AUDITORY DETECTION OF THE HUMAN BRAIN-STEM AUDITORY EVOKED-RESPONSE

The human brainstem auditory evoked response (BAER) is a far-field electrical potential recorded from the scalp in response to transient acoustic stimuli. Typically, voltage measurements are obtained for a period of about 10 msec following the acoustic stimulus, which is repeated and summed several hundred or thousand times to permit extraction of the response from ongoing nonauditory neural activity. The judgment about whether a response has been obtained is normally based on the pattern observed in a visual display of the waveform. In this study, we investigated whether listeners can distinguish BAERs elicited by acoustic clicks from control waveforms obtained with no acoustic stimulus when the waveforms were presented auditorily. For this purpose, BAER and control waveforms were transduced by an earphone and used in an auditory detection task. Several presentation strategies were examined, including lengthening the waveform by playing it at a lower sampling rate, playing the waveform repetitively, and using the waveform to frequency modulate a pure-tone carrier. The results indicated that the BAER, when extended in duration and used to frequency modulate a 1000-Hz pure tone, was highly detectable in a YES-NO paradigm for BAERs elicited with high-level (e.g., 70 dB re. behavioral detection threshold) acoustic clicks. Performance declined to near chance as the level of the BAER-eliciting stimulus was lowered to 10 dB. In general, detection performance for stimuli presented visually was slightly, but consistently, superior to that which occurred for stimuli presented auditorily.