Mixture analysis of smooth pursuit eye movements in schizophrenia

The goal of this study was to replicate and extend previous findings indicating that the eye movement data of schizophrenic patients is best represented by the mixture of two groups, one of which has distinctly poor performance. Forty-nine schizophrenic patients and 32 normal controls had their smooth pursuit eye movements quantified by calculating the root mean square (RMS) deviation between the target and eye waveforms. Based on the finding of mixture in the distribution of RMS error, the patients were divided into low (better tracking) and high (worse tracking) RMS error subgroups. The high RMS error patients had abnormally decreased gain. Both patient subgroups had abnormally increased frequency of catch-up saccades and increased phase lag. Distinguishing between these two subgroups may be useful in clarifying the pathophysiology of abnormal pursuit and its relationship to heterogeneity in schizophrenia.