The Bench-to-Bedside Approach for Central Auditory Processing Disorder
Academy Editor-in-Chief Erin Schafer, PhD, spoke with Drs. Musiek and Chermak about the diagnosis and treatment of CAPD as well as the Third Global Conference on Central Auditory Processing Disorder: Synergies Between Lab and Clinic, at AAA 2019, March 30, in Columbus, Ohio.
Central auditory processing disorder (CAPD) continues to be of great interest to many audiologists given the complex interconnectivity of the central auditory nervous system. The diagnosis and treatment of CAPD continues to evolve with a blending of scientific evidence from audiology, neuroscience, speech-language pathology, psychology, and many other fields. I had the distinct honor of interviewing Dr. Musiek and Dr. Chermak, who will share with us their thoughts on the current state of CAPD as well as give us an introduction to the slate of speakers for the upcoming Third Global Conference on Central Auditory Processing Disorder.
- What is your current working definition for this complex disorder?
CAPD is a disorder of the central auditory nervous system (CANS) that can occur in adult and pediatric populations. The predominant deficits characterizing CAPD manifest in the auditory modality. As a result, deficits are present in the perceptual processing of auditory stimuli in the central nervous system, and in the underlying neurobiological activity that gives rise to the electrophysiologic auditory evoked potentials and behavioral tests.
- Why is the word "central" an integral component of the CAPD acronym?
We understand why some prefer the term APD or auditory processing disorder given that processing begins in the cochlea and continues in peripheral neural sites (i.e., VIII nerve). We prefer CAPD because it refers to the overall area of the auditory system (CANS) from which the preponderance of the processing deficits we measure are derived. In other words, including "central" in the name of the disorder ensures the terminology is "ecologically" valid and an "operational" definition of how processing actually occurs. Moreover, the word central in the term CAPD suggests how we should go about measuring 'auditory processing.'
We believe our test battery provides reasonably good insight as to the level(s) in the CANS where the dysfunction is likely originating (or at least contributing to the dysfunction). Of course, our behavioral CAP test battery typically cannot identify the specific site of lesion in the absence of radiology or surgery, but what behavioral (or electrophysiological) test definitively can? Many examples are out there—but for example—the pure tone audiogram doesn't tell us as much as we thought about the health of the apical end of the basilar membrane. The point is well taken that the VIII nerve is part of the peripheral auditory system, but the audiogram is not the best measure of its integrity. While it is true that auditory processing occurs in the cochlea, it can require measures other than the audiogram to reveal the source of abnormal or absent optoacoustic emissions (OAEs) in the presence of a normal audiogram. And yes, we would agree APD can include CAPD (as argued by the Bruton group in 2000), but if the processing deficits are truly stemming from more central neuroanatomy, then the term CAPD better communicates the type of intervention that will be required. Finally, there is more than abundant basic and clinical research showing that, when the CANS is damaged with the periphery intact, there are auditory symptoms that ensue, indicating the neural substrate that is involved, which is not peripheral, yields these symptoms.
- Do you see CAPD as a distinct diagnosis, or can it co-exist with other diagnoses, such as a language disorder or autism spectrum disorder?
CAPD is a distinct diagnosis; however, co-morbidity is common due to brain organization. Brain organization and function is comprised of nonmodular, temporally coupled, interfacing, polymodal, overlapping, and interconnected, synchronized networks. In short, the auditory system is extensive and overlaps other systems. This brain organization underlies co-morbidity and complex clinical profiles. It also underlies a great many opportunities for Intervention by a multidisciplinary team.
CAPD may contribute to, be associated with, or co-exist with difficulties in higher-order language, learning, cognitive and communication function due to shared neuroanatomical substrates and vasculature, parallel/distributed processing, temporal coupling and interactions across brain regions, and other factors. However, true CAPD is not the result of dysfunction in other modalities (not caused by multimodal or higher-order, global disorders). Rather, true CAPD results from CANS dysfunction.
- Are there any new clinical tests that may be used in the test battery for diagnosing CAPD?
There are a few fairly recent tests (within the last 10 years) with confirmed efficiency that many audiologists have incorporated in their test batteries. For example, the Listening in Spatialized Noise-Sentences test and Gaps-in-Noise (GIN) test. The LiSN-S test1 assesses the listener's ability to use spatial cues as well as cues from different voices to identify target speech stimuli in noise. The GIN, of which there are several that are clinically available2, is a test of temporal resolution that measures the ability of the listener to discern short, silent intervals usually imbedded in a broadband noise. Both tests have become popular as components of a central auditory test battery. Although not yet commonly used in clinical test batteries, we have seen published reports of hybrid—behavioral/ electrophysiological approaches—in which auditory evoked potentials (AEPs) are recorded in response to stimuli used in behavioral CAP tests, as well as recording AEPs while subjects actually perform a central auditory test. These types of approaches might move from bench to bedside in the not too distant future.
- What are the most exciting bench-to-beside findings over the past few years?
Perhaps the fact that more audiologists are becoming aware of and accepting the concept that the pure tone audiogram has significant limitations, especially in regard diagnosing central auditory disorder. Also, schizophrenia and auditory hallucinations may have as their basis an anatomical correlate resulting, at least in part, from alterations of the auditory cortex. Audiologists may serve an important role in evaluating these patients.
In addition, the interaction between cognition and CAP requires audiologists to fully assess the status of research participants as well as utilize clinical approaches that minimize such interactions, including involving multidisciplinary evaluations of patients with complex clinical profiles. See for example Brenneman et al.3
The auditory neuroscience literature reminds us that neurobiology guides central auditory test development and guides interpretation of auditory performance. This literature also demonstrates the need for early and aggressive intervention to exploit neuroplasticity--during sensitive periods, mere exposure to auditory enrichment can result in large functional changes in the CANS. Finally, auditory neuroscience makes clear that the shared neural substrate across domains creates multidisciplinary intervention opportunities.
- Are there any new promising treatments for CAPD in children or adults?
Intensive auditory training remains the most promising treatment to mitigate central auditory processing (skill) deficits. Hearing assistance technology should also be considered to enhance the acoustic signal and listening environment. However, because central auditory processing depends on many systems and processes, comprehensive, 'bottom-up' and 'top-down' intervention approaches are needed to maximize effectiveness. Auditory training strengthens auditory processes—as derived from our understanding of neurobiology (for example the auditory training technique known as the 'DIID'—dichotic interaural intensity difference training). Neurobiology also directs us to harness central resources to complement auditory training by utilizing multimodal, crossmodal, and supramodal neural interfaces.
- Can you give us a preview of the Third Global Conference on Central Auditory Processing Disorder: Synergies Between Lab and Clinic, which will be held on March 30, 2019 at the Greater Columbus Convention Center?
This program as, indicated by its title, promises to be an excellent mixture of concepts in applicability as well as new, foundational scientific information in regard to CAPD. The conference's global array of presenters and participants should create a broad-based learning environment for all.
Some of the conference highlights include:
- The keynote address by Vivian Iliadou, MD, PhD—An Evidence-Based Approach to APD
- Podium presentations by
- Barbara Shinn-Cunningham, PhD—Individual Differences in Temporal Processing and Their Influence on Everyday Auditory Perception
- Frederick (Erick) Gallun, PhD—Laboratory Testing Gets Portable: Using iPads to Test Auditory Processing Abilities
- Frank Musiek, PhD—Auditory Hallucinations: A New Frontier in Central Auditory Assessment?
- Panel discussions by
- Teri Bellis, PhD—CAPD in College Students: Diagnosis to Successful Intervention
- Jeanane Ferre, PhD—Why Training Auditory Specific Skills IS Educationally Relevant
- Dimitra Loomis, AuD—From Science to Practice to Community
- Eliane Schochat, PhD—From Lab to Clinic: What a Long Path
- Frank Musiek, PhD, and Gail Chermak, PhD—Experts ask the experts
- Excellent scientific posters
- The closing keynote address by Mridula Sharma, PhD—The Role of Auditory Processing in Functional Outcomes Across a Life Span
Thank you Drs. Musiek and Chermak for providing answers to these burning questions about CAPD. Based on the synergistic topics and slate of speakers for the Third Global Conference on Central Auditory Processing Disorder, it promises to be an excellent program to which we will look forward to attending.
Frank Musiek, PhD, is a professor and the director of the NeuroAudiology Lab, Department of Speech and Hearing Sciences, University of Arizona. He has made notable research and clinical contributions in CAPD, functional neuroanatomy and auditory evoked potentials.
Gail D. Chermak, PhD, is chair of the Department of Speech and Hearing Sciences and Interim Associate Dean for Faculty Affairs, Elson S. Floyd College of Medicine, Washington State University Health Sciences, Spokane, Washington. She is recognized internationally for her contributions to the diagnosis and treatment of central auditory processing disorder.
1Cameron S, Dillon H. (2007) Listening in Spatialized Noise - Sentence Test (Version 2.400) [Computer Software]. Sydney. NSW: National Acoustic Laboratories.
2Gaps in Noise (GIN) [Compact Disc]. (2015) Retrieved from https://auditec.com/2015/09/22/gaps-in-noise-gin/
3Brenneman L, Cash E, Chermak GD, et al. (2017) The relationship between central auditory processing, language, and cognition in children being evaluated for central auditory processing disorder. J Am Acad Audiol 28(8):758-769