When a line judge at Wimbledon rules on a hair-splittingly close call and says the ball is out, the inevitably disgruntled player should not only consider challenging the call for review by digital replay system. He should consult a recent issue of Current Biology.
A vast majority of near-the-line shots called incorrectly by Wimbledon line judges have come on balls ruled out that were actually in, a study published in October by researchers at the University of California-Davis showed.
To the vision scientist, the finding added to the growing knowledge of how the human eye and brain misperceive high-speed objects. To the tennis player, it strongly suggests which calls are worth challenging and which are best left alone.
The researchers identified 83 missed calls during the 2007 Wimbledon tournament. Some were challenged by players and overruled, while others were later identified as unquestionably wrong through frame-by-frame video. Seventy of those 83 calls, or 84 percent, were on balls ruled out — essentially, shots that line judges believed had traveled farther than they actually did.
Called perceptual mislocalization by vision scientists, this subconscious bias is known less formally to Wimbledon fans as “You cannot be serious” — John McEnroe’s infamous dissent when, yes, a 1981 shot was ruled out.
Now that players can resort to a more evolved appeals procedure, the researchers’ discovery suggests that players should generally use their limited number of challenges on questionable out calls rather than those that are called in, because such out calls have a far better chance of being discovered as mistaken on review, then overturned.
“What we’re really interested in is how visual information is processed, and how it can be used to a player’s advantage,” said David Whitney, an associate professor at UC-Davis’ Center for Mind and Brain and the paper’s lead author. “There is a delay of roughly 80 to 150 milliseconds from the first moment of perception to our processing it, and that’s a long time. That’s one reason why it’s so hard to catch a fly — the fly’s ability to dance around is faster than our ability to determine where it is.”
This is the third Wimbledon in which players can challenge questionable calls for review by Hawk Eye, which uses high-speed video cameras to record balls’ flight. About 25 percent of all challenges are upheld.
There is no cost to the player when a call is proved correct, but after three such episodes in a set a player may not challenge again. Whether through strategy or residual tennis etiquette, most players leave many challenges unused.
Theoretically, line judges should be equally prone to call an out ball in as they are an in ball out. But when objects travel faster than humans’ eyes and brains can precisely track them — for example, Andy Roddick’s 240kph serves — they are left having to fill in the gaps in their perception. In doing so they tend to overshoot the object’s actual location and think it traveled slightly farther than it truly did.
Both successful challenge calls, as well as the overlooked mistakes that the researchers later identified, were several times more likely to come on “long” calls than “in” calls. The same pattern existed at Wimbledon last year, Whitney said, although the paper did not present that data.