Infants' understanding of the definite/indefinite article in a third-party communicative situation

The present study examines how infants use their emergent perspective-taking and language comprehension abilities to make sense of interactions between two human agents. In the study, one agent (Agent1) could see only one of two identical balls on an apparatus because of a screen obstructing her view while the infant and another agent (Agent2) could see both balls. 19-month-old English-learning monolingual infants seemed to expect Agent2 to grasp the ball visible to Agent1 when she said to Agent2 "Give me the ball" but not when she said "Give me a ball." 14-month-olds appeared to accept that Agent2 could grasp either ball when Agent1 said "Give me the ball." Therefore, by 19 months of age, English-learning infants seem to attend to the specific linguistic units used, e.g., the definite article, to identify the referent of others' speech. Possible reasons in connection with language acquisition processes and/or environmental factors for the two age groups' respective failures with the definite and the indefinite articles are discussed.