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How Perceptual and Cognitive Factors
are Involved in a Car Accident:
A Case Study

By: Vanessa Dominguez & Marc Gentzler | Mentor: Dr. Andrew P. Daire

General Visibility

The human eye functions best at high levels of illumination. This is due to visual receptors called cones, which are densely packed in the fovea of the retina that control vision in brighter light. Since cones allow for better determination of fine details and color, they provide higher levels of visual acuity in the fovea. Night driving uses mostly the peripheral vision (outside of the fovea), however there is still some light hitting the eye making the cones still somewhat operative. The peripheral area is mostly filled with rod receptors that are more sensitive to light than cones, but have very poor ability to perceive detail. Thus humans have lower visual acuity at night. Environmental factors such as driving at night and rain degrades the visual acuity of cones, increasing the risk of a crash. Konstantopoulos, Chapman, and Crundall (2010) explained that both of these factors may be related to drivers' visual search strategies that become more efficient with increased experience.

Clarke and team (2006) showed that time of day influenced both the severity and rate of crashes. Furthermore, it has been found that the fatal crash risk is increased up to four times when driving at night compared to daytime (Williams, 2003). Visual problems associated with low light conditions leading to an increase in reaction times contribute to the higher number of nighttime car crashes (Plainis & Murray, 2002). Leibowitz and Owens (1977) found that although night driving conditions produced little effect on peripheral vision, it contributed to focal vision impairment, resulting in the neglect of low luminance objects while driving at night.

Factors contributing to the lack of general visibility in the described accident included night driving, poor weather conditions such as fog and rain, worn road markings, glare from wet roads, and an absence of roadside lighting. Being able to judge depth perception, distance, and speed all prove important for safe driving (Baumberger et. al, 2005; Chan et. al, 2010; Nawrot et. al, 2004). Depth cues, which are important in determining where objects are in space and their speed are largely absent at night. A lack of street lighting did not help the situation. Fog and rain clearly reduce visibility, particularly with headlights shining on the precipitation. Glare as mentioned in the previous section reduces visibility by scattering light in the eyeball, making it less focused. It is difficult to see worn and wet road markings at night. This can make someone question which lane they are in and where the boarders of the road are, especially in confusing situations. These factors influenced the decisions the driver of Vehicle A had to make. Furthermore, his low-beam headlights reach approximately 150 to 200 feet away from his viewpoint, thus limiting visibility beyond that point. Going almost 100 feet a second, a stationary obstacle on the road that a driver perceives 200 feet away would be unavoidable.

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