We investigate how family characteristics contribute to language produced in homes. Specifically, we investigate the effects of older siblings on the amounts and types of child-directed and overheard speech that infants hear. We analyzed 76 daylong audio home recordings from 26 American families with infants between the ages of 6-12 months. To annotate the recordings, we randomly sampled 2 h from each recording comprised of 30s intervals and coded all sampled utterances for the speaker and addressee. We found that infants with older siblings had about half as much speech directed to them as did infants without older siblings. This effect was entirely driven by contexts in which the older sibling was physically present; we observed no differences in amounts of directed speech when older siblings were not present. However, when combining all child-directed input (to either the infant or the siblings) there were no differences between families with and without siblings. Further, the nature of overheard speech varied with the presence of a sibling, not only as an additional speaker in the home, but as in the physical presence of the sibling during day-to-day activities. The set of individuals in a home have substantial consequences for the speech that is produced and amounts of overheard- and child-directed speech may vary more widely in American homes than previously assumed.
Galindo et al. (Sun,) studied this question.