A team of researchers led by Dr Alison Bruderer, a postdoctoral fellow at the University of British Columbia, has discovered a direct link between tongue movements of infants and their ability to distinguish speech sounds.

“Until now, research in speech perception development and language acquisition has primarily used the auditory experience as the driving factor. Researchers should actually be looking at babies’ oral-motor movements as well,” said Dr Bruderer, who is the lead author on a study published in the Proceedings of the National Academy of Sciences on October 12, 2015.

In the study, teething toys were placed in the mouths of six-month-old English-learning infants 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 sounds.

But when their tongues were free to move, the babies were able to make the distinction.

“Before infants are able to speak, their articulatory configurations affect the way they perceive speech, suggesting that the speech production system shapes speech perception from early in life,” the scientists said.

“These findings implicate oral-motor movements as more significant to speech perception development and language acquisition than current theories would assume and point to the need for more research.”

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 study’s senior author Prof. Janet Werker, also of the University of British Columbia.

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Alison G. Bruderer et al. Sensorimotor influences on speech perception in infancy. PNAS, published online October 12, 2015; doi: 10.1073/pnas.1508631112