Contrast Sensitivity (CS) is the ability to discriminate detail under varying light conditions. Outdoor sports frequently take place under varying light conditions. Because the sporting environment is often dynamic, the constantly changing conditions make it harder to discriminate objects, which can result in inaccurate information for the brain to process.
If there is a deficit in this function, then 'reading' a tennis ball in overcast weather or negotiating undulations of the snow when skiing would be awry. This means not picking up the ball quickly or stumbling in the snow. Shooters have long realized that wearing certain color lenses helps their performance in one type of light, while different color lenses benefit them in other types of light.
Clay pigeon (skeet) shooters, for example, often use vermillion-colored lenses when they are aiming at orange clays against a moderately-bright background, yellow tints in poor light and brown tints in bright light. In tennis, a yellow tint, similar to the colour of the ball, highlights the contrast and visibility of the ball.
In golf, a green tint with brown overtones increases the ball's contrast against the blue sky and the green fairway. Training to improve CS does not exist but, as indicated, this function can be helped by using appropriate tinted lenses. However, the choice is subjective and often person-specific.
CS is measured by the subject viewing a series of sine-wave gratings of varying spatial frequencies and of varying contrast. For each frequency a contrast threshold is obtained and serial measurements yield a CS function (CSF). The point where the CSF intercepts the spatial frequency axis represents the quality of the visual acuity.
Color Vision (CV) is the ability to discriminate colors in the spectrum. Color defectives (cds) are unable to do this well. There are a variety of types and degrees of severity of color deficiency. Cds confuse certain colors according to the type of defect. Those who are actually color-blind can only see shades of grey and are extremely rare.
Most color defects are inherited in the X-link manner so that the females are the carriers of the genetic defect and rarely show it. The population of male cds genetically is about 5 percent, but some diseases and drug treatments can cause this condition, for example, diabetes and digitalis, which is given in some heart treatments.
Deficits in color vision can make it difficult to find one's own teammates if the opponents' strip is of a 'confusing' color. It can also make it difficult to see a ball against a 'confusing' background, so that it is missed or mistimed. Snooker players who are red/green deficient see the brown ball and the red balls as similarly colored, with dire results.
Since there is no training or treatment to remedy this defect, the cd looks for brightness/luminance clues which help him differentiate 'confusing' colors. Wearing a red contact lens in the non-dominant eye has helped some cds, but sceptics believe that it only works by altering brightness levels and red cellophane would do the job just as well.
CV is usually tested with the Ishihara Plates, but they have drawbacks: they are too sensitive and can only detect red/green defectives. The City University test is considered too insensitive but at least it does have plates for blue/yellow discrimination. There are a number of other CV tests, and using a whole battery of them enables a clearer diagnosis to be made.
The Motor Visual Parameters
Eye-hand coordination involves the integration of the eyes and the hand(s) as a unit. Any deficit in this ability will show itself in clumsy handling of the ball in sports like rugby and basketball, and poor racket control in sports like tennis and squash.
Wayne Saccadic Fixator (WSF)
This ability can be trained and measured on some of the WSF's programs. The WSF, as described in PP in August, is a 30-inch square instrument consisting of 33 lights set in three concentric circles around a central light. Its effectiveness is proven by the fact that some stroke patients have used the programs as part of their rehabilitation.
The central light of the WSF is placed at eye level and the subject is instructed to touch a light in order to extinguish it. The lights come on in a random fashion and for a set time (one per second), while the whole exercise is set for one minute. The test is therefore a re-active one. The total number of direct hits is displayed, with 60 the maximum possible score.
This program, as with most of those on the WSF, can be modified. For example, in another more difficult measure of this facility, the lights can be programmed to come on for only half-a-second and/or the duration can be extended to two minutes.
This is a soft solid rubber ball with six protruding areas, so that it has an unpredictable bounce. It is useful in training eye-hand coordination when the subject has to catch the ball after it bounces, but it is not measurable.
Eye-hand speed is the time required to perceive and respond with the hand(s) to a visual stimulus. It is the ability for the eyes and hands to be not only highly coordinated but fast. The best boxers are often said to have 'fast hands', i.e. they can throw a volley of punches in a second. Table-tennis players, too, have fast hands. A deficit in this parameter makes for slower responses, poor timing and the sports person may appear sluggish.
A slightly different program to the one just described can train and measure this ability. The instruction is to hit out the light as soon as it is seen, then do the same with the next light that comes on, and so on. The subject then governs the number of lights that come on, so that the quicker the lights are extinguished, the more chance there is of achieving a higher score, which is displayed.
This is a pro-active test, a form of faster eye-hand coordination. Again, the duration is usually set for one minute, but other time variations can be introduced to add novelty and difficulty.
Another program on the WSF measures precisely how long it takes for the subject to depress two lights in sequence from opposite ends of the instrument. The reaction time is displayed in hundredths of a second.
Eye-foot speed is the time required to perceive, and respond by moving the feet, to a visual stimulus. Any sport involving a high degree of mobility needs good eye-foot speed - for instance, fencing, racket games and, of course, football. A deficit in this ability reveals itself when a player does not move quickly enough to reach a ball, moves away from an attack, etc. Motor racing, where a mistake in a fraction of a second can prove fatal, is a sport where both eye-hand and eye-feet speeds must both be of a high order.
This instrument is ideal for training and measuring eye-foot speed. It consists of nine 1-foot squares making up a checkerboard pattern. The subject begins by standing on the central square and looking toward a light console where the pattern of the lights mimics the checkerboard pattern.
The lights come on in a random order, one at a time, and the subject has to move to the appropriate square as quickly as possible. Other program on Quick Feet can be used to enhance foot agility and raw motor speed.
Eye-body balance is the ability to shift one's center of gravity so that the body is always balanced. Along with fitness and concentration, it is common to all elite sports people. It can be seen to particularly good effect in winter sports such as downhill skiing, slalom racing and the luge, as well as in a summer sport like wind-surfing. Failure to have good body balance makes the athlete appear ungainly and awkward - in short, uncomfortable.
The subject stands on an 18-inch-square balance board which has four contact points that correspond to the north, south, east and west lights on the WSF. The lights on the WSF will come on at any one of these four positions. Subjects face the WSF and are instructed to tilt their body weight on the balance board in the direction of the illuminated lights on the WSF.
Each correct shift in balance when the correct contact point touches the floor registers a point scored on the display panel. The lights can be set to remain until the shift is correctly done, or for a limited time to make it harder.
To maintain a steady balance, the subject, while standing on the board, is instructed to follow the lights in their pursuit mode, and every time the board is not balanced (the contact points this time should not touch the floor), a penalty score is displayed.
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Anticipation Speed (AS) is the ability to be in the right place in good time. It can be seen in good players in team games like football and volleyball. In skeet shooting, it is the gun which has to be pointing and firing in the right place at the right time. AS is closely allied to speed of recognition, in that if the visual clues are read early enough it allows time to be in the right place.
An elite sportsperson is often considered as 'finding space' in a team game and being unhurried. Having good timing is a consequence of highly developed AS. Failure to have this ability gives a player poor timing, slowness and wrong-footedness. Commentators often talk of a reflex shot or save, when really it is a learned response. It is a combination of using visual recognition quickly and having good AS.
Bassin Anticipation Timer (BAT)
AS is best enhanced on this instrument. It consists of tracks (which can be extended) along which runs a sequence of LEDs (light-emitting diodes). Their timing can be set up to reach hundreds of mph. The exercise is for the subject to anticipate when the LEDs reach a designated spot by hitting across it with a hand, foot, bat or racket.
The track can be laid face-on to simulate batting in cricket, or angled across the body to simulate a ball arriving in such a direction. Any attempt is displayed as too early (-) or too late (+) in fractions of a second. As the ability improves, the speed is increased.
Another program on the WSF exists to train and measure AS. The lights come on sequentially in a spiral fashion at variable speeds and the designated light has to be hit. The timing, either early or late, is displayed in 1/100ths of a second.
The lights can be set to run horizontally and vertically as well. Since AS is reduced when running, both instruments can be used with the subject running on the spot.
Eye-body speed is the speed at which the body as a whole moves in response to a visual stimulus. If highly developed it amounts to being 'quick off the mark.' It is an essential quality in many sports, often seen as a sudden acceleration, e.g. in ball games and in some cycling events where the rider suddenly pounces from an almost stationary position.
ReAct Coach (RAC)
This instrument is essentially a small console which displays LEDs in an arrow formation. The arrows are programmed to point to the left, right, forward and backward at random. The subject is asked to run as fast as possible from a standing start in the direction of the arrow displayed to a designated mark,and return to the start position before the instrument gives a 'bleep' sound.
The number of times, the distance run and the interval between the start and the bleep can all be modified according to the level of intensity required. After the required number of runs, the time taken for each can be 'scrolled.' It can be seen if there are deficits to be worked on with the RAC. Footballers, racquet players and fielders in cricket often have to backpedal, and the RAC can help speed up that action.
For quick changes in direction, the RAC with its tripod and remote control unit can be used on site. The subject runs in the direction of the arrow while keeping an eye on the console. Any change in the arrow direction has to be followed, either through 90 or 180 degrees. Once again, the times can be scrolled.
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Reactions are quicker to sound than to vision. Asking tennis players, for example, to wear earplugs when practising heightens their visual awareness. All the computerized equipment that is used in SVT (sports vision training) has volume controls.
If there is no aural feedback, a bleep, then there is a tendency for the subject to glance at the display score panel, which leads to a drop in scoring ability. Switching off the volume controls is another way of increasing the level of difficulty.
Concentration And Noise
In this context 'noise' means a distraction, a disturbance of concentration. Paradoxically, it is a way of learning to improve concentration while doing any of the exercises. The noise can take a number of forms:
- Questioning the subject
- Playing music not to his/her liking
- Literally, making a noise.
If the subject can maintain the same level of ability with 'noise', then it imbues him/her with confidence in the knowledge that any adverse circumstances in the sport proper can be overcome, e.g. sudden changes in wind direction, crowd disturbances or provocative opponents. Exercising in this way involves two tasks creating divided attention.
Two other ways to improve abilities by having to concentrate very hard are using rotary prismatic spectacles and stroboscopic spectacles (SS). The prisms can be smoothly rotated to change the way the world appears.
They can cause spatial displacement when rotated in one position, and they can make demands on the vergence system when rotated in another direction.
Attempting any of the exercises when wearing them needs a period of adjustment. This again can be likened to a sudden change in playing conditions. Mastering the exercises while wearing these spectacles extends visual abilities.
SS are new, but the principle is well-established. They are spectacles whose lenses are stroboscopic - when the shutter is open for the same time as it is closed, then any object is only seen for half the time. The shutter speed is adjustable so that having the shutter open maximally at first is almost the same as seeing all the time.
When exercising with SS, the time that the shutter is open is slowly reduced. In practice, for instance, when a tennis ball is served at 20 mph, it appears as 40 mph with the shutter speed at half on/half off mode.
When the SS are removed, a ball hit at 20 mph appears much slower - at half the actual speed. After following the practice protocol, and then removing the SS, the player has much more time to see the ball.
Often you read about a player's wonderful 'vision' or having a marvellous 'eye.' These are players who have a highly tuned visual system. They are the ones who see clearly, quickly, read only essential cues and have the motor responses to act quickly and accurately. In fact, these are the qualities that SVT tries to instill.
The transfer from improvement in the laboratory/consulting room to the sporting arena has not been proved; all the benefits achieved have been largely anecdotal.
The multi-factorial nature of sports performance make its study complex, so that the effect of SVT is not clear. The area needs well-constructed and well-controlled studies to prove (or disprove) a positive relationship between SVT and performance.
Recent research - for instance, an as-yet unpublished PhD thesis by S. Calder (1996) or an article in International Journal of Sports Vision by B.E. Worrell on the impact of SVT on baseball batting averages (1995) - is leading the way.
SVT cannot change recreational players into great ones, but it can help to improve their sporting performance, as well as giving an edge to elite performers.