Interrogating Early Word Knowledge: Factors That Influence the Alignment Between Caregiver‐Report and Experimental Measures

Questions about early word knowledge pervade the literature on both typical and atypical language trajectories. To determine which words an infant knows, researchers have relied on two types of measures-caregiver-report and eye-gaze behavior. When these measures are compared, however, their results frequently fail to converge, making it difficult to ascertain whether a given infant knows a given set of words. What are the reasons for these misalignments in gold-standard tasks that are designed to investigate the same underlying construct, and can convergent validity be improved? The current study was designed to investigate multiple methodological features of caregiver-report and looking-while-listening (LWL) tasks hypothesized to contribute to their alignment. American English-learning infants (18-20 months; N = 52) completed an LWL task assessing their understanding of eight early-acquired words. Caregivers reported their child's knowledge of the same eight words, as well as their confidence in their responses and the amount of time they spend with their child. Overall, caregivers' reports of word knowledge did not predict infants' eye-gaze behavior. However, the measures were more likely to be aligned when caregivers reported higher confidence in their responses. Caregivers' reports about both the target and the distractor word on each trial were related to infants' eye-gaze behavior, suggesting that LWL tasks capture knowledge about the labels of both objects tested, not just the label of the target object. The results suggest several critical methodological modifications that could be implemented to improve the measurement validity of both caregiver-report and eye-gaze measures of word comprehension. SUMMARY: This study provides novel insights to improve the validity of infant vocabulary measurement by highlighting factors that explain differences between caregivers' reports and eye-gaze behavior. Caregivers' reports of individual word knowledge failed to converge with infants' eye-gaze behavior during a looking-while-listening (LWL) task. Caregivers' reports of individual word knowledge aligned more strongly with their infant's eye-gaze behavior when caregivers reported more confidence in their responses. Caregivers' reports of both the target and the distractor words predicted infants' eye gaze behavior.