Tennis line judges call more 'out' balls incorrectly

A brain bias may be responsible for the tendency of tennis line judges to incorrectly call 'out' rather than incorrectly call 'in', according to research from California.

Researchers found that of 83 incorrect calls, 70 were incorrect 'out' calls. The cause is apparently the time lag of a few hundred milliseconds between the image hitting the retina and being processed by the brain.

The authors of the study say that this bias could be used by players in the 'challenge' system. A fast moving object, such as a tennis ball, could produce an illusion that the object has moved slightly further than it actually has to overcome the time lag. This could lead to line judges 'seeing' the ball falling over the line when it has in fact bounced on the line.