What is deviant about deviant smooth pursuit eye movements in schizophrenia?

Smooth pursuit eye movements of schizophrenic, hospitalized nonpsychotic, and normal control subjects (18 per group) were measured in low and high target information conditions. A computer method for measuring saccade frequency and velocity was used. The results indicated that the frequency of saccades was significantly greater in both tracking conditions for schizophrenic than for hospitalized nonpsychotic or normal subjects. Consistent with our earlier finding, the reduction in saccade frequency with high information was greatest for schizophrenic subjects. The results also yielded a unique finding: the velocity of saccades within smooth pursuit records was significantly greater for schizophrenic than for hospitalized nonpsychotic or normal subjects. Greater saccade velocity was not a result of increased saccade size; there was no significant difference in the size of saccades for normal and schizophrenic subjects. Yet, the duration of saccades was significantly less for schizophrenics than for other subjects. Target information affected the frequency, duration and size, yet not the velocity of saccades emitted by all subjects. In contrast to earlier interpretations of deviant smooth pursuit eye movements in schizophrenia, the results may provide the first evidence of differences in the functioning of the saccadic eye movement systems of schizophrenic and normal subjects.