Abstract
Whole nerve action potentials (AP) and auditory brain stem responses (ABR) were studied when produced by varying intensities of sound or electrical stimuli, respectively. The sound stimulus used was a frequency-shifted tone with amplitude modulation. The sharp tuning curve of the AP obtained in response to the frequency-shifted tone, and the 1.7:1 ratio of the latency differences between 515 and 1,150 Hz and between 1,150 and 2,230 Hz indicated that the AP is “place specific.” The latency of the AP decreased with increasing sound intensity levels. The amplitude of the AP increased with increasing intensity up to 75 dB, beyond which it showed a flat or a twin peak with decreased amplitude. These waveform changes were observed in both normal and abnormal cochleae. The amplitude of each wave of electrically elicited ABR increased with increasing current levels, but the latency remained constant. This indicates that an electrically elicited response consists of well-synchronized firings and may cause a different sensation from natural stimuli. Hence patients with cochlear implants are likely to need special training to gain full benefit from their implants.
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