Solving the Complexity of Object Occlusions in Scenes: The Grouping of Adjacent Surfaces and Non-Adjacent but Connected Surfaces

In contrast with classic Gestalt examples of perceptual grouping, most natural environments contain multiple objects, each with multiple surfaces. Each object is likely to occlude other objects partially and is itself likely to be partially occluded. A central question, therefore, is how the visual system resolves the resulting surface correspondence problem by successfully determining which surfaces belong to which objects (Guzman, 1969). To this end, a recently developed dynamic grouping methodology determines whether pairs of adjacent surfaces are grouped together (Hock & Nichols, 2012; Hock & Schöner, 2015). The grouping of adjacent surfaces, which depends on their affinity state, is indicated by the direction of perceived motion across one surface when its luminance (and thus, its luminance similarity with the adjacent surface) is perturbed. It is shown here that dynamic grouping also can occur for nonadjacent surfaces, providing they are linked in two-dimensions by a connecting surface. METHOD: Three disconnected horizontal surfaces with the same luminance are presented with two darker surfaces that connect them. Dynamic grouping motion is created by decreasing the central horizontal surface's luminance, decreasing its similarity with the flanking horizontal surfaces (while simultaneously increasing its similarity with the darker connecting surfaces). RESULTS: The perception of outward (diverging) dynamic grouping motion toward the flanking horizontal surfaces indicated that the central horizontal surface was grouped with the nonadjacent, but connected flanking horizontal surfaces. This was consistent with connectivity functioning as a grouping variable, which was first reported by Palmer and Rock (1994). Preliminary evidence indicates that the dynamic grouping motion is stronger when the nonadjacent but connected horizontal surfaces are aligned, and the connecting surfaces function as occluders (in this case dark vertical bars), consistent with amodal completion requiring the perceptual grouping of nonadjacent surfaces behind an occluding surface. Meeting abstract presented at VSS 2017