Comparison of the responses of auditory nerve fibers to consonant-vowel syllables with predictions from linear models.

The responses of cat auditory-nerve fibers to synthesized consonant-vowel syllables were compared with predictions from linear models based on individual fibers' threshold tuning curves. Comparisons with the linear predictions provided information about the specific effects of peripheral nonlinearities on the representation of speech sounds. Spectral peaks, such as the formants of vowels, were more prominently represented in synchronized discharge patterns than in the linear predictions. Suppression of responses to other spectral peaks and to stimulus components between spectral peaks accounted for the differences. While profiles of fibers' synchronized responses were usually dominated by a single formant, predicted linear responses often included broad responses having two or more formants as well as components near the fibers' characteristic frequencies. In contrast, when no stimulus peak fell within a fiber's response area, the agreement between the neural response and the linear prediction was quite good. The results suggest that one role for peripheral nonlinearities in the auditory system may be to enhance the neural representation of spectral features such as formants.