Abstract
We examined the effect of external and internal references on the judgment of positions of objects in a visual scene. We used a 3D exocentric pointing task in which an observer had to direct a pointer toward a target with a remote control. We varied the positions of the observer, the pointer and the target. We measured deviations from veridical settings in the horizontal plane and in the vertical plane. We found that observers differed in dependence on certain references. Some people showed smaller deviations in the horizontal plane when the pointing-direction was parallel to one of the walls, others showed smaller deviations in the horizontal plane when the pointing-direction was in the frontoparallel plane, while a third group showed an interaction between these two effects. For the deviations in the vertical plane, we found no effect of the presence of a wall parallel to the pointing-direction. Frontoparallelity, however, influenced the settings of the observers. The deviations in the vertical plane are differently dependent on references than the deviations in the horizontal plane. Thus, our conclusion is twofold: first, the structure of the environment that is used for judging positions of objects is observer-dependent and second, visual space is anisotropic.
The investigations reported here were supported by the Research Council for Earth and Life Sciences (ALW), with financial aid from the Netherlands Organisation for Scientific Research (NWO)