Proceedings of the Annual Meeting of the Cognitive Science Society

Previous research has suggested that first-born infants acquire words faster than their later-born peers (Berglund etal., 2005), but may have some disadvantages in other aspects of syntactic and socio-communicative development (e.g. Hoff,2006). Here we analyzed infants’ early lexical development alongside their caregiver input from 6-18 months, in relation to howmany siblings they have. We find that having more siblings (rather than being first- or later-born) has a gradient and negativerelationship with infants’ language development. This affect appears to be manifested in caregiver input: across three differentmeasures of input quality/quantity, disadvantages were found for infants with more siblings. Having a larger number of siblingsdiminished the quality of the input and led to slower overall lexical development. Implications for language development andlearning within dyadic and multi-member contexts are discussed.