Infant-directed song potentiates infants' selective attention to adults' mouths over the first year of life.

The mechanisms by which infant-directed speech and song support language development in infancy are poorly understood, with most prior investigations focused on the auditory components of these signals. However, the visual components of infant-directed communication are also of fundamental importance for language learning: over the first year of life, infants' visual attention to caregivers' faces during infant-directed speech switches from a focus on the eyes to a focus on the mouth, which provides synchronous visual cues that support speech and language development. Caregivers' facial displays during infant-directed song are highly effective for sustaining infants' attention. Here we investigate if infant-directed song specifically enhances infants' attention to caregivers' mouths. 299 typically developing infants watched clips of female actors engaging them with infant-directed song and speech longitudinally at six time points from 3-12 months of age while eye-tracking data was collected. Infants' mouth-looking significantly increased over the first year of life with a significantly greater increase during infant-directed song versus speech. This difference was early-emerging (evident in the first 6 months of age) and sustained over the first year. Follow-up analyses indicated specific properties inherent to infant-directed song (e.g., slower tempo, reduced rhythmic variability) in part contribute to infants' increased mouth-looking, with effects increasing with age. The exaggerated and expressive facial features that naturally accompany infant-directed song may make it a particularly effective context for modulating infants' visual attention and supporting speech and language development in both typically developing infants and those with or at risk for communication challenges. This article is protected by copyright. All rights reserved.