Change in perceived spatial directions due to context

We examined the influence of context an exocentric pointing. In a virtual t hree-dimensional set-up, we asked our subjects to aim a pointer toward a ta rget in two conditions: The target and the pointer were visible alone, or t hey were visible with planes through each of them. The planes consisted of a regular grid of horizontal and vertical Lines. The presence of the planes had a significant influence on the indicated direction. These changes in i ndicated direction depended systematically on the orientation of the planes relative to the subject and on the angle between the planes. When the orie ntation of the (perpendicular) planes varied from asymmetrical to symmetric al to the frontoparallel plane, the indicated direction varied over a range of 15 degrees-from a slightly larger slant to a smaller slant-as compared with the condition without the contextual planes. When the dihedral angle b etween the two planes varied from 90 degrees to 40 degrees, the indicated d irection varied over a range of less than 5 degrees: A smaller angle led to a slightly larger slant. The standard deviations in the indicated directio ns (about 3 degrees) did not change systematically The additional structure provided by the planes did not lead to more consistent pointing. The syste matic changes in the indicated direction contradict all theories that assum e that the perceived distance between any two given points is independent o f whatever else is present in the visual field-that is, they contradict all theories of visual space that assume that its geometry is independent of i ts contents (e.g., Gilinsky, 1951; Luneburg, 1947; Wagner, 1985).