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Johnell O. Brooks, Richard A. Tyrrell, Benjamin R. Stephens; The accuracy of observers' estimates of their ability to see and steer in low luminances. Journal of Vision 2007;7(9):246. doi: 10.1167/7.9.246.
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Drivers are comfortable overdriving their headlights at night. Leibowitz & Owens (1977) hypothesized that drivers are unaware of the “selective degradation” of focal visual functions (their ability to recognize objects and hazards at night) in part because ambient visual functions (including visual guidance / steering) are preserved at low luminances. Previous researchers have confirmed that the ability to steer - but not the ability to see details - is robust to lowered luminances (e.g. Brooks, Tyrrell & Frank, 2005; Owens & Tyrrell, 1999). However, no empirical investigations have directly explored the extent to which drivers are aware of how luminance affects steering and acuity. We asked 36 visually healthy, licensed drivers from three age groups (18–21, 35–50, and 65–78 years) to drive a fixed-base driving simulator (150° horizontal by 50° vertical) at a moderately high speed on an empty but continuously curvy road in a broad range of luminance conditions (−3 to 1 log cd/m2). First, participants were dark adapted and then, at each luminance, predicted both their ability to steer the vehicle and their ability to discern optotypes. Following another period of dark adaptation, at each of the 5 luminances observers spent five minutes driving the curvy road and had their acuity assessed. The older drivers overestimated their acuity while both young and middle-age adults underestimated their acuity. Importantly, participants correctly estimated that their high and low contrast acuity would decline as luminance decreased but were unaware that their steering capabilities would not. These results indicate that drivers fail to appreciate that acuity and steering are supported by separate visual mechanisms.
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