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June 2004
Chromatic perception affects snowplow visibility
Orange snowplows are a common sight during winter in Minnesota
On a clear winter day, a bright orange snowplow is easy to spot. Even under low-visibility conditions—such as blowing snow or fog—it may seem that the plows' distinctive orange paint would make avoiding these huge vehicles easy. But appearances can be deceiving under certain conditions, according to researchers Albert Yonas and Lee Zimmerman.
When plows are operating in blowing snow, Zimmerman said, their orange color may actually make it harder for other drivers to judge their movement. Although white snow is very different in hue from the orange plow, the white and orange are similar in luminance, or brightness. This "low-luminance contrast" makes it difficult for the brain to judge the plow's motion relative to the observer, even when the observer is able to see that the plow is there.
Zimmerman graphically demonstrated this effect for session attendees using a color projector and a sheet of translucent white material—a surprising example of how the mind can play tricks on even an alert observer with no other distractions.
In terms of visual perception, Zimmerman explained, "we're not a camera." Several distinct mental systems handle object detection, localization, and other tasks necessary for us to perceive the world around us accurately. If any of these systems become confused, we may only realize that there is a problem when we bump into something—and bumping into a snowplow can have disastrous consequences.
Yonas and Zimmerman plan to continue their work on chromatic motion perception in order to determine if changes in color warning markings, chromatically controlled lighting, or other factors could improve driving safety.