Clinical and Oculomotor Eye-Tracking Publications
EyeLink eye tracker clinical and oculomotor research publications up until 2024 (with some early 2025s) are listed below by year. You can search the eye-tracking publications using keywords such as Saccadic Adaptation, Schizophrenia, Nystagmus, etc. You can also search for individual author names, and limit searches by year (choose the year then click the search button). If we missed any EyeLink clinical or oculomotor articles, please email us!
2014 |
Harriet Goschy; A. Isabel Koch; Hermann J. Müller; Michael Zehetleitner Early top-down control over saccadic target selection: Evidence from a systematic salience difference manipulation Journal Article In: Attention, Perception, & Psychophysics, vol. 76, no. 2, pp. 367–382, 2014. @article{Goschy2014,Previous research on the contribution of top-down control to saccadic target selection has suggested that eye movements, especially short-latency saccades, are primarily salience driven. The present study was designed to systematically examine top-down influences as a function of time and relative salience difference between target and distractor. Observers performed a saccadic selection task, requiring them to make an eye movement to an orientation-defined target, while ignoring a color-defined distractor. The salience of the distractor was varied (five levels), permitting the percentage of target and distractor fixations to be analyzed as a function of the salience difference between the target and distractor. This analysis revealed the same pattern of results for both the overall and the short-latency saccades: When the target and distractor were of comparable salience, the vast majority of saccades went directly to the target; even distractors somewhat more salient than the target led to significantly fewer distractor, as compared with target, fixations. To quantify the amount of top-down control applied, we estimated the point of equal selection probability for the target and distractor. Analyses of these estimates revealed that, to be selected with equal probability to the target, a distractor had to have a considerably greater bottom-up salience, as compared with the target. This difference suggests a strong contribution of top-down control to saccadic target selection-even for the earliest saccades. |
Michael J. Gray; Annabelle Blangero; James P. Herman; Josh Wallman; Mark R. Harwood Adaptation of naturally paced saccades Journal Article In: Journal of Neurophysiology, vol. 111, no. 11, pp. 2343–2354, 2014. @article{Gray2014,In the natural environment, humans make saccades almost continuously. In many eye movement experiments, however, observers are required to fixate for unnaturally long periods of time. The resulting long and monotonous experimental sessions can become especially problematic when collecting data in a clinical setting, where time can be scarce and subjects easily fatigued. With this in mind, we tested whether the well-studied motor learning process of saccade adaptation could be induced with a dramatically shortened intertrial interval. Observers made saccades to targets that stepped left or right either ∼250 ms or ∼1,600 ms after the saccade landed. In experiment I, we tested baseline saccade parameters to four different target amplitudes (5°, 10°, 15°, and 20°) in the two timing settings. In experiments II and III, we adapted 10° saccades via 2° intrasaccadic steps either backwards or forwards, respectively. Seven subjects performed eight separate adaptation sessions (2 intertrial timings × 2 adaptation direction × 2 session trial lengths). Adaptation proceeded remarkably similarly in both timing conditions across the multiple sessions. In the faster-paced sessions, robust adaptation was achieved in under 2 min, demonstrating the efficacy of our approach to streamlining saccade adaptation experiments. Although saccade amplitudes were similar between conditions, the faster-paced condition unexpectedly resulted in significantly higher peak velocities in all subjects. This surprising finding demonstrates that the stereotyped "main sequence" relationship between saccade amplitude and peak velocity is not as fixed as originally thought. |
Xiao-Jing Gu; Ming Hu; Bing Li; Xin-Tian Hu The role of contrast adaptation in saccadic suppression in humans Journal Article In: PLoS ONE, vol. 9, no. 1, pp. e86542, 2014. @article{Gu2014,The idea of retinal and ex-retinal sources of saccadic suppression has long been established in previous studies. However, how they are implemented in local circuit remains unknown. Researchers have suggested that saccadic suppression was probably achieved by contrast gain control, but this possibility has never been directly tested. In this study, we manipulated contrast gain control by contrast-adapting observers with sinusoidal gratings of different contrasts. Presaccadic and fixational contrast thresholds were measured and compared to give estimates of saccadic suppression at different adaptation states. Our results reconfirmed the selective saccadic suppression in achromatic condition, and further showed that, achromatic saccadic suppression diminished as contrast adaptation was accentuated, whereas no significant chromatic saccadic suppression was induced by greater contrast adaptation. Our data provided evidence for the involvement of contrast gain control in saccadic suppression in achromatic channel. We also discussed how the negative correlation between contrast adaptation and saccadic suppression could be interpreted with contrast gain control. |
James J. Harrison; Tom C. A. Freeman; Petroc Sumner In: Journal of Experimental Psychology: General, vol. 143, no. 5, pp. 1923–1938, 2014. @article{Harrison2014,As a potential exemplar for understanding how volitional actions emerged from reflexes, we studied the relationship between an ancient reflexive gaze stabilization mechanism (optokinetic nystagmus [OKN]) and purposeful eye movements (saccades) that target an object. Traditionally, these have been considered distinct (except in the kinematics of their execution) and have been studied independently. We find that the fast-phases of OKN clearly show properties associated with saccade planning: (a) They are characteristically delayed by irrelevant distractors in an indistinguishable way to saccades (the saccadic inhibition effect), and (b) horizontal OKN fast-phases produce curvature in vertical targeting saccades, just like a competing saccade plan. Thus, we argue that the saccade planning network plays a role in the production of OKN fast-phases, and we question the need for a strict distinction between eye movements that appear to be automatic or volitional. We discuss whether our understanding might benefit from shifting perspective and considering the entire "saccade" system to have developed from an increasingly sophisticated OKN system. |
William J. Harrison; Roger W. Remington; Jason B. Mattingley Visual crowding is anisotropic along the horizontal meridian during smooth pursuit Journal Article In: Journal of Vision, vol. 14, no. 1, pp. 1–16, 2014. @article{Harrison2014b,Humans make smooth pursuit eye movements to foveate moving objects of interest. It is known that smooth pursuit alters visual processing, but there is currently no consensus on whether changes in vision are contingent on the direction the eyes are moving. We recently showed that visual crowding can be used as a sensitive measure of changes in visual processing, resulting from involvement of the saccadic eye movement system. The present paper extends these results by examining the effect of smooth pursuit eye movements on the spatial extent of visual crowding-the area over which visual stimuli are integrated. We found systematic changes in crowding that depended on the direction of pursuit and the distance of stimuli from the pursuit target. Relative to when no eye movement was made, the spatial extent of crowding increased for objects located contraversive to the direction of pursuit at an eccentricity of approximately 3°. By contrast, crowding for objects located ipsiversive to the direction of pursuit remained unchanged. There was no change in crowding during smooth pursuit for objects located approximately 7° from the fovea. The increased size of the crowding zone for the contraversive direction may be related to the distance that the fovea lags behind the pursuit target during smooth eye movements. Overall, our results reveal that visual perception is altered dynamically according to the intended destination of oculomotor commands. |
Jessica Heeman; Jan Theeuwes; Stefan Van der Stigchel The time course of top-down control on saccade averaging Journal Article In: Vision Research, vol. 100, pp. 29–37, 2014. @article{Heeman2014,When objects in a visual scene are positioned in close proximity, eye movements to these objects tend to land at an intermediate location between the objects (i.e. the global effect). This effect is most pronounced for short latency saccades and is therefore believed to be reflexive and dominantly controlled by bottom-up information. At longer latencies this effect can be modulated by top-down factors. The current study established the time course at which top-down information starts to have an influence on bottom-up averaging. In a standard global effect task two peripheral stimuli (a red and a green abrupt onset) were positioned within an angular distance of 20°. In the condition in which observers received no specific target instruction, the eyes landed in between the red and green element establishing the classic global effect. However, when observers were instructed to make a saccade to the red element during a whole block or when the target color varied from trial-to-trial (red or green), a clear effect of the target instruction on the accuracy of the landing position of the primary saccade was found. With increasing saccade latencies, the eyes landed closer to the instructed target. Crucially, however, this effect was even seen for the shortest saccade latencies (as early as 200ms), suggesting that saccade averaging is affected early on by top-down processes. |
Thérèse Collins Trade-off between spatiotopy and saccadic plasticity Journal Article In: Journal of Vision, vol. 4, no. 12, pp. 1–14, 2014. @article{Collins2014,Saccadic eye movements bring objects of interest onto the high-resolution fovea. They also change the retinal location of objects, but our impression of the visual world is stable: We represent our visual world in spatiotopic coordinates. Visual stability could be the result of a null hypothesis that things do not move during a saccade, or of realigning retinal images based on an internal copy of the eye movement (remapping). The current studies disentangled these hypotheses. Subjects saccaded to peripheral targets that were displaced by different amounts during execution, and detected or discriminated displacement direction. Evidence for a null hypothesis was provided by the relatively poor perceptual performance, and evidence for remapping by the independence of performance from saccade endpoint. There was a trade-off between spatiotopic performance and saccadic plasticity: Good performance (perception of displacements) led to small compensative modifications in saccade amplitude on the next trial while poor performance led to larger modifications. Results also showed that variations in saccade amplitude also depended on the size of the retinal error and of the saccade itself. These results suggest that when faced with a discrepancy between the saccade endpoint and visual target, the visual system attributes the discrepancy to object displacement or to saccade error, in which case the subsequent saccade is corrected. This result reconciles the two hypotheses by suggesting that accurate remapping serves oculomotor accuracy but not visual stability. Internal copies of eye movements may thus be used separately to establish spatiotopic representations and to maintain oculomotor accuracy. |
Francisco M. Costela; Jorge Otero-Millan; Michael B. McCamy; Stephen L. Macknik; Xoana G. Troncoso; Ali Najafian Jazi; Sharon M. Crook; Susana Martinez-Conde Fixational eye movement correction of blink-induced gaze position errors Journal Article In: PLoS ONE, vol. 9, no. 10, pp. e110889, 2014. @article{Costela2014,Our eyes move continuously. Even when we attempt to fix our gaze, we produce "fixational" eye movements including microsaccades, drift and tremor. The potential role of microsaccades versus drifts in the control of eye position has been debated for decades and remains in question today. Here we set out to determine the corrective functions of microsaccades and drifts on gaze-position errors due to blinks in non-human primates (Macaca mulatta) and humans. Our results show that blinks contribute to the instability of gaze during fixation, and that microsaccades, but not drifts, correct fixation errors introduced by blinks. These findings provide new insights about eye position control during fixation, and indicate a more general role of microsaccades in fixation correction than thought previously. |
Sébastien M. Crouzet; Morten Overgaard; Niko A. Busch The fastest saccadic responses escape visual masking Journal Article In: PLoS ONE, vol. 9, no. 2, pp. e87418, 2014. @article{Crouzet2014,Object-substitution masking (OSM) occurs when a briefly presented target in a search array is surrounded by small dots that remain visible after the target disappears. The reduction of target visibility occurring after OSM has been suggested to result from a specific interference with reentrant visual processing while the initial feedforward processing is thought to be left intact. We tested a prediction derived from this hypothesis: the fastest responses, being triggered before the beginning of reentrant processing, should escape the OSM interference. In a saccadic choice reaction time task, which gives access to very early stages of visual processing, target visibility was reduced either by OSM, conventional backward masking, or low stimulus contrast. A general reduction of performance was observed in all three conditions. However, the fastest saccades did not show any sign of interference under either OSM or backward masking, as they did under the low-contrast condition. This finding supports the hypothesis that masking interferes mostly with reentrant processing at later stages, while leaving early feedforward processing largely intact. |
2013 |
Julie Brisson; Marc Mainville; Dominique Mailloux; Christelle Beaulieu; Josette Serres; Sylvain Sirois Pupil diameter measurement errors as a function of gaze direction in corneal reflection eyetrackers Journal Article In: Behavior Research Methods, vol. 45, no. 4, pp. 1322–1331, 2013. @article{Brisson2013,Pupil dilation is a useful, noninvasive technique for measuring the change in cognitive load. Since it is implicit and nonverbal, it is particularly useful with preverbal or nonverbal participants. In cognitive psychology, pupil dilation is most often measured by corneal reflection eye-tracking devices. The present study investigates the effect of gaze position on pupil size estimation by three common eye-tracking systems. The task consisted of a simple object pursuit situation, as a sphere rotated around the display screen. Systematic errors of pupil size estimation were found with all three systems. Implications for task-elicited pupillometry, especially for gaze-contingent studies such as object tracking or reading, are discussed. |
Janet H. Bultitude; Stefan Van der Stigchel; Tanja C. W. Nijboer Prism adaptation alters spatial remapping in healthy individuals: Evidence from double-step saccades Journal Article In: Cortex, vol. 49, no. 3, pp. 759–770, 2013. @article{Bultitude2013,The visual system is able to represent and integrate large amounts of information as we move our gaze across a scene. This process, called spatial remapping, enables the construction of a stable representation of our visual environment despite constantly changing retinal images. Converging evidence implicates the parietal lobes in this process, with the right hemisphere having a dominant role. Indeed, lesions to the right parietal lobe (e.g., leading to hemispatial neglect) frequently result in deficits in spatial remapping. Research has demonstrated that recalibrating visual, proprioceptive and motor reference frames using prism adaptation ameliorates neglect symptoms and induces neglect-like performance in healthy people - one example of the capacity for rapid neural plasticity in response to new sensory demands. Because of the influence of prism adaptation on parietal functions, the present research investigates whether prism adaptation alters spatial remapping in healthy individuals. To this end twenty-eight undergraduates completed blocks of a double-step saccade (DSS) task after sham adaptation and adaptation to leftward- or rightward-shifting prisms. The results were consistent with an impairment in spatial remapping for left visual field targets following adaptation to leftward-shifting prisms. These results suggest that temporarily realigning spatial representations using sensory-motor adaptation alters right-hemisphere remapping processes in healthy individuals. The implications for the possible mechanisms of the amelioration of hemispatial neglect after prism adaptation are discussed. |
Chih-Yang Chen; Ziad M. Hafed Postmicrosaccadic enhancement of slow eye movements Journal Article In: Journal of Neuroscience, vol. 33, no. 12, pp. 5375–5386, 2013. @article{Chen2013,Active sensation poses unique challenges to sensory systems because moving the sensor necessarily alters the input sensory stream. Sensory input quality is additionally compromised if the sensor moves rapidly, as during rapid eye movements, making the period immediately after the movement critical for recovering reliable sensation. Here, we studied this immediate postmovement interval for the case of microsaccades during fixation, which rapidly jitter the "sensor" exactly when it is being voluntarily stabilized to maintain clear vision. We characterized retinal-image slip in monkeys immediately after microsaccades by analyzing postmovement ocular drifts. We observed enhanced ocular drifts by up to ~28% relative to premicrosaccade levels, and for up to ~50 ms after movement end. Moreover, we used a technique to trigger full-field image motion contingent on real-time microsaccade detection, and we used the initial ocular following response to this motion as a proxy for changes in early visual motion processing caused by microsaccades. When the full-field image motion started during microsaccades, ocular following was strongly suppressed, consistent with detrimental retinal effects of the movements. However, when the motion started after microsaccades, there was up to ~73% increase in ocular following speed, suggesting an enhanced motion sensitivity. These results suggest that the interface between even the smallest possible saccades and "fixation" includes a period of faster than usual image slip, as well as an enhanced responsiveness to image motion, and that both of these phenomena need to be considered when interpreting the pervasive neural and perceptual modulations frequently observed around the time of microsaccades. |
Wei-Ying Chen; Piers D. Howe; Alex O. Holcombe Resource demands of object tracking and differential allocation of the resource Journal Article In: Attention, Perception, & Psychophysics, vol. 75, no. 4, pp. 710–725, 2013. @article{Chen2013a,The attentional processes for tracking moving objects may be largely hemisphere-specific. Indeed, in our first two experiments the maximum object speed (speed limit) for tracking targets in one visual hemifield (left or right) was not significantly affected by a requirement to track additional targets in the other hemifield. When the additional targets instead occupied the same hemifield as the original targets, the speed limit was reduced. At slow target speeds, however, adding a second target to the same hemifield had little effect. At high target speeds, the cost of adding a same-hemifield second target was approximately as large as would occur if observers could only track one of the targets. This shows that performance with a fast-moving target is very sensitive to the amount of resource allocated. In a third experiment, we investigated whether the resources for tracking can be distributed unequally between two targets. The speed limit for a given target was higher if the second target was slow rather than fast, suggesting that more resource was allocated to the faster of the two targets. This finding was statistically significant only for targets presented in the same hemifield, consistent with the theory of independent resources in the two hemifields. Some limited evidence was also found for resource sharing across hemifields, suggesting that attentional tracking resources may not be entirely hemifield-specific. Together, these experiments indicate that the largely hemisphere-specific tracking resource can be differentially allocated to faster targets. |
Francisco M. Costela; Michael B. McCamy; Stephen L. Macknik; Jorge Otero-Millan; Susana Martinez-Conde Microsaccades restore the visibility of minute foveal targets Journal Article In: PeerJ, vol. 1, pp. 1–14, 2013. @article{Costela2013,Stationary targets can fade perceptually during steady visual fixation, a phenomenon known as Troxler fading. Recent research found that microsaccades-small, involuntary saccades produced during attempted fixation-can restore the visibility of faded targets, both in the visual periphery and in the fovea. Because the targets tested previously extended beyond the foveal area, however, the ability of microsaccades to restore the visibility of foveally-contained targets remains unclear. Here, subjects reported the visibility of low-to-moderate contrast targets contained entirely within the fovea during attempted fixation. The targets did not change physically, but their visibility varied intermittently during fixation, in an illusory fashion (i.e., foveal Troxler fading). Microsaccade rates increased significantly before the targets became visible, and decreased significantly before the targets faded, for a variety of target contrasts. These results support previous research linking microsaccade onsets to the visual restoration of peripheral and foveal targets, and extend the former conclusions to minute targets contained entirely within the fovea. Our findings suggest that the involuntary eye movements produced during attempted fixation do not always prevent fading-in either the fovea or the periphery-and that microsaccades can restore perception, when fading does occur. Therefore, microsaccades are relevant to human perception of foveal stimuli. |
Laurent Madelain; James P. Herman; Mark R. Harwood Saccade adaptation goes for the goal Journal Article In: Journal of Vision, vol. 13, no. 4, pp. 1–15, 2013. @article{Madelain2013,The oculomotor system maintains saccade accuracy by adjusting saccades that are consistently inaccurate. Four experiments were performed to determine the relative contribution of background and target postsaccadic displacement. Unlike typical saccade adaptation experiments, we used natural image scenes and masked target and background displacements during the saccade to exclude motion signals from allowing detection of the displacements. We found that the background had no effect on saccade gain while the target drove gain changes. Only when the target was blanked after the saccade did we observe some adaptation in the direction of the background displacement. We conclude that target selection is critical to saccade adaptation, and operates effectively against natural image backgrounds. |
Jun Maruta; Kristin J. Heaton; Elisabeth M. Kryskow; Alexis L. Maule; Jamshid Ghajar Dynamic visuomotor synchronization: Quantification of predictive timing Journal Article In: Behavior Research Methods, vol. 45, no. 1, pp. 289–300, 2013. @article{Maruta2013,When a moving target is tracked visually, spatial and temporal predictions are used to circumvent the neural delay required for the visuomotor processing. In particular, the internally generated predictions must be synchronized with the external stimulus during continuous tracking. We examined the utility of a circular visual-tracking paradigm for assessment of predictive timing, using normal human subjects. Disruptions of gaze-target synchronization were associated with anticipatory saccades that caused the gaze to be temporarily ahead of the target along the circular trajectory. These anticipatory saccades indicated preserved spatial prediction but suggested impaired predictive timing. We quantified gaze-target synchronization with several indices, whose distributions across subjects were such that instances of extremely poor performance were identifiable outside the margin of error determined by test-retest measures. Because predictive timing is an important element of attention functioning, the visual-tracking paradigm and dynamic synchronization indices described here may be useful for attention assessment. |
Michael B. McCamy; Niamh Collins; Jorge Otero-Millan; Mohammed Al-Kalbani; Stephen L. Macknik; Davis Coakley; Xoana G. Troncoso; Gerard Boyle; Vinodh Narayanan; Thomas R. R. Wolf; Susana Martinez-Conde Simultaneous recordings of ocular microtremor and microsaccades with a piezoelectric sensor and a video-oculography system Journal Article In: PeerJ, vol. 1, pp. 1–18, 2013. @article{McCamy2013,Our eyes are in continuous motion. Even when we attempt to fix our gaze, we produce so called "fixational eye movements", which include microsaccades, drift, and ocular microtremor (OMT). Microsaccades, the largest and fastest type of fixational eye movement, shift the retinal image from several dozen to several hundred photoreceptors and have equivalent physical characteristics to saccades, only on a smaller scale (Martinez-Conde, Otero-Millan & Macknik, 2013). OMT occurs simultaneously with drift and is the smallest of the fixational eye movements (∼1 photoreceptor width, >0.5 arcmin), with dominant frequencies ranging from 70 Hz to 103 Hz (Martinez-Conde, Macknik & Hubel, 2004). Due to OMT's small amplitude and high frequency, the most accurate and stringent way to record it is the piezoelectric transduction method. Thus, OMT studies are far rarer than those focusing on microsaccades or drift. Here we conducted simultaneous recordings of OMT and microsaccades with a piezoelectric device and a commercial infrared video tracking system. We set out to determine whether OMT could help to restore perceptually faded targets during attempted fixation, and we also wondered whether the piezoelectric sensor could affect the characteristics of microsaccades. Our results showed that microsaccades, but not OMT, counteracted perceptual fading. We moreover found that the piezoelectric sensor affected microsaccades in a complex way, and that the oculomotor system adjusted to the stress brought on by the sensor by adjusting the magnitudes of microsaccades. |
Michael B. McCamy; Ali Najafian Jazi; Jorge Otero-Millan; Stephen L. Macknik; Susana Martinez-Conde The effects of fixation target size and luminance on microsaccades and square-wave jerks Journal Article In: PeerJ, vol. 1, pp. 1–12, 2013. @article{McCamy2013a,A large amount of classic and contemporary vision studies require subjects to fixate a target. Target fixation serves as a normalizing factor across studies, promoting the field's ability to compare and contrast experiments. Yet, fixation target parameters, including luminance, contrast, size, shape and color, vary across studies, potentially affecting the interpretation of results. Previous research on the effects of fixation target size and luminance on the control of fixation position rendered conflicting results, and no study has examined the effects of fixation target characteristics on square-wave jerks, the most common type of saccadic intrusion. Here we set out to determine the effects of fixation target size and luminance on the characteristics of microsaccades and square-wave jerks, over a large range of stimulus parameters. Human subjects fixated a circular target with varying luminance and size while we recorded their eye movements with an infrared video tracker (EyeLink 1000, SR Research). We detected microsaccades and SWJs automatically with objective algorithms developed previously. Microsaccade rates decreased linearly and microsaccade magnitudes increased linearly with target size. The percent of microsaccades forming part of SWJs decreased, and the time from the end of the initial SWJ saccade to the beginning of the second SWJ saccade (SWJ inter-saccadic interval; ISI) increased with target size. The microsaccadic preference for horizontal direction also decreased moderately with target size . Target luminance did not affect significantly microsaccades or SWJs, however. In the absence of a fixation target, microsaccades became scarcer and larger, while SWJ prevalence decreased and SWJ ISIs increased. Thus, the choice of fixation target can affect experimental outcomes, especially in human factors and in visual and oculomotor studies. These results have implications for previous and future research conducted under fixation conditions, and should encourage forthcoming studies to report the size of fixation targets to aid the interpretation and replication of their results. |
Shah Khalid; Ulrich Ansorge The Simon effect of spatial words in eye movements: Comparison of vertical and horizontal effects and of eye and finger responses Journal Article In: Vision Research, vol. 86, pp. 6–14, 2013. @article{Khalid2013,Spatial stimulus location information impacts on saccades: Pro-saccades (saccades towards a stimulus location) are faster than anti-saccades (saccades away from the stimulus). This is true even when the spatial location is irrelevant for the choice of the correct response (Simon effect). The results are usually ascribed to spatial sensorimotor coupling. However, with finger responses Simon effects can be observed with irrelevant spatial word meaning, too. Here we tested whether a Simon effect of spatial word meaning in saccades could be observed for words with vertical ("above" or "below") and horizontal ("left" or "right") meanings. We asked our participants to make saccades towards one of the two saccade targets depending on the color of the centrally presented spatial word, while ignoring their spatial meaning (Experiment 1 and 2a). Results are compared to a condition in which finger responses instead of saccades were required (Experiment 2b). In addition to response latency we compared the time course of vertical and horizontal effects. We found the Simon effects due to irrelevant spatial meaning of the words in both saccades and finger responses. The time course investigations revealed different patterns for vertical and horizontal effects in saccades, indicating that distinct processes may be involved in the two types of Simon effects. |
Jonas Knöll; M. Concetta Morrone; Frank Bremmer Spatio-temporal topography of saccadic overestimation of time Journal Article In: Vision Research, vol. 83, pp. 56–65, 2013. @article{Knoell2013,Rapid eye movements (saccades) induce visual misperceptions. A number of studies in recent years have investigated the spatio-temporal profiles of effects like saccadic suppression or perisaccadic mislocalization and revealed substantial functional similarities. Saccade induced chronostasis describes the subjective overestimation of stimulus duration when the stimulus onset falls within a saccade. In this study we aimed to functionally characterize saccade induced chronostasis in greater detail. Specifically we tested if chronostasis is influenced by or functionally related to saccadic suppression. In a first set of experiments, we measured the perceived duration of visual stimuli presented at different spatial positions as a function of presentation time relative to the saccade. We further compared perceived duration during saccades for isoluminant and luminant stimuli. Finally, we investigated whether or not saccade induced chronostasis is dependent on the execution of a saccade itself. We show that chronostasis occurs across the visual field with a clear spatio-temporal tuning. Furthermore, we report chronostasis during simulated saccades, indicating that spurious retinal motion induced by the saccade is a prime origin of the phenomenon. |
Oleg V. Komogortsev; Corey D. Holland; Sampath Jayarathna; Alex Karpov 2D linear oculomotor plant mathematical model: Verification and biometric applications Journal Article In: ACM Transactions on Applied Perception, vol. 10, no. 4, pp. 1–18, 2013. @article{Komogortsev2013a,This article assesses the ability of a two-dimensional (2D) linear homeomorphic oculomotor plant mathematical model to simulate normal human saccades on a 2D plane. The proposed model is driven by a simplified pulse-step neuronal control signal and makes use of linear simplifications to account for the unique characteristics of the eye globe and the extraocular muscles responsible for horizontal and vertical eye movement. The linear nature of the model sacrifices some anatomical accuracy for computational speed and analytic tractability, and may be implemented as two one-dimensional models for parallel signal simulation. Practical applications of the model might include improved noise reduction and signal recovery facilities for eye tracking systems, additional metrics from which to determine user effort during usability testing, and enhanced security in biometric identification systems. The results indicate that the model is capable of produce oblique saccades with properties resembling those of normal human saccades and is capable of deriving muscle constants that are viable as biometric indicators. Therefore, we conclude that sacrifice in the anatomical accuracy of the model produces negligible effects on the accuracy of saccadic simulation on a 2D plane and may provide a usable model for applications in computer science, human-computer interaction, and related fields. |
Oleg V. Komogortsev; Alex Karpov Automated classification and scoring of smooth pursuit eye movements in the presence of fixations and saccades Journal Article In: Behavior Research, vol. 45, pp. 203–215, 2013. @article{Komogortsev2013,Ternary eye movement classification, which separates fixations, saccades, and smooth pursuit from the raw eye positional data, is extremely challenging. This article develops new and modifies existing eye-tracking algorithms for the purpose of conducting meaningful ternary classification. To this end, a set of qualitative and quantitative behavior scores is introduced to facilitate the assessment of classification performance and to provide means for automated threshold selection. Experimental evaluation of the proposed methods is conducted using eye movement records obtained from 11 subjects at 1000 Hz in response to a step-ramp stimulus eliciting fixations, saccades, and smooth pursuits. Results indicate that a simple hybrid method that incorporates velocity and dispersion thresholding allows producing robust classification performance. It is concluded that behavior scores are able to aid automated threshold selection for the algorithms capable of successful classification. |
Miyoung Kwon; Anirvan S. Nandy; Bosco S. Tjan Rapid and persistent adaptability of human oculomotor control in response to simulated central vision loss Journal Article In: Current Biology, vol. 23, no. 17, pp. 1663–1669, 2013. @article{Kwon2013,The central region of the human retina, the fovea, provides high-Acuity vision. The oculomotor system continually brings targets of interest into the fovea via ballistic eye movements (saccades). Thus, the fovea serves both as the locus for fixations and as the oculomotor reference for saccades. This highly automated process of foveation is functionally critical to vision and is observed from infancy [1, 2]. How would the oculomotor system adjust to a loss of foveal vision (central scotoma)? Clinical observations of patients with central vision loss [3, 4] suggest a lengthy adjustment period [5], but the nature and dynamics of this adjustment remain unclear. Here, we demonstrate that the oculomotor system can spontaneously and rapidly adopt a peripheral locus for fixation and can rereference saccades to this locus in normally sighted individuals whose central vision is blocked by an artificial scotoma. Once developed, the fixation locus is retained over weeks in the absence of the simulated scotoma. Our data reveal a basic guiding principle of the oculomotor system that prefers control simplicity over optimality. We demonstrate the importance of a visible scotoma on the speed of the adjustment and suggest a possible rehabilitation regimen for patients with central vision loss. |
Saurabh Dhawan; Heiner Deubel; Donatas Jonikaitis Inhibition of saccades elicits attentional suppression Journal Article In: Journal of Vision, vol. 13, no. 6, pp. 1–12, 2013. @article{Dhawan2013,Visuospatial attention has been shown to have a central role in planning and generation of saccades but what role, if any, it plays in inhibition of saccades remains unclear. In this study, we used an oculomotor delayed match- or nonmatch-to-sample task in which a cued location has to be encoded and memorized for one of two very different goals-to plan a saccade to it or to avoid making a saccade to it. We measured the spatial allocation of attention during the delay and found that while marking a location as a future saccade target resulted in an attentional benefit at that location, marking it as forbidden to saccades led to an attentional cost. Additionally, saccade trajectories were found to deviate away more from the "don't look" location than from a saccade-irrelevant distractor confirming greater inhibition of an actively forbidden location in oculomotor programming. Our finding that attention is suppressed at locations forbidden to saccades confirms and complements the claim of a selective and obligatory coupling between saccades and attention-saccades at the memorized location could neither be planned nor suppressed independent of a corresponding effect on attentional performance. |
L. L. Di Stasi; M. Marchitto; A. Antolí; J. J. Cañas Saccadic peak velocity as an alternative index of operator attention: A short review Journal Article In: European Review of Applied Psychology, vol. 63, no. 6, pp. 335–343, 2013. @article{DiStasi2013,Introduction Automation research has identified the need to monitor operator attentional states in real time as a basis for determining the most appropriate type and level of automated assistance for operators doing complex tasks. Objective The development of a methodology that is able to detect on-line operator attentional state variations could represent a good starting point to solve this critical issue. Results We present a short review of the literature on different indices of attentional state and discuss a series of experiments that demonstrates the validity and sensitivity of a specific eye movement index: saccadic peak velocity (PV). PV was able to detect variations in mental state while doing complex and ecological tasks, ranging from air traffic control simulated tasks to driving simulator sessions. Conclusion This research could provide several guidelines for designing adaptive systems (able to allocate tasks between operators and machine in a dynamic way) and early fatigue-and-distraction warning systems to reduce accident risk. © 2013 Elsevier Masson SAS. All rights reserved. |
Leandro Luigi Di Stasi; Michael B. Mccamy; Andrés Catena; Stephen L. Macknik; José J. Cañas; Susana Martinez-Conde Microsaccade and drift dynamics reflect mental fatigue Journal Article In: European Journal of Neuroscience, vol. 38, no. 3, pp. 2389–2398, 2013. @article{DiStasi2013c,Our eyes are always in motion. Even during periods of relative fixation we produce so-called 'fixational eye movements', which include microsaccades, drift and tremor. Mental fatigue can modulate saccade dynamics, but its effects on microsaccades and drift are unknown. Here we asked human subjects to perform a prolonged and demanding visual search task (a simplified air traffic control task), with two difficulty levels, under both free-viewing and fixation conditions. Saccadic and microsaccadic velocity decreased with time-on-task whereas drift velocity increased, suggesting that ocular instability increases with mental fatigue. Task difficulty did not influence eye movements despite affecting reaction times, performance errors and subjective complexity ratings. We propose that variations in eye movement dynamics with time-on-task are consistent with the activation of the brain's sleep centers in correlation with mental fatigue. Covariation of saccadic and microsaccadic parameters moreover supports the hypothesis of a common generator for microsaccades and saccades. We conclude that changes in fixational and saccadic dynamics can indicate mental fatigue due to time-on-task, irrespective of task complexity. These findings suggest that fixational eye movement dynamics have the potential to signal the nervous system's activation state. |
Michael Dorr; Peter J. Bex Peri-saccadic natural vision Journal Article In: Journal of Neuroscience, vol. 33, no. 3, pp. 1211–1217, 2013. @article{Dorr2013,The fundamental role of the visual system is to guide behavior in natural environments. To optimize information transmission, many animals have evolved a non-homogeneous retina and serially sample visual scenes by saccadic eye movements. Such eye movements, however, introduce high-speed retinal motion and decouple external and internal reference frames. Until now, these processes have only been studied with unnatural stimuli, eye movement behavior, and tasks. These experiments confound retinotopic and geotopic coordinate systems and may probe a non-representative functional range. Here we develop a real-time, gaze-contingent display with precise spatiotemporal control over high-definition natural movies. In an active condition, human observers freely watched nature documentaries and indicated the location of periodic narrow-band contrast increments relative to their gaze position. In a passive condition under central fixation, the same retinal input was replayed to each observer by updating the video's screen position. Comparison of visual sensitivity between conditions revealed three mechanisms that the visual system has adapted to compensate for peri-saccadic vision changes. Under natural conditions we show that reduced visual sensitivity during eye movements can be explained simply by the high retinal speed during a saccade without recourse to an extra-retinal mechanism of active suppression; we give evidence for enhanced sensitivity immediately after an eye movement indicative of visual receptive fields remapping in anticipation of forthcoming spatial structure; and we demonstrate that perceptual decisions can be made in world rather than retinal coordinates. |
George T. Gitchel; Paul A. Wetzel; Mark S. Baron Slowed saccades and increased square wave jerks in essential tremor Journal Article In: Tremor and Other Hyperkinetic Movements, vol. 3, 2013. @article{Gitchel2013,BACKGROUND: Eye movements in essential tremor (ET) are poorly described and may present useful information on the underlying pathophysiology of the disorder. METHODS: Sixty patients with ET, including 15 de novo untreated patients, and 60 age-matched controls constitute the study population. A video-based eye tracker was used to assess binocular eye position. Oculomotor function was assessed while subjects followed random horizontally and vertically step-displaced targets. RESULTS: For all reflexive saccades, latencies were increased in ET subjects by a mean of 16.3% (p<0.01). Saccades showed reduced peak velocities with a lengthy, wavering velocity plateau, followed by slowed decelerations. For larger 30°+ saccades, peak velocities were decreased by a mean of 25.2% (p<0.01) and durations increased by 31.8% (p<0.01). The frequency of square wave jerks (SWJs) in patients was more than triple that of controls (p<0.0001). Despite frequent interruptions by SWJs, fixations were otherwise stable and indistinguishable from controls (root mean square [RMS] velocity |
Jon Guez; Adam P. Morris; Bart Krekelberg Intrasaccadic suppression is dominated by reduced detector gain Journal Article In: Journal of Vision, vol. 13, no. 8, pp. 1–11, 2013. @article{Guez2013,Human vision requires fast eye movements (saccades). Each saccade causes a self-induced motion signal, but we are not aware of this potentially jarring visual input. Among the theorized causes of this phenomenon is a decrease in visual sensitivity before (presaccadic suppression) and during (intrasaccadic suppression) saccades. We investigated intrasaccadic suppression using a perceptual template model (PTM) relating visual detection to different signal-processing stages. One stage changes the gain on the detector's input; another increases uncertainty about the stimulus, allowing more noise into the detector; and other stages inject noise into the detector in a stimulus-dependent or -independent manner. By quantifying intrasaccadic suppression of flashed horizontal gratings at varying external noise levels, we obtained threshold-versus-noise (TVN) data, allowing us to fit the PTM. We tested if any of the PTM parameters changed significantly between the fixation and saccade models and could therefore account for intrasaccadic suppression. We found that the dominant contribution to intrasaccadic suppression was a reduction in the gain of the visual detector. We discuss how our study differs from previous ones that have pointed to uncertainty as an underlying cause of intrasaccadic suppression and how the equivalent noise approach provides a framework for comparing the disparate neural correlates of saccadic suppression. |
Ziad M. Hafed Alteration of visual perception prior to microsaccades Journal Article In: Neuron, vol. 77, no. 6, pp. 775–786, 2013. @article{Hafed2013,Gaze fixation is an active process, with the incessant occurrence of tiny eye movements, including microsaccades. While the retinal consequences of microsaccades may be presumed minimal because of their minute size, a significant perceptual consequence of these movements can also stem from active extraretinal mechanisms associated with corollaries of their motor generation. Here I show that prior to microsaccade onset, spatial perception is altered in a very specific manner: foveal stimuli are erroneously perceived as more eccentric, whereas peripheral stimuli are rendered more foveal. The mechanism for this perceptual " compression of space" is consistent with a spatially specific gain modulation of visual representations caused by the upcoming eye movements, as is hypothesized to happen for much larger saccades. I then demonstrate that this perimicrosaccadic perceptual alteration has at least one important functional consequence: it mediates visual-performance alterations similar to ones classically attributed to the cognitive process of covert visual attention |
Peng Han; Daniel R. Saunders; Russell L. Woods; Gang Luo Trajectory prediction of saccadic eye movements using a compressed exponential model Journal Article In: Journal of vision, vol. 13, no. 8, pp. 1–13, 2013. @article{Han2013,Gaze-contingent display paradigms play an important role in vision research. The time delay due to data transmission from eye tracker to monitor may lead to a misalignment during eye movements, and therefore compromise the contingency. We present a method to reduce this misalignment by using a compressed exponential function to model the trajectories of saccadic eye movements. Our algorithm was evaluated using experimental data from 1,212 saccades ranging from 3deg to 30deg, which were collected with an EyeLInk 1000 and a Dual-Purkinje Image (DPI) eye tracker. The model fits eye displacement with a high agreement (R^2 > 0.96). When assuming a 10-millisecond time delay, prediction of 2D saccade trajectories using our model could reduce the misalignment by 30% to 60% with the EyeLink tracker and 20% to 40% with the DPI tracker fo saccades larger than 8%. Because a certain number of samples are required for model fitting, the prediction did not offer improvement for most small saccades and the early stages of large saccades. Evaluation was also performed for a simulated 100-Hz gaze-contingent display using the prerecorded saccade data. With prediction, the percentage of misalignment larger than 2deg dropped from 45% to 20% for EyeLink and 42% to 26% for DPI data. These results suggest that the saccade-prediction algorithm may help create more accurate gaze-contingent displays. |
William J. Harrison; Jason B. Mattingley; Roger W. Remington Eye movement targets are released from visual crowding Journal Article In: Journal of Neuroscience, vol. 33, no. 7, pp. 2927–2933, 2013. @article{Harrison2013,Our ability to recognize objects in peripheral vision is impaired when other objects are nearby (Bouma, 1970). This phenomenon, known as crowding, is often linked to interactions in early visual processing that depend primarily on the retinal position of visual stimuli (Pelli, 2008; Pelli and Tillman, 2008). Here we tested a new account that suggests crowding is influenced by spatial information derived from an extraretinal signal involved in eye movement preparation. We had human observers execute eye movements to crowded targets and measured their ability to identify those targets just before the eyes began to move. Beginning ∼50 ms before a saccade toward a crowded object, we found that not only was there a dramatic reduction in the magnitude of crowding, but the spatial area within which crowding occurred was almost halved. These changes in crowding occurred despite no change in the retinal position of target or flanking stimuli. Contrary to the notion that crowding depends on retinal signals alone, our findings reveal an important role for eye movement signals. Eye movement preparation effectively enhances object discrimination in peripheral vision at the goal of the intended saccade. These presaccadic changes may enable enhanced recognition of visual objects in the periphery during active search of visually cluttered environments. |
John F. Ackermann; Michael S. Landy Choice of saccade endpoint under risk Journal Article In: Journal of Vision, vol. 13, no. 3, pp. 1–20, 2013. @article{Ackermann2013,Eye movements function to bring detailed information onto the high-resolution region of the retina. Previous research has shown that human observers select fixation points that maximize information acquisition and minimize target location uncertainty. In this study, we ask whether human observers choose the saccade endpoint that maximizes gain when there are explicit rewards associated with correctly detecting the target. Observers performed an 8-alternative forced-choice detection task for a contrast-defined target in noise. After a single saccade, observers indicated the target location. Each potential target location had an associated reward that was known to the observer. In some conditions, the reward at one location was higher than at the other locations. We compared human saccade endpoints to those of an ideal observer that maximizes expected gain given the respective human observer's visibility map, i.e., d' for target detection as a function of retinal location. Varying the location of the highest reward had a significant effect on human observers' distribution of saccade endpoints. Both human and ideal observers show a high density of saccades made toward the highest rewarded and actual target locations. But humans' overall spatial distributions of saccade endpoints differed significantly from the ideal observer as they made a greater number of saccade to locations far from the highest rewarded and actual target locations. Suboptimal choice of saccade endpoint, possibly in combination with suboptimal integration of information across saccades, had a significant effect on human observers' ability to correctly detect the target and maximize gain. |
Artem V. Belopolsky; Stefan Van der Stigchel Saccades curve away from previously inhibited locations: Evidence for the role of priming in oculomotor competition Journal Article In: Journal of Neurophysiology, vol. 110, no. 10, pp. 2370–2377, 2013. @article{Belopolsky2013,The oculomotor system serves as the basis for representing concurrently competing motor programs. Here, we examine whether the oculomotor system also keeps track of the outcome of competition between target and distractor on the previous trial. Participants had to perform a simple task of making a saccade toward a predefined direction. On two-thirds of the trials, an irrelevant distractor was presented to either the left or right of the fixation. On one-third of the trials, no distractor was present. The results show that on trials without a distractor, saccades curved away from the empty location that was occupied by a distractor on the previous trial. This result was replicated and extended to cases when different saccade directions were used. In addition, we show that repetition of distractor location on the distractor-present trials results in a stronger curvature away and in a shorter saccade latency to the target. Taken together, these results provide strong evidence that the oculomotor system automatically codes and retains locations that had been ignored in the past to bias future behavior. |
Hans-Joachim Bieg; Jean-Pierre Bresciani; Heinrich H. Bülthoff; Lewis L. Chuang Saccade reaction time asymmetries during task-switching in pursuit tracking Journal Article In: Experimental Brain Research, vol. 230, no. 3, pp. 271–281, 2013. @article{Bieg2013,We investigate how smooth pursuit eye movements affect the latencies of task-switching saccades. Participants had to alternate their foveal vision between a continuous pursuit task in the display center and a discrete object discrimination task in the periphery. The pursuit task was either carried out by following the target with the eyes only (ocular) or by steering an on-screen cursor with a joystick (oculomanual). We measured participants' saccadic reaction times (SRTs) when foveal vision was shifted from the pursuit task to the discrimination task and back to the pursuit task. Our results show asymmetries in SRTs depending on the movement direction of the pursuit target: SRTs were generally shorter in the direction of pursuit. Specifically, SRTs from the pursuit target were shorter when the discrimination object appeared in the motion direction. SRTs to pursuit were shorter when the pursuit target moved away from the current fixation location. This result was independent of the type of smooth pursuit behavior that was performed by participants (ocular/oculomanual). The effects are discussed in regard to asymmetries in attention and processes that suppress saccades at the onset of pursuit. |
A. R. Bogadhi; Anna Montagnini; Guillaume S. Masson Dynamic interaction between retinal and extraretinal signals in motion integration for smooth pursuit Journal Article In: Journal of Vision, vol. 13, no. 13, pp. 1–26, 2013. @article{Bogadhi2013,Due to the aperture problem, the initial direction of tracking responses to a translating bar is biased towards the direction orthogonal to the bar. This observation offers a powerful way to explore the interactions between retinal and extraretinal signals in controlling our actions. We conducted two experiments to probe these interactions by briefly (200 and 400 ms) blanking the moving target (458 or 1358 tilted bar) during steady state (Experiment 1) and at different moments during the early phase of pursuit (Experiment 2). In Experiment 1, we found a marginal but statistically significant directional bias on target reappearance for all subjects in at least one blank condition (200 or 400 ms). In Experiment 2, no systematic significant directional bias was observed at target reappearance after a blank. These results suggest that the weighting of retinal and extraretinal signals is dynamically modulated during the different phases of pursuit. Based on our previous theoretical work on motion integration, we propose a new closed- loop two-stage recurrent Bayesian model where retinal and extraretinal signals are dynamically weighted based on their respective reliabilities and combined to compute the visuomotor drive. With a single free parameter, the model reproduces many aspects of smooth pursuit observed across subjects during and immediately after target blanking. It provides a new theoretical framework to understand how different signals are dynamically combined based on their relative reliability to adaptively control our actions. Overall, the model and behavioral results suggest that human subjects rely more strongly on prediction during theearly phasethaninthe steady state phase of pursuit. |
Sabine Born; Ulrich Ansorge; Dirk Kerzel Predictability of spatial and non-spatial target properties improves perception in the pre-saccadic interval Journal Article In: Vision Research, vol. 91, pp. 93–101, 2013. @article{Born2013,In a dual-task paradigm with a perceptual discrimination task and a concurrent saccade task, we examined participants' ability to make use of prior knowledge of a critical property of the perceptual target to improve discrimination. Previous research suggests that during a short time window before a saccade, covert attention is imperatively directed towards the saccade target location. Consequently, discrimination of perceptual targets at the saccade target location is better than at other locations. We asked whether the obligatory pre-saccadic attention shift prevents perceptual benefits arising for perceptual target stimuli with predictable as opposed to non-predictable properties. We compared conditions in which the color or location of the perceptual target was constant to conditions in which those properties varied randomly across trials. In addition to the expected improvements of perception at the saccade target location, we found perception to be better with constant than with random properties of the perceptual target. Thus, color or location information about an upcoming perceptual target facilitates perception even while spatial attention is shifted to the saccade target. The improvement occurred irrespective of the saccade target location, which suggests that the underlying mechanism is independent of the pre-saccadic attention shift, but alternative interpretations are discussed as well. |
James P. Herman; C. Phillip Cloud; Josh Wallman End-point variability is not noise in saccade adaptation Journal Article In: PLoS ONE, vol. 8, no. 3, pp. e59731, 2013. @article{Herman2013,When each of many saccades is made to overshoot its target, amplitude gradually decreases in a form of motor learning called saccade adaptation. Overshoot is induced experimentally by a secondary, backwards intrasaccadic target step (ISS) triggered by the primary saccade. Surprisingly, however, no study has compared the effectiveness of different sizes of ISS in driving adaptation by systematically varying ISS amplitude across different sessions. Additionally, very few studies have examined the feasibility of adaptation with relatively small ISSs. In order to best understand saccade adaptation at a fundamental level, we addressed these two points in an experiment using a range of small, fixed ISS values (from 0° to 1° after a 10° primary target step). We found that significant adaptation occurred across subjects with an ISS as small as 0.25°. Interestingly, though only adaptation in response to 0.25° ISSs appeared to be complete (the magnitude of change in saccade amplitude was comparable to size of the ISS), further analysis revealed that a comparable proportion of the ISS was compensated for across conditions. Finally, we found that ISS size alone was sufficient to explain the magnitude of adaptation we observed; additional factors did not significantly improve explanatory power. Overall, our findings suggest that current assumptions regarding the computation of saccadic error may need to be revisited. |
Frouke Hermens; Tandra Ghose; Johan Wagemans Advance information modulates the global effect even without instruction on where to look Journal Article In: Experimental Brain Research, vol. 226, no. 4, pp. 639–648, 2013. @article{Hermens2013,When observers are asked to make an eye movement to a visual target in the presence of a near distractor, their eyes tend to land on a position in between the target and the distractor, an effect known as the global effect. While it was initially believed that the global effect is a mandatory eye movement strategy, recent studies have shown that explicit instructions to make an eye movement to a certain part of the scene can overrule the effect. We here investigate whether such top-down influences are also found when people are not actively involved in an explicit eye movement task, but instead, make eye movements in the service of another task. Participants were presented with arrays of yellow and green discs, each containing a letter, and were asked to identify a target letter. Because the discs were presented away from fixation, participants made an eye movement to the array of discs on most of the trials. An analysis of the landing sites of these eye movements revealed that, even without an explicit instruction, observers take the advance information about the colour of the disc containing the target into account before moving their eyes. Moreover, when asking participants to maintain fixation for intervals of different durations, it was found that the implicit top-down influences operated on a very similar time-scale as previously observed for explicit eye movement instructions. |
Halim Hicheur; Steeve Zozor; Aurélie Campagne; Alan Chauvin Microsaccades are modulated by both attentional demands of a visual discrimination task and background noise Journal Article In: Journal of Vision, vol. 13, no. 13, pp. 1–20, 2013. @article{Hicheur2013,Microsaccades are miniature saccades occurring once or twice per second during visual fixation. While microsaccades and saccades share similarities at the oculomotor level, the functional roles of microsaccades are still debated. In this study, we examined the hypothesis that the microsaccadic activity is affected by the type of noisy background during the execution of a particular discrimination task. Human subjects had to judge the orientation of a tilted stimulus embedded in static or dynamic backgrounds in a forced choice-task paradigm, as adapted from Rucci, Iovin, Poletti, and Santini (2007). Static backgrounds induced more microsaccades than dynamic ones only during the execution of the discrimination task. A directional bias of microsaccades, dictated by the stimulus orientation, was temporally coupled with this period of increased activity. Both microsaccade rates and orientations were comparable across background types after the response time although subjects maintained fixation until the end of the trial. This represents a background-specific modulation of the microsaccadic activity driven by attentional demands. The visual influence of microsaccades on discrimination performances was modeled at the retinal level for both types of backgrounds. A higher simulated microsaccadic activity was necessary for static backgrounds in order to achieve discrimination performance scores comparable to that of dynamic ones. Taken together, our experimental and theoretical findings further support the idea that microsaccades are under attentional control and represent an efficient sampling strategy allowing spatial information acquisition. |
Rumi Hisakata; Masahiko Terao; Ikuya Murakami Illusory position shift induced by motion within a moving envelope during smooth-pursuit eye movements Journal Article In: Journal of Vision, vol. 13, no. 12, pp. 1–12, 2013. @article{Hisakata2013,The static envelope of a Gabor patch with a moving carrier appears to shift in the direction of the carrier motion; this phenomenon is known as the motion-induced position shift (De Valois & De Valois, 1991; Ramachandran & Anstis, 1990). This conventional stimulus configuration contains at least three covarying factors: the retinal carrier velocity, the environmental carrier velocity, and the carrier velocity relative to the envelope velocity, which happens to be zero. We manipulated these velocities independently to identify which is critical, and we measured the perceived position of the moving Gabor patch relative to a reference stimulus moving in the same direction at the same speed. In the first experiment, the position of the moving envelope observed with fixation appeared to shift in the direction of the carrier velocity relative to the envelope velocity. Furthermore, the illusion was more pronounced when the carrier moved in a direction opposite to that of the envelope. In the second and third experiments, we measured the illusion during smooth-pursuit eye movement in which the envelope was either static or moving, thereby dissociating retinal and environmental velocities. Under all conditions, the illusion occurred according to the envelope-relative velocity of the carrier. Additionally, the illusion was more pronounced when the carrier and envelope moved in opposite directions. We conclude that the carrier's envelope-relative velocity is the primary determinant of the motion-induced position shift. |
Malou Janssen; Jelmer P. De Vries; Britta K. Ischebeck; Maarten A. Frens; Josef N. Geest Small effects of neck torsion on healthy human voluntary eye movements Journal Article In: European Journal of Applied Physiology, vol. 113, no. 12, pp. 3049–3057, 2013. @article{Janssen2013,PURPOSE: Although several lines of research suggest that the head and eye movement systems interact, previous studies have reported that applying static neck torsion does not affect smooth pursuit eye movements in healthy controls. This might be due to several methodological issues. Here we systematically investigated the effect of static neck torsion on smooth pursuit and saccadic eye movement behavior in healthy subjects. METHODS: In twenty healthy controls, we recorded eye movements with video-oculography while their trunk was in static rotation relative to the head (7 positions from 45° to the left to 45° to right). The subject looked at a moving dot on the screen. In two separate paradigms, we evoked saccadic and smooth pursuit eye movements, using both predictable and unpredictable target motions. RESULTS: Smooth pursuit gain and saccade peak velocity decreased slightly with increasing neck torsion. Smooth pursuit gains were higher for predictable target movements than for unpredictable target movements. Saccades to predictable targets had lower latencies, but reduced gains compared to saccades to unpredictable targets. No interactions between neck torsion and target predictability were observed. CONCLUSION: Applying static neck torsion has small effects on voluntary eye movements in healthy subjects. These effects are not modulated by target predictability. |
Beth P. Johnson; Nicole J. Rinehart; Owen B. White; Lynette Millist; Joanne Fielding Saccade adaptation in autism and Asperger's disorder Journal Article In: Neuroscience, vol. 243, pp. 76–87, 2013. @article{Johnson2013,Autism and Asperger's disorder (AD) are neuro- developmental disorders primarily characterized by deficits in social interaction and communication, however motor coordination deficits are increasingly recognized as a prevalent feature of these conditions. Although it has been proposed that children with autism and AD may have diffi- culty utilizing visual feedback during motor learning tasks, this has not been directly examined. Significantly, changes within the cerebellum, which is implicated in motor learning, are known to be more pronounced in autism compared to AD. We used the classic double-step saccade adaptation paradigm, known to depend on cerebellar integrity, to inves- tigate differences in motor learning and the use of visual feedback in children aged 9–14 years with high-functioning autism (HFA; IQ > 80; n = 10) and AD (n = 13). Performance was compared to age and IQ matched typically developing children (n = 12). Both HFA and AD groups successfully adapted the gain of their saccades in response to perceived visual error, however the time course for adaptation was prolonged in the HFA group. While a shift in saccade dynamics typically occurs during adaptation, we revealed aberrant changes in both HFA and AD groups. This study contributes to a growing body of evidence centrally impli- cating the cerebellum in ocular motor dysfunction in autism. Specifically, these findings collectively imply functional impairment of the cerebellar network and its inflow and outflow tracts that underpin saccade adaptation, with greater disturbance in HFA compared to AD. |
Donatas Jonikaitis; Martin Szinte; Martin Rolfs; Patrick Cavanagh Allocation of attention across saccades Journal Article In: Journal of Neurophysiology, vol. 109, no. 5, pp. 1425–1434, 2013. @article{Jonikaitis2013,Whenever the eyes move, spatial attention must keep track of the locations of targets as they shift on the retina. This study investigated transsaccadic updating of visual attention to cued targets. While observers prepared a saccade, we flashed an irrelevant, but salient, color cue in their visual periphery and measured the allocation of spatial attention before and after the saccade using a tilt discrimination task. We found that just before the saccade, attention was allocated to the cue's future retinal location, its predictively "remapped" location. Attention was sustained at the cue's location in the world across the saccade, despite the change of retinal position whereas it decayed quickly at the retinal location of the cue, after the eye landed. By extinguishing the color cue across the saccade, we further demonstrate that the visual system relies only on predictive allocation of spatial attention, as the presence of the cue after the saccade did not substantially affect attentional allocation. These behavioral results support and extend physiological evidence showing predictive activation of visual neurons when an attended stimulus will fall in their receptive field after a saccade. Our results show that tracking of spatial locations across saccades is a plausible consequence of physiological remapping. |
Donatas Jonikaitis; Jan Theeuwes Dissociating oculomotor contributions to spatial and feature-based selection Journal Article In: Journal of Neurophysiology, vol. 110, no. 7, pp. 1525–1534, 2013. @article{Jonikaitis2013a,Saccades not only deliver the high-resolution retinal image requisite for visual perception, but processing stages associated with saccade target selection affect visual perception even before the eye movement starts. These presaccadic effects are thought to arise from two visual selection mechanisms: spatial selection that enhances processing of the saccade target location and feature-based selection that enhances processing of the saccade target features. By measuring oculomotor performance and perceptual discrimination, we determined which selection mechanisms are associated with saccade preparation. We observed both feature-based and space-based selection during saccade preparation but found that feature-based selection was neither related to saccade initiation nor was it affected by simultaneously observed redistribution of spatial selection. We conclude that oculomotor selection biases visual selection only in a spatial, feature-unspecific manner. |
Sally R. Ke; Jessica Lam; Dinesh K. Pai; Miriam Spering Directional asymmetries in human smooth pursuit eye movements Journal Article In: Investigative Ophthalmology & Visual Science, vol. 54, no. 6, pp. 4409–4421, 2013. @article{Ke2013,PURPOSE: Humans make smooth pursuit eye movements to bring the image of a moving object onto the fovea. Although pursuit accuracy is critical to prevent motion blur, the eye often falls behind the target. Previous studies suggest that pursuit accuracy differs between motion directions. Here, we systematically assess asymmetries in smooth pursuit. METHODS: In experiment 1, binocular eye movements were recorded while observers (n = 20) tracked a small spot of light moving along one of four cardinal or diagonal axes across a featureless background. We analyzed pursuit latency, acceleration, peak velocity, gain, and catch-up saccade latency, number, and amplitude. In experiment 2 (n = 22), we examined the effects of spatial location and constrained stimulus motion within the upper or lower visual field. RESULTS: Pursuit was significantly faster (higher acceleration, peak velocity, and gain) and smoother (fewer and later catch-up saccades) in response to downward versus upward motion in both the upper and the lower visual fields. Pursuit was also more accurate and smoother in response to horizontal versus vertical motion. CONCLUSIONS. Our study is the first to report a consistent up-down asymmetry in human adults, regardless of visual field. Our findings suggest that pursuit asymmetries are adaptive responses to the requirements of the visual context: preferred motion directions (horizontal and downward) are more critical to our survival than nonpreferred ones. |
Manon W. Jones; Jane Ashby; Holly P. Branigan Dyslexia and fluency: Parafoveal and foveal influences on rapid automatized naming Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 39, no. 2, pp. 554–567, 2013. @article{Jones2013,The ability to coordinate serial processing of multiple items is crucial for fluent reading but is known to be impaired in dyslexia. To investigate this impairment, we manipulated the orthographic and phonological similarity of adjacent letters online as dyslexic and nondyslexic readers named letters in a serial naming (RAN) task. Eye movements and voice onsets were recorded. Letter arrays contained target item pairs in which the second letter was orthographically or phonologically similar to the first letter when viewed either parafoveally (Experiment 1a) or foveally (Experiment 1b). Relative to normal readers, dyslexic readers were more affected by orthographic confusability in Experiment 1a and phonological confusability in Experiment 1b. Normal readers were slower to process orthographically similar letters in Experiment 1b. Findings indicate that the phonological and orthographic processing problems of dyslexic readers manifest differently during parafoveal and foveal processing, with each contributing to slower RAN performance and impaired reading fluency. |
Evgenia Kanonidou; Irene Gottlob; Frank A. Proudlock The effect of font size on reading performance in strabismic amblyopia: An eye movement investigation Journal Article In: Investigative Ophthalmology & Visual Science, vol. 55, no. 1, pp. 451–459, 2013. @article{Kanonidou2013,PURPOSE: We investigated the effect of font size on reading speed and ocular motor performance in strabismic amblyopes during text reading under monocular and binocular viewing conditions. METHODS: Eye movements were recorded at 250 Hz using a head-mounted infrared video eye tracker in 15 strabismic amblyopes and 18 age-matched controls while silently reading paragraphs of text at font sizes equivalent to 1.0 to 0.2 logMAR acuity. Reading under monocular viewing with amblyopic eye/nondominant eye and nonamblyopic/dominant eye was compared to binocular viewing. Mean reading speed; number, amplitude, and direction of saccades; and fixation duration were calculated for each font size and viewing condition. RESULTS: Reading speed was significantly slower in amblyopes compared to controls for all font sizes during monocular reading with the amblyopic eye (P = 0.004), but only for smaller font sizes for reading with the nonamblyopic eye (P = 0.045) and binocularly (P = 0.038). The most significant ocular motor change was that strabismic amblyopes made more saccades per line than controls irrespective of font size and viewing conditions (P < 0.05 for all). There was no significant difference in saccadic amplitudes and fixation duration was only significantly longer in strabismic amblyopes when reading smaller fonts with the amblyopic eye viewing. CONCLUSIONS: Ocular motor deficits exist in strabismic amblyopes during reading even when reading speeds are normal and when visual acuity is not a limiting factor; that is, when reading larger font sizes with nonamblyopic eye viewing and binocular viewing. This suggests that these abnormalities are not related to crowding. |
Pilyoung Kim; Joseph Arizpe; Brooke H. Rosen; Varun Razdan; Catherine T. Haring; Sarah E. Jenkins; Christen M. Deveney; Melissa A. Brotman; R. James R. Blair; Daniel S. Pine; Chris I. Baker; Ellen Leibenluft Impaired fixation to eyes during facial emotion labelling in children with bipolar disorder or severe mood dysregulation Journal Article In: Journal of Psychiatry and Neuroscience, vol. 38, no. 6, pp. 407–416, 2013. @article{Kim2013a,Background: Children with bipolar disorder (BD) or severe mood dysregulation (SMD) show behavioural and neural deficits during facial emotion processing. In those with other psychiatric disorders, such deficits have been associated with reduced attention to eye regions while looking at faces. Methods: We examined gaze fixation patterns during a facial emotion labelling task among children with pediatric BD and SMD and among healthy controls. Participants viewed facial expressions with varying emotions (anger, fear, sadness, happi- ness, neutral) and emotional levels (60%, 80%, 100%) and labelled emotional expressions. Results: Our study included 22 children with BD, 28 with SMD and 22 controls. Across all facial emotions, children with BD and SMD made more labelling errors than controls. Compared with controls, children with BD spent less time looking at eyes and made fewer eye fixations across emotional expressions. Gaze patterns in children with SMD tended to fall between those of children with BD and controls, although they did not differ significantly from either of these groups on most measures. Decreased fixations to eyes correlated with lower labelling accuracy in children with BD, but not in those with SMD or in controls. Limitations: Most children with BD were medicated, which precluded our ability to evaluate med- ication effects on gaze patterns. Conclusion: Facial emotion labelling deficits in children with BD are associated with impaired attention to eyes. Future research should examine whether impaired attention to eyes is associated with neural dysfunction. Eye gaze deficits in children with BD during facial emotion labelling may also have treatment implications. Finally, children with SMD exhibited decreased attention to eyes to a lesser extent than those with BD, and these equivocal findings are worthy of further study. |
Lisa Kloft; Benedikt Reuter; Anja Riesel; Norbert Kathmann Impaired volitional saccade control: First evidence for a new candidate endophenotype in obsessive-compulsive disorder Journal Article In: European Archives of Psychiatry and Clinical Neuroscience, vol. 263, pp. 215–222, 2013. @article{Kloft2013,Recent research suggests that patients with obsessive-compulsive disorder (OCD) have deficits in the volitional control of saccades. Specific evidence comes from increased latencies of saccadic eye movements when they were volitionally executed but not when they were visually guided. The present study sought to test whether this deviance represents a cognitive endophenotype. To this end, first-degree relatives of OCD patients as genetic risk carriers were compared with OCD patients and healthy controls without a family history of OCD. Furthermore, as volitional response generation comprises selection and initiation of the required response, the study also sought to specify the cognitive mechanisms underlying impaired volitional response generation. Twenty-two unaffected first-degree relatives of OCD patients, 22 unmedicated OCD patients, and 22 healthy comparison subjects performed two types of volitional saccade tasks measuring response selection or only response initiation, respectively. Visually guided saccades were used as a control condition. Our results showed that unaffected first-degree relatives and OCD patients were significantly slowed compared to healthy comparison subjects in volitional response selection. Patients and relatives did not differ from each other. There was no group difference in the visually guided control condition. Taken together, the study provides first evidence that dysfunctional volitional response selection is a candidate endophenotype for OCD. |
Fiona C. Glen; Nicholas D. Smith; David P. Crabb Saccadic eye movements and face recognition performance in patients with central glaucomatous visual field defects Journal Article In: Vision Research, vol. 82, pp. 42–51, 2013. @article{Glen2013,Patients with more advanced glaucoma are likely to experience problems with everyday visual tasks such as face recognition. However, some patients still perform well at face recognition despite their visual field (VF) defects. This study investigated whether certain eye movement patterns are associated with better performance in the Cambridge Face Memory Test. For patients with bilateral VF defects in their central 10° of VF, making larger saccades appeared to be associated with better face recognition performance (rho = 0.60 |
Esther G. González; Linda Lillakas; Alexander Lam; Brenda L. Gallie; Martin J. Steinbach Horizontal saccade dynamics after childhood monocular enucleation Journal Article In: Investigative Ophthalmology & Visual Science, vol. 54, no. 10, pp. 6463–6471, 2013. @article{Gonzalez2013,PURPOSE: We investigated the effects of monocularity on oculomotor control by examining the characteristics of the horizontal saccades of people with one eye, and comparing them to those of a group of age-matched controls who viewed the stimuli monocularly and binocularly. METHODS: Participants were tested in a no-gap, no-overlap saccadic task using a video-based remote eye tracker. One group consisted of unilaterally eye enucleated participants (N = 15; mean age, 31.27 years), the other of age-matched people with normal binocular vision (N = 18; mean age, 30.17 years). RESULTS: The horizontal saccade dynamics of enucleated people are similar to those of people with normal binocularity when they view monocularly and, with the exception of latency, when they view binocularly. The data show that the monocular saccades of control and enucleated observers have longer latencies than the binocular saccades of the control group, the saccades of the enucleated observers are as accurate as those of the controls viewing monocularly or binocularly, smaller saccades are more accurate than the larger ones, and abducting saccades are faster than adducting saccades. CONCLUSIONS: Our data suggest that the true monocularity produced by early enucleation does not result in slower visual processing in the afferent (sensory) pathway, or in deficits in the efferent (motor) pathways of the saccadic system. Possible mechanisms to account for the effects of monocular vision on saccades are discussed. |
Martin Gorges; Hans Peter Müller; Dorothée Lulé; Albert C. Ludolph; Elmar H. Pinkhardt; Jan Kassubek In: Brain Connectivity, vol. 3, no. 3, pp. 265–272, 2013. @article{Gorges2013a,In addition to the skeleto-motor deficits, patients with Parkinson's disease (PD) frequently present with oculomotor dysfunctions such as impaired smooth pursuit and saccadic abnormalities. There is increasing evidence for an impaired cortical function to be responsible for oculomotor deficits that are associated with lack of inhibitory control; however, these pathomechanisms still remain poorly understood. By means of "task-free" resting-state functional magnetic resonance imaging (rs-fMRI), functional connectivity changes in PD within the default mode network (DMN) have been reported. The aim of this study was to investigate whether altered functional connectivity within the DMN was correlated with oculomotor parameter changes in PD. Twelve PD patients and 13 matched healthy controls underwent rs-fMRI at 1.5 T and videooculography (VOG) using Eye-Link-System. Rs-fMRI seed-based region-to-region connectivity analysis was performed, including medial prefrontal cortex (mPFC), medial temporal lobe (MTL), posterior cingulate cortex (PCC), and hippocampal formation (HF); while VOG examination comprised ocular reactive saccades, smooth pursuit, and executive tests. Rs-fMRI analysis demonstrated a decreased region-to-region functional connectivity between mPFC and PCC as well as increased connectivity between bilateral HF in PD compared with controls. In VOG, patients and controls differed in terms of executive tests outcome, smooth pursuit eye movement, and visually guided reactive saccades but not in peak eye velocity. A significant relationship was observed between saccadic accuracy and functional connectivity strengths between MTL and PCC. These results suggest that PD-associated changes of DMN connectivity are correlated with PD-associated saccadic hypometria, in particular in the vertical direction. |
Joshua A. Granek; Laure Pisella; John Stemberger; Alain Vighetto; Yves Rossetti; Lauren E. Sergio Decoupled visually-guided reaching in optic ataxia: Differences in motor control between canonical and non-canonical orientations in space Journal Article In: PLoS ONE, vol. 8, no. 12, pp. e86138, 2013. @article{Granek2013,Guiding a limb often involves situations in which the spatial location of the target for gaze and limb movement are not congruent (i.e. have been decoupled). Such decoupled situations involve both the implementation of a cognitive rule (i.e. strategic control) and the online monitoring of the limb position relative to gaze and target (i.e. sensorimotor recalibration). To further understand the neural mechanisms underlying these different types of visuomotor control, we tested patient IG who has bilateral caudal superior parietal lobule (SPL) damage resulting in optic ataxia (OA), and compared her performance with six age-matched controls on a series of center-out reaching tasks. The tasks comprised 1) directing a cursor that had been rotated (180° or 90°) within the same spatial plane as the visual display, or 2) moving the hand along a different spatial plane than the visual display (horizontal or para-sagittal). Importantly, all conditions were performed towards visual targets located along either the horizontal axis (left and right; which can be guided from strategic control) or the diagonal axes (top-left and top-right; which require on-line trajectory elaboration and updating by sensorimotor recalibration). The bilateral OA patient performed much better in decoupled visuomotor control towards the horizontal targets, a canonical situation in which well-categorized allocentric cues could be utilized (i.e. guiding cursor direction perpendicular to computer monitor border). Relative to neurologically intact adults, IG's performance suffered towards diagonal targets, a non-canonical situation in which only less-categorized allocentric cues were available (i.e. guiding cursor direction at an off-axis angle to computer monitor border), and she was therefore required to rely on sensorimotor recalibration of her decoupled limb. We propose that an intact caudal SPL is crucial for any decoupled visuomotor control, particularly when relying on the realignment between vision and proprioception without reliable allocentric cues towards non-canonical orientations in space. |
Michael A. Grubb; Nancy J. Minshew; David J. Heeger; Marisa Carrasco Exogenous spatial attention: Evidence for intact functioning in adults with autism spectrum disorder Journal Article In: Journal of Vision, vol. 13, no. 14, pp. 1–13, 2013. @article{Grubb2013,Deficits or atypicalities in attention have been reported in individuals with autism spectrum disorder (ASD), yet no consensus on the nature of these deficits has emerged. We conducted three experiments that paired a peripheral precue with a covert discrimination task, using protocols for which the effects of covert exogenous spatial attention on early vision have been well established in typically developing populations. Experiment 1 assessed changes in contrast sensitivity, using orientation discrimination of a contrast-defined grating; Experiment 2 evaluated the reduction of crowding in the visual periphery, using discrimination of a letter-like figure with flanking stimuli at variable distances; and Experiment 3 assessed improvements in visual search, using discrimination of the same letter-like figure with a variable number of distractor elements. In all three experiments, we found that exogenous attention modulated visual discriminability in a group of high-functioning adults with ASD and that it did so in the same way and to the same extent as in a matched control group. We found no evidence to support the hypothesis that deficits in exogenous spatial attention underlie the emergence of core ASD symptomatology. |
Christoph Helmchen; Stefan Glasauer; Andreas Sprenger Inverse eye position dependency of downbeat nystagmus in midline medullary lesion Journal Article In: Journal of Neurology, vol. 260, no. 11, pp. 2908–2910, 2013. @article{Helmchen2013,Downbeat nystagmus (DBN) is a persisting ocular motor sign most often found in vestibulo-cerebellar midline lesions. DBN typically increases on lateral and downward gaze and decreases with upward gaze [3], and thereby obeys Alexander's law which states that the slow phase velocity (SPV) is higher with gaze in the fast phase direction of nystagmus compared with gaze in the slow phase direction [11]. DBN may reverse into upward beating nystagmus on upward gaze or in the supine position [3, 4]. Only exceptionally, DBN may occur in midline pontomedullary [12], pontine [6] or medullary [1, 8] brainstem lesions. Current pathophysiological models on DBN are based on a dysfunction of the cerebellar flocculus and an impaired cerebellar negative feedback loop to the brainstem neural integrator, which accounts for the typical gaze- dependent increase of DBN with lateral and downward gaze [5]. Contrary to this concept, we here report about a patient with a confined lesion in the midline medullary brainstem presenting with an inverse eye position dependency: DBN increased with upgaze and decreased with downgaze. This may shed some new light on the impact of floccular afferents, i.e., the paramedian medullary tract (PMT) cells, on the eye position dependency of DBN and it may have some new clinical implications. |
Timothy L. Hodgson; Petroc Sumner; Dimitra Molyva; Ray Sheridan; Christopher Kennard Learning and switching between stimulus-saccade associations in Parkinson's disease Journal Article In: Neuropsychologia, vol. 51, no. 7, pp. 1350–1360, 2013. @article{Hodgson2013,Making flexible associations between what we see and what we do is important for many everyday tasks. Previous work in patients with focal lesions has shown that the control of saccadic eye movements in such contexts relies on a network of areas in the frontal cerebral cortex. These regions are reciprocally connected with structures in the basal ganglia although the contribution of these sub-cortical structures to oculomotor control in complex tasks is not well understood. We report the performance of patients with idiopathic Parkinsons disease (PDs) in a test which required learning and switching between arbitrary cue-saccade rules. In Experiment 1 feedback was given following each response which reliably indicated which of the two possible rules was correct. PDs were slower to learn the first cue-saccade association presented, but did not show increased error or reaction time switch costs when switching between two rules within blocks. In a follow up experiment the feedback given by the computer was adjusted to be probabilistic such that executing a response based upon the "correct" rule only resulted in positive feedback on 80% of trials. Under these conditions patients were impaired in terms of response latencies and number of errors. In all conditions PDs showed multi-stepping/hypometria of saccades consistent with a motoric deficit in executing actions based on cognitive cues. The findings are consistent with a role for the nigrostriatal dopamine system in the reinforcement of saccade-response-outcome associations. Intact performance of PDs when associations are not stochastically reinforced suggests that striatal learning systems are complemented by cognitive representations of task rules which are unaffected in the early stages of PD. |
Silvia Primativo; Lisa S. Arduino; Maria De Luca; Roberta Daini; Marialuisa Martelli Neglect dyslexia: A matter of "good looking" Journal Article In: Neuropsychologia, vol. 51, no. 11, pp. 2109–2119, 2013. @article{Primativo2013,Brain-damaged patients with right-sided unilateral spatial neglect (USN) often make left-sided errors in reading single words or pseudowords (neglect dyslexia, ND). We propose that both left neglect and low fixation accuracy account for reading errors in neglect dyslexia.Eye movements were recorded in USN patients with (ND+) and without (ND-) neglect dyslexia and in a matched control group of right brain-damaged patients without neglect (USN-). Unlike ND- and controls, ND+ patients showed left lateralized omission errors and a distorted eye movement pattern in both a reading aloud task and a non-verbal saccadic task. During reading, the total number of fixations was larger in these patients independent of visual hemispace, and most fixations were inaccurate. Similarly, in the saccadic task only ND+ patients were unable to reach the moving dot. A third experiment addressed the nature of the left lateralization in reading error distribution by simulating neglect dyslexia in ND- patients. ND- and USN- patients had to perform a speeded reading-at-threshold task that did not allow for eye movements. When stimulus exploration was prevented, ND- patients, but not controls, produced a pattern of errors similar to that of ND+ with unlimited exposure time (e.g., left-sided errors).We conclude that neglect dyslexia reading errors may arise in USN patients as a consequence of an additional and independent deficit unrelated to the orthographic material. In particular, the presence of an altered oculo-motor pattern, preventing the automatic execution of the fine saccadic eye movements involved in reading, uncovers, in USN patients, the attentional bias also in reading single centrally presented words. |
Eryl O. Roberts; Frank A. Proudlock; Kate Martin; Michael A. Reveley; Mohammed Al-Uzri; Irene Gottlob Reading in schizophrenic subjects and their nonsymptomatic first-degree relatives Journal Article In: Schizophrenia Bulletin, vol. 39, no. 4, pp. 896–907, 2013. @article{Roberts2013,Previous studies have demonstrated eye movement abnormalities during smooth pursuit and antisaccadic tasks in schizophrenia. However, eye movements have not been investigated during reading. The purpose of this study was to determine whether schizophrenic subjects and their nonsymptomatic first-degree relatives show eye movement abnormalities during reading. Reading rate, number of saccades per line, amplitudes of saccades, percentage regressions (reverse saccades), and fixation durations were measured using an eye tracker (EyeLink, SensoMotoric Instruments, Germany) in 38 schizophrenic volunteers, 14 nonaffected first-degree relatives, and 57 control volunteers matched for age and National Adult Reading Test scores. Parameters were examined when volunteers read full pages of text and text was limited to progressively smaller viewing areas around the point of fixation using a gaze-contingent window. Schizophrenic volunteers showed significantly slower reading rates (P = .004), increase in total number of saccades (P ≤ .001), and a decrease in saccadic amplitude (P = .025) while reading. Relatives showed a significant increase in total number of saccades (P = .013) and decrease in saccadic amplitude (P = .020). Limitation of parafoveal information by reducing the amount of visible characters did not change the reading rate of schizophrenics but controls showed a significant decrease in reading rate with reduced parafoveal information (P < .001). Eye movement abnormalities during reading of schizophrenic volunteers and their first-degree relatives suggest that visual integration of foveal and parafoveal information may be reduced in schizophrenia. Reading abnormalities in relatives suggest a genetic influence in reading ability in schizophrenia and rule out confounding effects of medication. |
Yasuo Terao; Hideki Fukuda; Yuichiro Shirota; Akihiro Yugeta; Masayuki Yoshioka; Masahiko Suzuki; Ritsuko Hanajima; Yoshiko Nomura; Masaya Segawa; Shoji Tsuji; Yoshikazu Ugawa Deterioration of horizontal saccades in progressive supranuclear palsy Journal Article In: Clinical Neurophysiology, vol. 124, no. 2, pp. 354–363, 2013. @article{Terao2013,Objective: To investigate horizontal saccade changes according to disease stage in patients with progressive supranuclear palsy (PSP). Methods: We studied visually and memory guided saccades (VGS and MGS) in 36 PSP patients at various disease stages, and compared results with those in 66 Parkinson's disease (PD) patients and 58 age-matched normal controls. Results: Both vertical and horizontal saccades were affected in PSP patients, usually manifesting as " slow saccades" but sometimes as a sequence of small amplitude saccades with relatively well preserved velocities. Disease progression caused saccade amplitude reduction in PSP but not PD patients. In contrast, VGS and MGS latencies were comparable between PSP and PD patients, as were the frequencies of saccades to cue, suggesting that voluntary initiation and inhibitory control of saccades are similar in both disorders. Hypermetria was rarely observed in PSP patients with cerebellar ataxia (PSPc patients). Conclusions: The progressively reduced accuracy of horizontal saccades in PSP suggests a brainstem oculomotor pathology that includes the superior colliculus and/or paramedian pontine reticular formation. In contrast, the functioning of the oculomotor system above the brainstem was similar between PSP and PD patients. Significance: These findings may reflect a brainstem oculomotor pathology. |
Charmaine L. Thomas; Lauren D. Goegan; Kristin R. Newman; Jody E. Arndt; Christopher R. Sears Attention to threat images in individuals with clinical and subthreshold symptoms of post-traumatic stress disorder Journal Article In: Journal of Anxiety Disorders, vol. 27, no. 5, pp. 447–455, 2013. @article{Thomas2013,Attention to general and trauma-relevant threat was examined in individuals with clinical and subthreshold symptoms of post-traumatic stress disorder (PTSD). Participants' eye gaze was tracked and recorded while they viewed sets of four images over a 6-s presentation (one negative, positive, and neutral image, and either a general threat image or a trauma-relevant threat image). Two trauma-exposed groups (a clinical and a subthreshold PTSD symptom group) were compared to a non-trauma-exposed group. Both the clinical and subthreshold PTSD symptom groups attended to trauma-relevant threat images more than the no-trauma-exposure group, whereas there were no group differences for general threat images. A time course analysis of attention to trauma-relevant threat images revealed different attentional profiles for the trauma-exposed groups. Participants with clinical PTSD symptoms exhibited immediate heightened attention to the images relative to participants with no-trauma-exposure, whereas participants with subthreshold PTSD symptoms did not. In addition, participants with subthreshold PTSD symptoms attended to trauma-relevant threat images throughout the 6-s presentation, whereas participants with clinical symptoms of PTSD exhibited evidence of avoidance. The theoretical and clinical implications of these distinct attentional profiles are discussed. |
Stefan Van der Stigchel; Richard A. I. Bethlehem; Barrie P. Klein; Tos T. J. M. Berendschot; Tanja C. W. Nijboer; Serge O. Dumoulin Macular degeneration affects eye movement behavior during visual search Journal Article In: Frontiers in Psychology, vol. 4, pp. 579, 2013. @article{VanderStigchel2013,Patients with a scotoma in their central vision (e.g., due to macular degeneration, MD) commonly adopt a strategy to direct the eyes such that the image falls onto a peripheral location on the retina. This location is referred to as the preferred retinal locus (PRL). Although previous research has investigated the characteristics of this PRL, it is unclear whether eye movement metrics are modulated by peripheral viewing with a PRL as measured during a visual search paradigm. To this end, we tested four MD patients in a visual search paradigm and contrasted their performance with a healthy control group and a healthy control group performing the same experiment with a simulated scotoma. The experiment contained two conditions. In the first condition the target was an unfilled circle hidden among c-shaped distractors (serial condition) and in the second condition the target was a filled circle (pop-out condition). Saccadic search latencies for the MD group were significantly longer in both conditions compared to both control groups. Results of a subsequent experiment indicated that this difference between the MD and the control groups could not be explained by a difference in target selection sensitivity. Furthermore, search behavior of MD patients was associated with saccades with smaller amplitudes toward the scotoma, an increased intersaccadic interval and an increased number of eye movements necessary to locate the target. Some of these characteristics, such as the increased intersaccadic interval, were also observed in the simulation group, which indicate that these characteristics are related to the peripheral viewing itself. We suggest that the combination of the central scotoma and peripheral viewing can explain the altered search behavior and no behavioral evidence was found for a possible reorganization of the visual system associated with the use of a PRL. Thus the switch from a fovea-based to a PRL-based reference frame impairs search efficiency. |
Stefan Van der Stigchel; Tanja C. W. Nijboer; Janet H. Bultitude; Robert D. Rafal Delayed oculomotor inhibition in patients with lesions to the human frontal oculomotor cortex: Evidence from a study on saccade averaging Journal Article In: Brain and Cognition, vol. 82, no. 2, pp. 192–200, 2013. @article{VanderStigchel2013a,The frontal oculomotor cortex is known to play an important role in oculomotor selection. The aim of the current study was to examine whether previously observed findings concerning the role of the frontal oculomotor cortex in the speed of saccade initiation and oculomotor inhibition might be related to a common underlying role of these areas in oculomotor selection. To this end, six patients with lesions to the frontal oculomotor cortex performed a double stimulus paradigm in which two elements were presented simultaneously in close proximity. Patients performed a block in which no specific task instruction was given and a block in which an instruction was provided about which of the two elements was the target. The rationale behind this manipulation was that the introduction of a specific task instruction would require a stronger involvement of top-down factors. In contrast to the block without a specific task instruction, saccade latencies to the contralesional visual field were longer than the ipsilesional visual field when a task instruction was given. This effect was strongest for saccades that landed away from the target and the distractor, reflecting trials in which strong oculomotor inhibition was applied. The observed deficits can be explained in terms of a slowing of the inhibitory signals associated with the rejection of a distractor. Given the known role of the Frontal Eye Fields and the location of the lesions, we attribute these findings to the Frontal Eye Fields, revealing their important role in the voluntary control of eye movements. |
Stefan Van der Stigchel; Robert D. Rafal; Janet H. Bultitude Temporal dynamics of error correction in a double step task in patients with a lesion to the lateral intra-parietal cortex Journal Article In: Neuropsychologia, vol. 51, no. 14, pp. 2988–2994, 2013. @article{VanderStigchel2013b,Five patients with lesions involving intra-parietal cortex (IPCx) were tested in a rapid version of the double step paradigm to investigate the role of the IPCx in the rapid, online, updating of a saccade program. Saccades were executed to a single target in either the contra- or the ipsilesional visual field. In two thirds of the trials, a step change in target position required that the saccade shifted to a new location within the same field but in the contra- or the ipsilesional direction, allowing us to investigate whether patients are able to update their saccade program given new exogenous information about the required endpoint of the saccade. This set-up resulted in three types of initial saccades: saccades to the target on no-step trials, uncorrected saccades to the original target location on step trials and corrected saccades to the new target location on step trials. Furthermore, if the updating of the original eye movement program failed, patients performed a second saccade to the new target location that required a rapid error correction. The analysis of the double-step task on a group level indicated that latencies for all trial types were longer when saccades were directed to the contralesional versus the ipsilesional field. Furthermore, longer latencies were required for patients to initiate a corrective second saccade after making an uncorrected first saccade in their contralesional compared to ipsilesional field. There were no differences in the ultimate landing positions of the eye movements for such corrected saccades. These results reveal that deficits in updating of saccade programs only seem to be present if the updating must occur after the gaze has shifted to a new location, pointing to a role of intra-parietal cortex in the processes involved in updating information when the current reference frame has to be updated. In conclusion, the paradigm deployed in the current study allows for a refinement of the role of the intra-parietal cortex in the updating of saccade programs. |
Kathleen Vancleef; Johan Wagemans; Glyn W. Humphreys Impaired texture segregation but spared contour integration following damage to right posterior parietal cortex Journal Article In: Experimental Brain Research, vol. 230, no. 1, pp. 41–57, 2013. @article{Vancleef2013,We examined the relations between texture segregation and contour integration in patients with deficits in spatial attention leading to left or right hemisphere extinction. Patients and control participants were presented with texture and contour stimuli consisting of oriented elements. We induced regularity in the stimuli by manipulating the element orientations resulting in an implicit texture border or explicit contour. Participants had to discriminate curved from straight shapes without making eye movements, while the stimulus presentation time was varied using a QUEST procedure. The results showed that only patients with right hemisphere extinction had a spatial bias, needing a longer presentation time to determine the shape of the border or contour on the contralesional side, especially for borders defined by texture. These results indicate that texture segregation is modulated by attention-related brain areas in the right posterior parietal cortex. |
J. Gablentz; Andreas Sprenger; M. Heldmann; T. F. Münte; Christoph Helmchen Acquired pendular nystagmus and its therapy in progressive supranuclear palsy (PSP) due to inferior olivary hypertrophy Journal Article In: Journal of Neurology, vol. 260, no. 9, pp. 2424–2426, 2013. @article{Gablentz2013,The hallmark of progressive supranuclear palsy (PSP) is a slowing of vertical saccades which may lead to gaze- dependent blurred vision [2]. Oscillopsia, the illusion of a moving visual world, is usually caused by nystagmus or saccadic intrusions. However, oscillopsia and nystagmus usually do not belong to symptoms and signs of PSP patients. We report about a PSP patient who complained about oscillopsia due to acquired pendular nystagmus (APN), which was secondary to bilateral hypertrophy of the inferior olivary nucleus (IOH). APN and oscillopsia were reduced by gabapentin. This sheds some light on the brainstem manifestations of PSP, mechanisms of ocular oscillations in PSP, its therapy and the differential diag- nosis of blurred vision in PSP. |
Robin Walker An iPad app as a low-vision aid for people with macular disease Journal Article In: British Journal of Ophthalmology, vol. 97, no. 1, pp. 110–112, 2013. @article{Walker2013,Age-related macular degeneration (AMD) is the single most common cause of vision loss in people over the age of 50. Individuals with low vision caused by macular disease, experience severe difficulty with everyday tasks such as reading, which has profound detrimental consequences for their quality of life. We have developed an app for the iPad (the MD evReader) that aims to improve reading (of electronic books) by enhancing the effectiveness of the eccentric viewing technique (EV) using dynamic text presentation. Eccentric viewing is a simple strategy adopted by individuals with AMD that involves using the relatively preserved peripheral region of their retina in order to see. A limiting factor of the EV technique is that it relies on the individual holding their gaze away from the focus of interest and suppressing the natural and strong, tendency to make eye-movements (saccades). During normal reading, for example, a stereotypical pattern of horizontal saccades are made, from left-to-right, enabling fixations to be made on each word4 – Figure 1a). The natural inclination to make saccades is, however, difficult to suppress and limits the effectiveness of eccentric viewing in people with macular disease. |
Veronica Whitford; Gillian A. O'Driscoll; Christopher C. Pack; Ridha Joober; Ashok Malla; Debra Titone In: Journal of Experimental Psychology: General, vol. 142, no. 1, pp. 57–75, 2013. @article{Whitford2013,Language and oculomotor disturbances are 2 of the best replicated findings in schizophrenia. However, few studies have examined skilled reading in schizophrenia (e.g., Arnott, Sali, Copland, 2011; Hayes & O'Grady, 2003; Revheim et al., 2006; E. O. Roberts et al., 2012), and none have examined the contribution of cognitive and motor processes that underlie reading performance. Thus, to evaluate the relationship of linguistic processes and oculomotor control to skilled reading in schizophrenia, 20 individuals with schizophrenia and 16 demographically matched controls were tested using a moving window paradigm (McConkie & Rayner, 1975). Linguistic skills supporting reading (phonological awareness) were assessed with the Comprehensive Test of Phonological Processing (R. K. Wagner, Torgesen, & Rashotte, 1999). Eye movements were assessed during reading tasks and during nonlinguistic tasks tapping basic oculomotor control (prosaccades, smooth pursuit) and executive functions (predictive saccades, antisaccades). Compared with controls, schizophrenia patients exhibited robust oculomotor markers of reading difficulty (e.g., reduced forward saccade amplitude) and were less affected by reductions in window size, indicative of reduced perceptual span. Reduced perceptual span in schizophrenia was associated with deficits in phonological processing and reduced saccade amplitudes. Executive functioning (antisaccade errors) was not related to perceptual span but was related to reading comprehension. These findings suggest that deficits in language, oculomotor control, and cognitive control contribute to skilled reading deficits in schizophrenia. Given that both language and oculomotor dysfunction precede illness onset, reading may provide a sensitive window onto cognitive dysfunction in schizophrenia vulnerability and be an important target for cognitive remediation. |
Tracey A. Williams; Melanie A. Porter; Robyn Langdon Viewing social scenes: A visual scan-path study comparing fragile X syndrome and williams syndrome Journal Article In: Journal of Autism and Developmental Disorders, vol. 43, no. 8, pp. 1880–1894, 2013. @article{Williams2013a,Fragile X syndrome (FXS) and Williams syndrome (WS) are both genetic disorders which present with similar cognitive-behavioral problems, but distinct social phenotypes. Despite these social differences both syndromes display poor social relations which may result from abnormal social processing. This study aimed to manipulate the location of socially salient information within scenes to investigate the visual attentional mechanisms of: capture, disengagement, and/or general engagement. Findings revealed that individuals with FXS avoid social information presented centrally, at least initially. The WS findings, on the other hand, provided some evidence that difficulties with attentional disengagement, rather than attentional capture, may play a role in the WS social phenotype. These findings are discussed in relation to the distinct social phenotypes of these two disorders. |
Heather Cleland Woods; Christoph Scheepers; K. A. Ross; Colin A. Espie; Stephany M. Biello What are you looking at? Moving toward an attentional timeline in insomnia: A novel semantic eye tracking study Journal Article In: Sleep, vol. 36, no. 10, pp. 1491–1499, 2013. @article{Woods2013,STUDY OBJECTIVES: To date, cognitive probe paradigms have been used in different guises to obtain reaction time measurements suggestive of an attention bias towards sleep in insomnia. This study adopts a methodology which is novel to sleep research to obtain a continual record of where the eyes-and therefore attention-are being allocated with regard to sleep and neutral stimuli.$backslash$n$backslash$nDESIGN: A head mounted eye tracker (Eyelink II,SR Research, Ontario, Canada) was used to monitor eye movements in respect to two words presented on a computer screen, with one word being a sleep positive, sleep negative, or neutral word above or below a second distracter pseudoword. Probability and reaction times were the outcome measures.$backslash$n$backslash$nPARTICIPANTS: Sleep group classification was determined by screening interview and PSQI (> 8 = insomnia, < 3 = good sleeper) score.$backslash$n$backslash$nMEASUREMENTS AND RESULTS: Those individuals with insomnia took longer to fixate on the target word and remained fixated for less time than the good sleep controls. Word saliency had an effect with longer first fixations on positive and negative sleep words in both sleep groups, with largest effect sizes seen with the insomnia group.$backslash$n$backslash$nCONCLUSIONS: This overall delay in those with insomnia with regard to vigilance and maintaining attention on the target words moves away from previous attention bias work showing a bias towards sleep, particularly negative, stimuli but is suggestive of a neurocognitive deficit in line with recent research. |
Xiao Lin Zhu; Shu Ping Tan; Fu De Yang; Wei Sun; Chong Sheng Song; Jie Feng Cui; Yan Li Zhao; Feng Mei Fan; Ya Jun Li; Yun Long Tan; Yi Zhuang Zou Visual scanning of emotional faces in schizophrenia Journal Article In: Neuroscience Letters, vol. 552, pp. 46–51, 2013. @article{Zhu2013a,This study investigated eye movement differences during facial emotion recognition between 101 patients with chronic schizophrenia and 101 controls. Independent of facial emotion, patients with schizophrenia processed facial information inefficiently; they showed significantly more direct fixations that lasted longer to interest areas (IAs), such as the eyes, nose, mouth, and nasion. The total fixation number, mean fixation duration, and total fixation duration were significantly increased in schizophrenia. Additionally, the number of fixations per second to IAs (IA fixation number/s) was significantly lower in schizophrenia. However, no differences were found between the two groups in the proportion of number of fixations to IAs or total fixation number (IA fixation number %). Interestingly, the negative symptoms of patients with schizophrenia negatively correlated with IA fixation number %. Both groups showed significantly greater attention to positive faces. Compared to controls, patients with schizophrenia exhibited significantly more fixations directed to IAs, a higher total fixation number, and lower IA fixation number/s for negative faces. These results indicate that facial processing efficiency is significantly decreased in schizophrenia, but no difference was observed in processing strategy. Patients with schizophrenia may have special deficits in processing negative faces, and negative symptoms may affect visual scanning parameters. |
Alexandre Lang; Marine Vernet; Qing Yang; Christophe Orssaud; Alain Londero; Zoï Kapoula Differential auditory-oculomotor interactions in patients with right vs. left sided subjective tinnitus: A saccade study Journal Article In: Frontiers in Human Neuroscience, vol. 7, pp. 47, 2013. @article{Lang2013,Subjective tinnitus (ST) is a frequent but poorly understood medical condition. Recent studies demonstrated abnormalities in several types of eye movements (smooth pursuit, optokinetic nystagmus, fixation, and vergence) in ST patients. The present study investigates horizontal and vertical saccades in patients with tinnitus lateralized predominantly to the left or to the right side. Compared to left sided ST, tinnitus perceived on the right side impaired almost all the parameters of saccades (latency, amplitude, velocity, etc.) and noticeably the upward saccades. Relative to controls, saccades from both groups were more dysmetric and were characterized by increased saccade disconjugacy (i.e., poor binocular coordination). Although the precise mechanisms linking ST and saccadic control remain unexplained, these data suggest that ST can lead to detrimental auditory, visuomotor, and perhaps vestibular interactions. |
J. R. Lukos; J. Snider; M. E. Hernandez; E. Tunik; S. Hillyard; Howard Poizner Parkinson's disease patients show impaired corrective grasp control and eye-hand coupling when reaching to grasp virtual objects Journal Article In: Neuroscience, vol. 254, pp. 205–221, 2013. @article{Lukos2013,The effect of Parkinson's disease (PD) on hand-eye coordination and corrective response control during reach-to-grasp tasks remains unclear. Moderately impaired PD patients (n= 9) and age-matched controls (n= 12) reached to and grasped a virtual rectangular object, with haptic feedback provided to the thumb and index fingertip by two 3-degree of freedom manipulanda. The object rotated unexpectedly on a minority of trials, requiring subjects to adjust their grasp aperture. On half the trials, visual feedback of finger positions disappeared during the initial phase of the reach, when feedforward mechanisms are known to guide movement. PD patients were tested without (OFF) and with (ON) medication to investigate the effects of dopamine depletion and repletion on eye-hand coordination online corrective response control. We quantified eye-hand coordination by monitoring hand kinematics and eye position during the reach. We hypothesized that if the basal ganglia are important for eye-hand coordination and online corrections to object perturbations, then PD patients tested OFF medication would show reduced eye-hand spans and impoverished arm-hand coordination responses to the perturbation, which would be further exasperated when visual feedback of the hand was removed. Strikingly, PD patients tracked their hands with their gaze, and their movements became destabilized when having to make online corrective responses to object perturbations exhibiting pauses and changes in movement direction. These impairments largely remained even when tested in the ON state, despite significant improvement on the Unified Parkinson's Disease Rating Scale. Our findings suggest that basal ganglia-cortical loops are essential for mediating eye-hand coordination and adaptive online responses for reach-to-grasp movements, and that restoration of tonic levels of dopamine may not be adequate to remediate this coordinative nature of basal ganglia-modulated function. © 2013 IBRO. |
Yan Ma; B. Douglas Ward; Kristina M. Ropella; Edgar A. Deyoe Comparison of randomized multifocal mapping and temporal phase mapping of visual cortex for clinical use Journal Article In: NeuroImage: Clinical, vol. 3, pp. 143–154, 2013. @article{Ma2013,fMRI is becoming an important clinical tool for planning and guidance of surgery to treat brain tumors, arteriovenous malformations, and epileptic foci. For visual cortex mapping, the most popular paradigm by far is temporal phase mapping, although random multifocal stimulation paradigms have drawn increased attention due to their ability to identify complex response fields and their random properties. In this study we directly compared temporal phase and multifocal vision mapping paradigms with respect to clinically relevant factors including: time efficiency, mapping completeness, and the effects of noise. Randomized, multifocal mapping accurately decomposed the response of single voxels to multiple stimulus locations and made correct retinotopic assignments as noise levels increased despite decreasing sensitivity. Also, multifocal mapping became less efficient as the number of stimulus segments (locations) increased from 13 to 25 to 49 and when duty cycle was increased from 25% to 50%. Phase mapping, on the other hand, activated more extrastriate visual areas, was more time efficient in achieving statistically significant responses, and had better sensitivity as noise increased, though with an increase in systematic retinotopic misassignments. Overall, temporal phase mapping is likely to be a better choice for routine clinical applications though random multifocal mapping may offer some unique advantages for selected applications. |
Jennifer Malsert; Nathalie Guyader; Alan Chauvin; Mircea Polosan; David Szekely; Thierry Bougerol; Christian Marendaz Saccadic performance and cortical excitability as trait-markers and state-markers in rapid cycling bipolar disorder: A two-case follow-up study Journal Article In: Frontiers in Psychiatry, vol. 3, pp. 112, 2013. @article{Malsert2013,Background: The understanding of physiopathology and cognitive impairments in mood disorders requires finding objective markers. Mood disorders have often been linked to hypometabolism in the prefrontal dorsolateral cortex, and to GABAergic and glutamatergic neurotransmission dysfunction. The present study aimed to discover whether saccadic tasks (involving DPLFC activity), and cortical excitability (involving GABA/Glutamate neurotransmission) could provide neuropsychophysical markers for mood disorders, and/or of its phases, in patients with rapid cycling bipolar disorders (rcBD). Methods: Two rcBD patients were followed for a cycle, and were compared to nine healthy controls. A saccade task, mixing prosaccades, antisaccades, and nosaccades, and an evaluation of cortical excitability using transcranial magnetic stimulation were performed. Results: We observed a deficit in antisaccade in patients independently of thymic phase, and in nosaccade in the manic phase only. Cortical excitability data revealed global intracortical deficits in all phases, switching according to cerebral hemisphere and thymic phase. Conclusion: Specific patterns of performance in saccade tasks and cortical excitability could characterize mood disorders (trait-markers) and its phases (state-markers). Moreover, a functional relationship between oculometric performance and cortical excitability is discussed. |
Kathryn L. McCabe; Jessica L. Melville; Dominique Rich; Paul A. Strutt; Gavin Cooper; Carmel M. Loughland; Ulrich Schall; Linda E. Campbell Divergent patterns of social cognition performance in autism and 22q11.2 deletion syndrome (22q11DS) Journal Article In: Journal of Autism and Developmental Disorders, vol. 43, no. 8, pp. 1926–1934, 2013. @article{McCabe2013,Individuals with developmental disorders frequently report a range of social cognition deficits including difficulties identifying facial displays of emotion. This study examined the specificity of face emotion processing deficits in adolescents with either autism or 22q11DS compared to typically developing (TD) controls. Two tasks (face emotion recognition and weather scene recognition) were used to explore group differences in visual scanpath strategy and concurrent recognition accuracy. For faces, the autism and 22q11DS groups demonstrated lower emotion recognition accuracy and fewer fixations compared to the TD group. Individuals with autism demonstrated fewer fixations to some weather scene stimuli compared to 22q11DS and TD groups, yet achieved a level of recognition accuracy comparable to the TD group. These findings provide evidence for a divergent pattern of social cognition dysfunction in autism and 22q11DS. |
Benjamin P. Meek; Keri Locheed; Jane M. Lawrence-Dewar; Paul Shelton; Jonathan J. Marotta Posterior cortical atrophy: An investigation of scan paths generated during face matching tasks Journal Article In: Frontiers in Human Neuroscience, vol. 7, pp. 309, 2013. @article{Meek2013,When viewing a face, healthy individuals focus more on the area containing the eyes and upper nose in order to retrieve important featural and configural information. In contrast, individuals with face blindness (prosopagnosia) tend to direct fixations toward individual facial features-particularly the mouth. Presented here is an examination of face perception deficits in individuals with Posterior Cortical Atrophy (PCA). PCA is a rare progressive neurodegenerative disorder that is characterized by atrophy in occipito-parietal and occipito-temporal cortices. PCA primarily affects higher visual processing, while memory, reasoning, and insight remain relatively intact. A common symptom of PCA is a decreased effective field of vision caused by the inability to "see the whole picture." Individuals with PCA and healthy control participants completed a same/different discrimination task in which images of faces were presented as cue-target pairs. Eye-tracking equipment and a novel computer-based perceptual task-the Viewing Window paradigm-were used to investigate scan patterns when faces were presented in open view or through a restricted-view, respectively. In contrast to previous prosopagnosia research, individuals with PCA each produced unique scan paths that focused on non-diagnostically useful locations. This focus on non-diagnostically useful locations was also present when using a restricted viewing aperture, suggesting that individuals with PCA have difficulty processing the face at either the featural or configural level. In fact, it appears that the decreased effective field of view in PCA patients is so severe that it results in an extreme dependence on local processing, such that a feature-based approach is not even possible. |
Dana Schneider; Virginia P. Slaughter; Andrew P. Bayliss; Paul E. Dux A temporally sustained implicit theory of mind deficit in autism spectrum disorders Journal Article In: Cognition, vol. 129, no. 2, pp. 410–417, 2013. @article{Schneider2013,Eye movements during false-belief tasks can reveal an individual's capacity to implicitly monitor others' mental states (theory of mind - ToM). It has been suggested, based on the results of a single-trial-experiment, that this ability is impaired in those with a high-functioning autism spectrum disorder (ASD), despite neurotypical-like performance on explicit ToM measures. However, given there are known attention differences and visual hypersensitivities in ASD it is important to establish whether such impairments are evident over time. In addition, investigating implicit ToM using a repeated trial approach allows an assessment of whether learning processes can reduce the ASD impairment in this ability, as is the case with explicit ToM. Here we investigated the temporal profile of implicit ToM in individuals with ASD and a control group. Despite similar performance on explicit ToM measures, ASD-diagnosed individuals showed no evidence of implicit false-belief tracking even over a one-hour period and many trials, whereas control participants did. These findings demonstrate that the systems involved in implicit and explicit ToM are distinct and hint that impaired implicit false-belief tracking may play an important role in ASD. Further, they indicate that learning processes do not alleviate this impairment across the presentation of multiple trials. |
Casey A. Schofield; Albrecht W. Inhoff; Meredith E. Coles Time-course of attention biases in social phobia Journal Article In: Journal of Anxiety Disorders, vol. 27, no. 7, pp. 661–669, 2013. @article{Schofield2013,Theoretical models of social phobia implicate preferential attention to social threat in the maintenance of anxiety symptoms, though there has been limited work characterizing the nature of these biases over time. The current study utilized eye-movement data to examine the time-course of visual attention over 1500. ms trials of a probe detection task. Nineteen participants with a primary diagnosis of social phobia based on DSM-IV criteria and 20 non-clinical controls completed this task with angry, fearful, and happy face trials. Overt visual attention to the emotional and neutral faces was measured in 50. ms segments across the trial. Over time, participants with social phobia attend less to emotional faces and specifically less to happy faces compared to controls. Further, attention to emotional relative to neutral expressions did not vary notably by emotion for participants with social phobia, but control participants showed a pattern after 1000. ms in which over time they preferentially attended to happy expressions and avoided negative expressions. Findings highlight the importance of considering attention biases to positive stimuli as well as the pattern of attention between groups. These results suggest that attention "bias" in social phobia may be driven by a relative lack of the biases seen in non-anxious participants. |
Tracey A. Shaw; Melanie A. Porter Emotion recognition and visual-scan paths in fragile X syndrome Journal Article In: Journal of Autism and Developmental Disorders, vol. 43, no. 5, pp. 1119–1139, 2013. @article{Shaw2013,This study investigated emotion recognition abilities and visual scanning of emotional faces in 16 Fragile X syndrome (FXS) individuals compared to 16 chronological-age and 16 mental-age matched controls. The relationships between emotion recognition, visual scan-paths and symptoms of social anxiety, schizotypy and autism were also explored. Results indicated that, com- pared to both control groups, the FXS group displayed specific emotion recognition deficits for angry and neutral (but not happy or fearful) facial expressions. Despite these evident emotion recognition deficits, the visual scanning of emotional faces was found to be at developmentally appropriate levels in the FXS group. Significant relation- ships were also observed between visual scan-paths, emo- tion recognition performance and symptomology in the FXS group. |
Viral Sheth; Irene Gottlob; Sarim Mohammad; Rebecca J. McLean; Gail D. E. Maconachie; Anil Kumar; Christopher Degg; Frank A. Proudlock Diagnostic potential of iris cross-sectional imaging in albinism using optical coherence tomography Journal Article In: Ophthalmology, vol. 120, no. 10, pp. 2082–2090, 2013. @article{Sheth2013,Purpose: To characterize in vivo anatomic abnormalities of the iris in albinism compared with healthy controls using anterior segment optical coherence tomography (AS-OCT) and to explore the diagnostic potential of this technique for albinism. We also investigated the relationship between iris abnormalities and other phenotypical features of albinism. Design: Prospective cross-sectional study. Participants: A total of 55 individuals with albinism and 45 healthy controls. Methods: We acquired 4.37×4.37-mm volumetric scans (743 A-scans, 50 B-scans) of the nasal and temporal iris in both eyes using AS-OCT (3-μm axial resolution). Iris layers were segmented and thicknesses were measured using ImageJ software. Iris transillumination grading was graded using Summers and colleagues' classification. Retinal OCT, eye movement recordings, best-corrected visual acuity (BCVA), visual evoked potential (VEP), and grading of skin and hair pigmentation were used to quantify other phenotypical features associated with albinism. Main Outcome Measures: Iris AS-OCT measurements included (1) total iris thickness, (2) stroma/anterior border (SAB) layer thickness, and (3) posterior epithelial layer (PEL) thickness. Correlation with other phenotypical measurements, including (1) iris transillumination grading, (2) retinal layer measurements at the fovea, (3) nystagmus intensity, (4) BCVA, (5) VEP asymmetry, (6) skin pigmentation, and (7) hair pigmentation (of head hair, lashes, and brows). Results: The mean iris thickness was 10.7% thicker in controls (379.3±44.0 μm) compared with the albinism group (342.5±52.6 μm; P > 0.001), SAB layers were 5.8% thicker in controls (315.1±43.8 μm) compared with the albinism group (297.7±50.0 μm; P=0.044), and PEL was 44.0% thicker in controls (64.1±11.7 μm) compared with the albinism group (44.5±13.9 μm; P < 0.0001). The most ciliary quartile of the PEL yielded a sensitivity of 85% and specificity of 78% for detecting albinism. Phenotypic features of albinism, such as skin and hair pigmentation, BCVA, and nystagmus intensity, were significantly correlated to AS-OCT iris thickness measurements. Conclusions: We have characterized in vivo abnormalities of the iris associated with albinism for the first time and show that PEL thickness is particularly affected. We demonstrate that PEL thickness has diagnostic potential for detecting iris abnormalities in albinism. Anterior segment OCT iris measurements are significantly correlated to BCVA and nystagmus intensity in contrast to iris transillumination grading measurements that were not. |
Andreas Sprenger; Monique Friedrich; Matthias Nagel; Christiane S. Schmidt; Steffen Moritz; Rebekka Lencer Advanced analysis of free visual exploration patterns in schizophrenia Journal Article In: Frontiers in Psychology, vol. 4, pp. 737, 2013. @article{Sprenger2013,Background: Visual scanpath analyses provide important information about attention allocation and attention shifting during visual exploration of social situations. This study investigated whether patients with schizophrenia simply show restricted free visual exploration behavior reflected by reduced saccade frequency and increased fixation duration or whether patients use qualitatively different exploration strategies than healthy controls. Methods: Scanpaths of 32 patients with schizophrenia and age-matched 33 healthy controls were assessed while participants freely explored six photos of daily life situations (20 s/photo) evaluated for cognitive complexity and emotional strain. Using fixation and saccade parameters, we compared temporal changes in exploration behavior, cluster analyses, attentional landscapes, and analyses of scanpath similarities between both groups. Results: We found fewer fixation clusters, longer fixation durations within a cluster, fewer changes between clusters, and a greater increase of fixation duration over time in patients compared to controls. Scanpath patterns and attentional landscapes in patients also differed significantly from those of controls. Generally, cognitive complexity and emotional strain had significant effects on visual exploration behavior. This effect was similar in both groups as were physical properties of fixation locations. Conclusions: Longer attention allocation to a given feature in a scene and less attention shifts in patients suggest a more focal processing mode compared to a more ambient exploration strategy in controls. These visual exploration alterations were present in patients independently of cognitive complexity, emotional strain or physical properties of visual cues implying that they represent a rather general deficit. Despite this impairment, patients were able to adapt their scanning behavior to changes in cognitive complexity and emotional strain similar to controls. |
Daniel Mirman; Allison E. Britt; Qi Chen Effects of phonological and semantic deficits on facilitative and inhibitory consequences of item repetition in spoken word comprehension Journal Article In: Neuropsychologia, vol. 51, no. 10, pp. 1848–1856, 2013. @article{Mirman2013,Repeating a word can have both facilitative and inhibitory effects on subsequent processing. The present study investigated these dynamics by examining the facilitative and inhibitory consequences of different kinds of item repetition in two individuals with aphasia and a group of neurologically intact control participants. The two individuals with aphasia were matched on overall aphasia severity, but had deficits at different levels of processing: one with a phonological deficit and spared semantic processing, the other with a semantic deficit and spared phonological processing. Participants completed a spoken word-to-picture matching task in which they had to pick which of four object images matched the spoken word. The trials were grouped into pairs such that exactly two objects from the first trial in a pair were present on screen during the second trial in the pair. When the second trial's target was the same as the first trial's target, compared to control participants, both participants with aphasia exhibited equally larger repetition priming effects. When the second trial's target was one of the new items, the participant with a phonological deficit exhibited a significantly more negative effect (i.e., second trial response slower than first trial response) than the control participants and the participant with a semantic deficit. Simulations of a computational model confirmed that this pattern of results could arise from (1) normal residual activation being functionally more significant when overall lexical processing is slower and (2) residual phonological activation of the previous trial's target having a particularly strong inhibitory effect specifically when phonological processing is impaired because the task was phonologically-driven (the spoken input specified the target). These results provide new insights into perseveration errors and lexical access deficits in aphasia. |
Jorge Otero-Millan; Rosalyn Schneider; R. John Leigh; Stephen L. Macknik; Susana Martinez-Conde Saccades during attempted fixation in Parkinsonian disorders and recessive ataxia: From microsaccades to square-wave jerks Journal Article In: PLoS ONE, vol. 8, no. 3, pp. e58535, 2013. @article{OteroMillan2013a,During attempted visual fixation, saccades of a range of sizes occur. These "fixational saccades" include microsaccades, which are not apparent in regular clinical tests, and "saccadic intrusions", predominantly horizontal saccades that interrupt accurate fixation. Square-wave jerks (SWJs), the most common type of saccadic intrusion, consist of an initial saccade away from the target followed, after a short delay, by a "return saccade" that brings the eye back onto target. SWJs are present in most human subjects, but are prominent by their increased frequency and size in certain parkinsonian disorders and in recessive, hereditary spinocerebellar ataxias. Here we asked whether fixational saccades showed distinctive features in various parkinsonian disorders and in recessive ataxia. Although some saccadic properties differed between patient groups, in all conditions larger saccades were more likely to form SWJs, and the intervals between the first and second saccade of SWJs were similar. These findings support the proposal of a common oculomotor mechanism that generates all fixational saccades, including microsaccades and SWJs. The same mechanism also explains how the return saccade in SWJs is triggered by the position error that occurs when the first saccadic component is large, both in the healthy brain and in neurological disease. |
Muriel T. N. Panouillères; Solène Frismand; Olivier Sillan; Christian Urquizar; Alain Vighetto; Denis Péisson; Caroline Tilikete Saccades and eye-head coordination in ataxia with oculomotor apraxia type 2 Journal Article In: Cerebellum, vol. 12, no. 4, pp. 557–567, 2013. @article{Panouilleres2013a,Ataxia with oculomotor apraxia type 2 (AOA2) is one of the most frequent autosomal recessive cerebellar ataxias. Oculomotor apraxia refers to horizontal gaze failure due to deficits in voluntary/reactive eye movements. These deficits can manifest as increased latency and/or hypometria of saccades with a staircase pattern and are frequently associated with compensatory head thrust movements. Oculomotor disturbances associated with AOA2 have been poorly studied mainly because the diagnosis of oculomotor apraxia was based on the presence of compensatory head thrusts. The aim of this study was to characterise the nature of horizontal gaze failure in patients with AOA2 and to demonstrate oculomotor apraxia even in the absence of head thrusts. Five patients with AOA2, without head thrusts, were tested in saccadic tasks with the head restrained or free to move and their performance was compared to a group of six healthy participants. The most salient deficit of the patients was saccadic hypometria with a typical staircase pattern. Saccade latency in the patients was longer than controls only for memory-guided saccades. In the head-free condition, head movements were delayed relative to the eye and their amplitude and velocity were strongly reduced compared to controls. Our study emphasises that in AOA2, hypometric saccades with a staircase pattern are a more reliable sign of oculomotor apraxia than head thrust movements. In addition, the variety of eye and head movements' deficits suggests that, although the main neural degeneration in AOA2 affects the cerebellum, this disease affects other structures. |
Angelina Paolozza; Rebecca Titman; Donald Brien; Douglas P. Munoz; James N. Reynolds Altered accuracy of saccadic eye movements in children with fetal alcohol spectrum disorder Journal Article In: Alcoholism: Clinical and Experimental Research, vol. 37, no. 9, pp. 1491–1498, 2013. @article{Paolozza2013,Background: Prenatal exposure to alcohol is a major, preventable cause of neurobehavioral dysfunction in children worldwide. The measurement and quantification of saccadic eye movements is a powerful tool for assessing sensory, motor, and cognitive function. The quality of the motor process of an eye movement is known as saccade metrics. Saccade accuracy is 1 component of metrics, which to function optimally requires several cortical brain structures as well as an intact cerebellum and brain-stem. The cerebellum has frequently been reported to be damaged by prenatal alcohol exposure. This study, therefore, tested the hypothesis that children with fetal alcohol spectrum disorder (FASD) will exhibit deficits in the accuracy of saccades.; Methods: A group of children with FASD (n = 27) between the ages of 8 and 16 and typically developing control children (n = 27) matched for age and sex, completed 3 saccadic eye movement tasks of increasing difficulty. Eye movement performance during the tasks was captured using an infrared eye tracker. Saccade metrics (e.g., velocity, amplitude, accuracy) were quantified and compared between the 2 groups for the 3 different tasks.; Results: Children with FASD were more variable in saccade endpoint accuracy, which was reflected by statistically significant increases in the error of the initial saccade endpoint and the frequency of additional, corrective saccades required to achieve final fixation. This increased variability in accuracy was amplified when the cognitive demand of the tasks increased. Children with FASD also displayed a statistically significant increase in response inhibition errors.; Conclusions: These data suggest that children with FASD may have deficits in eye movement control and sensory-motor integration including cerebellar circuits, thereby impairing saccade accuracy. |
Kirsten A. Dalrymple; Alexander K. Gray; Brielle L. Perler; Elina Birmingham; Walter F. Bischof; Jason J. S. Barton; Alan Kingstone Eyeing the eyes in social scenes: Evidence for top-down control of stimulus selection in simultanagnosia Journal Article In: Cognitive Neuropsychology, vol. 30, no. 1, pp. 25–40, 2013. @article{Dalrymple2013,Simultanagnosia is a disorder of visual attention resulting from bilateral parieto-occipital lesions. Healthy individuals look at eyes to infer people's attentional states, but simultanagnosics allocate abnormally few fixations to eyes in scenes. It is unclear why simultanagnosics fail to fixate eyes, but it might reflect that they are (a) unable to locate and fixate them, or (b) do not prioritize attentional states. We compared eye movements of simultanagnosic G.B. to those of healthy subjects viewing scenes normally or through a restricted window of vision. They described scenes and explicitly inferred attentional states of people in scenes. G.B. and subjects viewing scenes through a restricted window made few fixations on eyes when describing scenes, yet increased fixations on eyes when inferring attention. Thus G.B. understands that eyes are important for inferring attentional states and can exert top-down control to seek out and process the gaze of others when attentional states are of interest. |
C. Hemptinne; Adrian Ivanoiu; Philippe Lefèvre; Marcus Missal How does Parkinson's disease and aging affect temporal expectation and the implicit timing of eye movements? Journal Article In: Neuropsychologia, vol. 51, no. 2, pp. 340–348, 2013. @article{Hemptinne2013,Anticipatory eye movements are often evoked by the temporal expectation of an upcoming event. Temporal expectation is based on implicit timing about when a future event could occur. Implicit timing emerges from observed temporal regularities in a changing stimulus without any voluntary estimate of elapsed time, unlike explicit timing. The neural bases of explicit and implicit timing are likely different. It has been shown that the basal ganglia (BG) play a central role in explicit timing. In order to determine the influence of BG in implicit timing, we investigated the influence of early Parkinson's disease (PD) and aging on the latency of anticipatory eye movements. We hypothesized that a deficit of implicit timing should yield inadequate temporal expectations, and consequently abnormally timed anticipatory eye movements compared with age-matched controls. To test this hypothesis, we used an oculomotor paradigm where anticipation of a salient target event plays a central role. Participants pursued a visual target that moved along a circular path at a constant velocity. After a randomly short (1200. ms) or long (2400. ms) forward path, the target reversed direction, returned to its starting position and stopped. Target motion reversal caused an abrupt 'slip' of the pursued target image on the retina and was a particularly salient event evoking anticipatory eye movements. Anticipatory eye movements were less frequent in PD patients. However, the timing of anticipation of target motion reversal was statistically similar in PD patients and control subjects. Other eye movements showed statistically significant differences between PD and controls, but these differences could be attributed to other factors. We conclude that all anticipatory eye movements are not similarly impaired in PD and that implicit timing of salient events seems largely unaffected by this disease. The results support the hypothesis that implicit and explicit timing are differently affected by BG dysfunction. |
Louis F. Dell'Osso; Jonathan B. Jacobs Normal pursuit-system limitations — first discovered in infantile nystagmus syndrome Journal Article In: Journal of Eye Movement Research, vol. 6, no. 1, pp. 1–24, 2013. @article{DellOsso2013,Infantile nystagmus syndrome (INS) patients occasionally have impaired pursuit. Model and patient data identified relative timing between target motion initiation and INS-waveform saccades as the cause. We used a new stimulus, the “step-pause-ramp” (SPR), to induce saccades proximal to target-velocity onset and test their effect on normal pursuit. Our OMS model predicted that proximal saccades impaired normal ramp responses, as in INS. Eye movements of subjects were calibrated monocularly and recorded binocularly; data were analyzed using OMtools software. Proximal saccades caused lengthened target acquisition times and steady-state position errors, confirming the model's predictions. Spontaneous pursuit oscillation supported the hypothesis that INS is caused by loss of smooth-pursuit damping. Snooth pursuit may be impaired by saccades overlapping targetmotion onset. |
Virginie Desestret; Nathalie Streichenberger; Muriel T. N. Panouillères; Denis Pélisson; B. Plus; Charles Duyckaerts; Dennis K. Burns; Christian Scheiber; Alain Vighetto; Caroline Tilikete An elderly woman with difficulty reading and abnormal eye movements Journal Article In: Journal of Neuro-Ophthalmology, vol. 33, no. 3, pp. 296–301, 2013. @article{Desestret2013,A 73-year-old woman was evaluated in our neuro- ophthalmology clinic with a 1-year history of progressive difficulty reading. The patient's visual acuity, pupillary reactions to light and near stimulation, visual fields, and fundi were normal. Examination of her eye movements revealed a supranuclear vertical gaze abnormality, charac- terized by lack of upward saccades but intact downward saccades. The patient also had had difficulty initiating voluntary, especially leftward horizontal saccades on command, but reactive horizontal saccades were relatively well preserved. She was able to follow a pencil light moved by the examiner using small saccades (saccadic smooth pursuit) and her vestibulo-ocular reflex (VOR) was intact. She had apraxia of lid closure. The patient had no cognitive deficit, behavioral or social disturbance, aphasia, alexia, limb apraxia, postural ataxia, pyramidal signsorparkinsonism. |
Jose Ignacio Egaña; Christ Devia; Rocío Mayol; Javiera Parrini; Gricel Orellana; Aida Ruiz; Pedro E. Maldonado Small saccades and image complexity during free viewing of natural images in schizophrenia Journal Article In: Frontiers in Psychiatry, vol. 4, pp. 37, 2013. @article{Egana2013,In schizophrenia, patients display dysfunctions during the execution of simple visual tasks such as antisaccade or smooth pursuit. In more ecological scenarios, such as free viewing of natural images, patients appear to make fewer and longer visual fixations and display shorter scanpaths. It is not clear whether these measurements reflect alterations in their proficiency to perform basic eye movements, such as saccades and fixations, or are related to high-level mechanisms, such as exploration or attention. We utilized free exploration of natural images of different complexities as a model of an ecological context where normally operative mechanisms of visual control can be accurately measured. We quantified visual exploration as Euclidean distance, scanpaths, saccades, and visual fixation, using the standard SR-Research eye tracker algorithm (SR). We then compared this result with a computation that includes microsaccades (EM). We evaluated eight schizophrenia patients and corresponding healthy controls (HC). Next, we tested whether the decrement in the number of saccades and fixations, as well as their increment in duration reported previously in schizophrenia patients, resulted from the increasing occurrence of undetected microsaccades. We found that when utilizing the standard SR algorithm, patients displayed shorter scanpaths as well as fewer and shorter saccades and fixations. When we employed the EM algorithm, the differences in these parameters between patients and HC were no longer significant. On the other hand, we found that image complexity plays an important role in exploratory behaviors, demonstrating that this factor explains most of differences between eye-movement behaviors in schizophrenia patients. These results help elucidate the mechanisms of visual motor control that are affected in schizophrenia and contribute to the finding of adequate markers for diagnosis and treatment for this condition. |
Joost Felius; Zainab A. Muhanna Visual deprivation and foveation characteristics both underlie visual acuity deficits in idiopathic infantile nystagmus Journal Article In: Investigative Ophthalmology & Visual Science, vol. 54, no. 5, pp. 3520–3525, 2013. @article{Felius2013,PURPOSE. Children with idiopathic infantile nystagmus (IIN) exhibit visual acuity deficits that have been modeled in terms of foveation characteristics of the nystagmus waveform. Here we present evidence for an additional component of acuity loss associated with the deprivation experienced during the sensitive period of visual development. METHODS. Binocular grating visual acuity and eye movement recordings were obtained from 56 children with IIN (age 4.8 6 3.2 years) and documented waveform history from longitudinal visits. Visual acuity was modeled in terms of foveation characteristics (Nystagmus Optimal Fixation Function, NOFF) and of each child's time course of pendular nystagmus during the sensitive period. RESULTS. Mean visual acuity was 0.25 6 0.19 logMAR below age norms, and the mean foveation fraction was 0.28 (NOFF ¼?0.9 6 2.3 logits). Nystagmus had a median onset at age 3 months and transitioned to waveforms with extended foveation at age 35 months. The best fit of the model showed the following: Poor foveation (0.01 foveation fraction) was associated with 0.60 logMAR acuity deficit; this deficit gradually reduced to zero for increasingly better foveation; pendular nystagmus during each decile of the sensitive period was associated with an additional 0.022 logMAR deficit. The model accounted for 57% of the variance in visual acuity and provided a better fit than either component alone. CONCLUSIONS. Visual acuity in IIN is explained better if, besides the child's foveation characteristics, an additional component is taken into account representing the nystagmus- induced visual deprivation during the sensitive period. These findings may have implications for the timing of treatment decisions in children with IIN. |
Gerardo Fernández; Pablo Mandolesi; Nora P. Rotstein; Oscar Colombo; Osvaldo Agamennoni; Luis E. Politi Eye movement alterations during reading in patients with early Alzheimer disease Journal Article In: Investigative Ophthalmology & Visual Science, vol. 54, no. 13, pp. 8345–8352, 2013. @article{Fernandez2013,Purpose: Eye movements follow a reproducible pattern during normal reading. Each eye movement ends up in a fixation point, which allows the brain to process the incoming information and to program the following saccade. Alzheimer disease (AD) produces eye movement abnormalities and disturbances in reading. In this work we investigated whether eye movement alterations during reading might be already present at very early stages of the disease. Methods: Twenty female and male adult patients with the diagnosis of probable AD and 20 age-matching individuals with no evidence of cognitive decline participated in the study. Participants were seated in front of a 20-inch LCD monitor and single sentences were presented on it. Eye movements were recorded with an eyetracker, with a sampling rate of 1000 Hz and an eye position resolution of 20-s arc. Results: Analysis of eye movements during reading revealed that patients with early AD decreased the amount of single fixations, increased their total number of first and second pass fixations, the amount of saccade regressions and the number of words skipped, compared with healthy individuals (controls). They also reduced the size of outgoing saccades, simultaneously increasing fixation duration. Conclusions: The present study shows that patients with mild AD evidenced marked alterations in eye movement behavior during reading, even at early stages of the disease. Hence, evaluation of eye movement behavior during reading might provide a useful tool for a more precise early diagnosis of AD and for dynamical monitoring of the pathology. |
Megan Freeth; Tom Foulsham; Alan Kingstone What affects social attention? Social presence, eye contact and autistic traits Journal Article In: PLoS ONE, vol. 8, no. 1, pp. e53286, 2013. @article{Freeth2013,Social understanding is facilitated by effectively attending to other people and the subtle social cues they generate. In order to more fully appreciate the nature of social attention and what drives people to attend to social aspects of the world, one must investigate the factors that influence social attention. This is especially important when attempting to create models of disordered social attention, e.g. a model of social attention in autism. Here we analysed participants' viewing behaviour during one-to-one social interactions with an experimenter. Interactions were conducted either live or via video (social presence manipulation). The participant was asked and then required to answer questions. Experimenter eye-contact was either direct or averted. Additionally, the influence of participant self-reported autistic traits was also investigated. We found that regardless of whether the interaction was conducted live or via a video, participants frequently looked at the experimenter's face, and they did this more often when being asked a question than when answering. Critical differences in social attention between the live and video interactions were also observed. Modifications of experimenter eye contact influenced participants' eye movements in the live interaction only; and increased autistic traits were associated with less looking at the experimenter for video interactions only. We conclude that analysing patterns of eye-movements in response to strictly controlled video stimuli and natural real-world stimuli furthers the field's understanding of the factors that influence social attention. |
Teresa C. Frohman; Scott L. Davis; Shin Beh; Benjamin M. Greenberg; Gina Remington; Elliot M. Frohman Uhthoff's phenomena in MS - clinical features and pathophysiology Journal Article In: Nature Reviews Neurology, vol. 9, no. 9, pp. 535–540, 2013. @article{Frohman2013,In the late 19(th) century, Wilhelm Uhthoff reported on a series of patients with acute optic neuritis who manifested similar recurrent, stereotyped visual symptoms that were of paroxysmal onset, short in duration, and reversible. These 'Uhthoff's phenomena', which are a feature of multiple sclerosis (MS) and other demyelinating diseases, can be triggered by factors including the perimenstrual period, exercise, infection, fever, exposure to high ambient temperatures, and psychological stress. Here, we characterize the clinical, pathophysiological and neurotherapeutic challenges associated with Uhthoff's phenomena, and discuss the differentiation of these events from other paroxysmal, acute or subacute changes in functional capabilities and neurological symptoms in MS. For instance, whereas MS exacerbations are contingent on immune dysregulation, Uhthoff's phenomena are predicated on ion channel modifications, in conjunction with thermoregulatory derangements that transiently alter the conduction properties of demyelinated axons. An understanding of these pathophysiological underpinnings of Uhthoff's phenomena is germane to their recognition and timely treatment. |
Franziska Geringswald; Anne Herbik; Michael B. Hoffmann; Stefan Pollmann Contextual cueing impairment in patients with age-related macular degeneration Journal Article In: Journal of Vision, vol. 13, no. 3, pp. 1–18, 2013. @article{Geringswald2013,Visual attention can be guided by past experience of regularities in our visual environment. In the contextual cueing paradigm, incidental learning of repeated distractor configurations speeds up search times compared to random search arrays. Concomitantly, fewer fixations and more direct scan paths indicate more efficient visual exploration in repeated search arrays. In previous work, we found that simulating a central scotoma in healthy observers eliminated this search facilitation. Here, we investigated contextual cueing in patients with age-related macular degeneration (AMD) who suffer from impaired foveal vision. AMD patients performed visual search using only their more severely impaired eye (n = 13) as well as under binocular viewing (n = 16). Normal-sighted controls developed a significant contextual cueing effect. In comparison, patients showed only a small nonsignificant advantage for repeated displays when searching with their worse eye. When searching binocularly, they profited from contextual cues, but still less than controls. Number of fixations and scan pattern ratios showed a comparable pattern as search times. Moreover, contextual cueing was significantly correlated with acuity in monocular search. Thus, foveal vision loss may lead to impaired guidance of attention by contextual memory cues. |
Neil K. Archibald; Samuel B. Hutton; Michael P. Clarke; Urs P. Mosimann; David J. Burn Visual exploration in Parkinson's disease and Parkinson's disease dementia Journal Article In: Brain, vol. 136, no. 3, pp. 739–750, 2013. @article{Archibald2013,Parkinson's disease, typically thought of as a movement disorder, is increasingly recognized as causing cognitive impairment and dementia. Eye movement abnormalities are also described, including impairment of rapid eye movements (saccades) and the fixations interspersed between them. Such movements are under the influence of cortical and subcortical networks commonly targeted by the neurodegeneration seen in Parkinson's disease and, as such, may provide a marker for cognitive decline. This study examined the error rates and visual exploration strategies of subjects with Parkinson's disease, with and without cognitive impairment, whilst performing a battery of visuo-cognitive tasks. Error rates were significantly higher in those Parkinson's disease groups with either mild cognitive impairment (P = 0.001) or dementia (P < 0.001), than in cognitively normal subjects with Parkinson's disease. When compared with cognitively normal subjects with Parkinson's disease, exploration strategy, as measured by a number of eye tracking variables, was least efficient in the dementia group but was also affected in those subjects with Parkinson's disease with mild cognitive impairment. When compared with control subjects and cognitively normal subjects with Parkinson's disease, saccade amplitudes were significantly reduced in the groups with mild cognitive impairment or dementia. Fixation duration was longer in all Parkinson's disease groups compared with healthy control subjects but was longest for cognitively impaired Parkinson's disease groups. The strongest predictor of average fixation duration was disease severity. Analysing only data from the most complex task, with the highest error rates, both cognitive impairment and disease severity contributed to a predictive model for fixation duration F(2,76) = 12.52, P 0.001, but medication dose did not (r = 0.18 |
Stephen P. Badham; Claire V. Hutchinson Characterising eye movement dysfunction in myalgic encephalomyelitis/ chronic fatigue syndrome Journal Article In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 251, no. 12, pp. 2769–2776, 2013. @article{Badham2013,BACKGROUND: People who suffer from myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often report that their eye movements are sluggish and that they have difficulties tracking moving objects. However, descriptions of these visual problems are based solely on patients' self-reports of their subjective visual experiences, and there is a distinct lack of empirical evidence to objectively verify their claims. This paper presents the first experimental research to objectively examine eye movements in those suffering from ME/CFS. METHODS: Patients were assessed for ME/CFS symptoms and were compared to age, gender, and education matched controls for their ability to generate saccades and smooth pursuit eye movements. RESULTS: Patients and controls exhibited similar error rates and saccade latencies (response times) on prosaccade and antisaccade tasks. Patients showed relatively intact ability to accurately fixate the target (prosaccades), but were impaired when required to focus accurately in a specific position opposite the target (antisaccades). Patients were most markedly impaired when required to direct their gaze as closely as possible to a smoothly moving target (smooth pursuit). CONCLUSIONS: It is hypothesised that the effects of ME/CFS can be overcome briefly for completion of saccades, but that continuous pursuit activity (accurately tracking a moving object), even for a short time period, highlights dysfunctional eye movement behaviour in ME/CFS patients. Future smooth pursuit research may elucidate and improve diagnosis of ME/CFS. |
Daniela Balslev; Bartholomäus Odoj; Hans-Otto Karnath Role of somatosensory cortex in visuospatial attention Journal Article In: Journal of Neuroscience, vol. 33, no. 46, pp. 18311–18318, 2013. @article{Balslev2013,The human somatosensory cortex (S1) is not among the brain areas usually associated with visuospatial attention. However, such a function can be presumed, given the recently identified eye proprioceptive input to S1 and the established links between gaze and attention. Here we investigated a rare patient with a focal lesion of the right postcentral gyrus that interferes with the processing of eye proprioception without affecting the ability to locate visual objects relative to her body or to execute eye movements. As a behavioral measure of spatial attention, we recorded fixation time during visual search and reaction time for visual discrimination in lateral displays. In contrast to a group of age-matched controls, the patient showed a gradient in looking time and in visual sensitivity toward the midline. Because an attention bias in the opposite direction, toward the ipsilesional space, occurs in patients with spatial neglect, in a second study, we asked whether the incidental coinjury of S1 together with the neglect-typical perisylvian lesion leads to a milder neglect. A voxelwise lesion behavior mapping analysis of a group of right-hemisphere stroke patients supported this hypothesis. The effect of an isolated S1 lesion on visual exploration and visual sensitivity as well as the modulatory role of S1 in spatial neglect suggest a role of this area in visuospatial attention. We hypothesize that the proprioceptive gaze signal in S1, although playing only a minor role in locating visual objects relative to the body, affects the allocation of attention in the visual space. |
Niraj Barot; Rebecca J. McLean; Irene Gottlob; Frank A. Proudlock Reading performance in infantile nystagmus Journal Article In: Ophthalmology, vol. 120, no. 6, pp. 1232–1238, 2013. @article{Barot2013,Objective: To characterize reading deficits in infantile nystagmus (IN), to determine optimal font sizes for reading in IN, and to investigate whether visual acuity (VA) and severity of nystagmus are good indicators of reading performance in IN. Design: Prospective cross-sectional study. Participants and Controls: Seventy-one participants with IN (37 idiopathic, 34 with albinism) and 20 age-matched controls. Methods: Reading performance was assessed using Radner reading charts and was compared with near logarithm of the minimum angle of resolution (logMAR) VA, nystagmus intensity, and foveation characteristics as quantified using eye movement recordings. Main Outcome Measures: Reading acuity (smallest readable font size), maximum reading speed, critical print size (font size below which reading is suboptimal), near logMAR VA, nystagmus intensity, and foveation characteristics (using the eXpanded Nystagmus Acuity Function). Results: Using optimal reading conditions, maximum reading speeds were 18.8% slower in albinism and 14.7% slower in idiopathic IN patients compared with controls. Reading acuities were significantly worse (P<0.001) in IN patients compared with controls. Also, the range of font sizes over which reading speeds were less than the optimum were much larger in IN patients compared with controls (P<0.001). Reading acuity was correlated strongly to near VA (r2= 0.74 albinism |