How Accurate is the Human Eye?

There's an interesting article about recent research into the accuracy tennis line faulting calls. The article points out the John McEnroe's perennial complaint about "bad calls" by judges is in fact wrong. A comparison of line judge's calls versus the player's assertions was checked using the Hawk-eye camera-based ball-tracking system. and it shows the judges were more accurate in their calls. What I find fascinating is how accurate the actual calls were given how fast the ball travels. It is amazing that a trained judge can be as good as they are.

A paper published on Wednesday in a British journal, Proceedings of the Royal Society B, has analysed 1,473 challenges to line calls by 246 professional tennis players in 2006 and 2007.

The study compares the line judge's call and the player's challenge with the final word from Hawk-Eye -- a hi-tech ball-tracking system used by the Association of Tennis Professionals (ATP) that can spot the position of a ball in play to within three millimetres (0.12 of an inch).

Professional players and line judges "are remarkably proficient" at judging ball bounce position, displaying an accuracy to within just a few centimetres (a couple of inches) when the ball is travelling at 50 metres per second (180 kilometers, 112 miles per hour), says author George Mather, a University of Sussex psychologist.

But the line judges were more reliable than the players. According to Mather's calculations, the judge is right 61 percent of the time when challenged. ...

Mather found most erroneous calls happened when a ball bounced within 100mm (3.9 inches) of a court line. Nearly one in 12 of such events were wrongly called by line judges.