Jack Katz, Ph.D., Nancy Austin Stecker, Ph.D., and Donald Henderson, Ph.D., describe auditory processing as "what we do with what we hear” in Central Auditory Processing: A Transdisciplinary View (1992). It is the ability of the brain (i.e., the central nervous system) to process incoming auditory signals.
Auditory Processing Disorder (APD), also called central auditory processing disorder (CAPD), happens when the brain is unable to process sounds. Individuals with APD have a neurological defect in the pathways from the auditory nerve through the higher auditory pathways in the brain.
Individuals with APD have difficulties with sound localization—the ability to identify sound sources, specifically their ability to isolate a sound source in social environments.
APD is distinct from hearing loss. A person with APD can hear sounds; in fact, many have normal audiogram results. With APD, the way the brain translates those sounds is disrupted, resulting in jumbled messages.
Individuals with APD often are unable to hear sounds as words and have learning problems, including difficulty in reading, spelling, and language comprehension.
Those with APD have trouble distinguishing between words or syllables that sound alike (auditory discrimination) and recalling what they heard (poor auditory memory). They show delayed responses to verbal requests and instructions and often will ask someone to repeat what has been said.
Sources: Auditory Processing Center; Texas School for the Blind and Visually Impaired