Ventral cochlear nucleus coding of voice onset time in naturally spoken syllables

Abstract

These experiments examined the coding of the voice onset time (VOT) of six naturally spoken syllables, presented at a number of intensities, by ventral cochlear nucleus (VCN) neurons in rats anesthetized with urethane. VOT is one of the cues for the identification of a stop consonant, and is defined by the interval between stop release and the first glottal pulse that marks the onset of voicing associated with a vowel. The syllables presented (/bot/, /dot/, /got/, /pot/, /tot/, /kot/) each had a different VOT, ranging between 10 and 108 ms. Extracellular recordings were made from single neurons ( N=202) with a wide range of best frequencies (BFs; 0.66–10 kHz) that represented the major VCN response types – primary-like (67.8% of sample), chopper (19.8%), and onset (12.4%) neurons. The different VOTs of the syllables were accurately reflected in sharp, precisely timed, and statistically significant changes in average discharge rate in all cell types, as well as the entire VCN sample. The prominence of the response to stop release and voice onset, and the level of activity prior to the VOT, were influenced by syllable intensity and the spectrum of stop release, as well as cell BF and type. Our results suggest that the responses of VCN cells with BFs above the first formant frequency are dominated by their sensitivity to the onsets of broadband events in speech, and allows them to convey accurate information about a syllable’s VOT.