article
In: Neurology, vol. 67, no. 3, pp. 485–487, 2006.
The authors examined oculomotor function to identify a biomarker of disease progression in genetically confirmed preclinical and early clinical Huntington disease (HD). Initiation deficits of voluntary-guided, but not reflexive, saccades were characteristic of preclinical HD. Saccadic slowing and delayed reflexive saccades were demonstrated in clinical but not preclinical HD. Saccadic measures provide biomarkers of disease progression in both preclinical and early clinical stages of HD.
Thomas Habekost; Randi Starrfelt
Alexia and quadrant-amblyopia: Reading disability after a minor visual field deficit Journal Article
In: Neuropsychologia, vol. 44, no. 12, pp. 2465–2476, 2006.
Reading difficulties caused by hemianopia are well described. We present a study of alexia in a patient (NT) with a milder visual field deficit. The patient had suffered a cerebral haemorrhage causing damage to the left occipital cortex and underlying white matter. NT's text reading was slow and prone to error, but recognition of single letters was preserved. Single word reading was accurate, but slower than normal. On perimetric testing NT initially showed an upper right quadrantanopia, but by attending covertly to this quadrant he could achieve luminance detection except in a small scotoma above the reading line. A whole report experiment showed that letter perception was severely compromised in the quadrant, consistent with cerebral amblyopia. On follow-up testing one and a half year post stroke, a clear spontaneous recovery had occurred, reflected in improved text reading with close to normal eye movements. Still, subtle reading difficulties and oculo-motor abnormalities remained. Overall, the study shows how amblyopia in one quadrant can lead to a characteristic form of alexia.
Patricia E. G. Bestelmeyer; Benjamin W. Tatler; Louise H. Phillips; Gillian Fraser; Philip J. Benson; David St.Clair
Global visual scanning abnormalities in schizophrenia and bipolar disorder Journal Article
In: Schizophrenia Research, vol. 87, no. 1-3, pp. 212–222, 2006.
Visual scanning of face images is widely reported to be abnormal in schizophrenia. This impaired processing has been proposed to be partly responsible for patients' disturbance in social interactions. The present study was designed to determine whether abnormal scanning is specific to images with social content or extends to other types of stimuli. Individuals with schizophrenia (n = 22), bipolar disorder (n = 19) and healthy controls (n = 37) were asked to view a series of 28 images with or without socially important content (i.e. faces, landscapes, fractals and noise patterns) while their eye movements were recorded video-oculographically. Temporal and spatial characteristics of scan paths were compared for each patient group and picture type. Independent of image content, patients with schizophrenia exhibited fewer fixations, longer fixation duration, longer saccade duration and peak velocity, and smaller saccade amplitude compared with healthy controls. Patients with schizophrenia and bipolar disorder did not differ significantly from one another on any of the temporal variables recorded. Fixation location distributions of participants with schizophrenia differed significantly from that of healthy controls on all picture types and from patients with bipolar disorder on all but face images. Abnormal scanning in schizophrenia and also bipolar disorder was independent of stimulus type and therefore reflects a global visual scanning impairment not specific to faces. Spatial scanning characteristics but not temporal ones may serve as biomarkers in the functional psychoses.
Geoffrey Bird; Caroline Catmur; Giorgia Silani; Chris Frith; Uta Frith
Attention does not modulate neural responses to social stimuli in autism spectrum disorders Journal Article
In: NeuroImage, vol. 31, no. 4, pp. 1614–1624, 2006.
We investigated whether individuals with autism spectrum disorders (ASD) would show attentional modulation for social (face) and non-social (house) stimuli. Sixteen individuals with ASD and 16 matched control participants completed a task in which pairs of face and house stimuli were present on every trial, with one of the pairs randomly assigned to attended locations and the other to unattended locations. Both mass-univariate (SPM) and region of interest analyses suggested that responses to houses were modulated by attention in both groups, but that only the control participants demonstrated attentional modulation of face-selective regions. Thus, the participants with ASD demonstrated a lack of attentional modulation which was particularly evident for the social stimulus. Analyses of effective connectivity indicated that these results were due to a failure of attention to modulate connectivity between extrastriate areas and V1. We discuss how these results may suggest a mechanism to explain the reduced salience of social stimuli in ASD.
Tanya Blekher; S. A. Johnson; James A. R. Marshall; K. White; S. Hui; Marjorie R. Weaver; J. Gray; Robert D. Yee; J. C. Stout; X. Berstian; Joanne Wojcieszek; Tatiana M. Foroud
Saccades in presymptomatic and early stages of Huntington disease Journal Article
In: Neurology, vol. 67, no. 2, pp. 394–399, 2006.
OBJECTIVE:To evaluate quantitative measures of eye movements as possible biomarkers in prediagnostic and early stages of Huntington disease (HD). METHODS:The study sample (n = 215) included individuals both at risk and recently diagnosed with HD. All participants completed a uniform clinical evaluation which included administration of the Unified Huntington's Disease Rating Scale (UHDRS) by a movement disorder neurologist and molecular testing to determine HD gene status. A high resolution, video-based eye tracking system was employed to quantify measures of eye movement (error rates, latencies, SD of latencies, velocities, and accuracies) during a computerized battery of saccadic and steady fixation tasks. RESULTS:Prediagnostic HD gene carriers and individuals with early HD demonstrated three types of significant abnormalities while performing memory guided and anti-saccade tasks: increased error rate, increased saccade latency, and increased variability of saccade latency. The eye movement abnormalities increased with advancing motor signs of HD. CONCLUSIONS:Abnormalities in eye movement measures are a sensitive biomarker in the prediagnostic and early stages of Huntington disease (HD). These measures may be more sensitive to prediagnostic changes in HD than the currently employed neurologic motor assessment.
Christian Bellebaum; Irene Daum; B. Koch; M. Schwarz; Klaus-Peter Hoffmann
The role of the human thalamus in processing corollary discharge Journal Article
In: Brain, vol. 128, no. 5, pp. 1139–1154, 2005.
Corollary discharge signals play an important role in monitoring self-generated movements to guarantee spatial constancy. Recent work in macaques suggests that the thalamus conveys corollary discharge information of upcoming saccades passing from the superior colliculus to the frontal eye field. The present study aimed to investigate the involvement of the thalamus in humans by assessing the effect of thalamic lesions on the processing of corollary discharge information. Thirteen patients with selective thalamic lesions and 13 healthy age-matched control subjects performed a saccadic double-step task in which retino-spatial dissonance was induced, i.e. the retinal vector of the second target and the movement vector of the second saccade were different. Thus, the subjects could not rely on retinal information alone, but had to use corollary discharge information to correctly perform the second saccade. The amplitudes of first and second saccades were significantly smaller in patients than in controls. Five thalamic lesion patients showed unilateral deficits in using corollary discharge information, as revealed by asymmetries compared with the other patients and controls. Three patients with lateral thalamic lesions including the ventrolateral nucleus (VL) were impaired contralaterally to the side of damage and one patient with a lesion in the mediodorsal thalamus (MD) was impaired ipsilaterally to the lesion. The largest asymmetry was found in a patient with a bilateral thalamic lesion. The results provide evidence for a thalamic involvement in the processing of corollary discharge information in humans, with a potential role of both the VL and MD nuclei