An Eye-tracking study of receptive verb knowledge in toddlers

Purpose: We examined receptive verb knowledge in 22-to 24-month-old toddlers with a dynamic video eye-tracking test. The primary goal of the study was to examine the utility of eye-gaze measures that are commonly used to study noun knowledge for studying verb knowledge. Method: Forty typically developing toddlers participated. They viewed 2 videos side by side (e.g., girl clapping, same girl stretching) and were asked to find one of them (e.g., “Where is she clapping?”). Their eye-gaze, recorded by a Tobii T60XL eye-tracking system, was analyzed as a measure of their knowledge of the verb meanings. Noun trials were included as controls. We examined correlations between eye-gaze measures and score on the MacArthur–Bates Communicative Development Inventories (CDI; Fenson et al., 1994), a standard parent report measure of expressive vocabulary to see how well various eye-gaze measures predicted CDI score. Results: A common measure of knowledge—a 15% increase in looking time to the target video from a baseline phase to the test phase—did correlate with CDI score but operationalized differently for verbs than for nouns. A 2nd common measure, latency of 1st look to the target, correlated with CDI score for nouns, as in previous work, but did not for verbs. A 3rd measure, fixation density, correlated for both nouns and verbs, although the correlation went in different directions. Conclusions: The dynamic nature of videos depicting verb knowledge results in differences in eye-gaze as compared to static images depicting nouns. An eye-tracking assessment of verb knowledge is worthwhile to develop. However, the particular dependent measures used may be different than those used for static images and nouns.