A Fine-Grained Analysis of Longitudinal Language Use in Toddlers with ASD: The Case of GAP Verbs

Background: Language delay is a primary concern for many toddlers with ASD (DeGiacomo & Fombonne, 1998), and the presence of language before age 5 in this population is a powerful predictor of functional outcome (Anderson et al., 2009). Research using parent-report measures suggests that vocabulary in ASD is delayed but not deviant in composition (Rescorla & Safyer, 2013), but little is known about word use in the real world, and even less about the productive lexicon over time. Although prior research has examined word classes at a gross level (e.g., proportion of nouns versus verbs; Tek et al., 2013) no studies to date have taken a fine-grained approach to productive language by measuring not only if children use words from a given class, but also which words are used when and how. The present research fills this gap by exploring two kinds of verbs: content verbs (Content; e.g., bite, juggle) and general all-purpose verbs or light verbs (GAP; e.g., go, want). GAP verbs are used more often in typical speech than content verbs, but these verbs have never been explored in toddlers with ASD.

Objectives: Characterize the developing nature of GAP and Content verb use in typical toddlers (TD) and toddlers with ASD. Given that the overall proportion of verbs to nouns is similar in language-matched ASD and TD children, and these children learn language via many common mechanisms, we hypothesize that children with ASD, like TD, will rely more on GAP verbs than Content verbs over time.

Methods: Seventeen toddlers with ASD (mean age=32.86 months) were matched to 18 TD toddlers (mean age=20.60 months) on Expressive and Receptive Language abilities (MSEL) at Visit 1 of a 6-visit longitudinal study.  The language produced by parents and children during three 30-minute semi-structured home-based play sessions (each 8 months apart; i.e., Visits 1, 3, 5) was recorded and transcribed in CHAT format.

Results: Growth curve analyses using linear mixed models revealed that change in the proportion of GAP verbs used by children over time did not differ by group (all p>.10). The average number of times each GAP verb was used (tokens/types) grew more steeply in TD than ASD (t=2.72, p=.009). This is likely due in part to lower rates of GAP verb use in the TD group at Time 1, and consistently high average usage of GAP verbs in the ASD group.

Conclusions: Toddlers with ASD and TD show similar patterns of GAP and Content verb use in a naturalistic play interaction. This analysis represents the first foray into a rich dataset that can answer a number of questions, including: which words within a class do toddlers with and without ASD actually use, and how do they use them? Do subgroups within ASD use different words, or use the same words differently? Future growth curve analyses will be conducted on verbs of communication (e.g., ask, say), internal state verbs (e.g., see, think), action verbs (e.g., jump, fall), and social verbs (e.g., share, help) across all 6 available time points.