Spatiotemporal coding of signals in the auditory periphery.

Abstract

Signal representation in the cochlea is often thought to involve either rate-place profiles or purely temporal, interspike interval codes. Spatio-temporal coding strategies based on phase-locking, cochlear delays, and coincidence detectors have also been proposed [Loeb et al., Biol. Cybern. (1983); K. & Shamma, J. Acoust. Soc. Am. 107 (2000); and Carney et al., Acoustica 88, 334–337 (2002)]. In this view, spatiotemporal patterns of spikes locked to relative phases of the traveling wave at specific cochlear places at a given time can convey information about a tone. We propose a general mathematical basis for using such spatial phase/amplitude patterns along the frequency axis to represent an arbitrary (approximately) time and bandwidth-limited signal. We posit that the spatial pattern of phases and amplitudes corresponds to locations at which (real and/or imaginary parts of) the Fourier transform of the signal crosses certain levels (e.g., zero level). Given these locations, we show that we can accurately reconstruct the original signal by solving a simple eigenvalue problem. Using this approach, we propose an analysis/synthesis algorithm to represent speech-like signals. We conjecture that a generalized representation of the forms of signals can be inferred from spatial, cross-CF patterns of phase relations present in the auditory nerve. [Work supported by AFSOR FA9550-09-1-0119.]