DIFFERENCES IN INFLUENCE BETWEEN PITCHED-FROM-VERTICAL LINES AND SLANTED-FROM-FRONTAL HORIZONTAL LINES ON EGOCENTRIC LOCALIZATION

The visual field exerts powerful effects on egocentric spatial localiz ation along both horizontal and vertical dimensions. Thus, (1) prism-p roduced visual pitch and visual slant generate similar: mislocalizatio ns of visually perceived eye level (VPEL) and visually perceived strai ght ahead (VPSA) and (2) in darkness curare-produced extraocular muscl e paresis under eccentric gaze generates similar mislocalizations in V PEL and VPSA that are essentially eliminated by introducing a normal v isual field. In the present experiments, however, a search for influen ces of real visual slant on VPSA. to correspond to the influences of v isual pitch on VPEL failed to find one. Although the elevation corresp onding to VPEL changes linearly with the pitch of a visual field consi sting of two isolated 66.5 degrees-long pitched-from-vertical lines, t he corresponding manipulation of change in the slant of either a horiz ontal two-line or a horizontal four-line visual field on VPSA did not occur. The average slope of the VPEL-versus-pitch function across 5 su bjects was +0.40 over a +/-30 degrees pitch range, but was indistingui shable from 0.00 for the VPSA-versus-slant function over a +/-30 degre es slant range. Possible contributions to the difference between susce ptibility of VPEL and VPSA to visual influence from extraretinal eye p osition information, gravity, and several retinal gradients are discus sed.