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Effects of yoked prism on spatial localization and stereolocalization

1 October 1994


The effects induced by yoked prism on spatial localization and on stereolocalization were assessed using two different two-dimensional spatial localization tasks and a polarized three dimensional localization apparatus. Subjects were 34 young healthy adults who met entrance criteria related to normal visual function. The subjects wore 15 prism diopter horizontal and vertical yoked prisms, and measurements were recorded assessing the shift of visual space perception in horizontal (x), vertical (y), and the perpendicular to (x) and (y), the near to far (z) axis. The effect of yoked prism on stereolocalization was examined by comparing perceived stereoscopic float of a vectographic target while subjects wore base up, base down, or plano lenses. Spatial perceptual shifts using two different tasks were quantified in visual feedback-free conditions. Significant shifts were detected in all testing conditions. The degree of spatial shift is related to the task performed. Also, on effect of vertical yoked prism on stereolocalization was statistically verified. Base up yoked prism creates perceptual modifications which cause subjects to stereolocalize 3cm further away in space (at a testing distance of 1.5m) than a plano lens condition. Base down prism moves stereolocalization responses 3cm closer to individuals than a plano lens condition. Perception of stereolocalization is altered by 6cm comparing 15pd base up to 15pd base down, at a testing distance of l.Sm. These results provide evidence of alterations in visual space perception associated with wear of yoked prism.


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