A Functional Model of Primary Auditory Cortex: Spectral Orientation Columns

Abstract

A functional model of the primary auditory cortex is proposed based on physiological maps of the receptive field organization in ferret AI (Shamma, Fleshman and Wiser [1990]). Systematic changes in the excitatory and inhibitory portions of the receptive fields along the isofrequency planes are approximated by a difference of gaussians function with spatially changing parameters. We consider here only the response properties to stationary stimuli, i.e. those with non-varying spectra. The fundamental functional principle that emerges from the analysis of the model is that the primary auditory cortex encodes the shape of the acoustic spectrum in the distribution of its responses along the isofrequency planes. Specifically, it maps to each isofrequency plane a normalized measure of the locally averaged gradient of the input spectrum at that frequency. Physiological and psychoacoustical correlates and implications of these findings are explained. Parallels to the functional organization of the visual cortex are also discussed.