To understand some aspects of conceptual development it is necessary to take cognitive architecture into account. For this purpose, the study of normal development is often not sufficient. Fortunately, one can also study neurodevelopmental disorders. For example, autistic children have severe difficulties developing certain kinds of concepts but not others. We find that whereas autistic children perform very poorly on tests of the concept, believes, they are at or near ceiling on comparable tasks that test understanding of pictorial representation. A similar pattern was found in a second study which looked at understanding of a false map or diagram: normal 4-year-olds showed a marked advantage in understanding a false belief over a false map, while the autistic subjects performed better on the map. These findings suggest that the concept, believes, develops as a domain-specific notion that is not equatable with "having a picture (map or diagram) in the head." This result supports the existence of a specialized cognitive mechanism, which subserves the development of folk psychological notions, and which is dissociably damaged in autism. We extend these ideas to outline a new model of the development of false belief performance.