EyeLink 临床和动眼神经眼球追踪出版物
EyeLink临床和oculomotor研究出版物至2023年(一些早于2024年)列在以下年份。您可以使用Saccadic Adaptation、Schizophrenia、Nystagmus等关键词搜索出版物。您还可以按年份搜索个人作者姓名和有限搜索(选择年份,然后单击搜索按钮)。如果我们错过了任何EyeLink临床或oculomotor文章,请给我们发电子邮件!
2006 |
F. Møller; M. L. Laursen; A. K. Sjølie Fixation topography in normal test persons Journal Article In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 244, pp. 577–582, 2006. @article{Moeller2006, BACKGROUND: The eye is moved so that the object of interest falls on the central fovea, where the spatial resolution is highest. In the present study we quantified eye movements of normal test persons during steady fixation and characterized the fixation using a 3D fixation plot (X horizontal eye position, Y vertical eye position, Z time in each eye position). METHOD: Fixation eye movements were quantified binocularly in ten normal test persons during a 40-s fixation task using an infrared recording technique. RESULTS: The fixation plot was characterized by a single preferred fixation locus in 17 eyes. One eye had two distinctly separated preferred fixation locations and in two eyes the configuration of fixation plot was flat with no single identifiable locus of fixation. The fixation plots were elliptical along the horizontal meridian in 9 eyes, elliptical along the vertical meridian in 8 eyes, and round in 3 eyes. The fixation area (RAF95) ranged between 1418 and 14182 arcmin(2), and a significant positive correlation was found between RAF95 and the mean microsaccadic amplitude (p<0.001). CONCLUSION: The fixation plots are often characterized by a single preferred fixation locus but may also be almost flat with no identifiable location of fixation. The individual fixations patterns resembles the cone density contour plots as found in histological studies, and it may be speculated, that the shape of the fixation plot is determined by the cone density topography. |
F. Møller; M. L. Laursen; A. K. Sjølie The contribution of microsaccades and drifts in the maintenance of binocular steady fixation Journal Article In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 244, no. 4, pp. 465–471, 2006. @article{Moeller2006a, BACKGROUND: The eye performs three types of eye movements during fixation: fast microsaccades are interrupted by slow drift movements, and tremor is superimposed on the drifts. The contribution of the microsaccades and drifts in maintaining fixation has been discussed since the late 1950s. Initially, microsaccades were thought to correct the misalignment from the optimal fixation locus induced by the drift movements, a theory still postulated in more recent work. The present study aimed to uncover to what extent each fixation movement contributes to maintain steady binocular fixation. METHOD: Binocular fixation during a 40-s fixation task was recorded using an infrared recording technique for ten normal test persons. Start and end point of each microsaccade and drift were superimposed on a fixation map, and the distance to the preferred retinal location of fixation (PRL) was measured. RESULTS: It was found that 32.6% of the microsaccades corrected the previous drift movement towards the PRL, whereas 53.1% of the drifts corrected the endpoint of the previous microsaccade towards the PRL. The overall mean post-microsaccadic and mean post-drift distance to the PRL for the ten normal test persons were 0.46 degrees and 0.41 degrees , respectively; the difference was not statistically significant. Interindividually, the mean post-microsaccadic distance to the PRL ranged between 0.21 degrees and 0.91 degrees and the mean post-drift distance to the PRL ranged between 0.20 degrees and 0.72 degrees . CONCLUSION: Neither the endpoints of the microsaccades nor the drifts bring the visual line to coincide with the centre of the PRL. Consequently, it must be the eye movements performed during the drifts ("slow control") that keep the visual line in the centre of the foveola. |
Leigh A. Mrotek; Martha Flanders; John F. Soechting Oculomotor responses to gradual changes in target direction Journal Article In: Experimental Brain Research, vol. 172, no. 2, pp. 175–192, 2006. @article{Mrotek2006, Smooth pursuit tracking of targets moving linearly (in one dimension) is well characterized by a model where retinal image motion drives eye acceleration. However, previous findings suggest that this model cannot be simply extended to two-dimensional (2D) tracking. To examine 2D pursuit, in the present study, human subjects tracked a target that moved linearly and then followed the arc of a circle. The subjects' gaze angular velocity accurately matched target angular velocity, but the direction of smooth pursuit always lagged behind the current target direction. Pursuit speed slowly declined after the onset of the curve (for about 500 ms), even though the target speed was constant. In a second experiment, brief perturbations were presented immediately prior to the beginning of the change in direction. The subjects' responses to these perturbations consisted of two components: (1) a response specific to the parameters of the perturbation and (2) a nonspecific response that always consisted of a transient decrease in gaze velocity. With the exception of this nonspecific response, pursuit behavior in response to the gradual changes in direction and to the perturbations could be explained by using retinal slip (image velocity) as the input signal. The retinal slip was parallel and perpendicular to the instantaneous direction of pursuit ultimately resulted in changes in gaze velocity (via gaze acceleration). Perhaps due to the subjects' expectations that the target will curve, the sensitivity to the image motion in the direction of pursuit was not as strong as the sensitivity to image motion perpendicular to gaze velocity. |
Lauri Nummenmaa; Jari K. Hietanen Gaze distractors influence saccadic curvature: Evidence for the role of the oculomotor system in gaze-cued orienting Journal Article In: Vision Research, vol. 46, no. 21, pp. 3674–3680, 2006. @article{Nummenmaa2006, We examined the role of the oculomotor system in gaze-triggered orienting of attention by measuring whether perceiving of task-irrelevant gaze distractors and peripheral spatial distractors influence saccadic curvature similarly. Participants performed reflexive, vertical saccades to designated target areas while their eye movements were recorded. Schematic faces with averted gaze or peripheral boxes were presented before or simultaneously (-100 ms/0 ms SOAs) with the imperative signal. Gaze distractors caused the saccades to curve away from the distractor direction at both SOAs and peripheral distractors only at the 0-ms SOA. The results imply that gaze-cued shifts of visual attention involve both cortical attention orienting systems and subcortical oculomotor systems. |
Ralf Engbert; Konstantin Mergenthaler Microsaccades are triggered by low retinal image slip Journal Article In: Proceedings of the National Academy of Sciences, vol. 103, no. 18, pp. 7192–7197, 2006. @article{Engbert2006, Even during visual fixation of a stationary target, our eyes perform rather erratic miniature movements, which represent a random walk. These "fixational" eye movements counteract perceptual fading, a consequence of fast adaptation of the retinal receptor systems to constant input. The most important contribution to fixational eye movements is produced by microsaccades; however, a specific function of microsaccades only recently has been found. Here we show that the occurrence of microsaccades is correlated with low retinal image slip approximately 200 ms before microsaccade onset. This result suggests that microsaccades are triggered dynamically, in contrast to the current view that microsaccades are randomly distributed in time characterized by their rate-of-occurrence of 1 to 2 per second. As a result of the dynamic triggering mechanism, individual microsaccade rate can be predicted by the fractal dimension of trajectories. Finally, we propose a minimal computational model for the dynamic triggering of microsaccades. |
Casper J. Erkelens Coordination of smooth pursuit and saccades Journal Article In: Vision Research, vol. 46, no. 1-2, pp. 163–170, 2006. @article{Erkelens2006, Smooth pursuit and saccades are two components of tracking eye movements. Their coordination has usually been studied by investigating latencies of pursuit onset in response to a moving target appearing simultaneously with the disappearance of the stationary fixation target. The general finding from such studies has been that latencies of saccades and pursuit are different and reflect independent processes. We discuss several limitations of the used targets. In this paper, we study latencies of saccades and smooth pursuit in response to a moving target that overlaps in time with a pursued moving target. We find that saccades and pursuit changes are synchronized. Furthermore, pursuit changes are made fast. Directional changes occur almost entirely within the accompanying saccade. To explain the results we hypothesize a two-stage mechanism for the coordinated generation of saccades and pursuit. |
Kai Essig; Marc Pomplun; Helge Ritter A neural network for 3D gaze recording with binocular eye trackers Journal Article In: International Journal of Parallel, Emergent and Distributed Systems, vol. 21, no. 2, pp. 79–95, 2006. @article{Essig2006, Using eye tracking for the investigation of visual attention has become increasingly popular during the last few decades. Nevertheless, only a small number of eye tracking studies have employed 3D displays, although such displays would closely resemble our natural visual environment. Besides higher cost and effort for the experimental setup, the main reason for the avoidance of 3D displays is the problem of computing a subject's current 3D gaze position based on the measured binocular gaze angles. The geometrical approaches to this problem that have been studied so far involved substantial error in the measurement of 3D gaze trajectories. In order to tackle this problem, we developed an anaglyph-based 3D calibration procedure and used a well-suited type of artificial neural network—a parametrized self-organizing map (PSOM)—to estimate the 3D gaze point from a subject's binocular eye-position data. We report an experiment in which the accuracy of the PSOM gaze-point estimation is compared to a geometrical solution. The results show that the neural network approach produces more accurate results than the geometrical method, especially for the depth axis and for distant stimuli. |
Danny Gagnon Transcranial magnetic stimulation of frontal oculomotor regions during smooth pursuit Journal Article In: Journal of Neuroscience, vol. 26, no. 2, pp. 458–466, 2006. @article{Gagnon2006, Both the frontal eye fields (FEFs) and supplementary eye fields (SEFs) are known to be involved in smooth pursuit eye movements. It has been shown recently that stimulation of the smooth-pursuit area of the FEF [frontal pursuit area (FPA)] in monkey increases the pursuit response to unexpected changes in target motion during pursuit. In the current study, we applied transcranial magnetic stimulation (TMS) to the FPA and SEF in humans during sinusoidal pursuit to assess its effects on the pursuit response to predictable, rather than unexpected, changes in target motion. For the FPA, we found that TMS applied immediately before the target reversed direction increased eye velocity in the new direction, whereas TMS applied in mid-cycle, immediately before the target began to slow, decreased eye velocity. For the SEF, TMS applied at target reversal increased eye velocity in the new direction but had no effect on eye velocity when applied at mid-cycle. TMS of the control region (leg region of the somatosensory cortex) did not affect eye velocity at either point. Previous stimulation studies of FPA during pursuit have suggested that this region is involved in controlling the gain of the transformation of visual signals into pursuit motor commands. The current results suggest that the gain of the transformation of predictive signals into motor commands is also controlled by the FPA. The effect of stimulation of the SEF is distinct from that of the FPA and suggests that its role in sinusoidal pursuit is primarily at the target direction reversal. |
Susana Martinez-Conde; Stephen L. Macknik; Xoana G. Troncoso; Thomas A. Dyar Microsaccades counteract visual fading during fixation Journal Article In: Neuron, vol. 49, no. 2, pp. 297–305, 2006. @article{MartinezConde2006, Our eyes move continually, even while we fixate our gaze on an object. If fixational eye movements are counteracted, our perception of stationary objects fades completely, due to neural adaptation. Some studies have suggested that fixational microsaccades refresh retinal images, thereby preventing adaptation and fading. However, other studies disagree, and so the role of microsaccades remains unclear. Here, we correlate visibility during fixation to the occurrence of microsaccades. We asked subjects to indicate when Troxler fading of a peripheral target occurs, while simultaneously recording their eye movements with high precision. We found that before a fading period, the probability, rate, and magnitude of microsaccades decreased. Before transitions toward visibility, the probability, rate, and magnitude of microsaccades increased. These results reveal a direct link between suppression of microsaccades and fading and suggest a causal relationship between microsaccade production and target visibility during fixation. |
Eugene McSorley Time course of oculomotor inhibition revealed by saccade trajectory modulation Journal Article In: Journal of Neurophysiology, vol. 96, no. 3, pp. 1420–1424, 2006. @article{McSorley2006, Selecting a stimulus as the target for a goal-directed movement involves inhibiting other competing possible responses. Both target and distractor stimuli activate populations of neurons in topographic oculomotor maps such as the superior colliculus. Local inhibitory interconnections between these populations ensure only one saccade target is selected. Suppress-ing saccades to distractors may additionally involve inhibiting corre-sponding map regions to bias the local competition. Behavioral evidence of these inhibitory processes comes from the effects of distractors on oculomotor and manual trajectories. Individual saccades may initially deviate either toward or away from a distractor, but the source of this variability has not been investigated. Here we investi-gate the relation between distractor-related deviation of trajectory and saccade latency. Targets were presented with, or without, distractors, and the deviation of saccade trajectories arising from the presence of distractors was measured. A fixation gap paradigm was used to manipulate latency independently of the influence of competing dis-tractors. Shorter-latency saccades deviated toward distractors and longer-latency saccades deviated away from distractors. The transition between deviation toward or away from distractors occurred at a saccade latency of around 200 ms. This shows that the time course of the inhibitory process involved in distractor related suppression is relatively slow. |
P. U. Tse; G. P. Caplovitz; P. -J. Hsieh Microsaccade directions do not predict directionality of illusory brightness changes of overlapping transparent surfaces Journal Article In: Vision Research, vol. 46, no. 22, pp. 3823–3830, 2006. @article{Tse2006a, Tse (2005) recently introduced a new class of illusory brightness changes where shifts of attention lead to shifts in perceived brightness across overlapping, transparent figures, under conditions of visual fixation. In the absence of endogenous attentional shifts, illusory brightness changes appear to shift from figure to figure spontaneously, much as occurs in other multistable phenomena. The goal of the present research is to determine whether fixational microsaccades are correlated with perceived brightness changes. It has recently been demonstrated that microsaccades can reveal the direction of covert attentional shifts either toward (Engbert, R. & Kliegl, R. (2003). Microsaccades uncover the orientation of covert attention. Vision Research, 43, 1035-1045; Hafed, Z. M. & Clark, J. J. (2002). Microsaccades as an overt measure of covert attention shifts. Vision Research, 42(22), 2533-2545) or away from (Rolfs, M., Engbert, R., & Kliegl, R. (2004). Microsaccade orientation supports attentional enhancement opposite a peripheral cue: commentary on Tse, Sheinberg, and Logothetis (2003). Psychological Science, 15(10), 705-707) a peripheral cue under certain circumstances. Others (Horwitz, G. D. & Albright, T. D. (2003). Short-latency fixational saccades induced by luminance increments. Journal of Neurophysiology, 90(2), 1333-1339; Tse, P. U., Sheinberg, D. L., & Logothetis, N. K. (2002). Fixational eye movements are not affected by abrupt onsets that capture attention. Vision Research, 42, 1663-1669; Tse, P. U., Sheinberg, D. L., & Logothetis, N. K. (2004). The distribution of microsaccade directions need not reveal the location of attention. Psychological Science, 15(10), 708-710) found no change in the distribution of microsaccade directions as a function of where attention is allocated, although changes in the rate of microsaccades were observed in all of these studies in response to the onset of attentional reallocation. It is therefore possible that the distribution of microsaccade directions will change as a function of which figure is perceived to darken, or that changes in this distribution predict which figure will subsequently darken. We find no correlation between this distribution and which figure undergoes the effect, and therefore conclude that microsaccade directionality is not influenced by and does not influence which figure undergoes the effect. Moreover, the directions of microsaccades that occur immediately prior to a perceptual switch are not correlated with the perceived position of the figure that undergoes the effect. However, we do find that the rate of microsaccades decreases upon a perceptual switch, signifying an attentional shift coincident with the perceptual shift. We conclude that microsaccade directionality does not determine, predict, or cause which figure will subsequently be perceived to undergo an illusory brightness change. |
Massimo Turatto; Elena Betta Redundant visual signals boost saccade execution Journal Article In: Psychonomic Bulletin & Review, vol. 13, no. 5, pp. 928–932, 2006. @article{Turatto2006, The redundant signal effect (RSE) refers to the fact that human beings react more quickly to a pair of stimuli than to only one stimulus. In previous studies of the RSE in the oculomotor system, bimodal signals have been used as the goal of the saccade. In consistency with studies using manual response times (RTs), saccadic RTs have been shown to be shorter for redundant multimodal stimuli than for single unimodal stimuli. In the present experiments, we extended these findings by demonstrating an RSE in the saccadic system elicited only by unimodal visual stimuli. In addition, we found that shorter saccadic RTs were accompanied by an increased saccadic peak velocity. The present results are of relevance for neurophysiological models of saccade execution, since the boost of saccades was elicited by two visual transients (acting as a "go" signal) that were presented not at the goal of the saccade but at various other locations. |
Josef N. Geest; Gerardina C. Lagers-van Haselen; Maarten A. Frens Saccade adaptation in Williams-Beuren syndrome Journal Article In: Investigative Ophthalmology & Visual Science, vol. 47, no. 4, pp. 1464–1468, 2006. @article{Geest2006, PURPOSE: To investigate the capacity for rapid saccade adaptation in Williams-Beuren Syndrome (WBS), a genetic neurodevelopmental disorder, in which it has been observed that saccadic accuracy is severely reduced. METHODS: Saccade amplitude modification was elicited by backward steps (30% of target eccentricity) during the primary saccade in a classic saccade-adaptation paradigm. RESULTS: Patients with WBS showed a significant decrease in saccade amplitude. Furthermore, we observed that higher saccade accuracy before adaptation was related to more adaptation. CONCLUSIONS: The increased variability in motor performance does not abolish the ability for saccadic adaptation in subjects with WBS. Our results are congruent with the notion that part of the behavioral deficits observed in WBS may have a cerebellar origin. |
Wieske Zoest; Mieke Donk Saccadic target selection as a function of time Journal Article In: Spatial Vision, vol. 19, no. 1, pp. 61–76, 2006. @article{Zoest2006, Recent evidence indicates that stimulus-driven and goal-directed control of visual selection operate independently and in different time windows (van Zoest et al., 2004). The present study further investigates how eye movements are affected by stimulus-driven and goal-directed control. Observers were presented with search displays consisting of one target, multiple non-targets and one distractor element. The task of observers was to make a fast eye movement to a target immediately following the offset of a central fixation point, an event that either co-occurred with or soon followed the presentation of the search display. Distractor saliency and target-distractor similarity were independently manipulated. The results demonstrated that the effect of distractor saliency was transient and only present for the fastest eye movements, whereas the effect of target-distractor similarity was sustained and present in all but the fastest eye movements. The results support an independent timing account of visual selection. |
Robin Walker; Eugene McSorley The parallel programming of voluntary and reflexive saccades Journal Article In: Vision Research, vol. 46, no. 13, pp. 2082–2093, 2006. @article{Walker2006, A novel two-step paradigm was used to investigate the parallel programming of consecutive, stimulus-elicited ('reflexive') and endogenous ('voluntary') saccades. The mean latency of voluntary saccades, made following the first reflexive saccades in two-step conditions, was significantly reduced compared to that of voluntary saccades made in the single-step control trials. The latency of the first reflexive saccades was modulated by the requirement to make a second saccade: first saccade latency increased when a second voluntary saccade was required in the opposite direction to the first saccade, and decreased when a second saccade was required in the same direction as the first reflexive saccade. A second experiment confirmed the basic effect and also showed that a second reflexive saccade may be programmed in parallel with a first voluntary saccade. The results support the view that voluntary and reflexive saccades can be programmed in parallel on a common motor map. |
Robin Walker; Eugene Mcsorley; Patrick Haggard The control of saccade trajectories : Direction of curvature depends on prior knowledge of target location and saccade latency Journal Article In: Perception and Psychophysics, vol. 68, no. 1, pp. 129–138, 2006. @article{Walker2006a, Recent reports have shown that saccades can deviate either toward or away from distractors. However, the specific conditions responsible for the change in initial saccade direction are not known. One possibility, examined here, is that the direction of curvature (toward or away from distractors) reflects preparatory tuning of the oculomotor system when the location of the target and distractor are known in advance. This was investigated by examining saccade trajectories under predictable and unpredictable target conditions. In Experiment 1, the targets and the distractors appeared unpredictably, whereas in Experiment 2 an arrow cue presented at fixation indicated the location of the forthcoming target prior to stimulus onset. Saccades were made to targets on the horizontal, vertical, and principal oblique axis, and distractors appeared simultaneously at an adjacent location (a separation of +/- 45 degrees of visual angle). On average, saccade trajectories curved toward distractors when target locations were unpredictable and curved away from distractors when target locations were known in advance. There was no overall difference in mean saccade latencies between the two experiments. The magnitude of the distractor modulation of saccade trajectory (either toward or away from) was comparable across the different saccade directions (horizontal, vertical, and oblique). These results are interpreted in terms of the time course of competitive interactions operating in the neural structures involved in the suppression of distractors and the selection of a saccade target. A relatively slow mechanism that inhibits movements to distractors produces curvature away from the distractor. This mechanism has more time to operate when target location is predictable, increasing the likelihood that the saccade trajectory will deviate away from the distractor. |
Guy Wallis The temporal and spatial limits of compensation for fixational eye movements Journal Article In: Vision Research, vol. 46, no. 18, pp. 2848–2858, 2006. @article{Wallis2006, High-fidelity eye tracking is combined with a perceptual grouping task to provide insight into the likely mechanisms underlying the compensation of retinal image motion caused by movement of the eyes. The experiments describe the covert detection of minute temporal and spatial offsets incorporated into a test stimulus. Analysis of eye motion on individual trials indicates that the temporal offset sensitivity is actually due to motion of the eye inducing artificial spatial offsets in the briefly presented stimuli. The results have strong implications for two popular models of compensation for fixational eye movements, namely efference copy and image-based models. If an efference copy model is assumed, the results place constraints on the spatial accuracy and source of compensation. If an image-based model is assumed then limitations are placed on the integration time window over which motion estimates are calculated. |
Z. Wang; Louis F. Dell'Osso; Z. Zhang; R. John Leigh; Jonathan B. Jacobs Tenotomy does not affect saccadic velocities: Support for the "small-signal" gain hypothesis Journal Article In: Vision Research, vol. 46, no. 14, pp. 2259–2267, 2006. @article{Wang2006, We investigated the effects of four-muscle tenotomy on saccadic characteristics in infantile nystagmus syndrome (INS) and acquired pendular nystagmus (APN). Eye movements of 10 subjects with INS and one with APN were recorded using infrared reflection, magnetic search coil, or high-speed digital video. The expanded nystagmus acuity function (NAFX) quantified tenotomy-induced foveation changes in the INS. Saccadic characteristics and peak-to-peak nystagmus amplitudes were measured. Novel statistical tests were performed on the saccadic data. Six out of the 10 INS subjects showed no changes in saccadic duration, peak velocity, acceleration, or trajectory. In the other four, the differences were less than in peak-to-peak amplitudes (from 14.6% to 39.5%) and NAFX (from 22.2% to 162.4%). The APN subject also showed no changes despite a 50% decrease in peak-to-peak amplitude and a 34% increase in NAFX. The "small-signal" changes (peak-to-peak nystagmus amplitude and NAFX) were found to far exceed any "large-signal" changes (saccadic). Tenotomy successfully reduced INS and APN, enabling higher visual acuity without adversely affecting saccadic characteristics. These findings support the peripheral, small-signal gain reduction (via proprioceptive tension control) hypothesis. Current linear plant models, limited to normal steady-state muscle tension levels, cannot explain the effects of the tenotomy. |
Brian J. White; Dirk Kerzel; Karl R. Gegenfurtner The spatio-temporal tuning of the mechanisms in the control of saccadic eye movements Journal Article In: Vision Research, vol. 46, no. 22, pp. 3886–3897, 2006. @article{White2006, We compared the spatio-temporal tuning of perception to the mechanisms that drive saccadic eye movements. Detection thresholds were measured for Gabor-targets presented left or right of fixation (4 or 8 deg eccentricity), at one of four spatial frequencies (1, 2, 4 or 8 cpd) oscillating at one of three temporal frequencies (1, 8 or 16 Hz). We then measured saccade latency to each target presented at various multiples of detection threshold. Consistent with previous research, latency decreased as a function of contrast. However, at equal detection performance, we found no systematic difference in saccadic latency and no difference in average oculometric performance (% correct saccade direction) across the different target spatio-temporal frequencies. Furthermore, position error remained fairly constant across all conditions. The results are consistent with the idea that the spatio-temporal signals used for perception are the same as those used by the mechanisms driving saccadic eye movements. |
Martin Rolfs; Jochen Laubrock; Reinhold Kliegl Shortening and prolongation of saccade latencies following microsaccades Journal Article In: Experimental Brain Research, vol. 169, no. 3, pp. 369–376, 2006. @article{Rolfs2006, When the eyes fixate at a point in a visual scene, small saccades rapidly shift the image on the retina. The effect of these microsaccades on the latency of subsequent large-scale saccades may be twofold. First, microsaccades are associated with an enhancement of visual perception. Their occurrence during saccade target perception could, thus, decrease saccade latencies. Second, microsaccades are likely to indicate activity in fixation-related oculomotor neurons. These represent competitors to saccade-related cells in the interplay of gaze holding and shifting. Consequently, an increase in saccade latencies would be expected after microsaccades. Here, we present evidence for both aspects of microsaccadic impact on saccade latency. In a delayed response task, participants made saccades to visible or memorized targets. First, microsaccade occurrence up to 50 ms before target disappearance correlated with 18 ms (or 8%) faster saccades to memorized targets. Second, if microsaccades occurred shortly (i.e., <150 ms) before a saccade was required, mean saccadic reaction time in visual and memory trials was increased by about 40 ms (or 16%). Hence, microsaccades can have opposite consequences for saccade latencies, pointing at a differential role of these fixational eye movements in the preparation of saccade motor programs. |
Dirk Neumann; Michael L. Spezio; Joseph Piven; Ralph Adolphs Looking you in the mouth: Abnormal gaze in autism resulting from impaired top-down modulation of visual attention Journal Article In: Social Cognitive and Affective Neuroscience, vol. 1, no. 3, pp. 194–202, 2006. @article{Neumann2006, People with autism are impaired in their social behavior, including their eye contact with others, but the processes that underlie this impairment remain elusive. We combined high-resolution eye tracking with computational modeling in a group of 10 high-functioning individuals with autism to address this issue. The group fixated the location of the mouth in facial expressions more than did matched controls, even when the mouth was not shown, even in faces that were inverted and most noticeably at latencies of 200-400 ms. Comparisons with a computational model of visual saliency argue that the abnormal bias for fixating the mouth in autism is not driven by an exaggerated sensitivity to the bottom-up saliency of the features, but rather by an abnormal top-down strategy for allocating visual attention. |
Helena Ojanpää; Risto Näsänen; Juha Päällysaho; Ritva Akila; Kiti Müller; Ari Kaukiainen; Markku Sainio Visual search and eye movements in patients with chronic solvent-induced toxic encephalopathy Journal Article In: Neurotoxicology, vol. 27, no. 6, pp. 1013–1023, 2006. @article{Ojanpaeae2006, Various aspects of visual perception have been found to be impaired in patients with occupational chronic solvent-induced toxic encephalopathy (CSE). The purpose of the study was to characterise the changes in eye movements and visual search performance in CSE patients. We measured eye movements of 13 CSE patients and 22 healthy controls during dynamic visual search task by using a fast video eye tracker. The task was to search for and identify a target letter among numerals presented in a rectangular stimulus matrix (3 × 3-10 × 10 items). Threshold search time, i.e. the duration of stimulus presentation required for identifying the target with a given probability was determined by using a psychophysical staircase method. The visual search times of the CSE patients were clearly longer, and they needed considerably more eye fixations than healthy controls to find the target. Thus, their reduced performance in this task was mainly related to the reduction in the number of items which could be processed during a single eye fixation (perceptual span). This reduction probably reflects a limited capacity of visual attention, since visual acuity, contrast sensitivity, and the oculomotor saccade velocity were found to be normal. The results suggest that motor slowness or low-level visual factors do not explain the poor performance of CSE patients in visual search tasks. The results are also discussed with respect to the effects of education, and compared to the performance in the widely used neuropsychological Trail Making Test, which uses similar stimuli and requires visual search. © 2006 Elsevier Inc. All rights reserved. |
Inger Montfoort; Willem P. A. Kelders; Josef N. Geest; Inger B. Schipper; Louw Feenstra; Chris I. De Zeeuw; Maarten A. Frens Interaction between ocular stabilization reflexes in patients with whiplash injury Journal Article In: Investigative Ophthalmology & Visual Science, vol. 47, no. 7, pp. 2881–2884, 2006. @article{Montfoort2006, PURPOSE: In the past few decades, the automobile has become an increasingly more popular means of transport, which has led to an increasing number of rear-end collisions and consequently has resulted in more patients with whiplash-associated disorders (WADs). Recently, it was found that the gain of one of the ocular stabilization reflexes-the cervico-ocular reflex (COR)-is elevated in patients with whiplash injury. The COR responds to proprioceptive signals from the neck and acts in conjunction with the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) to preserve stable vision on the retina during head motion. Therefore, an investigation was conducted to determine whether the reported elevation of the COR in WADs is accompanied by changes in VOR or OKR. METHODS: Eye movements of 13 patients and 18 age-matched healthy controls were recorded with an infrared eye-tracking device. RESULTS: Analysis confirmed a significant increase in COR gain in whiplash patients. Meanwhile the VOR and OKR gains remained the same. No correlation was found between the gains of the reflexes in individual patients. This is in contrast to earlier observations in elderly subjects and subjects with labyrinthine defects, who showed increases in COR gain and decreases in VOR gain. CONCLUSIONS: Impaired neck motion, altered proprioception of the neck, or disorganization in the process of VOR plasticity could explain the lack of change in VOR gain. |
Jan L. Souman; Ignace T. C. Hooge; Alexander H. Wertheim Frame of reference transformations in motion perception during smooth pursuit eye movements Journal Article In: Journal of Computational Neuroscience, vol. 20, no. 1, pp. 61–76, 2006. @article{Souman2006, Smooth pursuit eye movements change the retinal image velocity of objects in the visual field. In order to change from a retinocentric frame of reference into a head-centric one, the visual system has to take the eye movements into account. Studies on motion perception during smooth pursuit eye movements have measured either perceived speed or perceived direction during smooth pursuit to investigate this frame of reference transformation, but never both at the same time. We devised a new velocity matching task, in which participants matched both perceived speed and direction during fixation to that during pursuit. In Experiment 1, the velocity matches were determined for a range of stimulus directions, with the head-centric stimulus speed kept constant. In Experiment 2, the retinal stimulus speed was kept approximately constant, with the same range of stimulus directions. In both experiments, the velocity matches for all directions were shifted against the pursuit direction, suggesting an incomplete transformation of the frame of reference. The degree of compensation was approximately constant across stimulus direction. We fitted the classical linear model, the model of Turano and Massof (2001) and that of Freeman (2001) to the velocity matches. The model of Turano and Massof fitted the velocity matches best, but the differences between de model fits were quite small. Evaluation of the models and comparison to a few alternatives suggests that further specification of the potential effect of retinal image characteristics on the eye movement signal is needed. |
Jan L. Souman; Ignace T. C. Hooge; Alexander H. Wertheim Localization and motion perception during smooth pursuit eye movements Journal Article In: Experimental Brain Research, vol. 171, no. 4, pp. 448–458, 2006. @article{Souman2006a, We investigated the relationship between compensation for the effects of smooth pursuit eye movements in localization and motion perception. Participants had to indicate the perceived motion direction, the starting point and the end point of a vertically moving stimulus dot presented during horizontal smooth pursuit. The presentation duration of the stimulus was varied. From the indicated starting and end points, the motion direction was predicted and compared with the actual indicated directions. Both the directions predicted from localization and the indicated directions deviated from the physical directions, but the errors in the predicted directions were larger than those in the indicated directions. The results of a control experiment, in which the same tasks were performed during fixation, suggest that this difference reflects different transformations from a retinocentric to a head-centric frame of reference. This difference appears to be mainly due to an asymmetry in the effect of retinal image motion direction on localization during smooth pursuit. |
Miriam Spering; Karl R. Gegenfurtner; Dirk Kerzel Distractor interference during smooth pursuit eye movements Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 32, no. 5, pp. 1136–1154, 2006. @article{Spering2006, When 2 targets for pursuit eye movements move in different directions, the eye velocity follows the vector average (S. G. Lisberger & V. P. Ferrera, 1997). The present study investigates the mechanisms of target selection when observers are instructed to follow a predefined horizontal target and to ignore a moving distractor stimulus. Results show that at 140 ms after distractor onset, horizontal eye velocity is decreased by about 25%. Vertical eye velocity increases or decreases by 1 degrees /s in the direction opposite from the distractor. This deviation varies in size with distractor direction, velocity, and contrast. The effect was present during the initiation and steady-state tracking phase of pursuit but only when the observer had prior information about target motion. Neither vector averaging nor winner-take-all models could predict the response to a moving to-be-ignored distractor during steady-state tracking of a predefined target. The contributions of perceptual mislocalization and spatial attention to the vertical deviation in pursuit are discussed. |
Minah Suh; Sambrita Basu; Rachel Kolster; Ranjeeta Sarkar; Bruce D. McCandliss; Jamshid Ghajar Increased oculomotor deficits during target blanking as an indicator of mild traumatic brain injury Journal Article In: Neuroscience Letters, vol. 410, no. 3, pp. 203–207, 2006. @article{Suh2006, Given the susceptibility of cerebellar-cortical tracts to shearing injury from traumatic brain injury (TBI), we investigated impairment in the generation of predictive eye movements and its relationship to cognitive deficits in mild TBI patients using a smooth pursuit target-blanking paradigm. Compared to a target-tracking paradigm without blanking, this paradigm more greatly necessitates the generation of predictive eye movements, which are subserved by brain regions involved in cognitive processing. Mild TBI patients showed impaired prediction of target trajectories during target blanking, demonstrated by generation of saccades at earlier and more variable time points, as well as greater and more variable oculomotor error compared to controls. In addition, California Verbal Learning Test (CVLT-II) scores related to working memory, learning, and executive function were more highly correlated with oculomotor variability during target blanking than during target tracking. Our results suggest that a disruption of cerebellar-cortical connections in TBI may account for both oculomotor and cognitive impairment, and that measures of predictive eye movements during target blanking may be a sensitive metric of cognitive deficits after mild TBI. |
Minah Suh; Rachel Kolster; Ranjeeta Sarkar; Bruce D. McCandliss; Jamshid Ghajar Deficits in predictive smooth pursuit after mild traumatic brain injury Journal Article In: Neuroscience Letters, vol. 401, no. 1-2, pp. 108–113, 2006. @article{Suh2006a, Given that even mild traumatic brain injury (TBI) may produce extensive diffuse axonal injury (DAI), we hypothesized that mild TBI patients would show deficits in predictive smooth pursuit eye movements (SPEM), associated with impaired cognitive functions, as these processes are dependent on common white matter connectivity between multiple cerebral and cerebellar regions. The ability to predict target trajectories during SPEM was investigated in 21 mild TBI patients using a periodic sinusoidal paradigm. Compared to 26 control subjects, TBI patients demonstrated decreased target prediction. TBI patients also showed increased eye position error and variability of eye position, which correlated with decreased target prediction. In all subjects, average target prediction, eye position error and eye position variability correlated with scores related to attention and executive function on the California Verbal Learning Test (CVLT-II). However, there were no differences between TBI and control groups in average eye gain or intra-individual eye gain variability, or in performance on the Wechsler Abbreviated Scale of Intelligence (WASI), suggesting that the observed deficits did not result from general oculomotor impairment or reduced IQ. The correlation between SPEM performance and CVLT-II scores suggests that predictive SPEM may be a sensitive assay of cognitive functioning, including attention and executive function. This is the first report to our knowledge that TBI patients show impaired predictive SPEM and eye position variability, and that these impairments correlate with cognitive deficits. |
Benjamin W. Tatler; Roland J. Baddeley; Benjamin T. Vincent The long and the short of it: Spatial statistics at fixation vary with saccade amplitude and task Journal Article In: Vision Research, vol. 46, no. 12, pp. 1857–1862, 2006. @article{Tatler2006, We recorded over 90,000 saccades while observers viewed a diverse collection of natural images and measured low level visual features at fixation. The features that discriminated between where observers fixated and where they did not varied considerably with task, and the length of the preceding saccade. Short saccades (<8°) are image feature dependent, long are less so. For free viewing, short saccades target high frequency information, long saccades are scale-invariant. When searching for luminance targets, saccades of all lengths are scale-invariant. We argue that models of saccade behaviour must account not only for task but also for saccade length and that long and short saccades are targeted differently. |
Patricia E. G. Bestelmeyer; Benjamin W. Tatler; Louise H. Phillips; Gillian Fraser; Philip J. Benson; David St.Clair Global visual scanning abnormalities in schizophrenia and bipolar disorder Journal Article In: Schizophrenia Research, vol. 87, no. 1-3, pp. 212–222, 2006. @article{Bestelmeyer2006, Visual scanning of face images is widely reported to be abnormal in schizophrenia. This impaired processing has been proposed to be partly responsible for patients' disturbance in social interactions. The present study was designed to determine whether abnormal scanning is specific to images with social content or extends to other types of stimuli. Individuals with schizophrenia (n = 22), bipolar disorder (n = 19) and healthy controls (n = 37) were asked to view a series of 28 images with or without socially important content (i.e. faces, landscapes, fractals and noise patterns) while their eye movements were recorded video-oculographically. Temporal and spatial characteristics of scan paths were compared for each patient group and picture type. Independent of image content, patients with schizophrenia exhibited fewer fixations, longer fixation duration, longer saccade duration and peak velocity, and smaller saccade amplitude compared with healthy controls. Patients with schizophrenia and bipolar disorder did not differ significantly from one another on any of the temporal variables recorded. Fixation location distributions of participants with schizophrenia differed significantly from that of healthy controls on all picture types and from patients with bipolar disorder on all but face images. Abnormal scanning in schizophrenia and also bipolar disorder was independent of stimulus type and therefore reflects a global visual scanning impairment not specific to faces. Spatial scanning characteristics but not temporal ones may serve as biomarkers in the functional psychoses. |
Geoffrey Bird; Caroline Catmur; Giorgia Silani; Chris Frith; Uta Frith Attention does not modulate neural responses to social stimuli in autism spectrum disorders Journal Article In: NeuroImage, vol. 31, no. 4, pp. 1614–1624, 2006. @article{Bird2006, We investigated whether individuals with autism spectrum disorders (ASD) would show attentional modulation for social (face) and non-social (house) stimuli. Sixteen individuals with ASD and 16 matched control participants completed a task in which pairs of face and house stimuli were present on every trial, with one of the pairs randomly assigned to attended locations and the other to unattended locations. Both mass-univariate (SPM) and region of interest analyses suggested that responses to houses were modulated by attention in both groups, but that only the control participants demonstrated attentional modulation of face-selective regions. Thus, the participants with ASD demonstrated a lack of attentional modulation which was particularly evident for the social stimulus. Analyses of effective connectivity indicated that these results were due to a failure of attention to modulate connectivity between extrastriate areas and V1. We discuss how these results may suggest a mechanism to explain the reduced salience of social stimuli in ASD. |
Tanya Blekher; S. A. Johnson; James A. R. Marshall; K. White; S. Hui; Marjorie R. Weaver; J. Gray; Robert D. Yee; J. C. Stout; X. Berstian; Joanne Wojcieszek; Tatiana M. Foroud Saccades in presymptomatic and early stages of Huntington disease Journal Article In: Neurology, vol. 67, no. 2, pp. 394–399, 2006. @article{Blekher2006, OBJECTIVE:To evaluate quantitative measures of eye movements as possible biomarkers in prediagnostic and early stages of Huntington disease (HD). METHODS:The study sample (n = 215) included individuals both at risk and recently diagnosed with HD. All participants completed a uniform clinical evaluation which included administration of the Unified Huntington's Disease Rating Scale (UHDRS) by a movement disorder neurologist and molecular testing to determine HD gene status. A high resolution, video-based eye tracking system was employed to quantify measures of eye movement (error rates, latencies, SD of latencies, velocities, and accuracies) during a computerized battery of saccadic and steady fixation tasks. RESULTS:Prediagnostic HD gene carriers and individuals with early HD demonstrated three types of significant abnormalities while performing memory guided and anti-saccade tasks: increased error rate, increased saccade latency, and increased variability of saccade latency. The eye movement abnormalities increased with advancing motor signs of HD. CONCLUSIONS:Abnormalities in eye movement measures are a sensitive biomarker in the prediagnostic and early stages of Huntington disease (HD). These measures may be more sensitive to prediagnostic changes in HD than the currently employed neurologic motor assessment. |
Stephen H. Butler; Iain D. Gilchrist; Casimir J. H. Ludwig; Keith Muir; Monika Harvey Impairments of oculomotor control in a patient with a right temporo-parietal lesion Journal Article In: Cognitive Neuropsychology, vol. 23, no. 6, pp. 990–999, 2006. @article{Butler2006, Goal-driven control over saccade target selection requires the inhibition of task-irrelevant, stimulus-driven saccades. A widely held assumption is that frontal structures are of critical importance for this function. Here we report the oculomotor capture behaviour of a patient with a right temporo-parietal lesion, which challenges this view. T.H. was asked to search for a target among distractors and to signal its location with a saccade. A task-irrelevant, additional distractor appeared with or without abrupt onset, and it was either similar or dissimilar in its colour to the target. Compared to controls, T.H. showed an elevated level of capture overall. He also showed spatial extinction, which was partially overridden by an abrupt onset distractor. These results support the view that effective oculomotor control depends on an intact network of frontal and posterior brain regions. We argue that stimulus-driven and goal-driven signals are computed at different stages, but are ultimately combined in a common functional salience map. |
Nagini Sarvananthan; Frank A. Proudlock; I. Choudhuri; H. Dua; Irene Gottlob Pharmacologic treatment of congenital nystagmus Journal Article In: Archives of Ophthalmology, vol. 124, pp. 916–917, 2006. @article{Sarvananthan2006, Pharmacologic treatment has been used in acquired nystagmus with mixed success. Treatments have included baclofen, sodium valproate, gabapentin, and memantine. However, in congenital nystagmus, little is known about the effect of drugs. We describe a patient with congenital nystagmus and corneal dystrophy who improved dramati- cally with gabapentin treatment. |
T. Shery; Frank A. Proudlock; N. Sarvananthan; Rebecca J. McLean; Irene Gottlob The effects of gabapentin and memantine in acquired and congenital nystagmus: A retrospective study Journal Article In: British Journal of Ophthalmology, vol. 90, no. 7, pp. 839–843, 2006. @article{Shery2006, Background: Pharmacological treatment has been successful in some forms of acquired neurological nystagmus. However, drugs are not known to be effective in idiopathic infantile nystagmus or nystagmus associated with ocular diseases. Methods: The authors retrospectively analysed Snellen visual acuity (VA), subjective visual function, and eye movement recordings of 23 patients with nystagmus (13 secondary to multiple sclerosis, three associated with other neurological diseases, two idiopathic infantile, and five with associated ocular diseases) treated with gabapentin or memantine. Results: With gabapentin, 10 of 13 patients with nystagmus secondary to multiple sclerosis (MS) showed some improvement. Memantine improved the VA in all three patients with MS who did not improve on gabapentin. There was no change of nystagmus in other neurological disorders. Patients with congenital nystagmus showed reduction of nystagmus and their VA changes depended on the ocular pathology. Conclusion: Gabapentin and memantine may be effective in acquired nystagmus secondary to MS. To the authors' knowledge this is the first series of patients showing that gabapentin is effective in improving nystagmus in congenital nystagmus/nystagmus associated with ocular pathology. Memantine may be useful as an alternative drug in treating patients with nystagmus. |
Caroline Tilikete; Ansgar Koene; Norbert Nighoghossian; Alain Vighetto; Denis Pélisson Saccadic lateropulsion in Wallenberg syndrome: A window to access cerebellar control of saccades? Journal Article In: Experimental Brain Research, vol. 174, no. 3, pp. 555–565, 2006. @article{Tilikete2006, Saccadic lateropulsion is characterized by an undershoot of contralaterally directed saccades, an overshoot of ipsilaterally directed saccades and an ipsilateral deviation of vertical saccades. In Wallenberg syndrome, it is thought to result from altered signals in the olivo-cerebellar pathway to the oculomotor cerebellar network. In the current study we aimed to determine whether saccadic lateropulsion results from a cerebellar impairment of motor related signals or visuo-spatial related signals. We studied the trajectory, the accuracy, the direction and the amplitude of a variety of vertical and oblique saccades produced by five patients and nine control subjects. Some results are consistent with previous data suggesting altered motor related signals. Indeed, the horizontal error of contralesional saccades in patients increased with the desired horizontal saccade size. Furthermore, the initial directional error measured during the saccadic acceleration phase was smaller than the global directional error, suggesting that the eye trajectory curved progressively. However, some other results suggest that the processes that specify the horizontal spatial goal of the saccades might be impaired in the patients. Indeed, the horizontal error of ipsilesional saccades in patients did not change significantly with the desired horizontal saccade size. In addition, when comparing saccades with similar intended direction, it was found that the directional error was inversely related to the vertical saccade amplitude. Thus we conclude that the cerebellum might be involved both in controlling the motor execution of saccades and in determining the visuo-spatial information about their goal. |
Waheeda Rahman; Frank A. Proudlock; Irene Gottlob Oral gabapentin treatment for symptomatic Heimann-Bielschowsky Pphenomenon Journal Article In: American Journal of Ophthalmology, vol. 141, pp. 221–222, 2006. @article{Rahman2006, PURPOSE: To describe a patient with symptomatic Heimann-Bielschowsky phenomenon (HBP) treated suc- cessfully with oral gabapentin. DESIGN: Interventional case report. METHODS: A 57-year-old patient with retinitis pigmentosa had a 12-month history of vertical oscillopsia. The right visual acuity was 20/200 and the left visual acuity was 20/60 with glasses. He had a coarse, slow, pendular, vertical movement of the right eye consistent with Heimann- Bielschowsky phenomenon. His treatment commenced with oral gabapentin with gradual increase in dose to 2400 mg/d. Eye movement recordings were performed before and after treatment. RESULTS: He became considerably less symptomatic on gabapentin. The right visual acuity improved to 20/80 with glasses. Eye movement recordings confirmed mark- edly reduced vertical oscillations of the right eye. The patient continues on gabapentin with no side effects and sustained effect. CONCLUSIONS: The vertical nystagmoid movement in HBP can be considerably reduced and symptoms remarkably improved when treated with oral gabapentin. |
Zhong Wang; Louis F. Dell'Osso; Jonathan B. Jacobs; Robert A. Burnstine; Robert L. Tomsak Effects of tenotomy on patients with infantile nystagmus syndrome: Foveation improvement over a broadened visual field Journal Article In: Journal of AAPOS, vol. 10, no. 6, pp. 552–560, 2006. @article{Wang2006a, Purpose: To investigate the effects of four-muscle tenotomy on visual function and gaze angle in patients with infantile nystagmus syndrome (INS). Methods: Eye movements of nine patients with infantile nystagmus were recorded using infrared reflection or high-speed digital video techniques. Experimental protocols were designed to record the patients' eye-movement waveforms, pre- and post-tenotomy, at different gaze angles. We used the eXpanded Nystagmus Acuity Function (NAFX) to measure tenotomy-induced changes in the nystagmus at primary position and various gaze angles. The longest foveation domains (LFD) were measured from fitted curves. Peak-to-peak nystagmus amplitudes and foveation-period durations were also measured. All measurements were made unmasked. Results: All seven patients with narrow, high-NAFX, gaze-angle regions showed broadening of these regions of higher visual function. Three patients showed moderate NAFX improvement (13.9-32.6%) at primary position, five showed large improvement (39.9-162.4%), and one showed no NAFX change (due to his high pretenotomy NAFX). Primary position measured acuities improved in six patients. All patients had reductions in nystagmus amplitudes ranging from 14.6 to 37%. The duration of the foveation period increased in all nine patients (11.2-200%). The percentage improvements in both the NAFX and the LFD decreased with higher pretenotomy values. Conclusions: In addition to elevating primary position NAFX, tenotomy also broadens the high-NAFX regions. This broadening effect is more prominent in patients who had sharp pretenotomy NAFX peaks. Four-muscle tenotomy produces higher primary position NAFX increases in infantile nystagmus patients whose pretenotomy values are relatively low, with the improvement decreasing at higher pretenotomy values. The tenotomy procedure improves visual function beyond primary position acuity. This extends the utility of surgical therapy to several different classes of patients with INS for whom other procedures are contraindicated. The pretenotomy NAFX can now be used to predict both primary position acuity improvements and broadening of a patient's high-NAFX range of gaze angles. © 2006 American Association for Pediatric Ophthalmology and Strabismus. |
Charlotte Golding; C. Danchaivijitr; Timothy L. Hodgson; Sarah J. Tabrizi; Christopher Kennard Identification of an oculomotor biomarker of preclinical Huntington disease Journal Article In: Neurology, vol. 67, no. 3, pp. 485–487, 2006. @article{Golding2006, The authors examined oculomotor function to identify a biomarker of disease progression in genetically confirmed preclinical and early clinical Huntington disease (HD). Initiation deficits of voluntary-guided, but not reflexive, saccades were characteristic of preclinical HD. Saccadic slowing and delayed reflexive saccades were demonstrated in clinical but not preclinical HD. Saccadic measures provide biomarkers of disease progression in both preclinical and early clinical stages of HD. |
Thomas Habekost; Randi Starrfelt Alexia and quadrant-amblyopia: Reading disability after a minor visual field deficit Journal Article In: Neuropsychologia, vol. 44, no. 12, pp. 2465–2476, 2006. @article{Habekost2006, Reading difficulties caused by hemianopia are well described. We present a study of alexia in a patient (NT) with a milder visual field deficit. The patient had suffered a cerebral haemorrhage causing damage to the left occipital cortex and underlying white matter. NT's text reading was slow and prone to error, but recognition of single letters was preserved. Single word reading was accurate, but slower than normal. On perimetric testing NT initially showed an upper right quadrantanopia, but by attending covertly to this quadrant he could achieve luminance detection except in a small scotoma above the reading line. A whole report experiment showed that letter perception was severely compromised in the quadrant, consistent with cerebral amblyopia. On follow-up testing one and a half year post stroke, a clear spontaneous recovery had occurred, reflected in improved text reading with close to normal eye movements. Still, subtle reading difficulties and oculo-motor abnormalities remained. Overall, the study shows how amblyopia in one quadrant can lead to a characteristic form of alexia. |
Jonathan B. Jacobs; Louis F. Dell'Osso; Richard W. Hertle; Gregory M. Acland; Jean Bennett Eye movement recordings as an effectiveness indicator of gene therapy in RPE65-deficient canines: Implications for the ocular motor system Journal Article In: Investigative Ophthalmology & Visual Science, vol. 47, no. 7, pp. 2865–2875, 2006. @article{Jacobs2006, PURPOSE: To perform ocular motility recordings of infantile nystagmus (IN) in RPE65-deficient canines and determine whether they can be used as a motor indicator of restored retinal function to investigate the effects of gene therapy. METHODS: Treated and untreated canines were comfortably suspended in a custom-built sling and encouraged to fixate on distant targets at gaze angles varying between +/-15 degrees horizontally and +/-10 degrees vertically. Ocular motility recordings were made, using two distinct methods-infrared reflection and high-speed video. The resultant recordings from three untreated, four treated, and three pre- and post-treatment dogs were analyzed for using the eXpanded Nystagmus Acuity Function (NAFX), which yields an objective assessment of best potential visual acuity, based on the duration and repeatable accuracy of foveation and centralisation. RESULTS: During fixation, the untreated dogs exhibited large-amplitude, classic IN waveforms, including pendular and jerk in both the horizontal and vertical planes, which prevented them from keeping the targets within the area centralis (the region of highest receptor density, spanning +/-3 degrees horizontally by +/-1.5 degrees vertically, analogous to the fovea). Some untreated dogs also had small-amplitude (0.5-1 degrees), high-frequency (6-9 Hz) oscillations. Under the same conditions, successfully treated canines no longer exhibited clinically detectable IN. Their IN was converted to waveforms with very low amplitudes that yielded higher NAFX values and allowed target images to remain well within the area centralis. Of note, uniocular treatment appeared to damp the IN in both eyes. Behaviorally, the treated dogs were able to successfully navigate through obstacles more easily without inadvertent contact, a task beyond the untreated dogs' ability. CONCLUSIONS: Gene therapy that successfully restored retinal function also reduced the accompanying IN to such a great extent that it was not clinically detectable approximately 90% of the time in many of the dogs. IN improvement, as quantified by the NAFX, is an objective motor indicator of visual improvement due to gene therapy. |
Stamatina A. Kabanarou; Michael D. Crossland; Caren Bellmann; Angela Rees; Louise E. Culham; Gary S. Rubin Gaze changes with binocular versus monocular viewing in age-related macular degeneration Journal Article In: Ophthalmology, vol. 113, no. 12, pp. 2251–2258, 2006. @article{Kabanarou2006, Purpose: To determine and explain gaze changes during binocular versus monocular viewing in patients with age-related macular degeneration (AMD). Design: Cross-sectional study. Participants: Twenty-nine patients with bilateral late-stage AMD. Methods: Distance acuity and fundus pathologic features were evaluated. Eye position was recorded while viewing a circular fixation target under monocular and binocular viewing conditions using an infrared eye tracker (SMI Gazetracker, SensoMotoric, Germany; Eyelink Software 2.04). Gaze changes were quantified by calculating the mean x-coordinate and y-coordinate eye position of the center of the bivariate contour ellipse area for a 30-second fixation task under both viewing conditions. Retinal loci used for monocular fixation for each eye were determined using the scanning laser ophthalmoscope (SLO; SLO 101, Rodenstock, Munich, Germany). Main Outcome Measure: Gaze position. Results: Nine patients showed no shift in gaze position from monocular to binocular viewing. Three patients demonstrated a shift in both eyes, and 17 patients demonstrated a shift in only 1 eye. The mean shift was 4.7±5° (standard deviation). The shift in gaze position in the worse eye was predictive of the distance between the 2 monocular preferred retinal loci (PRLs; better and worse eye; r2= 0.59; P<0.0001), whereas there was no association between the shift in gaze position in the better eye and distance (r2= 0.00; P = 0.91). Conclusions: Most AMD patients shift gaze position in 1 or both eyes when viewing binocularly compared with monocularly. These changes suggest that different retinal locations are used for fixation under the 2 viewing conditions. The SLO data showed that these patients are likely to demonstrate monocular PRLs that fall on noncorresponding areas. These results may have implications for the effective development of eccentric viewing and binocular behavior of AMD patients. |
2005 |
Stamatina A. Kabanarou; C. Bellmann; Michael D. Crossland; Angela Rees; Mary P. Feely; Louise E. Culham; Gary S. Rubin Binocular versus monocular viewing in patients with age-related macular degeneration Journal Article In: International Congress Series, vol. 1282, pp. 613–616, 2005. @article{Kabanarou2005, This paper compares monocular versus binocular viewing in AMD patients during fixation and the potential of binocular function. Twenty-seven patients with bilateral AMD were recruited. A scanning laser ophthalmoscope was used to identify PRLs and map retinal scotomas monocularly. An infrared eye tracker was used to evaluate gaze position changes (and indirectly retinal locus changes) between monocular and binocular fixation. Through their combined use the retinal loci used for fixation under binocular viewing conditions were identified. Binocular function was tested with Bagolini striated glasses and fusion at the PRLs was tested with a computer-driven display. It was found that only five patients used the same PRL to fixate under monocular and binocular conditions for both eyes. 44.4% of the patients with symmetrical scotomas but only one patient with asymmetrical scotomas showed no shift in gaze position. However, there was no difference between them (chi-square |
Willem P. A. Kelders; Gert Jan Kleinrensink; J. N. Van Der Geest; Inger B. Schipper; Louw Feenstra; Chris I. De Zeeuw; Maarten A. Frens The cervico-ocular reflex is increased in whiplash injury patients Journal Article In: Journal of Neurotrauma, vol. 22, no. 1, pp. 133–137, 2005. @article{Kelders2005, Whiplash-associated disorders (WAD) are a major problem in the Western world, which put a formidable financial burden on modern society and which evoke an emerging debate on the true nature of their origin. To date there is no generally accepted test that allows us to diagnose WAD objectively. Because whiplash injury causes dysfunction of proprioception in the neck, we investigated the characteristics of the cervico-ocular reflex (COR) of presumptive WAD patients. These patients and age-matched healthy controls were rotated at different stimulus peak velocities in the dark while their head was fixed in space. The gain values of the COR were significantly increased in the patient population at a wide range of stimulus peak velocities with maximum difference at the lower frequencies (p = 0.037, ANOVA). Hence, although larger numbers of patients should be measured, the COR gain appears to be a parameter that may permit an objective diagnosis of WAD. |
Brian Sullivan; Jelena Jovancevic; Mary Hayhoe; Gwen Sterns Use of gaze in natural tasks in Stargardt's disease: A preferred retinal region Journal Article In: International Congress Series, vol. 1282, pp. 608–612, 2005. @article{Sullivan2005, Use of a preferred retinal locus (PRL) in patients with central scotomas has been extensively investigated in reading. However, less is know about how consistently a PRL is used in ordinary behavior, where high resolution may not always be needed. We investigated eye movements of a Stargardt's disease patient, with bilateral central scotomas, in three tasks in both real and virtual environments. While making a sandwich, the subject predominantly located the object being manipulated in the lower left visual field, scattered over a 20° × 30° region. While catching a ball our subject positioned the ball in the lower left visual quadrant and also exhibited pursuit eye movements driven by the peripheral retina. While walking in a virtual environment, the patient did not use a PRL but instead centered gaze on pedestrians, whose vertical extent surpassed the boundaries of the scotoma. In the natural tasks studied the PRL is very broadly defined and depends on the resolution required for the task. We therefore suggest use of the term "preferred retinal region". |
Shery Thomas; P. Crilehley; M. Lawden; S. Farooq; A. Thomas; Frank A. Proudlock; Cris S. Constantinescu; I. Gottlob Stiff person syndrome with eye movement abnormality, myasthenia gravis, and thymoma Journal Article In: Journal of Neurology, Neurosurgery and Psychiatry, vol. 76, no. 1, pp. 141–142, 2005. @article{Thomas2005, Stiff person syndrome with eye movement abnormality, myasthenia gravis, and thymoma Stiff person syndrome (SPS) is a rare disorder of the central nervous system characterised by progressive fluctuating rigidity and painful spasms of the body musculature. We describe a patient with SPS with positive glutamic acid decarboxylase (GAD) antibodies who developed diplopia. Thymoma was detected by computed tomography (CT), and after thymectomy his symptoms improved. One month after thymectomy, he tested posi- tive for antiacetylcholine receptor (AchR) antibodies. |
Sabira K. Mannan; Dominic J. Mort; Timothy L. Hodgson; Jon Driver; Christopher Kennard; Masud Husain Revisiting previously searched locations in visual neglect: Role of right parietal and frontal lesions in misjudging old locations as new Journal Article In: Journal of Cognitive Neuroscience, vol. 17, no. 2, pp. 340–354, 2005. @article{Mannan2005, Right-hemisphere patients with left neglect often demonstrate abnormal visual search, re-examining stimuli to the right while ignoring those to the left. But re-fixations alone do not reveal if patients misjudge whether they have searched a location before. Here, we not only tracked the eye movements of 16 neglect patients during search, but also asked them to click a response button only when they judged they were fixating a target for the very first time. ‘‘Re-clicking'' on previously found targets would indicate that patients erroneously respond to these as new discoveries. Lesions were mapped with high-resolution MRI. Neglect patients with damage involving the right intraparietal sulcus or right inferior frontal lobe ‘‘re-clicked'' on previously found targets on the right at a pathological rate, whereas those with medial occipito-temporal lesions did not. For the intraparietal sulcus patients, the prob- ability of erroneous reclicks on an old target increased with time since first discovering it; whereas for frontal patients it was independent of search time, suggesting different underlying mechanisms in these two types of patient. Re-click deficits correlated with degree of leftward neglect, mainly due to both being severe in intraparietal cases. These results demonstrate that misjudging previously searched locations for new ones can contribute to pathological search in neglect, with potentially different mechanisms being involved in intraparietal versus inferior frontal patients. When combined with a spatial bias to the right, such deficits might explain why many neglect patients often re-examine rightward locations, at the expense of items to their left. |
Andreas Sprenger; Elisabeth Zils; Holger Rambold; Thurid Sander; Christoph Helmchen Effect of 3,4-diaminopyridine on the postural control in patients with downbeat nystagmus Journal Article In: Annals of the New York Academy of Sciences, vol. 1039, pp. 395–403, 2005. @article{Sprenger2005, Downbeat nystagmus (DBN) is a common, usually persistent ocular motor sign in vestibulocerebellar midline lesions. Postural imbalance in DBN may increase on lateral gaze when downbeat nystagmus increases. 3,4-Diaminopyridine (3,4-DAP) has been shown to suppress the slow-phase velocity component of downbeat nystagmus and its gravity-dependent component with concomitant improvement of oscillopsia. Because the pharmacological effect is thought to be caused by improvement of the vestibulocerebellar Purkinje cell activity, the effect of 3,4-DAP on the postural control of patients with downbeat nystagmus syndrome was examined. Eye movements were recorded with the video-based Eyelink II system. Postural sway and pathway were assessed by posturography in lateral gaze in the light and on eye closure. Two out of four patients showed an improvement of the area of postural sway by 57% of control (baseline) on eye closure. In contrast, downbeat nystagmus in gaze straight ahead and on lateral gaze did not benefit in these two patients, implying a specific influence of 3,4-DAP on the vestibulocerebellar control of posture. It was concluded that 3,4-DAP may particularly influence the postural performance in patients with downbeat nystagmus. |
Tobias Pflugshaupt; Urs P. Mosimann; Roman Von Wartburg; Wolfgang J. Schmitt; Thomas Nyffeler; René M. Müri Hypervigilance-avoidance pattern in spider phobia Journal Article In: Journal of Anxiety Disorders, vol. 19, no. 1, pp. 105–116, 2005. @article{Pflugshaupt2005, Cognitive-motivational theories of phobias propose that patients' behavior is characterized by a hypervigilance-avoidance pattern. This implies that phobics initially direct their attention towards fear-relevant stimuli, followed by avoidance that is thought to prevent objective evaluation and habituation. However, previous experiments with highly anxious individuals confirmed initial hypervigilance and yet failed to show subsequent avoidance. In the present study, we administered a visual task in spider phobics and controls, requiring participants to search for spiders. Analyzing eye movements during visual exploration allowed the examination of spatial as well as temporal aspects of phobic behavior. Confirming the hypervigilance-avoidance hypothesis as a whole, our results showed that, relative to controls, phobics detected spiders faster, fixated closer to spiders during the initial search phase and fixated further from spiders subsequently. |
Keith Rayner; Rebecca L. Johnson Letter-by-letter acquired dyslexia is due to the serial encoding of letters Journal Article In: Psychological Science, vol. 16, no. 7, pp. 530–534, 2005. @article{Rayner2005, Letter-by-letter acquired dyslexia (pure alexia) is assumed to be related to the serial encoding of letters, but the evidence for this assumption is somewhat indirect. Here, we demonstrate that the deficit is indeed due to serial encoding by comparing the performance of a letter-by-letter dyslexic reader with the performance of normal readers who were forced to read letter by letter; the data patterns are remarkably similar. |
Angela Rees; Stamatina A. Kabanarou; Louise E. Culham; Gary S. Rubin Can retinal eccentricity predict visual acuity and contrast sensitivity at the PRL in AMD patients? Journal Article In: International Congress Series, vol. 1282, pp. 694–698, 2005. @article{Rees2005, Most patients with age-related macular degeneration (AMD) and bilateral central scotomas adopt a preferred retinal locus (PRL) for eccentric viewing. It is postulated that the optimal PRL position is inferior visual space as it provides a larger uninterrupted visual span for reading and mobility. However, the majority of patients place their PRL to the left of their scotoma in visual field space. The purpose of this study was to investigate which factors determine PRL location and specifically, whether the PRL develops in the area of peripheral retina with best visual acuity (VA) and contrast sensitivity (CS). 24 patients were recruited. They were tested on a scanning laser ophthalmoscope to identify the PRL in their better eye. An eyetracker was used to assess peripheral VA and CS. In 19 patients, the PRL was located near the area of best VA. In only 11 patients, the PRL was located near the area of best CS. Patients had worse VA and CS at their PRLs compared to normal vision subjects. VA was best near the PRL, but this was not the case for CS. We cannot distinguish whether the PRL develops at the area of best VA or if it improves at the PRL through practice. |
Stefan Hawelka; Heinz Wimmer Impaired visual processing of multi-element arrays is associated with increased number of eye movements in dyslexic reading Journal Article In: Vision Research, vol. 45, no. 7, pp. 855–863, 2005. @article{Hawelka2005, For assessing simultaneous visual processing in dyslexic and normal readers a multi-element processing task was used which required the report of a single digit of briefly presented multi-digit arrays. Dyslexic readers exhibited higher recognition thresholds on 4- and 6-digit, but not on 2-digit arrays. Individual recognition thresholds on the multi-digit arrays were associated with number of eye movements during reading. The dyslexic multi-element processing deficit was not accompanied by deficient coherent motion detection or deficient visual precedence detection and was independent from deficits in phonological awareness and rapid naming. However, only about half of the dyslexic readers exhibited a multi-element processing deficit. |
Jin Rong Liang; Shay Moshel; Ari Z. Zivotofsky; Avi Caspi; Ralf Engbert; Reinhold Kliegl; Shlomo Havlin Scaling of horizontal and vertical fixational eye movements Journal Article In: Physical Review E, vol. 71, no. 3, pp. 1–6, 2005. @article{Liang2005, Eye movements during fixation of a stationary target prevent the adaptation of the photoreceptors to continuous illumination and inhibit fading of the image. These random, involuntary, small, movements are restricted at long time scales so as to keep the target at the center of the field of view. Here we use the Detrended Fluctuation Analysis (DFA) in order to study the properties of fixational eye movements at different time scales. Results show different scaling behavior between horizontal and vertical movements. When the small ballistics movements, i.e. micro-saccades, are removed, the scaling exponents in both directions become similar. Our findings suggest that micro-saccades enhance the persistence at short time scales mostly in the horizontal component and much less in the vertical component. This difference may be due to the need of continuously moving the eyes in the horizontal plane, in order to match the stereoscopic image for different viewing distance. |
Eugene McSorley; Patrick Haggard; Robin Walker Spatial and temporal aspects of oculomotor inhibition as revealed by saccade trajectories Journal Article In: Vision Research, vol. 45, no. 19, pp. 2492–2499, 2005. @article{McSorley2005, The spatial and temporal effect of distractor related inhibition on stimulus elicited (reflexive) and goal driven (voluntary) saccades, was examined using saccade trajectory deviations as a measure. Subjects made voluntary and reflexive saccades to a target location on the vertical midline, while the distance of a distractor from the target was systematically manipulated. The trajectory curvature of both voluntary and reflexive saccades was found to be subject to individual differences. Saccade curvature was found to decrease monotonically with increasing distractor distance from target for some subjects while for others no reduction in curvature or even an increase was found. These results could not be explained by latency differences or landing position effects. The different patterns of distractor effects on saccade trajectories suggest the additional influence of a non-spatial inhibitory mechanism. |
Christian Bellebaum; Irene Daum; B. Koch; M. Schwarz; Klaus-Peter Hoffmann The role of the human thalamus in processing corollary discharge Journal Article In: Brain, vol. 128, no. 5, pp. 1139–1154, 2005. @article{Bellebaum2005, Corollary discharge signals play an important role in monitoring self-generated movements to guarantee spatial constancy. Recent work in macaques suggests that the thalamus conveys corollary discharge information of upcoming saccades passing from the superior colliculus to the frontal eye field. The present study aimed to investigate the involvement of the thalamus in humans by assessing the effect of thalamic lesions on the processing of corollary discharge information. Thirteen patients with selective thalamic lesions and 13 healthy age-matched control subjects performed a saccadic double-step task in which retino-spatial dissonance was induced, i.e. the retinal vector of the second target and the movement vector of the second saccade were different. Thus, the subjects could not rely on retinal information alone, but had to use corollary discharge information to correctly perform the second saccade. The amplitudes of first and second saccades were significantly smaller in patients than in controls. Five thalamic lesion patients showed unilateral deficits in using corollary discharge information, as revealed by asymmetries compared with the other patients and controls. Three patients with lateral thalamic lesions including the ventrolateral nucleus (VL) were impaired contralaterally to the side of damage and one patient with a lesion in the mediodorsal thalamus (MD) was impaired ipsilaterally to the lesion. The largest asymmetry was found in a patient with a bilateral thalamic lesion. The results provide evidence for a thalamic involvement in the processing of corollary discharge information in humans, with a potential role of both the VL and MD nuclei |
Christian Bellebaum; Klaus-Peter Hoffmann; Irene Daum Post-saccadic updating of visual space in the posterior parietal cortex in humans Journal Article In: Behavioural Brain Research, vol. 163, no. 2, pp. 194–203, 2005. @article{Bellebaum2005a, Updating of visual space takes place in the posterior parietal cortex to guarantee spatial constancy across eye movements. However, the timing of updating with respect to saccadic eye movements remains a matter of debate. In the present study, event-related potentials (ERPs) were recorded in 15 volunteers during a saccadic double-step task to elucidate the time course of the updating process. In the experimental condition updating of visual space was required, because both saccade targets had already disappeared before the first saccade was executed. A similar task without updating requirements served as control condition. ERP analysis revealed a significantly larger slow positive wave in the retino-spatial dissonance condition compared to the control condition, starting between 150 and 200 ms after first saccade onset. Source analysis showed an asymmetry with respect to the direction of the first saccade. Whereas the source was restricted to the right PPC in trials with leftward first saccades, left and right PPC were involved in rightward trials. The results of the present study suggest that updating of visual space in a saccadic double-step task occurs not earlier than 150 ms after the onset of the first saccade. We conclude that extraretinal information about the first saccade is integrated with motor information about the second saccade in the inter-saccade interval. |
Anne Lise V. Holahan; Gillian A. O'Driscoll Antisaccade and smooth pursuit performance in positive- and negative-symptom schizotypy Journal Article In: Schizophrenia Research, vol. 76, no. 1, pp. 43–54, 2005. @article{Holahan2005, Schizophrenic patients have well-documented abnormalities in smooth pursuit eye movements and antisaccade performance. In populations at risk for schizophrenia, smooth pursuit abnormalities are also well documented. Antisaccade deficits have been replicated in high-risk populations as well, but the findings are more variable and the reasons for the variability are not clear. Some evidence suggests that antisaccade deficits increase in high-risk populations in relation to the presence of positive symptoms. Whether antisaccade deficits increase in relation to negative symptoms in high-risk populations is relatively uninvestigated. We evaluated antisaccade and pursuit performance in "psychometric schizotypes" who had elevated scores on either the Perceptual Aberration Scale (PerAb; i.e., positive symptoms) or the Physical Anhedonia Scale (PhysAnh; i.e., negative symptoms) but not both, and in normal controls. We used the standard version of the antisaccade task, for which results in positive-symptom schizotypes have previously been reported, and investigated performance on a gap and overlap version. We replicated the finding that a significantly larger percentage of positive-symptom schizotypes than controls have elevated antisaccade error rates on the standard antisaccade task (P=0.03); the percentage of negative-symptom schizotypes with elevated antisaccade error rates did not differ from that of control subjects. Neither schizotypal group was impaired on the gap or overlap versions of the task. On the pursuit task, a higher percentage of positive- and negative-symptom schizotypes were classified as having deviant performance than control subjects (both Ps<0.04). These findings suggest that antisaccade deficits may be better at identifying high-risk subjects with positive symptoms. Pursuit deficits identified both positive- and negative-symptom schizotypes, but was better at identifying the latter. |
Samuel B. Hutton; D. Tegally The effects of dividing attention on smooth pursuit eye tracking Journal Article In: Experimental Brain Research, vol. 163, no. 3, pp. 306–313, 2005. @article{Hutton2005, Attentional processes have traditionally been closely linked to the production of saccadic eye movements, but their role in the control of smooth pursuit eye movements remains unclear. In two experiments we used dual task paradigms to vary the attentional resources available for pursuit eye tracking. In both experiments we found that attentionally demanding secondary tasks impaired smooth pursuit performance, resulting in decreased velocity and increased position error. These findings suggest that attention is important for the maintenance of accurate smooth pursuit, and do not support the hypothesis that pursuit is a relatively automatic function that proceeds optimally in the absence of attentional control. These results add weight to the suggestion that a similar functional architecture underlies both pursuit and saccadic eye movements. |
Dirk Kerzel; Nathalie E. Ziegler Visual short-term memory during smooth pursuit eye movements Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 31, no. 2, pp. 354–372, 2005. @article{Kerzel2005a, Large-scale whole genome association studies are increasingly common, due in large part to recent advances in genotyping technology. With this change in paradigm for genetic studies of complex diseases, it is vital to develop valid, powerful, and efficient statistical tools and approaches to evaluate such data. Despite a dramatic drop in genotyping costs, it is still expensive to genotype thousands of individuals for hundreds of thousands single nucleotide polymorphisms (SNPs) for large-scale whole genome association studies. A multi-stage (or two-stage) design has been a promising alternative: in the first stage, only a fraction of samples are genotyped and tested using a dense set of SNPs, and only a small subset of markers that show moderate associations with the disease will be genotyped in later stages. Multi-stage designs have also been used in candidate gene association studies, usually in regions that have shown strong signals by linkage studies. To decide which set of SNPs to be genotyped in the next stage, a common practice is to utilize a simple test (such as a chi2 test for case-control data) and a liberal significance level without corrections for multiple testing, to ensure that no true signals will be filtered out. In this paper, I have developed a novel SNP selection procedure within the framework of multi-stage designs. Based on data from stage 1, the method explicitly explores correlations (linkage disequilibrium) among SNPs and their possible interactions in determining the disease phenotype. Comparing with a regular multi-stage design, the approach can select a much reduced set of SNPs with high discriminative power for later stages. Therefore, not only does it reduce the genotyping cost in later stages, it also increases the statistical power by reducing the number of tests. Combined analysis is proposed to further improve power, and the theoretical significance level of the combined statistic is derived. Extensive simulations have been performed, and results have shown that the procedure can reduce the number of SNPs required in later stages, with improved power to detect associations. The procedure has also been applied to a real data set from a genome-wide association study of the sporadic amyotrophic lateral sclerosis (ALS) disease, and an interesting set of candidate SNPs has been identified. |
Jochen Laubrock; Ralf Engbert; Reinhold Kliegl Microsaccade dynamics during covert attention Journal Article In: Vision Research, vol. 45, no. 6, pp. 721–730, 2005. @article{Laubrock2005, We compared effects of covert spatial-attention shifts induced with exogenous or endogenous cues on microsaccade rate and direction. Separate and dissociated effects were obtained in rate and direction measures. Display changes caused microsaccade rate inhibition, followed by sustained rate enhancement. Effects on microsaccade direction were differentially tied to cue class (exogenous vs. endogenous) and type (neutral vs. directional). For endogenous cues, direction effects were weak and occurred late. Exogenous cues caused a fast direction bias towards the cue (i.e., early automatic triggering of saccade programs), followed by a shift in the opposite direction (i.e, controlled inhibition of cue-directed saccades, leading to a 'leakage' of microsaccades in the opposite direction). |
Valérie Gaveau; Nadia Alahyane; Roméo Salemme; Michel Desmurget Self-generated saccades do not modify the gain of adapted reactive saccades Journal Article In: Experimental Brain Research, vol. 162, no. 4, pp. 526–531, 2005. @article{Gaveau2005, The gain of reactive saccades was manipulated in 17 subjects using a target-jump paradigm. Following adaptation three sub-groups were formed: (1) rest 15 min in the dark, eyes closed; (2) perform self-generated saccades for 15 min; (3) perform reactive saccades for 15 min. The series of saccades were the same in groups 2 and 3 (amplitude, sequence), except that group 3 performed fewer saccades (same number as the lowest number of saccades performed by one subject in group 2). Neither the rest period nor the series of self-generated saccades affected the adapted gain. The series of reactive saccades generated, by contrast, quick de-adaptation. These results support the conclusion that the gain of self-generated and reactive saccades is independently controlled. |
F. Møller; M. L. Laursen; A. K. Sjølie Binocular fixation topography in patients with diabetic macular oedema: Possible implications for photocoagulation therapy Journal Article In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 243, no. 9, pp. 903–910, 2005. @article{Moeller2005, During retinal photocoagulation for diabetic maculopathy, there is a potential risk of foveal burns, and laser scars may later enlarge to be sight-threatening when involving retinal areas previously used during fixation. Since the retinal area used during binocular steady fixation has been found to vary considerably in the normal test person and central fixation may be even further compromised in patients with diabetic maculopathy, the sight-threatening side effects could possibly be reduced by taking into account the fixation area individually. However, no study has described and quantified the retinal area of fixation binocularly in patients with clinically significant macular oedema (CSME). |
Anna Montagnini; Leonardo Chelazzi The urgency to look: Prompt saccades to the benefit of perception Journal Article In: Vision Research, vol. 45, no. 27, pp. 3391–3401, 2005. @article{Montagnini2005, Researchers have shown that the promptness to initiate a saccade is modulated by countless factors pertaining to the visual context and the task. However, experiments on saccadic eye movements are usually designed in such a way that oculomotor performance is dissociated from the natural role of saccades, namely that of making crucial perceptual information rapidly available for high-resolution, foveal analysis. Here, we demonstrate that the requirement to perform a difficult perceptual judgment at the saccade landing location can reduce saccadic latency (by >15%) and increase saccadic peak velocity. Importantly, the effect cannot be explained in terms of arousal, as latency changes are specific to the location where the perceptual judgement is required. These results indicate that mechanisms for voluntary saccade initiation are under the powerful indirect control of perceptual goals. |
Shay Moshel; Jinrong Liang; Avi Caspi; Ralf Engbert; Reinhold Kliegl; Shlomo Havlin; Ari Z. Zivotofsky Phase-synchronization decay of fixational eye movements Journal Article In: Annals of the New York Academy of Sciences, vol. 1039, pp. 484–488, 2005. @article{Moshel2005, In nonstationary noisy systems the traditional cross-correlation method may not appropriately detect all cases of interdependencies between coupled systems. The phase-synchronization method was previously found use-ful in detecting synchronization in several systems. We here applied the phase-synchronization decay to study the synchronization between six combinations of binocular fixational eye movement components. We found that only two compo-nents were synchronized: the right and left horizontal with each other and the right and left vertical. Furthermore, the vertical-vertical components were much more synchronized than the horizontal. |
Nadia Alahyane; Denis Pélisson Long-lasting modifications of saccadic eye movements following adaptation induced in the double-step target paradigm Journal Article In: Learning and Memory, vol. 12, no. 4, pp. 433–443, 2005. @article{Alahyane2005, The adaptation of saccadic eye movements to environmental changes occurring throughout life is a good model of motor learning and motor memory. Numerous studies have analyzed the behavioral properties and neural substrate of oculomotor learning in short-term saccadic adaptation protocols, but to our knowledge, none have tested the persistence of the oculomotor memory. In the present study, the double-step target protocol was used in five human subjects to adaptively decrease the amplitude of reactive saccades triggered by a horizontally-stepping visual target. We tested the amplitude of visually guided saccades just before and at different times (up to 19 days) after the adaptation session. The results revealed that immediately after the adaptation session, saccade amplitude was significantly reduced by 22% on average. Although progressively recovering over days, this change in saccade gain was still statistically significant on days 1 and 5, with an average retention rate of 36% and 19%, respectively. On day 11, saccade amplitude no longer differed from the pre-adaptation value. Adaptation was more effective and more resistant to recovery for leftward saccades than for rightward ones. Lastly, modifications of saccade gain related to adaptation were accompanied by a decrease of both saccade duration and peak velocity. A control experiment indicated that all these findings were specifically related to the adaptation protocol, and further revealed that no change in the main sequence relationships could be specifically related to adaptation. We conclude that in humans, the modifications of saccade amplitude that quickly develop during a double-step target adaptation protocol can remain in memory for a much longer period of time, reflecting enduring plastic changes in the brain. |
Nadia Alahyane; Denis Pélisson Retention of saccadic adaptation in humans Journal Article In: Annals of the New York Academy of Sciences, vol. 1039, pp. 558–562, 2005. @article{Alahyane2005a, In the present study, we tested in human subjects the persistence of the oculomotor changes resulting from saccadic adaptation up to 19 days after exposure to the double step target protocol. The main results indicate that the reduction of saccade gain related to the adaptation session (mean gain change of 5 subjects = 22 +/- 4.7%) was partially but significantly retained after 1 day and 5 days (mean amount of retention = 36 +/- 17% and 19.7 +/- 13.3%, respectively) but was no longer significant at day 11 and 19. Unexpectedly, gain changes were larger for leftward than for rightward saccades. No change in saccade dynamics was observed. These data suggest that in humans, adaptive mechanisms induce long lasting changes in visually-guided saccade amplitude, probably reflecting plastic changes in the brain. |
Thomas Nyffeler; Tobias Pflugshaupt; Helene Hofer; Uli Baas; Klemens Gutbrod; Roman Von Wartburg; Christian W. Hess; René M. Müri Oculomotor behaviour in simultanagnosia: A longitudinal case study Journal Article In: Neuropsychologia, vol. 43, no. 11, pp. 1591–1597, 2005. @article{Nyffeler2005, The aim of the present single case study was to investigate oculomotor recovery in a patient with simultanagnosia due to biparietal hypoxic lesions. Applying visual exploration as well as basic oculomotor tasks in three consecutive test sessions - i.e. 8 weeks, 14 weeks, and 37 weeks after brain damage had occurred - differential recovery was observed. While visual exploration remarkably improved, an impaired disengagement of attention persisted. The improvement of exploration behaviour is interpreted within an oculomotor network theory and implications for a deficit-specific recovery from simultanagnosia are discussed. |
Leo Trottier; Jay Pratt Visual processing of targets can reduce saccadic latencies Journal Article In: Vision Research, vol. 45, no. 11, pp. 1349–1354, 2005. @article{Trottier2005, Normal human saccadic reaction times (SRTs) have been thought to be approximately 200 ms. The present study, using an experimental method that takes advantage of what the saccade system has evolved to do (by instructing subjects to rapidly acquire detailed visual information from the environment), shows that human SRTs are actually on the order of 150 ms. Moreover, when combined with the sensory-based "gap" effect (removal of gaze fixation object prior to target presentation), this method yielded extremely low SRTs. These findings imply that previous approximations of human SRTs may have been too conservative, and that the group of saccades often classified as "express" may instead represent the norm. |
Loes C. J. Dam; Raymond Ee The role of (micro)saccades and blinks in perceptual bi-stability from slant rivalry Journal Article In: Vision Research, vol. 45, no. 18, pp. 2417–2435, 2005. @article{Dam2005, We exposed the visual system to an ambiguous 3D slant rivalry stimulus consisting of a grid for which monocular (perspective) and binocular (disparity) cues independently specified a slant about a horizontal axis. When those cues specified similar slants, observers perceived a single slant. When the difference between the specified slants was large, observers alternatively perceived a perspective- or a disparity-dominated slant. Eye movement measurements revealed that there was no positive correlation between a perceptual flip and both saccades (microsaccades as well as larger saccades) and blinks that occurred prior to a perceptual flip. We also found that changes in horizontal vergence were not responsible for perceptual flips. Thus, eye movements were not essential to flip from one percept to the other. After the moment of a perceptual flip the occurrence probabilities of both saccades and blinks were reduced. The reduced probability of saccades mainly occurred for larger voluntary saccades, rather than for involuntary microsaccades. We suggest that the reduced probability of voluntary saccades reflects a reset of saccade planning. |
Brian J. White; Karl R. Gegenfurtner; Dirk Kerzel Effects of structured nontarget stimuli on saccadic latency Journal Article In: Journal of Neurophysiology, vol. 93, no. 6, pp. 3214–3223, 2005. @article{White2005, It has been suggested that the remote distractor effect is the result of nontarget stimulation of a central region representing a collicular fixation zone near the time of target onset. The distributed network of the cells responsible for this effect is believed to extend over a large area, responding to distractors < or =10 deg in the periphery. Several studies also implicate the superior colliculus as the substrate behind an inhibited saccadic response arising from a display change. We investigated this further by using a patch of pink noise of various sizes as a nontarget stimulus. We show that the onset of a small patch (2.3 x 2.3 deg) of centrally displayed pink noise can produce a significant increase in saccadic latency to a simultaneously presented peripheral Gabor target. In contrast, a large patch (36 x 36 deg) of pink noise did not increase latency despite the fact that it also stimulated the region representing the fixation zone. Furthermore, only the large patch of noise facilitated latency when presented before target onset. We also examined the effect of patch sizes between these two extremes and found a steady decrease in latency as patch size increased. This confirms that nontarget stimulation of the region representing the fixation zone near the time of target onset is not in itself sufficient to produce the increase in latency typically found with remote distractors. The results are consistent with the idea that only a spatially confined object leads to a discharge of collicular fixation neurons. |
John F. Soechting; Leigh A. Mrotek; Martha Flanders Smooth pursuit tracking of an abrupt change in target direction: Vector superposition of discrete responses Journal Article In: Experimental Brain Research, vol. 160, no. 2, pp. 245–258, 2005. @article{Soechting2005, The directional control of smooth pursuit eye movements was studied by presenting human subjects with targets that moved in a straight line at a constant speed and then changed direction abruptly and unpredictably. To minimize the probability of saccadic responses in the interval following the target's change in direction, target position was offset so as to eliminate position error after the reaction time. Smooth pursuit speed declined at a latency of 90 ms, whereas the direction of smooth pursuit began to change later (130 ms). The amplitude of the offset in target position did not affect the subsequent smooth pursuit response. In other experiments, the target's speed or acceleration was changed abruptly at the time of the change in direction. Step changes in speed elicited short-latency responses in smooth pursuit tracking but step changes in acceleration did not. In all instances, the earliest component of the response did not depend on the parameters of the stimulus. The data were fit with a model in which smooth pursuit resulted from the vector addition of two components, one representing a response to the arrest of the initial target motion and the other the response to the onset of target motion in the new direction. This model gave an excellent fit but further analysis revealed nonlinear interactions between the two vector components. These interactions represented directional anisotropies both in terms of the initial tracking direction (which was either vertical or 45 degrees ) and in terms of the cardinal directions (vertical and horizontal). |
Jan L. Souman; Ignace T. C. Hooge; Alexander H. Wertheim Perceived motion direction during smooth pursuit eye movements Journal Article In: Experimental Brain Research, vol. 164, no. 3, pp. 376–386, 2005. @article{Souman2005, Although many studies have been devoted to motion perception during smooth pursuit eye movements, relatively little attention has been paid to the question of whether the compensation for the effects of these eye movements is the same across different stimulus directions. The few studies that have addressed this issue provide conflicting conclusions. We measured the perceived motion direction of a stimulus dot during horizontal ocular pursuit for stimulus directions spanning the entire range of 360 degrees. The stimulus moved at either 3 or 8 degrees/s. Constancy of the degree of compensation was assessed by fitting the classical linear model of motion perception during pursuit. According to this model, the perceived velocity is the result of adding an eye movement signal that estimates the eye velocity to the retinal signal that estimates the retinal image velocity for a given stimulus object. The perceived direction depends on the gain ratio of the two signals, which is assumed to be constant across stimulus directions. The model provided a good fit to the data, suggesting that compensation is indeed constant across stimulus direction. Moreover, the gain ratio was lower for the higher stimulus speed, explaining differences in results in the literature. |
Jan L. Souman; Ignace T. C. Hooge; Alexander H. Wertheim Vertical object motion during horizontal ocular pursuit: Compensation for eye movements increases with presentation duration Journal Article In: Vision Research, vol. 45, no. 7, pp. 845–853, 2005. @article{Souman2005a, Smooth pursuit eye movements change the retinal image motion of objects in the visual field. To enable an observer to perceive the motion of these objects veridically, the visual system has to compensate for the effects of the eye movements. The occurrence of the Filehne-illusion (illusory motion of a stationary object during smooth pursuit) shows that this compensation is not always perfect. The amplitude of the illusion appears to decrease with increasing presentation durations of the stationary object. In this study we investigated whether presentation duration has the same effect when an observer views a vertically moving object during horizontal pursuit. In this case, the pursuit eye movements cause the perceived motion path to be oblique instead of vertical; this error in perceived motion direction should decrease with higher presentation durations. In Experiment 1, we found that the error in perceived motion direction indeed decreased with increasing presentation duration, especially for higher pursuit velocities. The results of Experiment 2 showed that the error in perceived motion direction did not depend on the moment during pursuit at which the stimulus was presented, suggesting that the degree of compensation for eye movements is constant throughout pursuit. The results suggest that longer presentation durations cause the eye movement signal that is used by the visual system to increase more than the retinal signal. |
Miriam Spering; Dirk Kerzel; Doris I. Braun; Michael J. Hawken; Karl R. Gegenfurtner Effects of contrast on smooth pursuit eye movements Journal Article In: Journal of Vision, vol. 5, pp. 455–465, 2005. @article{Spering2005, It is well known that moving stimuli can appear to move more slowly when contrast is reduced (P. Thompson, 1982). Here we address the question whether changes in stimulus contrast also affect smooth pursuit eye movements. Subjects were asked to smoothly track a moving Gabor patch. Targets varied in velocity (1, 8, and 15 deg/s), spatial frequency (0.1, 1, 4, and 8 c/deg), and contrast, ranging from just below individual thresholds to maximum contrast. Results show that smooth pursuit eye velocity gain rose significantly with increasing contrast. Below a contrast level of two to three times threshold, pursuit gain, acceleration, latency, and positional accuracy were severely impaired. Therefore, the smooth pursuit motor response shows the same kind of slowing at low contrast that was demonstrated in previous studies on perception |
Michael D. Crossland; Louise E. Culham; Stamatina A. Kabanarou; Gary S. Rubin Preferred retinal locus development in patients with macular disease Journal Article In: Ophthalmology, vol. 112, no. 9, pp. 1579–1585, 2005. @article{Crossland2005, Objective: To observe the development of the preferred retinal locus (PRL) in a group of patients with central scotomas caused by recent onset macular disease (MD). Design: Prospective observational case series. Participants: Twenty-five individuals with bilateral central scotomas caused by MD. All patients had experienced visual loss in their better eye in the 2 weeks before recruitment. Methods: Patients were assessed at baseline and at 4 further visits for up to 12 months. At each visit, the retinal area used for fixation was assessed using a scanning laser ophthalmoscope, the infrared Gazetracker was used to determine the number of discrete retinal areas used for fixation in 5 positions of gaze, and reading speed was measured using MN-Read-style sentences. Results: All 25 patients developed a PRL within 6 months. Sixteen patients (64%) made an adaptation whereby they were unaware of using an eccentric retinal area for fixation. Multiple fixation loci were exhibited by 11 patients at the end of the study. Nineteen patients used a consistent number of PRLs under all positions of gaze. Reading speed was not associated with PRL location or the presence of multiple PRLs. Conclusions: All of the patients in this study developed a repeatable preferred retinal locus within 6 months of visual loss in their second affected eye. Reading performance was better in patients who were not aware of using eccentric viewing strategies and who used a repeatable number of PRLs under all positions of gaze. These findings are relevant for counseling patients with MD and for the design of rehabilitation programs for patients with central vision loss. |
Michael D. Crossland; Louise E. Culham; Gary S. Rubin Reading speed and the perceptual span in patients with macular disease Journal Article In: International Congress Series, vol. 1282, pp. 498–501, 2005. @article{Crossland2005a, This presentation describes the results of a longitudinal assessment of the perceptual span, eye movements and reading speed in a group of patients with macular disease (MD). Eighteen patients with MD were recruited. All patients had developed a scotoma in their second affected eye in the 2 weeks prior to recruitment. Patients were assessed within 2 weeks of recruitment and again 3-12 months later. Eye movements were recorded whilst reading MN-Read style sentences using an infra-red gazetracker. Perceptual span was closely related to reading speed at the first (r2= 0.53, p < 0.001) and the second visit (r2= 0.72, p < 0.0001). In some patients the perceptual span changed by as much as two letters. Changes in the perceptual span were strongly related to change in reading speed (r2= 0.43, p < 0.005). These results lend support to the hypothesis that a reduced perceptual span is one cause of impaired reading in patients with macular disease. These results are relevant to the development of rehabilitation and training programs for patients with macular disease. |
2004 |
Michael D. Crossland; Louise E. Culham; Gary S. Rubin Fixation stability and reading speed in patients with newly developed macular disease. Journal Article In: Ophthalmic and Physiological Optics, vol. 24, pp. 327–333, 2004. @article{Crossland2004a, Background: Patients with macular disease and central scotomas must use a peripheral, preferred retinal locus (PRL) in place of their damaged fovea. This paper investigates the development of the PRL, with particular reference to the stability of fixation. Methods: Twenty-five patients with age-related and juvenile macular disease were recruited. All patients had developed a scotoma in their better eye within the previous 2 weeks. Patients were assessed using a scanning laser ophthalmoscope and an infra-red gazetracker on four further occasions over the next 12 months. Results: A linear relationship exists between reading speed and fixation stability for patients and control subjects. Fixation stability was not related to scotoma size, visual acuity or contrast sensitivity. Changes in fixation stability account for 54% of the variance in change in reading speed over the course of this study. Conclusions: The deficit in reading speed in patients with macular disease can be partially attributed to impairments in fixation stability. |
Michael D. Crossland; M. Sims; R. F. Galbraith; Gary S. Rubin Evaluation of a new quantitative technique to assess the number and extent of preferred retinal loci in macular disease Journal Article In: Vision Research, vol. 44, no. 13, pp. 1537–1546, 2004. @article{Crossland2004, Patients with scotomas due to macular disease may use more than one preferred retinal locus (PRL) for fixation. We have developed and evaluated an objective, quantitative technique to determine the number of PRLs used during an episode of fixation and the extent of each locus. In five of eight adults with macular disease our techniques consistently indicated the presence of multiple PRLs. Patients with multiple PRLs were more likely to have suffered recent vision loss in the tested eye. Our technique describes fixation more fully than the traditional method of calculating a single bivariate contour ellipse area. |
Caren Bellmann; Mary P. Feely; Michael D. Crossland; Stamatina A. Kabanarou; Gary S. Rubin Fixation stability using central and pericentral fixation targets in patients with age-related macular degeneration Journal Article In: Ophthalmology, vol. 111, no. 12, pp. 2265–2270, 2004. @article{Bellmann2004, To determine fixation stability for central and pericentral fixation targets in patients with age-related macular degeneration (AMD). Comparative study. Twelve patients having late-stage AMD involving the fovea and 10 age-matched controls having no other eye diseases and visual acuity better than 20/25. Six different fixation targets (1°cross; 1°filled circle; 1°letter x; small 4-point diamond; large 4-point diamond using dimensions as in a field analyzer; large-crossover whole-image diagonal with open 1°center) were presented on a high-resolution monitor. Before examination, subjects were given verbal instructions to move their eye to see the center of the target best. Fixation stability was measured for the preferred eye, with the fellow eye occluded, using a gaze tracker. Fixation stability was quantified by calculating the bivariate contour ellipse area (BCEA) over 30 seconds for each target. For statistical analysis, BCEA values (minutes of arc2) were converted into their logarithms. The absolute retinal scotoma for the study eye was determined using a scanning laser ophthalmoscope. Bivariate contour ellipse area. Visual acuity in patients (age range, 57-87 years) ranged from 20/32 to 20/600. The lowest BCEA values were found for the 1°letter x in patients (mean, 12052.2%±254.0%) and for the 1°cross in normal subjects (mean, 1286.9%±47.8%); the highest BCEA values were found for the small 4-point diamond in patients (mean, 23109.5%±298.3%) and for the large 4-point diamond in normals (age range, 62-79 years) (mean, 3229.2%±105.4%). The difference between the targets was significant for normal subjects (analysis of variance [ANOVA], P<0.01) but not for patients (ANOVA, P>0.05). In normals, BCEA values were significantly lower for central fixation targets than for pericentral fixation targets (P<0.01). Fixation is significantly less stable for pericentral fixation targets in normal subjects, indicating an advantage for central fixation targets. These results are particularly significant for any clinical and experimental testing method that requires the patient to maintain stable fixation. |
T. M. Blekher; Robert D. Yee; S. C. Kirkwood; A. M. Hake; J. C. Stout; Marjorie R. Weaver; Tatiana M. Foroud Oculomotor control in asymptomatic and recently diagnosed individuals with the genetic marker for Huntington's disease Journal Article In: Vision Research, vol. 44, no. 23, pp. 2729–2736, 2004. @article{Blekher2004, We compared oculomotor control among individuals in the early stages of Huntington’s disease (HD), with that of individuals who are presymptomatic HD gene carriers (PSGC) and nongene carriers (NGC). The oculomotor testing paradigm included both traditional tests and a novel experimental procedure to assess visual scanning. Traditional tests elicited saccades, pursuit and optokinetic nystagmus (OKN). HD patients demonstrated marked delay in the initiation of volitional saccades (anti-saccade and memory-guided saccades), a reduced number of correct volitional saccades, reduced velocity of saccades, and a decreased OKN gain. We also studied visual scanning while the participants completed the Digit Symbol Subscale of the Wechsler Adult Intelligence Survey-Revised (WAIS-R). The HD participants demonstrated an abnormal gaze strategy, which may be associated with attention and/or planning deficits.Differences between the PSGC and NGC groups were only observed for two measures: PSGC had a decreased number of memory-guided saccades and a subtle delay in the initiation of volitional saccades. Our results suggest that oculomotor measures are a sensitive biomarker in the early stage of HD and demonstrate that the combination of more traditional oculomotor tests with visual scanning tests is useful in the evaluation of visual performance. © 2004 Elsevier Ltd. All rights reserved. |
Jay Pratt; Jiye Shen; Jos J. Adam The planning and execution of sequential eye movements: Saccades do not show the one target advantage Journal Article In: Human Movement Science, vol. 22, no. 6, pp. 679–688, 2004. @article{Pratt2004, The present experiment examined the one-target advantage (OTA) with regard to saccadic eye movements. The OTA, previously found with manual pointing responses, refers to the finding that movements are executed faster when the limb is allowed to stop on the target compared to the situation where it has to proceed and hit a second target. Using an adapted limb movement OTA task, saccades of 5° and 15° were made to (a) a single target (one-target), (b) one target and immediately to another target without a change in direction (two-target-extension), and (c) one target and immediately back to the start location (two-target-reversal). Unlike manual movements, the movement times for the initial saccade in the two-target-extension condition were not prolonged compared to either of the other two conditions. Moreover, this pattern of results was found for both the shorter and longer amplitude saccades. The results indicate that the OTA does not occur in the oculomotor system and therefore is not a general motor control phenomenon. |
Eyal M. Reingold; Dave M. Stampe Saccadic inhibition in reading Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 30, no. 1, pp. 194–211, 2004. @article{Reingold2004, In 5 experiments, participants read text that was briefly replaced by a transient image for 33 ms at random intervals. A decrease in saccadic frequency, referred to as saccadic inhibition, occurred as early as 60-70 ms following the onset of abrupt changes in visual input. It was demonstrated that the saccadic inhibition was influenced by the saliency of the visual event (Experiment 3) and was not produced in response to abrupt but irrelevant auditory stimuli (Experiment 1). Display changes restricted to an area either inside or outside the perceptual span required for normal reading produced strong saccadic inhibition (Experiment 2). Finally, Experiments 4 and 5 demonstrated higher level cognitive or attentional modulation of the saccadic inhibition effect. |
Millard Reschke; Jeffrey T. Somers; R. John Leigh; Jody M. Krnavek; Ludmila Kornilova; Inessa Kozlovskaya; Jacob J. Bloomberg; William H. Paloski Sensorimotor recovery following spaceflight may be due to frequent square-wave saccadic intrusions Journal Article In: Aviation Space and Environmental Medicine, vol. 75, no. 8, pp. 700–704, 2004. @article{Reschke2004, Square-wave jerks (SWJs) are small, involuntary saccades that disrupt steady fixation. We report the case of an astronaut (approximately 140 d on orbit) who showed frequent SWJs, especially postflight, but who showed no impairment of vision or decrement of postflight performance. These data support the view that SWJs do not impair vision because they are paired movements, consisting of a small saccade away from the fixation position followed, within 200 ms, by a corrective saccade that brings the eye back on target. Since many returning astronauts show a decrement of dynamic visual function during postflight locomotion, it seems possible that frequent SWJs improved this astronaut's visual function by providing postsaccadic enhancement of visual fixation, which aided postflight performance. Certainly, frequent SWJs did not impair performance in this astronaut, who had no other neurological disorder. |
D. C. Rijkaart; Josef N. Geest; Willem P. A. Kelders; Chris I. De Zeeuw; Maarten A. Frens Short-term adaptation of the cervico-ocular reflex Journal Article In: Experimental Brain Research, vol. 156, no. 1, pp. 124–128, 2004. @article{Rijkaart2004, The cervico-ocular reflex (COR) works in conjunction with the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) in order to prevent visual slip over the retina during head movement. The COR induces eye movements in response to proprioceptive signals from the neck. We investigated whether the COR gain can be adapted by inducing a mismatch between vision and neck proprioception, in analogy to VOR adaptation. Thirteen healthy subjects were rotated in the dark in a trunk-to-head manner (the head fixed in space while the body passively rotated sinusoidally with a peak velocity of 1.25 degrees /s). Eye movements were recorded with infrared video-oculography under various adaptive conditions. Analysis showed a small but significant reduction in COR gain in the suppression conditions. This means that the cervico-ocular reflex can be modified after only 10 min of concurrent visual and cervical stimulation. |
Martin Rolfs; Ralf Engbert Microsaccade orientation supports attentional enhancement opposite a peripheral cue Journal Article In: Psychological Science, vol. 15, no. 10, pp. 705–707, 2004. @article{Rolfs2004, Tse, Sheinberg, and Logothetis (2003) exploited a change-blindness paradigm to map the redistribution of spatial attention in response to a peripherally flashed cue. The probability of change detection at a given location was used as a measure of attention allocation. Using this measure, a ‘‘hot spot'' of attention (i.e., close to perfect change detection) was found along the cue-fixation axis. This hot spot ex- tended in the hemifield opposite the cued location. Here we show that an analysis of fixational eye movements in a spatial-cuing paradigm supports this important finding. During fixation of a stationary target, micromovements of the eyes occur involuntarily. These fixational eye movements are classified as drift, tremor, and microsaccades. Microsaccades are the fastest of these three components, with amplitudes typically smaller than 11 of visual angle. Using a classical spatial-cuing paradigm (Posner, 1980) with central arrow cues indicating the most probable location of a later target, we recently demonstrated that microsaccades are modulated by visual attention (Engbert & Kliegl, 2003b). About 300 ms after cue presentation, the angular distribution of microsaccades was oriented toward the expected target location. In the study reported here, we used pilot data from a larger ex- perimental study to examine the impact of peripheral cues on the rate and orientation of microsaccades. Using peripheral flashes—similar to the uninformative stimuli employed by Tse et al. (2003)—we found an orientation shift of microsaccades in the direction opposite the cued location. Taken together with our results on the coupling of visuo- spatial attention and microsaccades (Engbert & Kliegl, 2003b), these results are in agreement with the attentional enhancement opposite the cued location observed by Tse et al. (2003). |
Gerben Rotman; Eli Brenner; Jeroen B. J. Smeets Mislocalization of targets flashed during smooth pursuit depends on the change in gaze direction after the flash Journal Article In: Journal of Vision, vol. 4, pp. 564–574, 2004. @article{Rotman2004, Subjects mislocalize the position of a target that is flashed while they are making pursuit eye movements. This mislocalization is in the direction of pursuit. However, it is not clear whether it is the movement of the eyes or the movement of the pursuit target that matters. Neither is it clear whether it is the movement after the flash or the movement before the flash that matters. To resolve these issues, we asked subjects to pursue a disk that regularly changed its movement direction. Each change was followed by a change in the direction of gaze movement. Subjects were asked to tap targets that were flashed close to the moment at which the pursuit disk changed direction. We measured the movements of the eyes, head, and index finger. Subjects did not make saccades to the position they tapped but kept pursuing the disk. We compared the direction of the mislocalization with the changes in gaze and in target position during different intervals relative to the flash. We found that the mislocalization is related to the change in gaze after the flash. |
Sonja Stork; Jochen Müsseler Perceived localizations and eye movements with action-generated and computer-generated vanishing points of moving stimuli Journal Article In: Visual Cognition, vol. 11, no. 2-3, pp. 299–314, 2004. @article{Stork2004, When observers localize the vanishing point of a moving target, localizations are reliably displaced beyond the final position, in the direction the stimulus was travelling just prior to its offset. We examined modulations of this phenomenon through eye movements and action control over the vanishing point. In Experiment 1 with pursuit eye movements, localization errors were in movement direction, but less pronounced when the vanishing point was self-determined by a key press of the observer. In contrast, in Experiment 2 with fixation instruction, localization errors were opposite movement direction and independent from action control. This pattern of results points at the role of eye movements, which were gathered in Experiment 3. That experiment showed that the eyes lagged behind the target at the point in time, when it vanished from the screen, but that the eyes continued to drift on the targets' virtual trajectory. It is suggested that the perceived target position resulted from the spatial lag of the eyes and of the persisting retinal image during the drift. |
Urs P. Mosimann; J. Felblinger; P. Ballinari; Christian W. Hess; René M. Müri Visual exploration behaviour during clock reading in Alzheimer's disease Journal Article In: Brain, vol. 127, no. 2, pp. 431–438, 2004. @article{Mosimann2004, Eye movement behaviour during visual exploration of 24 patients with probable Alzheimer's disease and 24 age-matched controls was compared in a clock reading task. Controls were found to focus exploration on distinct areas at the end of each clock hand. The sum of these two areas of highest fixation density was defined as the informative region of interest (ROI). In Alzheimer's disease patients, visual exploration was less focused, with fewer fixations inside the ROI, and the time until the first fixation was inside the ROI was significantly delayed. Changes of fixation distribution correlated significantly with the ability to read the clock correctly, but did not correlate with dementia severity. In Alzheimer's disease patients, fixations were longer and saccade amplitudes were smaller. The altered visual exploration in Alzheimer's disease might be related to parietal dysfunction or to an imbalance between a degraded occipito-parietal and relatively preserved occipito-temporal visual network. |
Wieske Zoest; Mieke Donk; Jan Theeuwes The role of stimulus-driven and goal-driven control in saccadic visual selection Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 30, no. 4, pp. 746–759, 2004. @article{Zoest2004, Four experiments were conducted to investigate the role of stimulus-driven and goal-driven control in saccadic eye movements. Participants were required to make a speeded saccade toward a predefined target presented concurrently with multiple nontargets and possibly 1 distractor. Target and distractor were either equally salient (Experiments 1 and 2) or not (Experiments 3 and 4). The results uniformly demonstrated that fast eye movements were completely stimulus driven, whereas slower eye movements were goal driven. These results are in line with neither a bottom-up account nor a top-down notion of visual selection. Instead, they indicate that visual selection is the outcome of 2 independent processes, one stimulus driven and the other goal driven, operating in different time windows. |
Christoph Helmchen; Andreas Sprenger; Holger Rambold; Thurid Sander; D. Kompf; D. Straumann Effect of 3,4-diaminopyridine on the gravity dependence of ocular drift in downbeat nystagmus Journal Article In: Neurology, vol. 63, no. 4, pp. 752, 2004. @article{Helmchen2004, The pathomechanism of downbeat nystagmus (DBN) remains controversial but each mechanism has to account for 1) its gaze-evoked vertical centripetal component which increases on down and lateral gaze,¹ and 2) the vertical bias component of the upward slow phase velocity (SPV) in gaze straight ahead. The vertical velocity bias of DBN has a gravity-dependent component which leads to maximal drift velocity when patients lie in prone position and minimal in supine position.² Recently, 3,4- diaminopyridine (3,4-DAP)³ has been shown to be effective in reducing DBN in patients with their heads upright. However, DBN of several of those patients showed only small changes. One reason might be that gravity-dependent mechanisms were not considered. |
Paresh Malhotra; Sabira K. Mannan; Jon Driver; Masud Husain Special section impaired spatial working memory: One component of the visual neglect syndrome ? Journal Article In: Cortex, vol. 40, no. 4-5, pp. 667–676, 2004. @article{Malhotra2004, Both impaired spatial working memory (SWM) and unilateral neglect may follow damage to the right parietal lobe. We propose that impaired SWM can exacerbate visual neglect, due to failures in remembering locations that have already been searched. When combined with an attentional bias to the ipsilesional right side, such a SWM impairment should induce recursive search of ipsilesional locations. Here we studied a left neglect patient with a right temporoparietal haemorrhage. On a nonlateralised, purely vertical SWM task, he was impaired in retaining spatial locations. In a visual search task, his eye position was monitored while his spatial memory was probed. He recursively searched through right stimuli, re-fixating previously inspected items, and critically treated them as if they were new discoveries, consistent with the SWM deficit. When his recovery was tracked over several months, his SWM deficit and left neglect showed concurrent improvements. We argue that impaired SWM may be one important component of the visual neglect syndrome. |
Josef N. Geest; Gerardina C. Lagers-van Haselen; J. M. Hagen; L. C. P. Govaerts; I. F. M. Coo; Chris I. De Zeeuw; Maarten A. Frens Saccade dysmetria in Williams-Beuren syndrome Journal Article In: Neuropsychologia, vol. 42, no. 5, pp. 569–576, 2004. @article{Geest2004, Numerous studies have described the poor visuo-spatial processing capacities of subjects with Williams-Beuren syndrome (WBS), a genetically based developmental disorder. Since visual perception and eye movements are closely related we hypothesized that the poor visuo-spatial processing capacities of subjects with WBS might be related to a poor saccadic control. Thereto, we recorded horizontal and vertical saccadic eye movements to targets using infrared video-oculography in 27 subjects with WBS and eight healthy controls. In the WBS group saccadic gains were highly variable, both between and within individual subjects, and they often needed more than one correction saccade to reach the target. Ten (out of a subgroup of 22) WBS subjects showed a large number of hypometric and/or hypermetric saccades, and, also a left-right asymmetry in saccadic gains was observed in WBS. We conclude that the observed impairments in saccadic control are likely to affect the proper processing of visuo-spatial information. |
Tobias Pflugshaupt; Stefanie Almoslöchner Bopp; Dörthe Heinemann; Urs P. Mosimann; Roman Von Wartburg; Thomas Nyffeler; Christian W. Hess; René M. Müri Residual oculomotor and exploratory deficits in patients with recovered hemineglect Journal Article In: Neuropsychologia, vol. 42, no. 9, pp. 1203–1211, 2004. @article{Pflugshaupt2004, Several studies on hemineglect have reported that patients recover remarkably well when assessed with neuropsychological screening tests, however, they show deficits on novel or complex tasks. We investigated whether such deficits can be revealed with eye movement analysis, applying two basic oculomotor tasks as well as two exploratory tasks. Eye movements were recorded in eight hemineglect patients at least eleven months after right-hemisphere brain damage had occurred. Sixteen healthy volunteers participated in the control group. Regarding the basic oculomotor tasks, only the overlap task revealed residual deficits in patients, suggesting that a directional deficit in disengaging attention persisted during recovery. Further residual deficits were evident in the exploratory tasks. When everyday scenes were explored, patients showed a bias in early orienting towards the ipsilateral hemispace. In a search task, they demonstrated the same orienting bias as well as a non-directional deficit concerning search times. Moreover, patients preferentially fixated in the contralateral hemispace, but did not benefit from this asymmetry in terms of search times, i.e. they did not detect contralateral targets faster than ipsilateral ones. This suggests a dissociation between oculomotor processes and attentional ones. In conclusion, we have identified behavioural aspects that seem to recover slower than others. A disengagement deficit and biases in early orienting have been the most pronounced residual oculomotor deficits. |
Lars Michels; Markus Lappe Contrast dependency of saccadic compression and suppression Journal Article In: Vision Research, vol. 44, no. 20, pp. 2327–2336, 2004. @article{Michels2004, In the occurrence of a saccadic eye movement vision becomes suppressed. Supra-threshold visual stimuli that are briefly presented at that time become perceptually compressed towards the saccade target (saccadic compression) and shifted in saccade direction (saccadic shift). We show that the strength of saccadic compression, like the strength of saccadic suppression, varies with stimulus contrast. Low contrast stimuli lead to stronger compression than high contrast stimuli. The similarity of contrast dependence and time course suggests that saccadic compression is related to saccadic suppression. Because the saccadic shift did not depend on contrast we suggest that shift and compression are different effects. |
Nadia Alahyane; Ansgar Koene; Denis Pélisson Transfer of adaptation from visually guided saccades to averaging saccades elicited by double visual targets Journal Article In: European Journal of Neuroscience, vol. 20, no. 3, pp. 827–836, 2004. @article{Alahyane2004a, The adaptive mechanisms that control the amplitude of visually guided saccades (VGS) are only partially elucidated. In this study, we investigated, in six human subjects, the transfer of VGS adaptation to averaging saccades elicited by the simultaneous presentation of two visual targets. The generation of averaging saccades requires the transformation of two representations encoding the desired eye displacement toward each of the two targets into a single representation encoding the averaging saccade (averaging programming site). We aimed to evaluate whether VGS adaptation acts upstream (hypothesis 1) or at/below (hypothesis 2) the level of averaging saccades programming. Using the double-step target paradigm, we simultaneously induced a backward adaptation of 17.5 degrees horizontal VGS and a forward adaptation of 17.5 degrees oblique VGS performed along the +/- 40 degrees directions relative to the azimuth. We measured the effects of this dual adaptation protocol on averaging saccades triggered by two simultaneous targets located at 17.5 degrees along the +/- 40 degrees directions. To increase the yield of averaging saccades, we instructed the subjects to move their eyes as fast as possible to an intermediate position between the two targets. We found that the amplitude of averaging saccades was smaller after VGS adaptation than before and differed significantly from that predicted by hypothesis 1, but not by hypothesis 2, with an adaptation transfer of 50%. These findings indicate that VGS adaptation largely occurs at/below the averaging saccade programming site. Based on current knowledge of the neural substrate of averaging saccades, we suggest that VGS adaptation mainly acts at the level of the superior colliculus or downstream. |
Nadia Alahyane; Denis Pélisson Eye position specificity of saccadic adaptation Journal Article In: Investigative Ophthalmology & Visual Science, vol. 45, no. 1, pp. 123–130, 2004. @article{Alahyane2004, PURPOSE: The accuracy of saccadic eye movements is maintained throughout life by adaptive mechanisms. With the double-step target paradigm, eight human subjects were investigated to determine whether saccadic adaptation depends only on the eye-displacement vector, or also on eye position as a context cue when two saccades of identical vector are adapted simultaneously. METHODS: First, bidirectional adaptations (BDAs) of horizontal saccades of the same vector were induced in a single training phase. Each direction of adaptation in BDAs (backward and forward) was linked to one vertical eye position (e.g., forward adaptation performed with the eyes directed 12.5 degrees upward and backward adaptation with the eyes 25 degrees downward) and alternated from trial to trial. Second, unidirectional adaptations (UDAs) were tested in two control conditions in which training trials of a single direction (backward or forward) were presented at both 12.5 degrees and -25 degrees eye elevations. RESULTS: Opposite changes in saccade amplitude could develop simultaneously in BDA, indicating that saccadic adaptation depends on orbital eye position. Comparing these data with the control conditions further indicated that eye position specificity was complete for backward, but not for forward, adaptation. CONCLUSIONS: The results indicate that saccadic adaptation mechanisms use vectorial eye displacement signals, but can also take eye position signals into account as a contextual cue when the training involves conflicting saccade amplitude changes. |
Casimir J. H. Ludwig; Iain D. Gilchrist; Eugene McSorley The influence of spatial frequency and contrast on saccade latencies Journal Article In: Vision Research, vol. 44, no. 22, pp. 2597–2604, 2004. @article{Ludwig2004, We characterised the impact of spatial frequency and contrast on saccade latencies to single Gabor patches. Saccade latencies decreased as a function of contrast, and increased with spatial frequency. The observed latency variations are qualitatively similar to those observed for manual reaction times. For single target detection, our findings highlight the similarity in the visual processes that support both saccadic and manual responses. |
Eugene McSorley; Patrick Haggard; Robin Walker Distractor modulation of saccade trajectories: Spatial separation and symmetry affects Journal Article In: Experimental Brain Research, vol. 155, no. 3, pp. 320–333, 2004. @article{McSorley2004, The trajectories of saccadic eye movements can be modulated by the presence of a competing visual distractor. In the present study the trajectories of vertical saccades curved away from a single visual distractor presented in one visual field, but tended to be straight when two distractors were presented at mirror symmetric locations in both visual fields. The spatial nature of the mirror distractor effect was examined by presenting a second distractor at mirror and non-mirror locations. Saccade trajectories also tended to be straight with both mirror and non-mirror symmetrical distractors. The relationship between the distractor location and saccade curvature was examined in a third experiment by manipulating the distractor-to-target spatial separation. Although there was a tendency for greater curvature when the distractor was presented in the same hemifield as the target there was no clear relationship between curvature and distractor location. The results show that the distractor modulation of saccade trajectory is not highly spatially specific and that it can be balanced by a second bilateral distractor in the opposite visual field. The results are interpreted in terms of a model in which the initial saccade direction and curvature back towards the saccade goal are controlled by separate processes. Initial saccade direction is modulated by the inhibition of distractor locations within a 'motor map' specifying saccade direction. Curvature back towards the saccade goal may be attributed to a feedback system, with a separate representation of the visual target location, that enables an on-line correction of the saccade during mid-flight. |
Ralf Engbert; Reinhold Kliegl Microsaccades keep the eyes' balance during fixation Journal Article In: Psychological Science, vol. 15, no. 6, pp. 431–436, 2004. @article{Engbert2004, During fixation of a stationary target, small involuntary eye movements exhibit an erratic trajectory—a random walk. Two types of these fixational eye movements are drift and microsaccades (small-amplitude saccades). We investigated fixational eye movements and binocular coordination using a statistical analysis that had previously been applied to human posture control. This random-walk analysis uncovered two different time scales in fixational eye movements and identified specific functions for microsaccades. On a short time scale, microsaccades enhanced perception by increasing fixation errors. On a long time scale, microsaccades reduced fixation errors and binocular disparity (relative to pure drift movements). Thus, our findings clarify the role of oculomotor processes during fixation. |
Jillian H. Fecteau; Crystal Au; Irene T. Armstrong; Douglas P. Munoz Sensory biases produce alternation advantage found in sequential saccadic eye movement tasks Journal Article In: Experimental Brain Research, vol. 159, no. 1, pp. 84–91, 2004. @article{Fecteau2004, In two-choice reaction time tasks, participants respond faster when the correct decision switches across consecutive trials. This alternation advantage has been interpreted as the guessing strategies of participants. Because the participants expect that the correct decision will switch across consecutive trials, they respond faster when this expectation is confirmed and they respond more slowly when it is disconfirmed. In this study, we evaluated the veracity of this expectancy interpretation. After replicating a long-lasting alternation advantage in saccadic reaction times (Experiment 1), we show that reducing the participants' ability to guess with a challenging mental rotation task does not change the alternation advantage, which suggests that expectancy is not responsible for the effect (Experiment 2). Next, we used prosaccade and antisaccade responses to dissociate between the sensory and motor contributions of the alternation advantage (Experiment 3) and we found that the alternation advantage originates from sensory processing. The implications of these findings are discussed with regard to guessing strategies, sensory processing, and how these findings may relate to inhibition of return. |