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Lenka Musilova, František Pluháček, Harold E Bedell, John Siderov; Number of flankers influences crowding and contour interaction differently. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1079.
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© ARVO (1962-2015); The Authors (2016-present)
Nearby contours have a deleterious effect on visual resolution. If the flankers are similar to the resolution target this influence is called crowding (CW); if the flankers are simple bars then the phenomenon is known as contour interaction (CI). The aim of this study is to compare the influence of the number of flankers on foveal CW and CI.
We analyzed the data of 4 normal observers from two laboratories, who viewed single, foveally presented high-contrast Sloan letters surrounded by 1, 2 or 4 high-contrast flankers under photopic conditions. Flankers were one of a selected set of Sloan letters (D, K, N, O for CW) that differed from the central target, or one-stroke-width bars (for CI), presented at several edge-to-edge separations. Single flankers were presented in the right, left, up or down position, 2 flankers were placed equally to the right and left or top and bottom of the central target, and 4 flankers were equally spaced in all four positions. Percent correct letter identification for each observer was determined for each type, number, position and separation of flankers based on 100 presentations of the stimulus and analyzed using repeated measures ANOVA.
Crowding and contour interaction were indicated by a significant effect of flanker separation (p < 2.1x10-13). Four and 2 flankers decreased target identification markedly in comparison with 1 flanker (p < 8.7x10-9). The effect of flanker number was especially apparent for smaller target-to-flanker separations, consistent with a significant interaction between number of flankers and separation (p < 10-13). The number of flankers showed a stronger influence on the percentage of correct responses for letter than bar flankers, as shown by a significant interaction between flanker type and number (p = 0.0053). Letter flankers also reduced the percentage of correct responses more than bar flankers at small target-to-flanker separations, as shown by a significant interaction between flanker type and separation (p < 1.8x10-6). However, the main effect of flanker type was not significant (p = 0.086).
The influence of nearby flankers on foveal letter identification increases with the number of flankers. The effect of letter flankers (i.e., crowding) is greater than bar flankers (i.e., contour interaction), especially for smaller target-to-flanker separations and a larger number of flankers.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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