When infants are spoken to, they will often pay special attention to a person’s lip movements. Even at 10 to 16 weeks, infants can match certain lip movements to the sounds they are hearing. In one experiment, infants heard recordings of nursery rhymes while watching adult faces on a screen. In some cases the lip movements were synchronized with the nursery rhymes, and at other times the lip movements were not. Infants looked longer when the lip movements matched the rhymes they heard. In another study, slightly older infants preferred to look at a face whose lips were forming the same vowel sound the infants heard to a face forming a different vowel sound.
Dodd, B. (1979). Lip reading in infants: Attention to speech presented in- and out-of-synchrony. Cognitive Psychology, 11, 478