I work in cognition, mostly trying to model and test hypotheses about representational development, where I have invented a few experimental techniques. I focused initially on picture-production and have moved to analysing the conceptual change in children’s beliefs about pictures, their theory of pictures. The application was in art-education, where I have been active. When I began, there had been no hypothesis-testing tradition with children's pictorial representation (apart from one precocious study in 1897). I published methods for posing simple pictorial puzzles, and rules for inferring children's strategies of bringing visual order onto a page. My second aim had been to acquire a range of cognitive research skills so as to be able flexibly to promote research as and when circumstances demanded. I transferred the same set of research habits collaboratively to publish refereed papers on topics as diverse as phonological impairment, effects of early cardiac surgery, semantic change, infant spatial search, theory-of-mind inference, early counting. All illuminate the complexity of representational changes.