The verb vocabularies and verb-learning mechanisms of late talkers
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While late talkers (LTs) are defined by their atypically small expressive vocabularies, far less is known about their receptive vocabularies or how they acquire new words. Some LTs, at least, appear to have receptive deficits (Dale et al., 2003), and in tasks of novel noun learning, LTs are less successful than their typically developing peers (TDs: Ellis Weismer, Venker, Evans, & Moyle, 2013). This dissertation explores LTs’ receptive vocabularies and word-learning, focusing on verb vocabulary. In verb learning, children rely on the linguistic context of the verb as a cue for its meaning (e.g., Naigles, 1990), but children who cannot parse the linguistic context do not learn (He, Kon, & Arunachalam, under revision). This may be particularly challenging for LTs, who are slower lexical processors than TDs (Fernald & Marchman, 2012). The first study (Chapter 2) compares LTs and TDs’ receptive verb vocabularies as measured through eye-tracking and dynamic scene stimuli. It was hypothesized that, as compared to TDs, LTs would know fewer verbs and be slower to process them; however, results of the study do not support either hypothesis. Other group differences were noted, though: As compared to TDs, LTs took longer to demonstrate knowledge of the target vocabulary items, spent less time looking to the target scene, and had greater rates of track loss. Together, these findings indicate subtle differences between LTs and TDs. The second study (Chapter 3) explores children’s capacity to learn novel verb meanings given variable linguistic processing demands. LTs and TDs were introduced to a novel verb, surrounded either only by content nouns or by both content nouns and pronouns. Variability benefits word-learning, and content nouns and pronouns each facilitate different aspects of the acquisition process (Childers & Tomasello, 2001; Hadley, Rispoli, & Holt, 2017; Mintz, 2003). However, variability also incurs a higher processing demand, which was hypothesized to be too great for LTs. Regression analysis revealed that LTs performed significantly worse given variable input as compared to consistent input. This indicates that LTs struggle to learn verb meaning when processing demands are high. The final study (Chapter 4) compares children’s performance on the receptive verb vocabulary task with their performance on the novel verb-learning task. Children who had larger receptive verb vocabularies and faster processing were expected to have learned more verbs during the verb-learning task as compared to children with smaller receptive vocabularies and slower lexical processing. Results of correlation analyses indicate no statistically significant correlations after Bonferroni correction, contrary to prediction. However, they do suggest areas for future research with a priori hypotheses about the relationship between concurrent language abilities and word learning. Taken together, the studies from this dissertation provide new insights into LTs’ verb vocabularies. Future research should continue to explore both between- and within-group differences. This work may ultimately provide insights into why LTs have poorer outcomes as compared to TDs (e.g., Rescorla, 2002; 2005; 2009), and may help identify which LTs are at greatest risk for developmental language disorder (Paul, 1996).