A study examined patterns of development in spoken interaction and types of causal thought that might reflect the human capacity to displace, that is, to shift reference from the present moment to another moment in time. Participants were four infants and their parents, who came to a laboratory for one-half hour every 2 weeks from the child's fifth and one-half month until the ninth month. Cognitive tasks for auditory memory, for causality, and for ends/means relationship were administered during each session. Free interaction was videotaped for 12 to 15 minutes. Results showed that three of the infants inhibited parent vocalization for 4 to 10 seconds after their own vocalization, from the age of seven and one-half months to nine months. Parents decreased mean utterances to 7 seconds or less by the infants' ninth month. There was no apparent direction of relationship between interactive speech and some types of causal thought. Although interactive speech changed between five and one-half and nine months toward increased infant influence and, at the same time, causal thought accomplishments also increased, there was no clear direction indicated for the relationship between interactive speech and causal thought. (Extensive tables of data are appended.) (FL)