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Central Auditory Processing Disorders (cAPD)

What is it?

Before we understand what an auditory processing disorder is, we must first understand how an average person hears.  Hearing, in the most basic sense, involves two main parts of our system, the ear and the brain.  The ears' job is to receive; code and process sound then send it up toward the brain.  The brain then receives this informational, "files" it, filters the extraneous, unnecessary portion and directs attention to the desired information.

When problems occur with this system we commonly look to the peripheral part of the ear as the culprit.  In some cases, however, the problems occur further up with abnormalities occurring in the processing of the information received.  This is what we refer to as an Auditory Processing Disorder, or APD.  Frank Muziek, PhD, an audiologist and leading researcher in this area describes auditory processing as “how well the ear talks to the brain and how well the brain understands what the ear tells it.”  In APD there is distortion, or a misunderstanding at the brain level, resulting in mixed messages. 

Our normal auditory (hearing) system allows us to complete a variety of tasks without thinking.  These included:

  1. Sound localization and lateralization: Localization is the ability to know where sound has occurred in space.  Localization is the ability to identify the source of a sound. 
  2. Auditory discrimination: The ability to discriminate one sound from another.  This is a function of our temporal processing of pitch, volume and timing to create a clearly recognized speech pattern.
  3. Auditory pattern recognition: The ability to determine similarities and differences in the pattern of sounds.  This involves various aspects of timing and the ability to fuse information together (auditory integration). 
  4. Temporal aspects of audition: The ability to process acoustic signals over time. This involves several aspects including, order, integration or resolving signals. 
  5. Auditory performance with competing acoustic signals: The ability to perceive speech or other sounds when another signal is present such as background noise, or competing speech and sounds. 
  6. Auditory performance decrements with degraded acoustic signals: The ability to perceive a signal in which information is missing.  Problems in this area are often manifested as difficulty hearing in background noise or filling in parts of speech/conversations that was missed. 

One or more problems in the above-mentioned areas are suggestive of auditory processing problems. 

There may be several different causes of APD.  It may occur in isolation or accompanied by well known disorders such as ADD, language and learning disorders, dyslexia or multiple sclerosis.  There is also believed to be some correlation between high fevers or repetitive ear infections.  While most often investigated in school age children it is not exclusive to this population.  Adults may have APD but have either adapted or managed around the difficulties.  We believe it may contribute to some people’s difficulty adapting to hearing aids or inability to function in some environments. 

What Are the Symptoms

People with CAPD typically have normal hearing and intelligence but may exhibit behavior similar to those with hearing loss such as:

What Are We Looking For?

Abnormalities in the auditory system take on different characteristics allowing us to roughly place them in 4 main categories.  Please note that individual APD problems may encompass more than one of these areas as well as several sub-categories.  The categories include:

  1. Temporal processing: This influences all aspects of speech, music and general listening tasks to include the ability to perceive the order of sounds, discrimination between similar words and consonants.  There are many aspects of temporal auditory system that may be affected.  Problems may manifest and misunderstanding speech, difficulty humming, missing sounds in words…
  2. Dichotic Listening (Binaural integration and separation): This refers to the ability to bring together or ignore differing stimuli presented simultaneously to each ear.  Problems in this area may show up as difficulty hearing in background noise or difficulty understanding when information is being presented to both ears (such as when more than one person is speaking at a time).
  3. Auditory closure/auditory figure ground: The ability to utilize external and internal redundancy to fill in missing portions in speech or auditorily presented information.  This may include hearing speech or other sounds in background noise, understanding dialects or people who do not speak clearly
  4. Binaural interaction/fusion: The ability for two ears to work together.  This may include localization, lateralization, hearing in noise, detection of sounds in noise as well as binaural fusion, the listener’s ability to fuse two different inputs together into one perception.  Problems in this area are manifested as difficulty localizing as well as difficulty tracking an auditory source.  The person may also have difficulty hearing in noise.

How Is CAPD Diagnosed?

While there is no standard APD battery of test, the first step to diagnosing APD is to rule out or identify any contributing factors associated with the complaint.  Specifically, this may include an ordinary peripheral hearing loss or accompanying language or learning disabilities.  For this reason a thorough case history is obtained and a comprehensive hearing test with an audiologist completed.  This will test for the presence of a possible hearing loss as a cause or contributing factor to the completed.  This will also alert the audiologist to any accompanying disorders that may influence the test results.

Screening Assessment: 

Before proceeding with the APD test we may request that the Screening Instrument for Targeting Educational Risk (S.I.F.T.E.R.) as well as the Fisher’s Auditory Problems Checklist be completed.  The SIFTER may be completed by both the parents and educators placing the child on a ration scale for certain behaviors.  The Fisher’s Checklist provides a 25 item checklist of auditory behaviors that may be affected. 

For adult patients, a comprehensive history form of hearing is determined to be normal, and then further testing may be indicated.  The results help to better tailor our battery of tests to assess the specific problem. 

APD Test Battery:

Our auditory testing battery takes approximately 1 hour.  Our general APD test battery includes tests that apply to most ages although there is better normative information for children older than 6 as well as adults.  Our battery of tests includes:

Additional Testing:

Depending on the findings from the initial examination, further testing may be recommended in targeted areas for a more specific diagnosis.  These tests may include:

Treatment of CAPD

There are various approaches to treating auditory processing issues.  One of the most important is realizing the APD is real.  This is not an issue of “selective hearing.  Thus said, it is the responsibility of the person with APD to employ the different strategies to manage their communication and their world.   Just as we expect a person with a hearing loss to wear a hearing aid if appropriate, we expect these strategies to be implemented for easier communication. 

Specifically:

Some more structured treatment options may be available as we develop more information regarding the nature of APD.  Further referral to a speech therapist may be beneficial to investigate structured treatment options.

Copyright 2007 Leah Keylard