Development of the Mechanisms Underlying Audiovisual Speech Perception Benefit.

The natural environments in which infants and children learn speech and language are noisy and multimodal. Adults rely on the multimodal nature of speech to compensate for noisy environments during speech communication. Multiple mechanisms underlie mature audiovisual benefit to speech perception, including reduced uncertainty as to when auditory speech will occur, use of correlations between the amplitude envelope of auditory and visual signals in fluent speech, and use of visual phonetic knowledge for lexical access. This paper reviews evidence regarding infants' and children's use of temporal and phonetic mechanisms in audiovisual speech perception benefit. The ability to use temporal cues for audiovisual speech perception benefit emerges in infancy. Although infants are sensitive to the correspondence between auditory and visual phonetic cues, the ability to use this correspondence for audiovisual benefit may not emerge until age four. A more cohesive account of the development of audiovisual speech perception may follow from a more thorough understanding of the development of sensitivity to and use of various temporal and phonetic cues.