a briefing document
|establishment psycho-bunk 1—‘lie detection’||establishment psycho-bunk is a sub-set of documents, within this document set. This document set shows how to apply empiric reasoning to social and psychological problems..|
|establishment psycho-bunk 2 —Ritalin and junk science||Intelligence: misuse and abuse of statistics||drugs, smoking and addiction|
|establishment psycho-bunk 3 —dyslexia||
||establishment psycho-bunk||cause, chance and Bayesian statistics|
|establishment psycho-bunk 4 —the myth of repressed memory||misuse and corruption in science|
|psycho-bunk 5 —what is memory, or intelligence? Incautious claims of ‘IQ’ genes||For related
empiric reasoning documents, start with
Why Aristotelian logic does not work
|psycho-bunk 6—‘traumatic’ ‘syndromes’ or ‘curing’ P.E.S.Ts|
The excerpt below on left-handedness starts with a lot of stuff on defining and counting left-handedness/right-handedness.
Burt notes more left-handedness among mentally backward and more among boys (5.8%) than girls (3.7%).
Burt speculates that the increase among backward may be weakness of both arms, rather than preference.
So the percentage of lefthanders is
rising. This abstraction is from the 1951 printing. The first edition
was in 1937, the second in 1946, and the third in 1950.
When I’ve done checks, left-handedness is nearer to 10%, and I did not notice a sex difference, but I was not very interested! I expect that, like most statistics, the values vary in different populations.
Burt comes to the belief that people are not really dvided by left- and right-handedness, but the left and right hand work together as a team, with the traditionally nominated, dominate hand being assigned to tasks requiring precision, and the other, more specialised, being used for strength or steadying purposes. One hand writes while the other steadies the paper, one hand guides the broom, while the other anchors it.
Burt notes that more tics, nervousness and other problems in left-handers. On page 290, he refers to, “[...] the older practice which maintained that any child holding a pen in his left hand should have his knuckles rapped [...] ”, but does not make the rather obvious connection between this sort of action and other emotional difficulties.
I. Methods, (definitions. The whole section on left-handedness comprises 90 pages: pp. 270 - 359.)
Complexity of the Problem.—Of all the special motor disabilities found among school children, that which interferes most widely with the ordinary tasks of the classroom is left-handedness; and no question is put by the teacher to the school psychologist more frequently than this: ‘How should I deal with a left-handed pupil?’ A condition so common and so perplexing will require examination at some length.
One fact must be emphasized at the outset. Left-handedness is by no means so definite a characteristic as is popularly supposed. Right-handedness and left-handedness are relative terms - indeed, somewhat ambiguous terms, not sharply defined alternatives, mutually exclusive and absolutely opposed. To describe a child as left-handed without further explanatory details conveys very little information about his manual habits generally and still less about his neuro-muscular co-ordination as a whole. Usually it simply means that the teacher has observed the child regularly writing with his left hand, and is tempted to infer some inherent and abnormal asymmetry in his nervous organization or brain.
Closer inquiry soon reveals that left-handedness can manifest itself in very different forms and with very different degrees of strength. Moreover, the mixed forms and the milder degrees prove quite as common as the thoroughgoing or extreme. How many persons are consistently left-handed—or, for that matter, consistently right-handed—for every transaction in which hands are required? We shall find ample evidence to show that, quite apart from any general inclination such as might be ascribed to an innate or hereditary tendency, individual preferences in this movement or in that are dictated now by habit, now by special circumstance, and now by the intrinsic delicacy of the muscular co-ordinations involved. Accordingly, mere casual observation of some particular stereotyped action, like writing or drawing, will be of little value by itself: such observations need to be supplemented by an inquiry into the conditions under which the action has been learnt, and by specially devised tests which will estimate the strength of any original or ineradicable bias.
Definition and Tests.—Before we can devise a proper test, we must clarify our conception of what left-handedness denotes. An exact definition is essential. By left-handedness  I understand a consistent tendency (whether congenital, or induced post-natally by accident or by some other change in the hand or its neuro-muscular apparatus) to undertake new dexterities with the left hand rather than with the right. It must be judged, therefore, not so much by long-standing habits as by an unfamiliar task, and not by a single action, but by several. The points to observe are not merely the child's customary mode of using the pencil or pen, but his power to throw a ball or pick up a weight, to hammer or bore, to sort marbles, deal cards, cut with a knife or scissors, stir with a teaspoon in a cup, turn a handle or wind cotton round a reel, more easily with the one hand than with the other. Probably the best single test for rapid use is to ask the child to cut paper with loose-riveted scissors.  Incidentally it is at times instructive to make a note of any half-unconscious manual habits that are not influenced by social pressure. For example, in clasping the hands, which thumb is placed on top? And perhaps a little more significant-in folding the arms, which hand is placed on top of the opposite arm?
If quantitative measurements are required, any of the tests of manual dexterity described above may be employed. The child carries out the test first with the hand that he usually writes with, and then with the other. The index of left-handedness most commonly adopted (generally, but inaccurately, termed ‘index of right-handedness’ or ‘dextrality’) is given by the simple formula L/R x 100, where R and L denote the number of marks scored with the right hand and with the left respectively; a somewhat better measure of right-handedness is given by the formula R-L/R+L.
So important is it to detect tendencies towards left-handedness at the earliest possible moment that a word or two may be added on the testing of young infants. The critical period lies between six and fifteen months. At this tender age a rough ‘reacting test’ is the easiest to apply. Provisionally, in default of first-hand studies in this country, I suggest that the experimenter should adopt the procedure and the norms worked out by Gesell in America. ‘A red rod’ (e.g. a red pencil) ‘is held in the median plane, and the child is encouraged to make repeated efforts to grasp it’. With the shy, the dull, and the mentally deficient, a sweet wrapped in coloured paper is sometimes more effective. The examiner is also instructed to note ‘whether the child uses one hand independently in his own spontaneous manipulations’—e.g. in picking things up or flinging them down.
Right- and Left-handedness in Two-handed Operations.—With older children more recent investigators have urged that tests such as I have mentioned, which they regard as tests of uni-manual activities only, should be accompanied by tests and inquiries upon bi-manual activities. These they divide into two sub-groups on a basis which at first sight seems purely empirical. The typical activities chosen are (i) throwing a ball (for the uni-manual test), and (for the bi-manual tests) (ii) using a cricket bat, a golf club, or an axe, and (iii) using a pitchfork, a shovel, or a broom—the use of the bat and the broom being generally taken as the most representative. A ‘handedness formula’ is then proposed which will indicate, by three letters, each individual’s habits in each of the three directions. Thus if he (i) throws with his right hand, (ii) bats with his left, and (iii) sweeps and digs with his right, he is classed as R L R. But what are we to regard as ‘right-handed’ batting or sweeping, when by hypothesis both hands are used? The criterion proposed is the hand which is held ‘nearer the business end of the instrument’—that is, the lower end, the end farthest from the shoulders.
To me this latter principle appears quite mistaken. The real question is-which of the two hands executes the greatest movement and consequently undertakes the more delicate and more active task of guiding or directing the instrument? In batting, as in wielding a hockey stick or golf club, the fulcrum is near the body, and the ‘business end’ executes the wider movement. The right-handed bats man, therefore, almost always places his right hand below the left. But in sweeping or digging it is usually the nearer end of the broom or spade that is chiefly moved. With the broom, it is true, various methods may be adopted. But in digging the movements are fairly uniform: the left hand generally holds the middle of the spade and supplies a fulcrum; the right hand moves the handle to balance the heavy earth at the other end. Should we call the ordinary method of using a billiard cue ‘left-handed’ because the left hand is ‘nearer the business end’? With each of these instruments, apart from special conditions (e.g. sweeping in awkward corners), the dominating tendency is for the operator to work always on the same side of the body. Thus a right-handed person keeps the handle of the bat, broom, or spade mainly on his right. It follows that the relative positions of the two hands on the handle will naturally be inverted for swinging and for thrusting movements respectively—for swinging as in using a cricket bat, and for thrusting as in sweeping, digging, or striking with a spear or pushing with a cue.
If these observations are correct, the third letter in the usual ‘handedness formula’ should evidently be reversed: R R L should be called R R R, and so throughout the series. And, in point of fact, the figures given by all investigators show that, in using the spade or broom, the vast majority of persons, who are otherwise right-handed, place the left hand down—i.e. ‘nearer the business end’. It seems wholly illogical to designate this a left-handed procedure.
Manual Types.—Those who lay stress on the difference between bi-manual and uni-manual operations believe that we must recognize a number of clear-cut types. Instead of splitting the whole population into two simple categories, the right-handed and the left-handed respectively, there are, they assert, at least half a dozen subdivisions. Each type is different in nature, and calls for a different treatment in the classroom. Hence they argue that all the earlier work on left-handedness as it affects the child at school is invalidated from the outset. It over-simplifies the problem.
Their detailed classification follows from the formula given above. A twofold division, as we have seen, is applied and re-applied on three successive principles. In theory this should furnish 23 = 8 possible types. But in practice, it is said, ‘there is no such combination as R L R and L R L .... When a man is seen throwing with the right hand and batting with the left hand, then it is certain that he will sweep and pitch hay with the left hand.’ Hence we are left with only six.
The suggestion emanates from America, where most of the more recent inquiries have been carried out. To check their deductions, and to verify my own hypotheses, I have collected the following data from English adults. The right-handed persons were mainly post-graduate students at a training college; and to obtain a larger number of left-handed types I have extended my investigations to all the alleged cases of left-handedness I have encountered at public lectures or in private life. The following table summarizes the chief results (Table XVIII)
At first sight the variety of combinations appears somewhat bewildering. They are largely accounted for when we look more closely into the nature of those two-handed activities that are taken as the basis of the sub-classification. As we have already seen, the movements in the first set (using a bat or a golf club) involve a swinging stroke, carefully aimed and skilfully applied: they are, in fact, difficult and dexterous operations; moreover, they are learnt and practised in teams or social groups; hence nonconforming methods are apt to be quizzed and criticized until they are brought into line. The activities in the second set (sweeping and digging) are by comparison coarse and unskilled processes: as usually carried out, they involve a push or thrust, and demand strength rather than precision. They are generally undertaken alone; hence individual oddities may pass uncorrected.
The following conclusions, suggested by the figures in the table, will now become intelligible.
Questionnaires and Group-tests.—For group inquiries a
questionnaire on the following lines will pick out about 90 per cent.
of those with left-handed tendencies.
Imagine yourself doing these things before you answer; and underline the true reply’. The words ‘left’, ‘right’, ‘either hand’, are printed as alternative answers against each question.
For group-tests in class the simpler of the tests of manual speed and dexterity can be readily applied. In my own investigations the ‘tapping’, ‘aiming’, and ‘tracing’ tests were chiefly employed.
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© abelard, 2007, 18 january
the address for this document is http://www.abelard.org/briefings/left_handedness.php