Retinotopic remapping of the visual system in deaf adults

Sound is a vital cue in helping hearing people orient their gaze and attention towards events outside their central line of sight, especially in the far periphery, where vision is poor. Without sound cues, deaf individuals must rely on vision as an ‘early warning system’ for peripheral events, and in fact numerous behavioural studies demonstrate that deaf adults have superior visual sensitivity, particularly to far peripheral stimuli. We asked whether an increased demand on peripheral vision throughout development might be reflected in early visual brain structures. Using functional magnetic resonance imaging (fMRI), we mapped visual field representations in 16 early, profoundly deaf adults and 16 hearing age-matched controls. To target the far periphery, we used wide-field retinotopic mapping stimuli to map visual field eccentricity out to 72°, well beyond conventional mapping studies. Deaf individuals exhibited a larger representation of the far peripheral visual field in both the primary visual cortex and the lateral geniculate nucleus of the thalamus. Importantly, this was not due to a total expansion of the visual map, as there was no difference between groups in overall size of either structure, but a smaller representation of the central visual field in the deaf group, suggesting a redistribution of neural resources. Here, we demonstrate for the first time that the demands placed on vision due to lifelong hearing loss can sculpt visual maps at the first level of inputs from the retina, increasing neural resources for processing stimuli in the far peripheral visual field

Does congenital deafness affect the structural and functional architecture of primary visual cortex?

Deafness results in greater reliance on the remaining senses. It is unknown whether the cortical architecture of the intact senses is optimized to compensate for lost input. Here we performed widefield population receptive field (pRF) mapping of primary visual cortex (V1) with functional magnetic resonance imaging (fMRI) in hearing and congenitally deaf participants, all of whom had learnt sign language after the age of 10 years. We found larger pRFs encoding the peripheral visual field of deaf compared to hearing participants. This was likely driven by larger facilitatory center zones of the pRF profile concentrated in the near and far periphery in the deaf group. pRF density was comparable between groups, indicating pRFs overlapped more in the deaf group. This could suggest that a coarse coding strategy underlies enhanced peripheral visual skills in deaf people. Cortical thickness was also decreased in V1 in the deaf group. These findings suggest deafness causes structural and functional plasticity at the earliest stages of visual cortex