Responses of "lower-spontaneous-rate" auditory-nerve fibers to speech syllables presented in noise. II: Glottal-pulse periodicities.
The responses of single cat auditory-nerve fibers to naturally spoken voiced sounds (the vowels [a, i, u] and the murmur [m]) presented at normal intensity (70 dB SPL) in various levels of speech-shaped noise were analyzed for the encoding of the glottal-pulse (fundamental) period. To quantify the strength of this fundamental-period encoding, selected segments of the response histograms were autocorrelated, rectified, and fitted with the best-fitting sinusoid of the fundamental frequency. The magnitude of this best-fitting sinusoid was taken as the magnitude of synchronization. In most cases, it was found that the "lower-SR" fibers (those with spontaneous discharge rates less than 20/s) encoded the fundamental periodicity more strongly and more robustly than did the "high-SR" fibers (those with spontaneous discharge rates greater than 20/s). When either a single strong spectral peak or a relatively "flat" spectrum excited a fiber, it showed poor synchronization to the fundamental period, regardless of its spontaneous-rate class. Judging from a few examples, the glottal-pulse synchronization appears to be intensity dependent, with the relative performance of the high-SR fibers improving at lower intensities. A conceptual model is given which accounts for the general characteristics of the data.
Geisler
C D
CD
Department of Neurophysiology, University of Wisconsin-Madison 53706.
Silkes
S M
SM
D000818:Animals; D002415:Cats; D004594:Electrophysiology; D005931:Glottis / Q000502:physiology; D008959:Models, Neurological; D009412:Nerve Fibers / Q000502:physiology*; D009622:Noise; D010699:Phonation / Q000502:physiology*; D010700:Phonetics; D013061:Speech Acoustics; D013997:Time Factors; D000159:Vestibulocochlear Nerve / Q000502:physiology*