On the development of voluntary and reflexive components in human saccade generation

Eye movements in neurodevelopmental disorders

PURPOSE OF REVIEW

The aim of this paper is to review the literature on eye-movement abnormalities associated with neurodevelopmental disorders. Eye-movement testing is a non-invasive quantitative approach for evaluating brain systems across the age spectrum. It thus provides a promising methodology for characterizing and documenting maturational abnormalities in brain systems associated with neurodevelopmental disorders.

RECENT FINDINGS

Recent oculomotor studies have made significant contributions to the understanding of neurodevelopmental disorders, most notably in autism, attention-deficit/hyperactivity disorder, and Tourette's syndrome. Notably different patterns of deficits have been found in these disorders and have helped to clarify their pathophysiology.

SUMMARY

Eye-movement studies have begun to serve as a useful approach for studying cognitive and neurophysiological aspects of neurodevelopmental disorders. They also have potential as a strategy for establishing quantitative endophenotypes for genetic research, and for monitoring beneficial and adverse effects of pharmacotherapies. Studies are needed that involve larger patient populations, longitudinal characterization of developmental failures, patients free from central nervous system-active medications, and that use functional imaging, as patients perform eye-movement tasks, for direct identification of clinically relevant abnormalities in brain systems.

The Emergence of Collaborative Brain Function: fMRI Studies of the Development of Response Inhibition

Adolescence marks the beginning of adult-level cognitive control of behavior supported by the brain maturation processes of synaptic pruning and myelination. Cognitive development studies on adolescence indicate that this period is characterized by improvements in the performance of existing abilities including speed and capacity of information processing and the ability to have consistent cognitive control of behavior. Although adolescents can behave at adult levels in some ways, brain imaging studies indicate that the functional organization of brain systems that support higher-cognitive processes are not fully mature. Synaptic pruning allows for more efficient local computations, enhancing the ability of discrete brain regions to support high-level cognitive control of behavior including working memory. Myelination increases the speed of neuronal transmission supporting the collaboration of a widely distributed circuitry, integrating regions that support top-down cognitive control of behavior. Functional brain imaging methods allow for the characterization of the relationship between cognitive development and brain maturation as we can map progressions in the establishment of distributed brain circuitry and its relation to enhanced cognitive control of behavior. We present a review on the maturation (as distinct from "development" in emphasizing the transition to maturity and stabilization) of response inhibition, brain structure, and brain function through adolescence. We also propose a model for brain-behavior maturation that allows for the qualitative changes in cognitive processes that occur during adolescence.

Age Equivalence in Switch Costs for Prosaccade and Antisaccade Tasks

This study examined age differences in task switching using prosaccade and antisaccade tasks. Significant specific and general switch costs were found for both young and old adults, suggesting the existence of 2 types of processes: those responsible for activation of the currently relevant task set and deactivation of the previously relevant task set and those responsible for maintaining more than 1 task active in working memory. Contrary to the findings of previous research, which used manual response tasks with arbitrary stimulus-response mappings to study task-switching performance, no age-related deficits in either type of switch costs were found. These data suggest age-related sparing of task-switching processes in situations in which memory load is low and stimulus-response mappings are well learned.

Aging and the Strategic Control of the Fixation Offset Effect

A study was conducted to examine potential age-related differences in the strategic control of exogenous and endogenous saccades within the context of the fixation offset effect (FOE; i.e., faster saccades when a fixation point is removed than when it is left on throughout a trial). Subjects were instructed to make rapid saccades either on the basis of a suddenly appearing peripheral visual stimulus (exogenous saccade) or in response to a tone (endogenous saccade). On half of the trials the fixation point was removed simultaneously with the occurrence of the cue stimulus. Subjects' preparatory set was varied by manipulating the proportion of saccades generated to a visual and auditory stimulus within a trial block. Young and old adults both produced FOEs, and the FOEs were strategically modulated by preparatory set. The data are discussed in terms of aging and oculomotor control.

Effect of Sleep Deprivation on Saccades and Eyelid Blinking

In this study the effect of sleep deprivation on specific components of eye and eyelid movement was investigated in a group of young and healthy subjects. The duration of sleep deprivation was 20 h. Each subject had to execute different saccade tasks: reflexive saccades, voluntary prosaccades and antisaccades. Saccade latency, number of saccade errors and blink rate during the saccade tasks were evaluated as predictors of performance decrements resulting from sleep deprivation. The present study showed no significant deterioration of latency and number of errors in the different saccade tasks. However, the blink rate was significantly higher after a night without sleep than before. It is concluded that the blink rate appears to be a promising psychophysical measurement and a more sensitive parameter than saccade performance to evaluate the effects of 20 h of sleep deprivation. These results encourage further research on this topic.

Antisaccade performance of 1,273 men: effects of schizotypy, anxiety, and depression

A total of 1,273 conscripts of the Greek Air Force performed antisaccades and completed self-reporting questionnaires measuring schizotypy and current state-dependent psychopathology. Only 1.0% of variability in antisaccade performance indices was related to psychometric scores in the population and could be attributed more to current state-dependent symptoms such as anxiety rather than to schizotypy. In contrast, a specific increase of error rate and response latency variability and a high correlation of these 2 variables was observed in a group with very high schizotypy scores. This effect was independent of anxiety and depression, suggesting that a specific group of psychosis-prone individuals has a characteristic deviance in antisaccade performance that is not present in the general population.

Altered control of visual fixation and saccadic eye movements in attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is characterized by the overt symptoms of impulsiveness, hyperactivity, and inattention. A frontostriatal pathophysiology has been hypothesized to produce these symptoms and lead to reduced ability to inhibit unnecessary or inappropriate behavioral responses. Oculomotor tasks can be designed to probe the ability of subjects to generate or inhibit reflexive and voluntary responses. Because regions of the frontal cortex and basal ganglia have been identified in the control of voluntary responses and saccadic suppression, we hypothesized that children and adults diagnosed with ADHD may have specific difficulties in oculomotor tasks requiring the suppression of reflexive or unwanted saccadic eye movements. To test this hypothesis, we measured eye movement performance in pro- and anti-saccade tasks of 114 ADHD and 180 control participants ranging in age from 6 to 59 yr. In the pro-saccade task, participants were instructed to look from a central fixation point toward an eccentric visual target. In the anti-saccade task, stimulus presentation was identical, but participants were instructed to suppress the saccade to the stimulus and instead look from the central fixation point to the side opposite the target. The state of fixation was manipulated by presenting the target either when the central fixation point was illuminated (overlap condition) or at some time after it disappeared (gap condition). In the pro-saccade task, ADHD participants had longer reaction times, greater intra-subject variance, and their saccades had reduced peak velocities and increased durations. In the anti-saccade task, ADHD participants had greater difficulty suppressing reflexive pro-saccades toward the eccentric target, increased reaction times for correct anti-saccades, and greater intra-subject variance. In a third task requiring prolonged fixation, ADHD participants generated more intrusive saccades during periods when they were required to maintain steady fixation. The results suggest that ADHD participants have reduced ability to suppress unwanted saccades and control their fixation behavior voluntarily, a finding that is consistent with a fronto-striatal pathophysiology. The findings are discussed in the context of recent neurophysiological data from nonhuman primates that have identified important control signals for saccade suppression that emanate from frontostriatal circuits.

Age-related effects of attentional and oculomotor capture by onsets and color singletons as a function of experience

The present experiment examined the degree to which experience with different stimulus characteristics affects attentional capture, particularly as related to aging. Participants were presented with onset target/color singleton distractor or color singleton target/onset distractor pairs across three experimental sessions. The target/distractor pairs were reversed in the second session such that the target in the first session became the distractor in the second and third sessions. For both young and old adults previous experience with color as a target defining feature influenced oculomotor capture with task-irrelevant color distractors. Experience with sudden onsets had the same effect for younger and older adults, although capture effects were substantially larger for onset than for color distractors. Experience-based capture effects diminished relatively rapidly after target and distractor-defining properties were reversed. The results are discussed in terms of top-down and stimulus-driven effects on age-related differences in attentional control.

Effects of direction on saccadic performance in relation to lateral preferences

A sample of 676 healthy young males performed visually guided saccades and antisaccades and completed the Porac-Coren questionnaire measuring lateral preferences. There was no difference in mean latency between rightward versus leftward saccades or for saccades executed in the left versus right hemispace. There was also no right/left asymmetry for individuals with left or right dominance as assessed by the lateral preferences questionnaire. The same results were observed for the latency of antisaccades and for the error rate in the antisaccade task. Finally, we did not confirm any substantial subpopulation of individuals with idiosyncratic left/right latency asymmetries that persisted both in the saccade and antisaccade task. These results suggest that neither latency nor antisaccade error rate are good indicators of lateral preferences in these tasks. Other oculomotor tasks might be more sensitive to hemifield differences, or cerebral hemispheric asymmetry is not present at the level of cortical organization of saccades and antisaccades.

Contribution of the primate prefrontal cortex to the gap effect

The introduction of a brief temporal gap between the disappearance of the initial fixation point and the presentation of a peripheral target leads to a general reduction in saccadic reaction times (SRTs), known as the gap effect. Moreover, extremely short latency express saccades frequently occur in this paradigm. Disorders of the prefrontal cortex (PFC) are often associated with increased numbers of express saccades and an inability to suppress reflexive saccades. To investigate the role of the PFC in the gap effect and in express saccade generation, we trained two rhesus monkeys on a gap saccade task in which the initial fixation point (FP) disappeared 200 ms or 600 ms before a peripheral stimulus appeared either 8 degrees to its left or right side. We recorded from the lateral PFC (areas 8 Ar and 46) in both monkeys the activity of 214 neurons, 84 (39%) of which exhibited task-related activity. These neurons could be further categorized into separate groups based on their discharge behaviour: fixation neurons with a decrease in activity during the gap (27%), FP offset neurons (12%), preparatory neurons with an increase in activity during the gap (30%), visual neurons (6%), post-saccadic neurons (8%), and reward-related neurons (12%). There were no obvious differences in the topography of these groups. Significant differences between express and regular saccade trials were found for fixation-related neurons. These neurons had a lower activity during the gap prior to the generation of contralateral express saccades. We hypothesize that a reduction in the activity of fixation-related neurons in the PFC may contribute to the elevated rate of express saccades in prefrontal disorders.

Commentary: eye movement research with clinical populations

The preceding set of chapters span the disciplines of neurology and psychiatry, and provide a diverse introduction to clinical eye movement research. They illustrate how oculomotor paradigms can be used to learn about acute and chronic perturbations in brain function, disturbances in brain development, disturbances in sensorimotor as well as cognitive systems, and the effects of therapeutic and illicit drugs on brain function. This commentary discusses these contributions, provides an overview of broad methodological issues involved in applying eye movement studies to psychiatric populations using the antisaccade task as an exemplar, and considers the potential of collaborations between eye movement and brain imaging researchers to advance understanding of clinical eye movement abnormalities and of what they reveal about the organization of the oculomotor system.

Development of pro- and antisaccades in children with attention-deficit hyperactivity disorder (ADHD) and healthy controls

To date, the investigation of the antisaccade task, a simple test of "executive functions," in children with ADHD has yielded inconsistent results. The present study aimed at contributing to this issue by (a) the investigation of a large sample of carefully diagnosed ADHD patients aged 7-15 years, and (b) the analyses of differential age effects in patients and controls. Healthy control children were pairwise matched with patients (N = 46; age = 136 +/- 24 months) for age and gender, and did not significantly differ in IQ. Horizontal pro- and antisaccades were elicited under the 200-ms gap and overlap conditions (blocks of 100 trials each). Overall, patients exhibited (a) augmented pro- and antisaccadic reaction times, (b) augmented error rates (antitasks), (c) augmented proportions of early responses (all conditions), and (d) reduced proportions of express saccades under the prosaccadic gap condition. The greater decline in anti- as compared to pro-SRT with increasing age that characterized controls was missing in patients. Confirming Barkley's (1997) neuropsychological theory of ADHD, these results altogether point to alterations in "executive functions" in ADHD patients that are presumably supported by frontal lobe structures, in particular the lateral prefrontal cortex and the frontal eye fields.

A turn-key transportable eye-tracking instrument for clinical assessment

This paper describes a combined instrument (eye tracker and target generator, both head mounted, with integrated data analysis) that tests parameters of saccadic eye movement and fixation control to give insight into the status of functional brain systems. Using three minilasers, the target generato rprojects three visual stimuli, a fixation point and two lateral stimuli, with programmable timing. The controller allows the selection of overlap, 200-msec gap, or remembered saccade trials. Size, maximal velocity, and reaction time are determined for each primary saccade. The number of prosaccades and antisaccades are counted. More saccades--for example, the occurrence and latency of corrective saccades--may be evaluated off line by an interactive PC analysis program. The eye position data can be transferred to a PC. Off-line analysis compares each observed variable relative to an age-matched control group (300 healthy control subjects 7-70 years of age, tested in the overlap condition with prosaccade instructions and in the gap condition with antisaccades). The diagnostic results can be used to elaborate an individual optomotor training program.

Does frontal normality exist in schizophrenia? A saccadic eye movement study

Many observations have supported the general idea of impaired frontal function in schizophrenia. In particular, neuropsychological studies have shown severe frontal deficits. However, other studies found normal cognitive function in a proportion of patients. Since saccadic tasks also provide an index of frontal function, we examined the presence of frontal deficits in patients by means of both neuropsychological and saccadic tasks, and compared the sensitivity of both approaches for frontal impairment. In addition, we examined the relationship between saccadic and neuropsychological measures. Twenty-four schizophrenic patients and twenty healthy controls completed an extensive neuropsychological battery and three saccadic tasks. Based on the neuropsychological battery alone, 42% of the patients showed frontal deficits, whereas combined use of neuropsychological and saccadic tasks resulted in 79% with frontal deficits. The antisaccade task appeared able to detect frontal deficits in patients who were without frontal impairment on the neuropsychological battery. Saccadic deficits were, however, not necessarily accompanied by deficits on frontal neuropsychological measures. This suggests that the saccadic and neuropsychological tasks used in the present study targeted different frontal functions. This view was supported by the lack of correlations between saccadic and frontal neuropsychological measures.

Development of saccade target selection in infants

To investigate the development of the target selection process for saccade generation, saccade latencies toward one of two targets were compared with those toward a target presented alone, under conditions where the timing of fixation stimulus offset was varied. 12 2-mo.-olds (7 boys and 5 girls), 12 3-mo.-olds (6 boys and 6 girls), and 12 5-mo.-olds (8 boys and 4 girls) participated. The latencies were longer when two saccade targets were presented on the left and right sides of the display (Double-target condition) than when one target was presented either on the left or right side of the display (Single-target condition). The difference between the Single and Double-target conditions tended to be larger in 2-mo. old infants than in 5-mo.-old infants when a central fixation target remained on after the onset of peripheral stimuli (Overlap condition). However, there was no difference between the 2-mo.-olds and the 5-mo.-olds when the fixation target was turned off before the peripheral stimuli were presented (Gap condition). The results provided evidence of the maturational development of a target selection process for saccade generation during 2 to 5 mo. of age.

Parsing cognition in schizophrenia using saccadic eye movements: a selective overview

Eye movements provide a behavioural measure of sensorimotor processing and higher cognitive functions of the brain. With the development of novel paradigms that can be used for the study of various cognitive operations, saccadic eye movements in particular, have become increasingly popular. Patients with schizophrenia have neurocognitive impairments that can be readily investigated with these paradigms. From animal, human lesion and neuroimaging studies, the cerebral centres underlying saccadic eye movements have been identified. The areas of the prefrontal cortex include the dorsolateral prefrontal cortex, the frontal eye fields, the supplementary eye fields, and the anterior cingulate cortex. Pathology of saccadic eye movements, therefore, provides information on the functional status of the underlying neural circuitry in brain disorders such as schizophrenia. In this paper, we evaluate: (i) methodological considerations that are central to the design and application of saccadic paradigms; (ii) brain activation that is associated with saccadic paradigms; (iii) recent findings in healthy subjects and schizophrenic patients; (iv) saccadic abnormalities in other psychiatric and neurological disorders and in individuals at risk for developing schizophrenia.

Maturation of widely distributed brain function subserves cognitive development

Cognitive and brain maturational changes continue throughout late childhood and adolescence. During this time, increasing cognitive control over behavior enhances the voluntary suppression of reflexive/impulsive response tendencies. Recently, with the advent of functional MRI, it has become possible to characterize changes in brain activity during cognitive development. In order to investigate the cognitive and brain maturation subserving the ability to voluntarily suppress context-inappropriate behavior, we tested 8-30 year olds in an oculomotor response-suppression task. Behavioral results indicated that adult-like ability to inhibit prepotent responses matured gradually through childhood and adolescence. Functional MRI results indicated that brain activation in frontal, parietal, striatal, and thalamic regions increased progressively from childhood to adulthood. Prefrontal cortex was more active in adolescents than in children or adults; adults demonstrated greater activation in the lateral cerebellum than younger subjects. These results suggest that efficient top-down modulation of reflexive acts may not be fully developed until adulthood and provide evidence that maturation of function across widely distributed brain regions lays the groundwork for enhanced voluntary control of behavior during cognitive development.

Eye movement dysfunction as a biological marker of risk for schizophrenia

OBJECTIVE

Our aim was to review smooth pursuit eye movement (SPEM) studies in schizophrenia and groups at high risk for schizophrenia, with a view to evaluating the utility of SPEM dysfunction as a biological marker of risk for schizophrenia.

METHOD

Smooth pursuit eye movement studies, related saccade function and the unresolved issues in this area of schizophrenia research were addressed. The different perspectives on the trait marker status of SPEM dysfunction, provided by both high-risk studies and related developmental research were considered. Attention was also given to the relationship between eye movement dysfunction and symptom profiles.

RESULTS

Converging evidence points to the robust and specific nature of SPEM dysfunction in schizophrenia, and highlights the role of frontal lobe and a related network dysfunction. The vast majority of 'high risk' studies support the view that SPEM dysfunction is also genetically specific to schizophrenia, and is not simply due to the overt expression of this illness. Studies assessing SPEM in relation to symptomatology show an association with the Disorganisation syndrome in particular.

CONCLUSIONS

Evidence for the specificity of SPEM dysfunction to diagnosed schizophrenia, as well as to healthy individuals with a genetic vulnerability to schizophrenia, suggests that the SPEM task has efficacy as a test of gene carrier status in schizophrenia, and therefore as a trait marker of risk for schizophrenia. Future studies should seek to explore the relationships between SPEM and other eye movement dysfunctions (antisaccades, express saccades), in view of evidence that some of these dysfunctions also show specificity for schizophrenia.

Influence of stimulus eccentricity and direction on characteristics of pro- and antisaccades in non-human primates

The ability to inhibit reflexes in favor of goal-oriented behaviors is critical for optimal exploration and interaction with our environment. The antisaccade task can be used to investigate the ability of subjects to suppress a reflexive saccade (prosaccade) to a suddenly appearing visual stimulus and instead generate a voluntary saccade (antisaccade) to its mirror location. To understand the neural mechanisms required to perform this task, our lab has developed a non-human primate model. Two monkeys were trained on a task with randomly interleaved pro- and antisaccade trials, with the color of the central fixation point (FP) instructing the monkey to either make a prosaccade (red FP) or an antisaccade (green FP). In half of the trials, the FP disappeared 200 ms before stimulus presentation (gap condition) and in the remaining trials, the FP remained visible (overlap condition) during stimulus presentation. The effect of stimulus eccentricity and direction was examined by presenting the stimulus at one of eight different radial directions (0-360 degrees ) and five eccentricities (2, 4, 8, 10, and 16 degrees ). Antisaccades had longer saccadic reaction times (SRTs), more dysmetria, and lower peak velocities than prosaccades. Direction errors in the antisaccade task were more prevalent in the gap condition. The difference in mean SRT between correct pro- and antisaccades, the anti-effect, was greater in the overlap condition. The difference in mean SRT between the overlap and the gap condition, the gap effect, was larger for antisaccades than for prosaccades. The manipulation of stimulus eccentricity and direction influenced SRT and the proportion of direction errors. These results are comparable to human studies, supporting the use of this animal model for investigating the neural mechanisms subserving the generation of antisaccades.

Optomotor and neuropsychological performance in old age

While a delayed initiation of visually guided saccades with increasing age has been documented in a number of studies, little research has been done on the control of antisaccades. The present study investigates aging effects on the control of visually guided saccades (prosaccades) and antisaccades as well as a selection of neuropsychological functions by the cross-sectional comparison of 14, 22, and 16 participants aged 20-35 years, 59-73 years, and 74-88 years, respectively. The geriatric and neurological status of the elder participants (including evidence from computed tomography, electroencephalography, and neurological soft signs) was assessed. In four task blocks of 200 trials each, pro- and antisaccades were elicited under the 200-ms-gap and overlap conditions. Left- and right-sided stimuli were presented in random order at 4 degrees, and the order of the task blocks was varied within each age group. In addition, the Wisconsin card-sorting test (WCST) and working memory, go-nogo discrimination, alertness, and stimulus-response incompatibility tests were administered. Participants aged 59-73 years exhibited widespread reductions of optomotor and neuropsychological performance, with greatest effect sizes of age differences in the optomotor parameters and the WCST measures. A further decay after the age of 73 years was discernible in those optomotor functions reflecting saccade disinhibition (in particular, directional errors during the antisaccade task and premature responses) and the performance in some neuropsychological tests. In line with previously published reports, variance in optomotor performance could be explained by two factors, accounting for a total of 76% of the age variance. Our results suggest that the investigation of saccade control may be a highly sensitive tool for neurodevelopmental aging research.

Voluntary saccadic control in dyslexia

The role of eye-movement control in dyslexia is still unclear. Recent studies, however, confirmed that dyslexics show poor saccadic control in single and sequential target tasks. In the present study we investigated whether dyslexic subjects are impaired on an antisaccade task requiring saccades against the direction of a stimulus. Altogether, 620 subjects between the ages of 7 and 17 years were classified as dyslexics (N = 506) or control subjects (N = 114) on the grounds of the discrepancy between their intellectual abilities and reading/spelling achievements. All subjects performed an overlap prosaccade and a gap antisaccade task with 100 trials to each side of stimulation in random order. Variables analysed were the overall saccadic reaction time of both tasks; and from the antisaccade task the number of errors (prosaccades), the number of corrected errors, and the number of trials in which the subjects still failed to reach the side opposite the stimulus even after two saccades. An analysis of variance was carried out taking into account the development of saccadic behaviour with age and the differences between the groups. The results confirm development of saccade control with age, especially in the voluntary component (a frontal-lobe function) for both groups, but indicate that the antisaccade task performance, as measured by the error and the correction rate, is significantly worse in the dyslexic group at ages above 8 years. Up to 50% of the dyslexics performed the antisaccade task 1.5 standard deviations below the mean of the controls.

Effects of visual training on saccade control in dyslexia

This study reports the effects of daily practice of three visual tasks on the saccadic performance of 85 dyslexic children in the age range of 8 to 15 years. The children were selected from among other dyslexics because they showed deficits in their eye-movement control, especially in fixation stability and/or voluntary saccade control. Their eye movements were measured in an overlap prosaccade and a gap antisaccade task before and after the training. The three tasks used for the training included a fixation, a saccade, and a distractor condition. In any of these tasks, the subject had to detect the last orientation of a small pattern which rapidly changed its orientation between up, down, right, and left, before it disappeared after some time. The task was to press one of four keys corresponding to the last orientation. The visual pattern was presented on an LCD display of a small hand-held instrument given to the children for daily use at home. The results indicate that daily practice improved not only the perceptual capacity, but also the voluntary saccade control, within 3 to 8 weeks. After the training, the group of dyslexics was no longer statistically different from the control group.

Are better eye movements an advantage in ball games? A study of prosaccadic and antisaccadic eye movements

The aim of this study was to compare prosaccadic and antisaccadic eye movements of experts in ball sports and controls. In the prosaccadic and antisaccadic task, subjects made saccades respectively towards and away from a suddenly appearing stimulus. By means of infrared-oculography, we compared horizontal eye movements of experts (n=18) and controls (n=20). Experts had shorter overall saccadic latencies, but significantly shorter latencies occurred only on the antisaccade task, not on the prosaccade task. Our findings seem to support the concept that prosaccades and antisaccades have different underlying mechanisms and that expertise in ball games mainly improves antisaccadic performance in terms of latency and variability.

On the production and correction of involuntary prosaccades in a gap antisaccade task

In an antisaccade task, where saccades in the direction opposite of a suddenly presented stimulus are required, certain numbers of prosaccades can occur. The hypothesis is put forward that poor fixation and poor voluntary saccade control constitute two independent sources for the errors. This possibility is investigated by including the corrections of the errors in the analysis. First, the eye movements of 346 normal subjects (group N) performing a gap antisaccade and an overlap prosaccade task were measured. For each subject the proportion of express saccades in the overlap prosaccade task and the proportion of prosaccades in the gap antisaccade task were determined. The data of 150 subjects with more than 20% proerrors were divided into two groups: group A with relatively many, group B with relatively few express saccades in the overlap prosaccade task. Group A subjects produced their errors after significantly shorter reaction times and they corrected their errors significantly faster and more often than group B subjects. Second, we analysed the data of three groups of subjects: the complete normal group N, a group D of dyslexic subjects (n=343), and a group T containing all subjects irrespective of their cognitive achievements (n=780). A highly significant negative correlation exists between the correction rates and the error rates. A factor analysis of the variables performed for each group separately results in only two factors, one describing prosaccade the other antisaccade control. Only the error rate contributes significantly to both factors indicating that high errors may have two independent reasons.

Development of voluntary control of saccadic eye movements. I. Age-related changes in normal children

To investigate the development of the voluntary control of saccadic eye movement, we examined eye movements in 99 normal children (4-13 years of age). Subjects were asked to fixate a central light for 3-5 s. A target was then presented, either to its right or left. In visually guided saccades, the mean latencies of the child group were longer than those of the adults, and decreased with age until the age of 12 where they reached adult levels. On the other hand, their peak saccadic velocities were not different from those of the adults. In the antisaccade task, they showed a higher rate of directional errors, indicating an inability to suppress reflexive saccades to the target. Mean latencies of correct antisaccades were significantly longer in the children than in the adults. Error rates and antisaccadic latency tended to decrease with age. We also examined the effects of an auditory warning signal during the fixation period and compared the results with those without. The warning stimulus was less effective in children than in adults in both tasks. Similar peak saccadic velocities between children and adults suggest the earlier development of the saccadic burst generator in the brainstem. In contrast, the delayed development of latency of saccades and antisaccades and the error rates of antisaccades suggest delayed maturation of the cerebral cortex, particularly the frontal association areas that are involved in both eye movement control and attentional processes.

Abnormal supranuclear eye movements in the child: a practical guide to examination and interpretation

Abnormal eye movements in the infant or voting child can be congenital or acquired. They may be a result of abnormal early visual development or a sign of underlying neurologic or neuromuscular disease. It is important to be able to detect these abnormalities and to distinguish them from normal but immature eye movements. The spectrum of disease in children differs from that in adults. Serious, potentially fatal but treatable disorders can be acquired in infancy, and abnormal eye movements in a sometimes apparently well child should never be labeled as congenital or benign without careful investigation. Eye movement analysis can indicate the presence of an underlying condition and help the clinician to classify different neurologic diseases. It is important to carefully examine the ocular motor system in any children at risk of neurologic disease. This review provides a practical guide to the examination and interpretation of eye movements in the child and includes recent literature on eye movement disorders of childhood. We describe supranuclear abnormalities of the ocular motor system in the order in which we would normally examine it: saccades, pursuit, convergence, vestibulo-ocular reflex, and optokinetic nystagmus. Nystagmus, internuclear ophthalmoplegia, cranial nerve abnormalities, and "miswiring" phenomena (such as Duane's syndrome and synergistic divergence) are not discussed.

Antisaccade task performance in questionnaire-identified schizotypes

Individuals who scored high on Perceptual Aberration-Magical Ideation Scales (Per-Mag; n = 90), the Social Anhedonia Scale (SocAnh; n = 39), and control participants (n = 89) were administered saccadic refixation (prosaccade) and saccadic suppression (antisaccade) tasks. Eye movements were scored in terms of error rates and latency. None of the groups differed in terms of their performance on the prosaccade task. Both the Per-Mag (p < 0.01) and SocAnh (p < 0.05) groups exceeded the controls in terms of mean antisaccade errors. The high-risk groups did not differ from each other. Eighteen of the Per-Mag individuals and 10 of the SocAnh individuals displayed deviant antisaccade performance. These findings are particularly interesting in light of suggestive evidence that antisaccade task deficits may serve as a marker of susceptibility to schizophrenia. It is hypothesized that the individuals who scored aberrantly on the Chapman scales and displayed antisaccade performance deficits are most likely to be at risk for the development of psychosis.

Poor saccadic control correlates with dyslexia

A large group of subjects, either average readers or reading/spelling disabled subjects (n = 185; age between 8-25 years; M = 13 +/- 4 years), were tested in various standardized cognitive tasks including reading/spelling assessment and in non-cognitive saccadic eye movement tasks. Dyslexics were separated into a subgroup (D1) with deficits in the serial auditory short-term memory and a subgroup (D2) with an isolated low achievement in reading/writing. Control subjects had no relevant cognitive deficit of any type. Saccadic eye movements were measured in a single target and in a sequential-target task. A significant correlation was found between abnormal saccadic control and reading disability. The two dyslexic groups showed only slight differences. As compared to the control group, the mean values of the standard deviations of the saccadic reaction times (SRT) and the amount of late saccades (SRT > 700) were significantly increased in both dyslexic groups and especially in group D1 who also showed an increased amount of anticipatory saccades. The number of express saccades (SRT = 80-134 ms) was increased, but not significantly, in D2 dyslexics. Both dyslexic groups produced significantly more regressive saccades in the sequential-target task. The correlation between saccadic variables and "reading factor" was 0.4. Significant deviations from normal performance of the saccadic variables were found in an estimated 50% of the dyslexics as compared to 20% of the control subjects. In spite of their worse level in saccadic control, dyslexics also developed with age in the eye movement performance as the control subjects did. Yet, the development was slower in group D1. It is suggested that reading process and saccade system are both controlled by visuo spatial attention and fixation systems that maybe impaired or develop slowly in many dyslexic subjects.

Primate antisaccades. I. Behavioral characteristics

The antisaccade task requires a subject to make a saccade to an unmarked location opposite to a flashed stimulus. This task was originally designed to study saccades made to a goal specified by instructions. Interest for this paradigm surged after the discovery that frontal lobe lesions specifically and severely affect human performance of antisaccades while prosaccades (i.e., saccades directed to the visual stimulus) are facilitated. Training monkeys to perform antisaccades was rarely attempted in the past, and this study is the first one that describes in detail the properties of such antisaccades compared with randomly intermingled prosaccades of varying amplitude in all directions. Such randomization was found essential to force the monkeys to use the instruction cue (pro- or anti-) and the location cue (peripheral stimulus) provided within a trial rather than to direct their saccades to the location of past rewards. Each trial began with the onset of a central fixation target that conveyed by its shape the instruction to make a pro- or an antisaccade to a subsequent peripheral stimulus. In one version of the task, the monkey was allowed to make an immediate saccade to the goal; in a second version, the saccade had to wait for a go signal. Analyses of the accuracy, velocity, and latency of antisaccades compared with prosaccades were performed on a sample of 7,430 pro-/antisaccades in the "immediate saccade" task (delayed saccades suffering from known distortions). Error rates fluctuated approximately 25%. Results were the same for the two monkeys with respect to accuracy and velocity, but they differed in terms of reaction time. Both monkeys generated antisaccades to stimuli in all directions, at various eccentricities, but antisaccades were significantly less accurate and slower than prosaccades elicited by the same stimuli. Interestingly, saccades to the stimulus could be followed by appropriate antisaccades with no intersaccadic interval. Such instances are here referred to as "turnaround saccades." Because they occurred sometimes with a long latency, turnaround saccades did not simply reflect the cancellation of an early foveation reflex. Consistent with human data, latencies of one monkey were longer for antisaccades than for prosaccades, but the reverse was true for the other monkey who was trained differently. In summary, this study demonstrates the feasibility of providing a subhuman primate model of antisaccade performance, but at the same time it suggests some irreducible differences between human and monkey performance.

The antisaccade: a review of basic research and clinical studies

The ability to suppress reflexive responses in favor of voluntary motor acts is crucial for everyday life. Both abilities can be tested with an oculomotor task, the antisaccade task. This task requires subjects to suppress a reflexive prosaccade to a flashed visual stimulus and instead to generate a voluntary saccade to the opposite side. This article reviews what is currently known about the neural structures and processes which are involved in the performance of this task. Current data show that a variety of brain lesions, neurological diseases and psychiatric disorders result in errors, i.e. prosaccades towards the stimulus, in this task. Brain imaging studies have shown that a widely distributed cortical and subcortical network is active during the generation of antisaccades. These findings are discussed and the potential of the antisaccade task for diagnostic purposes is evaluated.

Cortical control of eye movements

Event related cortical potentials and imaging provide information about roles of the cerebral hemispheres in generating voluntary and reflexive saccades. This review also discusses relationships between smooth pursuit and visual discrimination of motion direction and the phenomenon of blindsight. Cortical effects of strabismus on motion processing and smooth pursuit are reviewed.

The analysis of saccadic eye movements from gap and overlap paradigms

This protocol describes the acquisition and evaluation of saccadic eye movement data for use in basic neuroscience research and clinical application. The experimental protocol requires the subject to make saccadic eye movements in response to visual stimuli presented, in random order, on consecutive trials. The gap and overlap paradigms are described together with the instruction to generate pro- or antisaccades. The protocol includes the description of saccade detection, the determination of the beginning, the end, the size, and the velocity of a saccade, the exact way of calculating the proportion of different kinds of trials, and the treatment of erratic or artifact trials. Relevant variables are defined. The results obtained from a large number (300) of subjects of different ages (8-65 years) are described and analysed with respect to their development with age. The protocol allows to test a subject's saccadic status in many different circumstances in particular with respect to diagnostic help in neurology, psychiatry and psychology.