Central Auditory Processing Disorders (CAPD)

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:

• Difficulty with language, specifically confusing syllable sequence or leaving off endings to words.  Tendency to confuse similar sounding words.
• Poor listening skills and a tendency to ignore a speaker when engrossed in something.
• Trouble paying attention to and remembering information presented orally.  More time is often needed to process orally presented information.
• Confuses or forgets/ has difficulty completing multi-step directions, especially if they include several sentences.
• Unusually greater sensitivity to or complaints about noise, especially hearing in noise.
• Difficulty with directionality.
• Low academic performance, especially in the areas of reading, comprehension, spelling or vocabulary.
• May have behavioral problems associated with perceived inattention.

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:

• Dichotic Digits Test:  Different stimuli are presented to each ear simultaneously.  The binaural integration part of the test requires the patient to repeat everything that is heard in both ears.  The binaural separation part requires them to ignore what is presented to one ear and repeat the information from the target ear.  This tests binaural separation and integration.
• Frequency (Pitch) Pattern and Duration Pattern Test: Tests temporal patterning and ordering by asking the patient to discriminate between different pitches presented to both ears.  The Duration Pattern Test asks the patient to discriminate the duration of tonal stimuli and describe it. This tests temporal processing.
• Gaps in Noise Test (GIN): Tests temporal (auditory time) resolution: This is a test of temporal resolution where the patient is asked to identify if one or two tones or clicks are heard.  The stimuli are presented in random order making it a more challenging task.  Another test of temporal processing.
• NU-6 Low Pass Filtered Speech: This tests auditory closure or our ability to “fill in the gaps”.  Each ear is tested independently with distorted words to assess the patient’s ability to understand and repeat.  This tests auditory closure. 
• Masking Level Difference: Tests for binaural interaction/binaural fusion.  The patient is asked to identify a tone or word as it emerges from competing background noise.   This tests binaural interaction/fusion.

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:

• Phonemic Synthesis Test: This assesses a patient’s ability to blend speech sounds together into words.  Sounds are presented to both ears. 
• Speech In Noise: This test assesses a patient’s ability to repeat back the correct word when it is presented in competition with background noise, often speech babble. 

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:

• Reduce background noise whenever possible.  When it is not possible, supplement with visual input (i.e. have the person look at you).  For children in school, it may be beneficial to use an FM device, as this would isolate the teacher’s voice and reduce background noise.
• Following directions is one of the main complaints for people with APD.  Family and friends should try using expressive sentences and speak at a slightly slower rate of speed.  They should make sure to enunciate.  This slows down your speech and provides better clarity for understanding.
• Writing notes helps everyone and general organization and scheduling may be beneficial.

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.