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Eugenie Roudaia, Patrick J. Bennett, Allison B. Sekuler; Effect of aging on the use of orientation and position in shape perception. Journal of Vision 2010;10(7):479. doi: 10.1167/10.7.479.
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Grouping local elements to extract shapes is a crucial task of the visual system. Recently, Day and Loffler (2009) showed that shape perception results from a weighted combination of local element positions and orientations, and the weighting of each cue depends on their relative strength. When elements whose orientations were consistent with a pentagon were positioned on circle, the orientation information dominated the percept and a pentagon shape was perceived. With increasing number of elements, the position information became more dominant and a circular shape was perceived.
Shape discrimination is unaffected by healthy aging (Habak et al., 2009). However, older adults are less influenced by local orientation information when integrating contours (Roudaia et al., 2008). Here, we examined whether the relative roles of orientation and position information in shape perception change with age.
Following Day and Loffler (2009), conflicting target stimuli were created by sampling the orientation of a rounded pentagon with Gabors and positioning them on a circle. Test stimuli were composed of Gabors whose positions and orientations were consistent with pentagon shapes of varying amplitude. On each trial, older (∼ 66 yrs) and younger (∼ 24 yrs) subjects viewed a target and test stimuli in two intervals and judged which shape looked more circular. The amplitude of the test stimulus was varied to measure the point of subjective equality between the perceived target and the test shapes. The number of Gabors comprising the stimuli was varied to manipulate the strength of position information. Consistent with previous findings, the perceived target shape was consistent with a pentagon for stimuli comprising 15 - 40 elements. This orientation dominance effect disappeared with denser sampling. Interestingly, this effect was equal in older and younger subjects across all sampling levels. These results support the findings that shape perception mechanisms are preserved in older age.
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