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Allison M. McKendrick, Anne E. Weymouth; The Effects Of Aging On Shape Discrimination: Closed Contours, And Textured Shapes Within Noise. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1880.
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© ARVO (1962-2015); The Authors (2016-present)
Previous reports suggest that aging minimally alters global closed shape discrimination. However, it has also been reported that older adults have more difficulty on tasks embedded in noise, including the extraction of contours such as required for global shape perception. In this study, we compare the effects of aging on two intermediate shape discrimination tasks: a global closed shape task (radial frequency (RF) patterns) and a glass pattern coherence task (discrimination of global shape signal from noise). Cortical area V4 is considered a key processing region for both stimuli, however, the mechanisms involved in the processing of these stimuli are likely to serve different purposes in normal vision. We predicted that the extraction of shape information from noise (Glass patterns) would not be robust to aging.
Fourteen younger (19-38 years, mean = 27) and 14 older (62-72 years, mean = 66) adults participated. Contrast detection thresholds were measured for the RF and Glass stimuli. Stimuli were then presented at 5 x contrast threshold for each participant for the shape discrimination tasks. A single-interval forced choice method of constant stimuli was used. For the RF task, the threshold sinusoidal amplitude for the discrimination of an RF3 (triangular) versus an RF4 (square) was measured. For the Glass pattern task, the threshold signal coherence level for the discrimination of concentric from radial patterns was determined.
Aging reduced performance on both shape discrimination tasks: RF: mean older = 27 sec arc, younger = 18 sec arc , t(26) = -3.14, p<0.01; Glass patterns: mean older = 29% coherence, younger = 16% coherence, t(26) = -5.67, p<0.01. To compare the magnitude of effect between tasks, effect sizes (Cohen’s d) were calculated as 2.1 for Glass patterns and 1.2 for RF patterns, demonstrating a relatively greater drop in performance for the glass pattern task with age.
Shape perception is not robust to the effects of aging. Greater deficits were manifest for the discrimination of shape from texture, than for the discrimination of closed contours. The data supports the premise that older adults have exacerbated difficulty on visual tasks that require extraction of signal from noise.
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