Topographic evoked potentials during backward masking in schizophrenics, patient controls and normal controls

1. A backward masking task with simultaneous measurement of topographically mapped evoked potentials was performed by normal, schizophrenic, and patient control subjects. 2. Behavioral results replicated previous studies demonstrating schizophrenic deficit and to a lesser extent patient control deficit in this task. 3. Two competing theories of (A) defects in "gating" mechanisms or (B) failure in early stimulus "registration" processes were tested. 4. Topographical evoked response maps indicated a significant absence of a negative going wave in the 70-100 msec epoch in the schizophrenic group relative to both control groups. 5. As the 70-100 msec negativitity attenuation occurred during target presentation, and well before mask onset, it was concluded that schizophrenic deficit in this task consists of a failure in initial stimulus "registration" processes within the time allowed for stimulus availability. 6. Such defective mechanisms may be significant in the pathogenesis of schizophrenia.