Auditory System Hearing Disorders Capd

Auditory processing occurs when the brain interprets sound information transmitted from the cochlea along the auditory nerve. Difficulty in processing sound information at this level is known as auditory processing disorder (APD), also called central auditory processing disorder (CAPD). Individuals with APD/CAPD have difficulty understanding auditory information, especially in the presence of background noise. Processing can be improved by improving the quality of the auditory signal.

What is Auditory Processing?

Auditory processing is the final step in the hearing process. Sound is transmitted through the outer, middle and inner ear, and is transformed into nerve impulses and sent to the brain along the auditory nerve. At this point, the brain must interpret this sound information, and assign meaning to the auditory input. This process is termed auditory processing, and helps us to make sense of the sound input from the environment. It is particularly important in understanding speech, as the brain must recognize the spoken words, and retrieve their meaning so we can understand spoken language.

Central Auditory Processing Disorder (CAPD)

When individuals have problems with auditory processing, they have trouble understanding sound input, even when their auditory acuity is normal. Auditory acuity refers to the physical ability to hear sound, as determined by the integrity of the auditory mechanism at the levels of the middle and inner ear. In people with auditory processing disorders, the brain is unable to properly make sense of auditory input that has been transmitted through the hearing mechanism. Causes of APD/CAPD are currently unknown.

Auditory processing disorders can be characterized by:

  • Difficulty differentiating between similar speech sounds
  • Difficulty retaining orally-presented information
  • Difficulty understanding speech with high levels of background noise present
  • Slow processing of auditory information.

Individuals with CAPD or auditory processing problems may also present with behavior problems or language difficulties secondary to their problems with processing sound. An audiologist can administer a specific battery of tests designed to examine auditory processing disorders. This can help to differentiate between CAPD and other problems, such as a hearing loss, or attention-deficit hyperactivity disorder (ADHD).

Treatment of CAPD

CAPD may be managed with use of an FM system. FM systems use FM radio waves to transmit sound wirelessly from a microphone (worn by a teacher or other speaker) to a receiver worn by the individual with CAPD. This system helps with processing by increasing the signal-to-noise ratio; it increases the volume and salience of the signal (e.g. a teacher’s voice) so that it is stronger than the interfering background noise. Improving room acoustics (e.g. reducing reverberation and decreasing background noise) will also help individuals with CAPD to process auditory information.


American Speech-Language-Hearing Association (2002). Guidelines for fitting and monitoring FM systems. Retrieved February 7, 2010, from American Speech-Language-Hearing Association Web site:

Bellis, T. (n.d.). Understanding auditory processing disorders in children. Retrieved February 7, 2010, from American Speech-Language-Hearing Association Web site:

National Institute on Deafness and Other Communication Disorders (n.d.). Auditory processing disorder in children. Retrieved February 7, 2010, from National Institute on Deafness and Other Communication Disorders Web site: