The Puzzle of Left-Handedness (24 page)
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Other Asymmetries and Preferences
Although in most cases we couldn’t say straight off whether the people around us, even those we know well, are left- or right-handed, there is one category of individuals concerning whom careful records are kept: sportspeople. Left-handedness is a far from trivial advantage to those engaged in sports in which contestants enter into single combat, such as tennis, fencing and boxing, and indeed baseball, which in essence comes down to a duel between pitcher and batter. The reason is not hard to discover; it lies in the simple fact that left-handers constitute a small minority.
Take training. Most of the time spent by anyone seriously involved in a sport is devoted to rigorous practice. Since most people are right-handed, each player has a right-handed opponent to train with around nine times out of ten. For left-handers this is somewhat awkward initially, since they’re faced with asymmetry, but after a while they become entirely used to playing against a right-hander. If they find themselves facing a fellow left-hander in a match, they have little difficulty coping; the situation may be slightly unfamiliar, but they’re suddenly in their element. At last the constellation is symmetrical. For well-trained left-handers it therefore matters little which hand an opponent prefers.
Not so right-handers. Like left-handers they train with right-handed people nine times out of ten and usually this suits them fine, but when they occasionally have to take on a left-hander they’re doubly disadvantaged. They’re forced to engage in an asymmetrical battle for which they’re poorly prepared, against an opponent who’s a dab hand at dealing with this type of asymmetry. No wonder that in the official rankings of boxing, tennis and fencing champions, left-handers are significantly over-represented, as they are on the lists of top scorers in baseball.
The sports world tells us something else too: hand preference is not the only kind of asymmetry people encounter. A minority of soccer players are left-footed. They prefer to use the right foot to stand on while kicking the ball with the left. Such players are in demand because they can shoot from angles that the majority of footballers find hard to deal with, and because they’re in a minority they’re just that bit more unpredictable and difficult for right-footed players to mark.
As well as right- and left-footed soccer players, there are some who can hold their ground equally well with either foot. They are fairly few in number but more common than two-handers. If people exist who can truly do everything just as easily with either hand – while still being reasonably dextrous – then they’re as scarce as hens’ teeth. ‘Two-footedness’ is encountered relatively frequently, possibly because the tasks of a preferred foot are a good bit simpler than the performances we expect from a hand. In the end it’s really only a matter of ball control, the equivalent of accurate throwing. Feet don’t have any other skills, if only because all our toes do is help us walk, or keep our balance when standing still, tasks that involve both feet equally. A single specific skill, however complex, can be mastered by the non-preferred side of the body as long as we train long and hard. Left-handers who have been forced to learn to write with their right hands are living proof of this, as are left-handed musicians who play right-handedly.
Yet most soccer players stick anxiously to their preferred foot, and many never manage to train the other to anything like the same standard, so a kick with the wrong boot often fails completely. This was demonstrated on one occasion by the legendary, pig-headed and exclusively left-footed Dutch footballer Willem van Hanegem, renowned for his curved balls, as they’re known. Once, in his prime, when he was selected to take a penalty that could have made him the country’s top scorer, he took it with his right foot out of sheer perversity – and missed by a mile. Vintage Van Hanegem.
If we have both a hand preference and a foot preference, might there not be other, similar kinds of asymmetry elsewhere in the human body? Aside from our arms and legs there is just one other body part that serves mainly to carry out active tasks so delicate or complex that it allows us to speak of a preference asymmetry: the tongue. True, we have only one, but it is symmetrical, and each half is controlled by the opposite half of the brain. It’s called upon to perform some of the most difficult jobs we face.
First of all the tongue is responsible for an efficient preliminary treatment of the food we put into our mouths. It has to ensure that nothing escapes the grinding force of the teeth while itself remaining out of their reach. When this occasionally goes wrong we’re instantly reminded why it’s important. Its second task is to form speech sounds, which rely upon the subtle curves and differences in shape assumed by the tongue one after the other at impressive speed, in close coordination with movements of the lips, lower jaw and vocal cords. Considering that most of us can speak at a rate of 180 words a minute without too much difficulty, and that on average a word consists of four or five different sounds, it’s clear that some fairly impressive acrobatic feats go on between our teeth.
Some people do indeed seem to have a preferred side. In normal circumstances we’re not aware of having a tongue preference, but it’s easy to identify. The trick is to place one side of the tongue, then the other, gently between the molars and hold it there while singing your national anthem. The tongue side that is free when the words of the song take the least effort to sing and the result sounds best is the preferred side. Sadly no information is available as to how many people have a clear preference, what proportion of people are right- or left-tongued, or whether there is any connection between that figure and the proportion of left- and right-handers.
All the other body parts in which some kind of preference can be seen are used not so much to interact with our surroundings as to detect and observe them. In other words, they perform sensory rather than motor functions. The most prominent among them are the eyes and ears, and those are also the only two about which reasonably reliable facts on the matter are known. In both cases people have a clear preference.
We generally use one of our eyes for seeing and the other for measuring; one looks while the other mainly serves to measure the angle by which what we see differs between the two eyes, so that we can judge distance. This is known as depth perception. In many people, one eye works better than the other. Those of us who wear glasses or contact lenses know this, since the lenses are usually of different strengths. You might expect people to prefer to use their better eye as their seeing eye, but it turns out this is not so. It seems eye preference is settled early in life and remains the same even if the accuracy of one or both eyes changes, as often happens around the beginning of puberty. There seems to be an echo here of the stubbornness with which laboratory rats stick to their paw preference through thick and thin.
Eye preference can be tested in all kinds of ways, but most methods are less than reliable because measurements are distorted by hand preference. There’s not much point in taking account of which eye someone uses to aim a gun or a bow and arrow, for instance, since hand preference determines how such weapons are held and therefore which eye is used. What does work reasonably well is to observe how a person looks through the lens of a telescope or microscope, or the viewfinder of a camera. In the case of small children a pleasingly simple test has been developed. All you need is a hollow tube, a rolled up newspaper for instance. You look through one end of the tube and ask the child, who is moving around the room freely, to look back at you through it. The eye that appears at the other end of the tube is the child’s preferred eye. Although various studies into eye preference have produced markedly different results, it does seem that almost everyone consistently favours one eye or the other. Roughly two-thirds of us give priority to the right eye, the rest to the left.
Ears are another matter entirely. We don’t know whether we have a true ear preference for the simple reason that it’s almost impossible to think of a test that could determine which one it is. There’s certainly no test that could do so without any interference from other preferences, such as right- or left-handedness. All the same, it’s clearly a point worth examining, since in detecting sounds, two perfectly healthy ears turn out to work differently. Whether one or the other is dominant depends on what sort of sound they’re picking up. In general it seems we hear sounds that have to do with language, in other words speech, better with the right ear than with the left.
The most important means by which this has been studied involves what are known as dichotic hearing tests. Simply put, the test subject wears headphones and different words are sent to each ear at the same time. The subject then has to repeat what he or she has heard. It often turns out that words fed into the right ear have stuck in the memory rather better than those delivered to the left. If the sounds are unconnected with language, musical tones for example, then the results are the opposite, though the difference is not very great.
We need to treat these results with some caution. Dichotic tests place quite exacting demands on the test subject. It’s therefore perfectly possible that the effect arises in part for spurious reasons. In an attempt to produce an acceptable answer, a subject may for example come up with clever strategies that ultimately have nothing to do with the nature of the material presented. The differences do seem significant enough to be taken seriously, however, so we need to ask what the causes could be. We are not dealing merely with differences in sensitivity, since a less good ear hears both speech and other sounds less well.
The only remaining possibility is that this has something to do with differences between the two halves of the brain as they process sound. Each ear is directly connected to both cerebral hemispheres. We might therefore assume that the shorter connection has precedence, either because it’s quicker or because it’s less subject to disturbance along the way. Yet this is not the case. Speech sounds are received better by the right ear even though the centres that process speech are usually on the left. Conversely, the right half of the brain is more involved in processing melodies and yet we hear musical sounds better with the left ear. It therefore seems as if the nerve pathways coming from the opposite ear drown out those that run to the closer side of the brain, rather in the way that adjacent telephone lines can disturb each other. Perhaps we don’t so much have an ear preference as one ear that’s better at hearing certain sounds, depending on the place in the brain where that kind of sound is processed and the architecture of the specific nerve circuits that connect our ears with those processing centres.
If ears distinguish between linguistic and non-linguistic sounds, might not something similar happen with vision, in the sense that letters and words are more effectively viewed using one half of the retina and non-linguistic, or perhaps we should say non-symbolic pictures and patterns are better processed by the other? The suggestion seems natural, but it’s difficult to prove or disprove. Attempts have been made, but so many interfering factors and uncertainties come into play that we wouldn’t be justified in drawing any firm conclusions.
The existence of such a broad range of asymmetries naturally raises the question of whether there’s any connection between them. Is a left-handed person also left-eyed, left-footed and left-tongued? And if there is such a connection, does it have to do with the way the brain is org a n ized? Could it be, for example, that in many respects left-oriented people have a distribution of functions between the two halves of the brain that approaches the opposite of that found in the rest of us? One person who was deeply convinced that a strong correlation existed between the various forms of left and right orientation was an American called Beaufort Sims Parson. In 1924 he published a foolproof method of determining innate left-handedness with a machine he had built himself, the manuscope.
It was developed to detect a person’s hand preference objectively and reliably. After all, not only are people less than entirely trustworthy in answering questions about their hand preference, they are sometimes pushed in the direction of right-handedness by their environment, even more so in Parson’s day than in our own. This happens mainly, although not exclusively, at school. At home too, since most parents are right-handed, children are shown how to do things with the right hand and many appliances are designed to be used by right-handers. Conversely, it’s possible that a child of left-handed parents who is essentially right-handed might behave in some respects like a left-hander.
This kind of social pressure is entirely absent when it comes to eye preference. We are generally not even aware that we have such a thing. Parson not only believed it was connected to hand preference, he saw it as the cause. This idea had already been enjoying a degree of popularity for some years. He therefore felt that with his manuscope he had created an Egg of Columbus. Once eye preference had been determined, Parson reasoned, it would be clear whether the person in question was left- or right-handed.
Unfortunately for Parson and the other adherents of the eye-preference theory, it later transpired that their assumption was simply wrong. A majority of us are right-eyed, just as a majority are right-handed, but the proportions are quite different. Moreover it turns out there are not significantly more left-eyed people among the left-handed than among the right-handed. People have a hand preference and an eye preference, but it seems the two preferences develop entirely independently of each other.
More or less the same applies to feet and legs. The right-legged seem to be in the majority, but again the proportions are different from those we see with hand preference, nor is there any direct, demonstrable connection between leg preference and hand preference. It may even be that leg preference is a product of chance, like paw preference in animals. Some people say our preferred leg is the one we set off walking with, but what does such a thing really demonstrate? The only activity that brings to light a difference that looks even remotely like hand preference is soccer, and most people can’t kick a football particularly accur ately with either foot. It may well be that the roughly 30 per cent of us who are left-footed are matched by a roughly equal number of right-footed people, with a large group in between who have no preference at all. A proportion of 30 per cent is not too far from the one in four that characterizes a chance distribution.
