Approximately 15% of 2-year olds are Late Talkers (LTs), defined as having atypically small expressive vocabu- laries in the absence of known etiologies or cognitive deficits. LT status is a risk factor for a later diagnosis of language disorder, and even LTs who do not have a diagnosis have poorer language outcomes as compared to typically developing peers (TDs). It is unknown why LTs struggle, and currently it is not possible to identify which LTs are most at risk of lan- guage disorder. This project examines LTs' verb knowledge because verbs determine sentence structure, and are therefore foundational to grammatical development. Further, older children with a diagnosed language disorder struggle with verb use particularly, and so verb deficits may serve as an early indicator of language disorder. TDs use the linguistic context in which a verb appears (e.g., the verb's ending) to learn its meaning; for example, TDs associate ?ing endings with manner meanings (i.e., how the event unfolds, as with walk or run) and ?ed endings with result meanings (i.e., the result of the event, as with open or close). However, children who struggle to process linguistic context may not use this cue to meaning. In processing nouns, at least, LTs are slower than TDs, which may indicate that their language processing skills are poor; how LTs process verbs is unknown. Given the importance of verbs to language development, it is critical to study 1) LTs' verb knowledge and pro- cessing and 2) how LTs acquire new verbs. In this project, 52 children (26 LT; 26 TD, ages 2;0-2;11) will participate in two experimental tasks designed to address these issues.
In Aim 1 /Study 1, children participate in an eye-tracking para- digm to assess receptive knowledge and processing of verbs. Children see two animated scenes and are asked to find which depicts the action of the target verb. Eye gaze is recorded: Knowledge is indicated via preference for the target over the distractor, and processing is measured as the speed to look toward the target following the prompt. A mixed-effects regression will reveal whether, as hypothesized, LTs know fewer verbs and are slower processors than TDs.
In Aim 2 /Study 2, children participate in a novel verb-learning task, again with eye-tracking. Children see an object performing two actions (one manner; one result) and are asked which is the referent of a novel verb. The novel verb's ending is ma- nipulated (?ing, ?ed), and serves as a linguistic cue to verb meaning. TDs are expected to succeed in learning a verb's meaning from its ending, consistent with prior research, but LTs are not; this will be tested via mixed-effects regressions.
In Aim 3, performance in Studies 1 and 2 is compared for all participants. Separate mixed-effects regressions for LTs and TDs will reveal whether lexical processing speed predicts performance on a novel verb-learning task, with children who are faster lexical processors hypothesized to be more successful in a novel-verb learning task. If true, this may indicate a mechanism by which LTs struggle, and may be used to predict which LTs are most at risk for later language disorder. This research is part of a 2-year training grant. The trainee will also engage in coursework, lab and clinical rota- tions, and seminars to develop skills in methods and analysis, theoretical training and professional development.
Approximately 15% of two-year-olds have atypically small expressive vocabularies with no known etiologies; critically, these ?late talkers? are at increased risk of language disorder as compared to their typically developing peers. Because of the important role that verbs play in later language development, we study whether there are differences between typically developing children and late talkers' 1) receptive verb vocabularies, 2) linguistic processing of familiar verbs, and 3) use of linguistic cues to learn the meaning of novel verbs. Results will provide insight into late talker language development and may indicate a mechanism by which late talkers struggle.
