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Eugenie Roudaia, Patrick J. Bennett, Allison B. Sekuler; High-contrast contour integration and aging. Journal of Vision 2008;8(6):418. doi: 10.1167/8.6.418.
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© ARVO (1962-2015); The Authors (2016-present)
Contours comprising elements aligned parallel to the contour are detected more easily than those comprising elements orthogonal to the contour (e.g., Saarinen and Levi. VisRes, 2001). Recently, we found that element orientation had no effect on the ability of older observers to detect C-shaped contours against a blank background (Roudaia et al, VSS 2006), indicating that aging impairs contour integration processes, at least in near-threshold conditions. Recently, using closed contours, Del Viva and Agostini (IOVS, 2007) suggested that aging also may affect contour integration in high-contrast patterns. Here we examine the effect of local orientation on contour integration in younger and older observers at suprathreshold contrast levels with clutter. We compared performance of older and younger adults in discriminating a high-contrast, C-shaped contour comprising 16 Gabor patches embedded in a field of identical, randomly-oriented distractor Gabors. The C shape appeared centrally with the gap facing one of four different directions. In two conditions, Gabors were presented in positive cosine phase and were all aligned along the contour or were all orthogonal to it. In the third condition, Gabors were aligned along the contour but alternated positive and negative cosine phase. Two interleaved staircases manipulated stimulus duration to estimate the minimum time required for correct gap localization. Both groups exhibited lower thresholds in the aligned conditions than in the orthogonal condition. Older observers had higher thresholds than younger observers in all conditions, but were most severely impaired in the orthogonal condition, where thresholds were four times higher for older observers than for younger observers. Thus, although younger and older observers show facilitation with collinear contour elements, aging appears to disproportionately impair the integration of orthogonal contours. We are presently investigating whether these results can be explained by reduced levels of retinal illumination in older adults.
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