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Kristina Rand, Margaret Tarampi, William Thompson, Sarah Creem-Regehr; The influence of object-ground contact on perception of distance and size under severely degraded vision. Journal of Vision 2011;11(11):79. doi: 10.1167/11.11.79.
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Important to successful navigation is accurate understanding of one's location relative to other objects within an environment. Past research has reliably revealed that observers are accurate in judging absolute distance in their environments, indicated through walking without vision to a previously viewed on-ground target, both under normal and degraded viewing conditions. However, less research has focused on perception of targets positioned off of the ground plane. This may be especially relevant for navigation under low vision, given the consequences of misperceiving target locations. We explored whether support for Gibson's ground theory (1950) would be found with degraded viewing as has been demonstrated with relative distance under normal viewing conditions (Meng & Sedgwick, 2001). In the current study, normally-sighted observers viewed white spherical targets placed on stands through goggles that severely reduced visual acuity and contrast sensitivity in one of two conditions. In the high-visibility condition, targets were placed on a stand painted black, resulting in high contrast with the gray carpet. In the low-visibility condition, stands were painted gray, making them undetectable under low vision conditions. In two counterbalanced blocks, participants made size and absolute distance judgments to three different sized spheres (.203, .304, or .406 meter diameters) at three target distances (1.5, 2.7, and 4 meters). Participants in the high-visibility condition exhibited accurate distance judgments, whereas low-visibility condition participants drastically overestimated target distances. Similarly, the size of targets in the low-visibility condition was judged to be significantly larger than the size of targets in the high-visibility condition. To allow safe travel for those with low vision, these findings point to the importance of highlighting how potential hazards make contact with the ground plane so that hazards are not perceived as more distant than they are actually located.
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