Neural mechanisms of auditory categorization: from across brain areas to within local microcircuits.

Joji Tsunada,Yale E Cohen

doi:10.3389/fnins.2014.00161

Abstract

Categorization enables listeners to efficiently encode and respond to auditory stimuli. Behavioral evidence for auditory categorization has been well documented across a broad range of human and non-human animal species. Moreover, neural correlates of auditory categorization have been documented in a variety of different brain regions in the ventral auditory pathway, which is thought to underlie auditory-object processing and auditory perception. Here, we review and discuss how neural representations of auditory categories are transformed across different scales of neural organization in the ventral auditory pathway: from across different brain areas to within local microcircuits. We propose different neural transformations across different scales of neural organization in auditory categorization. Along the ascending auditory system in the ventral pathway, there is a progression in the encoding of categories from simple acoustic categories to categories for abstract information. On the other hand, in local microcircuits, different classes of neurons differentially compute categorical information.

Highlights

Auditory categorization is a computational process in which sounds are classified and grouped based on their acoustic features and other types of information
In order to analyze the linguistic content transmitted by speech sounds, we can ignore the unique pitch, timbre etc. of each speaker and categorize the sound into the distinct word category “Hello.” auditory categorization enables humans and nonhuman animals to extract, manipulate, and efficiently respond to sounds (Miller et al, 2002, 2003; Russ et al, 2007; Freedman and Miller, 2008; Miller and Cohen, 2010)
At the population level, the category sensitivity for speech sounds in the prefrontal cortex was weaker than that in the lateral belt neural activity in the prefrontal cortex transmitted a significant amount of categorical information

Summary

INTRODUCTION

Auditory categorization is a computational process in which sounds are classified and grouped based on their acoustic features and other types of information (e.g., semantic knowledge about the sounds). In certain situations, small changes in the physical properties of an acoustic stimulus can cause large changes in a listener’s perception of a sound. The stimuli, which cause these large changes in perception, straddle the boundary between categories. When we hear a continuum of smoothly varying speech sounds (i.e., a continuum of morphed stimuli between the phoneme prototypes “ba” and “da”), we experience a discrete change in perception. A small change in the features of a sound near the middle of this continuum (i.e., at the category boundary between a listener’s perception of “ba” and “da”) will cause a large change in a listener’s perceptual report. An abstract category is one in which a group of arbitrary stimuli are linked together as a category based on some shared features, a common functional characteristic, semantic information, www.frontiersin.org

Tsunada and Cohen

CONCLUSIONS AND FUTURE DIRECTIONS