Effects of nonlinearities on speech encoding in the auditory nerve

TLDR: 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 and aspects of two rate‐related nonlinearities, rate saturation and two‐tone suppression, are reviewed.

Abstract: In this paper we will consider some effects of auditory‐nerve nonlinearities on the representation of complex stimuli such as vowels. 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, primarily because of effects of rate saturation. In addition, effects related to two‐tone suppression act strongly on units with characteristic frequencies in the vicinity of the second and third formants, suppressing their responses at high levels and contributing to the loss of distinct peaks in this region. Units with spontaneous rates less than about 1/s show the effects of suppression more dramatically than do higher spontaneous units; despite the suppression, however, this population retains formant peaks in its rate profiles up to levels at least 20 dB higher than does the higher spontaneous rate popula...