Representation of steady-state vowels in the temporal aspects of the discharge patterns of populations of auditory-nerve fibers

Abstract

This paper is concerned with the representation of the spectra of synthesized steady-state vowels in the temporal aspects of the discharges of auditory-nerve fibers. The results are based on a study of the responses of large numbers of single auditory-nerve fibers in anesthetized cats. By presenting the same set of stimuli to all the fibers encountered in each cat, we can directly estimate the population response to those stimuli. Period histograms of the responses of each unit to the vowels were constructed. The temporal response of a fiber to each harmonic component of the stimulus is taken to be the amplitude of the corresponding component in the Fourier transform of the unit's period histogram. At low sound levels, the temporal response to each stimulus component is maximal among units with CFs near the frequency of the component (i.e., near its place). Responses to formant components are larger than responses to other stimulus components. As sound level is increased, the responses to the formants, particularly the first formant, increase near their places and spread to adjacent regions, particularly toward higher CFs. Responses to nonformant components, exept for harmonics and intermodulation products of the formants (2F1,2F2,F1 + F2, etc), are suppressed; at the highest sound levels used (approximately 80 dB SPL), temporal responses occur almost exclusively at the first two or three formants and their harmonics and intermodulation products. We describe a simple calculation which combines rate, place, and temporal information to provide a good representation of the vowels' spectra, including a clear indication of at least the first two formant frequencies. This representation is stable with changes in sound level at least up to 80 dB SPL; its stability is in sharp contrast to the behavior of the representation of the vowels' spectra in terms of discharge rate which degenerates at stimulus levels within the conversational range.

Frequency selectivity of phase-locking of complex sounds in the auditory nerve of the rat

“…This was shown by earlier studies to be true for noise [ 10,281, for tones [21] and for vowels [43]. In this report we have also shown that the output of a linear model based on the first-order cross-correlation functions deviates little from the output of fibers which show a large change in their tuning properties when the stimulus intensity is raised from just above threshold to physiological levels (50-70 dB above threshold).…”

Spectral integration plasticity in cat auditory cortex induced by perceptual training

“…Accordingly, several physiological studies of the peripheral and central auditory system of animals have used speech-like stimuli to elucidate potential coding strategies of the human auditory system (e.g., Delgutte and Kiang, 1984;Eggermont, 1995;Sachs and Young, 1979;Schreiner, 1998;Steinschneider et al, 1990;Wong and Schreiner, 2003;Young and Sachs, 1979). Studies of general features of human and animal vocalizations, such as fundamental frequency of the sound source (e.g.…”

Coding of Sounds in the Auditory System and Its Relevance to Signal Processing and Coding in Cochlear Implants

“…Phase locking may be particularly important for coding the relative levels of components in complex sounds (23). When the level of a component is increased relative to that of the other components, the degree of phase locking to that component increases.…”

“…2. By the relative amount of phase locking to the different frequency components in neurons with different CFs (23). For example, if a speech sound has a formant with a frequency of 1,400 Hz, neurons with CFs around 1,400 Hz will show phase locking to the formant frequency.…”