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Junjun Zhang, Myron Braunstein, George Andersen; The effects of size and speed on perceived 3D object motion at different distances. Journal of Vision 2011;11(11):738. doi: 10.1167/11.11.738.
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© ARVO (1962-2015); The Authors (2016-present)
Variations in projected size and projected speed provide information about the motion of objects in 3D space. Projected speed information is available in both polar and parallel projections (Todd, 1984), but projected size is only informative about changes in depth in perspective (polar) projections. The usefulness of size information in judging 3D motion should therefore diminish faster with increased viewing distance than the usefulness of speed information. We therefore predicted an interaction between size information and speed information in determining the accuracy of 3D motion judgments as simulated viewing distance was increased. The stimuli were simulated motions of a ball in a convex circular arc in a horizontal plane at eye level. The curvature of the ball's trajectory was indicated either by changes in both the projected size and projected speed or by changes in the projected size only or in the projected speed only. There were three levels of curvature and three levels of simulated eye distance. Initial sizes and speeds were randomized across displays. Observers were presented with two displays on each trial, both at the same simulated eye distance and both providing the same information for curvature (size, speed or both). The displays differed in the curvature of the ball's trajectory and the observer's task was to indicate which display showed the more curved trajectory. Accuracy was higher with size information alone than with speed information alone at the closest viewing distance. At the greatest viewing distance, accuracy with either size information alone or speed information alone dropped to near chance levels, but accuracy remained high when both types of information were available. This indicates that even when speed information does not provide a high level of accuracy in isolation, it can combine with size information to markedly increase the level of accuracy available at increased distance.
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