Abstract
It has been previously shown that the interaction between vision and audition involves early sensory cortices. However, the functional role of these interactions and their modulation due to sensory impairment is not yet understood. To shed light on the impact of vision on auditory spatial processing, we recorded ERPs and collected psychophysical responses during space and time bisection tasks in sighted and blind participants. They listened to three consecutive sounds and judged whether the second sound was either spatially or temporally further from the first or the third sound. We demonstrate that spatial metric representation of sounds elicits an early response of the visual cortex (P70) which is different between sighted and visually deprived individuals. Indeed, only in sighted and not in blind people P70 is strongly selective for the spatial position of sounds, mimicking many aspects of the visual-evoked C1. These results suggest that early auditory processing associated with the construction of spatial maps is mediated by visual experience. The lack of vision might impair the projection of multi-sensory maps on the retinotopic maps used by the visual cortex.
Highlights
Space representation is one of the hardest problems the brain has to solve, given the multiple and diverse information it is constantly receiving by our senses
In the case of the space bisection task, distances reflected the spatial positions of S2: narrow/wide first distances corresponded to S2 delivered from the left (−4.5°)/right (+4.5°) side of the subject respectively
No differences emerged between the two groups considering either S1 or S2 in the temporal bisection task. This is the first study reporting that early contralateral occipital activation to sound is strong in sighted individuals and dramatically lower in blind individuals
Summary
Space representation is one of the hardest problems the brain has to solve, given the multiple and diverse information it is constantly receiving by our senses (for review see[1,2,3]). Different studies have reported an amplification/reduction of the visual response based on the existence of congruency between visual and auditory signals[36,42,47,48,49,50], and the encoding by the early visual cortex of the abstract information of acoustic object shapes[31,32,33,34,35,37,39] Taken together, these findings point to an important role of the visual cortex in audio-visual integration[40,51,52,53,54,55,56]
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