Abstract
Eye dominance switches depending on whether the observer is looking left or right (Khan & Crawford, 2001). It is not known whether the switch is caused by a change in the eyes' positions, by a change in relative image magnification, or by both. We investigated the cause of dominance switch by independently manipulating eye position and image magnification. The stimuli were presented in a custom haploscope. A small target was presented in the center of a square. The target had zero disparity and the square had crossed disparity. Eye position was manipulated by rotating the arms of the haploscope so that the observer had to turn the eyes to look at the stimuli. Relative image magnification was manipulated by calculating the magnification associated with a variety of azimuths and applying them to the dichoptic square. On each trial, observers indicated whether the target appeared displaced leftward or rightward from the center of the square. If the left eye was dominant, the target would appear displaced to the left. If the right eye was dominant, it would be displaced rightward. The results showed, in agreement with Khan and Crawford, that the left eye was more dominant when the eyes were turned leftward and the right eye more dominant when they were turned rightward. The results also showed that relative image magnification affected dominance. For example, when the eyes were turned rightward, but the image was larger in the left eye, dominance shifted toward the left eye. We conclude that the shift in eye dominance that occurs with viewing direction is caused by both eye position and relative image magnification.
This research was support by grants from NIH and NSF.