Smooth pursuit eye movements in schizophrenics--what constitutes quantitative assessment?

Although a voluminous literature exists on the eye movements of schizophrenic and affective disorder patients, many of the assessments made of smooth pursuit have been qualitative in nature. Most of them have not differentiated between abnormal functioning of the smooth pursuit system and intrusion of inappropriate saccades during a smooth tracking task. Specific identification of the pursuit or saccadic defect is necessary if the origins of the abnormalities are to be understood and related to psychopathology. Analytical techniques, such as the ln(S/N) ratio, although numerical in nature, are still unable to discriminate among pursuit and saccadic defects, as shown by our analysis of simulated tracking. Thus, to understand the effects of psychiatric disorders on the ocular motor system, specific defects must be identified and quantified.