EFFECTS OF SOUND INTENSITY ON A MIDLATENCY EVOKED-RESPONSE TO REPEATED AUDITORY-STIMULI IN SCHIZOPHRENIC AND NORMAL SUBJECTS

Inhibitory gating of response to repeated stimuli is demonstrated by s everal event-related potentials, including the auditory P50 wave. The present study examined the effects of variation in sound intensity on this phenomenon in schizophrenics and normal subjects. Paired clicks, 500 ms apart, were presented 50 dB above threshold to 10 normal subjec ts and 10 schizophrenics, The normal subjects demonstrated significant ly more decrement of response to the second stimulus than did the schi zophrenics. When the sounds were noticeably louder(70 dB above thresho ld), no such difference was observed. Rather, both groups had similarl y diminished gating of response. A significant difference between schi zophrenics and normal subjects was also observed when the sounds were 30 dB above threshold, but the difference was smaller than that at 50 dB. At any stimulus intensity, concomitant eye movements led to loss o f gating of P50 in the normal subjects.