PSYCHOLOGY:

Some tennis fans and players feel that grunting (i.e. emitting a sudden, brief, loud noise) during a tennis shot distracts the opponent, and therefore provides an unfair competitive advantage. Many professional tennis players grunt; one of them (Maria Sharapova) is reported to grunt at over 100 decibels.

To put this in perspective, such a grunt is as loud as a snowmobile, and is above the point at which sustained exposure may result in hearing loss. That's impressive, at least to me.

Whether grunting is an unfair tactic (deliberate or not) is subjective. However, whether it is or is not distracting, and therefore does or does not provide a competitive advantage, is a legitimate and fully testable scientific (psychological) question.

Scott Sinnett (University of Hawaii, United States) and Alan Kingstone (University of British Columbia, Canada) have performed such a scientific test. They have found clear evidence that grunting during a tennis shot is distracting.

Why might grunting be distracting?

Some tennis fans and players feel that it's important to hear the tennis ball strike the racket, a sound which is masked by grunting. There's a scientific basis to this argument.

Sound can alter one's perception of visual motion (e.g. the direction of the tennis ball or the swing of the racket). Furthermore, sound can also direct attention to the source of the sound (e.g. away from the tennis ball).

In other words, grunting may block the sound of the ball hitting the racket, or draw auditory and/or visual attention away from the ball. However, the argument that grunting during a tennis shot may distract the opponent has not yet been subjected to a rigorous scientific experiment, such as that carried out by Sinnett and Kingstone.

Grunting experiments.

The scientists studied 33 undergraduate students who were not competitive tennis players. Each one had normal (or corrected to normal) vision and normal hearing.

Each student sat 5 feet (60 centimeters) away from a computer screen in a sound-isolated, dimly-lit room. They watched 384 video clips of professional tennis players hitting a tennis ball, either backhand or forehand, to either the left or right of a camera (at the tennis court level) facing the players.

Each video clip was edited to either end at contact with the tennis ball or 100 milliseconds after contact, and to either include or exclude a grunt. In this case, the "grunt" was 500 milliseconds of 60 decibel (e.g. the volume of normal conversation) white noise during the shot, played from speakers on both sides of the computer screen.

Professional tennis players often grunt far louder than 60 decibels. Therefore, if this volume is distracting, then it's highly probable that grunting during professional tennis is also distracting.

How was distraction measured? The students were asked to quickly predict the direction of each tennis shot, pressing the X key if it was going to the left and the M key if it was going to the right.

These experiments were performed in three blocks of 128 video clips each. This should be plenty of time for resting between sets of experiments.

Grunting is distracting.

Grunting slowed down student response time by between 21 and 33 milliseconds, and the students made between 3% and 4% more predicted directional errors, whether the video clips ended at contact with the ball or 100 milliseconds afterwards. These differences in time and error were statistically significant.

When I first read this, I didn't think it was too big of a deal. However, the scientists put it into a perspective that proves it's a very big deal.

Assume that an incoming tennis ball is approaching at 50 miles per hour (they can come in at over 100 miles per hour). A time delay of 21 to 33 milliseconds translates to a tennis ball traveling two extra feet before the opponent can react.

Furthermore, given the average number of shots per professional tennis game, an increased directional error rate of 3% to 4% translates to one extra error per game. Given the small number of points awarded during a game, this may also be a big deal.

Final comments.

The scientists are currently performing more experiments to determine the possible contributions of auditory and visual attention, and auditory masking, that contribute to the distraction and error induced by grunting during a tennis shot. They also intent to test professional tennis players, and to use actual tennis grunts, to determine the effect of real-world grunting on real-world professional tennis players.

Also note that the simulated grunting (low-volume white noise) used in this research is far quieter than the grunts used by professional tennis players. It's likely (but as of yet untested) that in the real world, grunting affects the opponents' performance to a far greater extent than that reported herein.

NOTE: The scientists' research was funded by the Natural Sciences and Engineering Research Council of Canada.

Sinnett, S., & Kingstone, A. (2010). A Preliminary Investigation Regarding the Effect of Tennis Grunting: Does White Noise During a Tennis Shot Have a Negative Impact on Shot Perception? PLoS ONE, 5 (10) DOI: 10.1371/journal.pone.0013148