Response to unexpected target changes during sustained visual tracking in schizophrenic patients

Background: Evidence supports an association between liability to schizophrenia and smooth-pursuit eye movement (SPEM) abnormalities. Knowledge of the biological mechanisms of SPEM abnormalities may provide critical insights into the etiology of schizophrenia. SPEM is elicited by sensory motor information from the movement of the object’s image on the retina (retinal motion signal) and subsequent extraretinal motion signals. Previous studies suggest that a deficit in predictive responses to extraretinal motion signals may underlie the SPEM phenotype in schizophrenia. Data suggest that at-risk individuals for schizophrenia depend less on extraretinal and more on retinal motion signals to maintain pursuit than healthy individuals. Methods: We designed a pursuit task that employs unexpected changes in target direction during smooth pursuit. The unpredictable task is unique in that performance is expected to be better if the subject’s response is biased towards retinal motion. Results: The study included 23 schizophrenia patients and 22 normal controls. Results showed that schizophrenia patients showed significantly superior performance (i.e. higher smooth pursuit gain) for a brief period after an unexpected change in target direction compared with healthy subjects. Conclusion: Findings of superior performance by schizophrenic patients are interesting because they circumvent confounds of generalized deficits. These results provide further evidence of specific deficit in the predictive pursuit mechanism and over-reliance on retinal error signals to maintain pursuit in schizophrenia.