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J. W. Kelly, A. C. Beall, J. M. Loomis; Accurate judgments of exocentric direction in large scale space. Journal of Vision 2002;2(7):718. doi: 10.1167/2.7.718.
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© ARVO (1962-2015); The Authors (2016-present)
Judgments of exocentric direction are quite common, especially in judging where others are looking. In this experiment, subjects were shown two targets in a large field and were asked to judge the direction specified by the targets. They did so by noting which point on a distant fence appeared collinear with the two targets. Thus, subjects had to imagine a line connecting the targets and then extrapolate this imagined line to the fence. The targets ranged in egocentric distance from 5 to 20 m with target-to-target angular separations of 45, 90, and 135 deg. Subjects estimated the point of collinearity by marking a hand-held 360 deg panoramic cylinder representing their vistas. The two targets and the judged point of collinearity were often in quite different directions; in some conditions, only one or two of these three points were within the subjects' momentary field of view. Overall, performance was quite accurate—the mean estimates in the 60 different configurations exhibited absolute errors averaging only 5 deg and signed errors were even smaller. To perform with such accuracy, subjects must have perceived the relative locations of the two targets quite accurately and must have exhibited little systematic error in the sensorimotor integration process involved in extrapolating the imagined line in space.
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