Perceiving absence: P3 signatures of surprise from occluded space

When navigating our world, we often feel that we see the whole scene around us. However, large parts of nearby space are often not visible because they are occluded by other objects. Behavioural evidence suggests that such occluded regions can be perceived as empty, which is known as the illusion of absence. Stage magicians use this illusion to make objects appear out of thin air. If an object emerges from seemingly empty space, its appearance should be surprising. We tested this prediction with EEG by revealing objects from behind an occluder while measuring the P3 component of event-related potentials, which is an established index of surprise. The occluder was a homogeneously grey field with holes that exposed the background. We manipulated occluder size by decreasing the size of the holes. Based on previous findings showing that the illusion of absence is more pronounced for smaller occluders, we expect that revealing an object from behind a small occluder will elicit a larger P3 amplitude than revealing it from behind a larger occluder. We will present results of this ongoing study. The findings of this study are relevant not only to the basic perceptual research of occluded space, but also to practical applications in road traffic safety, as well as stage magic, where objects seem to appear from empty spaces.