MEASUREMENT of the sensory evoked cerebral response in man has been greatly facilitated by the advent of electronic techniques for averaging out the background activity.1This development has fostered increased interest in the possibility of finding physiological correlates of psychologic phenomena in both healthy and mentally ill populations. In normal subjects, sensory evoked response characteristics have been found to vary with changes in perception, attention, stimulus uncertainty, and extroversion.2-11There are also differences relating to sex and age.11Psychiatric patients have been shown to differ from nonpatients in the reactivity cycle and in the intensity response gradient of the somatosensory evoked response.12-15In psychotic depressed patients, the reactivity cycle was found to improve as their clinical condition improved.13Similarly, abnormalities in the auditory evoked response in schizophrenics were found to change toward normal as their clinical state improved.