A study shows that those suffering from early deafness develop sharper peripheral vision to the detriment of central vision. It is the brain’s response to detect dangers sooner.
Not being able to rely on a perceptive channel leads to sharpening the remaining senses: we have known this for some time, but now a study on people suffering from profound early deafness, deaf since birth or early childhood, demonstrates the extent to which the brain is able to adapt to these absences and make the best of what it has.
Permanent deafness seems to alter the visual field, enhancing the visual abilities at its extremities: a result that seems to depend on the need to rely on sight also to identify suddenly dangerous situations, not detectable through sound stimuli.
In an article published in the scientific journal PNASresearchers from the University of York in the United Kingdom demonstrate how this reorganization of neural resources occurs at a very early point in visual processing, even before the signals captured by the retina reach the vision control center in the brain. At its core is brain plasticity, the brain’s ability to vary function and structure in response to experience and learning, and to compensate or repair damage suffered.
Resources allocated where they are needed most
Many previous studies show, on a behavioral level, how individuals suffering from early deafness have greater visual sensitivity, especially in response to stimuli in the peripheral visual field. The authors of the study mapped the representation of the visual field in 16 adults with profound deafness from early childhood and compared them with those of 16 hearing people of the same age.
Deaf people showed brain activity more geared toward peripheral vision both in the primary visual cortex (V1), a region at the back of the brain that processes visual information, and “before” visual projections reach the brain. This propensity for peripheral vision is in fact already noted in the lateral geniculate nucleus (NGL) of the thalamus, a structure in the brain that collects visual information from the retina and sends it to the visual cortex.
It’s not a question of volume
The difference is not due to a different volume of the primary visual cortex. Rather, the researchers write, it depends “on a smaller representation of the central visual field in the deaf group, suggesting a redistribution of neural resources.” Greater lifelong dependence on vision in deaf people had led them to a neural preference for peripheral vision; in contrast, hearing people showed a neural preference for more central vision.
The authors explain the results as follows: «Sound can act as a vital signal, helping hearing people to orient their gaze and attention towards events outside their central line of sight, especially in the extreme periphery where vision is generally poor. Without sound cues, deaf people use their vision as an “early warning system” for peripheral events; Indeed, deaf adults show superior performance on peripheral tasks that involve detecting or attending to transient or moving targets.”
