The Role of Early Gesture on Expressive and Receptive Vocabulary in Infants at High and Low Risk for Autism Spectrum Disorder

Background:   Gesture use has been found to predict infant’s later language abilities (Iverson & Goldin-Meadow, 2005). Infants who have an older sibling with ASD (HR-sibs) have been found to produce fewer gestures (Stone, McMahon, Yoder, & Walden, 2007), understand fewer words (Mitchell et al., 2006) and produce fewer words (Zwaigenbaum et al., 2005) in their second year of life than low-risk controls (LR-sibs). However, less is known about the developmental trajectories of expressive and receptive vocabulary and the extent to which gesture use and language interact during this pivotal period for communication development. 

Objectives:   To assess the extent to which early gesture use and ASD risk status predict: (1) growth in expressive (EV) and receptive vocabulary (RV) from 12 to 18 months and (2) the level of EV and RV at 18 months. 

Methods:   Gesture use, EV, and RV were examined in HR-sibs (n=69; male=36) and LR-sibs (n=42; male=23)  at 12, 15, and 18 months using the MacArthur-Bates Communicative Development Inventory (MCDI; Fenson et al., 2007). Gesture use was measured via the Total Gestures summary score. EV and RV were measured using the “Words Produced” and “Words Understood” total scores, respectively. Hierarchical linear modeling was employed to examine the contributions of infants’ 12-month gesture use and ASD risk on receptive and expressive growth and levels.

Results: The overall trajectory of EV and RV from 12 to 18 months was best characterized by significant positive, linear growth, ps<.01. EV and RV showed little variability across individuals at 12 months; therefore, the intercept was set at 18 months. Gesture use at 12 months did not predict growth in EV or RV from 12 to 18 months,,ps > .05, but significantly predicted 18-month levels of EV and RV. For every additional type of gesture infants produced at 12 months, they produced 1 more word at 18 months, b=1.25, p=.002, and understood 4 more words at 18 months, b=4.15, p<.001. Risk status significantly predicted growth in EV from 12 to 18 months, b = 5.31, p = .003, and levels of EV at 18 months, such that HR-sibs demonstrated slower growth and lower levels of EV at 18 months than LR-sibs. HR-sibs produced on average 5 fewer words per month between 12 and 18 months and 28 fewer words at 18 months than LR-sibs, b=28.37, p<.01. In contrast, risk status did not predict growth in RV, p>.05, but did significantly predict RV at 18 months. HR-sibs understood 40 fewer vocabulary words at 18 months than LR-sibs, b=40.12, p<.001. Infants’ use of gestures did not interact with their risk group status to predict either growth of EV or RV or 18-month levels, ps>.05.

Conclusions: Although gesture use and risk status independently predicted 18-month levels of expressive and receptive vocabulary, no interactions were found.  Implications of these findings will be discussed.