Audiovisual integration in phonetic perception without visual awareness and its age-related decline.

Speech is essential for everyday communication during the entire lifespan of an individual. Visual lip movement can support auditory speech perception, particularly in noisy environments and among older adults with hearing impairments. This study investigated whether visual information is integrated with auditory phonetic information without visual awareness and how this process changes with age. Participants heard low signal-to-noise monosyllables (/ba/, /da/, or /ga/) accompanied by visual lip movements under either visible or invisible conditions, the latter being achieved using continuous flash suppression. Three types of visual stimuli were used: incongruent (eliciting the McGurk effect), congruent, and no-lip movements. Participants identified the syllable they heard on each trial. Under continuous flash suppression, stimulus visibility was assessed via subjective reports in Experiment 1 and a four-alternative choice line localization task in Experiment 2. In both experiments, the McGurk effect was observed in both age groups under the visible conditions but only in younger adults under continuous flash suppression. These findings suggest that younger adults can integrate visual and auditory phonetic information without visual awareness, whereas this process may decline with age and be replaced by a more effortful, conscious mechanism-at least under low auditory signal-to-noise conditions. (PsycInfo Database Record (c) 2025 APA, all rights reserved).