The relationship between interaction with the caregiver and the emergence of play activities during the one-word period was examined. In particular, investigation centered on Vygotsky's views regarding the importance of social interaction as the source of the child's knowledge of the world. To empirically examine the role of the caregiver, observations were made of six children (two children were observed at each of three levels of semantic development within the one-word period). At each of the three levels, the children's performance during interactive play sequences was found to be more advanced than their performance during noninteractive sequences. These results lend support to Vygotsky's contention that cultural activities are first acquired on the interpersonal level and later displayed at the intrapersonal level. (Author/MP)