Social control of form diversity and the emergence of new forms in children's blockbuilding.

The blockbuilding behavior of three preschool girls was analyzed in terms of the forms manifest in any completed block construction, and found to contain few different forms in baseline sessions. Social reinforcement, given contingent on the production of any form not previously constructed within the current session (i.e., every first appearance of any form within a session was reinforced but no subsequent appearances of that form within that session were), increased the number of different forms built per sessions. Social reinforcement, given for all second and later appearances within the session, decreased the number of different forms built per session. Furthermore, it was found that new forms (forms never seen before in the child's total prior sequence of blockbuilding sessions) emerged at higher rates during periods of reinforcement of different forms (first appearances) than during periods of baseline or reinforcement of same forms (second and later appearances).