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Up to this point, the introspective side of the psychology of attention has not been considered. One of the surest of all introspective observations belongs right here, to the effect that we are more conscious of that to which we are attending than of anything else. Of two stimuli acting at once upon us, we are the more conscious of that one which catches our attention; of two acts that we perform simultaneously, that one is more conscious that is performed attentively.
We need not be entirely unconscious of the act or the stimulus to which we are not attending. We may be dimly conscious of it. There are degrees of consciousness. Suppose, for example, you are looking out of the window while "lost in thought". You are most conscious of the matter of your thoughts, but conscious to a degree of what you see out of the window. Your eyes are focused on some particular object outside, and you are more conscious of this than of other objects seen in indirect vision, though even of these last you are not altogether unconscious. Consciousness shades off from high light to dim background.
The "field of attention" is the maximum or high light of consciousness; it comprises the object under attentive observation, the reaction attentively performed. The "field of consciousness" includes the field of attention and much besides. It includes objects of which we are vaguely aware, desires active but not clearly formulated, feelings of pleasantness or unpleasantness, of tension, excitement, confidence, etc.
Apparently the field of consciousness shades off gradually into the field of unconscious activity. Some physiological processes go on unconsciously, and very habitual movements may be almost or entirely unconscious. The boundary{266}between what is vaguely conscious and what is entirely unconscious is necessarily very vague itself, but the probability is that the field of consciousness is broader than we usually suspect, and that many activities that we ordinarily think of as unconscious, because we do not observe them at the time nor remember them later, lie really near the margin of the field of consciousness, but inside that field. "Unconscious motives", such as spite or pride often seem to be, are probably vaguely conscious rather than unconscious. We shall return to the fascinating topic of the unconscious at the close of the book.
Degree of consciousness does not always tally with intensity of sensation or energy of muscular action. You may be more conscious of a slight but significant sound than of much louder noises occurring at the same time. You may be more conscious of a delicate finger movement than of a strong contraction of big muscles occurring at the same time. Degree of consciousness goes with degree of mental activity. Of all the reactions we are making at the same time--and usually there are several--the most active in a mental way is the most conscious. The slight sound arouses intense mental response because it means something of importance--like the faint cry of the baby upstairs, noticed instead of the loud noises of the street. The delicate finger movement aims at some difficult result, while the big muscles may be doing their accustomed work automatically.
It is not always the most efficient mental process that is most conscious; indeed, practising an act makes it both more efficient and less conscious. It is, rather, the less efficient processes that require attention, because they require mental work to keep them going straight.
Our sixth law of attention, emerging from this introspective study, is naturally of a different style from the remainder of the list, which were objectively observed; yet it{267}is no less certain and perhaps no less significant. It may be called:
(6) Thelaw of degrees of consciousness, and thus stated:An attentive response is conscious to a higher degree than any inattentive response made at the same time. An inattentive response may be dimly conscious or, perhaps, altogether unconscious. The less familiar the response, and the higher it stands in the scale of mental performances, the more attentive it is, and the more conscious.
Attentive observation is more trustworthy than inattentive, and also gives more facts. Attentive movement is more accurate than inattentive, and may be quicker as well. Attentive study gives quicker learning than inattentive, and at the same time fixes the facts more durably.
Shall we say, then, "Do everything attentively"? But that is impossible. We sense so many stimuli at once that we could not possibly attend to all of them. We do several things at once, and cannot give attention to them all. A skilful performance consists of many parts, and we cannot possibly give careful attention to all the parts. Attention is necessarily selective, and the best advice is, not simply to "be attentive", but to attend to the right things.
In observation, the best plan is obviously to decide beforehand exactly what needs to be observed, and then to focus attention on this precise point. That is the principle underlying the remarkably sure and keen observation of the scientist. Reading may be called a kind of observation, since the reader is looking for what the author has to tell; and the rule that holds for other observation holds also for reading. That is to say that the reader finds the most when he knows just what he is looking for. We can learn{268}something here from story-reading, which is the most efficient sort of reading, in the sense that you get the point of the story better than that of more serious reading matter, the reason being that attention is always pressing forward in the story, looking for something very definite. You want to know how the hero gets out of the fix he is in, and you press forward and find out with great certainty and little loss of time. The best readers of serious matter have a similar eagerness to discover what the author has to say; they get the author's question, and press on to find his answer. Such readers are both quick and retentive. The dawdling reader, who simply spends so much time and covers so many pages, in the vague hope that something will stick, does not remember the point because he never got the point, and never got it because he wasn't looking for it.
In skilled movement, or skilled action of any sort, the best rule is to fix attention on the end-result or, if the process is long, on the result that immediately needs to be accomplished. "Keep your eye on the ball" when the end just now to be achieved is hitting the ball. Attention to the details of the process, though necessary in learning a skilled movement, is distracting and confusing after skill has been acquired. The runner does not attend to his legs, but to the goal or, if that is still distant, to the runner just ahead of him.
The chief facts to take account of in attempting to form a conception of the brain action in attention are mobility, persistence in spite of mobility, and focusing.
The mobility of attention must mean that brain activities are in constant flux, with nerve currents continually shooting hither and thither and arousing ever fresh groups of neurones; but sustained attention means that a brain{269}activity (representing the desire or interest or reaction-tendency dominant at the time) may persist and limit the range of the mobile activities, by facilitating some of these and inhibiting others.
The "focusing" of mental activity is more difficult to translate into neural terms. The fact to be translated is that, while several mental activities may go on at once, only one occupies the focus of attention. This must mean that, while several brain activities go on at once, one is superior in some way to the rest. The superiority might lie in greater intensity of neurone action, or in greater extent; that is, one brain activity is bigger in some way than any other occurring at the same time--bigger either because the neurones in it are working more energetically or because it includes a larger number of active neurones.
But why should not two equally big brain activities sometimes occur at the same moment, and attention thus be divided? The only promising hypothesis that has been offered to explain the absence of divided attention is that of "neurone drainage", according to which one or the other of two neurone groups, simultaneously aroused to activity, drains off the energy from the other, so putting a quietus on it. Unfortunately, this hypothesis explains too much, for it would make it impossible for minor brain activities to go on at the same time as the major one, and that would mean that only one thing could be done at a time, and that the field of consciousness was no broader than the field of attention. On the whole, we must admit that we do not know exactly what the focusing of attention can mean in brain terms.
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1. Outline the chapter, in the form of a number of "laws", putting under each law the chief facts that belong there.2. See if you can verify, by watching another person's eyes, the statements made on page 250 regarding eye movements.3. Choose a spot where there is a good deal going on, stay there for five minutes and jot down the things that attract your attention. Classify the stimuli under the several "factors of advantage".4. Mention some stimulus to which you have a habit of attention, and one to which you have a habit of inattention.5. Close the eyes, and direct attention to the field of cutaneous and kinesthetic sensations. Do sensations emerge of which you are ordinarily only dimly conscious? Does shifting occur?6. Of the several factors of advantage, which would be most effective in catching another person's attention, and which in holding his attention?7. How does attention, in a blind person, probably differ from that of a seeing person?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.
Walter B. Pillsbury gives a full treatment of the subject in his book onAttention, 1908, and a condensed account of the matter in Chapter V of hisEssentials of Psychology, 2nd edition, 1920.
Another full treatment is that of Titchener, in hisTextbook of Psychology, 1909, pp. 265-302.
On the topic of distraction, see John J. B. Morgan'sOvercoming of Distraction and Other Resistances, 1916.
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Before leaving the general topic of native traits and passing to the process of learning or acquiring traits, we need to complete our picture of the native mental constitution 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 constitution, as the fact that, among the lower animals, some species are more intelligent than others is due to the native constitution 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 constitutions 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 analysis of these methods may also serve to indicate what is included under the term "intelligence".
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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 anysingletest 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 pass 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 pass 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 pass the test.{273}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 pass the tests of that age.
Intelligence is measured by Binet on a scale ofmental 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 passes all the tests for eight years and below, and three of the six tests for age nine; or passes 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 assistance beyond what is prescribed. Many superior persons have looked down on the psychological examiner with his (or her) assortment 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 assistance), but whether hedoesthem 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 retarded.
Brightness or dullness can also be measured by theintelligence 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 classes, 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.
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.
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 Association 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 class range from very easy to fairly difficult.
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The principal 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 constitutionally 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. ofdrafted men college freshmenmaking these making theseScores ScoresScores0-14 points 3 015-29 12 030-44 15 045-59 16 060-74 13 075-89 11 190-104 9 4105-119 7 8120-134 6 14135-149 4 23150-164 2 24165-179 1.3 13180-194 0.5 7195-212 0.2 1----- ---100 100
The "drafted men", consisting of men between the ages of twenty-one and thirty-one, fairly represent the adult male white population of the country, except in two respects. Many able young men were not included in the draft, having previously volunteered for officers' training camps or for special services. Had they been included, the percentages making the higher scores would have gone up slightly. On the other hand, many men of very low intelligence never reached the receiving camps at all, being inmates of institutions for the feebleminded or excluded from the draft because of known mental deficiency; and, of those who reached{280}the camps, many, being illiterate, did not take the Alpha test. It is for this reason that the graph for drafted men stops rather short at the lower end; to picture fairly the distribution of intelligence, it should taper off to the left, beyond the zero of the Alpha test.
Fig. 46.--Distribution of the scores of drafted men, and also of college freshmen, in the Alpha test. The height of the broken line above the base line is made proportional to the percent of the group that made the score indicated just below along the base line. (Figure text: army median--65, freshman median--150)
College freshmen evidently are, as they should be, a highly selected group in regard to intelligence. The results obtained at different colleges differ somewhat, and the figures here given represent an approximate average of results obtained at several colleges of high standing. The median{281}score for freshmen has varied, at different colleges, from 140 to 160 points.
[Footnote: The "median" is a statistical measure very similar to the average; but, while the average score would be obtained by adding together the scores of all the individuals and dividing the sum by the number of individuals tested, the median is obtained by arranging all the individual scores in order, from the lowest to the highest, and then counting off from either end till the middle individual is reached; his score is the median. (If the number of individuals tested is an even number, there are two middle individuals, and the point midway between them is taken as the median.) Just as many individuals are below the median as above it. The median is often preferred to the average in psychological work, not only because it is more easily computed, but because it is less affected by the eccentric or unusual performances of a few individuals, and therefore more fairly represents the whole population.]
It will be noticed in the graph that none of the freshmen score as low as the median of the drafted men. All of the freshmen, in fact, lie well above the median for the general population. A freshman who scores below 100 points finds it very difficult to keep up in his college work. Sometimes, it must be said, a freshman who scores not much over 100 in the test does very well in his studies, and sometimes one who scores very high in the test has to be dropped for poor scholarship, but this last is probably due to distracting interests.
No such sampling of the adult female population has ever been made as was afforded by the draft, and we are not in a position to compare the average adult man and woman in regard to intelligence. Boys and girls under twelve average almost the same, year by year, according to the Binet tests. In various other tests, calling for quick, accurate work, girls have on the average slightly surpassed boys of the same age, but this may result from the fact that girls mature earlier than boys; they reach adult height earlier, and perhaps also adult intelligence. College women, in the Alpha test, score on the average a few points below college men, but this, on the other hand, may be due to the fact that the Alpha test, being prepared for men, includes a few questions that lie rather outside the usual range of women's interests. On the whole, tests have given very little evidence of any significant difference between the general run of intelligence in the two sexes.
Tests of the Binet or Alpha variety evidently do not cover the whole range of intelligent behavior. They do not test{282}the ability to manage carpenter's or plumber's tools or other concrete things, they do not test the ability to manage people, and they do not reach high enough to test the ability to solve really big problems.
Regarding the ability to manage concrete things, we have already mentioned the performance tests, which provide a necessary supplement to the tests that deal in ideas expressed in words. It is an interesting fact that some men whose mental age is below ten, according to the Binet tests, nevertheless have steady jobs, earn good wages, and get on all right in a simple environment. There are many others, with a mental age of ten or eleven, who cannot master the school work of the upper grades, and yet become skilled workmen or even real artists. Now, it takes mentality to perform skilled or artistic work; only, the mentality is different from that demanded by what we call "intellectual work".
Managing people requires tact and leadership, which are obviously mental traits, though not easily tested. It is seldom that a real leader of men scores anything but high in the intelligence tests, but it more often happens that an individual who scores very high in the tests has little power of leadership. In part this is a matter of physique, or of temperament, rather than of intelligence, but in part it is a matter ofunderstandingpeople and seeing how they can be influenced and led.
Though the intelligence tests deal with "ideas", they do not, as so far devised, reach up to the great ideas nor make much demand on the superior powers of the great thinker. If we could assemble a group of the world's great authors, scientists and inventors, and put them through the Alpha test, it is probable that they would all score high, but not higher than the upper ten per cent, of college freshmen. Had their IQ's been determined when they were children,{283}probably all would have measured over 180 and some as high as 200, but the tests would not have distinguished these great geniuses from the gifted child who is simply one of a hundred or one of a thousand.
There is no opposition between "general intelligence", as measured by the tests, and the abilities to deal with concrete things, with people, or with big ideas. Rather, there is a considerable degree of correspondence. The individual who scores high in the intelligence tests is likely, but not certain, to surpass in these respects the individual who scores low in the tests. In technical language, there is a "positive correlation" between general intelligence and ability to deal with concrete things, people and big ideas, but the correlation is not perfect.
Correlationis a statistical measure of the degree of correspondence. Suppose, for an example, we wish to find out how closely people's weights correspond to their heights. Stand fifty young men up in single file in order of height, the tallest in front, the shortest behind. Then weigh each man, and shift them into the order of their weights. If no shifting whatever were needed, the correlation between height and weight would be perfect. Suppose the impossible, that the shortest man was the heaviest, the tallest the lightest, and that the whole order needed to be exactly reversed; then we should say that the correlation was perfectly inverse or negative. Suppose the shift from height order to weight order mixed the men indiscriminately, so that you could not tellanythingfrom a man's position in the height order as to what his position would be in the weight order; then we should have "zero correlation". The actual result, however, would be that, while the height order would be{284}somewhat disturbed in shifting to the weight order, it would not be entirely lost, much less reversed. That is, the correlation between height and weight is positive but not perfect.
Statistics furnishes a number of formulae for measuring correlations, formulae which agree in this, that perfect positive correlation is indicated by the number + 1, perfect negative correlation by the number - 1, and zero correlation by 0. A correlation of +.8 indicates close positive correspondence, though not perfect correspondence; a correlation of +.3 means a rather low, but still positive, correspondence; a correlation of -.6 means a moderate tendency towards inverse relationship.
The correlation between two good intelligence tests, such as the Binet and the Alpha, comes out at about +.8, which means that if a fair sample of the general population, ranging from low to high intelligence, is given both tests, the order of the individuals as measured by the one test will agree pretty closely with the order obtained with the other test. The correlation between a general intelligence test and a test for mechanical ability is considerably lower but still positive, coming to about +.4. Few if any real negative correlations are found between different abilities, but low positive or approximately zero correlations are frequent between different, rather special abilities.
In other words, there is no evidence of any antagonism between different sorts of ability, but there is plenty of evidence that different special abilities may have little or nothing in common.
[Footnote]Possibly some readers would like to see a sampleof the statistical formulae by which correlationis measured. Here is one of the simplest. Numberthe individuals tested in their order as givenby the first test, and again in their order asgiven by the second test, and find thedifference between each individual's two ranknumbers. If an individual who ranks no. 5 in onetest ranks no. 12 in the other, the differencein his rank numbers is 7. Designate thisdifference by the letter D. and the whole numberof individuals tested by n. Square each D, andget the sum of all the squares, calling this sum"sum of D2[squared]". Then the correlation isgiven by the formula,1 - ( ( 6 X sum of D[squared] ) / (n x ( n[squared] - 1)) )As an example in the use of this formula, take the following:Individuals Rank of each Rank of each D D[squared]tested individual in individual infirst test second testAlbert 3 5 2 4George 7 6 1 1Henry 5 3 2 4James 2 1 1 1Stephen 1 4 3 9Thomas 4 2 2 4William 6 7 1 1n = 7sum of D[squared] = 24n[squared] - 1 = 486 x sum of D[squared] = 1446 x sum of D[squared] / n ( n[squared] - 1 )= 1 - 144/(7 x 48)= +.57In order to get a full and true measure of thecorrelation between two tests, the followingprecautions are necessary:(1) Thesame individualsmust be givenboth tests.(2) The number of individuals tested must be asgreat as 15 or 20, preferably more.(3) The individuals should be a fair sample ofthe population in regard to the abilitiestested; they should not be so selected as torepresent only a small part of the total rangeof ability.(4) The tests should be thorough enough todetermine each individual's rank in each test,with a high degree of certainty. Sloppy testinggives a correlation nearer zero than it shouldbe, because it "pies" the true orders to someextent.[End footnote]
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If now we try to analyze intelligence and see in what it consists, we can best proceed by reviewing the intelligence tests, and asking how it is that an individual succeeds in them. Passing the tests is a very specific instance of{286}intelligent behavior, and an analysis of the content of the tests should throw some light on the nature of intelligence.
The first thing that strikes the eye in looking over the tests is that they call for so many different reactions. They call on you to name objects, to copy a square, to tell whether a given statement is true or false, to tell wherein two objects are alike or different. The first impression, then, is that intelligence consists simply in doing a miscellaneous lot of things and doing them right.
But can we not state in more general terms how the individual who scores high in the tests differs from one who scores low? If you survey the test questions carefully, you begin to see that the person who passes them must possess certain general characteristics, and that lack of these characteristics will lead to a low score. We may speak of these characteristics as "general factors" in intelligent behavior.
First, the tests evidently require the use of past experience. They call, not for instinctive reactions, but for previously learned reactions. Though the Binet tests attempt to steer clear of specific school knowledge, they do depend upon knowledge and skill picked up by the child in the course of his ordinary experience. They depend on the ability to learn and remember. One general factor in intelligence is thereforeretentiveness.
But the tests do not usually call for simple memory of something previously learned. Rather, what has been previously learned must be applied, in the test, to a more or less novel problem. The subject is asked to do something a little different from anything he has previously done, but similar enough so that he can make use of what he has learned. He has tosee the pointof the problem now set him, and toadaptwhat he has learned to this novel situation. Perhaps "seeing the point" and "adapting oneself to{287}a novel situation" are to be held apart as two separate general factors in intelligence, but on the whole it seems possible to include both under the general head,responsiveness to relationships, and to set up this characteristic as a second general factor in intelligence.
In the form board and picture completion tests, this responsiveness to relationships comes out clearly. To succeed in the form board, the subject must respond to the likeness of shape between the blocks and their corresponding holes. In picture completion, he must see what addition stands in the most significant relationship to the total picture situation. In telling how certain things are alike or different, he obviously responds to relationships; and so also in distinguishing between good and poor reasons for a certain fact. This element of response to relationships occurs again and again in the tests, though perhaps not in the simplest, such as naming familiar objects.
Besides these two intellectual factors in intelligent behavior, there are certain moral or impulsive factors. One ispersistence, which is probably the same thing as the mastery or self-assertive instinct. The individual who gives up easily, or succumbs easily to distraction or timidity, is at a disadvantage in the tests or in any situation calling for intelligent behavior.
But, as we said before, in discussing the instincts, excessive stubbornness is a handicap in meeting a novel situation, which often cannot be mastered by the first mode of response that one makes to it. Some giving up, somesubmissivenessin detail along with persistence in the main effort, is needed. The too stubborn young child may waste a lot of time trying with all his might to force the square block into the round hole, and so make a poorer score in the test, than if he had given up his first line of attack and tried something else. Intelligent behavior must perforce{288}often have something of the character of "trial and error", and trial and error requires both persistence in the main enterprise and a giving up here in order to try again there.
Finally, the instinct ofcuriosityor exploration is evidently a factor in intelligence. The individual who is stimulated by novel things to explore and manipulate them will amass knowledge and skill that can later be utilized in the tests, or in intelligent behavior generally.
We distinguish between the general factors in intelligence, just mentioned, and special aptitudes for dealing with colors, forms, numbers, weights etc. A special aptitude is a specific responsiveness to a certain kind of stimulus or object. The special aptitudes are factors in intelligent behavior--as we may judge from the content of the intelligence tests--only, the tests are so contrived as not to depend too much on any one or any few of the special aptitudes. Arithmetical problems alone would not make a fair test for intelligence, since they would lay undue stress on the special aptitude for number; but it is fair enough to include them along with color naming, weight judging, form copying, and word remembering, and so to give many special aptitudes a chance to figure in the final score.
There are tests in existence for some special aptitudes: tests for color sense and color matching, for musical ability, for ability in drawing, etc.; but as yet we have no satisfactory list of the special aptitudes. They come to light when we compare one individual with another, or one species with another. Thus, while man is far superior to the dog in dealing with colors, the dog is superior in dealing with odors. Man has more aptitude for form, but some animals are fully his equal in sense of location and ability to find{289}their way. Man is far superior in dealing with numbers and also with tools and mechanical things. He is superior in speech, in sense of rhythm, in sense of humor, in sense of pathos. Individual human beings also differ markedly in each of these respects. They differ in these special directions as well as in the "general factors" of intelligence.
Let us now return to the question raised at the very outset of the chapter, whether or not intelligence is a native trait. We then said that the differing intelligence of different species of animals must be laid to their native constitutions, but left the question open whether the differing intelligence of human individuals was a matter of heredity or of environment.
Intelligence is of course quite different from instinct, in that it does not consist in ready-made native reactions. The intelligence of an individual at any age depends on what he has learned previously. But the factors in intelligent behavior--retentiveness, responsiveness to relationships, persistence, etc.--may very well be native traits.
But whatevidenceis there that the individual's degree of intelligence is a native characteristic, like his height or color of hair? The evidence is pretty convincing to most psychologists.
First, we have the fact that an individual's degree of intelligence is an inherent characteristic, in the sense that it remains with him from childhood to old age. Bright child, bright adult; dull child, dull adult. That is the rule, and the exceptions are not numerous enough to shake it. Many a dull child of well-to-do parents, in spite of great pains taken with his education, is unable to escape from his inherent limitations. The intelligence quotient remains fairly{290}constant for the same child as he grows up, and stands for an inherent characteristic of the individual, namely, the rate at which he acquires knowledge and skill. Give two children the same environment, physical and social, and you will see one child progress faster than the other. Thus, among children who grow up in the same community, playing together and going to the same schools, the more rapid mental advance of some than of others is due to differences in native constitution, and the IQ gives a measure of the native constitution in this respect. There are exceptions, to be sure, depending on physical handicaps such as deafness or disease, or on very bad treatment at home, but in general the IQ can be accepted as representing a fact of native constitution.
Another line of evidence for the importance of native constitution in determining degrees of intelligence comes from the study of mental resemblance among members of the same family. Brothers or sisters test more alike than children taken at random from a community, and twins test more alike than ordinary brothers and sisters. Now, as the physical resemblance of brothers or sisters, and specially of twins, is accepted as due to native constitution, we must logically draw the same conclusion from their mental resemblance.
The way feeble-mindedness runs in families is a case in point. Though, in exceptional instances, mental defect arises from brain injury at the time of birth, or from disease (such as cerebrospinal meningitis) during early childhood, in general it cannot be traced to such accidents, but is inherent in the individual. Usually mental defect or some similar condition can be found elsewhere in the family of the mentally defective child; it is in the family stock. When both parents are of normal intelligence and come from families with no mental abnormality in any ancestral line, it is practically unknown that they should have a feeble-minded{291}child; but if mental deficiency has occurred in some of the ancestral lines, an occasional feeble-minded child may be born even of parents who are themselves both normal. If one parent is normal and the other feeble-minded, some of the children are likely to be normal and others feeble-minded; but if both parents are feeble-minded, it is said that all the children are sure to be feeble-minded or at least dull.
These facts regarding the occurrence of feeble-mindedness cannot be accounted for by environmental influences, especially the fact that some children of the same family may be definitely feeble-minded and others normal. We must remember that children of the same parents need not have precisely similar native constitutions; they are not always alike in physical traits such as hair color or eye color that are certainly determined by native constitution.
The special aptitudes also run in families. You find musical families where most of the children take readily to music, and other families where the children respond scarcely at all to music, though their general intelligence is good enough. You find a special liking and gift for mathematics cropping out here and there in different generations of the same family. No less significant is the fact that children of the same family show ineradicable differences from one another in such abilities. In one family were two brothers, the older of whom showed much musical ability and came early to be an organist and composer of church music; while the younger, possessing considerable ability in scholarship and literature, was never able to learn to sing or tell one tune from another. Being a clergyman, he desired very much to be able to lead in singing, but he simply could not learn. Such obstinate differences, persisting in spite of the same home environment, must depend on native constitution.
Native constitution determines mental ability in two respects. It fixes certain limits which the individual cannot{292}pass, no matter how good his environment, and no matter how hard he trains himself; and, on the positive side, it makes the individual responsive to certain stimuli, and so gives him a start towards the development of intelligence and of special aptitudes.
There is certainly some connection between the brain and intelligent behavior. While the spinal cord and brain stem vary according to the size of the body, and the cerebellum with the motility of the species of animal, the size of the cerebrum varies more or less closely with the intelligence of the species. It does vary also with bodily size, as illustrated by the whale and elephant, which have the largest cerebrum of all animals, including man. But the monkey, which shows more intelligence than most animals, has also a very large cerebrum for his size of body; and the chimpanzee and gorilla, considerably surpassing the ordinary monkeys in intelligence, have also a much larger cerebrum. The cerebrum of man, in proportion to the size of his body, far surpasses that of the chimpanzee or gorilla.
The cerebrum varies considerably in size from one human individual to another. In some adults it is twice as large as in others, and the question arises whether greater intelligence goes with a larger brain. Now, it appears that an extremely small cerebrum spells idiocy; not all idiots have small brains, but all men with extremely small brains are idiots. The brain weight of quite a number of highly gifted men has been measured in post-mortem examination, and many of these gifted men have had a very large cerebrum. On the whole, the gifted individual seems to have a large brain, but there are exceptions, and the relationship between brain size and intelligence cannot be very close. Other factors must enter, one factor being undoubtedly the fineness{293}of the internal structure of the cortex. Brain function depends on dendrites and end-brushes, forming synapses in the cortex, and such minute structures make little impression on the total brain weight.
While intelligence is related to the cerebrum as a whole, rather than to any particular "intelligence center", there is some likelihood that the special aptitudes are related to special parts of the cortex, though it must be admitted that few aptitudes have as yet been localized. The pretended localizations of phrenology are all wrong. But we do know that each sense has its special cortical area, and that adjacent to these sensory areas are portions of the cortex intimately concerned in response to different classes of complex stimuli. Near the auditory center the cortex is concerned in recognizing spoken words, and in following music; near the visual center it is concerned in recognizing printed words, in recognizing seen objects, in finding one's way by the sense of sight, etc. These special aptitudes thus have a fairly definite cortical localization, and possibly others have also.
Examined microscopically, the cortex shows differences of structure in different parts, and to the structural differences probably correspond differences of function. Now it is practically impossible that such a function as attention or memory should have any localized cortical center, for these are general functions. The instincts are specialized enough to have local centers, but none have so far been localized. What has been localized is of the nature of special aptitudes.