8. Doing two things at once. Prepare several columns of one-place numbers, ten digits in a column. Try to add these columns, at the same time reciting a familiar poem, and notice how you manage it, and how accurate your work is.

9. Consider what would be the best way to secure sustained attention to some sort of work from which your mind is apt to wander.

REFERENCES

Walter B. Pillsbury gives a full treatment of the subject in his book on _Attention_, 1908, and a condensed account of the matter in Chapter V of his _Essentials of Psychology_, 2nd edition, 1920.

Another full treatment is that of t.i.tchener, in his _Textbook of Psychology_, 1909, pp. 265-302.

On the topic of distraction, see John J. B. Morgan's _Overcoming of Distraction and Other Resistances_, 1916.

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CHAPTER XII

INTELLIGENCE

HOW INTELLIGENCE IS MEASURED, WHAT IT CONSISTS IN AND EVIDENCE OF ITS BEING LARGELY A MATTER OF HEREDITY

Before leaving the general topic of native traits and pa.s.sing to the process of learning or acquiring traits, we need to complete our picture of the native mental const.i.tution by adding intelligence to reflex action, instinct, emotion, feeling, sensation and attention.

Man is an intelligent animal by nature. The fact that he is the most intelligent of animals is due to his native const.i.tution, as the fact that, among the lower animals, some species are more intelligent than others is due to the native const.i.tution of each species. A rat has more intelligence than a frog, a dog than a rat, a monkey than a dog, and a man than a monkey, because of their native const.i.tutions as members of their respective species.

But the different individuals belonging to the same species are not all equal in intelligence, any more than in size or strength or vitality. Some dogs are more intelligent than others, and the same is notably true of men. Now, are these differences between members of the same species due to heredity or environment? This question we can better approach after considering the methods by which psychologists undertake to measure intelligence; and an a.n.a.lysis of these methods may also serve to indicate what is included under the term "intelligence".

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Intelligence Tests

Not far from the year 1900 the school authorities of the city of Paris, desiring to know whether the backwardness of many children in school resulted from inattention, mischievousness and similar difficulties of a moral nature, or from genuine inability to learn, put the problem into the hands of Alfred Binet, a leading psychologist of the day; and within a few years thereafter he and a collaborator brought out the now famous Binet-Simon tests for intelligence. In devising these tests, Binet's plan was to leave school knowledge to one side, and look for information and skill picked up by the child from his elders and playmates in the ordinary experience of life.

Further, Binet wisely decided not to seek for any _single_ test for so broad a matter as intelligence, but rather to employ many brief tests and give the child plenty of chances to demonstrate what he had learned and what he could do. These little tests were graded in difficulty from the level of the three-year-old to that of the twelve-year-old, and the general plan was to determine how far up the scale the child could successfully pa.s.s the tests.

These were not the first tests in existence by any means, but they were the first attempt at a measure of general intelligence, and they proved extraordinarily useful. They have been added to and revised by other psychologists, notably by Terman in America, who has extended the scale of tests up to the adult level. A few samples from Terman's revision will give an idea of the character of the Binet tests.

From the tests for three-year-olds: Naming familiar objects--the child must name correctly at least three of five common objects that are shown him.

Six-year test: Finding omissions in pictures of faces, from which the nose, or one eye, etc., is left out. Four such pictures are shown, and three correct responses are required to pa.s.s the test.

Eight-year test: Tell how wood and coal are alike; and so with three other pairs of familiar things; two out of four correct responses are required to pa.s.s the test.

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Twelve-year test: Vocabulary test--rough definitions showing the child's understanding of forty words out of a standard list of one hundred.

The question may be raised, "Why such arbitrary standards-three out of five required here, two out of four there, forty out of a hundred the next time?" The answer is that the tests have been standardized by actual trial on large numbers of children, and so standardized that the average child of a given age can just barely pa.s.s the tests of that age.

Intelligence is measured by Binet on a scale of _mental age_. The average child of, let us say, eight years and six months is said to have a mental age of eight years and six months; and any individual who does just as well as this is said to have this mental age, no matter what his chronological age may be. The average child of this age pa.s.ses all the tests for eight years and below, and three of the six tests for age nine; or pa.s.ses an equivalent number of tests from the total series. Usually there is some "scatter" in the child's successes, as he fails in a test here and there below his mental age, and succeeds here and there above his mental age, but the failures below and the successes above balance each other in the average child, so that he comes out with a mental age equal to his chronological age.

[Footnote: The Binet scale, it must be understood, is an instrument of precision, not to be handled except by one who has been thoroughly trained in its use. It looks so simple that any student is apt to say, "Why, I could give those tests!" The point is that he couldn't--not until he knew the tests practically by heart, not till he had standardized his manner of conducting them to agree perfectly with the prescribed manner and till he knew how to score the varying answers given by different children according to the scoring system that goes with the tests, and not till, by experience in handling children in the tests, he was able to secure the child's confidence and get him to do his best, without, however, giving the child any a.s.sistance beyond what is prescribed. Many superior persons have looked down on the psychological examiner with his (or her) a.s.sortment of little tests, and have said, "Certainly no special training is necessary to give these tests. You simply want to find out whether the child can do these stunts. I can find out as well as you." They miss the point altogether. The question is not whether the child can do these stunts (with an undefined amount of a.s.sistance), but whether he _does_ them under carefully prescribed conditions. The child is given two, three or four dozen chances to see how many of them he will accept; and the whole scale has been standardized by try-out on many children of each age, and so adapted that when given according to instructions, it will give a correct measure of the child's mental age. But when given by superior persons in ignorance of its true character, it gives results very wide of the mark. So much by way of caution.]

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If a child's mental age is the same as his chronological age, he is just average, neither bright nor dull. If his mental age is much above his chronological, he is bright; if much below, dull. His degree of brightness or dullness can be measured by the number of years his mental age is above or below his chronological age. He is, mentally, so many years advanced or r.e.t.a.r.ded.

Brightness or dullness can also be measured by the _intelligence quotient_, which is employed so frequently that it is customarily abbreviated to "IQ". This is the mental age divided by the chronological, and is usually expressed in per cent. The IQ of the exactly average child, of any age, is 1, or 100 per cent. The IQ of the bright child is above 100 and of the dull child below 100. About sixty per cent. of all children have an IQ between 90 and 110, twenty per cent, are below 90 and twenty per cent, above 110. The following table gives the distribution in somewhat greater detail:

IQ below 70, 1% IQ 70-79, 5% IQ 80-89, 14% IQ 90-99, 30% IQ 100-109, 30% IQ 110-119, 14% IQ 120-129, 5% IQ over 129, 1% --- 100

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For convenience, those with IQ under 70 are sometimes labeled "feeble-minded", and the others, in order, "borderline", "low normal", "average" (from 90 to 110), "superior", "very superior", "exceedingly superior"; but this is arbitrary and really unscientific, for what the facts show is not a separation into cla.s.ses, but a continuous gradation from one extreme to the other. The lower extreme is near zero, and the upper extreme thus far found is about 180.

While the mental age tells an individual's intellectual level at a given time, the IQ tells how fast he has progressed. An IQ of 125 means that he has picked up knowledge and skill 25 per cent. faster than the average individual--that he has progressed as far in four years as the average child does in five, or as far in eight as the average does in ten, or as far in twelve as the average does in fifteen. The IQ usually remains fairly constant as the child grows older, and thus represents his rate of mental growth. It furnishes a pretty good measure of the individual's intelligence.

Performance Tests

Since, however, the Binet tests depend greatly on the use of language, they are not fair to the deaf child, nor to the child with a speech defect, nor to the foreign child. Also, some persons who are clumsy in managing the rather abstract ideas dealt with in the Binet tests show up better in managing concrete objects. For all such cases, _performance tests are useful. Language plays little part in a performance test_, and concrete objects are used. The "form board" is a good example. Blocks of various simple shapes are to be fitted into corresponding holes in a board; the time of performance is measured, and the errors (consisting in trying to put a block into a differently shaped hole) are also counted. To the normal adult, this task seems too simple {276} to serve as a test for intelligence, but the young child finds it difficult, and the mentally deficient adult goes at it in the same haphazard way as a young child, trying to force the square block into the round hole. He does not pin himself down to the one essential thing, which is to match blocks and holes according to shape.

Another good performance test is the "picture completion". A picture is placed before the child, out of which several square holes have been cut. These cut-out pieces are mounted on little blocks, and there are other similar blocks with more or less irrelevant objects pictured on them. The child must select from the whole collection of little blocks the one that belongs in each hole in the picture. The better his understanding of the picture, the better his selection.

Group Testing

The tests so far described, because they have to be given to each subject individually, require a great deal of time from the trained examiner, and tests are also needed which can be given to a whole group of people at once. For persons who can read printed directions, a group test can easily be conducted, though much preliminary labor is necessary in selecting and standardizing the questions used. Group testing of foreigners, illiterates, and young children is more difficult, but has been accomplished, the directions being conveyed orally or by means of pantomime.

The first extensive use of group intelligence tests was made in the American Army during the Great War. A committee of the American Psychological a.s.sociation prepared and standardized the tests, and persuaded the Army authorities to let them try them out in the camps.

So successful were these tests--when supplemented, in doubtful cases, by individual tests--that they were adopted in the receiving {277} camps; and they proved very useful both in detecting those individuals whose intelligence was too low to enable them to learn the duties of a soldier, and those who, from high intelligence, could profitably be trained for officers.

The "Alpha test", used on recruits who could read, consisted of eight pages of questions, each page presenting a different type of problem for solution. On the first page were rows of circles, squares, etc., to which certain things were to be done in accordance with spoken commands. The subject had to attend carefully to what he was told to do, since he was given each command only once, and some of the commands called for rather complicated reactions. The second page consisted of arithmetical problems, ranging from very simple at the top of the page to more difficult ones below, though none of them went into the more technical parts of arithmetic. One page tested the subject's information on matters of common knowledge; and another called for the selection of the best of three reasons offered for a given fact, as, for example, "Why is copper used for electric wires?

Because--it is mined in Montana--it is a good conductor--it is the cheapest metal." Another page presented disarranged sentences (as, "wet rain always is", or "school horses all to go"), to be put straight mentally, and indicated on the paper as true or false.

Many group tests are now in use, and among them some performance tests. In the latter, pictures are often employed; sometimes the subject has to complete the picture by drawing in a missing part, sometimes he has to cancel from the picture a part that is superfluous. He may have to draw a pencil line indicating the shortest path through a maze, or he may have to continue a series of marks which starts off according to a definite plan. The problems set him under each cla.s.s range from very easy to fairly difficult.

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Some Results of the Intelligence Tests

The princ.i.p.al fact discovered by use of standardized intelligence tests is that the tests serve very well the purpose for which they were intended. In expert hands they actually give a fairly reliable measure of the individual's intelligence. They have located the trouble in the case of many a backward school child, whose intelligence was too low to enable him to derive much benefit from the regular school curriculum. His schooling needed to be adjusted to his intelligence so as to prepare him to do what he was const.i.tutionally able to do.

On the other hand, it sometimes happens that a child who is mischievous and inattentive in school, and whose school work is rather poor, tests high in intelligence, the trouble with him being that the work set him is below his mental level and therefore unstimulating.

Such children do better when given more advanced work. The intelligence tests are proving of great service in detecting boys and girls of superior intelligence who have been dragging along, forming lazy habits of work, and not preparing for the kind of service that their intelligence should enable them to give.

Some results obtained by the "Alpha test" are given in the following table, and in the diagram which restates the facts of the table in graphic form. The Alpha test included 212 questions in all, and a correct answer to any question netted the subject one point. The maximum score was thus 212 points, a mark which could only be obtained by a combination of perfect accuracy and very rapid work (since only a limited time was allowed for each page of the test). Very seldom does even a very bright individual score over 200 points. The table shows the approximate per cent, of individuals scoring between certain limits; thus, {279} of men drafted into the Army, approximately 8 per cent. scored below 15 points, 12 per cent. scored from 16 to 29 points, etc. Of college freshmen, practically none score below 76 points, 1 per cent. score from 76 to 89 points, etc.

Per cent. of Per cent. of drafted men college freshmen making these making these Scores Scores Scores 0-14 points 3 0