Deficient cancellation of the vestibular ocular reflex in schizophrenia

Schizophrenia has long been associated with difficulties in visual tracking of a moving object. Deficits are most notable in tracking tasks that require inhibition of saccades during active smooth pursuit. In order to assess whether there is a more global problem in inhibition of other eye movement systems while the smooth pursuit system is active, this study examined cancellation of the vestibular ocular reflex (VOR). Cancellation of the VOR occurs in a task in which the subject is rotated while looking at a target that is also being rotated. This requires the subject to use the pursuit system to override the VOR, maintain the eye at a stable location within the orbit, and thus retain visual gaze upon the target. Thirteen individuals with schizophrenia and 15 normals were assessed during clockwise rotation at 60 degrees s-1. Schizophrenic subjects had a significant increase in counterclockwise slow velocity eye movements, suggesting an impaired ability to cancel the VOR. Cancellation of the VOR is thus another example of a breakthrough of an alternative eye movement system while the smooth pursuit system is active. Because of the simplicity of the VOR and its suitability for animal modeling, investigation of this phenomenon may delineate more precisely the mechanisms of visual tracking dysfunction in schizophrenia.