Monday, 21 January 2013

The A - Z of Sports Vision - Gaze

The difference between gaze control and eye movements is that gaze control takes into account movements of the head as well as just the eyes. Often, if you’re following an object such as a moving ball, you need to move your head so that you can accurately fixate the point at which you make contact with the ball (by bat, foot, racket etc.) In many sports, the ball moves too fast for the athlete to be able to follow it accurately without moving your head. In fact, the common exhortation to “keep your eyes on the ball” simply isn't possible. In cricket, Land & McLeod (2000) found that elite batsmen actually moved their gaze ahead of the ball, so that they were “lying in wait” for the bounce of the ball on the pitch. This enabled them to make the most appropriate stroke response. Similar strategies were found in table tennis by Ripoll and Fleurance (1988). Players need to be able to track the path of the ball early in its flight so they can predict the bounce point. In tennis, Ripoll & Fleurance found that players visually tracked the ball for on average 150 milliseconds for flat forehands, and 185ms if there was topspin as well. Similarly in cricket, Land & McLeod found that elite batsmen tracked the ball for the first 150 – 200ms of its flight. Just because you’re looking at one place, doesn't necessarily mean that your attention is focused on the same spot. For instance, a boxer who wants to make a body shot can do so without taking his eyes off his opponent’s face. If he had to look down every time, it would give his intention away to his opponent. The fact that he doesn't have to suggests that the two systems – gaze control and attention – are completely separate. However, more recent research has suggested otherwise. Shepard et al (1986) found that it wasn't possible for participants in their studies to change their gaze from one point to another whilst maintaining their visual attention on the initial point. Studies using brain imaging have since discovered that the same nerve pathways within the brain are involved in both moving the gaze and shifting visual attention. So athletes can be looking at one place whilst thinking about somewhere else, but moving the eyes means shifting the attention. It’s also been found by Shepard and others that the shift of attention comes before the shift in gaze. Elite athletes seem to be able to control their attention and gaze on crucial positions at crucial moments in many sports. This is the “Quiet Eye”. But you’ll have to wait until “Q” to find out more about that. David Donner

Friday, 11 January 2013

The A - Z of Sports Vision - Feedback

When you are learning a new skill, you want feedback as to how you are doing. In fact there are two kinds of feedback: one gives you knowledge of the result (did I score a goal?) and the other gives you knowledge about your performance (did I kick the ball correctly?) Salmoni (1984) suggested that although feedback guides the performer to the correct movement, it can have negative effects when provided too frequently. The brain has its own feedback system from the senses, including feedback from our muscles as we carry out physical tasks. The problem is that the learner can become so dependent on the feedback provided by the coach, that this natural learning system is undermined, and there’s nothing to rely on when the coach’s feedback is no longer available. Feedback that is provided at the same time as the movement is particularly detrimental to learning. This type of feedback typically has very strong performance-enhancing effects during practice; but clear performance decrements, relative to when feedback is provided after the movement, are seen in transfer and retention tests (Park, Shea and Wright, 2000 for example). A problem with a lot of the feedback given to learners is that it tends to direct their attention to their own movements, which is generally less effective for learning than concentrating on the effects of one’s movements. Reducing the relative feedback frequency, on the other hand, might give the learner a chance, at least once in a while, to perform the movement without being too concerned about their performance. Janelle et al (1997) gave participants a throwing task using their non-dominant hand. There were three groups: two received additional feedback in the form of a video replay and comments from an expert, and one group didn't receive this. Of those that received the extra feedback, one group received after each group of five throws, and the other received the feedback only when they requested it. In the practice phase, those who received the extra feedback threw better than those who didn't receive it. However, on a retention test some days later, participants who had received additional feedback only when they had asked for it during practice demonstrated better throwing form and accuracy than participants in the other groups. This suggests that skill retention may be enhanced if instructors provide feedback only when learners request it during practice sessions. Great coaches are able to design practice so that feedback is embedded into the drill, leading to automatic readjustment, which in turn improves the quality of the feedback, generating further improvements and so on. Positioning oneself in this kind of feedback loop produces astonishing improvements (Syed 2011). David Donner

The A - Z of Sports Vision - Eye Dominance

If you point to a distant object, close one eye and then the other, you’ll notice that when one eye is closed you’re no longer lined up. This is the effect of parallax, when there are two lines of sight, one for each eye. The brain has to choose one eye for alignment, and this is known as the dominant eye, though “aligning eye” might be a better description. You might think that eye dominance would match handedness, but there are many instances of “cross dominance”, For instance, Griffiths (2002) found that 40% of left-handed batsmen playing for Scotland were right-eye dominant. Even in archery, where aiming is obviously the essence of the sport, 18.75% of internationals studied were found to have cross dominance. In his study, Griffiths found that deliberately making the dominant eye blurred strongly affected the performance of clay pigeon shooters, not surprisingly. But for tennis players, the greater effect came from blurring the non-dominant eye. And these weren't just any tennis players: they included previous winners and finalists at Wimbledon, The US, Australian and French Open Championships. And it was those who were right-handed and right-eye dominant who were most affected when their non-dominant (left eye) was blurred. This suggests that it would be their depth perception that was affected. In cricket, eye dominance can affect the stance, with a right-eye dominant right-handed batsman requiring a slightly more open stance to ensure that the right eye is aligned with the ball. Unfortunately, this stance is often coached to youngsters without checking their eye dominance first. Eye dominance may also be part of the explanation for the number of elite cricketers whose batting stance is the opposite of their bowling action. Misalignment of the dominant eye is a well documented cause of errors when putting in golf. I've seen several cases where a consistent missing of putts to one side has been caused by using different eyes when aligning the ball with the hole and the putter to the ball. I use a different eye for alignment depending on which hand I use for putting, which is why both hands should be used when testing for eye dominance. Bizarrely, I naturally align with my left eye when I point with my right hand, and vice versa. I've no idea why I do this, but it does explain why, when I used to shoot, my first shot was always off target, and I had to aim to the side to compensate. If I’d known, I could have just closed my left eye. David Donner