Of holes and wholes: the perception of surrounded regions.

Fully enclosed regions in a two-dimensional image can often be perceived either as an object in front of a surface or as a hole through a surface. Several experiments were conducted to determine what factors affect perception of holes versus objects. Three types of factors were tested and found to influence this outcome. First, depth factors directly indicate that the enclosed region lies behind its surrounding surface. Second, grouping factors relate the enclosed region to an outer region that is generally perceived as a continuation of the surface seen through the hole. Finally, figural factors indicate whether the enclosed region is to be perceived as figure or ground. Relations among these factors and their implications for perceptual organization are discussed.