Numerous psychophysical findings emphasize the importance of surface completion and depth cues in visual perception. Thus, if MIB is affected by these factors it will regulate in accordance to simple occlusion principles. In their study, Graf et al. (2002) stereoscopically presented a moving grid stimulus set behind, in front of, or in the same plane as the static dots. They then showed involuntary completion of the grid elements into a surface interacting with the static targets - creating an illusion of . When the grid appeared in front of the targets the proportion of disappearance was larger than when it was behind or on the same plane. Although to a lesser extent, MIB did nonetheless occur in the conditions where the perceptual occlusion was not taking place (targets were in front of the mask).