Individual differences in cochlear implant users' audiovisual integration and links to speech proficiency

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PROJECT SUMMARY Cochlear implants (CIs) allow those with profound hearing loss to experience sound, some of them for the first time. This highly successful neuroprosthetic device can drastically improve speech comprehension for some individuals; however, postoperative speech proficiency remains highly variable and difficult to predict. Although visual orofacial articulations play a crucial role in verbal communication both before and after cochlear implantation, clinical measures assessing implant candidacy and monitoring postoperative performance are currently limited to auditory-only speech measures. As a result, current assessments may be providing only a partial picture of aural rehabilitation with a CI. This proposal asserts that the degraded sound provided by a CI presents a unique computational challenge for the central nervous system and that, for speech in particular, visual information is almost certainly recruited to increase comprehension. We believe that extending performance assessments to include the visual domain increases the ecological validity of speech intelligibility measures and may also reveal an additional variable in successful outcomes–the integration of sensory streams to achieve multisensory enhancement. Our first aim is to characterize audiovisual integration in a cohort of postlingually deafened CI users. This includes unisensory and multisensory speech perception at the phoneme and word level. Doing so enables us to relate illusory tasks (i.e. the McGurk effect) to proficiency at comprehending words embedded in speech-like noise–a challenging listening environment for nearly all CI users, and one where effective sensory integration is key. Our second aim is to investigate the neural basis of variability in audiovisual integration seen in both our preliminary work and in the literature. Functional Near Infrared Spectroscopy (fNIRS) is a noninvasive imaging technique that is safe for all CI users. Hemodynamic responses measured with this optical imaging technique will allow us to determine whether auditory, visual, and audiovisual stimuli activate the temporal lobe differently between 1) CI users and NH controls, 2) proficient and non-proficient CI users, and 3) McGurk illusion perceivers and non-perceivers. The goal of this proposal is to better understand atypical audiovisual integration and how it relates to variability in both neural processing and speech comprehension in cochlear implant (CI) users. This knowledge is essential for our understanding of speech proficiency with a CI and, most importantly, for how users can best utilize all sensory information to enhance intelligibility and improve quality of life.