Monaural, cross-frequency coincidence detection as a mechanism for decoding perceptual cues provided by the cochlear amplifier

Abstract

Basilar membrane (BM) response properties associated with the cochlear amplifier are consistent with broadened BM tuning as level increases from approximately 20 to 90 dB SPL or higher. Associated with broadened tuning are compressive BM magnitude responses and level-dependent phase changes. To evaluate the perceptual significance of the cochlear amplifier, the associated nonlinear response properties of the auditory nerve (AN) and physiologically realistic mechanisms for decoding the perceptual cues they provide were studied. Most AN fibers’ rate and synchrony responses to tones are saturated above 40 dB SPL; however, nonlinear phase changes with level are encoded in AN responses up to 90 dB SPL or higher. Broadened tuning produces an increase in the correlation between adjacent AN fibers. Monaural coincidence detection is a physiologically realistic mechanism that can extract nonlinear phase cues across AN fibers with similar characteristic frequencies over a wide dynamic range. Methods from statistical decision theory [Colburn, J. Acoust. Soc. Am. 54, 1458–1470 (1973)] were combined with an analytical AN model to provide a quantitative framework for evaluating the potential of a coincidence detector to explain human performance in pure-tone intensity and frequency discrimination. [Work supported by NIH Grant No. T32DC00038 and NSF Grant No. 9601215.]