Matthew J. Goupell, Ph.D. - US grants

The proposed research aims to combine the areas of speech understanding, binaural hearing, sound localization, and cochlear implants (CIs). The proposed research Is novel because it aims to understand the advantages, capabilities, and limitations of bilateral CIs under controlled multi-electrode stimulation and of more realistic auditory stiniuli that are modulated in time. Controlled multi-electrode stimulation research and research on binaural modulated stimuli has only started recently. Research on this topic Is a logical next |step in bilateral CI researx;h; moving to less controlled and more complex auditory stimuli. It would help provide understanding of an important advantage of bilateral Implantation, that of understanding speech in noisy environments. the main hypothesis driving this work Is that current CI systems introduce fundamental differences from [the Wealthy auditory system, and these differences alter important acoustic information enough to significantly diminish any binaural hearing advantage. These differences include, but are not limited to: interjaural tonotopic place mismatch, unequal interaural neural survival, varying loudness growth between indi\>idual electrodes and ears, channel interactions, partial or complete lack of interaural sound fusion, and lack;of travelling wave of an acoustic stimulus along the basilar membrane. Some of these limitations may be compensated by different processing schemes or changes to the physical devices. Other limitations are intrinsic to electrical stimulation and cannot be compensated with the current generation of CIs. The mentored phase of the proposed research focused on single-electrode binaural signal detection and sound localization. The independent phase of the proposed research will focus on multi-electrode binaural signal [detection, sound localization, and understanding speech in realistic listening environments. The ultimate aim is to provide a binaural advantage to bilateral CI users' ability to localize sounds and to understand speech in difficult listening environments, like noisy or reverberant rooms. This research has potential to guide the clinical implementation of a Unlfonn method of bilateral fitting of CIs.

ABSTRACT: A cochlear-implant (CI) restores high levels of speech understanding to individuals across the lifespan. However, a gap in knowledge exists because we do not understand how aging affects hearing in CI users. Aging is associated with changes at multiple levels of the brain, thereby making it difficult to determine if the poorer auditory performance that occurs with advancing age is a result of changes in the auditory periph- ery, central auditory neural structures, cognition, or a combination of the three mechanisms. Since a CI by- passes the cochlea, we propose an innovative approach for investigating aging and hearing by using a human CI model. Using age (younger vs older adults) and group (CI vs normal hearing, NH) comparisons will allow us to determine the age-related contributions of cochlear and central factors to hearing. The long-term goals of this project are to (1) determine how to maximally remediate age-related auditory and cognitive processing def- icits with a CI and (2) better understand the biological effects of auditory aging. The objective of this grant is to establish age as an observable and significant factor for auditory temporal processing in CI users. Our central hypothesis is that advancing age significantly degrades central temporal processing and speech understanding abilities in CI users, which is independent of the age-related peripheral hearing loss that occurs in acoustically- hearing subjects. The rationale for the proposed research is that there is a rapidly increasing number of older adults that elect to receive a CI, but there is essentially no research on this specific population that fully utilizes the available array of research tools to study hearing in this population; our field arguably has minimal direct evidence and understanding of age-related changes to auditory processing of electrical stimulation. With strong preliminary data in hand, the central hypothesis will be tested by pursuing three specific aims: (1) De- termine the extent to which temporal processing abilities decrease with age using highly-controlled and simple (non-speech) stimuli in CI subjects; (2) Determine the extent to which age-related temporal processing factors affect speech understanding in CI subjects; and (3) Determine the extent to which aging affects cortical tem- poral encoding of speech in CI subjects. This approach is innovative because: (1) the topic of aging in older CI users is an under-studied area and (2) by using a CI model, we will better understand the biological factors un- derlying how aging affects hearing. Our outcomes will provide a significant positive impact on hearing and un- derstanding speech with a CI, which will increase CI users' quality of life.

The proposed supplement is relevant to the ?Alzheimer's-focused administrative supplements for NIH grants that are not focused on Alzheimer's disease? because it will enhance our understanding of how to evaluate for Alzheimer's Disease and other related dementias in people with cochlear implants (CIs) ? bionic devices that partially restore hearing to people with moderate-to-profound hearing loss. Previous studies provide limited value in the general area of cognition in older CI users because of methodological limitations: (1) using cognitive measures with some degree of auditory demand; (2) using limited measurements and screeners in the clinic that are prone to inaccuracy; and (3) excluding participants with possible Alzheimer?s Disease (i.e., possible selection bias). This poor methodology has generated a clear gap in knowledge, where the mechanisms underlying poor cognitive performance in older CI users are unknown. The long-term goals of this supplement will move the current line of research to: 1) better understanding of the prevalence of cognitive impairment and Alzheimer's Disease in older CI users, 2) better understanding of the potential for CIs to diminish cognitive impairment and Alzheimer's Disease, and 3) development of appropriate evaluation tools for cognitive impairment and Alzheimer's Disease in older CI listeners by addressing potential sensory (hearing and vision) deficits. The short-term goals of this supplement are to create a team of hearing scientists (from the PI?s lab; experts in CIs, hearing, and aging) and medical professionals (experts in diagnosing Alzheimer's Disease and clinical audiology) to learn how neuropsychological evaluations are best performed in CI users, how our current hearing tests can be performed in CI users with cognitive impairment, and produce data that will be used for future grant applications on the topic. Our central hypothesis is aging and degradation of auditory input from the CI causes effortful speech understanding, which limit cognitive reserves and diminish cognitive abilities. We plan to test our central hypothesis via one specific aim: Determine how poor cognitive scores in older CI listeners are a result of clinically diagnosed age-related cognitive impairment, listening effort, and/or testing modality. Our expected outcome is that we will better understand the impacts of CI use on cognitive processing, cognitive decline, dementia, and Alzheimer?s Disease. This outcome is expected to have a significant positive impact as it will help uncover the mechanisms causing relatively poor cognitive and speech understanding performance in older CI users. Our successful results will provide guidance to clinicians to prevent, assess, and treat cognitive decline and Alzheimer?s Disease in CI users.