Assessment and Rehabilitation of Blast-Related Auditory Processing Disorders

Beyond hearing loss caused from damage to the outer, middle, and/or inner ear, Service members (SMs) with a history of blast exposure or traumatic brain injury (b/TBI) have demonstrated auditory deficits that impair receptive communication and executive functioning. When these patients have normal to near-normal audiometric thresholds and report difficulties understanding speech in complex environments, military and Department of Veterans Affairs audiologists have generally accepted the convention of labeling this condition as a type of Central Auditory Processing Disorder (CAPD) or b/TBI CAPD. As a result of b/TBI CAPD, patients may experience difficulty understanding speech in adverse listening conditions, integrating auditory and visual information, and dual-tasking in efforts requiring executive function. Three recent studies conducted at Walter Reed National Military Medical Center (WRNMMC) found that as many as 40%-45% of listeners with a history of deployment-related blast exposure who would be identified as 'normal hearing' on the basis of their pure tone thresholds fell in the bottom 5% of normal performance on tasks involving the detection of spatial cues and the comprehension of fast speech in reverberation. Further evidence collected at our laboratory suggests that high functioning b/TBI personnel have difficulty integrating auditory and visual information when engaged in complex tasks.

The current study extends these findings by addressing the role of executive attention in multimodal dual-tasking by using speech to assess communication abilities in complex listening environments and by examining the viability of b/TBI CAPD rehabilitative measures. The proposed research effort will first develop tools that identify speech communication and executive functioning deficits in real-world environments, and second evaluate the effectiveness and the feasibility of treatment protocols designed to address auditory complaints of listeners with b/TBI. The tools developed to better identify and rehabilitate b/TBI CAPD SMs will provide insight into the underlying deficiencies contributing to auditory processing deficiencies as well as evidence guiding future clinical standards of care.

One of the greatest challenges in the assessment and treatment of b/TBI CAPD is establishing a link between clinically available standardized tests of central and peripheral auditory function and the actual performance deficits that b/TBI listeners complain about having in complex real-world listening environments. The clinically available tools evaluating CAPD typically focus on one area of clinical dysfunction at a time, rather than on tasks that require the simultaneous integration of complex information across multiple sensory modalities. The current proposal will use the Computer Assisted Rehabilitation Environment (CAREN) to assess multimodal integration and executive function in dual-tasking paradigms and further assess complex communication task performance in real-world environments identified as being most difficult for b/TBI CAPD listeners. To address the lack of evidence identifying the best treatment approaches for b/TBI CAPD, we will evaluate rehabilitative strategies with immediate and direct clinical application. While there is some evidence suggesting pediatric patients with CAPD can benefit from the use of low-gain hearing aids and that auditory training programs may improve speech perception for CAPD patients, the logistical feasibility and the optimal parameters for these strategies in the b/TBI CAPD population are not established. We expect patients to immediately benefit from improved fitness for duty evaluations and use of hearing aids, and within 3-5 years for application-based auditory training modules. Ultimately, the current proposal will provide direct insight to improve clinicians' ability to recognize and classify b/TBI CAPD and contribute evidence to support feasible recommendations for rehabilitation with minimal risk to SMs. It is this evidence that will best characterize b/TBI deficits that are reported but sometimes not identified with standard clinical tests and that will further provide insight into optimal management of b/TBI CAPD.