Audiovisual listening in cochlear implant users

Abstract

Cochlear implants (CIs)-widely considered the most successful neuroprosthetic devices-afford over half a million users worldwide access to sound perception following severe-to-profound hearing loss. However, visual cues remain vitally important for many CI users to interpret the impoverished auditory information that implants convey. While auditory-only speech understanding is well characterized in clinical outcome measures, relatively little is known about audiovisual (AV) speech comprehension in this cohort. In total, we recruited 116 normal hearing controls and 86 CI users (with 119 implanted ears) for a series of experiments that test: perceptions of the McGurk illusion and the sound-induced flash illusion (chapter 2), unisensory and multisensory listening in noise (chapter 4), speech-evoked cortical activity via near-infrared spectroscopy (chapters 3 and 4), and the underlying temporal processing for how auditory and visual speech and non-speech stimuli are integrated (chapter 5). The results of these studies suggest that CI users perceptually weight visual speech more highly than auditory speech-a strategy that we describe as "visuocentric listening." Given that clinical outcome measures for CI users are both highly variable and difficult to predict, an important factor for addressing this variability is to identify where in the auditory pathway it is introduced. This dissertation addresses central mechanisms of brain plasticity with a focus on multimodal sensory integration. The overall goal of this work is to better understand audiovisual integration and how it relates to speech comprehension of CI users, particularly in ecological listening conditions that are naturally multisensory. This knowledge is essential for our understanding of proficiency with a CI and, most importantly, how users can best utilize all sensory information to enhance speech intelligibility and improve quality of life.