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Robert G. Meyerson, Martin S. Banks; The visual system does not compensate for different image sizes in the two eyes that result from eccentric gaze. Journal of Vision 2005;5(8):256. doi: 10.1167/5.8.256.
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© ARVO (1962-2015); The Authors (2016-present)
When the eyes are in eccentric gaze, the image is larger in one eye than the other. Previous research has shown, with the eyes in forward gaze, that images of different sizes are difficult to fuse and do not allow fine stereopsis. We asked whether the deleterious effects of differential magnification in the two eyes affect stereopsis in eccentric gaze. Ogle suggested that the visual system compensates for differential magnification in eccentric gaze. He proposed that a neural mechanism, triggered by eccentric gaze, adjusts the relative sizes of the two images so that fusion and fine stereopsis remain possible. We tested Ogle's hypothesis. Specifically, we measured disparity thresholds (the lowest discernible amplitude in a sinusoidal depth corrugation) as a function of relative image magnification in the two eyes and as a function of eccentric gaze. We found, as others have, that threshold is lowest in forward gaze when the image sizes are similar. We also found no effect of gaze eccentricity; in other words, disparity thresholds remained lowest in eccentric gaze when the size difference in the retinal images was minimal. These results show quite clearly that retinal-image magnification is not adjusted neurally with changes in gaze eccentricity. We will describe the implications of this finding for everyday vision.
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