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Longitudinal, Cross-Modal Associations Appear to Differ in Typically Developing Toddlers As Compared to Children with ASD
Recent research has found evidence that expressive language “drives” later receptive language in young, minimally verbal children with autism spectrum disorder (ASD) (Woynaroski et al., 2015). This result was interpreted as “atypical” because receptive language is presumed to drive expressive language in typically developing (TD) children. This assumption regarding what constitutes “typical” language development, however, rests largely on findings from descriptive research. For example, TD children have been observed to understand words before they are able to produce words and, at any given point in time, to have a larger receptive vocabulary than expressive vocabulary (e.g., Benedict, 1979). However, cross-modal longitudinal associations between expressive and receptive language in TD children have not been explicitly tested. Doing so would help researchers understand how the developmental trajectory found in ASD differs from typically developing children.
Objectives: To compare the cross-modal, longitudinal associations between expressive and receptive vocabulary in mental-age-matched TD toddlers and in young children with ASD who participated in Woynaroski et al. (2015).
Methods:
Participants included 62 TD toddlers with an average mental age equivalent of 14.4 months as assessed by the Mullen Scales of Early Learning. Parent-reported vocabulary was assessed at two time points, eight months apart, via the MacArthur Bates Communicative Development Inventories (MCDI) vocabulary checklist. Receptive and expressive vocabulary sizes were operationalized as the raw number of words that parents reported their children “understood” and “said”, respectively. Missing data was handled using multiple imputation. . In making the cross-lagged comparison, this statistic takes into account concurrent associations across modalities and longitudinal associations within each language modality. We descriptively contrast our current results to Woynaroski et al.’s (2015) report on an ASD sample (n= 87), whose mental age equivalent was similar to the existing sample. Data collection and analysis procedures in the present study were identical to those employed by Woynaroski and colleagues.
Results: Cross-lagged, cross modal associations were high for both early receptive language to later expressive language (r = .74), and early expressive language to later receptive language (r = .75) for our TD sample. The difference in cross-lagged, cross-modal correlation magnitudes was not statistically significant (ZPF = -0.17, p= 0.87; See Figure 1). Table 1 juxtaposes results with the previously reported ASD sample.
Conclusions: This study provides added support for Woynaroski et al.’s interpretation of an “expression driven” profile observed for children with ASD as “atypical.” Surprisingly, we did not find evidence that receptive language drives expressive language for TD children, as has previously been theorized. Unlike children with ASD, TD children experience a bi-directional effect of reception and expression. Further research is needed to tease apart divergent developmental trajectories in these two groups.