DIAGNOSIS

People with Auditory Processing Disorder (APD) pass standard hearing tests, sometimes leading to false reassurance that there is not a hearing problem.  Specialised audiological tests are required to diagnose APD.

Who can diagnose APD?

Audiologists are the professionals responsible for diagnosing APD (American Academy of Audiology, American Speech Language Hearing Association). Various professionals may carry out screening tests that can suggest the presence of APD, but a confirmed diagnosis requires a specialised battery of audiological tests administered and interpreted by an audiologist.

Specialised audiological tests

Standard APD tests are carried out in a sound-treated room, in most cases through headphones. Some tests use words and some use non-speech tasks. Typical tasks are to

  • repeat back words or sentences that are distorted
  • repeat back words or sentences in the presence of competing speech or noise
  • repeat back words or sentences heard in one ear while ignoring competing noise or speech in the other ear
  • repeat back sequences of numbers
  • repeat back the pattern of a sequence of high and low tones (eg Low-Low-High)
  • listen for very brief gaps in a tone or noise burst.

The tests are selected to evaluate different functions and locations in the central auditory system.

The tests described above are behavioural tests in which the person being tested responds as instructed.  Sometimes electrophysiological tests are also used to assess the integrity of the central auditory system. In these tests electrodes are applied to the head, auditory signals are presented via headphones or loudspeakers, and the electrical response from the brain is recorded.  Because of complexity and expense electrophysiological tests are employed less frequently.

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Amblyaudia (hearing weakness on one side)

One-sided hearing weakness is detected by tests in which different words are played to the two ears simultaneously via headphones (dichotic tests). The normal auditory system can attend to either side and hear all of the words.  To test for amblyaudia various dichotic speech tests are used. Care must be taken to select tests for each client that are neither too easy nor too difficult, otherwise any performance difference between the ears may be missed.

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Other evaluations

The results of auditory processing tests cannot be properly evaluated in isolation. In order to diagnose Auditory Processing Disorder in a child the audiologist must be able to rule out

  • “peripheral” hearing loss (hearing loss in the outer, middle or inner ear)
  • cognitive impairment (insufficient cognitive skill to perform the APD tests reliably)
  • language impairment (language skills must be at a sufficient level to cope with the speech-based APD tests)

The evaluation should therefore also include

  • standard hearing tests
  • cognitive screening
  • language screening.

Questionnaires about auditory skills and listening behaviour are also usually requested from the teacher and parents to provide additional information about any auditory problems.

If APD is diagnosed it is also useful to carry out more comprehensive assessments of language and literacy skills to ascertain the weak areas that need therapy.  (Children with APD typically have poor phonological awareness skills which may in turn affect spelling, reading and language.) 

Age range of tests

A number of factors affect the age at which APD can be diagnosed with certainty. The central auditory system continues to mature into adolescence.  In children under seven years there is considerable variance in the maturation of the auditory system.  Also some tests have been evaluated and proven on younger children than others (“test norms”).  

With current tests Auditory Processing Disorder can be readily diagnosed from about six years of age and considerable information about auditory processing skills can be measured at age five.  Some information can be determined at age four.  Below age seven however a confirmed diagnosis of APD should be made with caution. Sometimes where there are strong indicators of APD at a young age the audiologist may make a “provisional” diagnosis of APD or state that the child is “at risk” of APD.  What is important is that as much information as possible is collected and treatment is commenced as early as possible if the child is clearly experiencing auditory impairment.  The earlier treatment begins the better.

APD and other hearing loss

Hearing loss can be simply divided into three categories depending on the “level” of the auditory system affected.

Conductive hearing loss           Outer or middle ear
Sensorineural hearing loss   Inner ear and auditory nerve
Central hearing loss (APD)   Auditory pathways, centres and circuits in the brain

Most children presenting with APD have normal “peripheral” hearing (the ears work normally) and are of normal intelligence.  They don’t achieve normally in school because they don’t hear normally. Of course children with other hearing losses or with more global developmental delay may also have APD as a complicating factor. In part the treatment they receive for their other disabilities may also help treat the effects of the APD.

Diagnosing APD in the presence of other hearing loss is difficult.  To an extent compensation in the loudness of the tests can be made.  If the tests are passed there is no APD.  If the tests are failed a diagnosis of APD must be made with caution in case it is the peripheral hearing loss that is affecting the results.

Without proper diagnostic assessment a condition called Auditory Neuropathy could be mistaken for Auditory Processing Disorder.  Auditory Neuropathy involves the neural connections from the inner ear to the auditory nerve rather than the central pathways and centres of the auditory system.  Sometimes an electrophysiological test, Auditory Brainstem Response audiometry (ABR), will be requested to rule out Auditory Neuropathy.