Smooth pursuit abnormalities have been observed in antipsychotic naive first-episode patients, su... more Smooth pursuit abnormalities have been observed in antipsychotic naive first-episode patients, suggesting that they are intrinsic to the illness. However, it is not clear whether these abnormalities are as severe as those observed in more chronic patients. In addition, although research suggests that there are no short-term effects of conventional antipsychotic medication, the effects of long-term antipsychotic medication on smooth pursuit eye movements are relatively unknown. To determine the short and long term effects of antipsychotic medication on the smooth pursuit performance of first-episode and chronic patients with schizophrenia. We compared the smooth pursuit performance of antipsychotic-treated and untreated first-episode and chronic schizophrenic patients with healthy controls using a comprehensive range of performance measures. This included velocity gain, the number, type and size of intrusive and corrective saccades, and the average time between the change in direction of the target and the change in direction of the eye movement, a measure of subjects' ability to predict target movement. Chronic schizophrenic patients had significantly reduced velocity gain, took longer to respond to the change in target direction and made more catch-up saccades than both first-episode schizophrenic patients and controls. First-episode patients were impaired relative to controls only on the measure of velocity gain. There were no differences between antipsychotic-naive and treated first-episode patients. Antipsychotic-free chronic patients were significantly less impaired on velocity gain than matched continuously treated chronic patients. These results were not influenced by group differences in age and symptom severity. These results show that: 1) the main index of smooth pursuit, velocity gain, is impaired early in the course of schizophrenia; 2) whereas velocity gain is unaffected by short-term (weeks) medication, it is worsened by chronic (years) treatment; 3) other indices of smooth pursuit, catch-up saccades and ability to predict target movement, are adversely influenced by illness chronicity rather than medication.
Saccades to a remembered target use non-visual feedback and rely on a normal functioning of the p... more Saccades to a remembered target use non-visual feedback and rely on a normal functioning of the projection from the caudate nucleus to the substantia nigra pars reticulata. The latter projection is known to be defective in Parkinson's disease and it seems therefore likely that remembered saccades are abnormal in such patients. In a series of three studies the characteristics of remembered saccades were compared with those of reflex saccades in patients with Parkinson's disease and normals. It was found that the remembered saccades of the patients were more hypometric than those of normals but that the final eye position was normal. Latency and peak velocity were normal as well. The patients exhibited an increased incidence of multistepping (“staircase saccades”). Using an inverse reconstruction technique, evidence was obtained for the presence of pulse doublets at the input of the oculomotor plant in such cases.
The Quarterly journal of experimental psychology, Aug 1, 1992
Ten patients with mild to moderate Parkinson's disease were compared with ten age-matched nor... more Ten patients with mild to moderate Parkinson's disease were compared with ten age-matched normal controls in a series of saccadic paradigms in order to test various hypotheses relating to the origin of the Parkinsonian saccadic defect. The paradigms comprised a reflex saccade paradigm, a standard remembered saccade paradigm, a remembered saccade paradigm with delayed centre-offset, and a remembered saccade paradigm with a second target flash immediately prior to saccade execution. Finally, subjects executed both reflex and remembered saccades in a standard remembered paradigm (the “two-saccade” paradigm). As has been reported previously, Parkinsonian subjects demonstrated hypometria on all remembered saccade paradigms, particularly the “two-saccade” paradigm. There was, however, no significant difference between the first three remembered saccade paradigms. These studies serve to refute a simple attentional capture hypothesis, and a hypothesis that suggests that the abnormality of remembered saccades is due to concurrent reflex saccade suppression. On the basis of the results, further hypotheses are advanced in an attempt to explain all published work on Parkinsonian saccades.
Attempts to determine the physiological nature of smoothpursuit dysfunction in schizophrenia have... more Attempts to determine the physiological nature of smoothpursuit dysfunction in schizophrenia have included many investigations of saccade rates, but the findings have been variable. The present investigation tested the hypothesis that the misclassification of blinks as saccades affects saccade rates in studies using only infrared oculography (IROG). Both IROG and vertical electro-oculography (VEOG), the latter of which provides an objective measure of blinking, were collected while 17 schizophrenia patients and 19 healthy control subjects were presented 0.4 Hz sinusoidal stimuli. Of the blinks identified with the VEOG, 42% were not identified, and 37% were misclassified as saccades when only the IROG was used. Most misclassified saccades masqueraded as catch-up saccades (CUS)(66%) and anticipatory saccades (AS) (34%). However, CUS and total saccade rates were significantly elevated in schizophrenia patients both before and after correction for misclassified blinks. Rates of other saccade subtypes and blinks did not differ. Therefore, the misclassification of blinks as saccades is likely to introduce some measurement error into estimates of saccade rates, but it is unlikely to account for the variability in estimates evidenced in the literature. However, when the blinkto-saccade ratio is larger, as it is in saccadic paradigms, saccade metrics may be vulnerable to the effects of blink misclassification
To provide evidence of an organic pathology for essential (idiopathic) blepharospasm, reflex sacc... more To provide evidence of an organic pathology for essential (idiopathic) blepharospasm, reflex saccadic eye movements in response to randomly stepped visual targets were assessed in seven affected patients and seven age-matched controls using the magnetic scleral search coil technique. The results indicate a significant prolongation in latency and a reduction in gain of horizontal saccades, and an increase in latency and reduction of peak velocity of large downward saccades. These findings suggest an organic component to the aetiology of blepharospasm, the pathology of which also appears to involve the oculomotor system. The pattern of the oculomotor disorder does not allow specific localisation but is consistent with the underlying pathology being localised in the basal ganglia.
Smooth pursuit abnormalities have been observed in antipsychotic naive first-episode patients, su... more Smooth pursuit abnormalities have been observed in antipsychotic naive first-episode patients, suggesting that they are intrinsic to the illness. However, it is not clear whether these abnormalities are as severe as those observed in more chronic patients. In addition, although research suggests that there are no short-term effects of conventional antipsychotic medication, the effects of long-term antipsychotic medication on smooth pursuit eye movements are relatively unknown. To determine the short and long term effects of antipsychotic medication on the smooth pursuit performance of first-episode and chronic patients with schizophrenia. We compared the smooth pursuit performance of antipsychotic-treated and untreated first-episode and chronic schizophrenic patients with healthy controls using a comprehensive range of performance measures. This included velocity gain, the number, type and size of intrusive and corrective saccades, and the average time between the change in direction of the target and the change in direction of the eye movement, a measure of subjects' ability to predict target movement. Chronic schizophrenic patients had significantly reduced velocity gain, took longer to respond to the change in target direction and made more catch-up saccades than both first-episode schizophrenic patients and controls. First-episode patients were impaired relative to controls only on the measure of velocity gain. There were no differences between antipsychotic-naive and treated first-episode patients. Antipsychotic-free chronic patients were significantly less impaired on velocity gain than matched continuously treated chronic patients. These results were not influenced by group differences in age and symptom severity. These results show that: 1) the main index of smooth pursuit, velocity gain, is impaired early in the course of schizophrenia; 2) whereas velocity gain is unaffected by short-term (weeks) medication, it is worsened by chronic (years) treatment; 3) other indices of smooth pursuit, catch-up saccades and ability to predict target movement, are adversely influenced by illness chronicity rather than medication.
Saccades to a remembered target use non-visual feedback and rely on a normal functioning of the p... more Saccades to a remembered target use non-visual feedback and rely on a normal functioning of the projection from the caudate nucleus to the substantia nigra pars reticulata. The latter projection is known to be defective in Parkinson's disease and it seems therefore likely that remembered saccades are abnormal in such patients. In a series of three studies the characteristics of remembered saccades were compared with those of reflex saccades in patients with Parkinson's disease and normals. It was found that the remembered saccades of the patients were more hypometric than those of normals but that the final eye position was normal. Latency and peak velocity were normal as well. The patients exhibited an increased incidence of multistepping (“staircase saccades”). Using an inverse reconstruction technique, evidence was obtained for the presence of pulse doublets at the input of the oculomotor plant in such cases.
The Quarterly journal of experimental psychology, Aug 1, 1992
Ten patients with mild to moderate Parkinson's disease were compared with ten age-matched nor... more Ten patients with mild to moderate Parkinson's disease were compared with ten age-matched normal controls in a series of saccadic paradigms in order to test various hypotheses relating to the origin of the Parkinsonian saccadic defect. The paradigms comprised a reflex saccade paradigm, a standard remembered saccade paradigm, a remembered saccade paradigm with delayed centre-offset, and a remembered saccade paradigm with a second target flash immediately prior to saccade execution. Finally, subjects executed both reflex and remembered saccades in a standard remembered paradigm (the “two-saccade” paradigm). As has been reported previously, Parkinsonian subjects demonstrated hypometria on all remembered saccade paradigms, particularly the “two-saccade” paradigm. There was, however, no significant difference between the first three remembered saccade paradigms. These studies serve to refute a simple attentional capture hypothesis, and a hypothesis that suggests that the abnormality of remembered saccades is due to concurrent reflex saccade suppression. On the basis of the results, further hypotheses are advanced in an attempt to explain all published work on Parkinsonian saccades.
Attempts to determine the physiological nature of smoothpursuit dysfunction in schizophrenia have... more Attempts to determine the physiological nature of smoothpursuit dysfunction in schizophrenia have included many investigations of saccade rates, but the findings have been variable. The present investigation tested the hypothesis that the misclassification of blinks as saccades affects saccade rates in studies using only infrared oculography (IROG). Both IROG and vertical electro-oculography (VEOG), the latter of which provides an objective measure of blinking, were collected while 17 schizophrenia patients and 19 healthy control subjects were presented 0.4 Hz sinusoidal stimuli. Of the blinks identified with the VEOG, 42% were not identified, and 37% were misclassified as saccades when only the IROG was used. Most misclassified saccades masqueraded as catch-up saccades (CUS)(66%) and anticipatory saccades (AS) (34%). However, CUS and total saccade rates were significantly elevated in schizophrenia patients both before and after correction for misclassified blinks. Rates of other saccade subtypes and blinks did not differ. Therefore, the misclassification of blinks as saccades is likely to introduce some measurement error into estimates of saccade rates, but it is unlikely to account for the variability in estimates evidenced in the literature. However, when the blinkto-saccade ratio is larger, as it is in saccadic paradigms, saccade metrics may be vulnerable to the effects of blink misclassification
To provide evidence of an organic pathology for essential (idiopathic) blepharospasm, reflex sacc... more To provide evidence of an organic pathology for essential (idiopathic) blepharospasm, reflex saccadic eye movements in response to randomly stepped visual targets were assessed in seven affected patients and seven age-matched controls using the magnetic scleral search coil technique. The results indicate a significant prolongation in latency and a reduction in gain of horizontal saccades, and an increase in latency and reduction of peak velocity of large downward saccades. These findings suggest an organic component to the aetiology of blepharospasm, the pathology of which also appears to involve the oculomotor system. The pattern of the oculomotor disorder does not allow specific localisation but is consistent with the underlying pathology being localised in the basal ganglia.
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Papers by Trevor Crawford