Relative roles of 3-D and 2-D coordinate systems in solving the correspondence problem in apparent motion

There has been a controversy in the apparent motion literature regarding the influence of 3-D distances between motion tokens on correspondence matching. The current series of experiments indicates that this discrepancy results because the effect of three-dimensional distance is too small to be detected unless the retinal coordinates of the motion tokens are carefully chosen so as to lead to ambiguous correspondence matches on identical trials. It is also shown that, even when the retinal coordinates of motion tokens are equated, such that the different solutions to the correspondence problem are generated with equal probability, the effect of 3-D distances obtained is relatively small when compared to the effect of the retinal coordinates of motion tokens.