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Shaw Gillespie, Myron Braunstein, George Andersen; Discriminating curved from straight motion trajectories in 3D scenes. Journal of Vision 2009;9(8):640. doi: 10.1167/9.8.640.
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© ARVO (1962-2015); The Authors (2016-present)
Our previous research (VSS, 2008) found that observers use available velocity information when judging the trajectory of moving objects and making decisions about the relative curvature of an object's path. The present study examined whether the presence of a ground plane affects how projected velocity and size change information are used in judging the motion trajectory of an object. Observers were asked to discriminate between straight and curved motion paths of a ball. Half of the observers viewed the ball moving through a 3D scene, while the other half viewed the identical motion against a blank background of similar color and luminance. The motion path of the ball was either straight or arced upward at one of three different levels of curvature as it moved toward the observer's point of view. The curvature was indicated by the size change function only, by the velocity function only or by both types of information. The projected path of the ball was identical in all conditions. Observers were able to discriminate curved from straight trajectories more accurately from the velocity change information alone than from size change information alone. Performance using only size change information was near chance for all conditions. Accuracy was similar for velocity information alone and combined size and velocity information. When velocity information was available, observers performed more accurately with the ball moving against a background scene with a ground plane than with the ball moving against a blank background. These results indicate (1) that variations in projected velocity indicating path curvature are more important than variations in projected size in discriminating between straight and curved trajectories and (2) that a background including a ground plane increases the accuracy of curvature discrimination.
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