What is a Central Auditory Processing Disorder (CAPD)?

A central auditory processing disorder is an umbrella term for a group of disorders that can result in a breakdown in the hearing process. In short, our brain struggles to make sense of the sounds we hear because the auditory signal is being delayed in some way.

Central auditory processing disorders are said to affect around 5% of children, but this figure can vary. Children who display auditory processing problems may show some or all of the following signs:

  • Delayed language development
  • Inability to listen effectively
  • Easily distracted by irrelevant background noise
  • Often have trouble retaining verbal instructions
  • Misinterpreting the sequence of words
  • May be more fatigued than usual after returning from school

What causes a CAPD?

The causes of CAPD are not precisely known, but the neural processes of the auditory pathway are involved in some manner. Children who have experienced repeated episodes of otitis media (glue ear) may be particularly susceptible to CAPD, perhaps due to the fact that their hearing levels fluctuate during periods of infection, affecting normal exposure to sound and compromising development of the auditory pathways. However, many children with CAPD have never had an ear infection. Routine audiological tests do not diagnose CAPD and pure tone audiometry results in this population are typically normal. If a CAPD is suspected, assessment involves a variety of specialised audiological tests.

How is CAPD assessed?

A CAPD assessment generally comprises three parts:

  • Peripheral hearing assessment
  • Listening in Spatialised Noise Sentences Test (LiSN-S)
  • Central Auditory Processing test battery (comprising tests of various processing abilities)

Peripheral hearing assessment:

The peripheral hearing assessment assesses the physical structures of the child’s ear. This Jacob include a basic hearing test, a visual examination of the child’s ear canals and eardrums, and immitance testing which measures the mobility and function of the child’s eardrums.

Listening in Spatialised Noise Sentences Test (LiSN-S):

The LiSN-S is an adaptive, virtual-reality, test that measures speech perception ability in noisy environments. Importantly, it also measures the ability of people to use the spatial cues that normally help differentiate a target talker from distracting speech sounds. An inability to use this information has been found to be a leading cause of difficulty understanding speech in noisy environments, such as the classroom.

Central Auditory Processing test battery:

These are various tests that measure different aspects of the central auditory system. These are selected on a case-by-case basis. The various tests Jacob assess aspects of processing that include:

  • Binaural integration: assesses the ability to listen to, comprehend, and separate a sound stimulus presented to both ears simultaneously.
  • Short-term memory: assesses the listener’s ability to retain and use short-term memory of both numbers and words.
  • Temporal processing: Assesses how well a listener uses the timing information of sound, and their ability to discriminate and separate tones, which is important in recognizing intonation, stress and rhythm in speech.
  • Auditory closure: Assesses how well a listener can complete a word that has some auditory information missing (e.g. sounds like a person is mumbling). The listener needs to draw on their vocabulary store to complete these assessments.

Treatment:

Traditionally, “treatment” recommendations for students with APD have focussed on compensating for the student’s processing difficulties. However, most health professionals now agree that a three-pronged approach to intervention is most effective, involving a combination of individualised compensatory strategies, learning environment modifications and skill building strategies.

The use of an FM system (frequency modulation) is a highly-effective option to use in the classroom and when at home. The FM system comprises of a transmitter (worn by a teacher or parent) and a pair of receivers (worn by the child) which allows the child the ability to be directly connected to the speech of the teacher/parent. FM systems are useful in overcoming background noise and will allow the child to hear the teacher or parent’s voice even if they are several metres away and even if their back is turned and the child is unable to use visual cues.