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Two experiments are described which explore the relationship between parental reports of infants' receptive vocabularies at 1 ; 6 (Experiment 1a) or 1;3, 1;6 and 1;9 (Experiment 1b) and the comprehension infants demonstrated in a preferential looking task. The instrument used was the Oxford CDI, a British English adaptation of the MacArthur-Bates CDI (Words & Gestures). Infants were shown pairs of images of familiar objects, either both name-known or both name-unknown according to their parent's responses on the CDI. At all ages, and on both name-known and name-unknown trials, preference for the target image increased significantly from baseline when infants heard the target's label. This discrepancy suggests that parental report underestimates infants' word knowledge.
Houston‐Price et al. (Wed,) studied this question.