PERCEPTION OF 3-DIMENSIONAL SHAPE FROM EGO-MOTION AND OBJECT-MOTION -COMPARISON BETWEEN SMALL-FIELD AND LARGE-FIELD STIMULI

We compare the performance in the detection of the shape of concave, p lanar and convex surfaces for small-field (8 deg) and large-field (90 deg) stimuli. Shape is perceived from head translations, object transl ations and object rotations. We find large differences between small-f ield and large-field stimulation. For small-field stimulation performa nce is best for object rotation, intermediate for self-motion and wors t for object translation. For large-field stimulation performance is s imilar across conditions. Few errors on the sign of the curvature are found for self-motion for both field sizes, indicating that self-motio n information disambiguates the curvature sign. For object rotation wi th small-field stimulation, the concave-convex ambiguity is strong wit h many apparent deformations. Tn contrast, large-field curvature signs are always accurately reported, suggesting that the weight of the rig idity hypothesis depends on field size.