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Brain Advance Access originally published online on May 28, 2009
Brain 2009 132(7):1953-1966; doi:10.1093/brain/awp127
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© The Author (2009). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Hemispheric competence for auditory spatial representation

Lucas Spierer1,*, Anne Bellmann-Thiran1,*, Philippe Maeder2, Micah M. Murray1,2,3,4 and Stephanie Clarke1

1 Neuropsychology and Neurorehabilitation Service, Vaudois University Hospital Center and University of Lausanne, Lausanne, Switzerland 2 Radiology Service, Vaudois University Hospital Center and University of Lausanne, Lausanne, Switzerland 3 Electroencephalography Brain Mapping Core, Center for Biomedical Imaging of Lausanne and Geneva, Lausanne, Switzerland 4 Department of Hearing and Speech Sciences, Vanderbilt University, Nashville, TN, USA

Correspondence to: Dr Lucas Spierer, Neuropsychology and Neurorehabilitation Service, CHUV, 1011 Lausanne, Switzerland E-mail: lucas.spierer{at}chuv.ch

Sound localization relies on the analysis of interaural time and intensity differences, as well as attenuation patterns by the outer ear. We investigated the relative contributions of interaural time and intensity difference cues to sound localization by testing 60 healthy subjects: 25 with focal left and 25 with focal right hemispheric brain damage. Group and single-case behavioural analyses, as well as anatomo-clinical correlations, confirmed that deficits were more frequent and much more severe after right than left hemispheric lesions and for the processing of interaural time than intensity difference cues. For spatial processing based on interaural time difference cues, different error types were evident in the individual data. Deficits in discriminating between neighbouring positions occurred in both hemispaces after focal right hemispheric brain damage, but were restricted to the contralesional hemispace after focal left hemispheric brain damage. Alloacusis (perceptual shifts across the midline) occurred only after focal right hemispheric brain damage and was associated with minor or severe deficits in position discrimination. During spatial processing based on interaural intensity cues, deficits were less severe in the right hemispheric brain damage than left hemispheric brain damage group and no alloacusis occurred. These results, matched to anatomical data, suggest the existence of a binaural sound localization system predominantly based on interaural time difference cues and primarily supported by the right hemisphere. More generally, our data suggest that two distinct mechanisms contribute to: (i) the precise computation of spatial coordinates allowing spatial comparison within the contralateral hemispace for the left hemisphere and the whole space for the right hemisphere; and (ii) the building up of global auditory spatial representations in right temporo-parietal cortices.

Key Words: auditory localization; auditory spatial representations; auditory cortex; hemispheric dominance; brain damage; human

Abbreviations: IID, interaural intensity difference; ITD, interaural time difference; LHD, left hemispheric damage; RHD, right hemispheric damage

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Received February 10, 2009. Revised April 15, 2009. Accepted April 16, 2009.

*These authors contributed equally to this work.


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