Cognitive psychology, of course, is a central cognitive-science discipline. Among recent work by cognitive psychologists that has been influential in cognitive science are the following: J. D. Bransford, J. R. Barclay, and J. J. Franks's (1972) findings that people actively construct mental representations of the ``propositional'' meaning of sentences, David Rumelhart's theory of story grammars (1975), and Roger Shepard's and Stephen Kosslyn's theories of mental imagery as a non-propositional kind of mental representation (Shepard & Judd 1976, Kosslyn 1981).