Slow Cortical Responses Evoked by Acoustic Stimuli

Abstract

Evoked responses of the waking human brain to acoustic stimuli can easily be recorded from external electrodes by means of an average response computer. The clearest responses are anatomically diffuse (strongest from frontal and vertex), long in latency, and are evoked by visual or tactile as well as auditory stimuli. Their amplitude varies quite widely across subjects, with the state of the subject, with the interval between stimuli (up to 10 seconds), and from one individual stimulus to the next. The average of a set of successive responses is sufficiently related to the intensity of the stimulus, however, to make the niethod useful for “objective” audiometry on a purely empirical basis, even though the response does not arise from the primary auditory cortical area. Our thresholds of detection of the average evoked responses of fifty severely hard-of-hearing children, 7 to 16 years old, were conipared with the children's subjective thresholds for the same filtered clicks. The mean difference was only 2.5 dB. The averages for five frequencies diverged by 18 dB or more in only two cases. The relation to their pure-tone thresholds, as determined in our clinic, was almost equally close.