Abstract
Purpose: :
Perceived egocentric visual direction (EVD, the direction referenced to one’s self) is based on the combination of eye position and retinal information (oculocentric visual direction, OVD). This study assessed whether (i) the eye-position information from both eyes contributes equally to the perceived EVD, (ii) the retinal information from both eyes contributes equally to the perceived OVD and, (iii) the two sources of information covary similarly within the same individuals.
Methods: :
Open-loop pointing responses to an isolated target presented randomly at several horizontal locations on a computer monitor at 50 cm were collected from thirteen subjects during four different magnitudes of asymmetric vergence, to estimate the contribution of the position information from each eye to perceived EVD. The direction at which a horizontally disparate (10.6 arc min) target with different interocular contrast and luminance ratios appeared aligned with a non-disparate target estimated the contribution of each eye’s retinal information to perceived OVD in thirteen and eight subjects, respectively.
Results: :
Between-eye differences in the contribution of eye-position information were statistically significant in seven subjects (p < 0.05). Statistically significant between-eye differences in the contribution of retinal information existed in four and three subjects for targets with different interocular contrast and luminance ratios, respectively. Across subjects, the relative contributions of the position information from the two eyes to perceived EVD correlated significantly with the relative contributions of the retinal information to perceived OVD, as determined using contrast- (r = 0.66; p = 0.02) and luminance- defined (r = 0.89; p = 0.003) targets.
Conclusions: :
The relative contributions of eye-position and the retinal information covary similarly in most subjects, as is generally assumed. However, the relative contributions of the two sources of information to perceived EVD do not agree quantitatively in all subjects.
Keywords: space and scene perception • vergence • constancy