The stone-base illusion

A popular method used to construct the post structure in traditional Korean buildings is simply placing a stone base on the ground in the natural form and a wooden post on top of the stone base. Interestingly, an illusory visual completion often occurs at the joint where the stone base and the post join. Thus, even though the wooden post stands on the top surface of the stone base, observers tend to perceive the post as embedded in the stone base. In Experiment 1, photographs of real stone bases and wooden posts were presented, and the results showed that the more uneven the stone base was, the more the post was judged as embedded in the stone base. In Experiment 2, 3D graphic models with a similar size and color were presented, and the results again showed that the unevenness of the stone base influenced the perceptual embedment of the post. The results are discussed in relation to several potential hypotheses, including figural goodness, edge similarity, and physical knowledge.