Visual AERs from left and right temperoparietal and occipital cortex were recorded using visual stimuli presented to the left and right hemiretinal fields and to both fields simultaneously. Subjects included normal controls and patients with acute schizophrenia, affective illness and right and left temporal lobectomies for epilepsy. One patient with partial agenesis of the corpus callosum was also studied. Differences in AER caused by attention were noticed especially in the left temperoparietal cortex when stimuli were presented separately to each field. Schizophrenic and lobectomy groups showed diminished asymmetry and attentional affects, whereas bipolar affective disorders showed generally enhanced attentional effects. Full visual field stimulation also produced attentional asymmetries, currently under study, in schizophrenics.