Abstract
A model of how humans perceive straight-line two- and three-dimensional geometric figures, for example, triangles, trapezoids, cubes, is presented. The model successfully predicts the judged complexity of a wide variety of two-dimensional figures; with some additional rationale it also predicts the perceived three-dimensionality of figures such as Necker cubes which can be seen in either two or three-dimensionality are supported but there are discrepancies and other important unresolved problems in the treatment of perceived three-dimensionality.