Fast balls: Bad calls!Biology News
When fast balls graze the tennis baseline, how can referees see whether they're in or out? Well, in fact, they can't, says a study in the journal Current Biology. David Whitney, the study's lead author, is an associate professor in the Department of Psychology at University of California Davis. His group investigates how the brain perceives the positions of objects. Whitney saw a challenge call at Wimbleton where the ref called a ball out and the replay showed it was actually in. This made him realize he could carry out his studies on position perception in a real world situation. Whitney says the referee made the wrong call because, when humans look at a fast-moving object, the brain estimates its trajectory. But a tennis ball makes an unpredictable change, it bounces, and the brain does a poor job of prediction in this sort of situation. The study shows that when a ball bounces instead of proceeding along a smooth trjectory, there is a slight perceptual error -- a shift in the apparent location of the bounce in the direction of ball's motion. This means that a ball bouncing near the baseline, the back line of a tennis court, looks as though its point of impact is slightly further back than it actually is. This will show on a slow motion replay. Due to this phenomenon, more balls will be called out of bounds than actually are out of bounds -- the miss-called balls look like they bounce just past the baseline, but actually bounce on it or just inside it. What does this mean for the competitive player? Challenge the ref only when he calls your ball out, not when he calls your opponent's in.
Adapted from materials obtained from the AAAS
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