The effect of the occluder on perceived slant difference that was found in the present set of experiments might be related to a perceptual grouping effect that has been referred to as amodal completion (Fanton et al.,
2004). When one object partially occludes another, we perceive the separate visible portions of the occluded object as parts of a single object. The perceptual completion of the visible features is called amodal completion (Michotte, Thines, & Crabbe,
1991). “Amodal” refers to the fact that the occluded features cannot be seen and do not have any sensory input to the visual system such as luminance or color. Many studies of amodal completion have been carried out to investigate the phenomenon and its origin (Liu, Jacobs, & Basri,
1999; Nakayama, Shimojo, & Silverman,
1989; Shimojo & Nakayama,
1990; Yin et al.,
2000). The weaker effect of the occluder when placed in uncrossed disparity is consistent with this hypothesis. However, we do not completely attribute our results to amodal completion, because the uncrossed disparity occluder also effected perceived slant, albeit reduced.