On the perception of some geometric properties of rotating three dimensional objects

Various observations and conjectures have been made about how we perceive three dimensional objects under monocular viewing conditions; in particular, when such objects are rotating. In this paper these proposals are reviewed and reinterpreted in the light of geometric properties of objects and their projections. Some results are also presented which support the conclusion that the visual system, in reconstructing the object from its projections, requires a fixed time to establish the objects curvature and torsion parameters. In the perceptual reconstruction process these parameters assume positive or negative values, and this equivocation is related to a form of the adjacency principle involving central projections and "perceptual geodesics".