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Aspects of [[auditory processing]] which may be affected by APD include "auditory discrimination", the ability to distinguish between similar sounds or words; "auditory figure-ground", the ability to distinguish relevant speech from background noise; and "auditory memory", the ability to recall what was heard.
 
Aspects of [[auditory processing]] which may be affected by APD include "auditory discrimination", the ability to distinguish between similar sounds or words; "auditory figure-ground", the ability to distinguish relevant speech from background noise; and "auditory memory", the ability to recall what was heard.
   
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==History==
==Difficulties encountered in diagnosing APD==
 
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The first research into APD began in 1954 with Helmer Myklebust’s study, "Auditory Disorders in Children".<ref>Myklebust, H. (1954). Auditory disorders in children. New York: Grune & Stratton.</ref> Myklebust’s work suggested auditory processing disorder was separate from [[language]] learning difficulties. His work sparked interest in auditory deficits after acquired brain lesions affecting the temporal lobes<ref>{{cite journal |author=Bocca E, Calearo C, Cassinari V |title=A new method for testing hearing in temporal lobe tumours; preliminary report |journal=Acta Oto-laryngologica |volume=44 |issue=3 |pages=219–21 |year=1954 |pmid=13197002 |doi= |url=}}</ref><ref>{{cite journal |author=Bocca E, Calearo C, Cassinari V, Migliavacca F |title=Testing "cortical" hearing in temporal lobe tumours |journal=Acta Oto-laryngologica |volume=45 |issue=4 |pages=289–304 |year=1955 |pmid=13275293 |doi= |url=}}</ref> and led to additional work looking at the physiological basis of auditory processing,<ref name="Kimura1961">{{cite journal|last1=Kimura|first1=Doreen|title=Cerebral dominance and the perception of verbal stimuli.|journal=Canadian Journal of Psychology/Revue canadienne de psychologie|
APD is recognised as a major cause of [[dyslexia]]. As APD is one of the more difficult information processing disorders to detect and diagnose, it may sometimes be misdiagnosed as [[Attention-deficit hyperactivity disorder|ADD/ADHD]], [[Aspergers]] and even [[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 who were not aware of APD would diagnose the disabilities as those which they were aware of.
 
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volume=15|issue=3|year=1961|pages=166–171|issn=0008-4255|doi=10.1037/h0083219}}</ref> but it was not until the late seventies and early eighties that research began on APD in depth.
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In 1977, a conference about APD started a new series of studies focussing on APD in children.<ref>Katz, J., & Illmer, R. (1972). Auditory perception in children with learning disabilities. In J. Katz (Ed.), Handbook of clinical audiology (pp. 540–563). Baltimore: Williams & Wilkins.</ref><ref>{{cite book |author=Keith, Robert W. |title=Central auditory dysfunction: University of Cincinnati Medical Center Division of Audiology and Speech Pathology symposium |publisher=Grune & Stratton |location=New York |year=1977 |pages= |isbn=0-8089-1061-2 |oclc=3203948 |doi= |accessdate=}}</ref><ref>{{cite journal |author=Sweetow RW, Reddell RC |title=The use of masking level differences in the identification of children with perceptual problems |journal=J Am Audiol Soc |volume=4 |issue=2 |pages=52–6 |year=1978 |pmid=738915 |doi= |url=}}</ref><ref>{{cite journal |author=Manning WH, Johnston KL, Beasley DS |title=The performance of children with auditory perceptual disorders on a time-compressed speech discrimination measure |journal=J Speech Hear Disord |volume=42 |issue=1 |pages=77–84 |year=1977 |month=February |pmid=839757 |doi= |url=}}</ref><ref>{{cite book |author=Willeford, J. A.; |chapter=Assessing central auditory behavior in children A test battery approach |title=Central auditory dysfunction |editors=Keith, Robert W. |publisher=Grune & Stratton |location=New York |year=1977 |pages=43–72 |isbn=0-8089-1061-2 |oclc=3203948 |doi= |accessdate=}}</ref> Virtually all tests currently used to diagnose APD originate from this work. These early researchers also invented many of the auditory training approaches, including interhemispheric transfer training and interaural intensity difference training. This period gave us a rough understanding of the causes and possible treatment options for APD.
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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. Scientists have worked on improving behavioral tests of auditory function, [[neuroimaging]], [[electroacoustic phenomena|electroacoustic]], and [[electrophysiologic]] testing.<ref>{{cite journal |author=Jerger J, Thibodeau L, Martin J, ''et al.'' |title=Behavioral and electrophysiologic evidence of auditory processing disorder: a twin study |journal=J Am Acad Audiol |volume=13 |issue=8 |pages=438–60 |year=2002 |month=September |pmid=12371661 |doi= |url=}}</ref><ref>{{cite journal |author=Estes RI, Jerger J, Jacobson G |title=Reversal of hemispheric asymmetry on auditory tasks in children who are poor listeners |journal=J Am Acad Audiol |volume=13 |issue=2 |pages=59–71 |year=2002 |month=February |pmid=11895008 |doi= |url=}}</ref> Working with new technology has led to a number of software programs for auditory training.<ref>{{cite journal |author=Chermak GD, Musiek FE |title=Auditory training: Principles and approaches for remediating and managing auditory processing disorders |journal=Seminars in Hearing |volume=23 |issue=4 |pages=287–295 |year=2002 |ISSN=0734-0451 |pmid= |doi= |url=http://ovidsp.tx.ovid.com/sp-3.5.1a/ovidweb.cgi?&S=EHMMFPKHIGDDCEMFNCALHHLBNNLPAA00&Complete+Reference=S.sh.15.17.18.21|5|1 }}</ref><ref>{{cite journal |author=Musiek F |title=Habilitation and management of auditory processing disorders: overview of selected procedures |journal=J Am Acad Audiol |volume=10 |issue=6 |pages=329–42 |year=1999 |month=June |pmid=10385875 |doi= |url=}}</ref> With global awareness of mental disorders and increasing understanding of [[neuroscience]], auditory processing is more in the public and academic consciousness than ever before.<ref>{{cite journal |author= Task Force on Central Auditory Processing Consensus Development |title=Central auditory processing: Current status of research and implications for clinical practice [Technical Report]|journal=American Journal of Audiology |volume=5 |issue= |pages=41–54 |year=1996 |doi=10.1044/policy.TR1996-00241 |url=http://www.asha.org/docs/html/TR1996-00241.html}}</ref><ref>{{cite journal |author=Jerger J, Musiek F |title=Report of the Consensus Conference on the Diagnosis of Auditory Processing Disorders in School-Aged Children |journal=J Am Acad Audiol |volume=11 |issue=9 |pages=467–74 |format=pdf |year=2000 |month=October |pmid=11057730 |doi= |url=http://www.bsnpta.org/geeklog/public_html/filemgmt/filemgmt_data/files/Auditory_Processing_Disorders_in_Children.pdf}}</ref><ref>{{cite book |author=Keith, Robert W. |title=Central auditory and language disorders in children |publisher=College-Hill Press |location=San Diego, CA |year=1981 |pages= |isbn=0-933014-74-0 |oclc=9258682 |doi= |accessdate=}}</ref><ref>{{cite book |author=Katz, Jack; Henderson, Donald; Stecker, Nancy Austin |title=Central auditory processing: a transdisciplinary view |publisher=Mosby Year Book |location=St. Louis, MO |year=1992 |pages= |isbn=1-55664-372-1 |oclc= 2587728 |doi= |accessdate=}}</ref><ref>{{cite book |author=Katz, Jack; Stecker, Nancy Austin |title=Central auditory processing disorders: mostly management |publisher=Allyn and Bacon |location=Boston |year=1998 |pages= |isbn=0-205-27361-0 |oclc=246378171 |doi= |accessdate=}}</ref>
   
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==Diagnosis==
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. They may be able to repeat the words back word for word, but the meaning of the message is lost. Simply repeating the instruction is of no use if a person with APD is not processing. Neither will increasing the volume help.
 
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APD is a difficult disorder to detect and diagnose. The subjective symptoms that lead to an evaluation for APD include an intermittent inability to process verbal information, leading the person to guess to fill in the processing gaps. There may also be disproportionate problems with decoding speech in noisy environments.
   
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APD has been defined anatomically in terms of the integrity of the auditory areas of the [[nervous system]].<ref>{{cite book | last1 = Rintelmann | first1 = W.F. | title = Assessment of central auditory dysfunction : foundations and clinical correlates | chapter = Monaural speech tests in the detection of central auditory disorders. | editors = Marilyn L Pinheiro and Frank E Musiek | publisher = Williams & Wilkins | year = 1985 | location = Baltimore | pages = 173–200 | accessdate = 2010-09-01 | isbn = 978-0-683-06887-0 | oclc= 11497885 }}</ref> However, children with symptoms of APD typically have no evidence of neurological disease and the diagnosis is made on the basis of performance on behavioral auditory tests. Auditory processing is "what we do with what we hear",<ref name='Katz 1992'>{{cite book | last1 = Katz | first1 = Jack | title = Central auditory processing : a transdisciplinary view | chapter = Classification of auditory processing disorders | editors = Jack Katz and Nancy Austin Stecker and Donald Henderson | publisher = Mosby Year Book | year = 1992 | location = St. Louis | pages = 81–92 | accessdate = 2010-09-01 | isbn = 978-1-55664-372-9| oclc= 25877287 }}</ref> and in APD there is a mismatch between peripheral hearing ability (which is typically normal) and ability to interpret or discriminate sounds. Thus in those with no signs of neurological impairment, APD is diagnosed on the basis of auditory tests. There is, however, no consensus as to which tests should be used for diagnosis, as evidenced by the succession of task force reports that have appeared in recent years. The first of these occurred in 1996.<ref name=cap1996/> This was followed by a conference organized by the American Academy of Audiology.<ref>{{cite journal |author=Jerger J, Musiek F |title=Report of the Consensus Conference on the Diagnosis of Auditory Processing Disorders in School-Aged Children |journal=J Am Acad Audiol |volume=11 |issue=9 |pages=467–74 |year=2000 |month=October |pmid=11057730 |doi= | url=http://www.taracentar.hr/download/diagnosis_apd_school.pdf | format = pdf}}</ref> Experts attempting to define diagnostic criteria have to grapple with the problem that a child may do poorly on an auditory test for reasons other than poor auditory perception: for instance, failure could be due to inattention, difficulty in coping with task demands, or limited language ability. 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, an ASHA committee subsequently rejected modality-specificity as a defining characteristic of auditory processing disorders.<ref name='ASHA 2005'/>
People with APD have an Auditory (Verbal) Processing Disorder, and text is only [[verbal code]], and so the Auditory Processing Disorder is extended into reading and writing as this [[auditory code]]. As a consequence, APD has been recognised as one of the major causes of dyslexia.
 
   
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The issue of modality-specificity has led to considerable debate among experts in this field. Cacace and McFarland have argued that APD should be defined as a ''modality-specific'' perceptual dysfunction that is not due to peripheral hearing loss.<ref name='Cacace McFarland 1995'>{{cite journal | title = Opening Pandora's Box: The Reliability of CAPD Tests | journal = American Journal of Audiology | date = 1995-07 | first = Anthony T. | last = Cacace | coauthors = Dennis J. McFarland | volume = 4 | pages = 61–62| id = | url = http://aja.asha.org/cgi/content/citation/4/2/61 | accessdate = 2010-08-31 | issue=2}}</ref><ref name='Cacace McFarland 2005'>{{cite journal | title = The Importance of Modality Specificity in Diagnosing Central Auditory Processing Disorder | journal = American Journal of Audiology | date = 2005-12 | first = Anthony T. | last = Cacace | pmid = 16489868 | coauthors = Dennis J. McFarland | volume = 14 | issue = 2 | pages = 112–123| doi = 10.1044/1059-0889(2005/012) | url = http://aja.asha.org/cgi/content/short/14/2/112 | accessdate = 2010-08-31}}</ref> They criticise more inclusive conceptualizations of APD as lacking diagnostic specificity.<ref name='Cacace McFarland 1998'>{{cite journal | title = Central Auditory Processing Disorder in School-Aged Children A Critical Review | journal = Journal of Speech, Language, and Hearing Research | date = 1998-04 | first = Anthony T. | last = Cacace | pmid = 9570588 | coauthors = Dennis J. McFarland | volume = 41 | issue = 2 | pages = 355–373 | id = | url = http://jslhr.asha.org/cgi/content/abstract/41/2/355 | accessdate = 2010-08-31}}</ref> A requirement for modality-specificity could potentially avoid including children whose poor auditory performance is due to general factors such as poor [[attention]] or [[memory]].<ref name ='Cacace McFarland 1995'/><ref name='Cacace McFarland 2005'/> 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. It is also impractical, as audiologists do not have access to standardized tests that are visual analogs of auditory tests. The debate over this issue remains unresolved. It is clear, however, that a modality-specific approach will diagnose fewer children with APD than a modality-general one, and that the latter approach runs a risk of including children who fail auditory tests for reasons other than poor auditory processing.
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.
 
   
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Another controversy concerns the fact that most traditional tests of APD use verbal materials.<ref name='D.R.Moore (2006)'>{{cite journal | title = Auditory processing disorder (APD): Definition, diagnosis, neural basis, and intervention | journal = Audiological Medicine | year = 2006 | first = David R. | last = Moore | volume = 4 | issue = 1 | pages = 4–11| doi = 10.1080/16513860600568573 | accessdate = 2010-08-31}}</ref> The British Society of Audiology<ref name='BSA2011'/> has embraced Moore's (2006) recommendation that tests for APD should assess processing of ''non-speech sounds''.<ref name='D.R.Moore (2006)'/> The concern is that if verbal materials are used to test for APD, then children may fail because of limited language ability. An analogy may be drawn with trying to listen to sounds in a foreign language. It is much harder to distinguish between sounds or to remember a sequence of words in a language you do not know well: the problem is not an auditory one, but rather due to lack of expertise in the language.
In many instances, APD comes as part of an 'invisible disability' package, and in some instances, the other disability may mask the APD. This multiple disability scenario indicates that a [[transdiscipline approach]] to [[research]], [[diagnosis]] and [[treatment]] is of the utmost importance, especially when APD can mimic many of the other 'invisible disabilities'.
 
   
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In recent years there have been additional criticisms of some popular tests for diagnosis of APD. Tests that use tape-recorded American English have been shown to over-identify APD in speakers of other forms of English.<ref>{{cite journal|title=The SCAN-C in testing for auditory processing disorder in a sample of British children.|first1=P|last1=Dawes |first2=D.V. M.|last2=Bishop|year=2007|journal=International Journal of Audiology|volume=46|pages=780–786|doi=10.1080/14992020701545906}}</ref> Performance on a battery of non-verbal auditory tests devised by the [[Medical Research Council (UK)|Medical Research Council]]'s Institute of Hearing Research was found to be heavily influenced by non-sensory task demands, and indices of APD had low reliability when this was controlled for.<ref name='Moore2010'>{{cite journal|title=Nature of auditory processing disorder in children.|first1=D.R.|last1=Moore|first2=M.A.|last2=Ferguson|first3=A.M.|last3=Edmondson-Jones|first4=S|last4=Ratib|first5=A|last5=Riley|year=2010|journal=Pediatrics|volume=126|issue=2|pages=e382-390|doi=10.1542/peds.2009-2826}}</ref>
==Behavioral manifestations==
 
Some of the manifestations below may be observed in individuals with other types of deficits or disorders, such as [[attention deficit]]s, [[hearing loss]], psychologically-based behavioral problems, and learning difficulties or dyslexia. Common behavioral characteristics often noted in individuals with APD include:
 
   
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Depending on how it is defined, APD may share common symptoms with [[Attention-deficit hyperactivity disorder|ADD/ADHD]], [[Specific language impairment]], [[Asperger syndrome]] and other forms of [[autism]]. A review showed substantial evidence for atypical processing of auditory information in autistic children.<ref>{{cite journal |author=O'Connor K |title=Auditory processing in autism spectrum disorder: A review |journal=Neurosci Biobehav Rev |volume= 36|issue= 2|pages= 836–54|year=2011 |month=December |pmid=22155284 |doi=10.1016/j.neubiorev.2011.11.008 |url=}}</ref> Dawes and Bishop noted how specialists in audiology and speech-language pathology often adopted different approaches to child assessment, and they concluded their review as follows: "We regard it as crucial that these different professional groups work together in carrying out assessment, treatment and management of children and undertaking cross-disciplinary research."<ref name='Dawes & Bishop(2009)'/> In practice, this seems rare.
:# Difficulty understanding what people are saying when there's background noise, such as noise at a party or wind on an outdoor hike
 
:# Difficulty following long conversations
 
:# Difficulty hearing conversations on the telephone
 
:# Preferring to learn a foreign language (or challenging vocabulary words, or difficult last names) by learning to read and write the words first, and then learning to hear and speak the words, and then only when the words are spoken slowly
 
:# 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 organizational skills
 
:# Difficulty following multi-step directions
 
:# Difficulty in dividing attention
 
:# Difficulty with reading and/or spelling
 
:# Preferring to watch movies with the subtitles or closed-captioning on
 
:# Sensitivity to certain noises (e.g., inability to "tune out" a television on in the background while "tuning in" a conversation with a person).
 
:# Difficulty picking out one musical instrument from a band or orchestra
 
   
==Causes of APD==
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==Causes: Acquired Auditory Processing Disorder==
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Acquired APD is not a unitary disorder. Any damage to or dysfunction of the central auditory nervous system can cause auditory processing problems.<ref>{{cite journal |author=Musiek FE, Chermak GD, Weihing J, Zappulla M, Nagle S |title=Diagnostic accuracy of established central auditory processing test batteries in patients with documented brain lesions |journal=J Am Acad Audiol |volume=22 |issue=6 |pages=342–58 |year=2011 |month=June |pmid=21864472 |doi=10.3766/jaaa.22.6.4 |url=}}</ref><ref>{{cite journal |author=Lew HL, Weihing J, Myers PJ, Pogoda TK, Goodrich GL |title=Dual sensory impairment (DSI) in traumatic brain injury (TBI)--An emerging interdisciplinary challenge |journal=NeuroRehabilitation |volume=26 |issue=3 |pages=213–22 |year=2010 |pmid=20448311 |doi=10.3233/NRE-2010-0557 |url=}}</ref> For an overview of neurological aspects of APD, see Griffiths.<ref>{{cite journal|last=Griffiths|first=T. D.|year=2002|title=Central auditory pathologies. |journal=British Medical Bulletin|volume=63|issue=1|pages=107–120| doi=10.1093/bmb/63.1.107}}</ref>
While there is no one cause, the disorder will occur in various locations along the path, followed by [[acoustic signal]]s as they are received, transition into [[neural signal]]s and then ultimately pass through [[neural network]]s from the ear to the brain for additional analysis (before the ultimate recognition or comprehension and response).
 
   
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==Causes: Developmental Auditory Processing Disorder==
In many people, the development of important [[auditory center]]s within the brain is linked directly to maturational delays which result in this disorder. In others, variations in [[brain development]] can lead to [[benign]] differences and create the deficits. For many, this is a [[genetic disorder]] which is inherited and runs in families. Sometimes, the disorder may relate to [[neurological problem]]s caused by [[tumor]]s, [[trauma]], surgical mishaps, disease, [[viral infection]]s, oxygen deficiency, [[lead poisoning]], [[auditory deprivation]], or anything along these lines.
 
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In the majority of cases of developmental APD, the cause is unknown. An exception is acquired epileptic [[aphasia]] or [[Landau-Kleffner syndrome]], where a child's development regresses, with language comprehension severely affected.<ref>{{cite journal |author=Fandiño M, Connolly M, Usher L, Palm S, Kozak FK |title=Landau-Kleffner syndrome: a rare auditory processing disorder series of cases and review of the literature |journal=Int. J. Pediatr. Otorhinolaryngol. |volume=75 |issue=1 |pages=33–8 |year=2011 |month=January |pmid=21074868 |doi=10.1016/j.ijporl.2010.10.001 |url=}}</ref> The child is often thought to be [[deaf]], but normal peripheral hearing is found. In other cases, suspected or known causes of APD in children include delay in [[myelin]] maturation,<ref>{{cite book |author= Weihing, Jeff; Musiek, Frank; |chapter=15 Dichotic Interaural Intensity Difference (DIID) |title=Auditory Processing Disorders: Assessment, Management and Treatment |editors=Ross-Swain, Deborah; Geffner, Donna S; |publisher=Plural Publishing Inc |location= |year=2007 |pages= |isbn=1-59756-107-X |oclc=255602759 |doi= |accessdate=}}</ref> ectopic (misplaced) cells in the [[auditory cortex|auditory cortical]] areas,<ref>{{cite journal |author=Boscariol M, Garcia VL, Guimarães CA, ''et al.'' |title=Auditory processing disorder in perisylvian syndrome |journal=Brain Dev. |volume=32 |issue=4 |pages=299–304 |year=2010 |month=April |pmid=19410403 |doi=10.1016/j.braindev.2009.04.002 |url=}}</ref> or genetic predisposition.<ref>{{cite journal |author=Bamiou DE, Campbell NG, Musiek FE, ''et al.'' |title=Auditory and verbal working memory deficits in a child with congenital aniridia due to a PAX6 mutation |journal=Int J Audiol |volume=46 |issue=4 |pages=196–202 |year=2007 |month=April |pmid=17454233 |doi=10.1080/14992020601175952 |url=}}</ref> In a family with [[autosomal dominant]] [[epilepsy]], [[seizures]] which affected the left temporal lobe seemed to cause problems with auditory processing.<ref>{{cite journal |author=Pisano T, Marini C, Brovedani P, Brizzolara D, Pruna D, Mei D, Moro F, Cianchetti C, Guerrini R |title=Abnormal phonologic processing in familial lateral temporal lobe epilepsy due to a new LGI1 mutation |journal=Epilepsia |volume=46 |issue=1 |pages=118–23 |year=2005 |month=January |pmid=15660777 |doi=10.1111/j.0013-9580.2005.26304.x }}</ref> 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.<ref>{{cite journal |author=Addis L, Friederici AD, Kotz SA, Sabisch B, Barry J, Richter N, Ludwig AA, Rübsamen R, Albert FW, Pääbo S, Newbury DF, Monaco AP |title=A locus for an auditory processing deficit and language impairment in an extended pedigree maps to 12p13.31-q14.3 |journal=Genes, Brain, and Behavior |volume=9 |issue=6 |pages=545–61 |year=2010 |month=August |pmid=20345892 |pmc=2948670 |doi=10.1111/j.1601-183X.2010.00583.x }}</ref>
   
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[[Hearing (sense)|Hearing]] begins [[in utero]], but the [[central auditory system]] continues to develop for at least the first decade.<ref name="Moore, 2002">{{cite journal |author=Moore DR |title=Auditory development and the role of experience |journal=British Medical Bulletin |volume=63 |issue= |pages=171–81 |year=2002 |pmid=12324392 |doi= |url=http://bmb.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=12324392}}</ref> There is considerable interest in the idea that disruption to hearing during a sensitive period may have long-term consequences for auditory development.<ref>{{cite journal |author=Thai-Van H, Veuillet E, Norena A, Guiraud J, Collet L |title=Plasticity of tonotopic maps in humans: influence of hearing loss, hearing aids and cochlear implants |journal=Acta Otolaryngol. |volume=130 |issue=3 |pages=333–7 |year=2010 |month=March |pmid=19845491 |doi=10.3109/00016480903258024 |url=}}</ref> 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.<ref>{{cite journal |author=Barkat TR, Polley DB, Hensch TK |title=A critical period for auditory thalamocortical connectivity |journal=Nature Neuroscience |volume=14 |issue=9 |pages=1189–94 |year=2011 |month=September |pmid=21804538 |doi=10.1038/nn.2882 |url=http://dx.doi.org/10.1038/nn.2882}}</ref> This points to connectivity between the [[thalamus]] and [[Cerebral cortex|cortex]] shortly after being able to hear (in vitro) as at least one critical period for auditory processing. Another study showed that rats reared in a single tone environment during critical periods of development had permanently impaired auditory processing.<ref>{{cite journal |author=Han YK, Köver H, Insanally MN, Semerdjian JH, Bao S |title=Early experience impairs perceptual discrimination |journal=Nature Neuroscience |volume=10 |issue=9 |pages=1191–7 |year=2007 |month=September |pmid=17660815 |doi=10.1038/nn1941 |url=http://dx.doi.org/10.1038/nn1941}}</ref> ‘Bad’ auditory experiences, such as temporary deafness by [[cochlear]] removal in rats leads to neuron shrinkage.<ref name="Moore, 2002"/> In a study looking at attention in APD patients, children with one ear blocked developed a strong right-ear advantage but were not able to modulate that advantage during directed-attention tasks.<ref>{{cite journal |author=Asbjørnsen A, Holmefjord A, Reisaeter S, Møller P, Klausen O, Prytz B, Boliek C, Obrzut JE |title=Lasting auditory attention impairment after persistent middle ear infections: a dichotic listening study |journal=Developmental Medicine and Child Neurology |volume=42 |issue=7 |pages=481–6 |year=2000 |month=July |pmid=10972421 |doi= |url=http://onlinelibrary.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=0012-1622&date=2000&volume=42&issue=7&spage=481}}</ref>
==What it is like to have APD ==
 
Persons with this condition often:
 
* have trouble paying attention to and remembering information presented orally;
 
* have problems carrying out multi-step directions given orally;
 
* have poor listening skills; and
 
* need more time to process information.
 
It appears to others as a problem with listening. Somebody with APD may be accused of "not listening".
 
   
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In the 1980s and 1990s, there was considerable interest in the role of chronic [[Otitis media]] (middle ear disease or 'glue ear') in causing APD and related language and literacy problems. 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.<ref>{{cite journal |author=Whitton JP, Polley DB |title=Evaluating the perceptual and pathophysiological consequences of auditory deprivation in early postnatal life: a comparison of basic and clinical studies |journal=J. Assoc. Res. Otolaryngol. |volume=12 |issue=5 |pages=535–47 |year=2011 |month=October |pmid=21607783 |doi=10.1007/s10162-011-0271-6 |url=}}</ref> Consistent with this, in a sample of young children with chronic ear infections recruited from a hospital otolargyngology department, increased rates of auditory difficulties were found later in childhood.<ref>{{cite journal |author=Hartley DE, Moore DR |title=Effects of otitis media with effusion on auditory temporal resolution |journal=International Journal of Pediatric Otorhinolaryngology |volume=69 |issue=6 |pages=757–69 |year=2005 |month=June |pmid=15885328 |doi=10.1016/j.ijporl.2005.01.009}}</ref> However, this kind of study will suffer from [[sampling bias]] because children with otitis media will be more likely to be referred to hospital departments if they are experiencing developmental difficulties. Compared with hospital studies, epidemiological studies, which assess a whole population for otitis media and then evaluate outcomes, have found much weaker evidence for long-term impacts of otitis media on language outcomes.<ref>{{cite journal|last1=Feldman|first1=H.M.|last2=et al|year=2003|title=Parent-reported language skills in relation to otitis media during the first 3 years of life|journal=Journal of Speech, Language and Hearing Research|volume=46|pages=273–287|doi=10.1044/1092-4388(2003/022)}}</ref>
One adult, who has had the disorder since childhood, writes:
 
   
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==Characteristics==
:"My hearing is fine, but what I hear is often garbled initially by my brain. Shortly later, I often figure it out. In conversation, about the same time I say "huh?', I figure out what it was that I just heard. Like the three-legged dog, I am told that my visual skills, in compensation, are much stronger than normal. My bottom line is: I do better with what I see than what I hear."
 
   
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The National Institute on Deafness and Other Communication Disorders<ref>{{cite web |url=http://www.nidcd.nih.gov/health/voice/auditory.html |title=Auditory Processing Disorder in Children [NIDCD Health Information] |work= |accessdate=}}</ref> state that children with Auditory Processing Disorder often:
==Coping skills and work-arounds==
 
 
* have trouble paying attention to and remembering information presented orally, and may cope better with visually acquired information
Adults who discover disabilities such as APD late in life have provided some insight into [[coping skill]]s they have found helpful. These include:
 
 
* have problems carrying out multi-step directions given orally; need to hear only one direction at a time
 
* have poor listening skills
 
* need more time to process information
  +
* have low academic performance
  +
* have behavior problems
  +
* have language difficulties (e.g., they confuse syllable sequences and have problems developing vocabulary and understanding language)
  +
* have difficulty with reading, comprehension, spelling, and vocabulary
   
  +
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, since spoken words may sound distorted either into irrelevant words or words that don't exist, depending on the severity of the auditory processing disorder.<ref>{{cite journal |author=Anderson S, Kraus N |title=Sensory-cognitive interaction in the neural encoding of speech in noise: a review |journal=J Am Acad Audiol |volume=21 |issue=9 |pages=575–85 |year=2010 |month=October |pmid=21241645 |pmc=3075209 |doi=10.3766/jaaa.21.9.3 |url=}}</ref> 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.<ref name='ASHA 2005'/> 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.
# Get directions and instructions in writing.
 
# Do not take notes yourself when information comes from others orally, as this may interfere with your processing strategies, but ask others to provide notes for you.
 
# Many APDs use [[body language]], [[lip reading]] and eye contact as a coping strategy.
 
# Rewrite text using multi-coloured text options to provide visual guide to changes in meaning or for new sentences, or use a set of coloured highlighters.
 
# Use [[closed captioning]] while watching television.
 
# Place with teachers whose speaking style is clear and organized, who are "good explainers," and who encourage questions, so that the person with ADP does not have to decode complex verbiage. Rules of language activities, including writing, need to be made overt and very explicit.
 
   
  +
As noted above, the status of APD as a distinct disorder has been queried, especially by speech-language pathologists<ref name='Kamhi2011'>{{cite journal|first=A.G.|last=Kamhi|year=2011|title= What speech-language pathologists need to know about Auditory Processing Disorder.|journal=Language Speech and Hearing Services in Schools|volume= 42|issue=3|pages=265–272|doi=10.1044/0161-1461(2010/10-0004)}}</ref> and psychologists,<ref name='Lovett2011'>{{cite journal|last=Lovett|first=B.J.|year=2011|title=Auditory processing disorder: School psychologist beware?|journal=Psychology in the Schools|volume=48|pages=855–867|doi=10.1002/pits.20595}}</ref> who note the overlap between clinical profiles of children diagnosed with APD and those with other forms of specific learning disability. 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.<ref>{{cite journal|journal=Hearing Journal|year=
==Remediations and Training==
 
  +
2001|volume = 54|issue =7|pages=10–25|doi=10.1097/01.HJ.0000294109.14504.d8|title=
No one program is a cure or help all for APD.
 
  +
Auditory processing disorder: An overview for the clinician|last=Chermak|first=Gail D}}</ref>
   
  +
==Relation to Specific language impairment and Developmental Dyslexia==
APD is about creating coping strategies to meet the challenges life presents and using the various strengths each of us may have.
 
  +
* [http://resources.apduk.org/manage_apd.htm Management of Auditory Processing Disorders] (includes the use of many programs)
 
  +
There has been considerable debate over the relationship between APD and [[Specific language impairment|Specific language impairment (SLI)]].
* [http://www.lblp.com/index.shtml Lindamood-Bell Learning Processes] (particularly, the Visualizing and Verbalizing program)
 
  +
* [[Neuro-linguistic programming]] (NLP)
 
  +
SLI is diagnosed when a child has difficulties with understanding or producing spoken language for no obvious cause. The problems cannot be explained in terms of peripheral hearing loss. The child is typically late in starting to talk, and may have problems in producing speech sounds clearly, and in producing or understanding complex sentences. Some theoretical accounts of SLI regard it as the result of auditory processing problems.<ref>{{cite journal|last=Miller|first=C. A.|year=2011|title= Auditory processing theories of language disorders: Past, present, and future.|journal=Language Speech and Hearing Services in Schools|volume=42|issue=3|pages=309–319|doi= 10.1044/0161-1461(2011/10-0040)}}</ref><ref name="Ferguson, 2011">{{cite journal|last1=Ferguson|first1= M. A.|last2=Hall|first2=R. L.|last3= Riley|first3=A|last4= Moore|first4= D. R.|year=2011|title=Communication, listening, cognitive and speech perception skills in children with auditory processing disorder (APD) or specific language impairment (SLI)|journal=Journal of Speech Language and Hearing Research|volume= 54|issue=1|pages=211–227| doi=10.1044/1092-4388(2010/09-0167)}}</ref> However, this view of SLI is not universally accepted, and others regard the main difficulties in SLI as stemming from problems with higher-level aspects of language processing. Where a child has both auditory and language problems, it can be hard to sort out cause-and-effect.<ref name="Ferguson, 2011"/>
* [http://www.braingym.org/faq.html Brain Gym] or Edu-Kinesthetics
 
  +
* Physical activities which require frequent crossing of the midline (e.g. [[occupational therapy]])
 
  +
Similarly with [[dyslexia|developmental dyslexia]], there has been considerable interest in the idea that for some children reading problems are downstream consequences of difficulties in rapid auditory processing. Again, cause and effect can be hard to unravel. This is one reason why experts such as Moore<ref name='D.R.Moore (2006)'/> have recommended using non-verbal auditory tests to diagnose APD.
* [[Auditory Integration Training]] (AIT)
 
  +
* [http://f3.grp.yahoofs.com/v1/cPj4Q9mCe7XTlUnK42sH2xuX8zKq41FjEaw1g6T75rqd_EuMMwAYXEiw4OvFOQojnXt9UWnLwAvusX9t_Y7AbA/auditory-input-trainingASHA2004.pdf Auditory Integration Training - ASHA Position Statement] 2004 [http://www.asha.org/default.htm American Speech language Hearing Association ASHA] Position Statement on Auditory Integration Training which includes references to the auditory integration therapies (AITs) Tomatis, Samonas Sound Therapy, and The Listening Program, and refers to correspondence with Advanced Brain regarding these products. To date, according to the ASHA 2004 statement, these treatments fall outside the range of safe, evidence based interventions.
 
  +
It has also been suggested that APD may be related to [[cluttering]],<ref>{{cite book |author=Pindzola, Rebekah H.; Haynes, William O.; Moran, Michael J. |title=Communication disorders in the classroom: an introduction for professionals in school setting |publisher=Jones and Bartlett Publishers |location=Boston |year=2006 |pages=251 |isbn=0-7637-2743-1 |oclc=59401841 |doi= |accessdate=}}</ref> a fluency disorder marked by word and phrase repetitions.
  +
  +
If, as is commonly done, APD is assessed using tests that involve identifying, repeating or discriminating speech, then a child may do poorly because of primary language problems.<ref name='Dawes & Bishop(2009)'/> In a study comparing children with a diagnosis of dyslexia and those with a diagnosis of APD, they found the two groups could not be distinguished.<ref name="Ferguson, 2011"/><ref>{{cite journal|last1=Dawes|first1=P|last2=Bishop|first2= D|year=2010|title=Psychometric profile of children with auditory processing disorder (APD) and children with dyslexia|journal=Archives of Disease in Childhood|volume=95|pages=432–436|doi=10.1136/adc.2009.170118}}
  +
</ref><ref>{{cite journal |last1=Miller|first1= C.A.|last2=Wagstaff|first2=D.A.|year=2011 |title=Behavioral profiles associated with auditory processing disorder and specific language impairment.|journal=Journal of Communication Disorders|volume=44|issue=6|pages=745–763 |doi=10.1016/j.jcomdis.2011.04.001}}</ref> obtained similar findings in studies comparing children diagnosed with SLI or APD.<ref>{{cite journal |author=Corriveau K, Pasquini E, Goswami U |title=Basic auditory processing skills and specific language impairment: a new look at an old hypothesis |journal=J. Speech Lang. Hear. Res. |volume=50 |issue=3 |pages=647–66 |year=2007 |month=June |pmid=17538107 |doi=10.1044/1092-4388(2007/046) |url=}}</ref><ref>{{cite journal |author=Dlouha O, Novak A, Vokral J |title=Central auditory processing disorder (CAPD) in children with specific language impairment (SLI). Central auditory tests |journal=Int. J. Pediatr. Otorhinolaryngol. |volume=71 |issue=6 |pages=903–7 |year=2007 |month=June |pmid=17382411 |doi=10.1016/j.ijporl.2007.02.012 |url=}}</ref> The two groups had very similar profiles. This raises the worrying possibility that the diagnosis that a child receives may be largely a function of the specialist they see: the same child who would be diagnosed with APD by an audiologist may be diagnosed with SLI by a speech-language therapist or with dyslexia by a psychologist.<ref name='D.R.Moore (2006)'/>
  +
  +
==Remediation and training==
  +
  +
{{See also|Alternative therapies for developmental and learning disabilities}}
  +
  +
There is a lack of well-conducted evaluations of intervention using [[randomized controlled trial]] methodology. Most evidence for effectiveness adopts weaker standards of evidence, such as showing that performance improves after training. This does not control for possible influences of practice, maturation, or placebo effects. Recent research has shown that practice with basic auditory processing tasks (i.e. auditory training) may improve performance on auditory processing measures<ref>{{cite journal |author=Chermak GD, Silva ME, Nye J, Hasbrouck J, Musiek FE |title=An update on professional education and clinical practices in central auditory processing |journal=J Am Acad Audiol |volume=18 |issue=5 |pages=428–52; quiz 455 |year=2007 |month=May |pmid=17715652 |doi= 10.3766/jaaa.18.5.7|url=}}</ref><ref name=MooreDR2007 >{{cite journal |author=Moore DR |title=Auditory processing disorders: acquisition and treatment |journal=J Commun Disord |volume=40 |issue=4 |pages=295–304 |year=2007 |pmid=17467002 |doi=10.1016/j.jcomdis.2007.03.005 |url=}}</ref> and phonemic awareness measures.<ref>{{cite journal |author=Moore DR, Rosenberg JF, Coleman JS |title=Discrimination training of phonemic contrasts enhances phonological processing in mainstream school children |journal=Brain Lang |volume=94 |issue=1 |pages=72–85 |year=2005 |month=July |pmid=15896385 |doi=10.1016/j.bandl.2004.11.009 |url=}}</ref> Changes after auditory training have also been recorded at the physiological level.<ref>{{cite journal |author=Russo NM, Nicol TG, Zecker SG, Hayes EA, Kraus N |title=Auditory training improves neural timing in the human brainstem |journal=Behav. Brain Res. |volume=156 |issue=1 |pages=95–103 |year=2005 |month=January |pmid=15474654 |doi=10.1016/j.bbr.2004.05.012 |url=}}</ref><ref>{{cite journal |author=Alonso R, Schochat E |title=The efficacy of formal auditory training in children with (central) auditory processing disorder: behavioral and electrophysiological evaluation |journal=Braz J Otorhinolaryngol |volume=75 |issue=5 |pages=726–32 |year=2009 |pmid=19893943 |doi=10.1590/S1808-86942009000500019 |url=}}</ref> Many of these tasks are incorporated into computer-based auditory training programs such as Earobics and [[Fast Forword|Fast ForWord]], an adaptive software available at home and in clinics worldwide, but overall, evidence for effectiveness of these computerised interventions in improving language and literacy is not impressive.<ref>{{cite journal|last1=Loo|first1=J.H.Y.|last2=Bamiou|first2=D.-E.|last3=Campbell|first3=N.|last4=Luxon|first4= L.M.|year=2010|title= Computer-based auditory training (CBAT): benefits for children with language- and reading-related learning difficulties|journal=Developmental Medicine and Child Neurology|volume=52|issue=8|pages=708–717|doi=10.1111/j.1469-8749.2010.03654.x}}</ref> One small-scale uncontrolled study reported successful outcomes for children with APD using auditory training software.<ref>{{cite journal |author=Cameron S, Dillon H |title=Development and Evaluation of the LiSN & Learn Auditory Training Software for Deficit-Specific Remediation of Binaural Processing Deficits in Children: Preliminary Findings |journal=Journal of the American Academy of Audiology |volume=22 |issue=10 |pages=678–96 |year=2011 |month=November |pmid=22212767 |doi=10.3766/jaaa.22.10.6 |url=}}</ref>
  +
  +
Treating additional issues related to APD can result in success. For example, treatment for phonological disorders (difficulty in speech) can result in success in terms of both the phonological disorder as well as APD. In one study, speech therapy improved auditory [[evoked potential]]s (a measure of brain activity in the auditory portions of the brain).<ref>{{cite journal |author=Leite RA, Wertzner HF, Matas CG |title=Long latency auditory evoked potentials in children with phonological disorder |journal=Pró-fono : Revista De Atualização Científica |volume=22 |issue=4 |pages=561–6 |year=2010 |pmid=21271117 |doi= |url=http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-56872010000400034&lng=en&nrm=iso&tlng=en}}</ref>
  +
  +
While there is evidence that language training is effective for improving APD, there is no current research supporting the following APD treatments:
  +
* [[Auditory Integration Training]] typically involves a child attending two 30-minute sessions per day for ten days.<ref>{{cite book
  +
|title= Controversial Therapies for Developmental Disabilities
  +
|editor= Jacobson JW, Foxx RM, Mulick JA (eds.)
  +
|chapter= Auditory integration training: a critical review
  +
|author= Mudford OC, Cullen C
  +
|pages=351–62
  +
|year=2004
  +
|publisher=Routledge
  +
|isbn=0-8058-4192-X}}</ref>
 
* Lindamood-Bell Learning Processes (particularly, the Visualizing and Verbalizing program)
 
* Physical activities that require frequent crossing of the midline (e.g., [[occupational therapy]])
  +
* Sound Field Amplification
  +
* Neuro-Sensory Educational Therapy
  +
  +
==See also==
  +
{{divbegin|columns=2}}
  +
<!-- please add Wikipedia links below -->
  +
*[[Asperger syndrome]]
  +
*[[Attention-Deficit Hyperactivity Disorder]]
  +
*[[Audiology]]
  +
*[[Auditory scene analysis]]
  +
*[[Auditory verbal agnosia]]
  +
*[[Cocktail party effect]]
  +
*[[Cognitive science]]
  +
*[[Cortical deafness]]
  +
*[[Dichotic listening test]]
  +
*[[Echoic memory]]
  +
*[[Hearing (sense)]]
  +
*[[Language processing]]
  +
*[[Listening]]
  +
*[[King-Kopetzky syndrome]] (now included in the UK Medical Research Councils definition of APD)
  +
*[[Spatial hearing loss]]
  +
<!-- please do not add Wikipedia links below </div> -->
  +
</div>
  +
  +
==References==
  +
  +
{{reflist|30em}}
   
 
==External links==
 
==External links==

Revision as of 16:11, 20 May 2013

Auditory Processing Disorder (APD)
ICD-10
ICD-9 388.4, 389.9, 389.12, or 389.14
OMIM {{{OMIM}}}
DiseasesDB {{{DiseasesDB}}}
MedlinePlus {{{MedlinePlus}}}
eMedicine {{{eMedicineSubj}}}/{{{eMedicineTopic}}}
MeSH {{{MeshNumber}}}

Auditory Processing Disorder (APD) (previously known as "Central Auditory Processing Disorder" (CAPD)) is not a hearing impairment (i.e., a person with APD usually has nothing wrong with his or her ears), but an inability to process what is heard. APD is an umbrella term that describe a variety of problems with the brain that can interfere with processing auditory information.

Definitions

The "American Speech + Language - Hearing Association" (ASHA) have recently published the first definitive (Central) Auditory Processing Disorders Technical Report, Jan 2005, which complements the UK's "Medical Research Council's Institute of Hearing Research's" Auditory Processing Disorder (APD) pamphlet, Oct 2004.

Both of these documents provide the first comprehensive definitions of APD in the respective countries, and a platform for future research and development of diagnostic systems and support programs. (There are links to both documents included in the External Links section below.) They cover the various causes of Auditory Processing Disorder including both the genetic causes and the acquired causes (such as severe ear infections and severe head injuries).

Aspects of auditory processing which may be affected by APD include "auditory discrimination", the ability to distinguish between similar sounds or words; "auditory figure-ground", the ability to distinguish relevant speech from background noise; and "auditory memory", the ability to recall what was heard.

History

The first research into APD began in 1954 with Helmer Myklebust’s study, "Auditory Disorders in Children".[1] Myklebust’s work suggested auditory processing disorder was separate from language learning difficulties. His work sparked interest in auditory deficits after acquired brain lesions affecting the temporal lobes[2][3] and led to additional work looking at the physiological basis of auditory processing,[4] but it was not until the late seventies and early eighties that research began on APD in depth. In 1977, a conference about APD started a new series of studies focussing on APD in children.[5][6][7][8][9] Virtually all tests currently used to diagnose APD originate from this work. These early researchers also invented many of the auditory training approaches, including interhemispheric transfer training and interaural intensity difference training. This period gave us a rough understanding of the causes and possible treatment options for APD. 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. Scientists have worked on improving behavioral tests of auditory function, neuroimaging, electroacoustic, and electrophysiologic testing.[10][11] Working with new technology has led to a number of software programs for auditory training.[12][13] With global awareness of mental disorders and increasing understanding of neuroscience, auditory processing is more in the public and academic consciousness than ever before.[14][15][16][17][18]

Diagnosis

APD is a difficult disorder to detect and diagnose. The subjective symptoms that lead to an evaluation for APD include an intermittent inability to process verbal information, leading the person to guess to fill in the processing gaps. There may also be disproportionate problems with decoding speech in noisy environments.

APD has been defined anatomically in terms of the integrity of the auditory areas of the nervous system.[19] However, children with symptoms of APD typically have no evidence of neurological disease and the diagnosis is made on the basis of performance on behavioral auditory tests. Auditory processing is "what we do with what we hear",[20] and in APD there is a mismatch between peripheral hearing ability (which is typically normal) and ability to interpret or discriminate sounds. Thus in those with no signs of neurological impairment, APD is diagnosed on the basis of auditory tests. There is, however, no consensus as to which tests should be used for diagnosis, as evidenced by the succession of task force reports that have appeared in recent years. The first of these occurred in 1996.[21] This was followed by a conference organized by the American Academy of Audiology.[22] Experts attempting to define diagnostic criteria have to grapple with the problem that a child may do poorly on an auditory test for reasons other than poor auditory perception: for instance, failure could be due to inattention, difficulty in coping with task demands, or limited language ability. 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, an ASHA committee subsequently rejected modality-specificity as a defining characteristic of auditory processing disorders.[23]

The issue of modality-specificity has led to considerable debate among experts in this field. Cacace and McFarland have argued that APD should be defined as a modality-specific perceptual dysfunction that is not due to peripheral hearing loss.[24][25] They criticise more inclusive conceptualizations of APD as lacking diagnostic specificity.[26] A requirement for modality-specificity could potentially avoid including children whose poor auditory performance is due to general factors such as poor attention or memory.[24][25] 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. It is also impractical, as audiologists do not have access to standardized tests that are visual analogs of auditory tests. The debate over this issue remains unresolved. It is clear, however, that a modality-specific approach will diagnose fewer children with APD than a modality-general one, and that the latter approach runs a risk of including children who fail auditory tests for reasons other than poor auditory processing.

Another controversy concerns the fact that most traditional tests of APD use verbal materials.[27] The British Society of Audiology[28] has embraced Moore's (2006) recommendation that tests for APD should assess processing of non-speech sounds.[27] The concern is that if verbal materials are used to test for APD, then children may fail because of limited language ability. An analogy may be drawn with trying to listen to sounds in a foreign language. It is much harder to distinguish between sounds or to remember a sequence of words in a language you do not know well: the problem is not an auditory one, but rather due to lack of expertise in the language.

In recent years there have been additional criticisms of some popular tests for diagnosis of APD. Tests that use tape-recorded American English have been shown to over-identify APD in speakers of other forms of English.[29] Performance on a battery of non-verbal auditory tests devised by the Medical Research Council's Institute of Hearing Research was found to be heavily influenced by non-sensory task demands, and indices of APD had low reliability when this was controlled for.[30]

Depending on how it is defined, APD may share common symptoms with ADD/ADHD, Specific language impairment, Asperger syndrome and other forms of autism. A review showed substantial evidence for atypical processing of auditory information in autistic children.[31] Dawes and Bishop noted how specialists in audiology and speech-language pathology often adopted different approaches to child assessment, and they concluded their review as follows: "We regard it as crucial that these different professional groups work together in carrying out assessment, treatment and management of children and undertaking cross-disciplinary research."[32] In practice, this seems rare.

Causes: Acquired Auditory Processing Disorder

Acquired APD is not a unitary disorder. Any damage to or dysfunction of the central auditory nervous system can cause auditory processing problems.[33][34] For an overview of neurological aspects of APD, see Griffiths.[35]

Causes: Developmental Auditory Processing Disorder

In the majority of cases of developmental APD, the cause is unknown. An exception is acquired epileptic aphasia or Landau-Kleffner syndrome, where a child's development regresses, with language comprehension severely affected.[36] The child is often thought to be deaf, but normal peripheral hearing is found. In other cases, suspected or known causes of APD in children include delay in myelin maturation,[37] ectopic (misplaced) cells in the auditory cortical areas,[38] or genetic predisposition.[39] In a family with autosomal dominant epilepsy, seizures which affected the left temporal lobe seemed to cause problems with auditory processing.[40] 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.[41]

Hearing begins in utero, but the central auditory system continues to develop for at least the first decade.[42] There is considerable interest in the idea that disruption to hearing during a sensitive period may have long-term consequences for auditory development.[43] 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.[44] This points to connectivity between the thalamus and cortex shortly after being able to hear (in vitro) as at least one critical period for auditory processing. Another study showed that rats reared in a single tone environment during critical periods of development had permanently impaired auditory processing.[45] ‘Bad’ auditory experiences, such as temporary deafness by cochlear removal in rats leads to neuron shrinkage.[42] In a study looking at attention in APD patients, children with one ear blocked developed a strong right-ear advantage but were not able to modulate that advantage during directed-attention tasks.[46]

In the 1980s and 1990s, there was considerable interest in the role of chronic Otitis media (middle ear disease or 'glue ear') in causing APD and related language and literacy problems. 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.[47] Consistent with this, in a sample of young children with chronic ear infections recruited from a hospital otolargyngology department, increased rates of auditory difficulties were found later in childhood.[48] However, this kind of study will suffer from sampling bias because children with otitis media will be more likely to be referred to hospital departments if they are experiencing developmental difficulties. Compared with hospital studies, epidemiological studies, which assess a whole population for otitis media and then evaluate outcomes, have found much weaker evidence for long-term impacts of otitis media on language outcomes.[49]

Characteristics

The National Institute on Deafness and Other Communication Disorders[50] state that children with Auditory Processing Disorder often:

  • have trouble paying attention to and remembering information presented orally, and may cope better with visually acquired information
  • have problems carrying out multi-step directions given orally; need to hear only one direction at a time
  • have poor listening skills
  • need more time to process information
  • have low academic performance
  • have behavior problems
  • have language difficulties (e.g., they confuse syllable sequences and have problems developing vocabulary and understanding language)
  • have difficulty with reading, comprehension, spelling, and vocabulary

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, since spoken words may sound distorted either into irrelevant words or words that don't exist, depending on the severity of the auditory processing disorder.[51] 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.[23] 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.

As noted above, the status of APD as a distinct disorder has been queried, especially by speech-language pathologists[52] and psychologists,[53] who note the overlap between clinical profiles of children diagnosed with APD and those with other forms of specific learning disability. 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.[54]

Relation to Specific language impairment and Developmental Dyslexia

There has been considerable debate over the relationship between APD and Specific language impairment (SLI).

SLI is diagnosed when a child has difficulties with understanding or producing spoken language for no obvious cause. The problems cannot be explained in terms of peripheral hearing loss. The child is typically late in starting to talk, and may have problems in producing speech sounds clearly, and in producing or understanding complex sentences. Some theoretical accounts of SLI regard it as the result of auditory processing problems.[55][56] However, this view of SLI is not universally accepted, and others regard the main difficulties in SLI as stemming from problems with higher-level aspects of language processing. Where a child has both auditory and language problems, it can be hard to sort out cause-and-effect.[56]

Similarly with developmental dyslexia, there has been considerable interest in the idea that for some children reading problems are downstream consequences of difficulties in rapid auditory processing. Again, cause and effect can be hard to unravel. This is one reason why experts such as Moore[27] have recommended using non-verbal auditory tests to diagnose APD.

It has also been suggested that APD may be related to cluttering,[57] a fluency disorder marked by word and phrase repetitions.

If, as is commonly done, APD is assessed using tests that involve identifying, repeating or discriminating speech, then a child may do poorly because of primary language problems.[32] In a study comparing children with a diagnosis of dyslexia and those with a diagnosis of APD, they found the two groups could not be distinguished.[56][58][59] obtained similar findings in studies comparing children diagnosed with SLI or APD.[60][61] The two groups had very similar profiles. This raises the worrying possibility that the diagnosis that a child receives may be largely a function of the specialist they see: the same child who would be diagnosed with APD by an audiologist may be diagnosed with SLI by a speech-language therapist or with dyslexia by a psychologist.[27]

Remediation and training

There is a lack of well-conducted evaluations of intervention using randomized controlled trial methodology. Most evidence for effectiveness adopts weaker standards of evidence, such as showing that performance improves after training. This does not control for possible influences of practice, maturation, or placebo effects. Recent research has shown that practice with basic auditory processing tasks (i.e. auditory training) may improve performance on auditory processing measures[62][63] and phonemic awareness measures.[64] Changes after auditory training have also been recorded at the physiological level.[65][66] 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 computerised interventions in improving language and literacy is not impressive.[67] One small-scale uncontrolled study reported successful outcomes for children with APD using auditory training software.[68]

Treating additional issues related to APD can result in success. For example, treatment for phonological disorders (difficulty in speech) can result in success in terms of both the phonological disorder as well as APD. In one study, speech therapy improved auditory evoked potentials (a measure of brain activity in the auditory portions of the brain).[69]

While there is evidence that language training is effective for improving APD, there is no current research supporting the following APD treatments:

  • Auditory Integration Training typically involves a child attending two 30-minute sessions per day for ten days.[70]
  • Lindamood-Bell Learning Processes (particularly, the Visualizing and Verbalizing program)
  • Physical activities that require frequent crossing of the midline (e.g., occupational therapy)
  • Sound Field Amplification
  • Neuro-Sensory Educational Therapy

See also

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References

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