Scientists at Florida Atlantic University say that at around six months old, babies start studying the mouths of whoever is talking to them, rather than just staring into their eyes.
Developmental psychologist David Lewkowicz says babies do this to "figure out how to shape their lips to make that particular sound they're hearing".
Lewkowicz, who led the study, said that language development in children was an "an incredibly complex process" but it doesn't take infants long to take in the lip formations which go with the sound they are hearing.
Once having mastered the lip shape, babies go back to eye contact. However, if they hear sounds that are unfamiliar to them - such as a foreign language - they go back to lip reading again!
The findings appear in the latest issue of the Proceedings of the National Academy of Sciences, and, as reported by USA Today, underlies the need for babies to have "quality face-time" with their parents or carers, rather than just baby DVDs or TV programmes.
What do you think?
Have you noticed your baby watching your mouth and then trying to copy the sound?