Implicit representation of the auditory space: contribution of the left and right hemispheres

Spatial cues contribute to the ability to segregate sound sources and thus facilitate their detection and recognition. This implicit use of spatial cues can be preserved in cases of cortical spatial deafness, suggesting that partially distinct neural networks underlie the explicit sound localization and the implicit use of spatial cues. We addressed this issue by assessing 40 patients, 20 patients with left and 20 patients with right hemispheric damage, for their ability to use auditory spatial cues implicitly in a paradigm of spatial release from masking (SRM) and explicitly in sound localization. The anatomical correlates of their performance were determined with voxel-based lesion-symptom mapping (VLSM). During the SRM task, the target was always presented at the centre, whereas the masker was presented at the centre or at one of the two lateral positions on the right or left side. The SRM effect was absent in some but not all patients; the inability to perceive the target when the masker was at one of the lateral positions correlated with lesions of the left temporo-parieto-frontal cortex or of the right inferior parietal lobule and the underlying white matter. As previously reported, sound localization depended critically on the right parietal and opercular cortex. Thus, explicit and implicit use of spatial cues depends on at least partially distinct neural networks. Our results suggest that the implicit use may rely on the left-dominant position-linked representation of sound objects, which has been demonstrated in previous EEG and fMRI studies.