Individual differences in object-processing explain the relationship between early gaze-following and later language development.

Gaze-following behaviors play an important role in language development. However, the way in which gaze-following contributes to language development remains unclear. By focusing on two abilities, namely following the gaze direction of others and processing a cued object, the present study investigated how these two influences work together to promote language development in a longitudinal approach on infants from 9 to 18months of age. The results demonstrated that infants who spent more time following the gaze direction toward an object were more efficient in processing the cued object at 9months and had larger vocabularies by 18months. Mediation analyses showed that the relationship between early gaze-following behavior and subsequent vocabulary size was explained by object-processing ability. Importantly, mere extended fixations on a target object without the initiation of another's gaze shift were not related to enhanced object-processing. Our findings suggest that following another's gaze shift toward the object has an impact on object-processing that could contribute to vocabulary development, elucidating a critical step in the path from early gaze-following ability to later language development.