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2004 |
Giovanni Galfano; Elena Betta; Massimo Turatto Inhibition of return in microsaccades Journal Article In: Experimental Brain Research, vol. 159, no. 3, pp. 400–404, 2004. @article{Galfano2004, Inhibition of return (IOR) is the term used to describe the phenomenon whereby stimuli appearing at recently attended locations are reacted to less efficiently than stimuli appearing at locations that have not yet been attended. In the present study, we employed a typical IOR paradigm with peripheral uninformative cues while participants maintained their eyes at fixation. Eye position was monitored at a high sampling rate (500 Hz) in order to detect miniature eye movements called microsaccades, which have been shown to be crucial for avoiding disappearance of visual image. However, recent studies have demonstrated a close relationship between covert endogenous attentional shifts and the direction of microsaccades. Here, we demonstrate that the direction of microsaccades can be biased away from the peripheral location occupied by a salient, although task-irrelevant, visual signal. Because microsaccades are known not to be under conscious control, our results suggest strong links between IOR and unconscious oculomotor programming. |
Hans Colonius; Adele Diederich Multisensory interaction in saccadic reaction time: A time-window-of-integration model Journal Article In: Journal of Cognitive Neuroscience, vol. 16, no. 6, pp. 1000–1009, 2004. @article{Colonius2004, Saccadic reaction time to visual targets tends to be faster when stimuli from another modality (in particular, audition and touch) are presented in close temporal or spatial proximity even when subjects are instructed to ignore the accessory input (focused attention task). Multisensory interaction effects measured in neural structures involved in saccade generation (in particular, the superior colliculus) have demonstrated a similar spatio-temporal dependence. Neural network models of multisensory spatial integration have been shown to generate convergence of the visual, auditory, and tactile reference frames and the sensorimotor coordinate transformations necessary for coordinated head and eye movements. However, because these models do not capture the temporal coincidences critical for multisensory integration to occur, they cannot easily predict multisensory effects observed in behavioral data such as saccadic reaction times. This article proposes a quantitative stochastic framework, the time-window-of-integration model, to account for the temporal rules of multisensory integration. Saccadic responses collected from a visual–tactile focused attention task are shown to be consistent with the time-window-of-integration model predictions. |
2003 |
Adele Diederich; Hans Colonius; Daniela Bockhorst; Sandra Tabeling Visual-tactile spatial interaction in saccade generation Journal Article In: Experimental Brain Research, vol. 148, no. 3, pp. 328–337, 2003. @article{Diederich2003, Saccadic reaction times to visual targets tend to be faster when non-visual stimuli are presented in close temporal or spatial proximity even if subjects are instructed to ignore the accessory input. The effect tends to decrease with increasing spatial distance between the stimuli. Multisensory interaction effects measured in neural structures involved in saccade generation have demonstrated a similar spatial dependence. The present study investigated visual-tactile interaction effects on saccadic reaction time using a focused attention paradigm. Compared to unimodal visual targets saccadic reaction time to bimodal stimuli was reduced by up to 30 ms. The effect was larger for ipsi- than for contralateral presentations, and it increased with the eccentricity of the visual target. The results are consistent with attributing part of the facilitation to a multisensory effect of bimodal neurons with overlapping visual and tactile receptive field structures in the deep layers of the superior colliculus. |
Dominic J. Mort; Richard J. Perry; Sabira K. Mannan; Timothy L. Hodgson; Elaine Anderson; Rebecca Quest; Donald McRobbie; Alan McBride; Masud Husain; Christopher Kennard Differential cortical activation during voluntary and reflexive saccades in man Journal Article In: NeuroImage, vol. 18, no. 2, pp. 231–246, 2003. @article{Mort2003, A saccade involves both a step in eye position and an obligatory shift in spatial attention. The traditional division of saccades into two types, the "reflexive" saccade made in response to an exogenous stimulus change in the visual periphery and the "voluntary" saccade based on an endogenous judgement to move gaze, is supported by lines of evidence which include the longer onset latency of the latter and the differential effects of lesions in humans and primates on each. It has been supposed that differences between the two types of saccade derive from differences in how the spatial attention shifts involved in each are processed. However, while functional imaging studies have affirmed the close link between saccades and attentional shifts by showing they activate overlapping cortical networks, attempts to contrast exogenous with endogenous ("covert") attentional shifts directly have not revealed separate patterns of cortical activation. We took the "overt" approach, contrasting whole reflexive and voluntary saccades using event-related fMRI. This demonstrated that, relative to reflexive saccades, voluntary saccades produced greater activation within the frontal eye fields and the saccade-related area of the intraparietal sulci. The reverse contrast showed reflexive saccades to be associated with relative activation of the angular gyrus of the inferior parietal lobule, strongest in the right hemisphere. The frequent involvement of the right inferior parietal lobule in lesions causing hemispatial neglect has long implicated this parietal region in an important, though as yet uncertain, role in the awareness and exploration of space. This is the first study to demonstrate preferential activation of an area in its posterior part, the right angular gyrus, during production of exogenously triggered rather than endogenously generated saccades, a finding which we propose is consistent with an important role for the angular gyrus in exogenous saccadic orienting. |
Nadia Alahyane; Denis Pélisson Adaptation of saccadic eye movements: Transfer and specificity Journal Article In: Annals of the New York Academy of Sciences, vol. 1004, no. 1, pp. 69–77, 2003. @article{Alahyane2003, The present study was designed to test whether the adaptation of saccadic eye movements depends only on the eye displacement vector of the trained saccade or also on eye position information. Using the double-step target paradigm in eight human subjects, we first induced in a single session two "opposite directions adaptations" (ODA) of horizontal saccades of the same vector. Each ODA (backward or forward) was linked to one vertical eye position (12.5 degrees up or 25 degrees down) and alternated from trial to trial. The results showed that opposite changes of saccade amplitude can develop simultaneously, indicating that saccadic adaptation depends on orbital eye position. This finding has important functional implications because in everyday life our eyes saccade from constantly changing orbital positions. A comparison of these data to two control conditions in which training trials of a single type (backward or forward) were presented at both 12.5 degrees and -25 degrees eye elevations further indicated that eye position specificity is complete for backward, but not for forward, adaptation. Finally, the control conditions also indicated that the adaptation of a single saccade fully transferred to untrained saccades of the same vector, but initiated from different vertical eye positions. In conclusion, our study indicates 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 |
Richard Amlôt; Robin Walker; Jon Driver; Charles Spence Multimodal visual–somatosensory integration in saccade generation Journal Article In: Neuropsychologia, vol. 41, no. 1, pp. 1–15, 2003. @article{Amlot2003, Neurophysiological studies have demonstrated multisensory interaction effects in the neural structures involved in saccade generation when visual, auditory or somatosensory stimuli are presented bimodally. Visual–auditory interaction effects have been demonstrated in numerous behavioural studies of saccades but little is known about interaction effects involving somatosensory stimuli. The present study examined visual–somatosensory interaction effects on saccade generation using a multisensory paradigm, whereby task-irrelevant distractors appeared spatially-coincident with, or remote from the designated saccade target. Somatosensory distractors reduced the latency of saccades when presented before the visual target and the greatest facilitation effectwas observed with spatially-coincident stimuli.Visual distractors spatially-coincident with a somatosensory target reduced latency (and increased peak velocity) when presented before and after the target.Visual distractors contralateral to somatosensory targets increased saccade latency and produced high error rates of saccades made to the distractor. The high error rates and latencymodulation with visual distractors is consistent with a bias for visual stimuli in the saccadic system. In the visual target condition, saccade latency was modulated by a somatosensory distractor that was entirely task-irrelevant and this effect was always greatest with spatially-coincident distractors. The multisensory distractor effects are discussed in terms of saccades being programmed to the non-target modality, the early triggering of a non-spatial saccade ‘when' signal, and multisensory neuronal enhancement effects. |
Benjamin T. Backus; Daniel Matza-Brown The contribution of vergence change to the measurement of relative disparity Journal Article In: Journal of Vision, vol. 3, no. 11, pp. 727–750, 2003. @article{Backus2003, The relative disparity between two objects in a scene can in principle be measured directly from the retinal images, without knowledge of eye position. But relative disparity increment thresholds are lowest when the relative disparity is small and the objects are not widely separated in the visual field: thus, some relative disparities are easier for the visual system to measure than others. We consider, after others, a second method by which the visual system could measure relative disparity, based on change in vergence ("delta vergence" or DV). The DV mechanism could be more reliable than the retinal mechanism when visual targets are widely separated in visual direction or depth. We used a cue-conflict paradigm to measure the extent to which perceived depth depends on DV. As target separation increased, so did reliance on DV. As intertarget disparity increased, reliance on DV increased for one observer but not for two others. |
Ryota Kanai; Josef N. Geest; Maarten A. Frens Inhibition of saccade initiation by preceding smooth pursuit Journal Article In: Experimental Brain Research, vol. 148, no. 3, pp. 300–307, 2003. @article{Kanai2003, In this study, we investigated the influence of smooth-pursuit eye movements on saccade initiation in response to a sudden jump of a continuously moving target. We replicated the finding by Tanaka et al. (1998) that saccadic eye movements in the direction opposite to preceding pursuit have longer latencies than those in the same direction. We confirmed that this asymmetry is indeed due to an inhibitory effect of smooth pursuit on saccade initiation in the opposite direction rather than facilitation of saccade initiation in the same direction. The inhibitory effect decreased strongly when subjects knew the jump direction in advance. This supports the notion that the prolonged latencies of backward saccades are not due to orbital mechanics or low-level motor processing. Furthermore, we found that the range of saccade direc- tions inhibited by a pursuit movement is broad, covering all directions that did not have the same horizontal component as the pursuit direction. This is in contrast with the predictions of “Inhibition of Saccade Return” (ISR, Hooge and Frens 2000), which is restricted to a smaller confined area. |
Ralf Engbert; Reinhold Kliegl Microsaccades uncover the orientation of covert attention Journal Article In: Vision Research, vol. 43, no. 9, pp. 1035–1045, 2003. @article{Engbert2003, Fixational eye movements are subdivided into tremor, drift, and microsaccades. All three types of miniature eye movements generate small random displacements of the retinal image when viewing a stationary scene. Here we investigate the modulation of microsaccades by shifts of covert attention in a classical spatial cueing paradigm. First, we replicate the suppression of microsaccades with a minimum rate about 150 ms after cue onset. Second, as a new finding we observe microsaccadic enhancement with a maximum rate about 350 ms after presentation of the cue. Third, we find a modulation of the orientation towards the cue direction. These multiple influences of visual attention on microsaccades accentuate their role for visual information processing. Furthermore, our results suggest that microsaccades can be used to map the orientation of visual attention in psychophysical experiments. |
Valérie Gaveau; Olivier Martin; Claude Prablanc; Denis Pélisson; Christian Urquizar; Michel Desmurget On-line modification of saccadic eye movements by retinal signals Journal Article In: Neuroreport, vol. 14, no. 6, pp. 875–878, 2003. @article{Gaveau2003, A saccade is a rapid shift of the position of the eyes (<100ms). Saccades are generally considered too quick to be inpoundsuenced by retinal signals.To address this idea, we displaced the visual target of a rightward horizontal saccade at eye movement onset (when there is suppression of conscious perception).To prevent adaptive and learning e¡ects to occur, jump saccadeswere always followed by a random series of 10 no-jump saccades. Results indicated that the target jump influenced significantly the amplitude and the peak velocity of the ongoing saccade (opposite e¡ects were found for rightward and leftward jumps). Changes in saccade kinematics occurred as early as 50ms after the target jump. These results show that retinal information is processed quickly during eye movements, presumably through sub-cortical pathways. |
Casimir J. H. Ludwig; Iain D. Gilchrist Target similarity affects saccade curvature away from irrelevant onsets Journal Article In: Experimental Brain Research, vol. 152, no. 1, pp. 60–69, 2003. @article{Ludwig2003, Saccade curvature away from visual distractors is a measure of the salience of these distractors for the oculomotor system. Three experiments are reported in which the integration of luminance onset signals and target similarity signals is examined, using a saccade curvature paradigm. Observers made saccades to a no-onset colour target in one of two positions on the vertical meridian. On most trials, an abrupt onset distractor that was either similar or dissimilar to the target appeared left or right on the horizontal midline. Saccades curved away from the irrelevant onsets; however, the amount of curvature was modulated by target similarity only when the onset appeared before the target (experiment 2) or when saccade initiation was delayed (experiment 3). These results suggest that the initial response to the onset is stimulus-driven and mediated by its transient component. Over time, the response is integrated with and augmented by top-down inputs. Visual and non-visual signals converge onto a common motor map to determine an item's salience. |
Michael Coesmans; Peter A. Sillevis Smitt; David J. Linden; Ryuichi Shigemoto; Tomoo Hirano; Yoshinori Yamakawa; Adriaan M. Alphen; Chongde Luo; Josef N. Geest; Johan M. Kros; Carlos A. Gaillard; Maarten A. Frens; Chris I. De Zeeuw Mechanisms underlying cerebellar motor deficits due to mGluR1-autoantibodies Journal Article In: Annals of Neurology, vol. 53, no. 3, pp. 325–336, 2003. @article{Coesmans2003, Patients with Hodgkin's disease can develop paraneoplastic cerebellar ataxia because of the generation of autoantibodies against mGluR1 (mGluR1-Abs). Yet, the pathophysiological mechanisms underlying their motor coordination deficits remain to be elucidated. Here, we show that application of IgG purified from the patients' serum to cerebellar slices of mice acutely reduces the basal activity of Purkinje cells, whereas application to the flocculus of mice in vivo evokes acute disturbances in the performance of their compensatory eye movements. In addition, the mGluR1-Abs block induction of long-term depression in cultured mouse Purkinje cells, whereas the cerebellar motor learning behavior of the patients is affected in that they show impaired adaptation of their saccadic eye movements. Finally, postmortem analysis of the cerebellum of a paraneoplastic cerebellar ataxia patient showed that the number of Purkinje cells was significantly reduced by approximately two thirds compared with three controls. We conclude that autoantibodies against mGluR1 can cause cerebellar motor coordination deficits caused by a combination of rapid effects on both acute and plastic responses of Purkinje cells and chronic degenerative effects. |
I. T. Armstrong; Douglas P. Munoz Inhibitory control of eye movements during oculomotor countermanding in adults with attention-deficit hyperactivity disorder Journal Article In: Experimental Brain Research, vol. 152, no. 4, pp. 444–452, 2003. @article{Armstrong2003a, Children with attention-deficit hyperactivity disorder (ADHD) are impulsive, and that impulsiveness can be measured using a countermanding task. Although the overt behaviors of ADHD attenuate with age, it is not clear how well impulsiveness is controlled in adults with ADHD. We tested ADHD adults with an oculomotor countermanding task. The task included two conditions: on 75% of the trials, participants viewed a central fixation marker and then looked to an eccentric target that appeared simultaneous with the disappearance of the fixation marker; on 25% of the trials, a signal was presented at variable delays after target appearance. The signal instructed subjects to stop, or countermand, an eye movement to the target. A correct movement in this case would be to hold gaze at the central fixation location. We expected ADHD participants to be impulsive in their countermanding performance. Additionally, we expected that a visual stop signal at the central fixation location would assist oculomotor countermanding because the signal is presented in the "stop" location, at fixation. To test whether a central stop signal positively biased countermanding, we used a three types of stop signal to instruct the stop: a central visual marker, a peripheral visual signal, and a non-localized sound. All subjects performed best with the central visual stop signal. Subjects with ADHD were less able to countermand eye movements and were influenced more negatively by the non-central signals. Oculomotor countermanding may be useful for quantifying impulsive dysfunction in adults with ADHD especially if a non-central stop signal is applied. |
I. T. Armstrong; Douglas P. Munoz Attentional blink in adults with attention-deficit hyperactivity disorder: Influence of eye movements Journal Article In: Experimental Brain Research, vol. 152, no. 2, pp. 243–250, 2003. @article{Armstrong2003, The attentional blink paradigm tests attention by overloading it: a list of stimuli is presented very rapidly one after another at the same location on a computer screen, each item overwriting the last, and participants monitor the list using two criteria [e.g. detect the target (red letter) and identify the probe (letter p)]. If the interval between the target and the probe is greater than about 500 ms, both are usually reported correctly, but, when the interval between the target and the probe is within 200-500 ms, report of the probe declines. This decline is the attentional blink, an interval of time when attention is supposedly switching from the first criterion to the second. The attentional blink paradigm should be difficult to perform correctly without vigilantly attending to the rapidly presented list. Vigilance tasks are often used to assess attention-deficit hyperactivity disorder (ADHD). Symptoms of the disorder include hyperactivity and attentional dysfunction; however, some people with ADHD also have difficulty maintaining gaze at a fixed location. We tested 15 adults with ADHD and their age- and sex-matched controls, measuring accuracy and gaze stability during the attentional blink task. ADHD participants reported fewer targets and probes, took longer to recover from the attentional blink, made more eye movements, and made identification errors consistent with non-perception of the letter list. In contrast, errors made by control participants were consistent with guessing (i.e., report of a letter immediately preceding or succeeding the correct letter). Excessive eye movements result in poorer performance for all participants; however, error patterns confirm that the weak performance of ADHD participants may be related to gaze instability as well as to attentional dysfunction. |
Hendrik Chris Dijkerman; Robert D. McIntosh; David Milner; Yves Rossetti; Caroline Tilikete; Richard C. Roberts Ocular scanning and perceptual size distortion in hemispatial neglect: Effects of prism adaptation and sequential stimulus presentation Journal Article In: Experimental Brain Research, vol. 153, no. 2, pp. 220–230, 2003. @article{Dijkerman2003, When asked to compare two lateralized shapes for horizontal size, neglect patients often indicate the left stimulus to be smaller. Gainotti and Tiacci (1971) hypothesized that this phenomenon might be related to a rightward bias in the patients' gaze. This study aimed to assess the relation between this size underestimation and oculomotor asymmetries. Eye movements were recorded while three neglect patients judged the horizontal extent of two rectangles. Two experimental manipulations were performed to increase the likelihood of symmetrical scanning of the stimulus display. The first manipulation entailed a sequential, rather than simultaneous presentation of the two rectangles. The second required adaptation to rightward displacing prisms, which is known to reduce many manifestations of neglect. All patients consistently underestimated the left rectangle, but the pattern of verbal responses and eye movements suggested different underlying causes. These include a distortion of space perception without ocular asymmetry, a failure to view the full leftward extent of the left stimulus, and a high-level response bias. Sequential presentation of the rectangles and prism adaptation reduced ocular asymmetries without affecting size underestimation. Overall, the results suggest that leftward size underestimation in neglect can arise for a number of different reasons. Incomplete leftward scanning may perhaps be sufficient to induce perceptual size distortion, but it is not a necessary prerequisite. |
Jeroen B. J. Smeets; Ignace T. C. Hooge Nature of variability in saccades Journal Article In: Journal of Neurophysiology, vol. 90, no. 1, pp. 12–20, 2003. @article{Smeets2003, We studied the variability in saccades by comparing the peak velocities of saccades with the same target amplitude made with different actual amplitudes. We tested three hypotheses: the pulse-height noise hypothesis (peak velocity and amplitude vary proportionally), the localization noise hypothesis (variability in amplitude and peak velocity lie along the main sequence), and the independent noise hypothesis (variability in amplitude and peak velocity are independent). We measured eye orientation in two experiments by a scleral coil and a video system. Surprisingly, the main source of variability of saccades depended on the measurement system used. A combination of localization noise and independent noise best describes the data obtained by the video system. The independent noise (e.g., measurement inaccuracy) was the main source of variability. For the scleral coils, the variability was considerably larger than for the less accurate video system. The pulse-height noise hypothesis best describes this additional variability. Therefore we conclude that pulse-height noise is the main source of variability in saccades measured with scleral coils. We discuss the influence of scleral coils on saccade generation and suggest that a change in motor strategy due to the discomfort of wearing the coils might be the cause of the increased variability. |
Masud Husain; Andrew Parton; Timothy L. Hodgson; Dominic J. Mort; Geraint Rees Self-control during response conflict by human supplementary eye field Journal Article In: Nature Neuroscience, vol. 6, no. 2, pp. 117–118, 2003. @article{Husain2003, Although medial frontal cortex is considered to have an important role in planning behavior and monitoring errors, the specific contributions of regions within it are poorly understood1, 2, 3. Here we report that a patient with a highly selective lesion of a medial frontal motor area—the supplementary eye field (SEF)—lacked control in changing the direction of his eye movement from either a previous intention or behavioral 'set'; however, he monitored his errors well and corrected them quickly. The results indicate a key new role for the SEF and show that medial frontal mechanisms for self-control of action may be highly specific, with the SEF critically involved in implementing oculomotor control during response conflict, but not in error monitoring. |
Caroline J. Ketcham; Timothy L. Hodgson; Christopher Kennard; George E. Stelmach Memory-motor transformations are impaired in Parkinson s disease Journal Article In: Experimental Brain Research, vol. 149, pp. 30–39, 2003. @article{Ketcham2003, Parkinson's disease patients are known to suffer loss of dopaminergic input to the rostral caudate nucleus. Recent functional magnetic resonance imaging (fMRI) studies have implicated this structure in the transformation of spatial information in memory to guide action, suggesting that memory to motor transformations may be selectively impaired in Parkinson's disease. In order to investigate this possibility we tested a group of Parkinson's disease patients (PDs) using a memory- guided pointing task. Of interest was whether patients showed reduced accuracy in the task as a function of memory load. Twelve PD patients and 13 elderly controls were asked to recall single or four step target sequences with 2 time delays (500 and 3,500 ms). In all memory- guided conditions PD patients showed increased variabil- ity in memory-guided movement end-points. This effect was not affected by delay, number of items, or the sequence familiarity. The results are consistent with increased variability in memory-motor transformations in early PD, due to dopamine depletion within the rostral caudate nucleus. |
Elliot M. Frohman; Padraig O'Suilleabhain; Richard B. Dewey; Teresa C. Frohman; Phillip D. Kramer A new measure of dysconjugacy in INO: The first-pass amplitude Journal Article In: Journal of the Neurological Sciences, vol. 210, no. 1-2, pp. 65–71, 2003. @article{Frohman2003, Background: The ratios of abducting to adducting eye movements (versional dysconjugacy index, VDI) for saccadic velocity and acceleration have been useful measures by which to objectively characterize internuclear ophthalmoparesis (INO). Amplitude measures of dysconjugacy have been less useful, given that many patients maintain the ability to ultimately reach a centrifugal fixation target and that traditional amplitude measures of VDI have focused on this 'final amplitude' (FA) position. Methods: We utilized infrared oculography to define a new amplitude measure of dysconjugacy in 42 multiple sclerosis (MS) patients with INO. The first-pass amplitude (FPA)-VDI is the ratio of abduction/adduction eye movement amplitudes computed at the time when the abducting eye initially achieves the centrifugal horizontal fixation target. Results: FPA-VDI values were significantly more sensitive and specific than FA-VDI values in demonstrating dysconjugacy in INO, and there was a 14-fold increase in dysconjugacy as measured by FPA-VDI Z-scores when compared to FA-VDI Z-scores. Conclusion: Consideration of velocity (pulse) and amplitude (step) components of dysconjugacy in patients with INO can provide a greater understanding of the dynamic aspects of this syndrome. We propose to characterize the relationship between the pathophysiology of INO and neuroradiologic measures of tissue injury in MS. |
Teresa C. Frohman; Elliot M. Frohman; Padraig O'Suilleabhain; A. R. Salter; Richard B. Dewey; N. Hogan; S. Galetta; A. G. Lee; D. Straumann; J. Noseworthy; D. Zee; J. Corbett; J. Corboy; V. M. Rivera; Phillip D. Kramer Accuracy of clinical detection of INO in MS: Corroboration with quantitative infrared oculography Journal Article In: Neurology, vol. 61, no. 6, pp. 848–850, 2003. @article{Frohman2003a, The authors compared the accuracy of clinical detection (by 279 physician observers) of internuclear ophthalmoparesis (INO) with that of quantitative infrared oculography. For the patients with mild adduction slowing, INO was not identified by 71%. Intermediate dysconjugacy was not detected by 25% of the evaluators. In the most severe cases, INO was not identified by only 6%. Oculographic techniques significantly enhance the precision of INO detection compared to the clinical exam. |
Monika Harvey; Iain D. Gilchrist; Bettina Olk; Keith Muir Eye-movement patterns do not mediate size distortion effects in hemispatial neglect: Looking without seeing Journal Article In: Neuropsychologia, vol. 41, no. 8, pp. 1114–1121, 2003. @article{Harvey2003, Over the last decade a range of studies have shown that some patients with hemispatial neglect subjectively underestimate the size of objects presented in their contralesional hemispace. Recently, it has been suggested that the effect is simply due to either hemianopia [Brain 124 (2001) 527], or the combination of neglect and hemianopia [Neurology 52 (1999) 1845]. In the current study we asked right hemisphere lesioned patients with and without neglect and hemianopia as well as healthy controls to judge either two horizontal or vertical lines presented simultaneously in right and left hemispace and monitored their eye movements. Three out of the six patients showed the predicted size distortion effect for horizontal lines. We found no evidence that the effect was mediated by eye movements. The two neglect patients who showed the strongest left side underestimation showed symmetrical (left, right) scanning of the lines both in terms of number of fixations and fixation time, yet they still failed to judge the relative size veridically. In addition, we did not find strong evidence for a link with hemianopia. We therefore propose that the effect reflects a computational/representational failure of processing for horizontal extent. |
N. J. Upton; Timothy L. Hodgson; G. T. Plant; Richard J. S. Wise; Alexander P. Leff "Bottom-up" and "top-down" effects on reading saccades: A case study Journal Article In: Journal of Neurology, Neurosurgery and Psychiatry, vol. 74, no. 10, pp. 1423–1428, 2003. @article{Upton2003, OBJECTIVE: To investigate the role right foveal/parafoveal sparing plays in reading single words, word arrays, and eye movement patterns in a single case with an incongruous hemianopia. METHODS: The patient, a 48-year-old right handed male with a macular sparing hemianopia in his left eye and a macular splitting hemianopia in his right eye, performed various reading tasks. Single word reading speeds were monitored using a "voice-trigger" system. Eye movements were recorded while reading three passages of text, and PET data were gathered while the subject performed a variety of reading tasks in the camera. RESULTS: The patient was faster at reading single words and text with his left eye compared with his right. A small word length effect was present in his right eye but not his left. His eye movement patterns were more orderly when reading text with his left eye, making fewer saccades. The PET data provided evidence of "top-down" processes involved in reading. Binocular single word reading produced activity in the representation of foveal V1 bilaterally; however, text reading with the left eye only was associated with activation in left but not right parafoveal V1, despite there being visual stimuli in both visual fields. CONCLUSIONS: The presence of a word length effect (typically associated with pure alexia) can be caused by a macular splitting hemianopia. Right parafoveal vision is not critically involved in single word identification, but is when planning left to right reading saccades. The influence of top-down attentional processes during text reading can be visualised in parafoveal V1 using PET. |
2002 |
M. L. M. Tant; Frans W. Cornelissen; Aart C. Kooijman; Wiebo H. Brouwer Hemianopic visual field defects elicit hemianopic scanning Journal Article In: Vision Research, vol. 42, no. 10, pp. 1339–1348, 2002. @article{Tant2002, Previous explanations for the variability in success of compensating for homonymous hemianopia (HH) has been in terms of extent of the brain injury. In using on-line eye movement registrations, we simulated HH in 16 healthy subjects and compared their scanning performance on a dot counting task to their own "normal" condition and to real HH patients' performance. We evidenced clear parallels between simulated and real HH, suggesting that hemianopic scanning behaviour is primarily visually elicited, namely by the visual field defect, and not by the additional brain damage. We further observed age-related processes in compensating for the HH. |
Frank A. Proudlock; Irene Gottlob; Cris S. Constantinescu Oscillopsia without nystagmus caused by head titubation in a patient with multiple sclerosis Journal Article In: Journal of Neuro-Ophthalmology, vol. 22, no. 2, pp. 88–91, 2002. @article{Proudlock2002, Oscillopsia in patients who have brain stem disorders but not nystagmus is attributed to a failure of the vestibular-ocular reflex (VOR) to compensate for head movements. We report a patient who had marked head titubation and oscillopsia in aggressive multiple sclerosis but no nystagmus. Her severe head titubation precluded our ability to measure a VOR accurately. Because oscillopsia has also been described after rapid voluntary head oscillations in normal subjects, we queried whether the oscillopsia in our patient could be ascribed to the head movement alone. Six normal control subjects did not experience oscillopsia while shaking their heads at the same frequency as the patient's titubation. We conclude that the oscillopsia in our patient was probably the result of an impaired VOR or an alternative compensatory mechanism. |
Timothy L. Hodgson; Dominic J. Mort; M. M. Chamberlain; Samuel B. Hutton; K. S. O'Neill; Christopher Kennard Orbitofrontal cortex mediates inhibition of return Journal Article In: Neuropsychologia, vol. 40, no. 12, pp. 1891–1901, 2002. @article{Hodgson2002, Recent accounts have proposed that orbitofrontal cerebral cortex mediates the control of behavior based on emotional feedback and its somatic correlates. Here, we describe the performance of a patient with circumscribed damage to orbitofrontal cortex during a task that requires switching between sensory-motor mappings, contingent on the occurrence of positive and negative reward feedbacks. In this test, normal subjects and other patients with prefrontal damage show an increase in latencies for eye movements towards locations at which a negative feedback was presented on the preceding trial. In contrast, our patient does not show this reward-dependent inhibition of return effect on saccades. She was also found to make an increased rate of ocular refixations during visual search and used a disorganized search strategy in a token foraging task. These findings suggest that orbital regions of the prefrontal cortex mediate an inhibitory effect on actions directed towards locations that have been subject to negative reinforcement. Further, this mechanism seems to play a role in controlling natural search and foraging behavior. |
Timothy L. Hodgson; B. Tiesman; Adrian M. Owen; Christopher Kennard Abnormal gaze strategies during problem solving in Parkinson's disease Journal Article In: Neuropsychologia, vol. 40, no. 4, pp. 411–422, 2002. @article{Hodgson2002a, We have taken a novel approach to the study of problem solving involving the detailed analysis of natural scanning eye movements during the 'one touch' Tower of London task. Control subjects and patients with idiopathic Parkinson's disease (PDs) viewed a series of pictures depicting two arrangements of coloured balls in pockets within the upper and lower halves of a computer display. The task was to plan (but not execute) the shortest movement sequence required to rearrange the balls in one half of the display (the Workspace) to match the arrangement in the opposite half (the Goalspace) and indicate the number of moves required for problem solution. As problem complexity increased, control subjects spent proportionally more time fixating the Workspace region. This pattern was found regardless of whether subjects were instructed to solve problems by rearranging balls in the lower or upper visual fields. The distribution of gaze within the Workspace was also found to be problem dependent, with gaze being selectively directed towards the problem critical balls. In contrast, PDs were found to make more errors in the task and failed to show any dissociation in the amount of time fixating the two halves of the display. This pattern suggests that the patients had difficulty in encoding and/or maintaining current goals during problem solving, consistent with a role for fronto-striatal circuits in mechanisms of working memory and attention. |
Sunila Jain; Frank A. Proudlock; Cris S. Constantinescu; Irene Gottlob Combined pharmacologic and surgical approach to acquired nystagmus due to multiple sclerosis Journal Article In: American Journal of Ophthalmology, vol. 134, no. 5, pp. 780–782, 2002. @article{Jain2002, PURPOSE: To describe a combined pharmacological and surgical approach to treating acquired nystagmus in a patient with multiple sclerosis. DESIGN: Interventional case report. METHODS: A 40-year-old patient with acquired horizontal and vertical nystagmus and severe oscillopsia secondary to multiple sclerosis had combined treatment with gabapentin and a vertical Kestenbaum-type procedure. RESULTS: After gabapentin treatment (3,000 mg orally daily) the horizontal nystagmus was significantly reduced, and the patient developed a marked chin-up position. The vertical nystagmus remained unchanged, dampening on downgaze. A recession of both inferior rectus muscles reduced the nystagmus significantly in primary position, the abnormal head position disappeared, and oscillopsia completely resolved. Treatment increased visual acuity from 6/24 in the right eye and 6/60 in the left eye to 6/9 in both eyes. CONCLUSIONS: Acquired nystagmus in multiple sclerosis can be significantly improved by using a combined pharmacological and surgical approach. |
Elliot M. Frohman; Teresa C. Frohman; Padraig O'Suilleabhain; H. Zhang; K. Hawker; M. K. Racke; W. Frawley; J. T. Phillips; Phillip D. Kramer Quantitative oculographic characterisation of internuclear ophthalmoparesis in multiple sclerosis: The versional dysconjugacy index Z score Journal Article In: Journal of Neurology, Neurosurgery and Psychiatry, vol. 73, pp. 51–55, 2002. @article{Frohman2002, Background: There is a poor correlation between multiple sclerosis disease activity, as measured by magnetic resonance imaging, and clinical disability. Objective: To establish oculographic criteria for the diagnosis and severity of internuclear ophthalmoparesis (INO), so that future studies can link the severity of ocular dysconjugacy with neuro- radiological abnormalities within the dorsomedial brain stem tegmentum. Methods: The study involved 58 patients with multiple sclerosis and chronic INO and 40 normal sub- jects. Two dimensional infrared oculography was used to derive the versional dysconjugacy index (VDI)—the ratio of abducting to adducting eye movements for peak velocity and acceleration. Diagnostic criteria for the diagnosis and severity of INO were derived using a Z score and histogram analysis, which allowed comparisons of the VDI from multiple sclerosis patients and from a control population. Results: For a given saccade, the VDI was typically higher for acceleration v velocity, whereas the Z scores for velocity measures were always higher than values derived from comparable acceleration VDI measures; this was related to the greater variability of acceleration measures. Thus velocity was a more reliable measure from which to determine Z scores and thereby the criteria for INO and its level of severity. The mean (SD) value of the VDI velocity derived from 40 control subjects was 0.922 (0.072). The highest VDI for velocity from a normal control subject was 1.09, which was 2.33 SD above the normal control mean VDI. We therefore chose 2 SD beyond this value (that is, a Z score of 4.33) as the minimum criterion for the oculographic confirmation of INO. Of patients thought to have unilateral INO on clinical grounds, 70% (16/23) were found to have bilateral INO on oculographic assessment. Conclusions: INO can be confirmed and characterised by level of severity using Z score analysis of quantitative oculography. Such assessments may be useful for linking the level of severity of a specific clinical disability with neuroradiological measures of brain tissue pathology in multiple sclerosis. I |
Casimir J. H. Ludwig; Iain D. Gilchrist Measuring saccade curvature: A curve-fitting approach Journal Article In: Behavior Research Methods, Instruments & Computers, vol. 34, no. 4, pp. 618–624, 2002. @article{Ludwig2002, Saccade curvature is becoming a popular measure for detecting the presence of competing saccadic motor programs. Several different methods of quantifying saccade curvature have been employed. In the present study, we compared these metrics with each other and with novel measures based on curve fitting. Initial deviation metrics were only moderately associated with the more widely used metric of maximum curvature. The latter was strongly related to a recently developed area-based measure and to the novel methods based on second- and third-order polynomial fits. The curve-fitting methods showed that although most saccades curved in only one direction, there was a population of trajectories with both a maximum and a minimum (i.e., double-curved saccades). We argue that a curvature metric based on a quadratic polynomial fit deals effectively with both types of trajectories and, because it is based on all the samples of a saccade, is less susceptible to sampling noise. |
F. Møller; M. L. Laursen; J. Tygesen; A. K. Sjølie Binocular quantification and characterization of microsaccades Journal Article In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 240, no. 9, pp. 765–770, 2002. @article{Moeller2002, BACKGROUND: The significance of microsaccades in the visual process has been discussed for more than 50 years. However, only a few studies have measured microsaccades binocularly, and detailed quantification and characterization of these small movements are needed in order to further understand their nature. METHOD: The amplitude, velocity, acceleration and direction of microsaccades were quantified binocularly in 10 normal test persons during a 40-s fixation task, using an infrared recording technique. RESULTS: All microsaccades for all test persons were performed simultaneously and individually with an almost identical amplitude in the right and left eye (a range of 0.003-0.042 deg between right and left eye mean values). The mean microsaccadic amplitude for the test persons was within a range of 0.223-1.079 deg. The directional difference between simultaneously-performed right and left eye microsaccades was less than 22.5 deg for 84.8% of the saccades, indicating that the majority of microsaccades are conjugated. Three different fixation patterns were identified and characterized: (1) a classic interplay between easily identified drifts and medium-sized microsaccades (mean amplitude range 0.328-0.413 deg); (2) long intersaccadic intervals (4-5 s) with almost absent drifts, followed by three or four large microsaccades (mean amplitude range 0.755-1.079 deg); and (3) low-amplitude drift movements interrupted by low-amplitude microsaccades (mean amplitude range 0.231-0.265 deg). CONCLUSION: Microsaccades are involuntary, predominantly conjugated, simultaneously performed, and of almost identical amplitude in the right and left eye, suggesting a central control mechanism for microsaccades at subcortical level. |
Veerle Gysen; Peter De Graef; Karl Verfaillie Detection of intrasaccadic displacements and depth rotations of moving objects Journal Article In: Vision Research, vol. 42, no. 3, pp. 379–391, 2002. @article{Gysen2002, In a display with a stationary and a moving object, subjects saccaded towards one of the objects and had to detect intrasaccadic changes in position or orientation of either the saccade target or the saccade flanker. Compared to performance for stationary objects, displacement detection for translating objects was better and unaffected by saccadic status of the changed object. This pattern proved to be specific to position changes in translating objects and did not generalize to other types of motion (i.e., rotation) or to other types of intrasaccadic changes (i.e., orientation shifts). Superior transsaccadic coding of the position of a translating object was also observed in control experiments with only a single object present on each trial. Possible accounts in terms of selective attention to moving objects and perceptual relevance of object position are pitted against the data, suggesting qualitative differences in the transsaccadic representation of translating and stationary objects. |
Monika Harvey; Bettina Olk; Keith Muir; Iain D. Gilchrist Manual responses and saccades in chronic and recovered hemispatial neglect: A study using visual search Journal Article In: Neuropsychologia, vol. 40, no. 7, pp. 705–717, 2002. @article{Harvey2002, Hemispatial neglect affects both the ability to respond to targets on the contralesional side of space and to programme saccades to such targets. In the current study, we looked in detail at saccade programming and manual reaction times (RTs) in a range of visual search tasks, in which task difficulty was systematically increased by changing the nature of the distractors. In condition 1, the target was presented with no distractors. In the other conditions, displays contained three distractors that were changed across conditions to manipulate similarity to the target and so task difficulty. We tested two neglect patients, one chronic, one recovered along with two RCVA control patients and 12 age-matched controls. Both neglect patients studied could successfully execute saccades into the neglected field when the target was presented alone. However, a dissociation emerged between the two patients when the target was presented with distractor items. Patient ERs first saccade to target performance in the three search conditions revealed clear effects of distractor type. In contrast for the recovered patient AF, the left/right difference was present for all search displays and appeared to be constant regardless of distractor type. This differential pattern of behaviour may reflect the different underlying neural causes of the neglect in these patients. In the current study, the measurement of saccades allowed the task to be fractionated, and thus, reveal the action of multiple mechanisms controlling saccades in search. |
Hyung-Chul O. Li; Eli Brenner; Frans W. Cornelissen; Eun-Soo Kim Systematic distortion of perceived 2D shape during smooth pursuit eye movements Journal Article In: Vision Research, vol. 42, no. 23, pp. 2569–2575, 2002. @article{Li2002b, Even when the retinal image of a static scene is constantly shifting, as occurs when the viewer pursues a small moving object with his or her eyes, the scene is usually correctly perceived to be static. Following early suggestions by von Helmholtz, it is commonly believed that this spatial stability is achieved by combining retinal and extra-retinal signals. Here, we report a perceptually salient 2D shape distortion that can arise during pursuit. We provide evidence that the perceived 2D shape reflects retinal image contents alone, implying that the extra-retinal signal is ignored when judging 2D shape. © 2002 Elsevier Science Ltd. All rights reserved. |
M. C. Doyle; Robin Walker Multisensory interactions in saccade target selection: Curved saccade trajectories Journal Article In: Experimental Brain Research, vol. 142, no. 1, pp. 116–130, 2002. @article{Doyle2002, In a series of experiments, we examined the change in saccade trajectories observed when distractors are presented at non-target locations. The primary aim of the experiments was to examine multisensory interaction effects between the visual, auditory and somatosensory modalities in saccade generation. In each experiment observers made saccades to visual targets above and below fixation in the presence of visual, auditory or tactile stimuli to the left or right of fixation. In experiment 1 distractor location indicated which of two stimuli was the target for the saccade. Saccade trajectories showed strong leftward curvature following right-side distractors and showed rightward curvature following left-side distractors. The largest effects on trajectories were observed for visual distractors, but significant curvature was observed with auditory and somatosensory distractors. In experiment 2 saccades were made following the onset of a visual target (reflexive) or following presentation of an arrow at fixation (voluntary), and task-irrelevant crossmodal distractors were presented simultaneously with target onset. Both voluntary and reflexive saccades were found to curve away from task-irrelevant visual distractors, but auditory and somatosensory distractors did not modulate saccade trajectories. In experiment 3 task-irrelevant distractors preceded the onset of the target by 100 ms. Reflexive saccades were found to curve away from visual, auditory and somatosensory distractors, but voluntary saccades curved away from visual distractors only. The modulation of saccade trajectories by distractors from different modalities is interpreted in terms of inhibitory processes operating in neural structures involved in saccade generation. Our findings suggest that visual, auditory and somatosensory distractors can all modulate saccade trajectories. Such effects could be related to the inhibition of populations of neurons, in a common motor map, for the selection of a saccade target. |
Danny Gagnon; Gillian A. O'Driscoll; Michael Petrides; G. B. Pike The effect of spatial and temporal information on saccades and neural activity in oculomotor structures Journal Article In: Brain, vol. 125, no. 1, pp. 123–139, 2002. @article{Gagnon2002, It has been argued that saccade generation is supported by two systems, a'where' system that decides the direction and extent of an impending saccade, and a 'when' system that is involved in the timing of the release of fixation. We evaluated the contributions of these systems to saccade latencies, and used functional MRI to identify the neural substrates of these systems. We found that advance knowledge of the direction and the timing of an impending target movement had both overlapping and discrete effects on saccade latencies and on neural activation. Knowledge of either factor decreased regular saccade latencies. However, knowledge of target direction increased the number of predictive and express saccades while knowledge of target timing did not. The brain activation data showed that advance knowledge of the direction or the timing of the target movement activated primarily overlapping structures. The precentral gyrus, in the region of the frontal eye fields, was more active in conditions in which some aspect of the target movement was predictable than in saccade control and fixation conditions. In the basal ganglia, activation discriminated between advance knowledge of target timing and target direction. The lenticular nuclei were more active when only target timing was known in advance, while the caudate was more active when only target direction was known in advance. These data suggest that the neural structures supporting the 'where' and 'when' systems are highly overlapping, although there is some dissociation sub-cortically. Knowledge of target timing and target direction converge in precentral gyrus, a region where there is strong evidence of context-dependent modulation of neural activity. |
Richard Godijn; Jan Theeuwes Programming of exogenous and endogenous saccades: Evidence for a competitive integration model Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 28, pp. 1039–1054, 2002. @article{Godijn2002, Participants were required to make a saccade to a uniquely colored target while ignoring the presentation of an onset distractor. The results provide evidence for a competitive integration model of saccade programming that assumes endogenous and exogenous saccades are programmed in a common saccade map. The model incorporates a lateral interaction structure in which saccade-related activation at a specific location spreads to neighboring locations but inhibits distant locations. In addition, there is top-down, location-specific inhibition of locations to which the saccade should not go. The time course of exogenous and endogenous activation in the saccade map can explain a variety of eye movement data, including endpoints, latencies, and trajectories of saccades and the well-known global effect |
Martin Greschner; Markus Bongard; Pal Rujan; Josef Ammermüller Retinal ganglion cell synchronization by fixational eye movements improves feature estimation Journal Article In: Nature Neuroscience, vol. 5, no. 4, pp. 341–347, 2002. @article{Greschner2002, Image movements relative to the retina are essential for the visual perception of stationary objects during fixation. Here we have measured fixational eye and head movements of the turtle, and determined their effects on the activity of retinal ganglion cells by simulating the movements on the isolated retina. We show that ganglion cells respond mainly to components of periodic eye movement that have amplitudes of roughly the diameter of a photoreceptor. Drift or small head movements have little effect. Driven cells that are located along contrast borders are synchronized, which reliably signals a preceding movement. In an artificial neural network, the estimation of spatial frequencies for various square wave gratings improves when timelocked to this synchronization. This could potentially improve stimulus feature estimation by the brain. |
Sonja Stork; Sebastiaan F. W. Neggers; Jochen Müsseler Intentionally-evoked modulations of smooth pursuit eye movements Journal Article In: Human Movement Science, vol. 21, no. 3, pp. 335–348, 2002. @article{Stork2002, When observers pursue a moving target with their eyes, they use predictions of future target positions in order to keep the target within the fovea. It was suggested that these predictions of smooth pursuit (SP) eye movements are computed only from the visual feedback of the target characteristics. As a consequence, if the target vanishes unexpectedly, the eye movements do not stop immediately, but they overshoot the vanishing point. We compared the spatial and temporal features of such predictive eye movements in a task with or without intentional control over the target vanishing point. If the observers stopped the target with a button press, the overshoot of the eyes was reduced compared to a condition where the offset was computer generated. Accordingly, the eyes started to decelerate well before the target offset and lagged further behind the target when it disappeared. The involvement of intentionally-generated expectancies in eye movement control was also obvious in the spatial trajectories of the eyes, which showed a clear flexion in anticipation of the circular motion path we used. These findings are discussed together with neurophysiological mechanisms underlying the SP eye movements. |
Eyal M. Reingold; Dave M. Stampe Saccadic inhibition in voluntary and reflexive saccades Journal Article In: Journal of Cognitive Neuroscience, vol. 14, no. 3, pp. 371–388, 2002. @article{Reingold2002b, The present study investigated saccadic inhibition in both voluntary and stimulus-elicited saccades. Two experiments examined saccadic inhibition caused by an irrelevant flash occurring subsequent to target onset. In each trial, participants were required to perform a single saccade following the presentation of a black target on a gray background, 4 degrees to the left or to the right of screen center. In some trials (flash trials), after a variable delay, a 33-msec flash was displayed at the top and bottom third of the monitor (these regions turned white). In all experimental conditions, histograms of flash-to-saccade latencies documented a decrease in saccadic frequency, forming a dip, time-locked to the flash and occurring as early as 60-70 msec following its onset. The fast latency of this effect strongly suggests a low-level, reflex-like, oculomotor effect, which was referred to as saccadic inhibition. A novel procedure was developed to allow comparisons of saccadic inhibition even across conditions, which in the absence of a flash (no-flash trials) produce dissimilar saccadic reaction times (SRTs) distributions. Experiment 1 examined the effects of the fixation stimulus on saccadic inhibition by contrasting three conditions: a gap condition (fixation stimulus disappeared 200 msec prior to target onset), a step condition (offset of the fixation stimulus was simultaneous with target onset), and an overlap condition (the fixation stimulus remained on for the duration of the trial). The overlap condition produced substantially stronger saccadic inhibition, relative to the gap and the step conditions. Experiment 2 contrasted the saccadic inhibition effect obtained for prosaccades (saccades aimed at the target) with the effect obtained for antisaccades (i.e., saccades aimed away from the same target). The onset of saccadic inhibition was earlier, and its magnitude was stronger, for antisaccades, relative to prosaccades. The plausibility that the superior colliculus is the neurophysiological locus of the saccadic inhibition effect was explored. |
Tanja R. M. Coeckelbergh; Frans W. Cornelissen; Wiebo H. Brouwer; Aart C. Kooijman The effect of visual field defects on eye movements and practical fitness to drive Journal Article In: Vision Research, vol. 42, no. 5, pp. 669–677, 2002. @article{Coeckelbergh2002, Eye movements of subjects with visual field defects due to ocular pathology were monitored while performing a dot counting task and a visual search task. Subjects with peripheral field defects required more fixations, longer search times, made more errors, and had shorter fixation durations than control subjects. Subjects with central field defects performed less well than control subjects although no specific impairment could be pinpointed. In both groups a monotonous relationship was observed between the visual field impairment and eye movement parameters. The use of eye movement parameters to predict viewing behavior in a complex task (e.g. driving) was limited. |
Charles A. Collin; Avi Chaudhuri Using MATLAB with the Psychophysics Toolbox to present the heterochromatic fusion nystagmus stimulus Journal Article In: Behavior Research Methods, Instruments & Computers, vol. 34, no. 4, pp. 500–508, 2002. @article{Collin2002, We present a program for MATLAB that generates and presents the heterochromatic fusion nystagmus stimulus. This stimulus allows assessment of isoluminant states through recordings of reflexive eye movements (optokinetic nystagmus). The reflexive nature of the subject's response makes this stimulus especially useful with nonverbal subjects, such as children and animals. Unfortunately, the stimulus is complex and difficult to program. By presenting the present program, we hope to help those who wish to use this tool in their research. The code of the function can be downloaded at www. dal.ca/-mcmullen/downloads.html. |
Bettina Olk; Monika Harvey; Iain D. Gilchrist First saccades reveal biases in recovered neglect Journal Article In: Neurocase, vol. 8, no. 4, pp. 306–313, 2002. @article{Olk2002, Hemispatial neglect affects the ability to explore space on the side opposite a brain lesion. This deficit is also mirrored in abnormal saccadic eye movement patterns. The present study investigated if the recovery of neglect is also reflected in saccadic eye movements. Patient AF, who displayed strong hemispatial neglect 1 month post-right thalamic stroke, had largely recovered 3 months later when tested on visual exploration tasks of the Behavioural Inattention Test. At this stage, AF was tested on a visual search task while his eye movements (direction, latencies and amplitudes of first saccades) and manual reaction times were recorded. The experimental conditions differed with respect to stimulus number and distracter type and increased in difficulty. AF correctly generated saccades into the neglected field when the target was presented alone. In contrast, a considerable left/right difference was present for all multiple-stimulus search displays. Although recovered from neglect in standardized assessment, AF showed a strong rightward bias resulting in highly asymmetric response times and eye movement behaviour. We conclude that eye movement patterns are far more susceptible to remaining spatial impairments and can thus provide a sensitive means to assess the extent of neglect recovery. |
Michael D. Crossland; Gary S. Rubin The use of an infrared eyetracker to measure fixation stability Journal Article In: Optometry and Vision Science, vol. 79, no. 11, pp. 735–739, 2002. @article{Crossland2002, PURPOSE: To assess fixation stability in patients, a scanning laser ophthalmoscope (SLO) has typically been required. Disadvantages of this technique include the need for a fixed viewing distance and rigid head support. Some modern infrared eyetrackers do not have these constraints. The purpose of this study was to compare fixation stability measurements made with these instruments. METHODS: Normal subjects were asked to fixate a 2.5 degrees high cross while fixation was measured with a SLO and an infrared eyetracker. Bivariate contour ellipse areas were calculated. RESULTS: There was a linear relationship between the bivariate contour ellipse areas measured using each instrument. Bivariate contour ellipse areas returned from the eyetracker were larger. There was no difference in test-retest variability between the instruments. CONCLUSIONS: The eyetracker indicates fixation to be less stable than the SLO does, perhaps because of eye movements to compensate for small head movements. Our eyetracker can be used to analyze fixation when viewing images at any distance, without the need for head immobilization. The eyetracker and the SLO complement each other in the investigation of visual behavior. |
2001 |
Albert V. Berg; J. A. Beintema; Maarten A. Frens Heading and path percepts from visual flow and eye pursuit signals Journal Article In: Vision Research, vol. 41, no. 25-26, pp. 3467–3486, 2001. @article{Berg2001, The percept of self-motion through the environment is supported by visual motion signals and eye movement signals. The interaction between these signals by decoupling of the eye movement and the pattern of retinal motion during brief simulated ego-movement on straight or circular trajectories was studied. A new response method enabled subjects to report perceived destination and perceived curvature of their future path simultaneously. Various combinations of simulated gaze rotation in the retinal flow and eye pursuit were investigated. Simulated gaze rotation ranged from consistent and larger than, to opponent and larger than eye pursuit. It was found that the perceived destination shifts non-linearly with the mismatch between simulated gaze rotation and eye pursuit. The non-linearity is also revealed in the perceived tangent heading direction and perceived path curvature, although to different extent in different subjects. For the same retinal flow, eye pursuit that is consistent with the simulated gaze rotation reduces heading error and the perceived path straightens out. In contrast, perceived path and/or heading do not become more curved or more biased in the direction opposite to pursuit when the eye -in-head rotation is opposite to the simulated gaze rotation. These observations point to modulation of the effect of the extra-retinal pursuit signal by the visual evidence for eye rotation. In a second experiment, one presented to a stationary eye the sum of a component of simulated gaze rotation and radial flow. It was found that the bi-circular flow component, that characterizes the change in pattern of flow directions by the gaze rotation, induces a shift of perceived heading without appreciable perceived path curvature. Conversely, the complementary component of simulated gaze rotation (bi-radial flow) evokes a percept of motion on a curved path with a small tangent heading error. It was suggested that bi-circular and bi-radial flow components contribute primarily to percepts of heading and path curvature, respectively. |
Elliot M. Frohman; Teresa C. Frohman; J. Fleckenstein; M. K. Racke; K. Hawker; Phillip D. Kramer Ocular contrapulsion in multiple sclerosis: Clinical features and pathophysiological mechanisms Journal Article In: Journal of Neurology, Neurosurgery and Psychiatry, vol. 70, no. 5, pp. 688–692, 2001. @article{Frohman2001, The objective was to describe in multiple sclerosis, a cerebellar eye movement syndrome that resulted from an acute episode of inflammatory demyelination. Contrapulsion is an ocular motor disturbance characterised by a triad of (1) hypermetric saccadic eye movements in a direction opposite from a precisely localised lesion within a specific white matter pathway, the uncinate fasciculus, at the level of the superior cerebellar peduncle (SCP); (2) hypometric saccades towards the side of the lesion; (3) oblique saccades directed away from the side of the lesion on attempted vertical saccades. Infrared oculography was used to demonstrate the characteristic features of contrapulsion in two patients with multiple sclerosis. Brain MRI showed lesions within the region of the uncinate fasciculus and superior cerebellar peduncle in both patients. Eye movement recordings showed saccadic hypermetria away from the side of the lesion and saccadic hypometria towards the side of the lesion. The hypometria decomposed into a series of stepwise movements as the eye approached the target. Oblique saccades directed away from the side of the lesion were seen on attempted vertical saccades. In conclusion, ocular contrapulsion can be seen in patients with multiple sclerosis and results from a lesion in the region of the SCP, involving the uncinate fasciculus. |
Elliot M. Frohman; H. Zhang; Phillip D. Kramer; J. Fleckenstein; K. Hawker; M. K. Racke; Teresa C. Frohman MRI characteristics of the MLF in MS patients with chronic internuclear ophthalmoparesis Journal Article In: Neurology, vol. 57, no. 5, pp. 762–768, 2001. @article{Frohman2001a, OBJECTIVE: The authors imaged the medial longitudinal fasciculus (MLF) in 58 patients with MS and chronic internuclear ophthalmoparesis (INO) to determine which MRI technique best shows the characteristic lesion associated with this ocular motor syndrome. METHODS: Using quantitative infrared oculography, the authors determined the ratios of abduction to adduction for velocity and acceleration, to confirm the presence of INO and to determine the severity of MLF dysfunction in 58 patients with MS and INO. Conventional MRI techniques, including proton density imaging (PDI), T2-weighted imaging, and fluid-attenuated inversion recovery (FLAIR) imaging, were used to ascertain which technique best shows MLF lesions within the brainstem tegmentum. T1-weighted imaging was performed to determine the frequency of brainstem tegmentum hypointensities. RESULTS: All patients studied had evidence of an MLF lesion hyperintensity on PDI, whereas T2-weighted imaging and FLAIR imaging showed these lesions in 88% and 48% of patients, respectively. With PDI, dorsomedial tegmentum lesions were seen in the pons in 93% of patients and in the midbrain of 66% of patients. Lesions were observed at both locations in 59% of patients. One patient had an MLF lesion with a corresponding T1 hypointensity. CONCLUSIONS: PDI best shows the MLF lesion in patients with MS and INO. |
Adrienne L. LeVasseur; J. Randall Flanagan; Richard J. Riopelle; Douglas P. Munoz Control of volitional and reflexive saccades in Tourette's syndrome Journal Article In: Brain, vol. 124, pp. 2045–2058, 2001. @article{LeVasseur2001, Tourette's syndrome is characterized by involuntary tics and, although the underlying pathogenesis and patho- physiology of Tourette's syndrome remains unclear, it is suspected that basal ganglia structures are involved. The basal ganglia also play an important role in the control of saccadic eye movements and we therefore hypothesize that Tourette's syndrome patients have abnormal control of saccadic eye movements. In this study, 10 subjects with Tourette's syndrome and 10 age- and sex-matched controls performed four different oculomotor paradigms requiring the execution and/or suppression of reflexive and/or voluntary saccades. In the immediate saccade tasks, sub- jects were required to look either toward (pro-saccade task) or away from (anti-saccade task) a peripheral target as soon as it appeared. In the delayed saccade tasks, subjects were instructed to wait for a central fixation point to disappear before initiating eye movements. Among Tourette's syndrome subjects, saccadic reaction times were longer in all tasks. Saccadic amplitudes were smaller in Tourette's syndrome subjects, and they made more saccades to reach the eccentric target. The occurrence of direction errors (i.e. reflexive pro-saccades on anti-saccade trials) was normal in the immediate anti-saccade task, suggesting that the ability to inhibit reflexive saccades towards novel stimuli was not impaired in Tourette's syndrome. Timing errors (i.e. eye movements made prior to disappearance of the central fixation point in delayed saccade tasks) were significantly greater among Tourette's syndrome subjects. Moreover, these errors were predominantly made towards the first target of the remembered sequence in a delayed memory-guided sequential saccade task. These results indicate that the ability to inhibit or delay planned motor programmes is significantly impaired in Tourette's syndrome. We hypothesize that altered cortical–basal ganglia circuitry leads to reduced cortical inhibition making it harder for Tourette's syndrome subjects to withhold the execution of planned motor programmes. |
Masud Husain; Sabira K. Mannan; Timothy L. Hodgson; Ewa Wojciulik; Jon Driver; Christopher Kennard Impaired spatial working memory across saccades contributes to abnormal search in parietal neglect Journal Article In: Brain, vol. 124, no. 5, pp. 941–952, 2001. @article{Husain2001, Visual neglect of left space following right parietal damage in humans involves a lateral bias in attention, apparent in many search tasks. We hypothesized that parietal neglect may also involve a failure to remember which locations have already been examined during visual search: an impairment in retaining searched locations across saccades. Using a new paradigm, we monitored gaze during search, while simultaneously probing whether observers judged they had found a new target, or judged instead that they were re-fixating a previously examined target. A patient with left neglect following focal right parietal infarction repeatedly re-fixated right locations. Critically, he often failed to remember that these locations had already been searched, treating old targets as new discoveries at an abnormal rate. In comparison, healthy age-matched control subjects rarely re-fixated targets, and mistook old targets as new targets even more rarely. The frequency of such mistakes in the parietal patient, for different conditions, correlated with the severity of his neglect. Control experiments indicated no perceptual localization deficit in non-search tasks. These results suggest a deficit in retaining searched locations across saccades in parietal neglect, in addition to the lateral spatial bias. Moreover, the former deficit exacerbates the latter, such that patients do not realize that the rightward locations favoured by their bias have already been examined during previous fixations and, for this reason, they saccade back to them repeatedly. The combination of the two deficits (a lateral bias plus a deficit in retaining locations already searched) may thus explain the pathological pattern of search that characterizes parietal neglect: why stimuli on the right are re-examined recursively, as if being searched for the first time, and hence why stimuli on the left continue to be ignored even with unlimited viewing time. These proposals accord with recent electrophysiological and functional imaging data, demonstrating posterior parietal involvement in the retention of target locations across saccades. |
Nomdo M. Jansonius; Ton (A) M. Vliet; Frans W. Cornelissen; Jan Willem R. Pott; Aart C. Kooijman In: Journal of Neuro-Ophthalmology, vol. 21, no. 1, pp. 26–29, 2001. @article{Jansonius2001, An otherwise healthy 15-year-old girl with a congenital nystagmus was evaluated at our department using visual evoked potential recording and magnetic resonance imaging. She appears to have the unique isolated inborn absence of the optic chiasm, described only once before in two unrelated girls. Unlike these previously described cases, our patient does not seem to display a see-saw nystagmus. |
Risto Näsänen; Helena Ojanpää; Ilpo Kojo Effect of stimulus contrast on performance and eye movements in visual search Journal Article In: Vision Research, vol. 41, no. 14, pp. 1817–1824, 2001. @article{Naesaenen2001a, According to the visual span control hypothesis, eye movements are controlled in relation to the size of visual span. In reading, the decrease of contrast reduces visual span, saccade sizes, and reading speed. The purpose of the present study is to determine how stimulus contrast affects the speed of two-dimensional visual search and how changes in eye movements and visual span could explain changes in performance. The task of the observer was to search for, and identify, an uppercase letter from a rectangular array of characters in which the other items were numerals. Threshold search time, i.e. the duration of stimulus presentation required for search that is successful with a given probability, was determined by using a multiple-alternative staircase method. Eye movements were recorded simultaneously by using a video eye tracker. Four different set sizes (the sizes of stimulus array) (3 × 3-10 × 10), and five different contrasts (0.0186 - 0.412) were used. At all set sizes, threshold search time decreased with increasing contrast. Also the average number of fixations per search decreased with increasing contrast. At the smallest set size (3 × 3), only one fixation was needed except at the lowest contrast. Average fixation duration decreased and saccade amplitudes increased slightly with increasing contrast. The reduction of the number of fixations with increasing contrast suggests that visual span, i.e. the area from which information can be collected at one fixation, increases with increasing contrast. The reduction of the number of fixations together with reduced fixation duration result in reduced search times when contrast increases. |
Sebastian Pannasch; Sascha M. Dornhoefer; Pieter J. A. Unema; Boris M. Velichkovsky The omnipresent prolongation of visual fixations: Saccades are inhibited by changes in situation and in subject's activity Journal Article In: Vision Research, vol. 41, no. 25-26, pp. 3345–3351, 2001. @article{Pannasch2001, Presenting a distractor prolongs not only saccadic reaction times in paced tasks but also fixation durations in unpaced tasks. To investigate whether the effect of a distractor is a pure optomotor reflex, we used both visual and auditory distractors in an unpaced picture-viewing paradigm. Results show a distractor effect for both modalities. Analysis of data from previous studies showed similar effects, even in amodal shifts of attention. These findings challenge the hypothesis that the effect is modality-specific and suggest that the distractor effect may be another expression of the orienting reflex. |
Melanie Doyle; Robin Walker Curved saccade trajectories: Voluntary and reflexive saccades curve away from irrelevant distractors Journal Article In: Experimental Brain Research, vol. 139, no. 3, pp. 333–344, 2001. @article{Doyle2001, In this study we examined the impact of irrelevant distractors upon trajectories of reflexive and voluntary saccades. Observers made saccades to visual targets above and below fixation as directed by target appearance (reflexive) or by a central directional cue (voluntary) in the presence of an irrelevant distractor stimulus (a cross) whose appearance was simultaneous with target onset. We recorded saccade latency, amplitude and the magnitude of saccade curvature relative to the direct route from the start-to-end of the saccade. Previous studies of saccades curvature have used distractors to provide information about the saccade task and, as a result, have only examined trajectories of voluntary saccades. However, we have shown that both reflexive and voluntary saccades curved away from irrelevant distractors. The effect of irrelevant distractors indicates that observers do not need to attend to distractors in a voluntary fashion for distractors to modify saccade trajectories. Furthermore, it highlights an important parallel in curvature of saccades and reach trajectories, namely that both curve away from irrelevant distractors. The second important observation was that reflexive, as well as voluntary, saccades curved away from distractors. This suggests that curvature is not solely a consequence of voluntary control. These results have been considered within the context of inhibition-based theories of curvature derived from studies of saccade and manual reach trajectories. |
2000 |
Diane C. Gooding; Meghan D. Miller; Thomas R. Kwapil Smooth pursuit eye tracking and visual fixation in psychosis-prone individuals Journal Article In: Psychiatry Research, vol. 93, no. 1, pp. 41–54, 2000. @article{Gooding2000a, Subjects identified by Perceptual Aberration-Magical Ideation (Per-Mag) scores (n = 97), Social Anhedonia (SocAnh) scores (n = 45), and Physical Anhedonia (PhysAnh) scores (n = 31) as well as normal controls (n = 94), underwent psychophysiological and clinical assessment. This is the first published investigation of pursuit system functioning in three groups of questionnaire-identified at-risk individuals. Pursuit during a simple non- monitor tracking task was measured using root-mean-square error (RMSE) scores and pursuit gain scores. Fixation performance was measured in terms of number of saccades away from the central fixation point. The at-risk subjects were more likely to display aberrant smooth pursuit tracking than controls, though there were no significant differences between the at-risk subjects endorsing items relevant to positive-symptom schizotypy and those endorsing items pertaining to negative-symptom schizotypy. The groups did not differ significantly in their visual fixation performance. Participants were also evaluated for the presence of Axis I symptomatology and psychotic-like experiences. Neither the experimental subjects nor the control subjects displayed a significant association between ocular motor performance and psychotic-like experiences. These findings are consistent with prior evidence that pursuit tracking is a trait characteristic, independent of clinical status. |
Gillian A. OʼDriscoll; Anne-Lise V. G. Wolff; Chawki Benkelfat; Patrik S. Florencio; Samarthji Lal; Alan C. Evans Functional neuroanatomy of smooth pursuit and predictive saccades Journal Article In: NeuroReport, vol. 11, no. 6, pp. 1335–1340, 2000. @article{OʼDriscoll2000, We used PET to study differences in cerebral blood flow (CBF) in smooth pursuit, predictive saccades and fixation. Eye movements were monitored in the scanner. Compared with fixation, pursuit and predictive saccades activated a network of highly similar areas, including frontal eye fields, supplementary eye fields, V5 and medial cuneus. Our findings are consistent with non-human primate studies that suggest that pursuit and saccades are controlled by similar and adjacent neural areas. Pursuit was associated with greater activation of caudate than saccades, suggesting a role for basal ganglia in pursuit that is consistent with studies of neurological populations. Saccades were associated with greater activation of cerebellum and frontal eye fields. A frontal-cerebellar loop may be important in coordinating the preparation and timing of saccades in predictive tracking. |
Alexander P. Leff; Sophie K. Scott; H. Crewes; Timothy L. Hodgson; A. Cowey; D. Howard; Richard J. S. Wise Impaired reading in patients with right hemianopia Journal Article In: Annals of Neurology, vol. 47, no. 2, pp. 171–178, 2000. @article{Leff2000, A left occipital stroke may result in alexia for two reasons, which may coexist depending on the distribution of the lesion. A lesion of the left lateroventral prestriate cortex or its afferents impairs word recognition ("pure" alexia). If the left primary visual cortex or its afferents are destroyed, resulting in a complete right homonymous hemianopia, rightward saccades during text reading are disrupted ("hemianopic" alexia). By using functional imaging, we showed two separate but interdependent systems involved in reading. The first, subserving word recognition, involved the representation of foveal vision in the left and right primary visual cortex and the ventral prestriate cortex. The second system, responsible for the planning and execution of reading saccades, consisted of the representation of right parafoveal vision in the left visual cortex, the bilateral posterior parietal cortex (left > right), and the frontal eye fields (right > left). Disruption of this distributed neural system was demonstrated in patients with severe right homonymous hemianopia, commensurate with their inability to perform normal reading eye movements. Text reading, before processes involved in comprehension, requires the integration of perceptual and motor processes. We have demonstrated these distributed neural systems in normal readers and have shown how a right homonymous hemianopia disrupts the motor preparation of reading saccades during text reading. |
Chiang-Shan Ray Li; Mon-Chu Chen; Yong-Yi Yang; Hsueh-Ling Chang; Chia-Yih Liu; Seng Shen; Ching-Yen Chen Perceptual alternation in obsessive compulsive disorder - implications for a role of the cortico-striatal circuitry in mediating awareness Journal Article In: Behavioural Brain Research, vol. 111, no. 1-2, pp. 61–69, 2000. @article{Li2000, Mounting evidence suggests that obsessive compulsive disorder (OCD) results from functional aberrations of the fronto-striatal circuitry. However, empirical studies of the behavioral manifestations of OCD have been relatively lacking. The present study employs a behavioral task that allows a quantitative measure of how alternative percepts are formed from one moment to another, a process mimicking the brain state in which different thoughts and imageries compete for access to awareness. Eighteen patients with OCD, 12 with generalized anxiety disorder, and 18 normal subjects participated in the experiment, in which they viewed one of the three Schroder staircases and responded by pressing a key to each perceptual reversal. The results demonstrate that the patients with OCD have a higher perceptual alternation rate than the normal controls. Moreover, the frequency of perceptual alternation is significantly correlated with the Yale-Brown obsessive compulsive and the Hamilton anxiety scores. The increase in the frequency of perceptual reversals cannot easily be accounted for by learning or by different patterns of eye fixations on the task. These results provide further evidence that an impairment of the inhibitory function of the cortico-striatal circuitry might underlie the etiology of OCD. The implications of the results for a general role of the cortico-striatal circuitry in mediating awareness are discussed. |
Diane C. Gooding; Jeffrey A. Grabowski; Christian S. Hendershot Fixation stability in schizophrenia, bipolar, and control subjects Journal Article In: Psychiatry Research, vol. 97, no. 2-3, pp. 119–128, 2000. @article{Gooding2000, A few investigators have suggested that visual fixation abnormalities may serve as an endophenotype of liability for schizophrenia. However, the data are equivocal. Conflicting reports regarding the specificity of fixation deficits to schizophrenia may be attributable to methodological differences. Thirty-four schizophrenia patients, 20 bipolar patients, and 30 non-patient controls were presented targets for central fixation. Fixation was scored in terms of frequency of saccades as well as qualitative ratings. Analysis of variance on the number of saccades produced during fixation revealed that the three groups did not differ. Similarly, we observed that the schizophrenia patients did not differ from either bipolar patients or controls in terms of ratings of fixation quality. It appears that schizophrenia patients are not characterized by poor visual fixation. The findings are discussed in terms of the viability of visual fixation as a marker of schizophrenic diathesis, as well as possible implications for the analysis of schizophrenia patients' visual search performance. |
1999 |
T. Niemann; Markus Lappe; A. Büscher; Klaus-Peter Hoffmann Ocular responses to radial optic flow and single accelerated targets in humans Journal Article In: Vision Research, vol. 39, no. 7, pp. 1359–1371, 1999. @article{Niemann1999, Self-movement in a structured environment induces retinal image motion called optic flow. Optic flow on one hand provides information about the direction of self-motion. On the other hand optic flow presents large field visual motion which will elicit eye movements for the purpose of image stabilization. We investigated oculomotor behavior in humans during the presentation of radial optic flow fields which simulated forward or backward self-motion. Different conditions and oculomotor tasks were compared. In one condition, subjects had to actively pursue single dots in a radial flow pattern. In a second condition, subjects had to pursue single dots over a dark background. These dots accelerated or decelerated similar to single dots in radial optic flow. In a third condition, subjects were asked to passively view the entire optic flow stimulus. Smooth pursuit eye movements with high gain were observed when dots were actively pursued. This was true for single dots moving over a homogeneous background and for single dots in the optic flow. Passive viewing of optic flow stimuli evoked eye movements that resembled an optokinetic nystagmus. Slow phase eye movements tracked the motion of elements in the optic flow. Gain was low for simulated forward self-motion (expanding optic flow) and high for simulated backward movement self-motion (contracting optic flow). Thus, voluntary pursuit and passive optokinetic responses yielded different gain for the tracking of elements of an expanding optic flow pattern. During passive viewing of the optic flow stimulus, gaze was usually at or near the focus of radial flow. Our results give insights into the oculomotor performances and needs for image stabilization during self-motion and in the role of gaze strategy for the detection of the direction of heading. |
Jan Theeuwes; Arthur F. Kramer; Sowon Hahn; David E. Irwin; Gregory J. Zelinsky Influence of attentional capture on oculomotor control Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 25, no. 6, pp. 1595–1608, 1999. @article{Theeuwes1999, Previous research has shown that when searching for a color singleton, top-down control cannot prevent attentional capture by an abrupt visual onset. The present research addressed whether a task-irrelevant abrupt onset would affect eye movement behavior when searching for a color singleton. Results show that in many instances the eye moved in the direction of the task-irrelevant abrupt onset. There was evidence that top-down control could neither entirely prevent attentional capture by visual onsets nor prevent the eye from starting to move in the direction of the onset. Results suggest parallel programming of 2 saccades: 1 voluntary goal-directed eye movement toward the color singleton target and 1 stimulus-driven eye movement reflexively elicited by the abrupt onset. A neurophysiologically plausible model that can account for the current findings is discussed. |
Gillian A. O'Driscoll; Chawki Benkelfat; Patrik S. Florencio; Anne-Lise V. G. Wolff; Ridha Joober; Samarthji Lal; Alan C. Evans Neural correlates of eye tracking deficits in first-degree relatives of schizophrenic patients Journal Article In: Archives of General Psychiatry, vol. 56, no. 12, pp. 1127–1134, 1999. @article{ODriscoll1999, BACKGROUND: Schizophrenia is thought to arise from the interaction of genetically mediated and environmentally triggered abnormalities in brain function. Reduced frontal activation, reported in schizophrenic patients, may be one expression of genetic risk. The present study investigated whether frontal activation in relatives of schizophrenic patients would be related to eye tracking deficits (ETD), which are considered a behavioral marker of risk for schizophrenia. METHODS: Subjects were first-degree relatives of schizophrenic patients (n = 17) and controls (n = 11). Relatives were divided into those with normal and abnormal pursuit based on qualitative ratings. Subjects were scanned using positron emission tomography and the H(2)15O bolus subtraction technique while performing smooth pursuit and fixation. Brain areas more active in pursuit than fixation were identified in the 3 groups. Correlations were used to investigate the relationship between activation of pursuit regions and pursuit gain in the relatives. RESULTS: Controls significantly activated frontal eye fields (FEFs) and posterior areas, including the motion processing area, V5, and cuneus. The 2 groups of relatives activated the same posterior regions as controls, but differed from each other in activation of FEFs. Relatives with normal tracking activated right dorsal FEFs while relatives with ETD did not. Individual subtractions revealed that 90% of controls and 100% of the relatives with normal tracking activated FEFs during pursuit compared with 42% of relatives with ETD (P = .009). Pursuit gain was significantly and selectively associated with percent activation of right dorsal FEFs (r = 0.74). CONCLUSIONS: Subtle frontal dysfunction seems to be a pathophysiological substrate of ETD in relatives of schizophrenic patients, and may be one aspect of genetically mediated differences in brain function relevant to schizophrenia |