Inhibiting infants’ tongue movements impedes their ability to distinguish between speech sounds, researchers with the University of British Columbia have found. The study is the first to discover a direct link between infants’ oral-motor movements and auditory speech perception.
In the study, published October 12 in the Proceedings of the National Academy of Sciences, teething toys were placed in the mouths of six-month-old English-learning babies while they listened to speech sounds—two different Hindi “d” sounds that infants at this age can readily distinguish. When the teethers restricted movements of the tip of the tongue, the infants were unable to distinguish between the two “d” sounds. But when their tongues were free to move, the babies were able to make the distinction.
Lead author Alison Bruderer, a postdoctoral fellow in the School of Audiology and Speech Sciences at UBC, said the findings call into question previous assumptions about speech and language development. “Until now, research in speech perception development and language acquisition has primarily used the auditory experience as the driving factor,” she said. “Researchers should actually be looking at babies’ oral-motor movements as well.”
The study does not mean parents should take their babies’ soothers and teething toys away, but it does raise questions about how much time infants need with ‘free’ tongue movement for speech perception to develop normally. It also has implications for speech perception in infants with motor impairments of the mouth, such as cleft palate, tongue-tie or paralysis.
“This study indicates that the freedom to make small gestures with their tongue and other articulators when they listen to speech may be an important factor in babies’ perception of the sounds,” said senior author Janet Werker, professor in the UBC Department of Psychology.
Researchers at UBC have discovered a link between infants’ tongue movements and the babies’ ability to distinguish speech sounds.
About this neurodevelopment research
Source:University of British Columbia Image Source: The image is adapted from the ubcpublicaffairs video Video Source: The video is available at the ubcpublicaffairs YouTube page Original Research: Full open access research for “Sensorimotor influences on speech perception in infancy” by Alison G. Bruderer, D. Kyle Danielson, Padmapriya Kandhadai, and Janet F. Werker in PNAS. Published online October 12 2015 doi:10.1073/pnas.1508631112
Sensorimotor influences on speech perception in infancy
The influence of speech production on speech perception is well established in adults. However, because adults have a long history of both perceiving and producing speech, the extent to which the perception–production linkage is due to experience is unknown. We addressed this issue by asking whether articulatory configurations can influence infants’ speech perception performance. To eliminate influences from specific linguistic experience, we studied preverbal, 6-mo-old infants and tested the discrimination of a nonnative, and hence never-before-experienced, speech sound distinction. In three experimental studies, we used teething toys to control the position and movement of the tongue tip while the infants listened to the speech sounds. Using ultrasound imaging technology, we verified that the teething toys consistently and effectively constrained the movement and positioning of infants’ tongues. With a looking-time procedure, we found that temporarily restraining infants’ articulators impeded their discrimination of a nonnative consonant contrast but only when the relevant articulator was selectively restrained to prevent the movements associated with producing those sounds. Our results provide striking evidence that even before infants speak their first words and without specific listening experience, sensorimotor information from the articulators influences speech perception. These results transform theories of speech perception by suggesting that even at the initial stages of development, oral–motor movements influence speech sound discrimination. Moreover, an experimentally induced “impairment” in articulator movement can compromise speech perception performance, raising the question of whether long-term oral–motor impairments may impact perceptual development.
“Sensorimotor influences on speech perception in infancy” by Alison G. Bruderer, D. Kyle Danielson, Padmapriya Kandhadai, and Janet F. Werker in PNAS. Published online October 12 2015 doi:10.1073/pnas.1508631112