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Rui Ni, Myron L Braunstein, George J Andersen; Interactions of motion parallax and ground contact in specifying distance in a 3-D scene. Journal of Vision 2003;3(9):17. doi: https://doi.org/10.1167/3.9.17.
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Meng and Sedgwick (2001, 2002) found that the perceived distance along a ground surface of an object in a stationary scene could be mediated through nested contact relations among intermediate surfaces. Without intermediate contact relations, the judged distance of an object that was floating above the ground was determined by the location at which its projection contacted the ground surface. We investigated whether motion parallax would allow observers to determine the distance of a floating object without intermediate contact relations. Our displays consisted of one or more computer-generated textured cylinders inserted into a motion picture or still image of an actual 3-D scene. In the motion displays both the cylinders and the scene translated horizontally. Observers adjusted the location of a marker on the ground surface to match the perceived distance of the cylinder, or the distance of the top cylinder if more than one cylinder was present. In the first experiment, the cylinders varied in height with the top surface at a constant distance above the ground and the bottom surface either contacting the ground or floating above the ground. The perceived distance of the floating cylinders was reduced in the motion displays, suggesting that they were perceived as floating rather than resting on the ground. In the second experiment, both the projected size and location in the image of a cylinder was kept constant while its speed was manipulated to correspond to three different distances along the ground surface. Observers were able to retrieve the location of the cylinders from the speed information. In the third experiment, one, two or three cylinders were separated vertically with no contact. Accuracy of distance judgments for the top cylinder increased with motion and with an increasing number of cylinders. These results suggest that motion parallax interacts with ground contact in determining the perceived depth of objects in a dynamic 3-D scene.
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