The Discrepancy Between Receptive and Expressive Vocabulary in Preschoolers with ASD

Background:  

Some studies indicate receptive age equivalencies are lower than expressive age equivalencies in young children with autism spectrum disorder (ASD). In such children, the discrepancy between receptive - expressive vocabulary size should be atypically small, although this has not been shown. This could occur because children with autism attend less than other children to child-directed speech, which results in missing opportunities to learn to associate words with their referents. However, this association has not been tested.

Objectives:  

1. Is there a lower receptive age equivalency than expressive age equivalency in preverbal children with ASD, and does this change over time?
2. Is there an atypically small receptive – expressive vocabulary size discrepancy?
3. Does early visual attention to speaker during child-directed speech predict the discrepancy between receptive – expressive vocabulary size 8 months later?

Methods:  

Eighty-seven children with ASD participated in this study (see Table 1). Parent-reported (MacArthur-Bates Communication Development Inventory, MBCDI) receptive and expressive vocabulary was measured at four measurement periods, each separated by 4 months. The vocabulary size scores were transformed to age equivalencies using the median age or interpolated median age at which typically developing children achieved the raw score. The discrepancy between the mean receptive and the mean expressive vocabulary size in the typically-developing (TD) population was computed for four target ages. These ages were the rounded average of the mean receptive and mean expressive age equivalencies of the children with ASD at each measurement period (see Table 2). The visual attention to speaker during child-directed speech was quantified as the proportion of time that the child looked at the speaker out of the total time child-directed speech was presented at Time 2. The total duration of looking was coded from video records with inter-observer reliability > .9.  

Results:

Children’s receptive ages were significantly lower than their expressive ages at all four periods (within-subject Cohen’s d values = .37, .34, .24, .24, respectively, all p values < .05). Table 2 indicates the atypically small discrepancy between receptive and expressive vocabulary size for the ASD sample. The difference between the normative gap for receptive versus expressive vocabulary size and that seen in the children with ASD grew over time. Time 2 visual attention to speaker during child-directed speech predicted the discrepancy between receptive and expressive vocabulary size at Time 4 (8 mos later), r = .35, p = .01. This association was significant, even after controlling for the receptive-expressive discrepancy at Time 1 (p < .02).

Conclusions:  

Receptive vocabulary size was smaller than expected given the size of the expressive lexicon for this sample of young children with ASD, consistent with the finding that receptive vocabulary age equivalency was lower than expressive vocabulary age equivalency at each age point. Visual attention to the speaker during child-directed speech was associated with, and thus may have been one of the reasons for the atypically small discrepancy between, receptive and expressive vocabulary size.  These findings suggest that enhancing attention to child-directed speech may be an important target of early language intervention.