We often see parents shaking their heads - how is it that it's both auditory and visual processing? But it's not some odd luck, the visual and auditory systems are tightly coupled, and each makes up for the other when some problem arises.
We shouldn't think of the brain having "deficits" - because reorganization is the rule rather than the exception, and generally loss in one domain, leads to compensatory changes in the other. Auditory processing problems are accompanied by increased sensitivities in other senses - and vision is one of the most common to cause trouble.
The first breakthrough in our understanding of the yin and yang of the brain's sensory system came in research studies examining subjects who were either completely deaf or completely blind. Before there was a technology to image these events in the brain, neuroscientists had pondered what the auditory part of brain might do in a deaf person, or what the visual part of the brain might do in a blind person. Was it a specialized area of brain that would just never get the right signal? Would it just sit there? Or would it be collared into doing something else?
The answer: it got put to work by the other senses.
In this remarkable figure, you can see that the outlined area of brain (auditory cortex) has now gotten recruited to work for the visual system. That's great you might say...if you can't hear, there are so many things that can creep up on you - so increased visual vigilance can protect you from danger. Yes -that's right, but increased visual sensitivity also comes with a price. The deaf are also much more sensitivity to visual distractibility (check out the teaching tips for the deaf, including recommendations to avoid shiny jewelery)...and in milder form, but no less significant, many children with central auditory processing disorders suffer this same fate.
Visual Reorganization in the Deaf
Visual Attention to the Periphery Enhanced in Deaf
Deaf or Hard of Hearing - Teaching & Learning Supports - Trinity College Dublin