[12][13] However, this theory is not universally accepted; others theorize that the main difficulties associated with SLI stem from problems with the higher-level aspects of language processing.
[13] Similarly with developmental dyslexia, researchers continue to explore the hypothesis that reading problems emerge as a downstream consequence of difficulties in rapid auditory processing.
[16][17] APD can be assessed using tests that involve identifying, repeating, or discriminating speech, and a child may perform poorly because of primary language problems.
[13][19][20] Analogous results were observed in studies comparing children diagnosed with SLI or APD, the two groups presenting with similar diagnostic criteria.
In other cases, suspected or known causes of APD in children include delay in myelin maturation,[34] ectopic (misplaced) cells in the auditory cortical areas,[35] or genetic predisposition.
[36] In one family with autosomal dominant epilepsy, seizures which affected the left temporal lobe seemed to cause problems with auditory processing.
[37] In another extended family with a high rate of APD, genetic analysis showed a haplotype in chromosome 12 that fully co-segregated with language impairment.
[40] One study showed thalamocortical connectivity in vitro was associated with a time sensitive developmental window and required a specific cell adhesion molecule (lcam5) for proper brain plasticity to occur.
Another study showed that rats reared in a single tone environment during critical periods of development had permanently impaired auditory processing.
Otitis media with effusion is a very common childhood disease that causes a fluctuating conductive hearing loss, and there was concern this may disrupt auditory development if it occurred during a sensitive period.
[44] Consistent with this, in a sample of young children with chronic ear infections recruited from a hospital otorhinolaryngology department, increased rates of auditory difficulties were found later in childhood.
[45] However, this kind of study will have sampling bias because children with otitis media will be more likely to be referred to hospital departments if they are experiencing developmental difficulties.
[47][48] Questionnaires which address common listening problems can be used to identify individuals who may have auditory processing disorder, and can help in the decision to pursue clinical evaluation.
[49][50] According to the respondents who participated in a study by Neijenhuis, de Wit, and Luinge (2017),[51] symptoms of APD which are characteristic in children with listening difficulties, and are typically problematic with adolescents and adults, include:[52] According to the New Zealand Guidelines on Auditory Processing Disorders (2017),[53] the following checklist of key symptoms of APD or comorbidities can be used to identify individuals who should be referred for audiological and APD assessment: Finally, the New Zealand guidelines state that behavioral checklists and questionnaires should only be used to provide guidance for referrals, for information gathering (for example, prior to assessment or as outcome measures for interventions), and as measures to describe the functional impact of auditory processing disorder.
Following a model described by Zoppo et al. (2015[60]), a 34-item questionnaire was developed that investigates auditory processing abilities in each of the six common areas of complaint in APD (listening and concentration, understanding speech, following spoken instructions, attention, and other.)
Validation data was acquired from subjects with language-learning or auditory processing disorders who were either self-reported or confirmed by diagnostic testing.
[61] However, children with symptoms of APD typically have no evidence of neurological disease, so the diagnosis is made based on how the child performs behavioral auditory tests.
In an attempt to rule out at least some of these factors, the American Academy of Audiology conference explicitly advocated that for APD to be diagnosed, the child must have a modality-specific problem, i.e. affecting auditory but not visual processing.
However, a committee of the American Speech-Language-Hearing Association subsequently rejected modality-specificity as a defining characteristic of auditory processing disorders.
[2] ASHA formally defines APD as "a difficulty in the efficiency and effectiveness by which the central nervous system (CNS) utilizes auditory information.
"[66] In 2018, the British Society of Audiology published a "position statement and practice guidance" on auditory processing disorder and updated its definition of APD.
[63] 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.
[76][77] Others, however, have argued that a modality-specific approach is too narrow, and that it would miss children who had genuine perceptual problems affecting both visual and auditory processing.
[14] The British Society of Audiology[67] has embraced Moore's (2006) recommendation that tests for APD should assess processing of non-speech sounds.
[83] The authors state that "a clearer understanding of the relative contributions of perceptual and non-sensory, unimodal and supramodal factors to performance on psychoacoustic tests may well be the key to unraveling the clinical presentation of these individuals.
Many audiologists, however, would dispute that APD is just an alternative label for dyslexia, SLI, or ADHD, noting that although it often co-occurs with these conditions, it can be found in isolation.
[94] Treatment of APD typically focuses on three primary areas: changing learning environment, developing higher-order skills to compensate for the disorder, and remediation of the auditory deficit itself.
[99][100] 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, but overall, evidence for effectiveness of these computerized interventions in improving language and literacy is not impressive.
Much of the work in the late nineties and 2000s has been looking to refining testing, developing more sophisticated treatment options, and looking for genetic risk factors for APD.
[118][119] With global awareness of mental disorders and increasing understanding of neuroscience, auditory processing is more in the public and academic consciousness than in years past.