Does the visual system exploit projective geometry to help solve the motion correspondence problem?

Projective geometry determines how the retinal image of an object deforms a s it moves through three-dimensional space. Does the visual system use cons traints derived from this information, such as rigidity, to aid the trackin g of moving objects? A novel psychophysical technique is introduced for ass essing which of two competing motion transformations is 'preferred' by the visual system, in a two-frame sequence. In the first experiment, relative p reference strengths for translations parallel and perpendicular to the majo r axis of a wire-frame object were measured by pitting the two against each other. It was found that parallel translations were preferred to perpendic ular ones. On the basis of these data a proximity measure for normalising d ifferent transformations, independent of any effects of figural similarity, was developed. In the second experiment, two wire-frame planar structures were used to pit one of five transformations (rotation, expansion, vertical expansion, shear and random jitter) against a translation. Preference stre ngth was measured as the translation distance at which the transformation a nd the translation were perceived with equal frequency. The PSEs were found to collapse on to a single line when plotted against the proximity magnitu de, with the exception of a residual preference for pure translation over a ll other transformations. In general, these results suggest that preference strength for moving wire-frame figures is determined primarily by the prox imity of local features on the displacing contour, with little regard for t he projective shape transformation. (C) 1998 Elsevier Science Ltd. All righ ts reserved.