Smooth pursuit eye movements to extraretinal motion signals: Deficits in relatives of patients with schizophrenia

BACKGROUND: Although mounting evidence supports the idea that smooth pursuit abnormality marks the genetic liability to schizophrenia, the precise ocular motor mechanism underlying the abnormality remains unknown. Based on recent findings in schizophrenia, we hypothesize that subtle deficits in the ability to hold online and/or use extraretinal motion information underlie the pursuit abnormality in vulnerable individuals. METHODS: The hypothesis was tested in 69 first-degree, biological relatives of probands with schizophrenia; 26 relatives had schizophrenia spectrum personalities (SSP). Subjects recruited from the community (n=71; 29 with SSP), without a known family history of psychosis, constituted the comparison groups. The traditional smooth pursuit gain measure, which is a ratio of smooth pursuit eye velocity in response to both retinal and extraretinal motion signals and the target velocity, was obtained. In addition, newly developed measures of predictive smooth pursuit (ie, in the presence of only extraretinal motion signals) were obtained. The latter measures were evaluated after the current retinal motion signals were made unavailable by briefly making the target invisible. RESULTS: Relatives, particularly those with SSP, showed significantly poorer predictive pursuit response to extraretinal motion signals (F(2,136)=6.51, P