Does a tennis grunt distract you or mislead you?

It misleads. Players watching occluded rallies with amplified, attenuated or muted grunts judged the ball to land further away the louder the grunt was, while radial prediction errors stayed flat. Distraction predicts the opposite pattern of errors, which leaves the sound being read as information about how fast the ball is traveling.

Grunting in tennis is a widespread phenomenon, and whether it influences opponents’ predictions of ball trajectory, and if so why, is the subject of ongoing debate. Two alternative hypotheses have been proposed for why grunting might impede those predictions.

They differ in mechanism. The distraction account holds that grunts capture attentional resources necessary for anticipation, while the multisensory integration account holds that auditory information from the grunt systematically influences a prediction typically assumed to rely on visual information.

The test puts them against each other. Tennis players were presented with a series of temporally occluded video clips of rallies featuring experimentally amplified, attenuated, or muted grunting sounds, and asked to predict the ball landing position.

Higher grunt intensities yielded judgments of longer ball trajectories, whereas radial prediction errors were not affected. That pattern is clearly at odds with the distraction account, which predicts larger errors after louder grunts, and it provides strong support for multisensory integration instead.