Ross K. Maddox, Ph.D. - US grants

DESCRIPTION (provided by applicant): Difficulty listening to one person speak in the presence of many other competing sounds is a significant problem for many people, even some with normal hearing test results. Understanding speech in these adverse conditions improves markedly when sound sources are spatially separated, an effect known as spatial release from masking. If a person looks toward a talker of interest, seeing that person's face provides visual spatial and temporal information that can improve understanding even more, making this a common and important audiologic rehabilitative strategy. However, recent work performed by the candidate hints at a perceptual benefit from the mere act of directing gaze toward that sound. Furthermore, despite wide acceptance of the importance of spatial hearing and visual information to auditory selective attention, the interplay between these processes is largely unexplored and little work has been done to characterize how differences in spatial hearing abilities among individual listeners affects their ability to listen in noisy situations. In the mentored training phase of this research program, the candidate will perform two experiments exploring the impact of eye gaze and visual information while receiving training in visual neuroscience. He will first build on his previous findings by measuring the effects of directed eye gaze on spatial release from masking in a multiple- talker speech task (Aim 1). Next he will assess the low-level benefits of spatial and temporal visual information to selective attention in task that uses stimuli that exhibit some of the basic characteristics of speech but are non-linguistic in nature (Aim 2). After progressing to the independent phase of the award, the candidate will examine the range of auditory spatial abilities in normal hearing listeners and the effects of binaural deficits on listening performance in multiple-talker environments, then whether deficits can be ascertained electrophysio- logically, and ultimately if spatial deficits change the way listeners leverage visual cues (Aim 3). This research is clinically relevant because it will provide important insights into listening in noise: how spatial hearing deficits affect understanding in the individual, and what specific visual factors underlie important audio-visual coping strategies. The work will facilitate the candidate's immediate career goals of becoming an audio-visual researcher with the necessary substantial experience in both sensory modalities and the ability to execute experiments using measures of both behavior and brain activity. Training during the mentored phase will be supplemented by formal coursework in the physiology and neuroscience of the visual system, meetings with the co-mentor's visual neuroscience group to learn the current literature and critically evaluate the candidate's own work, and by learning nonscientific skills such as mentoring and lab management from the primary mentor as well as institution-wide seminars. The research performed and training provided during this award will be critical for the candidate's long-term goal of directing a lab whose research yields important new insights into how people understand and navigate their sensory world.

Project Summary/Abstract The goal of this proposal is to develop a new kind of frequency-specific auditory brainstem response (ABR) exam?the parallel ABR (pABR)?which is designed to provide faster, more informative diagnoses. Measuring the ABR involves presenting brief sounds over a range of frequencies and intensities and recording the brain's response through electrodes placed on the head. Approximately 150,000 infants are referred for a diagnostic ABR exam each year in the United States. The results of this exam inform important clinical decisions that affect the child's long-term speech and language development. To ensure good recording quality in pediatric use, the test is performed while the patient sleeps. There are many measurements to make in a single exam, and if the patient wakes up early then the test is cut short, leading to incomplete diagnoses or the need to return for a second visit, which may result in attrition and delayed access to sound. In some patients it may be necessary to use sedatives or general anesthesia to ensure good measurements, but recent studies have found that early exposure to such drugs may damage the developing brain and cause cognitive problems later in childhood. Our preliminary data show that the pABR provides rapid measurement that could address traditional techniques' major shortcoming. In this project we will run experiments that test key aspects of the pABR which are essential to understand before its translation to the clinic. These experiments will be run in adult subjects for three reasons. First, it is a new technique whose feasibility needs to be demonstrated before testing in infants. Second, we will be able to determine the accuracy of the pABR by comparing its results to the behavioral tests of hearing loss that are possible in adults. Third, ABRs mature at a young age, making adults a reasonable model. In Aim 1 we will test the hypothesis that specific combinations of stimulus parameters (how fast they are presented and their intensity) will provide optimal signal-to-noise ratios and measurement times. In Aim 2 we will test the hypothesis that the pABR will accurately predict hearing thresholds and be faster in clinical use than traditional ABR. We will recruit people with hearing ranging from normal to severe loss. We will test pABR accuracy by comparing its threshold predictions to behavioral audiograms. We will test speed by comparing acquisition time of pABR to that of standard diagnostic ABR. In Aim 3 will test the hypothesis that the pABR provides cochlear place specific responses, particularly at high stimulus levels where these are hard to obtain due to spread of excitation. We will employ established methods using high-pass masking noise to determine this. Traditional ABR is an important and necessary diagnostic tool for pediatric audiology, but it carries significant time and financial cost. The aims of this project will answer basic questions about the pABR in adult subjects with normal hearing and with hearing loss. These studies will pave the way for the pABR's future translation, which would positively impact thousands of infants and children each year.