The redeployment of attention to the mouth of a talking face during the second year of life.

Previous studies have found that when monolingual infants are exposed to a talking face speaking in a native language, 8- and 10-month-olds attend more to the talker's mouth, whereas 12-month-olds no longer do so. It has been hypothesized that the attentional focus on the talker's mouth at 8 and 10 months of age reflects reliance on the highly salient audiovisual (AV) speech cues for the acquisition of basic speech forms and that the subsequent decline of attention to the mouth by 12 months of age reflects the emergence of basic native speech expertise. Here, we investigated whether infants may redeploy their attention to the mouth once they fully enter the word-learning phase. To test this possibility, we recorded eye gaze in monolingual English-learning 14- and 18-month-olds while they saw and heard a talker producing an English or Spanish utterance in either an infant-directed (ID) or adult-directed (AD) manner. Results indicated that the 14-month-olds attended more to the talker's mouth than to the eyes when exposed to the ID utterance and that the 18-month-olds attended more to the talker's mouth when exposed to the ID and the AD utterance. These results show that infants redeploy their attention to a talker's mouth when they enter the word acquisition phase and suggest that infants rely on the greater perceptual salience of redundant AV speech cues to acquire their lexicon.

Selective attention to a talker's mouth in infancy: role of audiovisual temporal synchrony and linguistic experience.

Previous studies have found that infants shift their attention from the eyes to the mouth of a talker when they enter the canonical babbling phase after 6 months of age. Here, we investigated whether this increased attentional focus on the mouth is mediated by audio-visual synchrony and linguistic experience. To do so, we tracked eye gaze in 4-, 6-, 8-, 10-, and 12-month-old infants while they were exposed either to desynchronized native or desynchronized non-native audiovisual fluent speech. Results indicated that, regardless of language, desynchronization disrupted the usual pattern of relative attention to the eyes and mouth found in response to synchronized speech at 10 months but not at any other age. These findings show that audio-visual synchrony mediates selective attention to a talker's mouth just prior to the emergence of initial language expertise and that it declines in importance once infants become native-language experts.

Perception of the multisensory coherence of fluent audiovisual speech in infancy: its emergence and the role of experience.

To investigate the developmental emergence of the perception of the multisensory coherence of native and non-native audiovisual fluent speech, we tested 4-, 8- to 10-, and 12- to 14-month-old English-learning infants. Infants first viewed two identical female faces articulating two different monologues in silence and then in the presence of an audible monologue that matched the visible articulations of one of the faces. Neither the 4-month-old nor 8- to 10-month-old infants exhibited audiovisual matching in that they did not look longer at the matching monologue. In contrast, the 12- to 14-month-old infants exhibited matching and, consistent with the emergence of perceptual expertise for the native language, perceived the multisensory coherence of native-language monologues earlier in the test trials than that of non-native language monologues. Moreover, the matching of native audible and visible speech streams observed in the 12- to 14-month-olds did not depend on audiovisual synchrony, whereas the matching of non-native audible and visible speech streams did depend on synchrony. Overall, the current findings indicate that the perception of the multisensory coherence of fluent audiovisual speech emerges late in infancy, that audiovisual synchrony cues are more important in the perception of the multisensory coherence of non-native speech than that of native audiovisual speech, and that the emergence of this skill most likely is affected by perceptual narrowing.