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GL McCormack, R Price, F Thorn; A Nonverbal Method for Estimating Distance Perception Beyond Arm's Reach . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4672.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To evaluate a new method for estimating distance perception for near and far target distances which does not use verbalization or head movement and is free of cognitive influence. Methods: Distance perception was assessed in 22 normally binocular observers. The new method required subjects to point both forearms, with elbows in an outward position, to target location. Apparent distance is computed by triangulation. The new method was compared to kinesthetic matching of the index finger of the dominant hand to target distance. Targets were presented statically for 5 seconds at each of six randomized distances: 20,25,30,35,40, and 45 cm. The target was a 4cm constantly luminant maltese cross binocularly viewed in darkness. Each target distance was shown 12 times. Subjects viewed the target through their habitual glasses six times ("normal viewing"). The other six times the observers wore 4.5Δ; base-out and -2.00 sph over each eye, in addition to their glasses ("prism viewing"). The order of the glasses and methods variables was block randomized. Results: Responses were quantified by the slope of the regression of apparent distance versus actual distance. In normal viewing the new method generated a mean slope of 0.75 compared to 0.99 for kinesthtic matching. Prism viewing lowered the slope for kinesthetic matching to 0.77 (F=73,p=.0001) but had no effect on the new method (F=1.2,p=0.294). Kinesthetic error during normal viewing averaged ±2.5cm and changed little with distance. New method error was ±3.5cm at 20cm and grew to ±8cm at 40cm. For both methods, error increased approximately 25% during prism viewing. Conclusion: The new method quantifies apparent distance, but is not equivalent to kinesthetic matching. We hypothesize that nonbinocular retinal image cues eliminated the effect of the prism glasses on the new method's slope, and reduced the effect of prism glasses on kinesthetic matching slope. The higher measurement error of the new method and its rate of growth with distance would require repeated measures for practical application.
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