Perceived 3D shape from continuous and static perspective changes

Abstract

Studies of structure-from-motion have generally found that perceived depth from motion is not veridical and depends on speed. However, some recent studies have found that observers are capable of accurate metric judgments of shape when there are large changes in perspective (Bingham & Lind, 2008; Lee et al., 2008). We investigated whether continuous motion is required for accurate metric shape judgments from large perspective changes, and whether amount of perspective change modulates the speed dependence of structure-from-motion. Stimuli were views of elliptical cylinders with depth-to-width ratios (0.5-1.5) and with different slants in depth (top face: 60°, 70° or 80°). In the SFM condition, the object was rotated around the normal axis by either ±10° or ±45°. The rotation was sinusoidal with peak speed of either 15°/s, 20°/s or 25°/s. In the static-views condition, the initial and most extreme views were presented as static images, with delay between images of 0.5s, 1.6s, 2.0s, or 2.4s. Observers adjusted the aspect ratio of a 2D ellipse to match the perceived shape of the elliptical face of the 3D object. For both the SFM and static-views conditions, we found that judgments were more accurate with large perspective change. With small perspective change, judgments showed overall underestimation of depth and compression of range. Large perspective change reduced these biases, and in the SFM condition judgments were close to veridical. Accuracy was lower with static-views than SFM, indicating that the improvement was not solely due to the extreme views. We found no effect of rotation speed even with small perspective change, contrary to expectations. We conclude that large perspective change can facilitate structure-from-motion and support near-veridical judgments of 3D shape.