Listening for the norm: adaptive coding in speech categorization.

Jingyuan Huang,Lori L Holt

doi:10.3389/fpsyg.2012.00010

Abstract

Perceptual aftereffects have been referred to as “the psychologist’s microelectrode” because they can expose dimensions of representation through the residual effect of a context stimulus upon perception of a subsequent target. The present study uses such context-dependence to examine the dimensions of representation involved in a classic demonstration of “talker normalization” in speech perception. Whereas most accounts of talker normalization have emphasized talker-, speech-, or articulatory-specific dimensions’ significance, the present work tests an alternative hypothesis: that the long-term average spectrum (LTAS) of speech context is responsible for patterns of context-dependent perception considered to be evidence for talker normalization. In support of this hypothesis, listeners’ vowel categorization was equivalently influenced by speech contexts manipulated to sound as though they were spoken by different talkers and non-speech analogs matched in LTAS to the speech contexts. Since the non-speech contexts did not possess talker, speech, or articulatory information, general perceptual mechanisms are implicated. Results are described in terms of adaptive perceptual coding.

Highlights

Perceptual systems adjust rapidly to changes in the environment, with neural and behavioral responses dynamically changing to mirror changes in the input (Sharpee et al, 2006; Gutinsky and Dragoi, 2008)
Rather than articulatory or talker-specific dimensions that typically have been proposed to account for talker normalization, listeners may rely on sounds’ long-term average spectrum (LTAS) to tune speech perception
The comparable influence of speech and non-speech contexts on speech categorization indicates a common substrate of interaction

Summary

INTRODUCTION

Perceptual systems adjust rapidly to changes in the environment, with neural and behavioral responses dynamically changing to mirror changes in the input (Sharpee et al, 2006; Gutinsky and Dragoi, 2008). From an adaptive coding perspective, the perceptual system’s response to preceding speech lingers to affect subsequent processing This can only be true to the extent that context and target share common neural resources. An input with a higher value along the dimension would result in strong Pool 2 response, reducing Pool 2 responsiveness in the short-term due to adaptation In this way, the context stimulus “lingers” in the perceptual system to affect the resources available to process subsequent stimuli. The same listeners categorized the same “bet” to “but” targets preceded by sequences of non-speech sine-wave tones with frequencies modeling the LTAS of the context phrases. These extremely simple acoustic contexts carried no talker- or speech-specific information. Rather than articulatory or talker-specific dimensions that typically have been proposed to account for talker normalization, listeners may rely on sounds’ LTAS to tune speech perception

MATERIALS AND METHODS

RESULTS

DISCUSSION