What the â Moonwalkâ Illusion Reveals about the Perception of Relative Depth from Motion

Date

2011-06-22

Authors

Kromrey, Sarah
Bart, Evgeniy
Hegéd, Jay

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Abstract

When one visual object moves behind another, the object farther from the viewer is progressively occluded and/or disoccluded by the nearer object. For nearly half a century, this dynamic occlusion cue has beenthought to be sufficient by itself for determining the relative depth of the two objects. This view is consistent with the self-evident geometric fact that the surface undergoing dynamic occlusion is always farther from the viewer than the occluding surface. Here we use a contextual manipulation ofa previously known motion illusion, which we refer to as theâ Moonwalkâ illusion, to demonstrate that the visual system cannot determine relative depth from dynamic occlusion alone. Indeed, in the Moonwalk illusion, human observers perceive a relative depth contrary to the dynamic occlusion cue. However, the perception of the expected relative depth is restored by contextual manipulations unrelated to dynamic occlusion. On the other hand, we show that an Ideal Observer can determine using dynamic occlusion alone in the same Moonwalk stimuli, indicating that the dynamic occlusion cue is, in principle, sufficient for determining relative depth. Our results indicate that in order to correctly perceive relative depth from dynamic occlusion, the human brain, unlike the Ideal Observer, needs additionalsegmentation information that delineate the occluder from the occluded object. Thus, neural mechanisms of object segmentation must, in addition to motion mechanisms that extract information about relative depth, play a crucial role in the perception of relative depth from motion.

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Keywords

Research Article, Biology, Computational Biology, Computational Neuroscience, Sensory Systems, Neuroscience, Cognitive Neuroscience, Cognition, Computational Neuroscience, Sensory Systems, Sensory Systems, Visual System, Sensory Perception, Computer Science, Computing Methods, Computer Inferencing, Medicine, Anatomy and Physiology, Sensory Systems, Mental Health, Psychology, Cognitive Psychology, Sensory Perception, Social and Behavioral Sciences, Psychology, Cognitive Psychology, Experimental Psychology, Psychometrics, Psychophysics, Sensory Perception

Citation

PLoS One. 2011 Jun 22; 6(6):e20951