Mothers provide differential feedback to infants' prelinguistic sounds

This paper reports 2 studies that explore the role of joint attentional processes in the child's acquisition of language. In the first study, 24 children were videotaped at 15 and 21 months of age in naturalistic interaction with their mothers. Episodes of joint attentional focus between mother and child--for example, joint play with an object--were identified. Inside, as opposed to outside, these episodes both mothers and children produced more utterances, mothers used shorter sentences and more comments, and dyads engaged in longer conversations. Inside joint episodes maternal references to objects that were already the child's focus of attention were positively correlated with the child's vocabulary at 21 months, while object references that attempted to redirect the child's attention were negatively correlated. No measures from outside these episodes related to child language. In an experimental study, an adult attempted to teach novel words to 10 17-month-old children. Words referring to objects on which the child's attention was already focused were learned better than words presented in an attempt to redirect the child's attentional focus.

The role of social stimulation in avian vocal learning is well documented. The separate contribution of social, as opposed to vocal, stimulation has been difficult to address, however, because in almost all cases both tutor and pupil sing. The opportunity to isolate such effects arose in cowbirds (Molothrus ater ater) after discovering that males housed with non-singing female cowbirds made vocal changes which related directly to the female preferences for native song. Here we report how females communicate with males about songs. We describe a visual display by females, a wing stroke, that is elicited by specific vocalizations. The songs that trigger wing strokes are in turn highly effective releasers of copulatory postures, and thus this previously unnoticed female display has biological significance. The data not only provide the first evidence of the tutorial role of male-female interactions during song ontogeny, they also clearly implicate visual stimulation in song learning, a process that has until now been assumed to be affected only by auditory information.