Dependence of impaired eye tracking on deficient velocity discrimination in schizophrenia

Background: Abnormal smooth pursuit eye movements have been found in many s chizophrenic patients and in about 40% of their first-degree biological rel atives. A velocity discrimination deficit has also been demonstrated in sch izophrenic patients. In this study, we address the relation between deficie nt velocity discrimination and impaired smooth pursuit eye movements, inasm uch as the brain regions responsible for processing velocity signals are im plicated in generating and maintaining smooth pursuit. Methods: Horizontal eye movements of 15 schizophrenic patients and 8 normal controls were recorded in response to sine wave (predictable) and step-ram p (nonpredictable) targets. Smooth pursuit eye movements were assessed duri ng both the initiation and maintenance periods. Correlations were computed between measures of smooth pursuit (qualitative rating, peak gain, saccade frequency, and initial acceleration) and contrast sensitivity for velocity discrimination. Results: Contrast sensitivity for fine velocity discrimination was signific antly correlated both with initial acceleration of smooth pursuit and with peak gain, but was not significantly correlated with saccade frequency and qualitative ratings of pursuit integrity. No significant correlations were found within the normal control group. Conclusion: Deficient processing of velocity information seems to be one co mponent that contributes to a dysfunction in the initiation and maintenance of smooth pursuit in schizophrenia.