The anecdotal evidence has been overwhelming -- deaf and blind people routinely report that their other senses are sharpened after losing their ability to hear or see, respectively. In an effort to explain how and why the brain compensates for the loss of senses, researchers at the University of Western Ontario studied congenitally deaf cats. They found that there are two visual abilities that are enhanced in deaf cats -- peripheral vision and motion detection. The researchers determined that the part of a deaf cat's auditory cortex that would normally translate peripheral sound switches roles and instead enhances peripheral vision. In essence, the auditory cortex performs the same function but "flips" from audio to visual.
More on the brain's reaction to hearing loss: