Time-domain analysis of firing-rate data from over 200 fibers from the auditory nerve of cat has been used to estimate the formants of the synthetic-syllable stimuli. Distinct groups of fibers are identified based on intervals between peaks in the fiber firing rates. The large extent of some of these groups--over an octave in terms of characteristic frequency--and the lack of short intervals in the longer-interval groups suggest that the behavior of the nonlinear cochlear filters for these signals is effectively wideband with steep high-frequency cutoffs. The measured intervals within each group are very similar, and correspond to the period of the formant that dominates the group's response. These intervals are used to estimate the dynamic speech formants. The overall formant estimates are better than those of the previous spectral analyses of the neural data, and the details of lower-formant dynamics are tracked more precisely. The direct temporal representation of the formant in contrasted with the diffuse spectral representation, the dependence of spectral peaks on nonformant parameters, and the distortion of the spectrum by rectification. It is concluded that a time-domain analysis of the responses to complex stimuli can be an important addition to frequency-domain analysis for neural data, cochlear models, and machine processing of speech.

Given the two-port description of a hair cell from Weiss [Hear. Res. 7, 353–360 (1982)], with the Davis model for the angle-dependent conductance representing the transduction channels [Leong and Weiss, Hear. Res. 20, 175–195 (1985)], and the data of Crawford and Fettiplace [J. Physiol. 364, 359–379 (1985)], Howard and Hudspeth [Neuron 1, 189–199 (1988)], and Holton and Hudspeth [J. Physiol. 375, 195–227 (1986)], analysis shows that (1) the feedback inherent in the two-port must be positive, and (2) degenerative (outward-flowing) channels must be present. The static nonlinear behavior of the system, and the small and large signal dynamics, have been studied. The system displays Q multiplication at low signal levels, bandwidth increase with signal level, a compressive nonlinearity at CF, and continuous oscillations if the parameters are slightly misadjusted—all well-documented physiological phenomena.

A time-domain analysis of firing-rate data from over 200 fibers from the auditory nerve of cat has been used to estimate the formants of synthetic speech syllables. Distinct groups of fibers are apparent in the neurograms of the firing-rate responses. The intervals between peaks in the firing-rates of the fibers in each group are very similar, and reflect the period of the formant that dominates the group's response. Analysis of these intervals confirms that they correspond directly to the formant periods. It is concluded that the cochlear filters have much shorter impulse responses than the formants to which they respond. The time-domain analysis tracks the changes of lower frequency formants with more precision than previous analyses of the same neural data [M. I. Miller and M. B. Sachs, J. Acoust. Soc. Am. 74, 502–517 (1983); S. A. Shamma, J. Acoust. Soc. Am. 78, 1622–1632 (1985)]. The direct representation of the formant period in the time domain is contrasted with the diffuse spectral representation of the formant, the dependence of spectral peaks on nonformant parameters, and the distortion of the spectrum by physiological nonlinearities.