A neuronal model of vowel normalization and representation.

A speculative neuronal model for vowel normalization and representation is offered. The neurophysiological basis for the premise is the "combination-sensitive" neuron recently documented in the auditory cortex of the mustached bat (N. Suga, W. E. O'Neill, K. Kujirai, and T. Manabe, 1983, Journal of Neurophysiology, 49, 1573-1627). These neurons are specialized to respond to either precise frequency, amplitude, or time differentials between specific harmonic components of the pulse-echo pair comprising the biosonar signal of the bat. Such multiple frequency comparisons lie at the heart of human vowel perception and categorization. A representative vowel normalization algorithm is used to illustrate the operational principles of the neuronal model in accomplishing both normalization and categorization in early infancy. The neurological precursors to a phonemic vocalic system is described based on the neurobiological events characterizing regressive neurogenesis.