Fawen Zhang - US grants

DESCRIPTION (provided by applicant): Temporal processing properties of the auditory system in cochlear implant users Description of the Project One of the major challenges in cochlear implants (CIs) is the large variability in CI patients'speech perception performance. Recent studies have shown significant correlations between this variability in speech performance and CI patients'psychophysically measured temporal processing. Besides these behavioral measures, the temporal properties of neural responses to repeated stimuli provide important information about the auditory system's processing of temporal cues in sounds. It is unclear how objectively measured neural responses are related to behavioral measures of temporal processing and speech perception. The goal of this project is to investigate the temporal properties of four types of auditory evoked potentials (AEPs) in CI patients: 1) the electric compound action potential (ECAP), 2) the electric auditory brainstem response (EABR), 3) the electric late auditory evoked potential (ELAEP), and 4) the acoustic LAEP. We will compare neurophysiological and behavioral measures of temporal processing and speech perception abilities in CI users. We hypothesize that the temporal properties of the LAEP are better correlated to behavioral measures than those of the ECAP and the EABR. Theoretically, the results from the proposed study will provide important insights into the large variability in CI patients'speech understanding. Practically, the proposed research will help to identify appropriate electrophysiological measures that can be used to objectively assess CI benefits. This research may lead to future efforts toward improving the temporal representation of sounds in CI users. PUBLIC HEALTH RELEVANCE: This project examines how the auditory system of cochlear implant users processes information of sounds over time using electrophysiological and behavioral methods. It will provide important insights into why some patients receive greater benefits than others from implantation. It will also lead to the identification of the most promising electrophysiological tools that can be used to objectively measure outcomes of implantation or the efficacy of rehabilitation strategies.

One of the major challenges in cochlear implants (CIs) is the large variability in CI patients? speech perception performance. There are currently no objective measures that can be used clinically to predict speech outcomes of CI users who cannot reliably perform tests requiring behavioral responses. Moreover, the lack of understanding of the large variability on CI outcomes is a barrier to customized rehabilitation. Our long-term goal is to understand the neural correlates of the variability in CI speech outcomes and to explore if these neural responses can serve as objective measures to assess and predict CI outcomes. Previous studies have shown that the capability to detect frequency changes of sound measured using psychophysical methods is highly correlated with speech outcomes in CI users. In fact, the ability to detect frequency changes may play an important role in the performance on pitch-related tasks that typically challenging for CI users such as speech perception in noisy environments. The acoustic change complex (ACC) is a type of cortically-generated auditory evoked response evoked by the change in the frequency, amplitude etc. of an acoustic stimulus. Recording the ACC does not require any behavioral response from an individual. The objective in this R15 project is to examine the predictive value of the ACC in CI adult users. In this project, we will determine the correlation between the ACC and behavioral performance of frequency change detection and speech perception when the stimuli are presented without a background noise (Aim 1) and with a background noise (Aim 2), respectively. Adult CI users and normal hearing (NH) controls will have their speech recognition abilities assessed and they will undergo electroencephalographic recordings while they perform the psychoacoustic task of identifying stimuli containing frequency changes. The ACC measures (peak amplitude, latency, and brain activation patterns) will be compared with the behavioral measures of frequency change detection and speech outcomes. The central hypothesis is that the ACC measures are significantly correlated to CI users? behavioral performance in frequency change detection and speech recognition abilities. This project will have significant implications: 1) the results from the proposed study will provide important insights into the large variability in CI patients? speech understanding, 2) the proposed research will help to identify electrophysiological measures that can be used to objectively assess CI benefits. Such objective measures are especially valuable for individuals who cannot reliably perform behavioral tests, and 3) this research may lead to future efforts toward improving the cortical encoding of frequency changes in CI users to maximize CI benefits.