Auditory Processing Disorder (APD) is an abnormality in the brain's ability to filter and process sounds and words. Individuals with APD have a neurological defect in the pathways from the auditory (hearing) nerve through the higher auditory pathways in the brain. This causes distortion and/or delay in auditory signal transmission, which results in inaccurate or incomplete coding of sound. Since these individuals struggle to process (or interpret) what they hear, it causes listening problems that often mimic a hearing loss.
Most people with APD will usually pass a hearing test and often have normal intelligence. However, since the brain receives sounds incorrectly, they may not recognize subtle differences between sounds in words (duh and guh for example), and they may have difficulty using those sounds for speech and language.
Many children with APD have trouble screening out background noise, so surrounding sounds from air conditioners, hallways, and noisy environments such as gymnasiums make it very difficult to understand speech. It’s like listening to a radio station with static or other stations interfering with the reception. In addition, these children typically try so hard to understand that they often forget parts of what they hear.