Effects of nonlinearities on speech encoding in the auditory nerve.

The representation of steady‐state vowels in terms of both average rate and temporal aspects of the discharge patterns of populations of auditory‐nerve fibers is discussed. The effects of auditory‐nerve nonlinearities on this representation is emphasized. Aspects of two rate‐related nonlinearities, rate saturation and two‐tone suppression, are reviewed. At low sound levels, profiles of discharge rate versus characteristic frequency in populations of auditory‐nerve fibers show well‐defined peaks at frequencies corresponding to the formants of a vowel stimulus. At levels above about 60 dB SPL, these peaks are not seen because of a combination of rate saturation and two‐tone suppression. Units with spontaneous rates less than 1/s show the effects of suppression more dramatically than do units with higher spontaneous rates; nonetheless, this population can retain formant peaks in its rate profiles up to levels at least 20 dB higher than does the higher spontaneous rate population. Aspects of phase‐locking to ...