Brain Slow to Judge Fast-Moving Objects Head-On

WEDNESDAY Aug. 6, 2008 -- If you are not experienced at dodging flying or speeding objects, your best bet may be to just get out of the way, a new study says.

People's visual systems judge objects -- balls or cars, for example -- coming straight toward them based more on past experience than actual perception, according to findings published in this week's issue of the Proceedings of the National Academy of Sciences. For most, the world is a slow place.

"We may think we live in a fast moving, hectic world, but statistically, our environment moves around us slowly," Andrew Welchman, a researcher with the Biotechnology and Biological Sciences Research Council, said in a council news release. "Apart from the odd speeding car, buildings, landscape and walls around us all move past us at slow and predictable speeds. Our brains are constantly building up a statistical picture of the world around and, based on experience, it is a statistically slow world."

"When an object moves quickly -- be it a football, cricket ball or, for our ancestors, a spear -- our brains have to interpret the movement rapidly and, because our brains draw on experience, it's often biased by what it already knows. The less certain we are about what we see, the more we are influenced by the brain's statistical assumptions, which means in some circumstances, we get it wrong."

Welchman and colleagues at the University of Birmingham and the Max Planck Institute in Tubingen, Germany, developed a mathematical model to show how the brain predicts the motion of an incoming object and tested this with experiments. While people are generally better at judging sideways movement, approaching objects tend to look slower than they are. They also tend to misperceive location, often thinking that an object will miss them, when it ends up hitting them.

The research explains why top athletes are better at making decisions about an approaching ball or player, and also has implications that could help improve road safety. For example, people driving in poor visual conditions, such as fog, often drive too fast for the conditions, because they judge speed inappropriately. This, the research shows, is because the brain relies more on its assumption that the world moves slowly, so a driver believes the car is moving slower than it really is.

"Although it is not surprising that sportsmen who practice a lot build up a better statistical picture in their minds about where a ball might go, it is surprising that what should be a vital survival skill is based on such a trial-and-error learning experience," Welchman said.

He thinks the finding will also help in the development of robotic vision systems.

"Capitalizing on nature's design is a good way of building artificial visual systems for robots, as humans get visual judgments right a lot more often than the best current robot systems. Further, knowing the situations in which humans get it wrong is a useful starting point for the design of assistive devices to help correct those errors before they have serious consequences," he said.

More information

The U.S. National Library of Medicine has more about eyes and vision.

Posted: August 2008


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