We saw in my last post, Batting 101, that for the first stages of a cricket ball’s flight toward the batsman, the batsman isn’t following the ball with his eyes. He is keeping his eyes still, allowing the ball to cross his field of vision, before flicking them quickly to the point on the pitch where he thinks the ball will bounce.
Why is this? The answer is related to how batsmen judge the speed of the ball. In baseball, where the ball is coming (almost) directly at the batter, batsmen use two factors to judge the ball’s speed: the ball appears bigger (known as image expansion) and the batter’s eyes see different things (binocular disparity) as the ball gets closer. The rate of change of these effects is related to the ball’s velocity.
But in cricket, the ball is not coming directly at the eye – it bounces. Land and McLeod conclude that image expansion and binocular disparity would be insufficient to allow the accuracy with which elite batsmen judge the balls flight. The evidence in support of this conclusion is that batsmen do not track the ball for most of the pre-bounce period.
Instead, batsmen rely on the change in the angular position of the ball – the angular velocity. To measure this most accurately, batsmen keep their eyes still, so that the brain doesn’t have to “factor out” the movement of the eye. An image of the ball in the centre of the batsman’s field of view is not needed. Once they can estimate the speed, and in particular the downward velocity of the ball, they can estimate where it will bounce.
This visual strategy is what Dr. Joan Vickers from the University of Calgary calls “the quiet eye”: a period of time when the eye is stable on a critical object or location prior to the body performing the movement. Elite volleyball players, for example, wait almost 0.4 seconds after the ball is served before taking their first step, while less skilled players have no quiet eye at all: they begin moving even before the ball was served, making it difficult to maintain gaze on the ball. In cricket, the gaze is fixed on the point where the bowler will release the ball. Here’s a short video on the quiet eye from Scientific American.
It is only after the bounce (or late in the trajectory if the ball bounces close to the batsman) that image expansion and binocular disparity become useful information for the batsman. Their use is primarily to gauge the amount of bounce – this is related to the hardness of the pitch (the coefficient of restitution, or “bounce coefficient”), which the batsman learns through experience, not an intuitive calculation.
How does this visual strategy relate to the mechanics of hitting the ball? Stay tuned for my next post!
Introduction to Batting in Cricket: Mechanics, Visual Strategy and Psychology
Other posts in this series:
Letters to Nature 