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A Pelah, R Hucknall, R Hedges, M Turner, J Shieh, H Apfelbaum, E Peli; Measures of Obstacle Avoidance While Walking in a Virtual Environment by Patients with Retinitis Pigmentosa . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3913.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: 1) To investigate obstacle avoidance strategies applied by individuals with limited peripheral visual fields, as due to retinitis pigmentosa (RP) or an artificially imposed visual field restriction; 2) To assess the contribution of non-visual walking-related signals for obstacle avoidance. Methods: We used a large, rear-projected screen placed in front of a treadmill to simulate the visual and non-visual signals experienced by a walker. In a trial, the monocular, centrally fixating subject was shown a motion clip representing forward advance at one of three angles presenting visual heading to either the left or right side of a fixed obstacle (a large vase), all placed within a virtual reconstruction of a shopping mall environment. Subjects were required to indicate whether their trajectory would take them to the «left’ or «right’ of the vase and do so as soon as they felt «confident’ of their choice, thus yielding two measures of performance: distance-from-obstacle and percent-correct. Better performance would be indicated by higher values in these measures. The two subject groups and five conditions included: 10 RP patients, walking or standing; and 14 controls, walking with peripheral field restriction (10 deg, coupled to head), and either walking or standing without the visual restriction. Results: Patients showed poorer performance overall compared to controls in all conditions, by both distance-from-obstacle and percent-correct measures. Restricting the visual field in walking controls reduced performance by both measures. However, whereas walking reduced performance by the distance-from-obstacle measure for both groups (possibly due to increased jitter from head movements), it did not change significantly the percent-correct measure in controls, and increased significantly percent-correct performance in patients. Conclusion: RP reduces the distance at which patients confidently judge their heading towards a looming potential obstacle and increases errors in such judgments; the non-visual signals accompanying walking in a virtual environment may affect heading for obstacle avoidance by promoting a strategy of delayed judgment for greater accuracy.
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