Saccadic Eye Movement Tasks Research Articles

Saccade dysfunction associated with chronic petrol sniffing and lead encephalopathy

Background: In chronic petrol sniffers, recent exposure to high levels of leaded petrol may give rise to a lead encephalopathy characterised by tremor, chorea, ataxia, hyperreflexia, convulsive seizures, and death....

Modulation by context of a scene in monkey anterior inferotemporal cortex during a saccadic eye movement task.

We investigated the effect of a scene on the activity of cells in the anterior inferotemporal (AIT) cortex while the monkey performed a saccadic eye movement (SEM) task with and without the context of a scene (gray frame). Most neurons did not code for the presence of a scene when it appeared alone (monkey free viewing) or when the monkey was fixating. Nevertheless, when a peripheral target was turned on and the monkey had to make a SEM to it, some cells were capable of differentially coding the presence of the scene before and after the saccade.

Differential effects of cigarette smoking on performance of a smooth pursuit and a saccadic eye movement task in schizophrenia

Schizophrenic patients demonstrate a number of physiological defects including smooth pursuit eye movement dysfunction (SPEM), involuntary reflexive saccades to a prepotent stimulus during saccadic tasks, and increased response to the second of two identical auditory stimuli, the P50 evoked potential response. The P50 deficit appears to be mediated by the α7 nicotinic cholinergic receptor. This study compared the failure of saccadic inhibition demonstrated in two different eye movement tasks, to see if either deficit, like the P50 inhibitory deficit, was normalized by nicotine. Fifteen smoking schizophrenic patients and 15 smoking non-schizophrenic subjects were compared on the percentage of premature saccades in a memory-guided saccadic task, and the frequency of intrusive small and large anticipatory saccades during a SPEM task. No significant effects or interactions of smoking, group or time on premature or large anticipatory saccades were detected. However, leading saccades demonstrated a significant group × time × smoking interaction. Leading saccades may therefore be a measure of cholinergic inactivity and thus part of the α7 nicotinic receptor dysfunction observed in schizophrenia. However, premature saccades and large anticipatory saccades, although measures of inhibitory dysfunction in schizophrenia, appear to be unrelated to the nicotinic system.

My eyes want to look where your eyes are looking: exploring the tendency to imitate another individual's gaze.

In this study we investigated the tendency of humans to imitate the gaze direction of other individuals. Distracting gaze stimuli or non biological directional cues (arrows) were presented to observers performing an instructed saccadic eye movement task. Eye movement recordings showed that observers performed less accurately when the distracting gaze and the instructed saccade had opposite directions, with a substantial number of saccades matching the direction of the distracting gaze. Static (Experiment 1) and dynamic (Experiment 2) gaze distracters, but not pointing arrows (Experiment 3), produced the effect. Results show a strong predisposition of humans to imitate somebody else's oculomotor behaviour, even when detrimental to task performance. This is likely linked to a strong tendency to share attentional states of other individuals, known as joint attention.

Locating the Human Frontal Eye Fields With Transcranial Magnetic Stimulation

The variability in the location and function of the human frontal eye fields (FEFs) was assessed using transcranial magnetic stimulation (TMS). Ten subjects performed a saccadic eye movement task previously shown to be influenced by TMS of the FEFs. A sequence of points over the prefrontal cortex was stimulated until an effective site of the TMS was found that induced contralateral saccade delays. In 7 out of the 10 subjects, we were able to localize a region in the prefrontal cortex that when stimulated produced delays in the execution of contralateral saccadic eye movements. The location of this functionally defined FEF region across these subjects was approximately 1.5 cm anterior to the motor hand area, although there was considerable variability in this measure. In the remaining 3 subjects, no site within our circumscribed probing was found that when disrupted with TMS produced delays in contralateral saccadic eye movements. The inter-individual differences in the location and function of the FEFs highlights the importance of using functional as well as anatomical landmarks when attempting to localize brain structures.

The effect of low dose sevoflurane on saccadic eye movement latency.

We investigated the effects of a low concentration of sevoflurane on a saccadic eye movement task that reflects the performance of higher neural decision and control mechanisms. The experiments were performed double-blind in five subjects, using either 0.15% end-tidal sevoflurane in oxygen, or pure oxygen as a placebo. Saccades were recorded and analysed using a computer-based recording system that also controlled the presentation of visual targets. Administration of oxygen produced no significant change in median latency compared with breathing air; but in four of the five subjects, administration of sevoflurane in oxygen caused a significant increase in latency. These results suggest that measurement of median saccadic latency may be a useful functional measurement of impairment of performance during recovery from anaesthesia.

The attentional disengagement processing reflected by ERPs and saccade reaction times during a gap task

In this study, we examined cerebral process of attentional disengagement using ERPs and saccade reaction time (SRT) during a saccadic eye movement task to produce the gap effect. Ten healthy adults participated in this study. Subjects were required to execute saccadic eye movement when the target appeared. In the gap condition, a fixation point disappeared 200 ms prior to the target stimulus presentation. In the overlap condition, a fixation point remained after the target stimulus presentation. ERPs were analyzed separately for target stimulus and saccadic eye movement. SRT in the gap condition was significantly shorter than that in the overlap condition. For the target-locked ERPs in the gap condition, central positivity appeared around 60 ms before the onset of the target stimulus. This would reflect an automatic processing of attentional disengagement elicited by the offset of a fixation point. For the saccade-locked ERPs, pre-saccadic positivities were observed in both conditions. In the overlap condition, it appeared earlier and higher than that in the gap condition. It reflects a processing of attentional disengagement to the fixation point. These results indicated that the cerebral processing of attentional disengagement would be differentiated by the existence of gap.

Neural basis of a perceptual decision in the parietal cortex (area LIP) of the rhesus monkey.

We recorded the activity of single neurons in the posterior parietal cortex (area LIP) of two rhesus monkeys while they discriminated the direction of motion in random-dot visual stimuli. The visual task was similar to a motion discrimination task that has been used in previous investigations of motion-sensitive regions of the extrastriate cortex. The monkeys were trained to decide whether the direction of motion was toward one of two choice targets that appeared on either side of the random-dot stimulus. At the end of the trial, the monkeys reported their direction judgment by making an eye movement to the appropriate target. We studied neurons in LIP that exhibited spatially selective persistent activity during delayed saccadic eye movement tasks. These neurons are thought to carry high-level signals appropriate for identifying salient visual targets and for guiding saccadic eye movements. We arranged the motion discrimination task so that one of the choice targets was in the LIP neuron's response field (RF) while the other target was positioned well away from the RF. During motion viewing, neurons in LIP altered their firing rate in a manner that predicted the saccadic eye movement that the monkey would make at the end of the trial. The activity thus predicted the monkey's judgment of motion direction. This predictive activity began early in the motion-viewing period and became increasingly reliable as the monkey viewed the random-dot motion. The neural activity predicted the monkey's direction judgment on both easy and difficult trials (strong and weak motion), whether or not the judgment was correct. In addition, the timing and magnitude of the response was affected by the strength of the motion signal in the stimulus. When the direction of motion was toward the RF, stronger motion led to larger neural responses earlier in the motion-viewing period. When motion was away from the RF, stronger motion led to greater suppression of ongoing activity. Thus the activity of single neurons in area LIP reflects both the direction of an impending gaze shift and the quality of the sensory information that instructs such a response. The time course of the neural response suggests that LIP accumulates sensory signals relevant to the selection of a target for an eye movement.

A Preliminary Study of Acute Responses to Clamped Alcohol Concentration and Family History of Alcoholism

The clamping method of alcohol administration was combined with a battery of dependent measures of frontal lobe brain function, and a novel index of acute adaptation, in a preliminary study in order to explore the paradigm's sensitivity to a familial history of alcoholism (FHA). Ten family history-positive (FHP) and 10 family history-negative (FHN) adult social drinkers of both genders underwent alcohol clamping. Twenty minutes after the start of an intravenous infusion of alcohol, the breath alcohol concentration was clamped at a target of 60+/-5 mg/dl for 150 min. Initial and adaptive responses to alcohol were assessed using scalar indices of change. One index assessed initial improvements or impairments in brain function after alcohol. The other index assessed acute adaptation (tolerance or sensitization) to alcohol while the brain's exposure to alcohol was held constant. The battery of dependent measures included subjective perceptions, neuropsychological tests, saccadic eye-movement tasks, and event-related potential (ERP) tasks. Effect sizes for FHA were estimated for 10 dependent variables that showed adequate baseline test-retest reliability (r>0.6). FHP subjects showed less intense initial responses to alcohol in subjective perceptions, but greater changes in the latency of volitional saccades and ERP P3 components than did the FHN controls. FHP subjects generally showed greater acute tolerance to alcohol than did controls, who showed more instances of acute sensitization at this moderate breath alcohol concentration. Effect sizes for FHA exceeded 0.4 in more than half of the indices. The BrAC clamping paradigm assesses initial and adaptive responses of a battery of behavioral and electrophysiological measures of frontal lobe function to ethanol that appear both reliable and sensitive to FHA.

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.

Age-related performance of human subjects on saccadic eye movement tasks.

We measured saccadic eye movements in 168 normal human subjects, ranging in age from 5 to 79 years, to determine age-related changes in saccadic task performance. Subjects were instructed to look either toward (pro-saccade task) or away from (anti-saccade task) an eccentric target under different conditions of fixation. We quantified the percentage of direction errors, the time to onset of the eye movement (saccadic reaction time: SRT), and the metrics and dynamics of the movement itself (amplitude, peak velocity, duration) for subjects in different age groups. Young children (5-8 years of age) had slow SRTs, great intra-subject variance in SRT, and the most direction errors in the anti-saccade task. Young adults (20-30 years of age) typically had the fastest SRTs and lowest intra-subject variance in SRT. Elderly subjects (60-79 years of age) had slower SRTs and longer duration saccades than other subject groups. These results demonstrate very strong age-related effects in subject performance, which may reflect different stages of normal development and degeneration in the nervous system. We attribute the dramatic improvement in performance in the anti-saccade task that occurs between the ages of 5-15 years to delayed maturation of the frontal lobes.

Activation of Overlapping but not Identical Frontal and Parietal Regions by Saccadic Eye Movement and Overt Spatial Attention Tasks

Activation of Overlapping but not Identical Frontal and Parietal Regions by Saccadic Eye Movement and Overt Spatial Attention Tasks

Familial transmission of two independent saccadic abnormalities in schizophrenia

Difficulties with inhibiting inappropriate responses, i.e. disinhibition, and problems with spatial memory are both presumed to be a part of the phenotypic expression of the genetic risk for schizophrenia. Schizophrenic probands are impaired on saccadic eye movement tasks which require (a) response inhibition to prepotent stimuli and (b) generation of an accurate response to a remembered or calculated spatial location, but it is unknown how these deficits are inherited. Sixteen schizophrenic probands, their 32 parents, and two normal control groups completed a delayed oculomotor response and an antisaccade task. The parents with a positive ancestral family history for chronic psychosis ( n = 8) were presumed to be more likely than their family history-negative spouses to be genetic carriers for schizophrenia. Probands and their positive family history parents had more failures of response inhibition than did normal control groups. However, it was the probands and their negative family history spouses who demonstrated impaired accuracy of the remembered- ot antisaccades. Disinhibition may be closely tied to a specific genetic risk for schizophrenia. However, a second familial factor related to the maintenance or manipulation of spatial information may also contribute to the genetic risk of the full clinical disorder.

Eye movements and psychopathology in schizophrenia and bipolar disorder.

The aim of this study was to examine multivariate patterns of relationships between oculomotor performance, psychopathology, and neuropsychology. Performance on smooth pursuit and saccadic eye movement tasks was assessed in three DSM-III-R diagnosis-based groups of subjects; normal (N = 55), schizophrenic (N = 29), and bipolar disorder (N = 26) and analyzed in relation to age, gender, scale for the Assessment of Negative Symptoms, Scale for the Assessment of Positive Symptoms, and Brief Psychiatric Rating Scale scores, Shipley intelligence quotient, and Wisconsin Card Sorting Test Performance. The greatest difference was a higher proportion of errors in the antisaccade task in the schizophrenic and bipolar groups, which was related to worse Wisconsin Card Sorting Test performance and was not accounted for by gender, age, education, or intelligence quotient. A significant gender and bipolar interaction showed bipolar women to have worse antisaccade performance. Abnormal smooth pursuit was more specific to schizophrenia. Antisaccade task and sine wave root-mean-square error were correlated in bipolar but not schizophrenic subjects. Scale for the Assessment of Negative Symptoms and Scale for the Assessment of Positive Symptoms scores had independent associations with the antisaccade task. Faster reaction times in the schizophrenic group to antisaccade errors were observed, suggesting an abnormality in visual attention processing and perhaps sensory gating functions. These results confirm abnormal smooth pursuit in schizophrenia and suggests that impairments in saccadic function are less specific to diagnostic group. Oculomotor performance and psychopathology seem related in complex ways to age, gender, intelligence quotient, and executive neuropsychological and possibly visual attention functions.

Saccadic Eye Movements and Dual-Task Interference

Four dual-task experiments required a speeded manual choice response to a tone in a close temporal proximity to a saccadic eye movement task. In Experiment 1, subjects made a saccade towards a single transient; in Experiment 2, a red and a green colour patch were presented to left and right, and the saccade was to which ever patch was the pre-specified target colour. There was some slowing of the eye movement, but neither task combination showed typical dual-task interference (the "psychological refractory effect"). However, more interference was observed when the direction of the saccade depended on whether a central colour patch was red or green, or when the saccade was directed towards the numerically higher of two large digits presented to the left and the right. Experiment 5 examined a vocal second task, for comparison. The findings might reflect the fact that eye movements can be directed by two separate brain systems--the superior colliculus and the frontal eye fields; commands from the latter but not the former may be delayed by simultaneous unrelated sensorimotor tasks.

Oculomotor performance in obsessive-compulsive disorder.

Neuroimaging studies have shown abnormalities of the frontal cortex and basal ganglia in persons with obsessive-compulsive disorder. Since lesions in the frontal cortex and basal ganglia areas affect performance on goal-guided saccadic eye movements, this study investigated the relation between the diagnosis of obsessive-compulsive disorder and oculomotor performance. Eleven patients with the clinical diagnosis of obsessive-compulsive disorder and 14 normal subjects were assessed with respect to their performance on both visual-guided and goal-guided oculomotor tasks. Fixation performance was also measured. The group with obsessive-compulsive disorder had a very significantly greater error rate and a significantly greater rate of inaccurate saccades on the goal-guided antisaccade task, whereas they were not different from the normal group in reaction time, saccadic velocity, and accuracy on the visual-guided saccade task. The distribution of error rates for the patients with obsessive-compulsive disorder was broad, with more than one-half outside the range of the normal group. Most of the abnormal findings were among male patients. The results support the hypothesis of a relationship between impaired performance on goal-guided saccadic eye movement tasks and the diagnosis of obsessive-compulsive disorder, but they also suggest a gender-related subgroup within the group with obsessive-compulsive disorder.