• E-mail
• Print
• Comment
• Font Size
• Digg
• del.icio.us
• Discuss article

Download full size image

Researchers Say ‘Brain Bias’ Causes Most Bad Tennis Calls

Posted on: Tuesday, 28 October 2008, 14:35 CDT

Researchers say tennis line judges are more likely to make mistakes when calling balls "out" rather than "in."

Of 83 incorrect calls, 70 of the errors were wrong "out" calls, said Californian scientists.

The team said it came down to a time lag of a few hundred milliseconds between an image hitting the retina and the viewer processing it.

Experts suggest this kind of bias could enable players to exploit the "challenge" system.

Decoding information about the position of objects can be a complex task, as the brain has to allow not only for the movement of the object, but also for the movement of the eye relative to it.

This causes a time lag of a few hundred milliseconds between an image hitting the retina and our becoming aware of it.

Scientists say that if the object is moving fast, the brain produces an illusion that the object has moved slightly further than it actually has in order to overcome this lag.

In tennis terms, this means a ball which bounces on the line could actually be perceived by the line judge or umpire as slightly further away and called "out" as a result, according to the team from the University of California, Davis.

The researchers tested the theory by examining video clips of 4,000 random Wimbledon points and logging any incorrect calls.

If this "bias" did not exist scientists would have expected the number of balls wrongly called "out" to equal the number wrongly judged "in". In fact, of 83 calls, 70 of the errors were wrong "out" calls.

The only ways to eliminate this are to either judge every shot using the "Hawk-Eye" radar method or via instant replay, or to make everyone play on clay, when the ball leaves a "skid mark" showing the exact point it bounced, researchers said.

They suggested there is potential for players to use the knowledge of the brain bias to improve their success rate when challenging line calls.

"As it stands, the skill of challenging referee calls is intertwined with the skill of playing tennis itself - those players who make better use of their challenges benefit more," they said.

"Players should maximize their challenges, because the referee error rate is rather high for close calls - it is a suboptimal strategy to leave unused challenges.

"Because players are allowed to continue challenging calls as long as the challenges are correct, players should predominantly challenge those calls consistent with the perceptual error revealed here."

Professor George Mather, from the University of Sussex, said it was possible the bias was introduced not as the brain processed the visual information from the court, but as it decided how to respond.

"It may well be that there is a contribution from both the perception stage, and the response stage, with some other reason why the decision to call 'out' is made wrongly more often," said Mather, who has conducted his own research into the accuracy of tennis line calls.

He said his own research found the risk of wrong decisions due to this kind of bias was a small one.

---

On the Net:

• University of California, Davis

Source: redOrbit Staff & Wire Reports

More News in this Category