Vehicle/motorcycle accident regularity possibly linked to brain miscalculating time of impact of smaller objects

Pat DeLucia, the coordinator of the Human Factors Psychology Program, said her results show that small, near objects can appear farther away than larger, farther objects. The study is published in Current Directions in Psychological Science.

An interest in softball as an undergraduate prompted DeLucia, also professor at Texas Tech's Department of Psychology, to study how the human brain perceives objects, their size and motion and an object's time to impact.

Her finding that an object's size affects distance perception may be the basis of car drivers miscalculating motorcyclists' distance and speed.

The brain uses two visual information cues for judging time to impact, she said. In the first, a moving object is reflected on the eye's retina. It expands as it approaches the eye, providing the brain accurate information about when the object will hit. This is called an optical invariant.

However, the brain also uses "rules of thumb" as well, such as various "artist" depth cues as a shortcut, she said. Many times, the brain interprets objects with a larger retinal image as closer. Since motorcycles are smaller than cars, the brain may use this shortcut to judge a smaller motorcycle farther away than it actually is, DeLucia said.

"With computer simulations, we had a big, far object and small, near object approaching the viewer, where the small object would hit first," she said. "We wondered if people would choose the big one, based on the artist depth cue of relative size or choose the smaller one based on the more accurate optical invariant. Unexpectedly, people picked the bigger object again and again. We found people relied on rules of thumb."

This effect of size on collision perception violates theories of perception that believe people evolved to rely on the most accurate information, such as optical invariants. Instead, DeLucia's findings suggest that perception is based on multiple information sources.

This size-arrival effect can lead drivers to misjudge when a vehicle would arrive at an intersection and could be considered a contributing factor in motorcycle/vehicle accidents.

DeLucia hopes to find funding from the Department of Transportation to create an education program to inform drivers of her findings to reduce the incidents of these types of accidents.