Congratulations to Roger Federer and his ATP Tennis final win this weekend in London but it got me thinking and researching from a Sports Vision point of view...
Linesmen are more likely to call a ball "out" when it was "in", rather than the other way. Why?
After an image is focused on the retina, there's a time delay of about 100 milliseconds before it is recreated in the brain. This is the image that we see, not the one on the retina.
Therefore, our perception of things lags fractionally behind reality. For moving objects, the visual system gets round this problem by shifting the image forward. This means that a tennis player can get their racket in the right place at the right time, and not fractionally late.
In theory then, when a ball bounces there's a likelihood that it will be perceived to have bounced further on (in the direction of travel) than it actually did.
To test the theory, Whitney et al (2008) reviewed more than 4,000 randomly selected Wimbledon points. They found 83 incorrect calls, of which 70 were of the type predicted.
The researchers suggest that players are therefore more likely to be successful challenging calls of "out" than calls of "in".
David Donner
Monday 29 November 2010
Wednesday 24 November 2010
Rugby Line Out
The importance of an accurate line-out throw was highlighted when Dylan Hartley’s overthrow led to an Australian try in the recent international.
One of the best ways of practising the line-out throw is to suspend a ball from the crossbar at the required height. This gives the hooker a target to aim for, and the catchers have to catch the thrown-in, as opposed to the suspended ball. When line-outs are contested, the hooker has to learn to give the ball the correct flight to beat the front jumpers. When the suspended ball is removed, the hooker has to imagine that there’s a ball there to aim at.
The importance of holding the ball in a consistent fashion has been demonstrated in research on basketball free throws.
Aglioti et al (2008) tested 10 elite professional players, 5 sports journalists, 5 sports coaches and 10 students who were complete novices. They were shown video clips of different lengths of a professional player taking free throws, and had to predict whether or not the throws were successful. They found that the professional players were able to predict significantly more successfully when the clips were stopped at the point when the ball left the hand. The other groups needed to see the trajectory of the ball after release before they could make accurate predictions.
Researchers then used transcranial magnetic stimulation (TMS) to assess activity in the brain when the participants were watching the video clips. They found that both expert players and watchers had increased activity in the parts of their brain concerned with movement when they watched video clips of free throws, as opposed to when they watched static pictures or videos of footballers taking a penalty. Novices did not show this higher level of brain activity.
The really interesting bit was when the researchers studied the brain activity of elite players when they watched a “miss”. At the moment the ball was released from the hand, there was a spike in activity in the area of the brain that controls a muscle in the little finger called the abductor digiti minimi. This muscle pulls the little finger away from the body’s midline.
The researchers also looked at the angles formed by the little finger, wrist and knee joints during free throws. At the point when the ball was released, when the elite players watching got their vital information, the only difference between shots that were accurate and those that missed was the little finger angle.
So, hookers note: if your little finger is in the wrong position at the moment the ball is released, your throw is likely to be off target.
David Donner
One of the best ways of practising the line-out throw is to suspend a ball from the crossbar at the required height. This gives the hooker a target to aim for, and the catchers have to catch the thrown-in, as opposed to the suspended ball. When line-outs are contested, the hooker has to learn to give the ball the correct flight to beat the front jumpers. When the suspended ball is removed, the hooker has to imagine that there’s a ball there to aim at.
The importance of holding the ball in a consistent fashion has been demonstrated in research on basketball free throws.
Aglioti et al (2008) tested 10 elite professional players, 5 sports journalists, 5 sports coaches and 10 students who were complete novices. They were shown video clips of different lengths of a professional player taking free throws, and had to predict whether or not the throws were successful. They found that the professional players were able to predict significantly more successfully when the clips were stopped at the point when the ball left the hand. The other groups needed to see the trajectory of the ball after release before they could make accurate predictions.
Researchers then used transcranial magnetic stimulation (TMS) to assess activity in the brain when the participants were watching the video clips. They found that both expert players and watchers had increased activity in the parts of their brain concerned with movement when they watched video clips of free throws, as opposed to when they watched static pictures or videos of footballers taking a penalty. Novices did not show this higher level of brain activity.
The really interesting bit was when the researchers studied the brain activity of elite players when they watched a “miss”. At the moment the ball was released from the hand, there was a spike in activity in the area of the brain that controls a muscle in the little finger called the abductor digiti minimi. This muscle pulls the little finger away from the body’s midline.
The researchers also looked at the angles formed by the little finger, wrist and knee joints during free throws. At the point when the ball was released, when the elite players watching got their vital information, the only difference between shots that were accurate and those that missed was the little finger angle.
So, hookers note: if your little finger is in the wrong position at the moment the ball is released, your throw is likely to be off target.
David Donner
Rugby Place Kicking
Place kicking is an area where visualisation and ritual can play a huge part in success. They are necessary because these are the occasions when the player has time to think about what he’s doing, which makes it more difficult to act instinctively.
When an action is so grooved that it becomes routine, it indicates that the subconscious brain, and the cerebellum in particular, has taken control. If, however, the conscious brain takes over, which is especially likely to happen on important kicks, performance is likely to deteriorate. Rituals, such as crouching, or tapping the feet, keep conscious thoughts at bay, and allow the player to follow a pre-set routine.
Many successful kickers visualise the whole process before executing it. The same patterns of the brain are stimulated when visualisation is used as when the actual activity is performed. So visualisation seems to prime neural circuits, and this also helps to exclude the conscious, analytical parts of the brain from the execution.
When Johnny Wilkinson was taking kicks for England, he’d imagine that there was a lady called Doris whom he could see through the posts sitting in the crowd. I think at one time he imagined she was reading a newspaper. Then he imagined she was holding a drink which he would try and knock out of her hand. He would then have an imaginary line, like an imaginary wire, the ball would follow on its way through the posts to Doris.
I’ve always assumed that the best kickers would focus on a particular part of the ball with which they would aim to make contact, rather than just focusing generally on the ball. I’d not seen any evidence for this, until I read a recent quote from Dave Alder, the Wasps fly half: “I was once practising with a set of six (balls) and something didn’t feel right about one of them. It was only after I’d been kicking for a while that I realised the logo on the ball had been printed upside down”.
If you could get a ball marked up with lots of different sectors, it would help those learning to kick to discover which parts of the ball they should be focusing on in order to execute the desired type of kick.
David Donner
When an action is so grooved that it becomes routine, it indicates that the subconscious brain, and the cerebellum in particular, has taken control. If, however, the conscious brain takes over, which is especially likely to happen on important kicks, performance is likely to deteriorate. Rituals, such as crouching, or tapping the feet, keep conscious thoughts at bay, and allow the player to follow a pre-set routine.
Many successful kickers visualise the whole process before executing it. The same patterns of the brain are stimulated when visualisation is used as when the actual activity is performed. So visualisation seems to prime neural circuits, and this also helps to exclude the conscious, analytical parts of the brain from the execution.
When Johnny Wilkinson was taking kicks for England, he’d imagine that there was a lady called Doris whom he could see through the posts sitting in the crowd. I think at one time he imagined she was reading a newspaper. Then he imagined she was holding a drink which he would try and knock out of her hand. He would then have an imaginary line, like an imaginary wire, the ball would follow on its way through the posts to Doris.
I’ve always assumed that the best kickers would focus on a particular part of the ball with which they would aim to make contact, rather than just focusing generally on the ball. I’d not seen any evidence for this, until I read a recent quote from Dave Alder, the Wasps fly half: “I was once practising with a set of six (balls) and something didn’t feel right about one of them. It was only after I’d been kicking for a while that I realised the logo on the ball had been printed upside down”.
If you could get a ball marked up with lots of different sectors, it would help those learning to kick to discover which parts of the ball they should be focusing on in order to execute the desired type of kick.
David Donner
Rugby and Sports Vision
Few sports demonstrate the interaction between vision and action better than rugby. And rarely has this been better highlighted than in England’s second try against Australia at Twickenham recently.
When Ben Youngs had the opportunity to clear the ball into touch from his own try line, he realised that Quade Cooper had over-committed himself. Instead of passing the ball immediately, Courtney Lawes drew the tackler first. Chris Ashton initially thought of going outside Drew Mitchell, but realised that the Australian was backing off, so cut infield to score under the posts.
These were split-second decisions made on analysis of the defender’s body position, as well as awareness of the positions of support attackers. There’s no time to think, which means that these decisions have to be made instinctively. And the only way to achieve that is through hours and hours of relevant practice.
Yet so much rugby coaching concentrates on teaching the skills in isolation. How much time is spent learning to pass the ball without any opposition? How many second-row forwards are given the opportunity to learn the skill of timing a pass from reading the defender’s body position, as opposed to always running with their head down? It’s perhaps no coincidence that Lawes, like Simon Shaw, came late to rugby. Both of them learned their ball-handling and spatial awareness skills though basketball and other sports they played as youngsters.
These skills can be, and probably need to be, learned from a young age. Playground games of tag, and other park or street games are an ideal start. They’re fun, largely unstructured, and have most of the required elements. Small-sided rugby games do a similar job.
When Courtney Lawes was young he used to accompany his dad to martial arts training, and judo, in particular is really useful for learning how to tackle, and be tackled, without being injured. A prime example is Thierry Dusautoir, yet another forward who didn’t take up rugby until in his teens, yet had been doing judo since the age of 4. When France defeated New Zealand in the World Cup quarter-final in 2007, Dusautoir made 38 tackles. That was more than the entire All Blacks team.
There are two areas where the visual requirement is largely an aiming skill: line-outs and place-kicking. So these shall have blogs of their own.
David Donner
When Ben Youngs had the opportunity to clear the ball into touch from his own try line, he realised that Quade Cooper had over-committed himself. Instead of passing the ball immediately, Courtney Lawes drew the tackler first. Chris Ashton initially thought of going outside Drew Mitchell, but realised that the Australian was backing off, so cut infield to score under the posts.
These were split-second decisions made on analysis of the defender’s body position, as well as awareness of the positions of support attackers. There’s no time to think, which means that these decisions have to be made instinctively. And the only way to achieve that is through hours and hours of relevant practice.
Yet so much rugby coaching concentrates on teaching the skills in isolation. How much time is spent learning to pass the ball without any opposition? How many second-row forwards are given the opportunity to learn the skill of timing a pass from reading the defender’s body position, as opposed to always running with their head down? It’s perhaps no coincidence that Lawes, like Simon Shaw, came late to rugby. Both of them learned their ball-handling and spatial awareness skills though basketball and other sports they played as youngsters.
These skills can be, and probably need to be, learned from a young age. Playground games of tag, and other park or street games are an ideal start. They’re fun, largely unstructured, and have most of the required elements. Small-sided rugby games do a similar job.
When Courtney Lawes was young he used to accompany his dad to martial arts training, and judo, in particular is really useful for learning how to tackle, and be tackled, without being injured. A prime example is Thierry Dusautoir, yet another forward who didn’t take up rugby until in his teens, yet had been doing judo since the age of 4. When France defeated New Zealand in the World Cup quarter-final in 2007, Dusautoir made 38 tackles. That was more than the entire All Blacks team.
There are two areas where the visual requirement is largely an aiming skill: line-outs and place-kicking. So these shall have blogs of their own.
David Donner
Wednesday 10 November 2010
OCT Scanning
When deciding whether or not to have an OCT scan, people sometimes say to me "See if you find anything during the eye examination that requires a scan."
But if I've found a problem just from looking in the eye, I usually don't need a scan to confirm it. The point about the OCT is that it enables us to see beneath the surface, to give information that I don't already know; to see what I haven't already seen.
This is particularly useful for glaucoma and macular degeneration, which I talk about separately. But it also shows up diabetic changes in the eye; it helps to distinguish between benign and malignant pigment spots; and it's even been used to diagnose a child at risk of getting colon cancer.
Using the Topcon OCT, we also get a photograph of the retina, which is really useful for seeing the changes to blood vessels that occur with raised blood pressure or high cholesterol levels. When you can combine the surface view and the view underneath, you get the complete picture. I recently saw a lady who had quite poor vision, especially in one eye, and cataracts. The OCT revealed a hole in the macula in one eye. But it also showed that a cataract operation in the other eye would restore her vision to normal.
In the 18 months since we've had the OCT, we've done thousands of scans. Most of them have shown normal, healthy eyes. But some have shown problems at a much earlier stage than we would otherwise have detected them. This has meant earlier and therefore more effective treatment, and much sight has been saved. I'm often thankful that we now have this technology.
David Donner
But if I've found a problem just from looking in the eye, I usually don't need a scan to confirm it. The point about the OCT is that it enables us to see beneath the surface, to give information that I don't already know; to see what I haven't already seen.
This is particularly useful for glaucoma and macular degeneration, which I talk about separately. But it also shows up diabetic changes in the eye; it helps to distinguish between benign and malignant pigment spots; and it's even been used to diagnose a child at risk of getting colon cancer.
Using the Topcon OCT, we also get a photograph of the retina, which is really useful for seeing the changes to blood vessels that occur with raised blood pressure or high cholesterol levels. When you can combine the surface view and the view underneath, you get the complete picture. I recently saw a lady who had quite poor vision, especially in one eye, and cataracts. The OCT revealed a hole in the macula in one eye. But it also showed that a cataract operation in the other eye would restore her vision to normal.
In the 18 months since we've had the OCT, we've done thousands of scans. Most of them have shown normal, healthy eyes. But some have shown problems at a much earlier stage than we would otherwise have detected them. This has meant earlier and therefore more effective treatment, and much sight has been saved. I'm often thankful that we now have this technology.
David Donner
OCT and Macular Degeneration
What is Macular Degeneration?
Macular degeneration is a condition in which the centre of the retina (known as the macula) becomes damaged. You may have seen the term "AMD", which stands for age-related macular degeneration. Macular degeneration is rare in younger people, but around 30% of people over 75 have early signs of AMD, and about 7% of those over 75 have more advanced AMD. This is why it's the most common cause of visual impairment in the UK.
Two types
There are two types of AMD; wet and dry. The dry type is more common and develops slowly. In the wet type, blood vessels beneath the macula leak fluid, which can damage the macula relatively quickly. Both types only affect central vision, which means that they don't cause complete blindness. Tasks like reading, however, can be very difficult when there's a blurred patch in the centre. An early symptom of wet AMD is when straight lines suddenly develop a kink in them.
Treatment
Wet AMD can now be treated with injections of new (anti-VEGF) drugs. The key to their success is early detection and treatment.
There's no real treatment for dry AMD at the moment. There's evidence, however, that progression from an intermediate to an advanced stage can be inhibited by taking a supplement of antioxidants and zinc.
OCT
Most of what happens in AMD, at least in the early stages, happens beneath the surface. Often, therefore, the standard eye examination with an ophthalmoscope yields only limited information.
But because the OCT shows a cross-section of the retina, we can see what's going on beneath the surface. This makes it possible to distinguish between wet and dry AMD. When wet AMD is detected, there's a fast track referral system in Surrey to ensure treatment starts quickly.
The OCT can also show other macular problems, such as an epimacular membrane. This is a collagen membrane that damages the surface of the macula and that sometimes requires surgery. Macular oedema is also clearly shown up in an OCT scan, and this is particularly useful when examining diabetics, in whom it's a major cause of loss of vision.
Quite often, people with AMD have cataracts as well. The OCT can give really useful information about whether the vision will be clear or still blurred after cataract surgery.
David Donner
Macular degeneration is a condition in which the centre of the retina (known as the macula) becomes damaged. You may have seen the term "AMD", which stands for age-related macular degeneration. Macular degeneration is rare in younger people, but around 30% of people over 75 have early signs of AMD, and about 7% of those over 75 have more advanced AMD. This is why it's the most common cause of visual impairment in the UK.
Two types
There are two types of AMD; wet and dry. The dry type is more common and develops slowly. In the wet type, blood vessels beneath the macula leak fluid, which can damage the macula relatively quickly. Both types only affect central vision, which means that they don't cause complete blindness. Tasks like reading, however, can be very difficult when there's a blurred patch in the centre. An early symptom of wet AMD is when straight lines suddenly develop a kink in them.
Treatment
Wet AMD can now be treated with injections of new (anti-VEGF) drugs. The key to their success is early detection and treatment.
There's no real treatment for dry AMD at the moment. There's evidence, however, that progression from an intermediate to an advanced stage can be inhibited by taking a supplement of antioxidants and zinc.
OCT
Most of what happens in AMD, at least in the early stages, happens beneath the surface. Often, therefore, the standard eye examination with an ophthalmoscope yields only limited information.
But because the OCT shows a cross-section of the retina, we can see what's going on beneath the surface. This makes it possible to distinguish between wet and dry AMD. When wet AMD is detected, there's a fast track referral system in Surrey to ensure treatment starts quickly.
The OCT can also show other macular problems, such as an epimacular membrane. This is a collagen membrane that damages the surface of the macula and that sometimes requires surgery. Macular oedema is also clearly shown up in an OCT scan, and this is particularly useful when examining diabetics, in whom it's a major cause of loss of vision.
Quite often, people with AMD have cataracts as well. The OCT can give really useful information about whether the vision will be clear or still blurred after cataract surgery.
David Donner
Saturday 6 November 2010
Practice Makes Expert
I’ve recently finished Matthew Syed’s excellent book “Bounce”. Much of it is based on the well known idea that to become an expert requires 10,000 hours of practice, but it’s fleshed out with plenty of good examples, including his own story of how he became a top table tennis player.
There are a couple of important points that I think should have been included. Firstly, how participating in several different sports can reduce the amount of sport-specific practice well below 10,000 hours. Also, the importance of deliberate play in establishing expertise in team sports was not mentioned.
Syed does make the excellent point that the practice must be challenging. He gives the example of someone who’s been driving for years without becoming a better driver, and even possibly becoming a worse driver through the accumulation of bad habits. This is because we’re not practising to improve our skill each time; we’re just trying to get somewhere.
His Chinese coach, Chen Xinhua, increased the intensity of his practice by firing lots of balls at him from different angles, with different spins and speeds. He even widened the table at Syed’s end to make him work harder. Syed’s world ranking rocketed.
Practising an individual (but not usually team) sport for hours on end is not actually inherently enjoyable. Individuals can be motivated to do it when they feel that their performance is improving. But they actually need to have been participating in the activity, and motivated to improve, before embarking on deliberate practice.
The role of parents in this early stage is often crucial. They will notice the child playing, having early attempts at the sport, and feel that there are signs of promise. Whether that feeling is justified or not doesn’t seem to matter much (Bloom 1985). What’s important is that they facilitate further practice and, possibly with the help of teachers or coaches, point out the improvement that they are making as a result of their practice. After a while, the child can monitor the effects of practice for themselves, whilst competitions can provide further motivation for practice. Eventually, practice becomes an integral part both of becoming an expert and of daily life (Ericsson et al 1993). But if the desire to compete at the highest level is lost, the motivation to maintain practice also goes. Kaminsky et al (1984) found that many elite adolescents who decided to stop competing remained active in the sport, but virtually stopped engaging in practice.
Elite performers generally start practising at an earlier age than lesser performers, and spend a large amount of time practising even at a young age: 20 hours a week for 13-year old tennis players (Monsaas 1985) and 24-30 hours a week for swimmers around the age of 11. Kaminsky et al (1984) found that national level swimmers, ice skaters and gymnasts aged 15-16 practised about 16 hours a week, 3 hours longer than those below national level. Sack (1975) found that male national level runners aged 17-18 trained on average 4.9 times a week; runners at regional and local levels trained on average 4.2 and 3.2 times a week respectively.
There is a limit, however, to how much practice is sensible. Studies have shown essentially no benefit from practising for more than 4 hours a day, and reduced benefit after 2 hours a day (Welford 1968). The actual desirable amount is limited by the individual’s ability to recover mentally and physically. If the individual can’t recover each day from a given level of practice, sustaining that level will lead to exhaustion and mental fatigue. In athletics, for instance, this results in injuries such as “runner’s knee”, shin splints and Achilles tendonitis.
An inability to recover mentally from practice leads to staleness and burnout, as well as the physical problems of fatigue and soreness. The individual may start to become unenthusiastic about practice, and may drop out of the sport altogether. This can be the fate of those who started practising at a later age than the best of their peers, and who try to catch up by suddenly increasing their hours of deliberate practice. But those who started earlier, and built up their practice hours more gradually, are able to sustain maximal levels without suffering from exhaustion. In contrast, those trying to catch up quickly by practising at the level or even above the level of the best performers are likely to encounter injuries and exhaustion.
Finally, the demands on parents, both financially and in terms of their spare time, can be very high at elite levels of sport. Back in 1988 in the US, Chambliss estimated the parents’ costs for a national level swimmer to be over $5,000 a year.
So, whilst an understanding of sports vision can improve performance, don’t expect it to turn you into a world beater overnight.
David Donner
www.donneroptometrists.co.uk
There are a couple of important points that I think should have been included. Firstly, how participating in several different sports can reduce the amount of sport-specific practice well below 10,000 hours. Also, the importance of deliberate play in establishing expertise in team sports was not mentioned.
Syed does make the excellent point that the practice must be challenging. He gives the example of someone who’s been driving for years without becoming a better driver, and even possibly becoming a worse driver through the accumulation of bad habits. This is because we’re not practising to improve our skill each time; we’re just trying to get somewhere.
His Chinese coach, Chen Xinhua, increased the intensity of his practice by firing lots of balls at him from different angles, with different spins and speeds. He even widened the table at Syed’s end to make him work harder. Syed’s world ranking rocketed.
Practising an individual (but not usually team) sport for hours on end is not actually inherently enjoyable. Individuals can be motivated to do it when they feel that their performance is improving. But they actually need to have been participating in the activity, and motivated to improve, before embarking on deliberate practice.
The role of parents in this early stage is often crucial. They will notice the child playing, having early attempts at the sport, and feel that there are signs of promise. Whether that feeling is justified or not doesn’t seem to matter much (Bloom 1985). What’s important is that they facilitate further practice and, possibly with the help of teachers or coaches, point out the improvement that they are making as a result of their practice. After a while, the child can monitor the effects of practice for themselves, whilst competitions can provide further motivation for practice. Eventually, practice becomes an integral part both of becoming an expert and of daily life (Ericsson et al 1993). But if the desire to compete at the highest level is lost, the motivation to maintain practice also goes. Kaminsky et al (1984) found that many elite adolescents who decided to stop competing remained active in the sport, but virtually stopped engaging in practice.
Elite performers generally start practising at an earlier age than lesser performers, and spend a large amount of time practising even at a young age: 20 hours a week for 13-year old tennis players (Monsaas 1985) and 24-30 hours a week for swimmers around the age of 11. Kaminsky et al (1984) found that national level swimmers, ice skaters and gymnasts aged 15-16 practised about 16 hours a week, 3 hours longer than those below national level. Sack (1975) found that male national level runners aged 17-18 trained on average 4.9 times a week; runners at regional and local levels trained on average 4.2 and 3.2 times a week respectively.
There is a limit, however, to how much practice is sensible. Studies have shown essentially no benefit from practising for more than 4 hours a day, and reduced benefit after 2 hours a day (Welford 1968). The actual desirable amount is limited by the individual’s ability to recover mentally and physically. If the individual can’t recover each day from a given level of practice, sustaining that level will lead to exhaustion and mental fatigue. In athletics, for instance, this results in injuries such as “runner’s knee”, shin splints and Achilles tendonitis.
An inability to recover mentally from practice leads to staleness and burnout, as well as the physical problems of fatigue and soreness. The individual may start to become unenthusiastic about practice, and may drop out of the sport altogether. This can be the fate of those who started practising at a later age than the best of their peers, and who try to catch up by suddenly increasing their hours of deliberate practice. But those who started earlier, and built up their practice hours more gradually, are able to sustain maximal levels without suffering from exhaustion. In contrast, those trying to catch up quickly by practising at the level or even above the level of the best performers are likely to encounter injuries and exhaustion.
Finally, the demands on parents, both financially and in terms of their spare time, can be very high at elite levels of sport. Back in 1988 in the US, Chambliss estimated the parents’ costs for a national level swimmer to be over $5,000 a year.
So, whilst an understanding of sports vision can improve performance, don’t expect it to turn you into a world beater overnight.
David Donner
www.donneroptometrists.co.uk
Monday 1 November 2010
Glaucoma and OCT
What is glaucoma?
That’s not as easy question to answer as you might think. One study, looking at a group of patients aged over 80, found that the prevalence of glaucoma amongst them varied between 0.5% and 6% depending on which definition of glaucoma they used.
Because glaucoma is generally a slowly progressive disease, it’s often difficult to tell whether it’s started or not unless you have accurate measurements from before.
Glaucoma is not the same as high pressures.
There’s a circulating fluid within the eye that has its own pressure, known as the intraocular pressure. Many people will be familiar with the measurement of this pressure, which is often by an instrument that blows air into the eye. Frequently, when I do this test, I hear the comment “this is the glaucoma test, isn’t it?”
Well, actually it isn’t. Raised intraocular pressure is just a risk factor for glaucoma. So glaucoma is now described as a group of diseases that cause progressive damage to the nerves at the back of the eye, with or without raised pressures. The most common of these is Primary Open Angle Glaucoma (POAG).
Half of all cases of glaucoma are undiagnosed
This refers to cases of POAG, according to surveys across several industrialised countries. In one study in East Anglia, 90% of those with undiagnosed glaucoma were found to have normal pressures.
If that isn’t bad enough, the figures in other parts of the world are far worse. The percentage of glaucomas that are undiagnosed was found to be 75% in Bangkok, 93% in India, and 100% in Mongolia (i.e. every case they found was undiagnosed). No wonder glaucoma is the leading cause of irreversible blindness in the world.
So how can you tell if someone has glaucoma or not?
Visual fields
As nerve fibres get damaged, there comes a point when vision starts getting lost. But it won’t appear as a big splodge in the centre of your vision; it’s the more peripheral areas that get affected first. The reason people don’t notice this is because the brain fills in the gaps from neighbouring images. By the time it is noticed (for instance when the car wing mirror keeps getting knocked) quite a lot of vision has already been lost.
We routinely test the field of vision, but analysis isn’t always straightforward. Factors affecting the visual field include pupil size, high prescriptions, other eye conditions, and normal aging. The best field tests are able to take these factors into account by examining in more detail those areas most likely to be affected by glaucoma, but these can be quite long and demanding. And, by the time some field is lost, quite a bit of nerve damage has already taken place.
The optic nerve
When we look into the eye, we can see where the optic nerve comes into the retina. As nerve damage occurs, it’s possible to see changes occurring to this part of the nerve. There’s a paler part in the centre, known as the cup, and this gets larger when the nerve gets damaged. The overall size of the nerve doesn’t change, so if the cup gets abnormally large in comparison, glaucoma is indicated. The difficulty is in deciding what’s normal and what’s abnormal, because some people (especially if they are short-sighted) have larger optic nerves than others, and this also affects the size of the cup.
Imagine you have two sets of equal numbers of cut flowers. One set goes in a narrow vase, and the other goes in a wide vase. In the narrow vase, the flowers will be bunched up with no space in the middle. But in the wide vase, the flowers will be arranged towards the outside, and the space in the middle will be the equivalent of the cup in the optic nerve. As the flowers die, the “cup” increases in size.
In the optic nerve, you can’t be sure that nerves have died (at least not in the early stages) unless you knew how many were there before. And this is where the OCT comes in.
OCT and Glaucoma
The OCT can measure the thickness of the nerve fibre layer, which indicates how many nerves are coming into the main optic nerve from all over the retina. This helps in the diagnosis of glaucoma in two ways.
Firstly, it compares the measurement against an average of people of the same age, sex and ethnicity, so it shows the likelihood of glaucoma by virtue of being out of step with average. The, secondly, it stores those measurements. Then, if they are repeated some time later, any deterioration can be picked up.
In one study (Paul 2010) OCT technology was shown to predict field defects that developed on average four years later.
Treatment
People often ask me if anything can be done about glaucoma once it’s been detected. The answer is “Yes, very much so”. The usual treatment is drops, to bring the pressures down, even if they aren’t especially high. But it needs to be detected early, because any vision that’s been lost can’t be regained. Also, once some nerve fibres died, the remaining ones seem to be especially sensitive to even normal pressure.
Closed angle glaucoma
In about 10% of all cases of glaucoma, the iris gets in the way of the drainage system. This is known as closed angle glaucoma because the angle between the drainage system and the iris gets very narrow and can even close completely. When this happens, the pressure builds up very rapidly in an acute attack. The eye becomes red and painful, and vision loss can occur rapidly without treatment. Unfortunately, two-thirds of those with closed angle glaucoma develop it slowly without any symptoms prior to an attack.
Another use of the OCT is that we can use it to see whether the angle is open or close, so we can detect those at risk of an acute glaucoma attack. Often, all that’s required is a little laser treatment to allow fluid to get through and prevent an attack.
Conclusion
OCT is now playing a vital part not only in the early detection of glaucoma, but also in monitoring the effectiveness of glaucoma treatment.
Contact me for more information on Glaucoma and OCT
David Donner
That’s not as easy question to answer as you might think. One study, looking at a group of patients aged over 80, found that the prevalence of glaucoma amongst them varied between 0.5% and 6% depending on which definition of glaucoma they used.
Because glaucoma is generally a slowly progressive disease, it’s often difficult to tell whether it’s started or not unless you have accurate measurements from before.
Glaucoma is not the same as high pressures.
There’s a circulating fluid within the eye that has its own pressure, known as the intraocular pressure. Many people will be familiar with the measurement of this pressure, which is often by an instrument that blows air into the eye. Frequently, when I do this test, I hear the comment “this is the glaucoma test, isn’t it?”
Well, actually it isn’t. Raised intraocular pressure is just a risk factor for glaucoma. So glaucoma is now described as a group of diseases that cause progressive damage to the nerves at the back of the eye, with or without raised pressures. The most common of these is Primary Open Angle Glaucoma (POAG).
Half of all cases of glaucoma are undiagnosed
This refers to cases of POAG, according to surveys across several industrialised countries. In one study in East Anglia, 90% of those with undiagnosed glaucoma were found to have normal pressures.
If that isn’t bad enough, the figures in other parts of the world are far worse. The percentage of glaucomas that are undiagnosed was found to be 75% in Bangkok, 93% in India, and 100% in Mongolia (i.e. every case they found was undiagnosed). No wonder glaucoma is the leading cause of irreversible blindness in the world.
So how can you tell if someone has glaucoma or not?
Visual fields
As nerve fibres get damaged, there comes a point when vision starts getting lost. But it won’t appear as a big splodge in the centre of your vision; it’s the more peripheral areas that get affected first. The reason people don’t notice this is because the brain fills in the gaps from neighbouring images. By the time it is noticed (for instance when the car wing mirror keeps getting knocked) quite a lot of vision has already been lost.
We routinely test the field of vision, but analysis isn’t always straightforward. Factors affecting the visual field include pupil size, high prescriptions, other eye conditions, and normal aging. The best field tests are able to take these factors into account by examining in more detail those areas most likely to be affected by glaucoma, but these can be quite long and demanding. And, by the time some field is lost, quite a bit of nerve damage has already taken place.
The optic nerve
When we look into the eye, we can see where the optic nerve comes into the retina. As nerve damage occurs, it’s possible to see changes occurring to this part of the nerve. There’s a paler part in the centre, known as the cup, and this gets larger when the nerve gets damaged. The overall size of the nerve doesn’t change, so if the cup gets abnormally large in comparison, glaucoma is indicated. The difficulty is in deciding what’s normal and what’s abnormal, because some people (especially if they are short-sighted) have larger optic nerves than others, and this also affects the size of the cup.
Imagine you have two sets of equal numbers of cut flowers. One set goes in a narrow vase, and the other goes in a wide vase. In the narrow vase, the flowers will be bunched up with no space in the middle. But in the wide vase, the flowers will be arranged towards the outside, and the space in the middle will be the equivalent of the cup in the optic nerve. As the flowers die, the “cup” increases in size.
In the optic nerve, you can’t be sure that nerves have died (at least not in the early stages) unless you knew how many were there before. And this is where the OCT comes in.
OCT and Glaucoma
The OCT can measure the thickness of the nerve fibre layer, which indicates how many nerves are coming into the main optic nerve from all over the retina. This helps in the diagnosis of glaucoma in two ways.
Firstly, it compares the measurement against an average of people of the same age, sex and ethnicity, so it shows the likelihood of glaucoma by virtue of being out of step with average. The, secondly, it stores those measurements. Then, if they are repeated some time later, any deterioration can be picked up.
In one study (Paul 2010) OCT technology was shown to predict field defects that developed on average four years later.
Treatment
People often ask me if anything can be done about glaucoma once it’s been detected. The answer is “Yes, very much so”. The usual treatment is drops, to bring the pressures down, even if they aren’t especially high. But it needs to be detected early, because any vision that’s been lost can’t be regained. Also, once some nerve fibres died, the remaining ones seem to be especially sensitive to even normal pressure.
Closed angle glaucoma
In about 10% of all cases of glaucoma, the iris gets in the way of the drainage system. This is known as closed angle glaucoma because the angle between the drainage system and the iris gets very narrow and can even close completely. When this happens, the pressure builds up very rapidly in an acute attack. The eye becomes red and painful, and vision loss can occur rapidly without treatment. Unfortunately, two-thirds of those with closed angle glaucoma develop it slowly without any symptoms prior to an attack.
Another use of the OCT is that we can use it to see whether the angle is open or close, so we can detect those at risk of an acute glaucoma attack. Often, all that’s required is a little laser treatment to allow fluid to get through and prevent an attack.
Conclusion
OCT is now playing a vital part not only in the early detection of glaucoma, but also in monitoring the effectiveness of glaucoma treatment.
Contact me for more information on Glaucoma and OCT
David Donner
Wednesday 13 October 2010
Reading, Dyslexia and the Eyes
One of my patients told me recently that her son had been referred to have some tests on his eye movements because he sometimes makes spelling mistakes. He can read perfectly well, and actually does OK in spelling tests, but just makes mistakes when writing. It struck me that if you referred every child who made spelling mistakes for special tests, you’d probably need to refer 98% of them. So how do these ideas come about, and what’s the story of eyes, reading and dyslexia?
Why reading – especially English – is difficult
Reading is a complicated task that requires the involvement of several different parts of the brain. The image of words falls on the retina and is transferred to the visual cortex of the brain. Here, the image that we see is formed. As part of the processing of that image, shapes are recognised. This information has to link up with the language centres, which recognise sound and meaning.
The written word is, in evolutionary terms, a relatively modern invention. Our brains are really set up to learn language through sound, as we nearly all manage to do easily when we learn to understand and speak our native language at a young age. So when we read, we still have to link the words with how they sound. Even expert readers will say the words in their head when they read.
English is a particularly difficult language to learn to read because there are so many words like “eye” or “cough” whose pronunciation isn’t obvious from the way they’re spelt. These words are generally learned through their meaning, and efficient readers go straight to the meaning when they read, so they don’t have to piece words together from the sounds. Because Italian is a much more phonetic language than English, there are only half as many diagnosed dyslexics in Italy than in England. It seems likely, however, that there are many more Italians whose dyslexia is too mild to be significant.
Reading and the brain
Cutting & Rimrodt (2010) found used a form of MRI scanning called Diffusion Tensor Imaging to study part of a branch of nerves that runs from the visual cortex to the areas at the front of the brain that are responsible for articulation and speech. They found that some of these nerve fibres were less well organised in dyslexics than in controls.
There have been many reports of differences in nerve structure in dyslexics, but these have not been consistent. Differences have been found in the temporal or parietal or occipital parts of the brain, as well as in the cerebellum. It may be that a well organised nerve structure is a sign of proficiency in that particular task, and that, for a mixture of genetic and environmental reasons, this is achieved more easily in some than in others. Italian dyslexics have been found to show the same kind of nerve activation when reading as English and French dyslexics (Paulesu et al 2001). They also had the same difficulty in tests that looked at their ability to recognise the sounds of words. It’s just that in Italian, there’s only one way to represent a sound, whereas in English there are lots, such as “their” or “there”.
Dyslexia and eye movements
Because anomalies have sometimes been found in the nerve pathways that control eye movements, and because dyslexics often have irregular eye movements when reading, it’s been suggested that poor control of eye movements is a cause of dyslexia.
Hutzler et al (2006) investigated this idea by showing dyslexics and controls groups of consonants, such as DSB, LQWB, ZBB and VPLL. The subjects had to say whether each group of consonants had a double letter in them or not. This meant that the subjects had to look at each “word” in a similar manner to reading, but no higher order skills of language and sound recognition were required. No difference in the eye movement patterns between dyslexics and non-dyslexics were found.
The researchers then changed things, so that the subjects had to try and pronounce “words” such as ZIB, VULL and CRUF. Now, the dyslexic subjects showed the same irregular eye movement patterns as had been found in previous research. Patients with diseases such as Parkinson’s and Huntingdon’s often have trouble with reading because of poor control of eye movements. However, they have a lot of other problems for the same reason, and this would not appear to be the case for the vast majority of dyslexics.
Dyslexia and the cerebellum
Similarly, because scans have sometimes shown anomalies in the cerebellum of dyslexics, it’s been suggested that the cerebellum holds the key to dyslexia. The cerebellum is in control of the things we do without thinking, such as brushing our teeth, and it also plays a crucial role in maintaining our balance. And it’s certainly true that dyspraxia (a disability affecting movement and coordination) and attention deficit hyperactivity disorder (ADHD) are more frequently found in dyslexics than non-dyslexics. On this basis, it’s suggested that specific exercises aimed at improving balance and coordination will improve reading.
One of the many problems with his idea is that there are plenty of elite sportsmen and sportswomen, who would appear to have excellent balance and coordination, but who have suffered from dyslexia. Another problem, and one shared with several other “miracle cures”, is that the statistics used to promote it are unreliable. One of the main reasons for this is a statistical phenomenon called “regression to the mean”.
Imagine 100 people took a multiple choice test in a subject about which they knew absolutely nothing, so had to guess every time. If each question had 2 choices, you’d expect the overall mark to be around 50%. Some people, however, would do rather better, and some worse. If you got the top 10% do another similar guessing test, their mean score would be about 50%, so on average, will have done worse on the second test than on the first. Similarly, a repeat test on the bottom 10% would see their average score improve. This is regression to the mean, and it’s why it’s easy to show that people who weren’t very good at something when you first tested them, can show a dramatic improvement when you test them again after their “treatment” compared with those who did well first time round. The only way round this is to have a genuine control group, who are as similar as possible to the treated group, and who have the same tests at the same time. So you would need to compare dyslexics of the same level of disability, with and without the treatment, to make a valid comparison. This seems to be rarely done.
Dyslexia and eye dominance
I recently read the claim by an optometrist offering diplomas in “Schoolvision” that the “predominant visual skill in reading is aiming”, and that this can be undermined by unstable eye dominance. The role of aiming in reading has been largely neglected up until now (for good reason, you might think), although the importance of eye dominance in aiming sports is widely accepted, including by myself.
But the idea that eye dominance is relevant to dyslexia is not a new one. Stein & Fowler (1982) claimed that more than half of the dyslexic population had an unfixed reference eye on a binocular vision test, compared with 1% of controls. The test used was the Dunlop Test, in which the eyes diverge until double vision occurs, and the child has to say in which direction an object has moved. The test is repeated ten times, and if they give inconsistent answers they’re said to have an unstable response. This doesn’t seem to bear much relation to reading, and, anyway, others (Newman et al 1985; Bishop et al 1979) found that excellent readers did just as badly as poor readers on this test.
Stein & Fowler went on to suggest that some dyslexic children might be helped by the occlusion of one eye. But when Bishop (1989) re-analysed the data, she found no evidence that occluding one eye improved reading scores, and described the original findings as “methodologically flawed”. And whilst some have claimed that cross-dominance (e.g. right eye dominant + left handedness) is especially prevalent in dyslexia, many studies of large numbers of dyslexics have failed to find this link.
What’s the answer?
Most dyslexics clearly don’t have something fundamentally wrong with them, otherwise they’d have a lot more problems than being slower than others in learning to read. Also, we wouldn’t see the differences between languages if vision were really at the heart of dyslexia.
Having said that, there are quite a lot of children who have difficulty when reading because of their vision, and some of them will be dyslexic. Their difficulty often arises because they have either a weakness of accommodation (ability to focus on near objects) or convergence (ability to bring the eyes together for near objects), or both. After a while, they find words go blurred and/or double.
These children generally respond very well to simple exercises, and rarely need glasses. So if your child is having reading difficulties, it’s worth getting their eyes examined to rule out this kind of problem.
Whatever the cause of dyslexia, the answer seems to be one-to-one tuition in reading. Whether this should be phonics or something else, I leave to others to debate.
David Donner
Why reading – especially English – is difficult
Reading is a complicated task that requires the involvement of several different parts of the brain. The image of words falls on the retina and is transferred to the visual cortex of the brain. Here, the image that we see is formed. As part of the processing of that image, shapes are recognised. This information has to link up with the language centres, which recognise sound and meaning.
The written word is, in evolutionary terms, a relatively modern invention. Our brains are really set up to learn language through sound, as we nearly all manage to do easily when we learn to understand and speak our native language at a young age. So when we read, we still have to link the words with how they sound. Even expert readers will say the words in their head when they read.
English is a particularly difficult language to learn to read because there are so many words like “eye” or “cough” whose pronunciation isn’t obvious from the way they’re spelt. These words are generally learned through their meaning, and efficient readers go straight to the meaning when they read, so they don’t have to piece words together from the sounds. Because Italian is a much more phonetic language than English, there are only half as many diagnosed dyslexics in Italy than in England. It seems likely, however, that there are many more Italians whose dyslexia is too mild to be significant.
Reading and the brain
Cutting & Rimrodt (2010) found used a form of MRI scanning called Diffusion Tensor Imaging to study part of a branch of nerves that runs from the visual cortex to the areas at the front of the brain that are responsible for articulation and speech. They found that some of these nerve fibres were less well organised in dyslexics than in controls.
There have been many reports of differences in nerve structure in dyslexics, but these have not been consistent. Differences have been found in the temporal or parietal or occipital parts of the brain, as well as in the cerebellum. It may be that a well organised nerve structure is a sign of proficiency in that particular task, and that, for a mixture of genetic and environmental reasons, this is achieved more easily in some than in others. Italian dyslexics have been found to show the same kind of nerve activation when reading as English and French dyslexics (Paulesu et al 2001). They also had the same difficulty in tests that looked at their ability to recognise the sounds of words. It’s just that in Italian, there’s only one way to represent a sound, whereas in English there are lots, such as “their” or “there”.
Dyslexia and eye movements
Because anomalies have sometimes been found in the nerve pathways that control eye movements, and because dyslexics often have irregular eye movements when reading, it’s been suggested that poor control of eye movements is a cause of dyslexia.
Hutzler et al (2006) investigated this idea by showing dyslexics and controls groups of consonants, such as DSB, LQWB, ZBB and VPLL. The subjects had to say whether each group of consonants had a double letter in them or not. This meant that the subjects had to look at each “word” in a similar manner to reading, but no higher order skills of language and sound recognition were required. No difference in the eye movement patterns between dyslexics and non-dyslexics were found.
The researchers then changed things, so that the subjects had to try and pronounce “words” such as ZIB, VULL and CRUF. Now, the dyslexic subjects showed the same irregular eye movement patterns as had been found in previous research. Patients with diseases such as Parkinson’s and Huntingdon’s often have trouble with reading because of poor control of eye movements. However, they have a lot of other problems for the same reason, and this would not appear to be the case for the vast majority of dyslexics.
Dyslexia and the cerebellum
Similarly, because scans have sometimes shown anomalies in the cerebellum of dyslexics, it’s been suggested that the cerebellum holds the key to dyslexia. The cerebellum is in control of the things we do without thinking, such as brushing our teeth, and it also plays a crucial role in maintaining our balance. And it’s certainly true that dyspraxia (a disability affecting movement and coordination) and attention deficit hyperactivity disorder (ADHD) are more frequently found in dyslexics than non-dyslexics. On this basis, it’s suggested that specific exercises aimed at improving balance and coordination will improve reading.
One of the many problems with his idea is that there are plenty of elite sportsmen and sportswomen, who would appear to have excellent balance and coordination, but who have suffered from dyslexia. Another problem, and one shared with several other “miracle cures”, is that the statistics used to promote it are unreliable. One of the main reasons for this is a statistical phenomenon called “regression to the mean”.
Imagine 100 people took a multiple choice test in a subject about which they knew absolutely nothing, so had to guess every time. If each question had 2 choices, you’d expect the overall mark to be around 50%. Some people, however, would do rather better, and some worse. If you got the top 10% do another similar guessing test, their mean score would be about 50%, so on average, will have done worse on the second test than on the first. Similarly, a repeat test on the bottom 10% would see their average score improve. This is regression to the mean, and it’s why it’s easy to show that people who weren’t very good at something when you first tested them, can show a dramatic improvement when you test them again after their “treatment” compared with those who did well first time round. The only way round this is to have a genuine control group, who are as similar as possible to the treated group, and who have the same tests at the same time. So you would need to compare dyslexics of the same level of disability, with and without the treatment, to make a valid comparison. This seems to be rarely done.
Dyslexia and eye dominance
I recently read the claim by an optometrist offering diplomas in “Schoolvision” that the “predominant visual skill in reading is aiming”, and that this can be undermined by unstable eye dominance. The role of aiming in reading has been largely neglected up until now (for good reason, you might think), although the importance of eye dominance in aiming sports is widely accepted, including by myself.
But the idea that eye dominance is relevant to dyslexia is not a new one. Stein & Fowler (1982) claimed that more than half of the dyslexic population had an unfixed reference eye on a binocular vision test, compared with 1% of controls. The test used was the Dunlop Test, in which the eyes diverge until double vision occurs, and the child has to say in which direction an object has moved. The test is repeated ten times, and if they give inconsistent answers they’re said to have an unstable response. This doesn’t seem to bear much relation to reading, and, anyway, others (Newman et al 1985; Bishop et al 1979) found that excellent readers did just as badly as poor readers on this test.
Stein & Fowler went on to suggest that some dyslexic children might be helped by the occlusion of one eye. But when Bishop (1989) re-analysed the data, she found no evidence that occluding one eye improved reading scores, and described the original findings as “methodologically flawed”. And whilst some have claimed that cross-dominance (e.g. right eye dominant + left handedness) is especially prevalent in dyslexia, many studies of large numbers of dyslexics have failed to find this link.
What’s the answer?
Most dyslexics clearly don’t have something fundamentally wrong with them, otherwise they’d have a lot more problems than being slower than others in learning to read. Also, we wouldn’t see the differences between languages if vision were really at the heart of dyslexia.
Having said that, there are quite a lot of children who have difficulty when reading because of their vision, and some of them will be dyslexic. Their difficulty often arises because they have either a weakness of accommodation (ability to focus on near objects) or convergence (ability to bring the eyes together for near objects), or both. After a while, they find words go blurred and/or double.
These children generally respond very well to simple exercises, and rarely need glasses. So if your child is having reading difficulties, it’s worth getting their eyes examined to rule out this kind of problem.
Whatever the cause of dyslexia, the answer seems to be one-to-one tuition in reading. Whether this should be phonics or something else, I leave to others to debate.
David Donner
Tuesday 31 August 2010
A Look At Shooting
If you’re shooting inaccurately, it could be due to poor alignment with the target, or it could be due to body movement or hand/arm tremors as you fire. There are now pistols equipped with lasers to help distinguish between these errors. The laser isn’t turned on until the shooter has aimed. If the laser centres on the target, then the problem is with body movement and not with aiming.
Because of the distance between the gun’s sight and the target, both cannot be seen clearly. So should one focus on the sight or the target? The general consensus is that you should focus on the sight. This makes sense, as it intuitively seems easier to put a clear object in the centre of a blurred ring, than trying to put a clear ring equidistant around a blurred object. It also explains why some short-sighted people have been excellent marksmen. But it does cause problems for older shooters.
Unless one is short-sighted, one’s ability to focus close objects, such as a gun sight, goes down as one gets older. It’s possible, however, to have a correcting lens for this, and there are special shooting spectacles which can be adjusted to ensure that the lens is perfectly positioned.
Ripoll et al (1985) compared the gaze strategies of international elite pistol shooters with national near-elite shooters. They found that the near-elite looked at their hand and weapon as they brought it up towards the target, whereas the elite shooters fixated the target, and then brought the pistol into line with their gaze before aiming and pulling the trigger. Compared with the near-elite, the elite shooters were quick to bring the pistol into line, but then took longer to aim and complete the shot.
Although this might appear to contradict the advice to focus on the sight, and not the target, it’s likely that the elite shooters did their final aiming adjustment fixated on the sight, but because the sight and target were in alignment, no difference in gaze would be found by the cameras monitoring them.
The gaze strategy of elite shooters goes beyond sport. For some, it’s been a matter of life and death.
Joan Vickers (of “Quiet Eye” fame) and Bill Lewinski (Force Science Research Centre) studied members of Britain’s Emergency Response Team. 11 were highly experienced, and 13 were younger rookies who’d just completed their training.
They set up a scenario in which the subjects were to provide security at an Embassy. A man gets into an argument with the receptionist, and at some point turns around, taking an object from his coat pocket, which is either a gun or a mobile phone.
In more than 60% of trials, the trainees fired when the assailant brandished a mobile phone, compared with only 18% of elite trials. When the assailant pulled out a gun, elite officers shot first 92.5% of the time, compared with 42% for the trainees. The elite officers were also more accurate in their shooting, with the trainees more likely to miss the target completely.
In the last half-second before aiming, in 82% of their tests the trainees took their eyes off the assailant and attempted to look at their own gun, trying to find or confirm the sight alignment as they aimed. Although 30% of the elite also looked at their gun, these fixations were before they aimed (and fired).
When most officers learn to shoot a handgun, they are taught to focus first on the rear sight, then on the front sight, and finally on the target, aligning all three before pulling the trigger. It seems that through experience, the elite officers had learned to keep most of their attention on the assailant’s weapon. Like Ripoll’s elite shooters, they kept their gaze on the assailant’s weapon and brought their gun up into their line of sight.
This research by Vickers & Lewinski is likely to result in changes to the way that officers learn to shoot. If this had been done before, might Jean Charles de Menezes still be alive today? DD
If you’re shooting inaccurately, it could be due to poor alignment with the target, or it could be due to body movement or hand/arm tremors as you fire. There are now pistols equipped with lasers to help distinguish between these errors. The laser isn’t turned on until the shooter has aimed. If the laser centres on the target, then the problem is with body movement and not with aiming.
Because of the distance between the gun’s sight and the target, both cannot be seen clearly. So should one focus on the sight or the target? The general consensus is that you should focus on the sight. This makes sense, as it intuitively seems easier to put a clear object in the centre of a blurred ring, than trying to put a clear ring equidistant around a blurred object. It also explains why some short-sighted people have been excellent marksmen. But it does cause problems for older shooters.
Unless one is short-sighted, one’s ability to focus close objects, such as a gun sight, goes down as one gets older. It’s possible, however, to have a correcting lens for this, and there are special shooting spectacles which can be adjusted to ensure that the lens is perfectly positioned.
Ripoll et al (1985) compared the gaze strategies of international elite pistol shooters with national near-elite shooters. They found that the near-elite looked at their hand and weapon as they brought it up towards the target, whereas the elite shooters fixated the target, and then brought the pistol into line with their gaze before aiming and pulling the trigger. Compared with the near-elite, the elite shooters were quick to bring the pistol into line, but then took longer to aim and complete the shot.
Although this might appear to contradict the advice to focus on the sight, and not the target, it’s likely that the elite shooters did their final aiming adjustment fixated on the sight, but because the sight and target were in alignment, no difference in gaze would be found by the cameras monitoring them.
The gaze strategy of elite shooters goes beyond sport. For some, it’s been a matter of life and death.
Joan Vickers (of “Quiet Eye” fame) and Bill Lewinski (Force Science Research Centre) studied members of Britain’s Emergency Response Team. 11 were highly experienced, and 13 were younger rookies who’d just completed their training.
They set up a scenario in which the subjects were to provide security at an Embassy. A man gets into an argument with the receptionist, and at some point turns around, taking an object from his coat pocket, which is either a gun or a mobile phone.
In more than 60% of trials, the trainees fired when the assailant brandished a mobile phone, compared with only 18% of elite trials. When the assailant pulled out a gun, elite officers shot first 92.5% of the time, compared with 42% for the trainees. The elite officers were also more accurate in their shooting, with the trainees more likely to miss the target completely.
In the last half-second before aiming, in 82% of their tests the trainees took their eyes off the assailant and attempted to look at their own gun, trying to find or confirm the sight alignment as they aimed. Although 30% of the elite also looked at their gun, these fixations were before they aimed (and fired).
When most officers learn to shoot a handgun, they are taught to focus first on the rear sight, then on the front sight, and finally on the target, aligning all three before pulling the trigger. It seems that through experience, the elite officers had learned to keep most of their attention on the assailant’s weapon. Like Ripoll’s elite shooters, they kept their gaze on the assailant’s weapon and brought their gun up into their line of sight.
This research by Vickers & Lewinski is likely to result in changes to the way that officers learn to shoot. If this had been done before, might Jean Charles de Menezes still be alive today?
"http://www.donneroptometrists.co.uk/sports-vision.htm"
Wednesday 11 August 2010
Brain Waves
Does the study of brain waves help us distinguish experts from novices, and can brain waves be altered to improve performance?
Four types of brain wave have been identified. Alpha waves (8 – 14 Hz) are seen when we are relaxed, daydreaming or visualising. Increases in alpha waves are often associated with reduced overall activity of the brain. Beta waves (15 – 38 Hz) are associated with conscious thought, with higher frequency beta being associated with anxiety or stress. Gamma and delta waves are mostly seen in different stages of sleep.
Neurofeedback, also known as EEG biofeedback, is a strategy to enable people to alter their own brainwaves. It has been used in the treatment of ADHD (Attention-deficit hyperactivity disorder). Often the patient is using a videogame that’s linked to their EEG, and the aim is usually to increase beta waves and reduce theta waves. When the desired effect is taking place, they get some kind of encouragement in the game, such as beep or a character moving in the desired direction.
Neurofeedback has also been used to improve the balance of patients who have suffered brain injury or stroke. Significant improvements have been found after just 8 – 10 sessions, whereas ADHD treatments usually take 40 – 50 sessions.
Before trying neurofeedback to improve sporting ability, one would need to know if experts demonstrate different brainwave activity compared with lesser players. And there is actually some evidence for that. It’s hard to play rugby or football when attached to the electrodes of EEG equipment, so most of the evidence comes from aiming sports, such as archery, shooting and golf putting.
Haufler et al (2000) found that during aiming, when marksmen were compared with novice shooters, marksmen exhibited less activation (increased alpha with less beta and gamma activity) at all electrode sites on the head, but especially in the left hemisphere. Kerick et al (2001) looked at skilled marksmen during shooting. Over an 8-second period preceding the pull of the trigger, they exhibited greater alpha activity in the left temporal area compared with when they were doing a control activity. Hatfield et al (1984) also found a progressive increase in alpha power in the left temporal area during the last 7.5 seconds of aiming, with no change in the right temporal area.
These results could fit in with the idea that the left hemisphere dominates in language, and that a lot of verbal thoughts could inhibit efficient sporting performance.
Landers et al (1991) used neurofeedback to try and improve the performance of pre-elite archers. On the basis that reduced cortical activity in the left hemisphere (associated with increased alpha waves and reduced beta waves) would increase accuracy, the archers were randomly assigned to one of three groups. One group was given “correct” feedback (reduced left hemisphere activity), another “incorrect” feedback (reduced right hemisphere activity), and a control with no feedback.
They found that those trained to have reduced left temporal activity showed a significant improvement in performance, whilst those trained to have reduced right temporal activity showed a significantly worse performance. The control group showed no change.
However, there’s a problem. Examination of the participants’ EEG spectra failed to show a clear pattern of change after the test compared with beforehand. It’s as if the feedback changed something, but not what it was supposed to.
Also, the link between brain waves and sport performance turns out not to be as simple as first thought. For instance, Del Percio et al (2007) found a correlation between a reduction in alpha output in part of the right hemisphere and skilled karate performance. In contrast, Collins et al (1990) found that skilled karate performance was linked to a bilateral increase in alpha output.
Crews & Landers (1994) found that in the last second before a golf putt, increased alpha waves in the right hemisphere were associated with increased putting accuracy. This is in contrast with the increase in the left hemisphere that had been found in shooting and archery. Looking at putting novices, however, Shelley-Trembley et al (2006) found that lower beta levels in the right hemisphere correlated with accuracy.
So it seems that we need to understand brain waves rather better before we can be sure that trying to change them will improve performance. Oh well, back to practise then.
David
www.donneroptometrists.co.uk
Four types of brain wave have been identified. Alpha waves (8 – 14 Hz) are seen when we are relaxed, daydreaming or visualising. Increases in alpha waves are often associated with reduced overall activity of the brain. Beta waves (15 – 38 Hz) are associated with conscious thought, with higher frequency beta being associated with anxiety or stress. Gamma and delta waves are mostly seen in different stages of sleep.
Neurofeedback, also known as EEG biofeedback, is a strategy to enable people to alter their own brainwaves. It has been used in the treatment of ADHD (Attention-deficit hyperactivity disorder). Often the patient is using a videogame that’s linked to their EEG, and the aim is usually to increase beta waves and reduce theta waves. When the desired effect is taking place, they get some kind of encouragement in the game, such as beep or a character moving in the desired direction.
Neurofeedback has also been used to improve the balance of patients who have suffered brain injury or stroke. Significant improvements have been found after just 8 – 10 sessions, whereas ADHD treatments usually take 40 – 50 sessions.
Before trying neurofeedback to improve sporting ability, one would need to know if experts demonstrate different brainwave activity compared with lesser players. And there is actually some evidence for that. It’s hard to play rugby or football when attached to the electrodes of EEG equipment, so most of the evidence comes from aiming sports, such as archery, shooting and golf putting.
Haufler et al (2000) found that during aiming, when marksmen were compared with novice shooters, marksmen exhibited less activation (increased alpha with less beta and gamma activity) at all electrode sites on the head, but especially in the left hemisphere. Kerick et al (2001) looked at skilled marksmen during shooting. Over an 8-second period preceding the pull of the trigger, they exhibited greater alpha activity in the left temporal area compared with when they were doing a control activity. Hatfield et al (1984) also found a progressive increase in alpha power in the left temporal area during the last 7.5 seconds of aiming, with no change in the right temporal area.
These results could fit in with the idea that the left hemisphere dominates in language, and that a lot of verbal thoughts could inhibit efficient sporting performance.
Landers et al (1991) used neurofeedback to try and improve the performance of pre-elite archers. On the basis that reduced cortical activity in the left hemisphere (associated with increased alpha waves and reduced beta waves) would increase accuracy, the archers were randomly assigned to one of three groups. One group was given “correct” feedback (reduced left hemisphere activity), another “incorrect” feedback (reduced right hemisphere activity), and a control with no feedback.
They found that those trained to have reduced left temporal activity showed a significant improvement in performance, whilst those trained to have reduced right temporal activity showed a significantly worse performance. The control group showed no change.
However, there’s a problem. Examination of the participants’ EEG spectra failed to show a clear pattern of change after the test compared with beforehand. It’s as if the feedback changed something, but not what it was supposed to.
Also, the link between brain waves and sport performance turns out not to be as simple as first thought. For instance, Del Percio et al (2007) found a correlation between a reduction in alpha output in part of the right hemisphere and skilled karate performance. In contrast, Collins et al (1990) found that skilled karate performance was linked to a bilateral increase in alpha output.
Crews & Landers (1994) found that in the last second before a golf putt, increased alpha waves in the right hemisphere were associated with increased putting accuracy. This is in contrast with the increase in the left hemisphere that had been found in shooting and archery. Looking at putting novices, however, Shelley-Trembley et al (2006) found that lower beta levels in the right hemisphere correlated with accuracy.
So it seems that we need to understand brain waves rather better before we can be sure that trying to change them will improve performance. Oh well, back to practise then.
David
www.donneroptometrists.co.uk
Wednesday 28 July 2010
Sprinting
With the European Championships in full swing in Barcelona, I turned my Sports Vision to Athletics...
When sprinters start from the blocks, in order to keep aligned their head needs to be down so that they’re in the most aerodynamic position.
Watching Asafa Powell compete at Gateshead recently, he seemed to keep his head down longer than all the other competitors in the race, and it helped him at the start of the race even if he wasn’t the quickest to react to the gun. Sadly for him, he was overtaken towards the end of the race by Tyson Gay, and the same thing happened a week later when he lost to Usain Bolt in
Fixating a point a few metres ahead can help to keep the head in the correct position. As the athlete comes to a more erect position, fixation needs to move to a point above the track, past the finishing point.
When running indoors, some athletes change their head posture in response to the wall in front of them in anticipation of having to stop rapidly (www.runningmechanics.com). To avoid this, they should be encouraged either to fixate a point on the wall that’s about head height above the ground, or to adopt a soft focus, as if they’re able to look through the wall.
David
Dealing With Errors – Oosthuizen’s Red Spot
A few weeks ago I was umpiring a junior cricket match when a young leg spinner came on to bowl. His first ball pitched in line with middle stump and turned so much that I had to think about whether I should call it a wide. At last, I thought, an English Shane Warne in the making.
Unfortunately, although he continued to turn the ball, whenever he bowled a bad ball, or even if the batsman managed to hit away quite a good ball, the bowler got increasingly down on himself. Although he wasn’t intended to be taken literally, by towards the end of his spell he was making comments such as “I think I should go home” and “I should give up cricket”. Whereas the best spin bowlers, like Warne, are able to put pressure on the batsman, luring him into a mistake even if the pitch isn’t helping him too much, this bowler was putting all the pressure on himself.
Although it’s easy to be critical, many of us do similar things when we perform badly at sport, getting increasingly cross with ourselves with each mistake. Golfers, in particular, are prone to letting one momentary lapse of concentration, or even an unlucky bounce, ruin an excellent round as their game collapses because their brain is constantly reliving the past, and they get more and more tense.
Even Shane Warne would occasionally bowl a bad ball, but the best sportsmen are able to put a previous mistake out of their mind and concentrate on what they’re doing next. Some sportsmen actively “park” the past by wiping it away; for instance, wiping their hand on their clothing or on the ground.
In a sport where you have time to prepare yourself, such as golf, or bowling in cricket, or serving in tennis, a pre-shot routine is really useful; focus on the visual target(s), visualise what you want to achieve, and carry it out, giving no thought to what happened before, or the pressure of the situation. Some golfers make a clear beginning to the pre-shot routine, for instance saying “Now” or “Start” to themselves when they take their club out of the bag, or just before they start their practice swing.
And this is where I think Louis Oosthuizen’s red spot comes in. The open champion didn’t used to have a set routine in his build-up to playing shots, and had problems keeping his mind focused in major tournaments. Golf psychologist Karl Morris suggested that Oosthuizen mark a red dot on the thumb of his glove. He could then look down at the spot as a way of re-focusing on the next task. The result – maintaining his lead over the last two rounds and winning by seven strokes - was mightily impressive. Let’s hope our young leg spinner finds a way of doing something similar.
Cycling and Running Tactics
There seemed to have been quite a lot of crashes in the early stages of the Tour de France this year. I suppose that shouldn’t be surprising when you have a pack of cyclists jostling for position at 45mph, and if the guy in front of you hits a problem, you don’t have much chance of avoiding them.
In middle distance athletics, some athletes seem better at keeping themselves out of trouble than others, and I wondered if this also might apply to cycling, and how one might train to improve ones tactical awareness when in a pack.
In cycling there does seem to be an answer – rollers. Rollers can be placed in several positions, such as line abreast or one behind the other, so that the riders can practice the different situations that they’re likely to experience in a race, including bumping and jostling.
I don’t see any reason why a similar idea couldn’t be used in athletics, either with several treadmills side by side or with one large one. Runners could even be attached to harnesses so they aren’t hurt if they trip up.
David
Friday 2 July 2010
World Cup
World Cup
The FA has a goalkeeper development website showing a woman goalkeeper in position to collect a low shot. She has clearly watched the path of the ball carefully, because everything is in alignment to intercept the ball. He hands are well forward, preparing to draw the ball in, “little fingers touching”, and her head is right over her hands, so will imminently be right over the ball. Because her body is square on, even if she fails to catch the ball, it could only bounce straight out. And because her head is so far forward, she could probably drop on to the ball easily if it did pop out.
As Robert Green tries to save a 25-yard shot from Clint Dempsey in England’s World cup match against USA, there are a number of differences from the textbook picture above. His head is not quite aligned with his hands, and neither is aligned with the ball. His hands are at uneven heights, and crossed. The ball appears to miss his left hand completely, hitting his right wrist. His body is twisted in the direction that the ball rebounds, into the net. It would appear that he did not track the ball accurately along its path, so did not align himself correctly.
And he is not the only one. You could see the same thing when Algerian goalkeeper Fawzi Chaouchi let in a goal against
One answer could be that they weren’t concentrating on the game adequately, so were simply late in seeing the shot coming towards them, and so didn’t have sufficient time to get into the correct position. This seems improbable for players at this level.
A more likely explanation is the effect of nerves. When you are nervous, the conscious, thinking part of the brain tries to take over, with the result that movements become a lot less smooth and efficient. Before the
You’re on a motorway, about to overtake the car in front. You check your mirrors, indicate and pull out to overtake, nearly hitting a car outside you that you hadn’t noticed. Although you looked, you didn’t look as carefully as you would have done if you’d been taking your test, for instance. You’ve actually been doing this for a while, but because on other occasions a car hadn’t been there, you had believed that what you had done was adequate, and it had become your routine in these situations.
For professional goalkeepers, a low shot from distance represents a relatively easy save. They can detect its path at an early stage, so might set themselves up on that basis, rather than following the path of the ball all the way. A less than perfect body position may also not matter on most occasions. But if the keeper’s made an early misjudgement, or nerves mean that his body has not moved as smoothly as normal, he can be found out.
Coaches need to watch out for a player who’s getting into bad habits, even if they seem to be getting away with it. Marking the ball with numbers or letters which the keeper has to call out as he catches it can ensure that he carefully follows the path of the ball. Players can sometimes give themselves a verbal reminder to ensure their technique remains solid.
I was umpiring a cricket match recently. It was near the end of the game, with the batting side about to win comfortably. I saw the batsman pull another ball to the boundary for four. It was only sometime later that the fielding side pointed out that the wicket had been broken. After seeing the player make the shot, I’d followed the ball, and hadn’t noticed that the batsman had hit his own wicket.
My mistake was a bit embarrassing, but some are rather more important. However, there, but for the grace of God, go all of us.
David
World Cup - The Ball
The Ball
There has been much discussion of the Jabulani, the football designed by Adidas that being used in the World Cup. Adidas say that it’s their most accurate ball ever, yet it doesn’t seem to be appreciated by a lot of the players.
It does seem as if players are having trouble controlling it when shooting, as if it doesn’t respond aerodynamically in the way they’re expecting, and it’s possible that playing at altitude may be part of the reason for this. But could there be another factor?
The ball that’s used on the English Premier League is the Nike Total 90 Omni. The manufacturers say that has a special graphic that makes the ball easier to see using peripheral vision. Its yellow colour makes it stand out if it’s in the central part of our vision because the light receptor cells there are particularly sensitive to yellow (the reason why high visibility jackets are yellow). The Jabulani is white with some multi-coloured areas.
What may be important here is not that one ball is necessarily much easier to see than the other, but the simple fact that they are quite different. When a professional footballer kicks a ball, he will be much more accurate in the part of the ball he kicks than a park player. In order to do this, he will have to focus on that particular part of the ball. But he will do it subconsciously, not realising that he’s doing it.
Faced with a different ball design, the subconscious brain will not immediately recognise the correct part of the ball for the shot. The shot is hit less accurately, with the result that it doesn’t follow the intended path.
In time, the brain recalibrates for the new ball. Those who have been training with the ball for longer, such as the Germans, will have an initial advantage. Others will catch up in time, but will they do so quickly enough?
David
New Balls Please
I was lucky enough to get Centre Court tickets to Wimbledon recently. Watching Andy Roddick play Michael Llodra, I thought I’d watch their head and eyes as they played the ball.
As time went by, however, I thought Roddick had brought his focus closer to the contact area, though still in front. Llodra, meanwhile, seemed to be less consistent, sometimes looking at he contact area, and sometimes a way in front. There wasn’t a complete correlation between where he looked and whether he won the point or not, but he seemed to be more likely to be successful when his focus was nearer the contact area. Roddick went on to win the next three sets and the match.
It’s certainly possible that my observations were mistaken, or that Roddick’s game improved and Llodra’s deteriorated, their gaze positions altered as a consequence. For instance, if Roddick started hitting the ball harder, Llodra might have had less time to get in position for his shots, including his head position.
So is there any evidence that where you look when you hit the ball is important in tennis? Actually, there is...
In 2007, Damien Lafont presented a paper entitled “Gaze Control during the Hitting Phase in Tennis”. Using high-speed photography, he found that most professional players looked out in front of the racket, sometimes into the opponent’s court at the moment of impact. However, the visual strategy of the very best players, such as Federer and Nadal, differed in two respects. Firstly, they fixated the contact zone, and secondly they maintained this fixation until after they had completed their swing.
This is a bit more than the traditional “keep your eye on the ball”. The ball can be arriving at speeds of over 130mph, which is too fast for the eyes to track accurately all the way. They must be able to make some early judgments about where the ball is going to go by watching their opponent’s actions as he plays the shot. There is likely to be some early pursuit of the ball to confirm this.
Knowing when to time your shot can be estimated from when the ball bounces in front of you, and then the elite players start focusing on the area, some way in front of them, where they intend to hit the ball – the contact area. It seems that they don’t actually watch the ball onto the racket, but instead watch the racket hit the ball in the contact area (as opposed to watching the swing of the racket as it hits the ball).
Federer adds one, possibly unique twist to this. He actually twists his head so that he can see the contact area through the back of the racket. He thus ensures that his head and eyes are still at the point of contact, and immediately afterwards, making it less likely hat he’ll snatch the shot by looking ahead too early.
Federer’s technique may not be for everybody, and he has been perfecting it over a number of years. Photographs show him doing this at the age of three. However, the idea of training yourself to focus on the contact zone as, and immediately after, you play the shot can be practised.
Many courts are surrounded by wire netting. You can push a ball into the netting to hold it in place at different heights and positions for different shots. Then, when you play, imagine the ball is held in place for a millisecond as you swing the racket. You then look for contact between your racket and the ball either from the front of the racket, like Nadal, or from the back, like Federer, whichever seems to suit you best.
David Donner
http://www.donneroptometrists.co.uk/sports-vision.htm
Wednesday 2 June 2010
Sports Vision - Fielding in Cricket
A ball is travelling towards you. How do you know when it’s going to arrive, so you can get your hands in the right position to catch it? Muscles in the hand must be prepared so that the hand is widest open before the ball hits just above the palm (ideally), the wrist forearm and elbow must be prepared to absorb the kinetic energy of the ball, and the finger joints must also be prepared to close around the ball after impact. Muscle responses need to start about 100 milliseconds before the ball arrives.
From physics, the time taken for the ball to arrive will be its distance away from you divided by the speed at which it’s travelling. The brain can deduce information about the ball’s position from the size of its image on the retina; the smaller the image, the further away it is. The rate at which the image is getting bigger tells the brain how fast the ball is coming towards you (i.e. its speed).
The brain doesn’t actually calculate the ratio between them, but it knows, through practice, that when this ratio reaches a critical level, it’s time to send the necessary messages to the arm and hand muscles.
Savelsbergh et al conducted an interesting experiment in 1991 using a balloon that deflated as it approached the catcher. Because the image size on the retina did not increase as normal, the catchers overestimated the time to contact, showing that they were using image size for their timing rather than just the speed of the ball. The effect was most noticeable when one eye was covered. It was still there when both eyes were open, but less so, suggesting that stereoscopic information from vision can also be used.
This is fine for a ball that’s travelling at a steady speed, but what about a ball that’s accelerating? An outfielder under a skied catch has to deal with a ball that’s dropping at a rate of 32 ft/sec², and they may have to run to get in line with it as well.
If the fielder is directly under a skier, the brain can use something known as the “zeta angle”. This is the apparent size of a falling object relative to its apparent size at the moment the object started to fall. If it can make an allowance for gravity, the brain can initiate the catching actions when the zeta angle reaches a certain level, as long as the point when the ball started to drop was observed.
Experiments on astronauts on board Space Shuttle Columbia have shown that we do indeed make an adjustment for the effect of gravity. In space, the astronauts were too early in their attempts to catch the ball, because their brains were programmed to take into account the effect of a non-existent gravity.
If the ball is coming straight to the fielder, then his angle of gaze – the angle between the eye and the ball – will remain constant. If it’s not coming straight at him, then the angle of gaze will vary as the ball travels. The brain can use this information by trying to keep the angle constant or within a certain range. This information will get enable the catch to be made (assuming the fielder can run fast enough). The brain doesn’t calculate where the ball will land: it just uses the visual information to get the fielder to where the ball will land.
Finally, the fielder needs to be in a position where the ball appears to be travelling at a constant speed. If it’s speeding up, you need to move back, or move forward if it appears to be slowing down.
The unsurprising conclusion from all of this is that the more experience of catching from a young age that one gets, the better.
For more information please visit http://www.donneroptometrists.co.uk/sports-vision.htm
Sports Vision - Bowling in Cricket
After 5 good deliveries, the bowler bowls a poor ball that gets hit for four. A batsman has been tied down by a spell of good bowling, and ten plays a wild shot, throwing his wicket away. A bowler has bowled several good overs, then a poor ball, “the worst ball I’ve bowled all day”, takes a wicket.
These things happen all the time in matches, but how often do they happen in the nets? Rarely, if ever. Most of the time, bowlers are used as fodder to give the batsmen time at the crease. Are they really practising their trade effectively?
In a match, the bowler can put pressure on a batsman by bowling a succession of testing deliveries. So why not get bowlers to ball 6 balls at a time in the nets? Markers on the nets can indicate fielders’ positions, and if you have an umpire in place, judgements can be made on appeals and runs scored.
Bowling is an aiming activity, with the point where the ball pitches being the target. This point will vary according to the type of delivery the bowler wants to bowl, as well as the style and stature of the striker. These can be marked on the floor of the net, and adjusted if necessary, for instance if the striker starts batting out of his crease. These marks may also help the striker pick up the length of deliveries, so they help both bowlers and batsmen.
For more information please visit http://www.donneroptometrists.co.uk/sports-vision.htm
Sports Vision - Batting in Cricket
“The head must be kept upright and turned towards the bowler with the eyes as level as possible” (The MCC Cricket Coaching Book).
But why should the eyes be as level as possible? According to the MCC, only in this position can “the batsman focus both eyes together”. But if you look at an object and twist your head slightly, you’ll notice that things don’t go blurred or double. The reason is that the balance organs in the ears register this head tilt and, via the vestibulo-ocular reflex, produce a counter-rotation of the eyes to maintain clear vision.
Another reason that’s commonly given is that keeping the eyes level helps speed up your reaction time. I have been unable to find much evidence to support this claim, however. I did find one experiment that showed a link between head tilt and lower reaction times, but there are one or two problems with applying it to batting. Firstly, subjects had to react to a sound. They were also sitting down………in the dark.
Even if there were a link, how much of batting is to do with reaction times, anyway? Sir Donald Bradman was found to have slower reactions than the average University student. Yet, as Jim Laker said “Bradman always seemed to know where the ball was going to pitch, what stroke he was going to play, and how many runs he was going to score”. It seems that batting has more to do with anticipation than reaction times.
This is not to say that one shouldn’t have ones eyes level. For some batsmen it might help them focus on the bowler’s action and release of the ball, and for others it might be necessary to ensure a consistency of eye dominance between watching the bowler and playing the shot. But it suggests that there isn’t one perfect technique that should be employed by everyone, but it’s more a question of the individual’s brain working out (ideally subconsciously) what works best for them. And is it possible that the twisting that’s’ required in order to get the eyes level from a sideways stance contributes to the back injuries suffered by many batsmen?
Bradman did not have a classic technique. He was entirely self-taught, and didn’t play on a grass pitch until he was 18, having been brought up on concrete pitches covered in matting. He had an unusual grip, with his right hand nearly facing straight down the pitch, and the “V” of his left hand in line with the splice. His bat was closed and locked between his feet, and he picked it up at an angle of 45 degrees to the flight of the ball. None of this could be found in any coaching manual, and led to much criticism early in his career. He was, however, the master of seeing the ball early, and playing it late.
He also fits into the classic profile of an elite sportsman in having had essentially unlimited access to practice in his developing years whilst pursuing a range of sports. In Bradman’s case, he spent many hours playing imaginary Test matches, throwing a golf ball against the brick base of a water tank and hitting it with a stump. He was a highly proficient billiards player, played off a scratch handicap in golf for many years, and excelled in tennis, which he played before taking up cricket.
There are three key visual stages in batting: watching the bowler’s action and release of the ball; watching the pitch of the ball; and watching the contact between bat and ball.
By observing the bowler’s action, Test match batsmen are able to determine what type of ball a swing bowler is delivering (outswinger, inswinger, short ball) by the time the front foot has landed. They can also determine a leg spinner’s delivery (leg spinner or googly) by the same time from observation of the bowler’s wrist. Accurate determination of the length of the delivery seems to require some early tracking of the ball after release.
Land & McLeod (2000) monitored the eye movements of expert batsmen when facing a bowling machine. They found that even elite batsmen weren’t able to track the ball throughout its flight. They would track it for a while and then jump ahead to the point where they expected the ball to pitch. If the ball was short-pitched, they would make that jump in fixation earlier. If it was over-pitched, they could track almost the whole way.
A very quick delivery may pitch less than a quarter of a second after the bowler releases it. Because novices aren’t so god at anticipating the length of the ball, they make their jump to the bounce point too late. Either they’re still trying vainly to follow the path of the ball, or they are making their jump as the ball pitches. Because vision is suppressed when one makes this jumping (“saccadic”) eye movement, they can lose sight of the ball completely.
If the batsman knows the where the ball has pitched, and the speed at which it’s travelling, he can work out when it will arrive. The brain doesn’t actually work out these calculations in a mathematical way. Rather it develops rules of thumb based on long periods of practice. But it still needs to pick up information about the speed of the ball and where it’s pitched in order to make the correct shot decisions.
A sense of the speed of the ball is obtained from the time it took to leave the bowler’s hand to reach the bounce point. An adjustment then needs to be made for loss of speed after pitching. This is why batsmen generally need to play themselves in: so they can make the necessary adjustments according to whether the pitch is fast or slow.
According to Land & McLeod, the position that the ball pitched can be determined by the formula B/tanФ, where B is the height of the batsman’s eye and Ф is the angle that the batsman’s eyes have had to look down. So the more the batsman has to look down, the closer to him the ball has pitched. It may be, however, that the brain establishes the pitch point from more general principles of how far away things are, for instance by using the different images that form on the two retinas from near objects.
However the brain does it, one clear message should be that it’s more useful to tell a batsman to concentrate on where the ball has pitched, than a general “watch the ball” instruction. If you know accurately where the ball has pitched, you’re most of the way to knowing what shot to play and when. It can be useful to ask batsmen in the nets where they think the ball pitched, so they can feedback on their perception.
The final key visual stage is the contact between bat and ball. In other interception sports, such as tennis, focusing on the contact point has been shown to be highly important for elite players. Some imagine a hitting area into which the ball arrives, and they maintain focus on that area even after the ball has been hit. Batting tees can be useful aids in concentrating on the contact point.
Differences in batting style have been observed when facing a bowling machine compared with facing a bowler (Pinder, Ross & Davids 2006), such as shorter and later backswing and shorter stride length. As an umpire, I’ve seen young batsmen display excellent stroke-play, but with no idea of how to build an innings, no shot placement, and often pre-meditating the shot. They look like they’re playing in a net, rather than in a match. So there’s clearly a danger in over-relying on net practice, and bowling machines in particular, although they clearly have their place.
It is therefore useful to try and make the nets more like a match, for instance by having two batsmen alternating the strike, and by marking fielder’s positions on the nets. Ideally, an umpire could stand and make decisions as well as giving a notional score for each shot.
When the batsman surveys the field, the obvious thing is just to note where the fielders are. However, this can often lead to the ball being struck precisely to where those fielders are. More useful is to focus on the gaps between the fielders, ideally to a specific point between them. This becomes much more powerful if the striker also visualises hitting the ball to that specific point.
For more information please visit http://www.donneroptometrists.co.uk/sports-vision.htm
Monday 10 May 2010
Does Colour Matter?
Researchers at the University of Chichester have found that footballers were more likely to miss a penalty if the keeper was wearing red.
40 university footballers took dozens of penalties against a keeper who saved 46% of them when wearing red, 31% in yellow, 28% in blue and 25% in green. They suggest that the colour red might have an unconscious influence on the perception of failure, causing strikers to perform worse.
The colour of footballers’ jerseys came to prominence in 1996 with Manchester United’s infamous grey kit. Having lost three games and drawn one whilst wearing the grey kit, Man Utd were 3-0 down at half time against
In 2008, Petr Cech started wearing a bright orange shirt which in theory would distract the opposing striker. In the 1990s, Mexican keeper Jorge Campos designed his own brightly coloured kits with the same purpose. However, these theories weren’t obviously effective in practice, so it could be that elite players aren’t distracted in the way that lesser players might be. The most popular colour for goalkeepers in the Premier League to wear is green, and none wear red. So is there any evidence that red is an advantage at a professional level? Actually, there is.
In 2007, Attrill, Gresty, Hill & Barton found that red shirts were associated with long-term success in English football. Across all league divisions, red teams had the best home record. No significant differences were found in away matches, when teams wear their away kit.
They also found that in all but one city (Sheffield), the team playing in red has been more successful since 1946 than the other available team playing in a different colour. They speculate, however, that in recent times the spending power of clubs might be a more significant factor in their success than shirt colour.
Real (white);
Inter (blue + black); AC (red + black stripes)
Roma (red); Lazio (blue + white)
Sampdoria (blue);
Juventus (black + white stripes);
Anderlecht (white);
CSKA (red + blue); Dynamo (blue); Spartak (red + white stripe); Lokomotiv (red)
What about international teams? Hill & Barton (2005) looked at the Euro 2004 Championships. They found that all teams that wore red in some of their matches, but not in all, had better results when they wore red. This was, however, a small sample.
In Germany, the national team’s away shirts were changed from black to red in November 2004 at the request of Jurgen Klinsmann, in the belief that teams in red were perceived as more intimidating as well as more successful. He hoped to use the red away shirt as first choice for the 2006 World Cup, despite the fact that they had less than impressive results in these colours, notably a 4-1 defeat by
In FIFA’s Top 10 ranking, Spain (1st) and Portugal (4th) play in red, and Croatia (10th) play in red and white. But if wearing red has a significant negative psychological effect on ones opponents, one would expect the advantage to be seen in other physical sports, such as rugby and American Football.
Out of the 12 teams in the Guinness Premiership, only one (Gloucester) has a significant amount of red in their home shirt. Out of the 10 teams in the Magners League, only two (
There is one area of sport where there is strong scientific evidence that wearing red is an advantage, although it’s because of the effect on the officials, rather than the players. In 2008, Hagemann et al showed 42 experienced tae kwon do referees video clips of 5 different male competitors. Each clip featured one athlete in red and another in blue, and the referees had to score the match. Some time later, they were shown the same clips, but with the colours digitally swapped, so that the athlete originally wearing red was now wearing blue. This single alteration had a significant effect on the outcome, with competitors wearing red scoring on average 13% more points than their opponents in blue. It was dubbed “the Chris de Burgh effect”, and is thought to be due to an assumption by the officials that competitors wearing red are more aggressive.
Professional footballers are less likely to be distracted by the colour of the opponents’ shirts, and more likely to be able to assess the most relevant information in their vision in order to make the most effective pass or shot.
It is 44 years since a team wearing red won the World Cup. If
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