The mediating role of social cue use in the relation between infant characteristics and early vocabulary
Canfield, Caitlin Ford
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Infants' characteristics, including temperament and cognitive ability, contribute to individual differences in language development. However, the process through which such traits influence language learning remains unclear. One possibility is that temperament and cognitive capacities affect the way in which infants learn words by influencing their ability to successfully use contextual referential cues. Social cues, such as eyegaze, pointing and gesturing, and emotional expressions, are one important type of referential cue. The present study explored the role of such social cues in the relation between infant characteristics and vocabulary in 71 18-month-olds. It was hypothesized that infants' characteristics would be associated with both their vocabulary and their use of such social cues, and that social cue use would be related to overall vocabulary. Further, it was predicted that infants' ability to use social cues effectively would mediate the relation between infants' temperament and cognitive ability, and their vocabulary. Participants watched six word-learning videos on a Tobii 1760 Eyetracker. In each video, a speaker labeled a novel object using one social referential cue. Infants' ability to use that cue to learn the object label was assessed by tracking the time spent looking toward the target object. Infants' cognitive and language abilities were assessed using the Bayley Scales of Infant and Toddler Development, 3rd edition. Both parents and observers provided ratings of child temperament, and parents also completed the MacArthur-Bates Communicative Development Inventory: Words and Sentences form. Both correlation and bias-corrected bootstrap mediation analyses were conducted. Temperament did not make a unique contribution to infants' vocabulary, but both cognitive ability and social cue use did. Mediation analyses indicated that social cue use did mediate the relation between early cognitive ability and vocabulary, but only for infants with lower than average cognitive ability. These results indicate that social cues may be especially important for language development in infants and young children with low IQ, possibly because they provide additional supports for word learning. This has important implications for both typically developing infants as well as young children with language disorders.