One woman’s blink of light was another woman’s fully formed narrative

Wednesday, March 10th, 2021

Tests of simple reaction time had done astonishingly little to help explain expert sports performance, David Epstein notes (in The Sports Gene):

The reaction times of elite athletes always hovered around one fifth of a second, the same as the reaction times when random people were tested.


So, in 1975, as part of her graduate work at [the University of] Waterloo, [Janet] Starkes invented the modern sports “occlusion” test.

She gathered thousands of photographs of women’s volleyball games and made slides of pictures where the volleyball was in the frame and others where the ball had just left the frame. In many photos, the orientation and action of players’ bodies were nearly identical regardless of whether the ball was in the frame, since little had changed in the instant when the ball had just exited the picture.

Starkes then connected a scope to a slide projector and asked competitive volleyball players to look at the slides for a fraction of a second and decide whether the ball was or was not in the frame that had just flashed before their eyes. The brief glance was too quick for the viewer actually to see the ball, so the idea was to determine whether players were seeing the entire court and the body language of players in a different way from the average person that allowed them to figure out whether the ball was present.

The results of the first occlusion tests astounded Starkes. Unlike in the results of reaction time tests, the difference between top volleyball players and novices was enormous. For the elite players, a fraction of a second glance was all they needed to determine whether the ball was present. And the better the player, the more quickly she could extract pertinent information from each slide.

In one instance, Starkes tested members of the Canadian national volleyball team, which at the time included one of the best setters in the world. The setter was able to deduce whether the volleyball was present in a picture that was flashed before her eyes for sixteen thousandths of a second. “That’s a very difficult task,” Starkes told me. “For people who don’t know volleyball, in sixteen milliseconds all they see is a flash of light.”

Not only did the world-class setter detect the presence or absence of the ball in sixteen milliseconds, she gleaned enough visual information to know when and where the picture was taken. “After each slide she would say ‘yes’ or ‘no,’ whether the ball was there,” Starkes says, “and then sometimes she would say, ‘That was the Sherbrooke team after they got their new uniforms, so the picture must have been taken at such and such a time.’”

One woman’s blink of light was another woman’s fully formed narrative. It was a strong clue that one key difference between expert and novice athletes was in the way they had learned to perceive the game, rather than the raw ability to react quickly.


  1. Wang Wei Lin says:

    I’m not sure what ‘perception’ means in this context, but neural processing is likely the difference. Years of competition builds neural networks specific to the task.

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