Eye movement and visual motion perception in schizophrenia I: Apparent motion evoked smooth pursuit eye movement reveals a hidden dysfunction in smooth pursuit eye movement in schizophrenia

To date, smooth pursuit eye movement in schizophrenia has only been investigated using a target stimulus in continuous motion. However, smooth pursuit can also be evoked by an oscillating jumping dot that appears to be in apparent motion and although there is no continuous motion on the retinal surface this apparently moving stimulus can effortlessly elicit smooth-pursuit eye movement. In the first of two experiments smooth pursuit eye movement was evoked by target stimuli in continuous (real) motion at seven target velocities from 5.0 to 35.0 deg/s, and in a second experiment it was measured in response to an oscillating jumping dot in apparent motion at eight target velocities from 5.0 to 25.0 deg/s in a group with mixed-symptoms in schizophrenia and in a control group. The results of Experiment 1 provided no evidence for a dysfunction in continuous motion evoked smooth pursuit eye movement in the group with schizophrenia. However, following the removal of saccadic eye movements in smooth pursuit, the group with schizophrenia showed significantly lower smooth pursuit eye velocity at target velocities from 20.0 to 35.0 deg/s. The results of Experiment 2 revealed that apparent motion evoked smooth pursuit eye velocity in the group with schizophrenia was significantly lower in comparison with normal observers at all target velocities up to 25.0 deg/s with the inclusion or exclusion of saccadic eye movements. The findings demonstrate that overall smooth pursuit eye movement evoked in response to a continuous (real) motion target in the group with schizophrenia may nevertheless contain a hidden temporal resolution and integration dysfunction that is revealed when smooth pursuit eye movement is evoked in response to an oscillating jumping dot in apparent motion. The findings also demonstrate that normal smooth pursuit eye movement in normal observers can be made to resemble the dysfunctional smooth pursuit eye movement that is naturally found in some people with schizophrenia by using a target stimulus in apparent motion.