The effects of familiarity and infant-directedness on six-month-olds' visual scanning of talking faces

In the latter half of the first year, infants exhibit a preference to look at the mouth when viewing speaking faces, which may serve as a mechanism through which native language is acquired. Infant-directed (ID) speech may also facilitate language acquisition by providing a perceptually-salient stimulus that highlights spoken language compared to adult-directed (AD) speech. Although 6-month-olds' visual attention to the mouth has been linked to greater expressive language skills later on, prior research does not consistently demonstrate a mouth preference at this age. Methodological confounds identified in the literature prompted the manipulations of face familiarity, infant-directedness, and modality in the current assessment of 6-month-olds' visual scanning of faces. Infants' visual fixations were tracked while they viewed videos of their own mothers or unfamiliar mothers in which the women spoke ID and AD speech in a series of visual only, audio only, or audiovisual stimuli. Infants were expected to exhibit a mouth preference to their mothers', but not unfamiliar mothers', audiovisual ID stimuli, which would support a mechanism through which familiarity and infant-directedness facilitate face processing and language acquisition. Results indicated that infants exhibited a mouth preference, though the preference was unrelated to familiarity and infant-directedness. Exploratory within-group analyses indicated that female infants' mouth preference was specific to their mothers' audiovisual stimuli, unrelated to speech style, whereas no other infant group exhibited a mouth preference to the audiovisual stimuli. These findings are discussed in relation to a proposed model of infant social-communicative development through which repeated social interactions with the primary caregiver over time may facilitate the development of face processing and language acquisition.