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P.S. Fuhr, L. Liu, T.K. Kuyk; Association Between Visual Search and Mobility in Visually Impaired Patients . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4609.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Much effort has been made to associate mobility difficulties of visually impaired (VI) patients with conventional vision tests such as visual acuity (VA), visual field (VF), contrast sensitivity (CS) and scanning ability (SCAN). Since visual search tasks require both the ability to discriminate visual features and the ability to process information in a large field of view, the association between feature search and mobility of VI patients was studied. Methods: 44 patients with severe visual impairment (VI group) and 24 age–matched normal controls (NV group) participated. Feature search task was to detect a 2x2 deg square target amid 1x1 deg square distracters. 8, 16 and 32 items were randomly displayed on a 6x6 virtual grid that covered 10x10, 20x20 or 40x40 deg fields. All subjects practiced one session per field–size/set–size combination each day for 4 days before taking the final test. Hits, false alarms and reaction times (RT) for target–present and target–absent trials were recorded. Mobility was evaluated on indoor high–density obstacle courses under photopic and mesopic illumination. Run time and obstacle contacts were recorded. VA, VF, CS and SCAN were also obtained. Results: The VI group was twice as slow as the NV group in feature search, and made more errors, but both groups had RTxSet slopes less than 10 msec/item under all field–size/set–size combinations. The VI group was slower and made significantly more obstacle contacts than the NV group on obstacle courses. When VF, VA, CS and SCAN were entered into multiple regression analyses, VF accounted for 30%–40% of variation of VI patients' mobility performance while others did not make a significant contribution. Combinations of visual search speeds accounted for 21% to 69% of variations in mobility measurements. Combination of VF and search speeds accounted for 46% to 73% of variations in mobility measurements. Conclusions: VI patients could perform slower, less accurate, but still parallel feature search. Search speed accounted for a large portion of mobility variation that could not be accounted for by conventional vision tests.
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