Perspectives on dichotic listening and the corpus callosum

Abstract

The present review summarizes historic and recent research which has investigated the role of the corpus callosum in dichotic processing within the context of audiology. Examination of performance by certain clinical groups, including split brain patients, multiple sclerosis cases, and other types of neurological lesions is included. Maturational, age related, and genetic factors are also discussed. Finally, some attention is given to recent trends in audiology research to develop improved diagnostic and rehabilitation tools for individuals with dichotic deficits potentially related to callosal dysfunction.

Introduction

It is well known that when listening to speech in competition the corpus callosum (CC) plays a critical role in transferring auditory information from one hemisphere to the other. This interhemispheric function has been studied from many perspectives. One of the most common is investigation of dichotic listening which yields the now well known right ear advantage (REA). This REA indicates that in dichotic listening to verbal stimuli the right ear usually outperforms the left ear yielding a modestly higher score. For this reason, it is sometimes referred to clinically as a “left ear deficit”. The underlying mechanism for the REA likely involves the CC and its interaction with the auditory cortices, although attention also certainly plays a role in dichotic laterality and in the modulation of the function of each of the hemispheres (Westerhausen & Hugdahl, 2008).

Much of what has been learned about dichotic listening and the CC has come from subjects who in one manner or another have incurred damage to the CC, and this has permitted the development of certain clinical correlates to dichotic listening performance (Bamiou, Sisodiya et al., 2007, Bamiou, Free et al., 2007, Musiek et al., 1979). To this end, the present review will focus primarily on what we have learned from studying the dichotic performance of subjects who present with a disordered CC. The perspective here will be audiological in that the approach leans toward studies that may provide information of potential clinical application. Specifically, split brain studies will be reviewed followed by other neurological disorders that have been shown to affect the CC and consequently dichotic listening. Maturation, aging, and genetic influences will also be touched upon. While the present review is not intended to be exhaustive, it will provide a level handed perspective and serve as a resource on findings related to dichotic listening measures on compromised CCs.