The role of language in acquiring object kind concepts in infancy.

Four experiments investigated whether 9-month-old infants could use the presence of labels to help them establish a representation of two distinct objects in a complex object individuation task. We found that the presence of two distinct labels facilitated object individuation, but the presence of one label for both objects, two distinct tones, two distinct sounds, or two distinct emotional expressions did not. These findings suggest that language may play an important role in the acquisition of sortal/object kind concepts in infancy: words may serve as "essence placeholders". Implications for the relationship between language and conceptual development are discussed.