Perceived structure from optic flow: Consistent versus variable mapping of3-D Euclidean structure

In an earlier study (Borjesson & Lind, 1996), the perception of Euclidean s tructure from polar projected two-frame apparent motion sequences was studi ed. The results showed that Euclidean structure is not perceived. However, at larger visual angles a certain consistency in the mapping between distal and perceived structure exists. The aim of the present study was to more p recisely examine how this degree of consistency varies as a function of vis ual angle. In Experiments 1 and 2, slant judgments of simulated and real pl anes indicated that the degree of consistency is a positive function of vis ual angle. No definite sign of a Euclidean mapping could, however, be found even in the full view condition. Experiment 3 examined texture gradients a nd the response method used. The results showed that texture gradients did not influence the degree of consistency of the mapping between distal and j udged depth and that the response method was both reliable and valid. Howev er, texture gradients did influence the absolute values of the slant judgme nts. The role of Euclidean and affine mappings of distal structure is discussed and it is proposed that the perceptually important distinction is not betwe en affine and Euclidean mapping, but rather between two types of affine map pings-consistent and variable.