Diverse perspectives among interdisciplinary team members involved in the evaluation process may result in different diagnoses (e.g., CAPD, phonological awareness disorder, language processing disorder; McNamara, Bailey, & Harbers, 2008; Richard, 2012). Therefore, a team including both audiologists and SLPs is valuable in the diagnosis of CAPD and the identification of language disorders that occur in association with CAPD.
- Audiologists are responsible for evaluating and diagnosing problems in the reception and/or transference of auditory signals in the peripheral auditory system and the CANS.
- SLPs are responsible for evaluating and diagnosing problems in the linguistic processing of the auditory signal.
- Audiologists and SLPs share responsibility for diagnosing problems in the phonemic processing of the auditory signal (Richard, 2013).
The goal of screening for a CAPD is to identify individuals who are potential candidates for a more comprehensive central auditory testing battery. Screening can be accomplished using abbreviated test protocols. A number of questionnaires and checklists are available to probe auditory behaviors related to academic achievement, listening skills, and communication and to allow for systematic observation of listening behavior.
There is no universally accepted method for screening for CAPD. There remains a need for valid and efficient screening tools.
There is currently no reference standard for diagnosing CAPD (American Academy of Audiology [AAA], 2010; ASHA, 2005; Vermiglio, 2016). The audiologist, on the basis of clinical presentation and the findings of assessment measures, makes the diagnosis of CAPD. There may be difficulties associated with diagnosing CAPD due to its heterogeneous presentation and the frequent overlap in symptoms with language disorders.
Assessment data may be gathered by the audiologist, the SLP, and other members of the interdisciplinary team (e.g., psychologist, special educator). These assessment data may identify the presence of disorders with symptoms similar to CAPD (e.g., peripheral hearing loss, ADHD, speech-language disorder, cognitive deficits) and help determine if further CAPD testing is warranted. The order in which assessments are completed may vary depending on the referral source and the needs of the individual (e.g., symptoms, case history information).
Case history information is obtained by one or more professionals involved in the comprehensive assessment process and may include the following:
- Age, including chronological and mental age in early childhood and age-related decline in older adults
- Auditory/behavioral complaints (e.g., difficulty understanding speech in noisy or reverberant environments, difficulty localizing sound, difficulty hearing on the phone, difficulty following rapid speech, difficulty following directions, inability to detect humor or sarcasm [prosody], distractibility, inattention)
- Cognitive status and psychological factors (e.g., attention, memory, motivation)
- Cultural and linguistic background (e.g., native language)
- Educational achievement (e.g., academic, learning, reading difficulties)
- Family/genetic history
- Health status (e.g., medical history and medications, previous illness or injury)
- Hearing status (e.g., peripheral auditory system)
- Pre-, peri-, and postnatal course (e.g., congenital and early infancy events)
- Prior and current related therapies
- Risk factors and comorbidities (e.g., learning disabilities, traumatic brain injury [TBI], epilepsy)
- Social development
- Speech, language, and literacy concerns
Audiologic Assessment Components
Audiologic Evaluation of Peripheral Auditory System
An undiagnosed hearing loss may contribute to behavioral complaints. The presence of a peripheral hearing loss does not necessarily preclude the assessment of CAPD; however, it may differentially affect testing (Baran & Musiek, 1999). When evaluating an individual with hearing loss,
tests that use stimuli minimally affected by peripheral impairment should be used whenever possible (Musiek, Baran, & Pinheiro, 1990). In some cases (e.g., profound hearing loss), testing cannot be completed.
Peripheral auditory disorders include conductive, sensorineural, and mixed hearing loss, as well as auditory neuropathy (Norris & Velenovsky, 2014) and cochlear synaptopathy (i.e., hidden hearing loss; Liberman, Epstein, Cleveland, Wang, & Maison, 2016). These disorders can affect an individual's ability to hear and understand speech in background noise to varying degrees. See the assessment sections of ASHA's Practice Portal pages on
Hearing Loss—Beyond Early Childhood and
Permanent Childhood Hearing Loss for information on assessing the peripheral auditory system.
Audiologic Evaluation of Central Auditory System
The audiologist selects the appropriate CAP test battery, on the basis of findings from the case history, interdisciplinary assessment (e.g., results of language and cognitive assessments), and peripheral audiologic evaluation. Audiologists should have knowledge of the strengths and weaknesses of the individual tests, required response mode, and areas of the CANS to which each test is most sensitive (Chermak, Bamiou, Iliadou, & Musiek, 2017).
The test battery may be used to diagnose impairment in one or more neurophysiologic processes that occur as auditory signals travel through the CANS. The identification of specific deficits in the CANS can lead to targeted recommendations and treatment plans.
There are two types of audiologic evaluation measures that can be used to assess auditory processing skills.
- Behavioral—assesses the functional capabilities of the auditory system
- Auditory discrimination tests to assess the ability to differentiate similar acoustic stimuli that differ in frequency, intensity, and/or temporal parameters.
- Auditory temporal processing and patterning tests to assess the ability to analyze acoustic events over time.
- Dichotic speech tests to assess the ability to separate (i.e., binaural separation) or integrate (i.e., binaural integration) disparate auditory stimuli presented to each ear simultaneously.
- Monaural low-redundancy speech tests to assess the recognition of degraded speech stimuli presented to one ear at a time, including speech-in-noise, speech-in-competition, low-pass filtered speech, or compressed (rapid) speech.
- Binaural interaction tests to assess the ability to combine complementary inputs distributed between the ears, synthesizing intensity, time, or spectral differences of otherwise identical stimuli presented simultaneously or sequentially.
For a discussion of behavioral tests, see McNamara and Hurley (2017).
- Electrophysiologic—assesses neural processes in the central auditory pathway and provides information about the integrity of the CANS from the vestibulocochlear nerve (also known as the "auditory vestibular nerve" or "eighth cranial nerve") to the auditory cortex. These measures include auditory brainstem response (ABR), middle latency response (MLR), late cortical response, P300, and mismatch negativity.
Electrophysiologic measures may be useful in cases where behavioral procedures are not feasible (e.g., infants and very young children, non-English speakers), when there is suspicion of frank neurologic disorder, when a confirmation of behavioral findings is needed, or when behavioral findings are inconclusive.
Test Principles of an Audiologic Evaluation of the Central Auditory System
Principles applied when determining the composition of a central auditory test battery include the following:
- The test battery process should not be test-driven; rather, it should be motivated by the referring complaint(s) and the relevant information available to the audiologist.
- A central auditory test battery should include measures that are sensitive to the integrity of the CANS.
- Tests should examine different central processes, tasks, and the integrity of multiple levels and regions of the CANS.
- Most available behavioral central auditory tests are more appropriate for administration to children 7 years of age and older due to the challenging nature of the tasks and considerable performance variability.
- Communication checklists, language tests, and cognitive tests can be used to identify younger children that may be "at risk" for auditory difficulties (Moore et al., 2013). A diagnosis should be withheld until formal testing can be completed.
- Tests should generally include both nonverbal and verbal stimuli to examine different aspects of auditory processing and different levels of the auditory nervous system.
- Individuals who are medicated successfully for attention, anxiety, or other disorders that may confound test performance should be tested under the influence of their medication.
- Neuromaturation, subject state, and cognitive factors may affect the outcomes of many electrophysiologic procedures when used with children younger than 10 years of age. These measures need to be administered and interpreted accordingly.
- The duration of the test session should be appropriate to the individual's attention, motivation, and energy level. As with all behavioral tests, it is important to monitor the individual's level of attention and effort and to take steps to maintain motivation throughout testing.
- Referral to the appropriate professional(s) should be made when there is a suspected speech or language impairment or intellectual, psychological, or other deficit. In some cases, this referral should precede CAP testing to ensure accurate interpretation of test results. Comorbid diagnoses may preclude CAP testing (e.g., significant intellectual deficit, severe hearing loss).
- Test findings should be corroborated by relating them to the individual's primary symptoms or complaints (e.g., difficulty hearing with the left ear vs. the right ear, difficulty understanding rapid speakers, difficulty hearing in the presence of competing noise).
Interpretation of Central Auditory Diagnostic Test Battery
Norm-based interpretation of test results involves comparing the individual's performance to normative group data. Patient-based interpretation involves comparing the individual's performance to his or her own baseline performance. Comparison of results observed across disciplines can also be helpful with interpretation.
Examples of suggested diagnostic criteria and interpretations of test results include the following:
- Performance deficits are noted in one or both ears of at least two standard deviations below the mean on two or more tests in the battery (Chermak & Musiek, 1997).
- If poor performance is observed on only one test:
- Diagnosis may be withheld unless performance falls at least three standard deviations below the mean or the finding is accompanied by significant functional difficulty in auditory behaviors that rely on the process being assessed.
- The failed test—and other tests that assess the same process—should be re-administered to confirm initial findings.
- Administering and comparing results for several tests that measure the same auditory process can be used to look for patterns in auditory processing abilities and to support the findings of the evaluation.
- Inconsistencies across tests might signal the presence of a non-auditory confound, even when CAPD criterion is met. Likewise, pervasive deficits on all tests may signal a cognitive deficit or other non-auditory confound.
Interdisciplinary Contributions to Assessment
Various professionals may be involved in providing essential information during the assessment period.
Speech and Language Assessment
A comprehensive speech and language assessment includes assessment of spoken and written language; phonemic awareness (e.g., ability to segment and blend sounds in syllables and words); phonological working memory and phonological retrieval; and social communication. See ASHA's Practice Portal pages on
Spoken Language Disorders,
Written Language Disorders,
Speech Sound Disorders: Articulation and Phonology, and
Social Communication Disorders.
Psychoeducational or Cognitive Assessment
These assessments include tests of memory, executive functioning, and attention. An educational psychologist or cognitive psychologist may perform these assessments.
CAPD is an auditory deficit; therefore, the audiologist is the professional who makes the diagnosis (ASHA, 2005). "However, many disorders present behavioral characteristics similar to CAPD that can cause the listener to perform poorly on behavioral central auditory function tests and/or exhibit similar functional listening difficulties" (Ferre, 2014, p. 589). Interdisciplinary assessment and differential diagnosis of CAPD and related/comorbid disorders is important in the development of appropriate intervention strategies. See also De Wit et al. (2017).
SLPs diagnose cognitive-communication and language-related disorders (including language processing disorders) that may co-occur with CAPD. Differentiating between language and phonological processing disorders and CAPD requires collaboration between audiologists and SLPs.