Amplitude criteria and anticipatory saccades during smooth pursuit eye movements in schizophrenia

Increased frequency of anticipatory saccades during smooth pursuit eye move ments is a potential marker of genetic risk for schizophrenia even in the a bsence of clinical symptomology. The operational definition of anticipatory saccades has often included an amplitude criterion; however, these amplitu de criteria have often differed across studies. This study reports on the e ffect of varying amplitude criteria on the effect size in a comparison of 2 9 schizophrenic adults and 29 normal subjects during a 16.7 degrees/s const ant velocity task. The inclusion of small amplitude anticipatory saccades, with amplitudes of 1-4 degrees, consistently increased effect size (largest effect size = 1.61). The inclusion of large anticipatory saccades, with am plitudes of 4 degrees or greater, had an inconsistent impact on effect size . The separation of anticipatory saccades into leading saccades (anticipato ry saccades with amplitude 1-4 degrees) and large anticipatory saccades (am plitude >4 degrees) deserves further exploration.