Neural Mechanisms of Spatial Auditory Attention with Magnified Interaural Level Differences

PROJECT SUMMARY/ABSTRACT Everyday listening requires auditory selective attention: the ability to direct attention to a single sound source (e.g., your friend talking to you) amongst competing sources (e.g., other patrons at a restaurant). Spatial information is particularly useful for identifying and directing our attention toward a sound source, and the perceptual benefit we receive from the spatial separation of sound sources is called spatial release from masking (SRM). Two pieces of acoustic information are useful in SRM: (1) the difference in the time of arrival of a sound between the two ears, or the interaural time difference (ITD), and (2) the difference in the intensity level of the sound at the two ears, or the interaural level difference (ILD). Normal hearing (NH) listeners rely on both ITD and ILD information to successfully deploy spatial auditory selective attention. However, bilateral cochlear implant (BiCI) users do not have robust access to ITDs, as their devices do not provide temporal information at a fine enough grain. Since ITDs are considered the dominant spatial cue, BiCI users demonstrate poorer spatial hearing outcomes than their normal hearing peers. Instead, they must rely on ILDs. In this project, we propose to remediate spatial hearing in BiCI users through ILD Magnification. This strategy enhances source lateralization by applying larger-than-natural ILDs. ILD Magnification has been shown to improve performance on spatial hearing tasks in both NH listeners listening to vocoded sound and BiCI users, but the neural mechanisms underlying this benefit remain unclear. Here, we will test whether ILD magnification provides a benefit to sound source segregation or to spatial selection. We will measure known neural signatures of auditory attention using functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG) while subjects complete a spatial attention task. These experiments will be conducted both in NH listeners (Aim 1) and BiCI users (Aim 2). These two aims will affirm the perceptual benefits of ILD magnification and identify the neural mechanisms underlying these benefits. This project offers essential training opportunities for the proposed fellow in his career as an auditory neuroscientist. This includes gaining experience in fNIRS and EEG data collection, as well as proficiency in signal processing and statistical analysis. Additionally, there will be hands-on experience in recruiting and working with cochlear implant patients and exposure to clinical procedures. The training will also encompass professional development, including teaching, mentoring, and science communication. The proposed work will contribute substantially to our knowledge of the relationship between spatial acoustic information and networks of auditory attention. Simultaneously, this project introduces a new method for improving spatial hearing outcomes in bilateral cochlear implant users, working toward the NIH's goal of the application of knowledge to improve health. Overall, the studies described here will improve our understanding of the neural mechanisms underlying spatial hearing and implement a possible solution for those with cochlear implants.