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Nathan Klein, Johnell Brooks; Impact of luminance and blur combinations on older drivers acuity and preferred speed. Journal of Vision 2008;8(6):425. doi: 10.1167/8.6.425.
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© ARVO (1962-2015); The Authors (2016-present)
Previous literature has shown that steering performance is robust to both reduced luminance and increased blur unlike visual acuity. While previous studies held driver speed constant focusing on steering performance to observe effects from the challenging visual conditions, the study reported here used ten older licensed adults, who drove a simulator on curvy rural roads with a 55 mph speed limit under nine conditions (luminance: 1, 0, and −1 log cd/m2; blur: 0, +2, and +5 D). These conditions were selected to represent ranges in luminance to correspond with civil twilight and common levels of refractive error, those that typically go unnoticed or untreated (excluding +5 D). After training, the vehicle speedometer was no longer available, and participants were instructed to drive at a speed where they could comfortably stay within the lane. Visual acuity significantly declined with each decrease in luminance and increase in blur. Steering performance was robust; drivers were within the lane a minimum of 90% of each trial. An investigation of driving speed failed to reveal a significant interaction or main effect of luminance. While a main effect of blur was identified, follow-up tests indicated that drivers slowed down only under the extreme blur condition (+5 D; M=38 mph). On average the speed for the +5 D blur condition was 5 mph slower than the more commonly occurring blur conditions (0 & +2 D). One unexpected finding was that drivers reduced their speeds when given a choice. Drivers slowed down from 53 mph when instructed to drive the speed limit using the speedometer to 47 mph when instructed to drive a comfortable speed without the speedometer. Future studies should examine how different instructions and speedometer use influence driver speed. More importantly, other age groups should be investigated for comparison with this sample of the older population.
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