This article is republished with permission from Hearing Review
By Gail D. Chermak, PhD, Frank E. Musiek, PhD, and Jeffrey Weihing, PhD
In part 1 of this article, the authors presented their perspectives on a number of issues, including the importance of well-defined participants to maximize the validity of research and draw accurate conclusions, the veracity of CAPD as a diagnostic entity, the need to diagnose CAPD on the basis of efficient test batteries that are sensitive to the integrity of the central auditory nervous system rather than questionnaires or patient report, and approaches to minimizeg confounds in diagnosing CAPD. In part 2, the authors focus on the current state of the evidence regarding the gold standard and the research demonstrating the efficiency of individual central auditory tests and central auditory test batteries, the importance of differential diagnosis by a multidisciplinary team to determine the most appropriate, effective, and efficient treatment and management for individuals with CAPD, and the purpose and efficacy of auditory training to improve auditory processes. The authors conclude part 2, citing Dr. James Jerger’s three lines of converging evidence supporting the reality “of a relatively pure auditory perceptual disorder,” and noting Dr. Frank Musiek’s introduction of the term the auditory footprint that reflects the extensive nature of the auditory system.
The Gold Standard and the Purpose of Central Auditory Test Batteries
Some have argued that there is no gold standard CAPD diagnostic test battery.4 Consistent with medical terminology, which defines gold standard as a method or procedure that is widely recognized as the best available,59 it is our position that while there might not be a universally accepted gold standard, we have a considerable body of research demonstrating the efficiency of individual central auditory tests and central auditory test batteries based on performance of individuals with confirmed CANS lesions, including such lesions in children.34-38,60,61
It behooves audiologists to fully assess the nature of an individual’s auditory deficits using efficient central auditory tests and test batteries to determine the primary source(s) of those difficulties, be they cognitive, language processing, peripheral hearing loss, CAPD, or other potential sources. While there is some variance in diagnostic criteria (eg, number of tests, number of standard deviations) across US professional association guidelines, this simply reflects the need for additional research with participants with confirmed CAPD, like that conducted by Musiek et al60 and Weihing et al,40 to determine which tests, how many tests, and use of strict or lax criteria lead to the most efficient (ie, sensitive and specific) diagnosis. It would be completely inappropriate to abandon the use of CAPD as a diagnostic entity, as Wilson and Arnott62 proposed, due to the expected variability in diagnosis rates using different criteria and tests, especially when those criteria and/or tests diverge from evidence-based, professional association guidelines. Similarly, it is incongruous to fault CAPD tests because they do not predict listening or reading ability.63
The purpose of the CAPD diagnostic test battery is to identify and categorize auditory impairment or dysfunction, not to predict behavioral or academic deficits that may or may not be directly related to CAPD. Reading and listening are influenced by many variables, some of which are far removed from the auditory domain.64
The Role of Patient Report
There have also been suggestions that our field might be wise to dispense with the “CAPD label,” and instead describe presenting symptoms and outline a treatment approach.4 While patient symptoms and complaints are important and must be considered, diagnosis must be based on patient performance, not exclusively on patient report. Terminology used by patients may be vague. Moreover, consider the false negative rates possible among patients in denial or simply reticent to complain or divulge, as well as the false positives if diagnosis were based on patients’ or parents’ reports, based, for example, on general information they gleaned from the Internet. Let us not forget that diagnosis and labeling conditions allow for clear communication among professionals, suggesting at least in general terms the most appropriate directions for intervention, and that diagnosis is essential to secure coverage by insurers for services rendered.
Comorbidity and Intervention
CAPD often presents co-morbidly with other disorders, including language impairment, dyslexia, ADHD, and autism spectrum disorder; however, comorbidity does not imply unity or that one disorder encompasses the other. Differential diagnosis by a multidisciplinary team is required to accurately identify the presence of a disorder and determine intervention. A child diagnosed with CAPD—whether the disorder exists alone or comorbid with another disorder in another domain—should receive deficit-specific auditory interventions. Interventions for general developmental or cognitive disorders typically do not include direct auditory remediation, and if they do, that remediation is offered within the context of other treatments (eg, language, memory, etc) more specific to these other disorders. Understanding and disentangling the effects of cognition and sensory processing are critical for appropriate, effective, and efficient treatment and management of individuals.64
Efficacy of Auditory Interventions
Some have criticized auditory training as ineffective because it does not improve language or reading skills7,63,65; however, as noted above, reading and language processing are influenced by many variables, some of which are far removed from the auditory domain.64 The purpose of auditory training is to improve auditory processes, not improve language or reading skills. Auditory training, as a bottom-up strategy, aims to improve sensory processing of individuals with auditory skills deficits2,3,66 with the expectation that such improvement is likely to benefit real-life listening situations. Improvement in areas not directly related to the targeted auditory deficit may occur, but is not the primary goal of auditory training.67
Several recent studies have provided behavioral and electrophysiological evidence that auditory training can improve the auditory processing skills of children with CAPD or auditory-based learning problems.66-73 Tests and procedures are needed to enable early diagnosis of CAPD in children 7 years and younger to maximize the efficacy of intervention. To do so, however, requires research to find measures of sufficient challenge to the CANS that can still be completed by young children without such variability that makes impossible reasonable “cut off” norms. In the meantime, we and others have recommended a number of informal interventions for children who are at risk but have not yet been diagnosed with CAPD.64,74
James Jerger, PhD, asserted almost two decades ago that three lines of converging evidence support the reality “of a relatively pure auditory perceptual disorder.” Dr Jerger wrote:
First, there is the accumulation, over the past 30 years, of audiological evidence from children and adults with known lesions of the central auditory system…We can make the not unreasonable inference that when similar symptomatology is observed in children with listening problems, a problem in central auditory processing in the brain is at least suspect. Second, there has been an accumulation, especially over the past decade, of in-depth studies of the specific auditory perceptual deficits of children and adults whose only complaint is an apparent inability to hear well in difficult listening situations. Third, it is becoming increasingly clear that the unique listening problems of elderly persons may, in at least some cases, be related to age-related changes in the central rather than the peripheral auditory system. These three converging lines of evidence provide, I think, more than sufficient basis for accepting the reality of the phenomenon. They demonstrate that, across the entire age range, there are individuals who seem to display symptoms of the auditory perceptual disorder so concisely described by Myklebust.[393-394]75
As cited throughout this commentary, the research base providing the evidence supporting the three lines of converging evidence Jerger noted has grown exponentially since 1998. In more recent years, Jerger recognized (as we also discussed above) that central auditory tests may impose some cognitive load and he encouraged efforts to document auditory processing dysfunction, as well as underlying cognitive mechanisms, that could impact performance on central auditory tests.76
We have also recognized these same interactions,77 but as we cited above, accumulating research substantiates that:
- The extent of cognitive influence on central auditory processing is limited, and
- Cognition does not drive central auditory processing performance.
As noted by co-author Frank Musiek, who introduced the term “auditory footprint,” the auditory system is extensive: there is a considerable amount of neural substrate involved in processing auditory signals.78 While it is true that the auditory system shares neural substrate with other domains, which is the source of sensory-cognitive interactions, as well as overlapping clinical profiles and co-morbidity, we have clinically useful tools available to determine the primary source(s) of listening difficulties. In addition to efficient auditory behavioral tests, we encourage the use of auditory event-related potentials (AERPs), such as the P300, to assist in clarifying the interplay among auditory, cognitive, and linguistic processes. Certainly, the CANS of individuals who successfully perform the behavioral task and produce repeatable AERPs for a given auditory task must present high auditory integrity, reflecting both the integrity of the neural substrate underlying the behavioral task as well as the neural substrate of the pathways responsible for generating the AERP.77 Consistent with Jerger and Martin’s recommendation,76 we have offered in this commentary (and elsewhere as cited above) clinically useful and effective approaches to disentangle these interactions.
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CORRESPONDENCE can be addressed to HR or Dr Chermak at: email@example.com
About the Authors
Gail Chermak, PhD, is Professor of Audiology and Chair of the Department of Speech and Hearing Sciences, Elson S. Floyd College of Medicine, Washington State University Health Sciences Spokane; Frank E. Musiek, PhD, is a Professor in the
Department of Speech, Language, Hearing Sciences at the University of Arizona; and Jeffrey Weihing, PhD, is an Assistant Professor in the School of Medicine at the University of Louisville.
Citation for this article. Chermak GD, Musiek FE, Weihing J. Beyond controversies: The science behind central auditory processing disorder. Hearing Review. 2017;24(5):20-24.