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Kerem Ozkan, Myron Braunstein; The position of objects relative to the horizon affects size-distance invariance. Journal of Vision 2007;7(9):286. doi: 10.1167/7.9.286.
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© ARVO (1962-2015); The Authors (2016-present)
We reported previously (VSS, 2006) that the higher of two objects equal in projected size in a 3D scene was judged larger when it was at or below the implied horizon but was judged smaller when it was above the horizon. The present study examined effects of location of objects relative to the horizon on distance judgments and on the relation between size and distance judgments. In the first experiment the scenes consisted of line drawings in which the simulated distance to the horizon and the separation between the visible texture and the horizon were varied. Observers judged the relative distance of two objects that were either both below the horizon, both above the horizon or one at the horizon and one above or below the horizon. Unlike the results found with size judgments, the higher object was always judged more distant, regardless of its position relative to the horizon. The relation between size and distance judgments for objects varying in position with respect to the horizon was investigated directly in two additional experiments, one using line drawings and one using photographs of real scenes, with separate blocks of size and distance judgments. With the higher object at or below the horizon, it was judged larger in size judgment blocks and more distant in distance judgment blocks, as would be expected according to size-distance invariance. The effect was reversed, however, when the higher object was above the horizon. In that case, the higher object was judged smaller and further back than the lower object. This is the type of paradoxical size-distance relation found, for example, in the moon illusion. These results suggest that the relation between judged size and judged distance for objects in a 3D scene depends on the positions of the objects relative to the horizon.
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