Smooth Pursuit Eye Tracking Research Articles

Recall bias in patients with schizophrenia

Thirty patients with a DSM-III-R diagnosis of schizophrenia were assessed for severity of schizophrenic symptoms using the Brief Psychiatric Rating Scale (BPRS) and were tested on a Continuous Performance Test (CPT) and a smooth pursuit eye tracking task. Negative symptoms were significantly correlated with eye tracking impairment (r=0.43, p<0.01) and CPT deficits (r=0.67, p<0.001), but performance on neither task was correlated with positive symptoms. CPT performance and eye tracking performance were modestly correlated with each other (r=0.39, p<0.01) and CPT performance was found to be a stronger predictor of negative symptoms than eye tracking performance. These data indicate that neurocognitive markers of vulnerability to schizophrenia are associated with negative rather than positive symptoms.

Sigma smooth pursuit eye tracking: constant k values revisited.

Effective sigma tracking, i.e., apparent movement perception when slow eye movements are made across a stationary repetitive pattern under stroboscopic illumination, has been shown to be a function of the distance between sequential stimuli (P(s)) and the flash frequency (f(s)). The relationship between these factors and eye velocity ( V (e)) has been formally specified as V (e)= k P(s)f(s)[deg s(-1)], where it has been argued that the value of k, which defines the rate limit for eye velocity, is normally 1, or exceptionally 2 or 3. However, theoretically the limitations on the maximum value for k are the maximum optimal pursuit speed for eye tracking (V(max)) and the minimum values which P(s) and f(s) can assume while preserving target discrimination, and since the values for V(max) are known to lie well beyond 20 deg/s and those for P(s) and f s) well below 0.3 deg and 10 Hz respectively, it should be possible to demonstrate empirically that k can assume integer values considerably larger than the indicated maximum of 3. To test this prediction, three subjects performed seven series of five EOG-monitored trials producing sigma-pursuit, with values of k ranging from 1 to 7. All subjects evidenced smooth pursuit eye tracking for every condition and reported experiencing sigma-type apparent motion in 95% of the trials. The results confirm theoretical expectations and unequivocally demonstrate that sigma tracking can be readily effected under conditions where k significantly exceeds the maximal values previously reported, in conformity with theory.

Biological markers and schizophrenia.

The delivery of biological markers for schizophrenia would greatly assist preventative strategies by identifying at-risk individuals who could then be monitored and treated in a manner with a view to minimising subsequent morbidity. This paper aims to present a selection of biological measures that may indicate risk of schizophrenia. A selective and brief review is provided of intensively studied putative markers, including enlarged cerebral ventricles, dopamine D2 receptor density, amphetamine-stimulated central nervous system dopamine release, plasma homovanillic acid and smooth pursuit eye tracking dysfunction. A number of biological measures have been reported to be correlated with schizophrenia. Presently, none of these measures has satisfactory performance characteristics in terms of predictive validity, noninvasiveness, ease of testing and low cost that would enable their widespread use. However, a few have potential for further investigation and development.

Heritability of different measures of smooth pursuit eye tracking dysfunction: A study of normal twins

Research studies have found that smooth pursuit eye movement dysfunction may serve as an index of genetic liability to develop schizophrenia. The heritability of various measures of smooth pursuit eye tracking proficiency and the saccades that occur during smooth pursuit was examined in 64 monozygotic (MZ) and 48 dizygotic (DZ) twin pairs. Two age cohorts were assessed (11–12 and 17–18 years of age). Intraclass correlations indicated significant similarity in the MZ twins for almost all measures in both age cohorts, whereas few of the DZ twin correlations attained significance. Biometrical modeling indicated that genetic mechanisms influence performance on both global and specific eye tracking measures, accounting for about 40% to 60% of the variance. These findings suggest that the underlying brain systems responsible for smooth pursuit and saccade generation during pursuit are under partial genetic control.

Heritability of different measures of smooth pursuit eye tracking dysfunction: A study of normal twins

Research studies have found that smooth pursuit eye movement dysfunction may serve as an index of genetic liability to develop schizophrenia. The heritability of various measures of smooth pursuit eye tracking proficiency and the saccades that occur during smooth pursuit was examined in 64 monozygotic (MZ) and 48 dizygotic (DZ) twin pairs. Two age cohorts were assessed (11-12 and 17-18 years of age). Intraclass correlations indicated significant similarity in the MZ twins for almost all measures in both age cohorts, whereas few of the DZ twin correlations attained significance. Biometrical modeling indicated that genetic mechanisms influence performance on both global and specific eye tracking measures, accounting for about 40% to 60% of the variance. These findings suggest that the underlying brain systems responsible for smooth pursuit and saccade generation during pursuit are under partial genetic control.

Smooth pursuit eye tracking over a structured background in first-episode schizophrenic patients

Whilst most laboratory smooth pursuit tasks are performed in the dark, in everyday life pursuit commonly occurs over a structured background. This background provides a powerful stimulus to the optokinetic reflex (OKR), inducing a background "drag" on pursuit eye movements. An inability to inhibit the influence of the OKR may be a contributing factor to the dysfunctional pursuit performance observed in many schizophrenic patients. Smooth pursuit performance was measured in 23 first-episode schizophrenic patients and 23 healthy controls matched for age and estimated IQ, both in the dark and over a structured background (a random checkerboard of black and white squares). Velocity gain was measured, as well as the number and size of corrective saccades (catch-up saccades) and intrusive saccades (anticipatory saccades and square wave jerks). Overall, schizophrenic patients had lower velocity gain and made more catch-up saccades than controls. The effect of the background was to lower velocity gain and increase the number of catch-up saccades to the same extent in schizophrenic patients and controls. There were no significant interactions between group and background effect. These results suggest that, although their overall level of performance was worse, the schizophrenic patients were as able as controls to inhibit the effect of the OKR. Since lesion studies show that inhibition of the OKR requires intact inferior parietal regions in man (Lawden et al., 1995), one hypothesis is that the parietal component of smooth pursuit may be intact in schizophrenia.

Biological Markers and Schizophrenia

ObjectiveThe delivery of biological markers for schizophrenia would greatly assist preventative strategies by identifying at-risk individuals who could then be monitored and treated in a manner with a view to minimising subsequent morbidity. This paper aims to present a selection of biological measures that may indicate risk of schizophrenia.MethodA selective and brief review is provided of intensively studied putative markers, including enlarged cerebral ventricles, dopamine D2receptor density, amphetamine-stimulated central nervous system dopamine release, plasma homovanillic acid and smooth pursuit eye tracking dysfunction.ResultsA number of biological measures have been reported to be correlated with schizophrenia.ConclusionsPresently, none of these measures has satisfactory performance characteristics in terms of predictive validity, noninvasiveness, ease of testing and low cost that would enable their widespread use. However, a few have potential for further investigation and development.

Relationship between nailfold plexus visibility and clinical, neuropsychological, and brain structural measures in schizophrenia

Background: Although all published studies investigating the association between nailfold plexus visibility and schizophrenia have found the subpapillary plexus (the vascular network into which capillaries drain) to be unusually visible in many schizophrenia patients, little else is known about this putative marker for schizophrenia liability. Methods: Plexus visibility was rated in 63 chronic schizophrenia, 67 first–episode schizophrenia, 9 schizophreniform, and 66 unipolar and bipolar depressed patients, all with psychosis, and 119 nonpsychiatric controls. Smooth–pursuit eye tracking, clinical features, neuropsychological performance, and lateral ventricle size were assessed. Results: Approximately 21% of chronic schizophrenia, 22% of first–episode schizophrenia, and 22% of schizophreniform patients had highly visible plexus compared to only 8% of unipolar, bipolar, and nonpsychiatric controls. Schizophrenia patients with visible plexus had worse oculomotor performance. Additionally, chronic schizophrenia patients with visible plexus had more negative symptoms, worse course, more severe illness, worse occupational functioning, and worse neuropsychological performance on tasks thought to be sensitive to frontal dysfunction. An inverse relationship between plexus visibility and lateral ventricle size was found. Conclusions: This study provides evidence that schizophrenia patients with plexus visibility are characterized by oculomotor dysfunction, negative symptoms, severe symptomatology, chronic course, neuropsychological dysfunction, and an absence of enlarged ventricles. Biol Psychiatry

Neuropsychological and oculomotor correlates of spatial working memory performance in schizophrenia patients and controls

Recent reports of spatial working memory deficits in schizophrenia provide evidence for dorsolateral prefrontal cortical (DLPFC) dysfunction. However, the question of how spatial working memory performance relates to other task impairments in schizophrenia considered reflective of frontal dysfunction, such as the Wisconsin Card Sorting Test (WCST) and smooth pursuit eye tracking, has been largely unexplored. Spatial working memory, as measured by a computerized visual–manual delayed response task (DRT), was evaluated in 42 schizophrenia patients and 54 normal controls. Subjects also completed a battery of neuropsychological and oculomotor tasks. Schizophrenia patients performed as accurately as controls on a no-delay, sensory–motor control condition, but showed a significant impairment in spatial accuracy with the addition of an 8-s delay and verbal distraction task. For the patients, working memory impairment was associated with fewer categories on the WCST, impaired eye tracking, fewer words learned on the Rey Auditory Verbal Learning Test, but not with measures of general cognitive and clinical functioning. Results suggest the presence of a sub-group of schizophrenia patients with common pathophysiology that accounts for the co-variance of several tasks implicating prefrontal dysfunction.

Psychophysical isolation of a motion-processing deficit in schizophrenics and their relatives and its association with impaired smooth pursuit.

Schizophrenia patients and many of their relatives show impaired smooth pursuit eye tracking. The brain mechanisms underlying this impairment are not yet known, but because reduced open-loop acceleration and closed-loop gain accompany it, compromised perceptual processing of motion signals is implicated. A previous study showed that motion discrimination is impaired in schizophrenia patients. Motion discrimination can make use of position and contrast as well as velocity cues. Here, we report that the motion discrimination deficit, which occurs in both schizophrenic patients and in their first-degree relatives, involves a failure of velocity detection, which appears when judging intermediate target velocities. At slower and faster velocities, judgments of velocity discrimination seemed normal until we experimentally disentangled velocity cues from nonmotion cues. We further report that compromised velocity discrimination is associated with sluggish initiation of smooth pursuit. These findings point to specific central nervous system correlates of schizophrenic pathophysiology.

Does Ketamine-Mediated N-methyl-D-aspartate Receptor Antagonism Cause Schizophrenia-like Oculomotor Abnormalities?

Evidence from histological and pharmacological challenge studies indicates that N-methyl-D-aspartate (NMDA) receptor hypofunction may play an important role in the pathophysiology of schizophrenia. Our goal was to characterize effects of NMDA hypofunction further, as related to schizophrenia-associated neuropsychological impairment. We administered progressively higher doses of ketamine (target plasma concentrations of 50, 100, 150, and 200 ng/ml) to 10 psychiatrically healthy young men in a randomized, single-blind, placebo-controlled design and assessed oculomotor, cognitive, and symptomatic changes. Mean ketamine plasma concentrations approximated target plasma concentrations at each infusion step. Verbal recall, recognition memory, verbal fluency, pursuit tracking, visually guided saccades, and fixation all deteriorated significantly during ketamine infusion; lateral gaze nystagmus explained some, but not all, of the smooth pursuit abnormalities. We concluded that ketamine induces changes in recall and recognition memory and verbal fluency reminiscent of schizophreniform psychosis. During smooth pursuit eye tracking, ketamine induces nystagmus as well as abnormalities characteristic of schizophrenia. These findings help delineate the similarities and differences between schizophreniform and NMDA–blockade-induced cognitive and oculomotor abnormalities.

Antisaccades and smooth pursuit eye tracking and schizotypy.

Eye tracking deficits are one of a few widely validated behavioral markers of risk for schizophrenia. Recently, it has been proposed that antisaccade performance may also constitute a marker of schizophrenia risk. This study investigated whether eye tracking and antisaccade deficits could be found in another population with putative liability to schizophrenia-nonclinical subjects with elevated scores on a psychometric index of perceptual aberrations. Subjects were 55 university students who received either high or normal scores on the Perceptual Aberration Scale, a measure of schizotypy indexing body image and perceptual distortions. Subjects completed a smooth pursuit eye tracking task and an antisaccade task. Eye movements were monitored using an infrared limbus tracker. Subjects with high Perceptual Aberration Scale scores (putative "schizotypes") had lower pursuit quality and a lower percentage correct on the antisaccade task than the controls. The 2 groups did not differ in antisaccade or error latencies. The increase in antisaccade errors in the schizotypes was accounted for almost entirely by an increase in perseverative errors, but virtually no difference between groups on random errors. Antisaccade performance was significantly related to pursuit quality. Subjects with elevated Perceptual Aberration Scale scores have performance deficits on oculomotor tasks that have been linked to latent liability to schizophrenia, namely, smooth pursuit and antisaccade performance. The antisaccade errors in the schizotype group were primarily perseverations, a behavioral pattern often associated with frontal lobe dysfunction and observed in the performance of schizophrenic patients.

Acute and Residual Effects of Marijuana in Humans

Marijuana continues to be the most commonly abused illicit drug in the United States. Because many people abuse marijuana during the evening and on weekends and then go to work or school the next day, more research is needed on the residual effects of marijuana. The current study sought to examine both acute and residual subjective, physiologic, and performance effects of smoking a single marijuana cigarette. Ten healthy male volunteers who reported recent use of marijuana resided on a residential research ward. On three separate days, subjects smoked one NIDA marijuana cigarette containing either 0%, 1.8%, or 3.6% Δ 9-tetrahydrocannabinol (THC) according to a paced puffing procedure. Subjective, physiologic, and performance measures were collected prior to smoking, five times following smoking on that day, and three times on the following morning. Subjects reported robust subjective effects following both active doses of marijuana, which returned to baseline levels within 3.5 h. Heart rate increased and the pupillary light reflex decreased following active dose administration with return to baseline on that day. A new finding was that marijuana smoking acutely produced decrements in smooth pursuit eye tracking. Although robust acute effects of marijuana were found on subjective and physiological measures, and on smooth pursuit eye tracking performance, no effects were evident the day following administration, indicating that the residual effects of smoking a single marijuana cigarette are minimal.

Inverse relationship of perinatal complications and eye tracking dysfunction in relatives of patients with schizophrenia: evidence for a two-factor model.

Because both smooth pursuit eye tracking dysfunction and obstetrical complications are significant risk factors for schizophrenia, the authors tested the predictions of a two-factor model of how eye tracking dysfunction and obstetrical complications covary in patients with schizophrenia, their siblings, and comparison subjects. Psychiatric diagnoses, eye tracking dysfunction, and obstetrical complications noted in birth records were independently assessed in 18 patients with schizophrenia, 16 of their siblings without schizophrenia, and 49 comparison subjects with neither personal nor family histories of schizophrenia. As hypothesized, 1) the combination of eye tracking dysfunction and perinatal obstetrical complications discriminated patients with schizophrenia significantly from subjects without schizophrenia, including siblings of patients with schizophrenia, and 2) eye tracking dysfunction and perinatal obstetrical complications manifested a significant inverse association in the nonschizophrenic siblings of patients with schizophrenia. These results support a two-factor model in which obstetrical complications often interact with genetic liability, indicated by eye tracking dysfunction, to produce schizophrenia.

Smooth pursuit and saccadic abnormalities in first-episode schizophrenia.

Previous studies of oculomotor dysfunction in schizophrenia have tended to concentrate on abnormalities of smooth pursuit eye tracking in chronic medicated patients. We report the results of a study of smooth pursuit, reflexive and antisaccade performance in drug naive and antipsychotic treated first-episode schizophrenic patients. Smooth pursuit and saccadic eye movements were recorded in 36 first-episode schizophrenic patients and 36 controls matched for age and estimated IQ. The schizophrenic patients were divided into drug-naive (N = 17) and antipsychotic treated groups (N = 19). Smooth pursuit velocity gain was significantly lower than controls only in the drug-naive patients. The treated patients did not differ significantly from either the controls or the untreated group. In an antisaccade paradigm both treated and drug-naive schizophrenic patients demonstrated an increased number of errors, but only drug-naive patients also demonstrated an increased latency in initiating correct antisaccades. These impairments are unlikely to be due to a generalized deficit in oculomotor function in the schizophrenic groups, as there were no differences between the groups in saccadic metrics on a reflexive saccade task. The results show that both smooth pursuit and saccadic abnormalities are present at the onset of schizophrenia and are integral to the disorder.

Development of oculomotor functioning in preadolescence, adolescence, and adulthood

We examined developmental differences in smooth pursuit eye tracking proficiency in a large sample of preadolescent, adolescent, and adult males. Smooth pursuit was quantified using general measures of oculomotor functioning and by examining the frequency and dynamic characteristics of specific saccadic events. Examination of age effects using general measures indicated that, by late adolescence, the smooth pursuit system reached adult levels of functioning. No significant differences were found between the adolescent and adult groups on most global measures. However, both groups had better eye tracking than the preadolescent group, suggesting that during preadolescence the oculomotor system is still developing and is not yet capable of optimal performance. Examination of the frequency and dynamic characteristics of the saccadic events yielded additional information regarding the nature of the smooth pursuit eye tracking differences of the three age groups.

Attentional and eye tracking deficits correlate with negative symptoms in schizophrenia

Thirty patients with a DSM-III-R diagnosis of schizophrenia were assessed for severity of schizophrenic symptoms using the Brief Psychiatric Rating Scale (BPRS) and were tested on a Continuous Performance Test (CPT) and a smooth pursuit eye tracking task. Negative symptoms were significantly correlated with eye tracking impairment ( r=0.43, p<0.01) and CPT deficits ( r=0.67, p<0.001), but performance on neither task was correlated with positive symptoms. CPT performance and eye tracking performance were modestly correlated with each other ( r=0.39, p<0.01) and CPT performance was found to be a stronger predictor of negative symptoms than eye tracking performance. These data indicate that neurocognitive markers of vulnerability to schizophrenia are associated with negative rather than positive symptoms.

Smooth pursuit eye movements in childhood-onset schizophrenia: Comparison with attention-deficit hyperactivity disorder and normal controls

Abnormalities of the smooth pursuit eye movements of adults with schizophrenia have been well described. We examined smooth pursuit eye movements in schizophrenic children, contrasting them with normal and attention-deficit hyperactivity disorder (ADHD) subjects, to determine whether there is continuity of eye movement dysfunction between childhood- and adult-onset forms of schizophrenia. Seventeen schizophrenic children with onset of illness by age 12, 18 ADHD children, and 22 normal children were studied while engaged in a smooth pursuit eye tracking task. Eye tracking variables were compared across the three groups. Schizophrenic children exhibited significantly greater smooth pursuit impairments than either normal or ADHD subjects. Within the schizophrenic group, there were no significant relationships between eye tracking variables and clinical variables, or ventricular/brain ratio. Childhood-onset schizophrenia is associated with a similar pattern of smooth pursuit abnormalities to that seen in later-onset schizophrenia.

Eye-tracking performance and adaptive functioning over the short-term course of first-episode psychosis

We examined the relationship of smooth pursuit eye tracking to the course of first-episode psychosis. Various measures of social, occupational, and psychological functioning were obtained for 134 persons with diagnoses of schizophrenia, schizophreniform disorder, or psychotic mood disorder at the time of their psychosis and 9 and 18 months later. Poor eye-tracking performance was associated with generally impaired functioning over the 18-month course of disorder for patients with schizophrenia. A similar association between smooth pursuit and adaptive functioning was not found in patients with schizophreniform or affective disorder. The results suggest that patients with schizophrenia who are characterized by poor eye tracking have a more severe disorder, indications of which are present at the onset of their psychosis.

The construct validity of root-mean-square error for quantifying smooth-pursuit eye tracking abnormalities in schizophrenia

Smooth-pursuit eye tracking abnormalities have been consistently observed among schizophrenia patients and their relatives (Iacono and Clementz 1993; Levy et al 1993). Using a statistical technique called mixture analysis, recent studies have demonstrated that distributions of both the patients' and their relatives' ocular motor data are best characterized by two distinct components (Blackwood et al 1991; Clementz et al 1992; Gibbons et al 1984; Iacono et al 1992; Ross et al in press; Sweeney et al 1993). One component overlaps the scoring distribution of normal subjects fairly closely, whereas the other component captures subjects with poor eye tracking performance. The pattern of results suggests that ocular motor measures are capturing differences in kind among schizophrenia subjects, and that these differences are indexing biologically distinct subgroups of patients in whose families ocular motor abnormalities are an indicator of vulnerability for some form of this illness. This conclusion is consistent with a report suggesting linkage between eye tracking abnormalities and markers on chromosome 6 (Arolt et al 1995; see also Wang et al 1995). The above results, which rely primarily on global measures of eye tracking performance, should be considered in light of current trends to use specific measures, such as saccadic performance and the calculation of smooth pursuit gain, to