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RS Ramchandran, DS Manoach, KA Lindgren, MV Cherkasova, JJ S Barton; Longer Latencies Result in Slower Peak Velocities for Saccadic Tasks in Schizophrenic Subjects . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2652.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previous studies have shown that, compared to normal subjects, the antisaccades but not the visual saccades of schizophrenic subjects have lower peak velocities and longer latencies. Whether the peak velocity of a saccade is related to its latency from target appearance is not known. Such a relation could be hypothesized given the reduced velocities of memory-guided saccades. This study investigated whether saccadic latencies are inversely correlated with peak velocities for visual saccades and antisaccades in both schizophrenic and normal populations. Methods: 16 normal and 21 schizophrenic subjects performed 200 visual saccades and 200 antisaccades trials each. The peak velocity and amplitude data were analyzed with randomized block ANOVAs, with subjects within group as the random factor and group (schizophrenic/normal), latency, and task (visual saccade/antisaccade) as factors. Results: As latency increased, the peak velocity of visual saccades significantly decreased in schizophrenic subjects, ultimately becoming equivalent at about 350ms to the peak velocity of antisaccades, which were not affected by latency. This decline was not seen in normal subjects. The interaction of task by latency was significant only in schizophrenic subjects and not in normal subjects. Amplitude did not vary with latency and were very similar for antisaccades and visual saccades in both schizophrenic and normal subjects. Conclusion: Schizophrenic but not normal subjects show a decline in visual saccadic peak velocity with increased saccadic latency, not attributable to changes in saccadic amplitude. This may be due to increased decay of the visual transient marking the target's appearance and/or an attentional failure related to frontal cortical dysfunction.
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