Smooth pursuit eye tracking over a structured background in first-episode schizophrenic patients

Whilst most laboratory smooth pursuit tasks are performed in the dark, in e veryday lire pursuit commonly occurs over a structured background. This bac kground provides a powerful stimulus to the optokinetic reflex (OKR), induc ing a background "drag" on pursuit eye movements. An inability to inhibit t he influence of the OKR may be a contributing factor to the dysfunctional p ursuit performance observed in many schizophrenic patients. Smooth pursuit performance was measured in 23 first-episode schizophrenic patients and 23 healthy controls matched for age and estimated IQ, both in the dark and ove r a structured background (a random checkerboard of black and white squares ). Velocity gain was measured, as well as the number and size of corrective saccades (catch-up saccades) and intrusive saccades (anticipatory saccades and square wave jerks). Overall, schizophrenic patients had lower velocity gain and made more catch-up saccades than controls. The effect of the back ground was to lower velocity gain and increase the number of catch-up sacca des to the same extent in schizophrenic patients and controls. There were n o significant interactions between group and background effect. These resul ts suggest that, although their overall level of performance was worse, the schizophrenic patients were as able as controls to inhibit the effect of t he OKR. Since lesion studies show that inhibition of the OKR requires intac t inferior parietal regions in man (Lawden et al., 1995), one hypothesis is that the parietal component of smooth pursuit may be intact in schizophren ia.