Exocentric pointing in three-dimensional space

A study is reported of an exocentric pointing task in all three dimensions, in near space, with only two visible luminous objects-a pointer and a targ et. The task of the subject was to aim a pointer at a target. The results c learly show that visual space is not isotropic, since every set direction a ppeared to consist of two independent components-one in the projection onto a frontoparallel plane (tilt), the other in depth (slant). The tilt compon ent shows a general trend across subjects, an oblique effect, and can be ju dged monocularly. The slant component is symmetrical in the mid-sagittal pl ane, requires the use of binocular information, and shows considerable diff erences between subjects. These differences seem to depend on the amount of binocular information used by each subject. There was a remarkably high le vel of consistency in the exocentric pointing, despite the absence of envir onmental cues. The within-subject consistency in the settings of the pointe r corresponds to a consistency of about 1 min of are in disparity of its ti p, even though the pointer and target are separated by more than 5 deg.