| Sumario: | In natural environments, speech is typically a dynamic multisensory stimulus, characterized by both an auditory and a visual stream. Non-invasive functional neuroimaging techniques can reveal the neural processes underlying the integration of multisensory processes required for speech understanding in humans. Nevertheless, noise (from functional MRI, fMRI) limits the usefulness in auditory experiments, and electromagnetic artifacts caused by electronic implants worn by subjects can severely distort the scans (EEG, fMRI). Therefore, we assessed audio- visual activation of temporal cortex with a silent, optical neuroimaging technique: functional near-infrared spectroscopy (fNIRS). In this study, we use fNIRS to record supra-threshold auditory, visual and audiovisual (AV) speech-evoked activity from temporal cortex of normalhearing adults and postlingually deaf unilateral CI users. Activation effects were visible; auditory, visual and audiovisual (AV) speech stimuli evoked concentration changes for all sensory modalities in both cohorts (p < 0.001). Auditory stimulation evoked larger concentration changes than visual stimuli (p < 0.001). A saturation effect was observed for the AV condition. The observed multisensory enhancement of an auditory cortical channel can be plausibly described by a simple addition of the auditory and visual signals with saturation.
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