Don't Try This At Home Either: Perceptual Enhancement Among the Deaf

If febrile convulsions can confer benefits to learning and memory, then might other neurological disorders offer similar cognitive enhancement? As it turns out, an article in the newest issue of the Journal of Cognitive Neuroscience speaks to this very question, and turns up some fascinating results.

Authors Stevens and Neville first consider whether there might be some brain regions that are more plastic than others. If so, they ask, wouldn't these regions be the most likely to be disrupted by some developmental disorders, and yet also more likely to be enhanced in an attempt to compensate for yet other deficits?

As the authors discovered, this very pattern had been observed in the magnocellular visual pathway, an input to the brain's "dorsal stream" that is largely responsible for motion processing and the perception of low spatial frequencies. Stevens & Neville found a number of studies reporting motion processing deficits in dyslexics, autistics, and those with Turner or Williams syndrome, and yet they also found a completely separate literature describing enhanced motion processing in congenitally deaf populations.

Unfortunately, the techniques used to assess cognition in deaf and developmentally disordered individuals are often very different; given these differences, it was impossible to use previous literature make a definitive claim about the plasticity of the magnocellular pathway, and its "double-edged" nature - in which an overly plastic area can be either selectively enhanced or deteriorated, according to circumstance.

So, in the first demonstration of both neurocognitive enhancement and deficit within the same paradigm, the authors tested motion and central field visual processing in 17 deaf adults, 15 dyslexic adults, and sex-, age-, handedness-, education-, video-game-use-, and socioeconomically-matched control subjects. The results showed that dyslexics could detect motion only in a much smaller field-of-view than the control group. In contrast, the deaf group could detect motion across a much larger field of view than control subjects. No group differences were found in the central field visual processing task, which is primarily sensitive to parvocellular (as opposed to magnocellular) function.

Stevens & Neville concluded that "motion processing is selectively modifiable," and that neurplasticity thus has a double-edge: highly plastic brain regions, such as the magnocellular pathway, are both more vulnerable to deterioration, and yet more promising for enhancement, than other brain regions.