DETECTION OF FIRST-ORDER STRUCTURE IN OPTIC FLOW-FIELDS

We measured psychophysical thresholds for the detection of four differ ent optic flow components in the presence of a translational velocity. We also measured thresholds for detection of rotation in the presence of expansion and for expansion in the presence of rotation. Our stimu li consisted of sparse random dot patterns. Detection thresholds are s imilar for all four optic flow components. Thus, our experiments indic ate that our subjects use a factor that is similar in all first-order flow components, namely the relative orientation of the velocity vecto rs. First-order components can be extracted independently of both each other and translational velocity.