Seminars in Hearing Research at Purdue (SHRP)

Title: Influence of Visual Speech Cues on Auditory Subcortical and Cortical Responses in Normal and Impaired Ears

Abstract: The human brain can integrate information from different sensory modalities to produce a unified representation of the external world. Temporally congruent auditory and visual stimulation facilitates multisensory perception and integration, allowing us to better process and understand the information presented to us, especially in the presence of background noise and for individuals with hearing difficulties. The influences of visual speech cues on behavioral speech perception are vastly studied. Functional magnetic resonance imaging and electrophysiological studies have mostly evaluated auditory cortical responses. Little is known about the influence of visual speech production cues on the auditory brainstem phase-locked ensemble responses in normal and individuals with sensorineural hearing loss. To address this knowledge gap, we evaluated the effects of congruent- and incongruent-audiovisual (AV) speech on scalp-recorded brainstem frequency following response (FFR) and the cortical acoustic change complex (ACC). For the FFR, both phase locking to envelope periodicity (FFRENV) and to the temporal fine structure (FFRTFS) were evaluated. I will present our initial results showing that visual speech cues do influence evoked responses at both cortical and brainstem levels, albeit differently. These results appear to suggest that neural activity relevant to audio-visual integration may be already emerging at the brainstem level. Thus, these measures have the potential to be developed as clinical metrics for evaluation of audio-visual integration, and as measures to evaluate hearing-aid outcomes and prognosis.