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Kristina Rand, Jon Bakdash, Jeanine Stefanucci, Sarah Creem-Regehr, Woodrow Gustafson; Perceptual Dependence of Size and Distance? A Within Subjects Variability Approach. Journal of Vision 2012;12(9):901. doi: 10.1167/12.9.901.
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Are percepts of size and distance coupled or independent? According to the size-distance invariance hypothesis and Emmert’s Law (Emmert, 1881; Gilinsky, 1951), perceived size is derived from apparent distance and the visual angle of the object. In contrast, Gibson (1979) posited that size and distance are perceived independently. Many studies have supported a relationship between estimates of size and distance, typically through positive correlations in mean values. However, to truly assess perceptual independence, mean values alone are insufficient as common visual information can produce a positive mean correlation (sampling dependence). Using principles of General Recognition Theory (GRT, Ashby & Townsend, 1986), means and variability of action measures of size and distance were compared to determine if the percepts converged on the same underlying construct, or were disassociated. In Experiment 1, participants viewed three spherical objects (one at a time) located on the ground plane. Participants performed two counterbalanced blocks of trials: a size judgment block (indicate object size using hands), and a distance judgment block (walk without vision to a previously viewed target location). A measure of intra-individual standard deviation was calculated for each participant for each block type. A repeated-measures correlation coefficient (rm) was calculated through the methods of Bland (1995), yielding a weak correlation between size and distance percepts, rm=.15, N=20. To alleviate the potential concern that participants used a memory strategy due to the small number of targets, in Experiment 2 we used 9 targets of 4 different colors, again yielding a weak correlation, rm= .08, N=12. Together, these results argue for the perceptual independence of size and distance percepts. Findings from a related experiment suggest that size and distance percepts might be less independent in conditions of degraded vision. We are currently conducting a follow-up study which compares size and distance judgments in degraded viewing conditions.
Meeting abstract presented at VSS 2012
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