MIXTURE ANALYSIS OF PURSUIT EYE-TRACKING DYSFUNCTION IN SCHIZOPHRENIA

Results of two recent studies suggest that a distinct subgroup of schi zophrenic patients and their relatives have particularly deviant eye t racking. Such heterogeneity could be of considerable importance, as it may indicate significant pathophysiologic or etiologic heterogeneity in schizophrenia. An analysis of 101 consecutive-admission schizophren ic patients confirmed the existence of two distinct subgroups of patie nts with higher and lower levels of spatial [root mean square (RMS)] e ye-tracking error. However, there was no heterogeneity in the disturba nce of pursuit eye movements. Anticipatory saccades, which by definiti on add very large amounts of spatial tracking error, were more frequen t in the ''high'' RMS error group. Rates of anticipatory saccades were similar in the ''low'' RMS error patient group and normal controls, a nd there was no heterogeneity in the expression of anticipatory saccad es. Apparent heterogeneity in global indices of eye-tracking impairmen t in schizophrenia appears to be a measurement artifact reflecting the powerful influence of anticipatory saccades on global performance ind ices, rather than true heterogeneity in the expression of any specific eye movement abnormality.