When "shoe" becomes free from "putting on": The link between early meanings of object words and object-specific actions.

Nouns referring to objects dominate children's early vocabulary over verbs referring to actions. However, some scholars have argued that early object-word meanings cannot be easily classified into specific object categories; rather, they have much undifferentiated meanings in which both objects and their specific actions are intertwined. We experimentally investigated this view using a two-alternative forced-choice task involving toddlers aged 18-23 months (n = 69). Both the cross-sectional and longitudinal results suggested that unlike older toddlers, younger ones could not select the correct referents when objects and object-specific actions were presented separately (e.g., "doing a filler action with shoes" vs. "putting on filler objects as if they were shoes") despite being successful when both were matched (e.g., "putting shoes on" vs. "doing a filler action with filler objects"). Additionally, toddlers failed to judge object-word referents solely by object-specific actions. These results indicated that early object-word meanings constitute the undifferentiated fusion of both objects and actions, and they subsequently differentiate into specific object categories independent of actions. Furthermore, the extent of such semantic differentiation is associated with the vocabulary growth of action words, suggesting that object-word meaning differentiation encouraged toddlers to develop new labels that could distinguish specific actions from objects. These findings revealed the uniqueness of young children's object-word comprehension, which is different from that of adults.