One of the fastest movements that the human body can make is with the eyes. When we move them to look at something that’s grabbed our interest, that short, sharp, jerky movement is called a saccade, and on average we make about three of them every second. Eye movements are interesting, because they represent both the first and last steps in seeing. They’re responsible for stabilising images that are transmitted to the brain against jitter caused by head movements, but they’re also a response to our representation of the world; to information about plans, goals, interests and even expectations about future events.
So eye movements are useful to research because understanding how, why and where we move our eyes can provide us with information on how the brain goes about making decisions. But they also pose a problem in things like ball sports – saccades take a certain amount of time to generate, so by the time you’ve decided to look at a ball, it will have already moved on. Say an eye movement takes about half a second to be programmed and executed, and a cricket ball is bowled at 70mph. In the time it takes to detect the ball and move your eyes to it, the ball will have travelled about 16 metres – more than three-quarters the length of the pitch. So how do expert cricketers (or any other sports people, for that matter) get over this apparent difficulty and hit the ball so consistently well?
In 2001, Mike Land at the University of Sussex and Peter MacLeod at Oxford University attempted to answer just that. They took three batters of differing skill levels and measured their eye movements while firing cricket balls at them from a bowling machine. What they found was that the batters would try to anticipate where the ball was going to be by making a saccade to the point of contact with the floor. In the case of the best batter, his eye movements were initiated a fifth of a second earlier than the worst batter’s, meaning that he had more time to take in information about the ball’s movement at the bounce point. In other words, expertise results in being able to predict more accurately where the cricket ball is going to be in the future.
So it’s not the case that batters track the ball all the way through its flight. But do they watch it when it hits the bat? Until recently, the answer was thought to be a resounding “no” – studies looking at the interaction between the vision and the motor systems argued that it couldn’t happen. But in a recent PLoS ONE paper, David Mann and colleagues pointed out that this doesn’t really sit well with anecdotal reports from world-class players who are adamant that they do see the ball when they hit it.
To investigate this properly, Mann and his team took two top batters, and recorded their head and eye movements while they hit balls delivered from a bowling machine in front of a projected video of a bowler. They found that the batters were able to synchronise their head movements with the trajectory of the ball incredibly precisely. The batters then made anticipatory eye movements towards their bat, so that they could see the moment the ball comes into contact with it. When the researchers looked at the eye and head movements of club-level players instead, they found that these batters weren’t as accurate in being able to couple their head movements to the movement of the ball. They also weren’t very good at making those anticipatory eye movements to see the ball come into contact with the bat.
All of these sorts of predictive movements provide the brain with more information about what’s going on around you, which in turn gives you a little bit more time to prepare and adjust your own movements. In the case of expert cricketers, even having a few hundredths of a second to adjust the orientation of their wrists could mean the difference between a boundary and a catch. However, it’s still not quite clear precisely why late information about the ball hitting the bat is useful. At any rate, the old adage is wrong – don’t keep your eye on the ball. Keep your eye on where the ball’s going to be.