Visual-to-auditory sensory substitution alters language asymmetry in both sighted novices and experienced visually impaired users.

Visual-to-auditory sensory substitution devices (SSDs) provide improved access to the visual environment for the visually impaired by converting images into auditory information. Research is lacking on the mechanisms involved in processing data that is perceived through one sensory modality, but directly associated with a source in a different sensory modality. This is important because SSDs that use auditory displays could involve binaural presentation requiring both ear canals, or monaural presentation requiring only one - but which ear would be ideal? SSDs may be similar to reading, as an image (printed word) is converted into sound (when read aloud). Reading, and language more generally, are typically lateralised to the left cerebral hemisphere. Yet, unlike symbolic written language, SSDs convert images to sound based on visuospatial properties, with the right cerebral hemisphere potentially having a role in processing such visuospatial data. Here we investigated whether there is a hemispheric bias in the processing of visual-to-auditory sensory substitution information and whether that varies as a function of experience and visual ability. We assessed the lateralization of auditory processing with two tests: a standard dichotic listening test and a novel dichotic listening test created using the auditory information produced by an SSD, The vOICe. Participants were tested either in the lab or online with the same stimuli. We did not find a hemispheric bias in the processing of visual-to-auditory information in visually impaired, experienced vOICe users. Further, we did not find any difference between visually impaired, experienced vOICe users and sighted novices in the hemispheric lateralization of visual-to-auditory information processing. Although standard dichotic listening is lateralised to the left hemisphere, the auditory processing of images in SSDs is bilateral, possibly due to the increased influence of right hemisphere processing. Auditory SSDs might therefore be equally effective with presentation to either ear if a monaural, rather than binaural, presentation were necessary.