Taking Aim in the Plane A van Doorn, J Koenderink, J Wagemans |
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Laboratory of Experimental Psychology, University of Leuven (KU Leuven), Belgium
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| In an experiment on 3D pictorial space we encountered an unexpected systematic error regarding the directions in the frontoparallel plane. To investigate the effect we devoted a special study to the same phenomenon in the purely 2D visual field. Observers view a large field filled with a uniform background texture, looking evidently frontoparallel. We superimpose a target and a pointer on this background, both presented at random locations. Thus both the mutual distance and direction are random.The task is to simply aim the pointer at the target for about a thousand target-pointer combinations. We find that observers commit both random and systematic errors, the latter dominating and amounting to as much as ten degrees. The systematic errors occur in a well defined pattern, which is the same for all observers. The deviations vanish for the vertical, the horizontal, and the diagonal directions. The settings deviate from the veridical away from the vertical and horizontal. Perhaps surprisingly, the mutual distance of target and pointer has only a minor influence. We relate this pattern to observations of orientation judgments and discriminations made through the nineteenth and twentieth century. |
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