We examined the hypothesis that aspects of processing that are most modifiable by experience (i.e., "plastic") display the most vulnerability in developmental disorders and the most compensatory enhancement after sensory deprivation. A large literature reports that motion processing and magnocellular visual function is selectively deficient in dyslexia. A smaller literature reports enhancements in such functions in deaf individuals. However, studies with dyslexic and deaf individuals have used different experimental paradigms to assess visual function, and no research has yet examined both sides of modifiability (i.e., enhancements and deficits) using the same experimental paradigm. In the present research, visual function was compared in dyslexic (n=15), deaf (n=17), and control adults by using automated peripheral kinetic and foveal static perimetry. In the kinetic perimetry task, the dyslexic group showed deficits ( p<.003), whereas the deaf group showed enhancements ( p<.001) for detecting moving light points in the periphery. In the foveal static perimetry task, neither the dyslexic ( p=.866) nor the deaf ( p=.632) group differed significantly from controls in foveal contrast sensitivity thresholds, and no group or individual approached ceiling performance on this task. Taken together, the present data bridge previous literatures and suggest that motion processing tasks are selectively modifiable, either to decrement or enhancement, whereas foveal contrast sensitivity does not differ in dyslexic or deaf groups.