Perceived egocentric direction (EVD) is based on the sensed position of the eyes in the orbit and the oculocentric visual direction (eye-centered, OVD). Previous reports indicate that in some subjects eye-position information from the two eyes contributes unequally to the perceived EVD. Findings from other studies indicate that the retinal information from the two eyes may not always contribute equally to perceived OVD. The goal of this study was to assess whether these two sources of information covary similarly within the same individuals. Open-loop pointing responses to an isolated target presented randomly at several horizontal locations were collected from thirteen subjects during different magnitudes of asymmetric vergence to estimate the contribution of the position information from each eye to perceived EVD. For the same subjects, the direction at which a horizontally or vertically disparate target with different interocular contrast or luminance ratios appeared aligned with a non-disparate target estimated the relative contribution of each eye’s retinal information. The results show that the eye-position and retinal information vary similarly in most subjects, which is consistent with a modified version of Hering’s law of visual direction.

Correctly perceiving the direction of a visible object with respect to one’s self (egocentric visual direction) requires that information about the location of the image on the retina (oculocentric visual direction) be combined with signals about the position of the eyes in the head. The Wells-Hering laws that govern the perception of visual direction and modern restatements of these laws assume implicitly that retinal and eye-position information are independent of one another. By measuring observers’ manual pointing responses to targets in different horizontal locations, we show that retinal and eye-position information are not treated independently in the brain. In particular, decreasing the relative visibility of one eye’s retinal image reduces the strength of the eye-position signal associated with that eye. The results can be accounted for by interactions between eye-specific retinal and eye-position signals at a common neural location.

The Wells-Hering's laws of perceived egocentric visual direction (EVD) assume that information about eye position includes equal contributions from both eyes. An implication of this assumption is that only versional eye movements should lead to a change in perceived EVD. Previously, we showed that a differential weighting of eye-position information occurs in some individuals during asymmetric vergence. To extend this finding, we determined here whether a differential weighting of eye-position information occurs also during symmetric vergence eye movements. Open-loop pointing responses to a bright target were obtained in five subjects to estimate the contribution of each eye's position information to perceived EVD during symmetric vergence demands that ranged from 6 prism diopters base in to 18 prism diopters base out. In all five subjects, the slopes of the lines fit to the pointing responses were in the direction that was predicted from an unequal weighting of eye-position information. We conclude that symmetric vergence movements can result in a change in perceived visual direction, contrary to an assumption of the Wells-Hering's laws.