Assessing receptive verb knowledge in late talkers and autistic children: Advances and cautionary tales.

Purpose: Using eye-tracking, we assessed the receptive verb vocabularies of late talkers and typically developing children (Experiment 1) and autistic preschoolers (Experiment 2). We evaluated how many verbs participants knew and how quickly they processed the linguistic prompt. Method: Participants previewed two dynamic scenes side-by-side (e.g., "stretching" and "clapping") and were then prompted to find the target verb. Children's eye gaze behaviors were operationalized using established approaches in the field with modifications in consideration for the type of stimuli (dynamic scenes versus static images) and the populations included. Accuracy was calculated as a proportion of time spent looking to the target, and linguistic processing was operationalized as latency of children's first look to the target. Results: In Experiment 1, there were no group differences in the proportion of verbs known, but late talkers required longer to demonstrate their knowledge than typically developing children. Latency was predicted by age but not language abilities. In Experiment 2, autistic children's accuracy and latency were both predicted by receptive language abilities. Conclusion: Eye gaze can be used to assess receptive verb vocabulary in a variety of populations, but in operationalizing gaze behavior, we must account for between- and within-group differences. Bootstrapped cluster-permutation analysis is one way to create individualized measures of children's gaze behavior, but more research is warranted using an individual differences approach with this type of analysis. Finally, latency may not be a valid measure for dynamic scene stimuli for children under three years old.