Auditory Processing Disorder (APD) in Children: Guide

APD tests and criteria

Referrals for APD evaluation from teachers, psychologists, speech-language pathologists, and other professionals are increasing, and parents are demanding appropriate services when they learn of the existence of APD on the Internet and other media sources.  Yet, despite the need for APD assessment and the availability of behavioural assessments, many audiologists have been reluctant to include APD assessment in their clinical practices (Kraus and Anderson, 2016)

The reason is that APD evaluation is both a complex and controversial area.  There is no gold standard for the tests that should be included in the test battery, or the diagnostic criteria that should be used.  This makes APD a challenging area for all involved.

Understanding the controversy surrounding what is known as the ‘traditional’ APD tests.

In the 1970s and 1980s, behavioural tests of auditory processing were developed based on performance of individuals with known brainstem and cortical lesions.  These tests have with time become known as the ‘traditional’ APD tests and are often used to assess auditory processing in children and adults who do not have identified anatomical abnormalities but have apparent hearing difficulties in more challenging listening situations (Kraus, 2016).  Four broad types of auditory processes are generally measured: (1) dichotic processing (e.g. dichotic digits test, competing sentence test), (2) temporal processing (e.g. frequency and duration pattern tests), 3) perception of monaural low-redundancy speech (e.g. filtered speech test) and (4) binaural interaction (e.g. masking level difference test).

These tests were developed to aid in the detection of frank brainstem and cortical lesions in adults, ahead of the powerful imaging techniques we have available today.  Inferences from frank lesions in adults to developmental delay in children are problematic.  The tests typically carry a high cognitive load, e.g. language, attention and memory.  Children with problems in these areas are thus likely to score poorly on the tests, even though auditory processing may not be the problem.  There are also concerns that the skills assessed are not representative of the real life difficulties, and that treatment of these discrete skills is not evidence-based and does not generalise to everyday life (BSA, 2018).  For example, dichotic stimuli (simultaneously different signals in the 2 ears) are not encountered in the real world in the form they are used in traditional dichotic tests.  Another consideration is the lack of normative data and poor validation for many of these tests.  Furthermore, the tests can only be used for children aged 7 years and older, which is worrying given the known advantages of early identification and intervention (BSA, 2018, Neijenhuis et al, 2019)

Another concern is the variable diagnostic criteria employed.  The most commonly used diagnostic criterion is ‘performance at or below 2 SD of the mean in at least 2 tests, or 3 SD below the mean on 1 test’ (ASHA, 2005; AAA, 2010) on the traditional test battery.  There are a number of problems with this criterion.  Firstly, there is no specification of the number of tests that are to be used.  Statistically, the more tests performed, the more likely any child is likely to fail two of them.  Secondly, there is no specification of the exact tests to be applied, and failure rates are likely to vary greatly from test to test, as do available normative data for these tests.  Thirdly, the criterion was arbitrarily decided, without any strong published underpinning evidence.  In a now well known study Wilson and Arnott (2013) showed the risk of using arbitrary criteria in a large sample of children where diagnostic rates of APD varied from 7% to 93% depending upon which criteria are applied, even when using the same traditional APD tests.  Adherence to arbitrary test batteries and criteria has unfortunately contributed to much of the current controversy in the field of APD (BSA, 2018,Neijenhuis et al, 2019)..

Chermak et al (2017) have suggested ways to minimize the effects of language and cognitive aspects on the traditional APD test battery.  These include using tests that employ nonverbal stimuli (e.g., gap detection, frequency and duration patterns, masking level difference), simple speech stimuli (e.g., digits), electrophysiological procedures, and doing a multidisciplinary assessment.  Although these recommendations may help minimize the effects of language and cognitive aspects the other concerns raised in the preceding paragraphs persist.

Electrophysiology and APD

In terms of electrophysiology there is no agreement as to when electrophysiology procedures should be included in the clinical evaluation of APD.  They are often not readily available in many audiology clinics. 

Although helpful from a research perspective there is little evidence to support the inclusion of these tests in cases of normal audiometry, with the exception of the ABR which when used with oto-acoustic emissions and/or cochlear microphonic potentials is necessary in identifying Auditory Neuropathy Spectrum Disorder (BSA, 2018).

Newer and emerging tests of APD

More recently the Listening in Spatialized Noise-Sentences (LiSN-S) test (Cameron et al, 2006) became available, which measures spatial release from masking, an area in which particularly children with a history of middle ear infections and glue ear have greater difficulty.  This test presents competing speech as a more real-world-like signal.  Spatial Processing Disorder is a specific type of APD.  It refers to an inability to utilize the directional cues embedded in sound in order to separate the speech we want to hear from background noise.  It occurs when the brain’s normal auditory processing abilities are unable to selectively focus on sounds coming from one direction and suppress sounds coming from other directions.

CLICK HERE for more information about Spatial Processing Disorder

Other researchers (Vermiglio, 2014; de Bonis, 2015) have suggested that focusing on speech in noise tests may be more appropriate, given that difficulty hearing speech-in-noise is the most common complaint of individuals presenting for an auditory processing assessment.  Vermiglio (2014) investigated APD and speech recognition-in-noise disorders in reference to the Sydenham-Guttentag criteria for meeting the definition of a clinical entity; namely that it must have (1) an unambiguous definition, (2) represent a homogenous group with a perceived limitation and (3) facilitate a diagnosis and intervention.  They concluded that speech-recognition-in-noise disorders met the criteria but APD did not.

There are also a number of apps emerging 

Feather Squadron has been developed to screen a range of discrete auditory skills, including lateralization, temporal processing, linguistic and non-linguistic auditory memory, linguistic and non-linguistic dichotic ability, degraded speech, tonal and pitch processing and speech in noise.  The validity of the app has not been well established.  Barker (partial owner and developer) and Purdy (2016) have published an initial investigation into the validity of Feather Squadron in 945 children, aged 5-14 years.  They concluded that a qualified audiologist (and not the Feather Squadron assessment alone) is important in making a diagnosis of APD.  They recommended that a thorough case history and standard audiological tests (e.g. pure tone, immittance, and speech audiometry) are also necessary, together with additional APD measures.

Portable Automated Rapid Testing (P.A.R.T) is another app, which is described as a free experimental interface.  It includes a range of measures of auditory processing.  One of the measures is the detection of spectrotemporal modulation, which is reported to correlate with speech-in-noise ability (Bernstein et al, 2013).

In conclusion, there is no ‘gold standard’ for the tests that should be included in the test battery, or the diagnostic criteria that should be used.  Although tempting to simply decide on a ‘new’ test battery and a ‘new’ criterion we need to be careful.  The use of arbitrary test batteries and criteria in the past is unfortunately what has contributed to much of the current controversy.  It is important to base decisions on good research evidence, as it unfolds.

Recommendations for assessing APD, based on best current evidence, are presented in the next section ‘APD testing-recommendations’.

References

Auditec Inc. Online company which sells auditory tests and training materials

American Academy of Audiology. (2010). Diagnosis, treatment and management of children and adults with central auditory processing disorder [Clinical Practice Guidelines].

American Speech-Language and Hearing Association. (2005). (Central) Auditory Processing Disorders: The Role of the Audiologist

Barker, M.D., & Purdy, S.C. (2016). An initial investigation into the validity of a computer-based auditory processing assessment (Feather Squadron). International Journal of Audiology, 55, 173–183.

Bernstein, J.G.W., Mehraei, G., Shamma, S., Gallun, F.J., Theodoroff, & S.M., Leek, M.R. (2013). Spectrotemporal Modulation Sensitivity as a Predictor of Speech Intelligibility for Hearing-Impaired Listeners. J Am Acad Audiol, 24(4), 293–306.

British Society of Audiology NHSP Clinical Group. (2013). Guidelines for the assessment and management of auditory neuropathy spectrum disorder in young Infants.

British Society of Audiology APD SIG. (2018). APD Position Statement and Practice Guidance.

Cameron, S., Dillon, H., & Newall, P. (2006). Development and evaluation of the listening in spatialized noise test. Ear Hear, 27(1), 30–42.

Chermak, G.D., Bamiou, D-E., Iliadou, V., & Musiek, F.E. (2017). Practical guidelines to minimize language and cognitive confounds in the diagnosis of CAPD: A brief tutorial. Int  J Audiol, 56, 493-500

De Bonis DA. (2015). It is time to rethink central auditory processing disorder. Protocols for school-aged children. Am J Audiol, 24, 124-136.

Kraus, N., & Anderson, S. (2016). Auditory Processing Disorder: Biological Basis and Treatment Efficacy. In Le Prell CG et al. (eds.): Translational Research in Audiology, Neurotology, and the Hearing Sciences, Springer Handbook of Auditory Research 58, Springer International Publishing, Switzerland
DOI 10.1007/978-3-319-40848-4_3

Neijenhuis, K., Campbell, N.G., Cromb, M., Luinge, M.R., Moore, D.R., Rosen, S. & de Wit E. (2019). An Evidence-Based Perspective on “Misconceptions” Regarding Pediatric Auditory Processing Disorder. Front. Neurol. 10:287. doi: 10.3389/fneur.2019.00287

Vermiglio, A.J. (2014). On the Clinical Entity in Audiology: (Central) Auditory Processing and Speech Recognition in Noise Disorders. J Am Acad Audiol, 25, 904–917.

Wilson, W.J., & Arnott, W. (2013). Using different criteria to diagnose central auditory processing disorder - How big a difference does it make? J Speech Lang Hear Res, 56, 63-70.