Electrophysiological evidence of illusory audiovisual speech percept in human infants. Proceedings of the National Academy of Sciences of the United States of America. 2008;105(32):11442-5. Abstract
Electrophysiological evidence of illusory audiovisual speech percept in human infants
How effortlessly and quickly infants acquire their native language remains one of the most intriguing questions of human development. Our study extends this question into the audiovisual domain, taking into consideration visual speech cues, which were recently shown to have more importance for young infants than previously anticipated [Weikum WM, Vouloumanos A, Navarra J, Soto-Faraco, S, Sebastian-Galles N, Werker JF (2007) Science 316:1159]. A particularly interesting phenomenon of audiovisual speech perception is the McGurk effect [McGurk H, MacDonald J (1976) Nature 264:746-748], an illusory speech percept resulting from integration of incongruent auditory and visual speech cues. For some phonemes, the human brain does not detect the mismatch between conflicting auditory and visual cues but automatically assimilates them into the closest legal phoneme, sometimes different from both auditory and visual ones. Measuring event-related brain potentials in 5-month-old infants, we demonstrate differential brain responses when conflicting auditory and visual speech cues can be integrated and when they cannot be fused into a single percept. This finding reveals a surprisingly early ability to perceive speech cross-modally and highlights the role of visual speech experience during early postnatal development in learning of the phonemes and phonotactics of the native language.
Visual speech contributes to phonetic learning in 6-month-old infants. Cognition. 2008;108(3):850-5. Abstract
Visual speech contributes to phonetic learning in 6-month-old infants
Previous research has shown that infants match vowel sounds to facial displays of vowel articulation [Kuhl, P. K., & Meltzoff, A. N. (1982). The bimodal perception of speech in infancy. Science, 218, 1138-1141; Patterson, M. L., & Werker, J. F. (1999). Matching phonetic information in lips and voice is robust in 4.5-month-old infants. Infant Behaviour & Development, 22, 237-2471], and integrate seen and heard speech sounds [Rosenblum, L. D., Schmuckler, M. A., & Johnson,J. A. (1997). The McGurk effect in infants. Perception & Psychophysics, 59, 347-357; Burnham, D., & Dodd, B. (2004). Auditory-visual speech integration by prelinguistic infants: Perception of an emergent consonant in the McGurk effect. Developmental Psychobiology, 45, 204-220]. However, the role of visual speech in language development remains unknown. Our aim was to determine whether seen articulations enhance phoneme discrimination, thereby playing a role in phonetic category learning. We exposed 6-month-old infants to speech sounds from a restricted range of a continuum between /ba/ and /da/, following a unimodal frequency distribution. Synchronously with these speech sounds, one group of infants (the two-category group) saw a visual articulation of a canonical /ba/ or /da/, with the two alternative visual articulations, /ba/ arid /da/, being presented according to whether the auditory token was on the /ba/ or /da/ side of the midpoint of the continuum. Infants in a second (one-category) group were presented with the same unimodal distribution of speech sounds, but every token for any particular infant was always paired with the same syllable, either a visual /ba/ or a visual /da/. A stimulusalternation preference procedure following the exposure revealed that infants in the former, and not in the latter, group discriminated the /ba/-/da/ contrast. These results not only show that visual information about speech articulation enhances phoneme discrimination, but also that it may contribute to the learning of phoneme boundaries in infancy. (C) 2008 Elsevier B.V. All rights reserved.