Lexical Category Acquisition Via Nonadjacent Dependencies in Context: Evidence of Developmental Change and Individual Differences

Abstract

Lexical categories like noun and verb are foundational to language acquisition, but these categories do not come neatly packaged for the infant language learner. Some have proposed that infants can begin to solve this problem by tracking the frequent nonadjacent word (or morpheme) contexts of these categories. However, nonadjacent relationships that frame categories contain reliable adjacent relationships making the type of context (adjacent or nonadjacent) used for category acquisition unclear. In addition, previous research suggests that infants show learning of adjacent dependencies earlier than learning of nonadjacent dependencies and that the learning of nonadjacent word relationships is affected by the intervening information (how informative it is and how familiar it is). Together these issues raise the question of whether the type of context used for category acquisition changes as a function of development. To address this question, infants ages 13, 15, and 18 months were exposed to an artificial language containing adjacent and nonadjacent information that predicted a category. Infants were then tested to determine whether they 1) detected the category using adjacent information 2) only detected the nonadjacent dependency, with no categorization, or 3) detected both the nonadjacent relationship and the category. The results showed high individual variability in the youngest age group with a gradual convergence towards detecting the category and the associated environments by 18 months. These findings suggest that both adjacent and nonadjacent information may be used at early stages in category acquisition. The results reveal a dynamic picture of how infants use distributional information for category acquisition and support a developmental shift consistent with previous infant studies examining dependencies between words.