Abstract
Previous research has shown that peripheral, task-irrelevant sounds elicit activity in contralateral visual cortex of sighted people, as revealed by a sustained positive deflection in the event-related potential (ERP) over the occipital scalp contralateral to the sound’s location. This Auditory-evoked Contralateral Occipital Positivity (ACOP) appears between 200–450 ms after sound onset, and is present even when the task is entirely auditory and no visual stimuli are presented at all. Here, we investigate whether this cross-modal activation of contralateral visual cortex is influenced by visual experience. To this end, ERPs were recorded in 12 sighted and 12 blind subjects during a unimodal auditory task. Participants listened to a stream of sounds and pressed a button every time they heard a central target tone, while ignoring the peripheral noise bursts. It was found that task-irrelevant noise bursts elicited a larger ACOP in blind compared to sighted participants, indicating for the first time that peripheral sounds can enhance neural activity in visual cortex in a spatially lateralized manner even in visually deprived individuals. Overall, these results suggest that the cross-modal activation of contralateral visual cortex triggered by peripheral sounds does not require any visual input to develop, and is rather enhanced by visual deprivation.
Highlights
Recent findings challenge the assumption that visual cortex is solely processing visual information, as several studies have revealed that nonretinal inputs can trigger neural responses in areas traditionally assumed to be visual in sighted individuals
event-related potential (ERP) elicited by noise bursts at central (C1/C2) and parieto-occipital (PO7/PO8) electrodes of blind and sighted subjects are reported in Figs 2 and 3 respectively
The present study investigated whether the lateralized enhancement of visual cortex by peripheral sounds previously observed in sighted individuals is present in the congenitally blind
Summary
Recent findings challenge the assumption that visual cortex is solely processing visual information, as several studies have revealed that nonretinal inputs can trigger neural responses in areas traditionally assumed to be visual in sighted individuals. Hearing a salient sound on the left side of space elicits a neural response over the right visual cortex and vice versa[3] In sighted individuals, these lateralized changes over occipital areas have been studied using cross-modal exogenous attention tasks in which peripheral sounds are followed by a visual target either at the same or opposite location as the sound, and have shown that the neural effects are associated with enhanced visual performance at the sound’s location[3,4]. Another possibility is that such mapping is inherent to the organization of the occipital cortex, reflecting a built-in mechanism of spatial attention across modalities which does not depend on audio-visual inputs To test these alternative hypotheses, we here examined congenitally blind and sighted individuals and compared the lateralized response over visual areas triggered by peripheral, salient sounds. It is unclear whether peripheral sounds activate contralateral occipital cortex in the blind, as has been observed in sighted individuals
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