US tab

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

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

Dark Adaptation

Another contributor to this accident may have been dark adaptation. Its implications for research led to further understanding of our visual system and the improvement of nighttime driving and vision by providing more and improved roadside lighting. The process of dark adaptation causes the eye to increase its sensitivity in the dark. The earliest research conducted on dark adaptation identified two aspects to this night vision process. Hecht, Haig, and Chase, (1937) found that the first portion of dark adaptation begins at once. This half is rapid and due to our cone function. The second portion, due to rod function, occurs much slower. Cone adaptation completes in 3 to 4 minutes, whereas rod adaptation takes at least 30 minutes. Their research indicated that the course of human eye dark adaptation depended on the intensity of light used before adaptation occurs. The adaptation time varied depending on the light level preceding the process. For example, their research showed that rod adaptation only occurs after exposure to light intensities below 200 photons. However, exposure to light intensities of 4000 photons or more caused cone adaptation first, followed by rod adaptation. Rod dark adaptation appeared in two types- a rapid and a delayed. The rapid rod dark adaptation became evident after pre-adaptations to low intensities corresponding to those usually associated with rod function (Goldstein, 2010). In the accident previously described, dark adaptation occurred in two phases- cone adaptation first, then rod adaptation.

In a 2004 study, Lamb and Pugh examined the effects of dark adaptation on the retinoid visual cycle. They found that adaptational ability breaks down in one situation. When exposed to intense or prolonged light, a bleaching occurred to a great portion of the visual pigment in photoreceptors of the human eye. This was activated by light in its colorless form. After exposure, it took several minutes before full visual sensitivity returned to normal. Their results showed that the most intense exposure, which produced an almost total bleach of pigment, had an initial increase five times the normal magnitude that occurred in participants' visual threshold. Their eyes then proceeded to recover in the normal two-part form. The first part of recovery occurred rapidly due to cone functioning and, after about 11 minutes, the rods began to recover. After a total of 40 minutes, participants' eyes were fully dark-adapted. With vitamin A deficiency, this process happened even slower.

The effect of dark adaptation on nighttime automobile accidents proves to be an important research area. An example would be nocturnal myopia, also known as night myopia or twilight myopia. Individuals with this condition possess a greater difficulty seeing in low illumination areas, even though his or her daytime vision is normal. This results from the eye's far point for an individual's focus varying with the level of light. Research indicated that night myopia was caused by pupils dilating, allowing in more light causing a person to become more nearsighted. Usually, those with myopic vision require a stronger prescription for night driving. Additionally, night myopia, usually found in younger people than older people (Chen, Schmid, & Brown B, 2003; Cohen, et al. 2007), contribute to more nighttime accidents; implying that selected groups of drivers should be examined for night myopia.

Dark adaptation potentially had a major influence on the car accident described. Driving for about ten minutes started the dark adaptation process. Coming from a bright room, the driver of Vehicle A's sensitivity to light would have been still quite low compared to if he were completely dark adapted, but significantly more sensitive than when he started his drive. As mentioned in the section on glare, the driver of Vehicle A suddenly had two sources of headlights pointing toward him, one set on each side of him, creating a large amount of light hitting his eyes. This illumination from both cars' headlights almost completely reset the dark adaptation process. The driver of Vehicle A's exposure to intense lighting of the oncoming headlights, after driving in the dark for some time, caused the photoreceptors in his retina to become bleached. Even though cone adaptation occurs rapidly after light exposure, the rods would have taken several minutes before they could have recovered. Essentially the driver of Vehicle A became blind once Vehicle C passed and the driver of Vehicle B turned off her lights, given his eyes' sensitivity level was very low leaving the driver of Vehicle A with only his headlights for illumination. It was as if he stepped into a bright room again but then turned off the lights. The driver of Vehicle B probably saw Vehicle A coming toward her and turned off her lights so she would not blind him. However, this actually caused a worse problem. There was not enough time for the driver of Vehicle A to adapt again to the lower level of light.

Road Illusions >>