Wx. Li et L. Matin, DIFFERENCES IN INFLUENCE BETWEEN PITCHED-FROM-VERTICAL LINES AND SLANTED-FROM-FRONTAL HORIZONTAL LINES ON EGOCENTRIC LOCALIZATION, Perception & psychophysics, 57(1), 1995, pp. 71-83
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.