Purchase this article with an account.
L. Liu, T.K. Kuyk, P.S. W. Fuhr; Eccentricity Effect of Visual Search in Visually Impaired Patients . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4599.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Progressive slowing of visual search performance with increasing eccentricity (eccentricity effect, EE) has been observed in both young and old normal observers. Explanations of EE are all based on the difference between foveal and peripheral visual or attentional functions. In severely visually impaired (VI) patients, however, differential contribution of fovea and periphery to visual search may not be a valid explanation, because of the severe damage to the fovea or the extensive loss of peripheral field. How do VI patients search features at different eccentricities? Methods: Feature search performance for a 2x2 deg target amid 1x1 deg distracters was measured in 57 patients with severe visual impairment (VI) and 27 age–matched normal controls (NV). Eight, 16 and 32 items were randomly displayed on a 6x6 virtual grid that covered 10x10, 20x20 and 40x40 deg fields. All subjects practiced one session per field–size/set–size combination each day for 4 days before taking the final test. Each 6x6 grid was made of 3 concentric square rings. Reaction time (RT) and search accuracy for targets on different rings were analyzed separately. Results: The NV and VI groups had similar search accuracy. The VI group searched 44% to 84% slower and made more errors than the NV group at all field–size, set–size and eccentricity combinations. All differences in RT were highly significant. However, at all field–sizes and eccentricities, set–size effect either did not reach significance (α=0.05), or had RTxSet slopes less than 10 msec/item. Both NV and VI groups showed no significant EE when field–size was 10 deg and showed significant EE when field size was 40 deg. The NV group showed significant EE in RT at 20 field–sizes for all set–sizes, while the VI group only showed significant EE at 20 deg field and 32 items. Conclusions: Both NV and VI groups could perform parallel feature search at all eccentricities up to 40 deg. The VI group searched much slower than the NI group, but with good accuracy. Search performance of both groups showed similar dependence on eccentricity under most field–size/set–size combinations.
This PDF is available to Subscribers Only