Human auditory steady-state responses (ASSRs) were recorded using stimulus rates of 78–95 Hz in normal young subjects, in elderly subjects with relatively normal hearing, and in elderly subjects with sensorineural hearing impairment. Amplitude-intensity functions calculated relative to actual sensory thresholds (sensation level or SL) showed that amplitudes increased as stimulus intensity increased. In the hearing-impaired subjects this increase was more rapid at intensities just above threshold ("electrophysiological recruitment") than at higher intensities where the increase was similar to that seen in normal subjects. The thresholds in dB SL for recognizing an ASSR and the intersubject variability of these thresholds decreased with increasing recording time and were lower in the hearing impaired compared to the normal subjects. After 9.8 minutes of recording, the average ASSR thresholds (and standard deviations) were 12.6 ± 8.7 in the normal subjects, 12.4 ± 11.9 dB in the normal elderly, and 3.6 ± 13.5 dB SL in the hearing-impaired subjects.
Key Words
Auditory steady-state responses - objective audiometry - physiological thresholds - signal-to-noise ratio
