Most of the empirical data is an in-press book, _Pretend play as
improvisation_. I could send you preprints of certain chapters depending
on your interest--your work does seem to touch on similar issues. Also,
there are some theoretical articles which I could refer you to. Contact
me off-line if you would like to request any of these, and thanks for
your interest.
Keith Sawyer
Department of Psychology
University of California, Santa Cruz
Santa Cruz, CA 95064