Auditory Processing Disorder  (APD)

An APD also known as Central Auditory Processing Disorder (CAPD) is a physical hearing impairment, but one which does not show up as a hearing loss on routine screenings or an audiogram. Instead, it affects the hearing system beyond the ear, whose job it is to separate a meaningful message from non-essential background sound and deliver that information with good clarity to the intellectual centers of the brain (the central nervous system). When we receive distorted or incomplete auditory messages we lose one of our most vital links with the world and other people; in other words one cannot process the information heard the same way others do.

Read more: 
    http://kidshealth.org/parent/medical/ears/central_auditory.html
    http://en.wikipedia.org/wiki/Auditory_processing_disorder 
    http://www.asha.org/public/hearing/disorders/understand-apd-child.htm 

My son was diagnosed with APD by an audiologist. First we thought possibly a hearing problem since he spoke very loud but his hearing results identified he hears at -10 decibels indicating his hearing is better than most. Since he hears so well he has the need to talk loud to match the way he hears. APD was identified in his left ear so when the sound messages travel from the left side of the brain to the right and then back to the left his decoding of what he hears is scrambled beyond understanding. For this reason he is best seated at the left of a classroom from where his teacher does the lesson so to process the information in his right ear.