Auditory nerve fiber responses predict the discriminability of VOT syllables

Abstract

Responses of chinchilla auditory nerve fibers to synthesized syllables differing in VOT were obtained. A continuum heard as /da/∼/ta/ was used. Many neurons responded with an increase in average discharge rate or with a change in synchronized response whose latency matched the nominal stimulus VOT. Response latency was treated as a random variable. For each VOT pair, a statistic analogous to d' was calculated from the distribution of the difference between two random variables. Thresholds for ΔVOT were interpolated from psychometric functions based on this statistic. Thresholds were lowest for standard VOTs of 30–40 ms, but were highly dependent on the direction of change from the standard. These characteristics were also typical of the chinchilla's psychophysical thresholds for ΔVOT, reported by Kuhl [J. Acoust. Soc. Am. 70, 340–349 (1981)]; in addition, the quantitative agreement between neural and behavioral thresholds was usually very good. For this VOT continuum, discriminability reflects the precision of stimulus coding at the level of the auditory nerve. [Work supported by NINCDS.]