On the invariance of speech percepts

Abstract

A fundamental question in the study of speech is about the invariance of the ultimate percepts, or features. The present paper gives an overview of the noninvariance problem and offers some hints towards a solution. Examination of various data on place and voicing perception suggests the following points. Features correspond to natural boundaries between sounds, which are included in the infant's predispositions for speech perception. Adult percepts arise from couplings and contextual interactions between features. Both couplings and interactions contribute to invariance. But this is at the expense of profound qualitative changes in perceptual boundaries implying that features are neither independently nor invariantly perceived. The question then is to understand the principles which guide feature couplings and interactions during perceptual development. The answer might reside in the fact that: (1) adult boundaries converge to a single point of the perceptual space, suggesting a context-free central reference; (2) this point corresponds to the neutral vocoïd, suggesting the reference is related to production; (3) at this point perceptual boundaries correspond to the natural ones, suggesting the reference is anchored in predispositions for feature perception. In sum, perceptual invariance seems to be grounded on a radial representation of the vocal tract around a singular point at which boundaries are context-fee, natural and coincide with the neutral vocoïd.