Scale invariance in near space: pointing under influence of context

This paper describes the results of a pointing task close to the observer. Unlike most research reported in literature, the stimuli were composed of real solid objects in an unambiguous context, free of any cue conflict. Moreover, the stimuli were either within arm-reach or just beyond arm-reach, thus having strong binocular depth cues. Surprisingly, systematic errors up to four times the standard deviation were found. These errors depended mainly on the variations in context and hardly on egocentric distance. In good first approximation, the results were scale invariant. These results are in direct conflict with classic theories about visual space. The stimuli were unambiguous real 3-D equivalents of the computer-generated stimuli we used in a previous experiment. A comparison of the results did not reveal a clear effect of a depth cue conflict between accommodation and disparity.