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Patrick J. Bennett, Christopher P. Taylor, Allison B. Sekuler; Preservation of position-encoding mechanisms across the life span. Journal of Vision 2006;6(6):106. doi: 10.1167/6.6.106.
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© ARVO (1962-2015); The Authors (2016-present)
Previous investigators (Garcia-Suarez, et al., 2004) have used position judgment tasks to investigate how the mechanisms that encode position change with age and found that older observers had more difficulty discriminating position. However, Garcia-Suarez et al.'s task required attentional-switching, which may have impaired performance in older observers. Here we re-examine whether aging affects position encoding, using a task that taps the foundation of position encoding: phase-reversal discrimination (Field, 1984; Bennett & Banks, 1991). Observers viewed horizontal compound sine wave gratings (f+2f), and discriminated stimuli where the phase of 2f differed by 180 deg (i.e., 0° vs 180°, and 90° vs 270°). In separate experiments, f was set to 0.75 cpd or to 3 cpd; f contrast was 0.1. We varied the contrast of 2f to determine 77% correct thresholds for relative phase discrimination and compound grating detection (i.e., discriminating f alone from f+2f). In both tasks, we used a match-to-sample procedure with unlimited viewing time. Stimuli were arranged on the screen in a triangular pattern with the sample centered in the top half of the screen and the two potentially matching stimuli presented in the lower half. When discrimination thresholds were normalized by detection thresholds, we found no difference between age groups at either frequency. Hence, unlike what has been found in other position discrimination tasks (Garcia-Suarez, et al., 2004), we find no effects of age on phase discrimination. Thus, the foundation of position encoding appears to be preserved across the life span.
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