Auditory-visual speech integration by prelinguistic infants: perception of an emergent consonant in the McGurk effect.

The McGurk effect, in which auditory [ba] dubbed onto [ga] lip movements is perceived as "da" or "tha," was employed in a real-time task to investigate auditory-visual speech perception in prelingual infants. Experiments 1A and 1B established the validity of real-time dubbing for producing the effect. In Experiment 2, 4 1/2-month-olds were tested in a habituation-test paradigm, in which an auditory-visual stimulus was presented contingent upon visual fixation of a live face. The experimental group was habituated to a McGurk stimulus (auditory [ba] visual [ga]), and the control group to matching auditory-visual [ba]. Each group was then presented with three auditory-only test trials, [ba], [da], and [(delta)a] (as in then). Visual-fixation durations in test trials showed that the experimental group treated the emergent percept in the McGurk effect, [da] or [(delta)a], as familiar (even though they had not heard these sounds previously) and [ba] as novel. For control group infants [da] and [(delta)a] were no more familiar than [ba]. These results are consistent with infants' perception of the McGurk effect, and support the conclusion that prelinguistic infants integrate auditory and visual speech information.