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

- Our study investigated how early gaze-following promotes language development.
- We focused on two abilities: gaze-following and object-processing.
- Object-processing mediated the relation between the cued looking duration and vocabulary size.
- We elucidate a key step on the path from gaze-following to 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 18 months 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 9 months and had larger vocabularies by 18 months. 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.