Poster #115 - Looking Beyond Mom: Language Input From Mothers and Other Individuals on Infants' Vocabulary Development

• In Event: 2-110 - Poster Session 07
  In Poster Session: PS 07 Section - Language, Communication

Integrative Statement

Infants who hear more child-directed speech (CDS) tend to have better language learning trajectories; however, the majority of the studies examining language input on infants' language development have only examined input produced by infants' mothers (e.g. Huttenlocher et al., 1991; 2010; Pan et al., 2005). For 2-year-olds the amount of CDS from all individuals in their environment is related to their later vocabulary development (Shneidman et al., 2013). However, it is unknown whether 12-month-olds also benefit from CDS spoken all individuals in their environment, or whether instead speech from their mother is most relevant. Two-year-olds are better at processing speech (Fernald et al., 2006), and have better memory and attention capabilities (Hayne et al., 1997; Rose et al., 2009) than 12-month-olds, which may allow them to better aggregate input from multiple speakers across time. Thus, it is likely that the features important for 12-month-olds differ from those that are important for two-year-olds. We tested whether all language input is important for infants' vocabulary growth and to what extent it matters whether the input is coming from the infants' mother or other individuals in their environment.

We collected recordings of language input in 12-month-olds' (N=50, Males=26) environment and coded how much CDS they heard from their mother and from other individuals. At 12-, 15-, and 18-months we collected parent-report measures of productive vocabulary.

Multilevel models were used to test how infants' language input at 12-months was related to their vocabulary growth from 12- to 18-months. The Level 1 equation contained an intercept, linear, and quadratic terms. Participants' age was centered at 12-months, the beginning of the study. At Level 2, we allowed the quadratic term to vary freely but we fixed the random effects for the intercept and linear terms, which set μ_0 and μ_1to 0. We found that mothers' CDS tokens interacted with the linear term, b=.001, p=.005, and the quadratic term, b=-.0002, p=.04. As infants heard more CDS tokens from their mother, their vocabulary was increasing but the rate of growth was nonetheless slowing. CDS tokens from all others in infants' environment significantly interacted with the linear term, b=.004, p<.001. The more CDS tokens produced by the other individuals in infants' environment, the greater the increases in infants' productive vocabulary (Figure 1).

We found that infants who heard more CDS, from all individuals, experienced greater gains in their productive vocabulary. This replicates the findings of Shneidman et al. (2013), demonstrating that CDS beyond the mother is related to infants' vocabulary growth and extends the current literature by demonstrating that language input beyond the primary caregiver is related to infants' vocabulary development at younger ages, when infants are just beginning to produce their first words. Overall, our findings provide further support for the role of language input on infants' vocabulary development and for the importance of collecting measures of the language input from all of the individuals in the infants' environment.

Authors

• Abbie Thompson, University of Notre Dame
  Presenting Author

• Jill Lany, University of Liverpool
  Non-Presenting Author