Integration of audiovisual speech perception: From infancy to older adults

One of the most prevalent and relevant social experiences for humans - engaging in face-to-face conversations - is inherently multimodal. In the context of audiovisual (AV) speech perception, the visual cues from the speaker's face play a crucial role in language acquisition and in enhancing our comprehension of incoming auditory speech signals. Nonetheless, AV integration reflects substantial individual differences, which cannot be entirely accounted for by the information conveyed through the speech signal or the perceptual abilities of the individual. These differences illustrate changes in response to experience with auditory and visual sensory processing across the lifespan, and within a phase of life. To improve our understanding of integration of AV speech, the current work offers a perspective for understanding AV speech processing in relation to AV perception in general from a prelinguistic and a linguistic viewpoint, and by looking at AV perception through the lens of humans as Bayesian observers implementing a causal inference model. This allowed us to create a cohesive approach to look at differences and similarities of AV integration from infancy to older adulthood. Behavioral and neurophysiological evidence suggests that both prelinguistic and linguistic mechanisms exhibit distinct, yet mutually influential, effects across the lifespan within and between individuals.