Central Auditory Processing Disorder (CAPD)
The ears listen, and the brain hears. Children with Central Auditory Processing Disorder (CAPD) may have perfectly good hearing when tested, but their brain do not process the sounds into meaning properly. Hence, they do not understand what is being said as well as they should. They don’t learn as well as other children, especially in large noisy classrooms and homes. They may understand only portions of what is said. They may behave as if they understand, but they lose track of the conversation when more than one person is talking, when there is background noise or when people are speaking rapidly with incomplete sentences. If the conversation has a high emotional content, understanding can be even more difficult.
Nearly all children with CAPD lose confidence and end up feeling insecure. Rather than get real help, they are criticised or punished. They feel incapable of overcoming their learning difficulties, and unable to improve. Some may become isolated, withdrawn and depressed. Others become bored and restless. Rather than feel incompetent and bored, many will become disruptive, risk takers or thrill seekers. They can appear to have difficulties paying attention or following instructions, and are often misdiagnosed as having ADHD. To cover up their deficits, some become cynical, argumentative and even aggressive when criticised
Some of the behavioural symptoms of CAPD?
Below is a listing of some of the common behavioural characteristics often noted in children with CAPD. It should be noted that many of these behavioural characteristics are not unique to CAPD. Some of these behaviours may also be noted in individuals with other types of deficits or disorders such as attention deficits, hearing loss, behavioural problems and learning difficulties or dyslexia. Therefore, one should not necessarily assume that the presence of any one or more of these behaviours indicates that the child has a CAPD. However, if any of these behaviours are noted, the child should be considered at risk for CAPD and referred for appropriate testing.
- Difficulty hearing in noisy situations
- Difficulty following long conversations
- Difficulty hearing conversations on the telephone
- Difficulty learning a foreign language or challenging vocabulary words
- Difficulty remembering spoken information (i.e., auditory memory deficits)
- Difficulty taking notes
- Difficulty maintaining focus on an activity if other sounds are present child is easily distracted by other sounds in the environment
- Difficulty with organisational skills
- Difficulty following multi-step directions
- Difficulty in directing, sustaining, or dividing attention
- Difficulty with reading and/or spelling
- Difficulty processing nonverbal information (e.g., lack of music appreciation)
Definitive diagnosis of a central auditory processing disorder cannot be made until specialised auditory testing is completed and other aetiologies have been ruled out.
How is CAPD assessed at the clinic?
CAPD is assessed through the use of special tests designed to assess the various auditory functions of the brain. However, before this type of testing begins, it is important that each person being tested receive a routine hearing test as outlined above. An audiologist must rule out any "physical" hearing problems. The audiologist will assess the ability of the ear to detect a normal range of frequencies, from low tones to high tones, without loss of sensitivity. We make this referral to an associate Audiologist experienced in assessing children.
The auditory tests that we use to assess central auditory function fall into two major categories: Behavioural tests and Electrophysiological tests. It should be noted that children being assessed for CAPD will not necessarily be given a test from each of these categories.
The selection of which test is used will depend upon a number of factors, including the age of the child, the specific auditory difficulties the child displays, the child's native language and cognitive status. Generally speaking, central auditory processing assessments may not be appropriate for children with significant developmental delays and cognitive deficits.
Space limitations preclude an exhaustive discussion of each of the tests used at the clinic. However, a brief overview of the major test categories is provided next, along with an abbreviated description of a few representative subtests that are available for use in central auditory assessments.
Electrophysiological tests are measures of the brain's response to sounds. A special cap with built in sensors is placed on the head of the child for the purpose of measuring the electrical activity that arise from the central nervous system in response to an auditory stimulus. An auditory stimulus, often a clicking sound, or two tones of different frequencies are delivered to the child's ear and the electrical responses are recorded.
Some evaluate processing low in the brain (auditory brainstem response), whereas others assess functioning higher in the brain (middle latency responses, late auditory evoked responses, auditory cognitive or P300 responses). The results obtained on these tests are compared to age-appropriate norms to determine if any abnormalities exist.
SCAN-3A Screening Test for Auditory Processing Disorders.
SCAN is used to identify children who have auditory processing disorders and who may benefit from intervention. The test is administered to children ages 5 to 11 in approximately 20 minutes. Three subtests include low pass filtered words, auditory figure ground and competing words.
The SCAN A: A Test for Auditory Processing Disorders in Adolescents and Adults was designed for individuals over 11 years. This instrument includes an additional subtest using competing sentences as stimuli.
Monaural Low-Redundancy Speech Tests
Due to the richness of the neural pathways in our auditory system and the redundancy of acoustic information in spoken language, a normal listener is able to recognise speech even when parts of the speech signal are missing. However, this ability is often compromised in the individual with CAPD. Monaural low-redundancy speech tests represent a group of tests designed to test an individual's ability to achieve auditory closure when information is missing. The speech stimuli used in these tests have been modified by changing one or more of the following characteristics of the speech signal: frequency, timing (phase), or amplitude characteristics. The test items are presented to each ear individually and the child is asked to repeat the words that have been presented. A percent correct score is derived for each ear and these are compared to age-appropriate norms.
Dichotic Speech Tests
In these tests different speech items are presented to both ears either simultaneously or in an overlapping manner and the child is asked to repeat everything that is heard (divided attention) or repeat whatever is heard in one specified ear (directed attention). The more similar and closely acoustically aligned the test items, the more difficult the task.
One of the more commonly used tests in this category is the Dichotic Digits test. The child is asked to listen to four numbers presented to the two ears at comfortable listening levels. In each test item two numbers are presented to one ear and two numbers are presented to the other ear. For example, in figure one, 5 is presented to the right ear at the same time 1 is presented to the left ear. Then the numbers 9 and 6 are presented simultaneously to the right and left ears. The child is asked to repeat all numbers heard and a percent correct score is determined for each ear and compared to age-appropriate norms.