The integration of orientation information in the motion correspondence problem

We examine how differently oriented components contribute to the discrimina tion of motion direction along a horizontal axis. Stimuli were two-frame ra ndom-dot kinematograms that were narrowband filtered in spatial frequency. On each trial, subjects had to state whether motion was to the left or the right. For each stimulus condition, D-max (the largest displacement support ing 80% correct direction discrimination performance) was measured. In expe riment 1, D-max was measured for orientationally narrowband stimuli as a fu nction of their mean orientation. D-max was found to increase as the orient ation of the stimuli became closer to the axis of motion. Experiment 2 used isotropic stimuli in which some orientation bands contained a coherent mot ion signal, and some contained only noise. When the noise band started at v ertical orientations and increased until only horizontal orientations conta ined a coherent motion signal. D-max increased slightly. This suggests that near-vertical orientations interfere with motion perception at large displ acements when they contain a coherent motion signal. When the noise band st arted at horizontal and increased until only vertical orientations containe d the motion signal, D-max decreased steadily. This implies that D-max depe nds at least partly on the most horizontal motion signal in the stimulus. T hese results were contrasted with two models. In the first, the visual syst em utilises the most informative orientations (nearest horizontal). In the second, all available orientations are used equally. Results supported an i ntermediate interpretation. in which all orientations are used but more inf ormative ones are weighted more heavily.