| Auditory processing disorder | |
|---|---|
| Classification and external resources | |
| ICD-9 | 315.32, 388.45 |
| MeSH | D001308 |
Auditory Processing Disorder (APD), also known as Central Auditory Processing Disorder (CAPD) is an umbrella term for a variety of disorders that affect the way the brain processes auditory information[1]. It is not a peripheral hearing disorder (inner ear) as individuals with APD usually have normal peripheral hearing ability. However, they cannot process the information they hear in the same way as others do, which leads to difficulties in recognizing and interpreting sounds, especially the sounds composing speech. It is thought that these difficulties arise from dysfunction in the central nervous system (e.g., brain).
APD can affect both children and adults, although the actual prevalence is currently unknown. Males are two times more likely to be affected by the disorder than females. [2] [3]
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The American Speech-Language-Hearing Association (ASHA) published "(Central) Auditory Processing Disorders" in January 2005 as an update to the "Central Auditory Processing: Current Status of Research and Implications for Clinical Practice (ASHA, 1996)"[4]. The American Academy of Audiology has released more current practice guidelines related to the disorder[5]. The UK's Medical Research Council has also defined the disorder in a pamphlet, [6] Auditory Processing Disorder (APD) pamphlet, Oct 2004.[7]
Auditory processing disorder can be genetic or acquired. It may result from ear infections, head injuries or developmental delays that cause central nervous system difficulties that affect processing of auditory information. This can include problems with: "...sound localization and lateralization (see also binaural fusion); auditory discrimination; auditory pattern recognition; temporal aspects of audition, including temporal integration, temporal discrimination (e.g., temporal gap detection), temporal ordering, and temporal masking; auditory performance in competing acoustic signals (including dichotic listening); and auditory performance with degraded acoustic signals."[8]
The Committee of UK Medical Professionals Steering the UK Auditory Processing Disorder Research Program have developed the following working definition of Auditory Processing Disorder: "APD results from impaired neural function and is characterized by poor recognition, discrimination, separation, grouping, localization, or ordering of speech sounds. It does not solely result from a deficit in general attention, language or other cognitive processes."[9]
As APD is one of the more difficult information processing disorders to detect and diagnose, it may sometimes be misdiagnosed as ADD/ADHD, Asperger syndrome and other forms of autism, but it may also be a comorbid aspect of those conditions if it is considered a significant part of the overall diagnostic picture. APD shares common symptoms in areas of overlap, such that professionals unfamiliar with APD might misdiagnose it as a condition they are aware of.
People with APD intermittently experience an inability to process verbal information. When people with APD have a processing failure, they do not process what is being said to them.
There are also many other hidden implications, which are not always apparent even to the person with the disability. For example, because people with APD are used to guessing to fill in the processing gaps, they may not even be aware that they have misunderstood something until after the fact.
APD has been defined anatomically in terms of the integrity of the auditory nervous system,[10] as "what we do with what we hear",[11] and in terms of performances on a selected group of behavioral auditory tests (Task Force for the American Speech, Language, and Hearing Association; ASHA, 1994). The ASHA Task Force definition considered APD to be any observed deficits in one or more of these so-called "behaviors". Problems inherent in test validation by consensus are highlighted by the succession of task force reports that have appeared in recent years. The first of these occurred in 1996.[4] This was followed by a conference organized by the American Academy of Audiology[12] that explicitly embraced modality specificity as a defining characteristic of auditory processing disorders. Subsequently, an ASHA committee rejected modality specificity as a defining characteristic of auditory processing disorders.[8]
There have been several commentaries questioning various aspects of these proposals.[13][14] Additionally, Moore suggests that APD is primarily a difficulty in processing non-speech sounds and that a population-based approach should be taken to identify outlying performers.[14] However, inclusive conceptualizations of APD have been criticized based on their lack of diagnostic specificity.[15] Auditory processing disorder has been defined as a modality specific perceptual dysfunction that is not due to peripheral hearing loss.[13][16] This viewpoint emphasizes the perceptual nature of auditory processing and asserts that the disorder should be conceptualized as being limited to problems in processing auditory material. Modality specificity has been advocated as a way to improve APD diagnosis.[13][16] There are several limitations to the approach suggested by proponents of modality specificity testing, including: major differences between primary auditory and visual cortices in the way information is coded and processed, how such approaches would separate children with both visual and auditory processing deficits from children with supramodal deficits, cross modal test equivalence, clinical infeasibility of visual processing test administration, lack of appropriate visual analogs to be used by audiologists, redundancy of modality specificity testing with neuropsychological assessment, and non-modularity of the central nervous system, among others.
APD is not a unitary disorder, as any pathological involvement of the central auditory nervous system can cause auditory dysfunction. Some suspected or known causes include: delay in myelin maturation [17], chronic otitis media during critical periods of language development[18], ectopic cells in the auditory cortical areas[19], genetic predisposition[20], neurologic issues (e.g., stroke, seizures, head injury) [21] [22][23][24], and auditory deprivation due to age related changes in hearing sensitivity[25].
The July 2001 volume of 'The Hearing Journal' has the article "Auditory Processing Disorder: An Overview for the Clinician". This summarizes the numerous disorders one can have from neuro/brain damage (notably amygdala). From severe TBIs to prolonged stress/trauma, - the amygdala can endure damage affecting so many cognitive functions, namely auditory functions.
The National Institute on Deafness and Other Communication Disorders [26] state that children with Auditory Processing Disorder often:
APD can manifest as problems determining the direction of sounds, difficulty perceiving differences between speech sounds and the sequencing of these sounds into meaningful words, confusing similar sounds such as "hat" with "bat", "there" with "where", etc. Fewer words may be perceived than were actually said, as there can be problems detecting the gaps between words, creating the sense that someone is speaking unfamiliar or nonsense words. Those suffering from APD may have problems relating what has been said with its meaning, despite obvious recognition that a word has been said, as well as repetition of the word. Background noise, such as the sound of a radio, television or a noisy bar can make it difficult to impossible to understand speech, depending on the severity of the auditory processing disorder. Using a telephone can be problematic for someone with auditory processing disorder, in comparison with someone with normal auditory processing, due to low quality audio, poor signal, intermittent sounds and the chopping of words.[8] Many who have auditory processing disorder subconsciously develop visual coping strategies, such as lip reading, reading body language, and eye contact, to compensate for their auditory deficit, and these coping strategies are not available when using a telephone.
APD shares some of these signs with related disorders, which may have other overlap areas, such as acquired brain injury, attention deficits, dyslexia, learning difficulties, hearing loss, and psychologically-based behavioral problems.
APD may be related to cluttering,[27] a fluency disorder marked by word and phrase repetitions.
Recent research has shown that practice with basic auditory processing tasks (i.e. auditory training) may improve performance on auditory processing measures[28][29] and phonemic awareness measures (Moore et al., 2005). These auditory training benefits have also been recorded at the physiological level (Russo et al., 2005; Alonso & Schochat, 2009). Many of these tasks are incorporated into computer-based auditory training programs such as Earobics and Fast ForWord, an adaptive software available at home and in clinics worldwide.
There is no research supporting the following APD treatments:
APD can also be confused with Specific language impairment (SLI).
SLI is more specifically a problem associated with the linking of words, both written and spoken, to semantics (meaning) and someone can have both APD and SLI. Unlike those with SLI, those with APD can usually get the meaning of language from written words where those with SLI show problems with both heard and read words, demonstrating that the basic issue is not an auditory one.
Those with APD have auditory difficulty distinguishing sounds including speech from extraneous sounds, e.g. fans or other chatter. APD is purely about processing what you hear both verbal and non-verbal. For those who have SLI, difficulty processing verbal language is only one of many symptoms.
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