Hearing acuity is only one part in the processing that occurs in the auditory system. There are many people, both children and adults, who have no trouble with actual hearing acuity, that is to say that the hearing is normal, but who have other types of auditory difficulties. Auditory processing is the ability to interpret the sounds that one has heard. In central auditory processing, the brain must identify the incoming sounds and make an analysis of those sounds and attach meaning to them. For instance, a person can have normal hearing but may have problems following directions or understanding conversations in noisy environments. They may have trouble sequencing a story of following a sequence of instructions. Because these individuals have normal hearing acuity, auditory processing problems may not be readily identified and may be mislabeled as a behavior problem or attention deficit disorder. In other words, auditory processing is what the listener does with the auditory information he/she receives.
WHAT IS CENTRAL AUDITORY PROCESSING DISORDER?
Central auditory processes are mechanisms responsible for several important phenomena such as sound localization, discrimination (understanding what we hear), auditory performance when the signal is degraded (think of an old record) and auditory performance in noise. A central auditory processing disorder is a deficiency in any of these areas. There is no one specific cause for a central auditory processing disorder. In children, auditory processing problems may be related to age and development of the auditory centers in the brain, which may or may not naturally resolve itself as the child matures. In other cases, trauma, viral infections, lack of oxygen or degenerative disorders can contribute to central auditory processing disorders. A definitive diagnosis of a central auditory processing disorder cannot be made until specialized auditory testing is completed and other etiologies such as dyslexia, hearing loss; attention deficit disorder or behavioral problems (to name a few) are ruled out.
HOW IS CENTRAL AUDITORY PROCESSING ASSESSED?
A multidisciplinary team approach is crucial in assessing and understanding problems associated with an auditory processing disorder. Teachers, diagnosticians, psychologists, speech-language pathologists and even work supervisors may shed light on problems associated with school or work. A good case history, academic profile, and descriptions of school and home behavior are essential. Valuable information can be gained through this multidisciplinary approach regarding an individuals strengths and weaknesses, but the actual diagnosis of a central auditory problem must be made by and audiologist.
There are many tests that an audiologist can use to assess central auditory function. Before this type of testing begins, each person will receive a routine hearing evaluation to test for auditory acuity. The tests for central auditory function fall into the categories of (1) behavioral and (2) electrophysical. Behavioral tests are broken down into four categories, which will be described in detail further in this brochure. They are: binaural interaction tests, dichotic speech tests, monaural low-redundancy speech tests and temporal patterning tests. The audiologist will select the battery of tests based on several factors including age, the specific difficulties presented, case history information, etc. The audiologist will discuss which tests have been selected, and why, before assessment begins. Assessment may need to be spaced out over a period of two sessions or more. These tests will be conducted in a sound treated room.
WHAT ARE ELECTROPHYSICAL TESTS?
Electrophysical tests involved in the assessment of central auditory disorders measure the brains response to sounds. Electrodes are place around the ear, either on the ear lobes or behind the ears, and on the head and forehead. Sound is introduced and the electrical responses are recorded. These tests are used to evaluate processes in the brainstem or higher in the brain. These tests are compared to normative data to determine if an abnormality is present. Think of an EKG and you will understand what type of test this is.
WHAT ARE THE BEHAVIORAL TESTS?
As stated previously, behavioral tests are broken down into four categories. These are tests which require a subjective response from the listener either by speaking, pointing, tapping, humming. BINAURAL INTERACTION TESTS require integration between auditory information that is presented to each ear. These tests assess the ability of the structures low in the brain (brainstem) to take incomplete information presented to the two ears (simultaneously) and integrate the information. For example one portion of the stimuli is presented to one ear and another portion is presented to the other ear at the same time. The two parts are unrecognizable separately, but a person with normal processing abilities is able to recognize and integrate the information to form the appropriate response. DICHOTIC SPEECH TESTS use different speech items that are presented to both ears either at the same time or in an overlapping fashion. The listener is asked to repeat everything that is heard, or to repeat what is heard from a specific ear. MONAURAL LOW-REDUNDANCE SPEECH TESTS are designed to test an individuals ability to achieve auditory closure when auditory information is missing. The speech signal is modified in some way and the listener is required to fill in the gaps so to speak. TEMPORAL PATTERNING TESTS are designed to test an individuals ability to process non-verbal auditory stimuli and recognize the order or the pattern of the presentation.
TREATING CENTRAL AUDITORY PROCESSING DISORDERS
Once a diagnosis of auditory processing disorder has been made and the type of auditory deficit has been identified, an individualized management and treatment plan can be recommended. It is important to realize that there is no one method or cure for an auditory processing disorder. Treatment generally focuses on changing the learning or communication environment, learning higher-order skills to help compensate for the disorder, and remediation of the auditory deficit itself. Direct treatment of the auditory processing problem includes a wide variety of activities from computer-assisted to one-on-one training with a therapist. Personal assistive devices may be recommended. Modification of the classroom, work area or home may be suggested. It is important to remember that the remediation program will be tailored to the individuals needs.