Using fNIRS to study audio-visual speech integration in post-lingually deafened cochlear implant users
The aim of this experiment was to investigate differences in audio-visual (AV) speech integration between cochlear implant (CI) users and normal hearing (NH) listeners using behavioural and functional near-infrared spectroscopy (fNIRS) measures. Participants were 16 post-lingually deafened adult CI users and 13 age-matched NH listeners. Participants’ response accuracy in audio-alone (A), visual-alone (V), and AV modalities were measured with closed-set /aCa/ non-words and with open-set CNC words. AV integration was quantified by using a probability model and a cue integration model that predicted participants’ AV performance given minimal or optimal integration. Using fNIRS, brain activation was measured when listening to or watching A, V, or AV speech with or without multi-talker babble. For fNIRS, evidence of AV integration was measured using the principle of inverse effectiveness (PoIE) model (comparing the difference in activation in two brain regions between A and AV modalities in quiet and noise conditions). Behavioural AV integration was similar in the two groups for CNC words but poorer in the CI group compared to NH group for consonant perception. Our fNIRS data did not demonstrate any AV integration in either NH listeners or CI users, by testing the PoIE.
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