Lip-reading: advances and unresolved questions in a key communication skill

Lip-reading, i.e., the ability to recognize speech using only visual cues, plays a fundamental role in audio-visual speech processing, intelligibility, and comprehension. This capacity is integral to language development and functioning; it emerges in early development, and it slowly evolves. By linking psycholinguistics, psychophysics, and neurophysiology, the present narrative review explores the development and significance of lip-reading across different stages of life, highlighting its role in human communication in both typical and atypical development, e.g., in the presence of hearing or language impairments. We examined how relying on lip-reading becomes crucial when communication occurs in noisy environments and, on the contrary, the impacts that visual barriers can have on speech perception. Finally, this review highlights individual differences and the role of cultural and social contexts for a better understanding of the visual counterpart of speech.