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

Increased frequency of anticipatory saccades during smooth pursuit eye movements is a potential marker of genetic risk for schizophrenia even in the absence of clinical symptomology. The operational definition of anticipatory saccades has often included an amplitude criterion; however, these amplitude criteria have often differed across studies. This study reports on the effect of varying amplitude criteria on the effect size in a comparison of 29 schizophrenic adults and 29 normal subjects during a 16.7°/s constant velocity task. The inclusion of small amplitude anticipatory saccades, with amplitudes of 1–4°, consistently increased effect size (largest effect size = 1.61). The inclusion of large anticipatory saccades, with amplitudes of 4° or greater, had an inconsistent impact on effect size. The separation of anticipatory saccades into leading saccades (anticipatory saccades with amplitude 1–4°) and large anticipatory saccades (amplitude >4°) deserves further exploration.