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Kerem Ozkan, Myron L. Braunstein; Background surface and horizon effects in the perception of relative size. Journal of Vision 2006;6(6):421. doi: 10.1167/6.6.421.
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The projected height of an object relative to a ground surface influences its perceived distance in a scene, but the effect of height should change when the object is moved above the horizon. The present study examined the effects of background surface and object height on perceived relative size, for objects equal in projected size. The background surfaces were line drawings representing ground and ceiling planes. There were four background conditions: ground only, ceiling only, ground and ceiling and no surfaces. Two ellipses with horizontal major axes appeared in each scene. The vertical separation of the ellipses was constant, but the pair of ellipses varied in height, with either both below the ground horizon position, both above the ceiling horizon position, or one at the ground horizon position and one at the ceiling horizon position. Observers were asked to indicate which disk appeared larger. The type of surface did not have an overall effect on size judgments, but interacted with the height of the disks in determining perceived relative size. The ground-only conditions were replicated with cylinders displayed against a real scene background. The higher cylinder was always judged to be larger when the lower cylinder was below the horizon, but was most often judged to be smaller when the lower cylinder was at or above the horizon. These results suggest that the perceived layout of objects in a scene depends both on the positions of the objects relative to a background surface and relative to the horizon.
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