Optimal combination of form and motion cues in human heading perception.

We examined what role motion-streak-like form information plays in heading perception. We presented observers with an integrated form and motion display in which random-dot pairs in a 3D cloud were oriented toward one direction on the screen (the form FOE) to form a radial Glass pattern while moving in a different direction in depth (the motion FOE). Observers' heading judgments were strongly biased toward the form FOE direction (weight: 0.78), and this bias decreased with the reduction of the salience of the global form structure in the Glass pattern. At the local level, the orientation of dot pairs in the Glass pattern can affect their perceived motion direction, leading to a shift of the perceived motion FOE direction in optic flow. However, this shift accounted for about half of the total bias. Using the measurements of the shifted motion FOE and the perceived form FOE directions, we found that at the global level, an optimal combination of these two cues could accurately predict the heading bias observed for the integrated display. Our findings support the claim that motion streaks are effective cues for self-motion perception, and humans make optimal use of both form and motion cues for heading perception.