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Allan Dobbins; Shadow-Induced Jumping in Depth. Journal of Vision 2012;12(9):898. doi: https://doi.org/10.1167/12.9.898.
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An object’s shadow can profoundly influence the perceived position and movement of the object in a scene (Kersten et al., 1997 Perception, 26: 171-192). When an object’s shadow makes a discrete jump from one location to another, the object can appear to jump in depth despite not having moved in the image (Kersten et al., 1997 Nature, 379: 31). Here we use a variant on these displays in which an object in a perspective scene is immobile while its shadow is successively in different locations. If the shadow is initially attached to the object and then detached beneath it, one perceives the object to have jumped forward in depth. In a variant of this display, the shadow is initially attached to the object and then disappears. The object appears to move forward in the scene and float above the ground just as if its detached shadow were present. Multiple interpretations of the shadow’s disappearance are possible including the sun being occluded by a cloud, the light source making an extreme jump in position and so forth. The perceived change in position may be due to the observer preferring the assumption of central tendency rather than the extreme position (at the end of the line of sight attached to the floor), or that the shadow has moved out of the viewport on the display. We find that one can perceive several objects jumping in depth if their shadows jump in the same direction in the scene. However, if the shadows undergo different directions of motion (e.g. consistent with some objects moving toward and others away from the viewer), one can perceive only a few (two or at most three) object jumps in depth, suggesting that the association of objects with unattached shadows is very taxing for the visual system.
Meeting abstract presented at VSS 2012
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