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W. Wittich, D. H. Watanabe, J. Faubert, M. A. Kapusta, O. Overbury; Age-Independent Asymmetries in Spatial Interval Discrimination Across the Central Visual Field. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2006.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research indicated that positional acuity has a potentially relevant function for vision testing in the clinical context, specifically in the elderly. Tasks such as spatial interval discrimination resist the effects of age and their accompanying optical changes (Latham & Barrett, Curr Eye Res, 1998). The present study investigated the use of a bisection test which evaluates the perceived point of equidistance of two peripheral targets in relation to fixation. It was hypothesized that performance on this task would not depend on the age of the participant but both on eccentricity and retinal location of the stimuli.
21 participants with normal or corrected-to-normal vision, ranging in age from 25 to 69 (M = 43, SD = 13), were tested monocularly on the spatial interval discrimination task, ranging in eccentricity from 1 to 7 dva. The task required participants to judge which of two simultaneously presented flanker dots was closer to the fixation target. The range of presented stimuli was scaled to retinal eccentricity. Psychometric functions were fit to the data, resulting in measures of error (accuracy) and slope of the function (precision). Data were grouped for each retinal location (nasal, temporal, inferior, superior).
For the proportional error scores [(accuracy-eccentricity)/eccentricity], a 7 x 4 (eccentricity x location) ANOVA revealed an interaction effect of eccentricity by location. The point of perceived equidistance was placed more centrally (closer to fovea) in the superior field at central eccentricities, and was judged to be more peripheral at distal eccentricities, p < .03, 2 = .10. The reverse was the case for data in the inferior visual field. For the slope values (precision), both main effects of eccentricity and location were significant, p < .001 for both, 2 = .44 and .23 respectively. As eccentricity increased, participants became more precise while judgments in the horizontal were generally more precise than in the vertical. For both analyses, age was not significant as a covariate.
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