Abstract
Purpose. The visual system shows impressive capabilities to form complete objects from fragments presented across gaps in both space and time. Research has revealed the importance of particular spatial and temporal relations, known as spatiotemporal relatability (STR) in dynamically occluded and illusory two-dimensional objects (Palmer et al., 2006). Other work has shown that related geometric constraints (3D relatability) predict interpolation in 3D static displays (e.g. Kellman et al., 2005). No previous work, however, has examined the ecologically important case of interpolation in moving 3D displays. We used an objective performance paradigm to test an extended theory of STR with moving illusory 3D objects. Methods. In Experiment 1, subjects viewed a 3D movie with an illusory shape, parts of which were defined by sequential, partial occlusion of narrow rectangles. The displays required spatiotemporal interpolation because pairs of inducing edges never appeared in any static frame. Object contours were relatable on half of the trials. Relatability was disrupted by shifting one fragment either laterally (2D disruption) or in depth (3D disruption). Experiment 2 was a monocular version of Experiment 1. Because conditions leading to unit formation have been shown previously to produce performance advantages in a shape discrimination paradigm, we expected greater sensitivity for the relatable conditions compared to the non-relatable ones. Results. There were two main effects. First, subjects showed greater sensitivity for differences in spatial configurations that were relatable than those that were not. Second, 2D disruptions of relatability had a greater effect on sensitivity than 3D disruptions. Conclusions. 3D misalignment in dynamic displays showed weaker effects on interpolation than in 3D static interpolation, possibly due to difficulty in extracting accurate depth information from moving, sequentially exposed object fragments. Under these conditions, 2D spatial relatability appears to be the major determinant of spatiotemporal object formation.