Loud grunts made by tennis players when hitting the ball could have a negative effect on opponents, say Canadian scientists.
Players such as Maria Sharapova and Rafael Nadal are notorious for their grunting, a practice which often triggers complaints in professional tennis, says Dr Scott Sinnett, lead author of the report that appears in the online journal PLoS ONE .
Researchers played 384 video clips of a tennis player hitting a ball to either the left or right of a video camera, to 33 students at the University of British Columbia , Canada.
The students were asked to quickly determine whether the ball was hit to the right or left. For some of the shots, a loud white noise was played as the racquet hit the ball.
"When an additional sound occurs at the same time as when the ball is struck, participants are significantly slower... and make significantly more decision errors," says the study.
A growing body of research shows that noise "distracts you from your ability to pay attention to what is going on," says Sinnett.
"A grunt doesn't allow you to place all your attention on what's happening. It blocks the ability to pay attention to a multi-sensory event."
Grunting could cause a tennis player to perceive a ball travelling 80 kilometres per hour to be "two feet (60 centimeters) closer to the opponent than it actually is," says Sinnett.
"This could increase the likelihood that opponents are out of position and make returning the ball more difficult."
"A lot of people have complained about grunting in the tennis world, that it's distracting, and even some professionals have said it's pretty much cheating," says Sinnett, who conducted the research as a post-doctoral fellow.
"The study raises a number of interesting questions for tennis. For example, if Rafael Nadal is grunting and Roger Federer is not, is that fair?"
Scientifically regulating tennis-players' grunts - some of which register at 100 decibels - "could be looked toward, because if it's distracting to opponent, then it's basically cheating," he says.