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A.W. Siu, G.Y. Tang, P.P. Lui, K.S. Wong, H.H. Chan; The Effects of Defocus on Crowded English and Chinese Simulated Road Sign Tasks . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3682.
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Visual efficiency is a key visual factor contributing to road safety. This study examined the effects of optical defocus on English and Chinese simulated road sign visual task recognitions at different crowding levels.
Recognition thresholds of English and Chinese characters were measured from 36 young bilingual subjects at 3 defocus (0.00D, +0.50D and +1.00D) and 4 inter–words separation levels (angular subtend of 2’30", 5’00", 7’30" and 10’00") in randomized orders. Recognition thresholds from isolated (non–crowded) characters were taken as controls.
Optical defocus increased the recognition thresholds of both English and Chinese tasks (p<0.0001). Recognition thresholds of crowded tasks were significantly higher than those of isolated tasks (p< 0.001) in all defocus levels and the effect was similar among various inter–words spacing levels. The thresholds of Chinese characters were found to be significantly higher than those of English in the clear (p<0.05) but not in the +1.00 D defocus condition (p>0.05).
For visual tasks displaying both English and Chinese, Chinese characters should be constructed on average 8.1% larger than the English tasks to be perceived equal. The effect is complicated by the lower recognition performance under optical blurs and crowded tasks arrangement. The results may help improve the design of road signs in the Asian bilingual cities.
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