Impaired smooth pursuit in schizophrenia results from prediction impairment only

Oculomotor abnormality is one of the endophenotypes in schizophrenia. The predictive component of smooth pursuit can be studied by comparing the gain, i.e., the ratio of smooth eye position to target position, during predictable (pure sinusoidal) and unpredictable (pseudorandom) target motions. The aim of this experiment was to study predictive and nonpredictive components of smooth pursuit in two groups of schizophrenia patients compared with control subjects.

Fifty-one schizophrenia patients (40 nondeficit and 11 deficit) and 21 control subjects were studied. During a predictable task, subjects were asked to track a sinusoidal target (.4 Hz). For the unpredictable task, the pseudorandom target motion consisted of five superimposed sinusoidal waveforms (.1, .2, .4, .6, and .8 Hz). The smooth eye position (eye position without saccades), gain, and phase were calculated for each frequency in each participant and for both tasks.

The mean sinusoidal smooth eye position gain was significantly lower in patients than in control subjects with no significant difference between deficit and nondeficit patients. During the pseudorandom task, all groups had a similar gain at .4 Hz.

Our study reveals that patients have a normal nonpredictive component of smooth pursuit, regardless of their level of negative symptoms. In contrast, the predictive mechanisms involved in eye pursuit were impaired in schizophrenia patients. These results indicate that poor pursuit performance during smooth pursuit is primarily a consequence of a predictive problem and is not related to the ability to generate an accurate pursuit maintenance response.