Psychology - A Study Of Mental Life
by Robert S. Woodworth
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Theory of Attention

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.



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 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 Titchener, 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.





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".


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 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.


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 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 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 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.]


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 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


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.

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 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.


Some Results of the Intelligence Tests

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

15-29 12 0

30-44 15 0

45-59 16 0

60-74 13 0

75-89 11 1

90-104 9 4

105-119 7 8

120-134 6 14

135-149 4 23

150-164 2 24

165-179 1.3 13

180-194 0.5 7

195-212 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.

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.

Limitations of the Intelligence Tests

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 of understanding people 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.

The Correlation of Abilities

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.

Correlation is 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 tell anything from 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 sample of the statistical formulae by which correlation is measured. Here is one of the simplest. Number the individuals tested in their order as given by the first test, and again in their order as given by the second test, and find the difference between each individual's two rank numbers. If an individual who ranks no. 5 in one test ranks no. 12 in the other, the difference in his rank numbers is 7. Designate this difference by the letter D. and the whole number of individuals tested by n. Square each D, and get the sum of all the squares, calling this sum "sum of D2[squared]". Then the correlation is given 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 in first test second test

Albert 3 5 2 4

George 7 6 1 1

Henry 5 3 2 4

James 2 1 1 1

Stephen 1 4 3 9

Thomas 4 2 2 4

William 6 7 1 1

n = 7

sum of D[squared] = 24

n[squared] - 1 = 48

6 x sum of D[squared] = 144

6 x sum of D[squared] / n ( n[squared] - 1 )

= 1 - 144/(7 x 48)

= +.57

In order to get a full and true measure of the correlation between two tests, the following precautions are necessary:

(1) The same individuals must be given both tests.

(2) The number of individuals tested must be as great as 15 or 20, preferably more.

(3) The individuals should be a fair sample of the population in regard to the abilities tested; they should not be so selected as to represent only a small part of the total range of ability.

(4) The tests should be thorough enough to determine each individual's rank in each test, with a high degree of certainty. Sloppy testing gives a correlation nearer zero than it should be, because it "pies" the true orders to some extent. [End footnote]


General Factors in Intelligence

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 therefore retentiveness.

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 to see the point of the problem now set him, and to adapt what 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 is persistence, 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, some submissiveness in 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 of curiosity or 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.

Special Aptitudes

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.

Heredity of Intelligence and of Special Aptitudes

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 what evidence is 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.

Intelligence and the Brain

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.



1. Outline the chapter.

2. Pick out the true statements from the following list:

(a) Man is the most intelligent of animals.

(b) Intelligence depends on the development of the cerebellum.

(c) It has not been found possible to use any single performance as a reliable index of intelligence.

(d) Children of different mental ages may have the same IQ.

(e) A child with a mental age of 10 years can do all the tests for 10 years and below, but none of those for the higher ages.

(f) The intelligence tests depend wholly on accurate response and not at all on speed of reaction.

(g) If intelligence tests depended upon previous training, they could not be measures of native intelligence.

(h) High correlation between the test scores of brothers and sisters is a fact that tends to indicate the importance of heredity in determining intelligence.

(i) The "general factors" in intelligence are the same as the instincts.

(j) Feeble-minded individuals include all those who are below the average intelligence.

3. It is found that eminent men very often have eminent brothers, uncles and cousins. How would this fact be explained?

4. It is also found that the wives of eminent men often have eminent relatives. How would this fact be explained?

5. How could it happen that a boy of 9, in the third school grade, with an IQ of 140, should be mischievous and inattentive? What should be done with him?

6. If a boy of 12, by industrious work, does pretty well in the fourth grade, why should we not accept the teacher's estimate of him as a "fairly bright boy"?

7. How might the brain of an idiot be underdeveloped, aside from the matter of the number of nerve cells in the cortex?

8. Can it be that high intelligence is a disadvantage in any form of industrial work, and, if so, how?

9. Show how "general intelligence" and "special aptitudes" may work together to give success in some special line of work.



For the Binet tests and some results obtained by their use, see Louis M. Terman, The Measurement of Intelligence, 1916.

The group tests used in the American Army during the War are described in detail In Vol. 15 of the Memoirs of the National Academy of Sciences, 1921, edited by Robert M. Yerkes. This large book describes the work of preparing and standardizing the tests, and also gives some results bearing on the Intelligence of different sections of the population. Some of the interesting results appear on pp. 507, 522, 528, 537, 693, 697, 705, 732, 743, 799, 815, 819, 829, 856 and 869.

For briefer treatments of the subject, see Walter S. Hunter's General Psychology, 1919, pp. 36-58, and W. B. Pillsbury's Essentials of Psychology, 2nd edition, 1920, pp. 388-407.

For the poor results obtained in attempting to judge intelligence from photographs, see an illustrated article by Rudolph Pintner, in the Psychological Review for 1918, Vol. 25, pp. 286-296.

For a study of one of the special aptitudes, see C. E. Seashore's Psychology of Musical Talent, 1919.

For a comprehensive survey of test methods and results, see the two volumes of Whipple's Manual of Mental and Physical Tests, 2nd edition, 1914, 1915.





Already, in considering intelligence, we have partially rounded the corner from native to acquired traits, and now, fairly around the corner, we see ahead of us a long straight stretch of road. For there is much to say regarding acquired traits and regarding the process of acquisition. All knowledge is acquired, the whole stock of ideas, as well as motor skill, and there are acquired motives in addition to the native motive forces that we called instincts, and acquired likes and dislikes in addition to those that are native; so that, all in all, there are thousands on thousands of acquired reactions, and the daily life of the adult is made up of these much more than of strictly native reactions.

It will take us several chapters to explore this new territory that now lies before us, a chapter on acquiring motor habits and skill, a chapter on memory, a chapter on acquired mental reactions, and a chapter devoted to the general laws that hold good in this whole field. Our general plan is to proceed from the simple to the complex, generalizing to some extent as we go, but leaving the big generalizations to the close of the discussion, where we shall see whether the whole process of acquiring reactions of all sorts cannot be summed up in a few general laws of acquisition, or "laws of association" as they are traditionally called. On reaching that {297} goal, the reader may well come back, with the general laws in mind, and see how well they fit in detail all the instances of acquired responses that we are about to describe. We might have begun by stating the general laws, but on the whole it will be better to proceed "inductively", beginning with the observed facts and working up to the general laws.

Acquired Reactions Are Modified Native Reactions

Though we have "turned a corner" in passing from native traits to acquired, it would be a mistake to suppose we had left what is native altogether behind. It would be a mistake to suppose that the individual outgrew and left behind his native reactions and acquired an entirely new outfit. The reactions that he acquires—or learns, as we speak of acquisition in the sphere of reactions—develop out of his native reactions. Consider this: how is the individual ever going to learn a reaction? Only by reacting. Without native reactions, he would be entirely inactive at the outset, and would never make a start towards any acquisition. His acquired reactions, then, are his native reactions modified by use.

The vast number of motor acts that the individual acquires are based upon the reflexes. They are modified reflexes. The simplest kind of modification is the mere strengthening of an act by exercise. By his reflex breathing and crying, the new-born baby exercises his lungs and breathing muscles and the nerve centers that control them, with the result that his breathing becomes more vigorous, his crying louder. The strengthening of a reaction through exercise is a fundamental fact.

But we should scarcely speak of "learning" if the only modification consisted in the simple strengthening of native reactions, and at first thought it is difficult to see how the {298} exercise of any reaction could modify it in any other respect. But many reflexes are not perfectly fixed and invariable, but allow of some free play, and then exercise may fix or stabilize them, as is well illustrated in the case of the pecking response of the newly hatched chick. If grains are strewn before a chick one day old, it instinctively strikes at them, seizes them in its bill and swallows them; but, its aim being poor and uncertain, it actually gets, at first, only a fifth of the grains pecked at; by exercise it improves so as to get over half on the next day, over three-fourths after another day or two, and about 86 percent (which seems to be its limit) after about ten days of practice. Exercise has here modified a native reaction in the way of making it more definite and precise, by strengthening the accurate movement as against all the variations of the pecking movement that were made at the start. Where a native response is variable, exercise tends towards constancy, and so towards the fixation of definite habits.

A reflex may come to be attached to a new stimulus, that does not naturally arouse it. A child who has accidentally been pricked with a pin, and of course made the flexion reflex in response to this natural stimulus, will make this same reaction to the sight of a pin approaching his skin. The seen pin is a substitute stimulus that calls out the same response as the pin prick. This type of modification gives a measure of control over the reflexes; for when we pull the hand back voluntarily, or wink at will, or breathe deeply at will, we are executing these movements without the natural stimulus being present.

Voluntary control includes also the ability to omit a response even if the natural stimulus is present. Holding the breath, keeping the eyes wide open in spite of the tendency to wink, not swallowing though the mouth is full of saliva, holding the hand steady when it is being pricked, and many {299} similar instances of control over reflexes are cases of detachment of a native reaction from its natural stimulus. Not "starting" at a sudden sound to which we have grown used and not turning the eyes to look at a very familiar object, are other instances of this detachment.

The substitute response is another modification to be placed alongside of the substitute stimulus. Here a natural stimulus calls out a motor response different from its natural response. The muttered imprecation of the adult takes the place of the child's scream of pain. The loose holding of the pen between the thumb and the first two fingers takes the place of the child's full-fisted grasp.

Finally, an important type of modification consists in the combination of reflex movements into larger cooerdinations. One hand grasps an object, while the other hand pulls, pushes or strikes it. Or, both hands grasp the object but in different ways, as in handling an ax or shovel. These cases illustrate simultaneous cooerdination, and there is also a serial cooerdination, in which a number of simple instinctive movements become hitched together in a fixed order. Examples of this are seen in dancing, writing a word, and, most notably, in speaking a word or familiar phrase.

In these ways, by strengthening, fixing and combining movements, and by new attachments and detachments between stimulus and response, the instinctive motor activity of the baby passes over into the skilled and habitual movement of the adult.

Acquired Tendencies

In the sphere of impulse and emotion the same kinds of modification occur. Detachment of an impulse or emotion from its natural stimulus is very much in evidence, since {300} what frightens or angers or amuses the little child may have no such power with the adult. One little boy of two could be thrown into gales of laughter by letting a spoon drop with a bang to the floor; and you could repeat this a dozen times in quick succession and get the response every time. But this stimulus no longer worked when he had advanced to the age of four.

The emotions get attached to substitute stimuli. Amusement can be aroused in an older child by situations that were not at all amusing to the baby. New objects arouse fear, anger, rivalry or curiosity. The emotions of the adult—with the exception of sex attraction, which is usually very weak in the child—are the emotions of the child, but they are aroused by different stimuli.

Not only so, but the emotions express themselves differently in the child and the adult. Angry behavior is one thing in the child, and another thing in the adult, so far as concerns external motor action. The child kicks and screams, where the adult strikes with his fist, or vituperates, or plots revenge. The internal bodily changes in emotion are little modified as the individual grows up—except that different stimuli arouse them—but the overt behavior is greatly modified; instead of the native reactions we find substitute reactions.

A little girl of three years, while out walking in the woods with her family, was piqued by some correction from her mother, but, instead of showing the instinctive signs of temper, she picked up a red autumn leaf and offered it to her mother, with the words, very sweetly spoken, "Isn't that a pretty leaf?" "Yes," said her mother, acquiescently. "Wouldn't you like to have that leaf?" "Yes, indeed." "I'll throw it away!" (in a savage tone of voice, and with a gesture throwing the leaf away). Here we have an early form of substitute reaction, and can glimpse how such {301} reactions become attached to the emotions. The natural outlet for the child's anger was blocked, probably because previous outbursts of rage had not had satisfactory consequences, so that the anger was dammed up, or "bottled up", for the instant, till the child found some act that would give it vent. Now supposing that the substitute reaction gave satisfaction to the child, we can well imagine that it would become attached to the angry state and be used again in a similar case. Thus, without outgrowing the emotions, we may outgrow emotional behavior that is socially unacceptable.

Emotions are also combined, much as reflexes are combined. The same object which on one occasion arouses in us one emotion may arouse another emotion on another occasion, so that eventually, whenever we see that object, we respond by a blend of the two emotions. Your chief may terrify you on some occasions, at other times amaze you by his masterly grasp on affairs, and again win your affection by his care for your own welfare; so that your attitude toward "the boss" comes to be a blend of fear, admiration and gratitude. Religion and patriotism furnish good examples of compound emotions.

Well, then, adult behavior compared with the instinctive behavior of the little child shows these several types of modification. This is interesting, but it is not all we wish to know. We want to know how the modification comes about; that is, we want to get an insight into the process of learning. Scientifically, this is one of the most fascinating topics in psychology—how we learn, how we are molded or modified by experience—and practically, it is just as important, since if we wish to educate, train, mold, improve ourselves or others, it is the process of modification that we must control; and to control it we must understand it.

To understand it we must watch the process itself; and {302} therefore we turn to studies that trace the course of events in human and animal learning.

Animal Learning

Animals do learn, all the vertebrates, at least, and many of the invertebrates. They often learn more slowly than men, but this is an advantage for our present purpose, since it makes the learning process easier to follow. Mere anecdotes of intelligent behavior in animals are of little value, but experimental studies, in which the animal's progress is followed, step by step, from the time when he is confronted with a perfectly novel situation till he has mastered the trick, have now been made in great numbers, and a few typical experiments will serve as a good introduction to the whole subject of learning.

The negative adaptation experiment.

Apply a harmless and meaningless stimulus time after time; at first the animal makes some instinctive exploring or defensive reaction; but with continued repetition of the stimulus, he ceases after a while to respond. The instinctive reaction has been detached from one of its natural stimuli.

Even in unicellular animals, negative adaptation can be observed, but in them is only temporary, like the "sensory adaptation" described in the chapter on sensation. Stop the stimulus and the original responsiveness returns after a short time. Nothing has been learned, for what is learned remains after an interval of rest.

In higher animals, permanent adaptation is common, as illustrated by a famous experiment on a spider. While the spider was in its web, a tuning fork was sounded, and the spider made the defensive reaction of dropping to the ground. It climbed back to its web, the fork was sounded again, the spider dropped again; but after several {303} repetitions in quick succession, the spider ceased to respond. Next day, to be sure, it responded as at first; but after the same performance had been repeated on several days, it ceased permanently to respond to this stimulus.

Negative adaptation is common in domestic animals, as well as in men. The horse "gets used" to the harness, and the dog to the presence of a cat in the house. Man grows accustomed to his surroundings, and to numerous unimportant sights and sounds.

The conditioned reflex experiment.

Put into a dog's mouth a tasting substance that arouses the flow of saliva, and at the same instant ring a bell; and repeat this combination of stimuli many times. Then ring the bell alone, and the saliva flows in response to the bell. The bell is a substitute stimulus, which has become attached to the salivary response by dint of having been often given along with the natural stimulus that arouses this response. At first thought, this is very weird, but do we not know of similar facts in every-day experience? The dinner bell makes the mouth water; the sight of food does the same, even the name of a savory dish will do the same.

Quite possibly, the learning process by which the substitute stimulus becomes attached to the salivary reaction is more complex in man's case. He may observe that the dinner bell means dinner, whereas the dog, we suppose, does not definitely observe the connection of the bell and the tasting substance. What the experiment shows is that a substitute stimulus can become attached to a reaction under very simple conditions.

A conditioned reflex experiment on a child deserves mention. A young child, confronted with a rabbit, showed no fear, but on the contrary reached out his hand to take the rabbit. At this instant a loud rasping noise was produced just behind the child, who quickly withdrew his hand with {304} signs of fear. After this had been repeated a few times, the child shrank from the rabbit and was evidently afraid of it. Probably it is in this way that many fears, likes and dislikes of children originate.

The signal experiment.

Place a white rat before two little doors, both just alike except that one has on it a yellow circle. The rat begins to explore. If he enters the door with the yellow sign, he finds himself in a passage which leads to a box of food; if he enters the other door he gets into a blind alley, which he explores, and then, coming out, continues his explorations till he reaches the food box and is rewarded. After this first trial is thus completed, place him back at the starting point, and he is very apt to go straight to the door that previously led to the food, for he learns simple locations very quickly. But meanwhile the experimenter may have shifted the yellow sign to the other door, connected the passage behind the marked door with the food box, and closed off the other passage; for the yellow disc in this experiment always marks the way to the food, and the other door always leads to a blind alley. The sign is shifted irregularly from one door to the other. Whenever the rat finds himself in a blind alley, he comes out and enters the other door, so finally getting his reward on every trial. But for a long time he seems incapable of responding to the yellow signal. However, the experimenter is patient; he gives the rat twenty trials a day, keeping count of the number of correct responses, and finds the number to increase little by little, till after some thirty days every response is correct and unhesitating. The rat has learned the trick.

He learns the trick somewhat more rapidly if punishment for incorrect responses is added to reward for correct responses. Place wires along the floor of the two passages, and switch an electric current into the blind alley, behind {305} the door that has no yellow circle on it. When the rat enters the blind alley and gets a shock, he makes a prompt avoiding reaction, scampering back to the starting point and cowering there for some time; eventually he makes a fresh start, avoids the door that led to the shock and therefore enters the other door, though apparently without paying any attention to the yellow sign, since when, on the next trial, the sign is moved, he avoids the place where he got the shock, without reference to the sign. But in a series of trials he learns to follow the sign.

Learning to respond to a signal might be classified under the head of substitute stimulus, since the rat learns to respond to a stimulus, the yellow disk, that at first left him unmoved. But more careful consideration shows this to be, rather, a case of substitute response. The natural reaction of a rat to a door is to enter it, not to look at its surface, but the experiment forces him to make the preliminary response of attending to the appearance of the door before entering it. The response of attending to the surface of the door is substituted for the instinctive response of entering. Otherwise put: the response of finding the marked door and entering that is substituted for the response of entering any door at random.

The maze experiment.

An animal is placed in an enclosure from which it can reach food by following a more or less complicated path. The rat is the favorite subject for this experiment, but it is a very adaptable type of experiment and can be tried on any animal. Fishes and even crabs have mastered simple mazes, and in fact to learn the way to a goal is probably possible for any species that has any power of learning whatever. The rat, placed in a maze, explores. He sniffs about, goes back and forth, enters every passage, and actually covers every square inch of the maze at least once; and in the course of these explorations {306} hits upon the food box. Replaced at the starting point, he proceeds as before, though with more speed and less dallying in the blind alleys. On successive trials he goes less and less deeply into a blind alley, till finally he passes the entrance to it without even turning his head. Thus eliminating the blind alleys one after another, he comes at length to run by a fixed route from start to finish.

At first thought, the elimination of useless moves seems to tell the whole story of the rat's learning process; but careful study of his behavior reveals another factor. When the rat approaches a turning point in the maze, his course bends so as to prepare for the turn; he does not simply advance to the turning point and then make the turn, but several steps before he reaches that point are organized or cooerdinated into a sort of unit.


The combination of steps into larger units is shown also by certain variations of the experiment. It is known that the rat makes little use of the sense of sight in learning the maze, guiding himself mostly by the muscle sense. Now if the maze, after being well learned, is altered by shortening one of the straight passages, the rat runs full tilt against the new end of the passage, showing clearly that he was proceeding, not step by step, but by runs of some length. Another variation of the experiment is to place a rat that has learned a maze down in the midst of it, instead of at {308} the usual starting point. At first he is lost, and begins exploring, but, hitting on a section of the right path, he gets his cue from the "feel" of it, and races off at full speed to the food box. Now his cue could not have been any single step or turn, for these would all be too much alike; his cue must have been a familiar sequence of movements, and that sequence functions as a unit in calling out the rest of the habitual movement.

In short, the rat learns the path by elimination of false reactions and by combination of single steps and turns into larger reaction-units.

The puzzle-box experiment.

Place a hungry young cat in a strange cage, with a bit of fish lying just outside, and you are sure to get action. The cat extends his paw between the slats but cannot reach the fish; he pushes his nose between the slats but cannot get through; he bites the slats, claws at anything small, shakes anything loose, and tries every part of the cage. Coming to the button that fastens {309} the door, he attacks that also, and sooner or later turns the button, gets out, and eats the fish. The experimenter, having noted the time occupied in this first trial, replaces the cat, still hungry, in the cage, and another bit of fish outside. Same business, but perhaps somewhat quicker escape. More trials, perhaps on a series of days, give gradually decreasing times of escape. The useless reactions are gradually eliminated, till finally the cat, on being placed in the cage, goes instantly to the door, turns the button, goes out and starts to eat, requiring but a second or two for the whole complex reaction. Perhaps 15 or 20 trials have been required to reach this stage of prompt, unerring response. The course of improvement is rather irregular, with ups and downs, but with no sudden shift from the varied reaction of the first trial to the fixed reaction of the last. The learning process has been gradual.

This is the typical instance of learning by "trial and error", which can be defined as varied reaction with gradual elimination of the unsuccessful responses and fixation of the successful one. It is also a case of the substitute response. At first, the cat responds to the situation by reaching or pushing straight towards the food, but it learns to substitute for this most instinctive response the less direct response of going to another part of the cage and turning a button.

The cat in this experiment is evidently trying to get out of the cage and reach the food. The situation of being confined in a cage while hungry arouses an impulse or tendency to get out; but this tendency, unable at once to reach its goal, is dammed up, and remains as an inner directive force, facilitating reactions that are in the line of escape and inhibiting other reactions. When the successful response is hit upon, and the door opened, the dammed-up energy is discharged into this response; and, by repetition, {310} the successful response becomes closely attached to the escape-tendency, so as to occur promptly whenever the tendency is aroused.

There is no evidence that the cat reasons his way out of the cage. His behavior is impulsive, not deliberative. There is not even any evidence that the cat clearly observes how he gets out. If he made a clean-cut observation of the manner of escape, his time for escaping should thereupon take a sudden drop, instead of falling off gradually and irregularly from trial to trial, as it does fall off. Trial and error learning is learning by doing, and not by reasoning or observing. The cat learns to get out by getting out, not by seeing how to get out.

Summary of Animal Learning

Let us take account of stock at this point, before passing to human learning, and attempt to generalize what we have observed in animals of the process of learning.

(1) Elimination of a response, which means detachment of a response from the stimulus that originally aroused it, occurs in three main cases:

(a) Elimination occurs most quickly when the response brings actual pain; the animal makes the avoiding reaction to the pain and quickly comes to make this response to the place where the pain occurred; and thus the positive reaction to this place is eliminated.

(b) Elimination occurs more gradually when the response, without resulting in actual pain, brings failure or delay in reaching a goal towards which the animal is tending. The positive response of entering and exploring a blind alley grows weaker and weaker, till the blind alley is neglected altogether.

(c) Elimination of a response also occurs, slowly, through negative adaptation to a stimulus that is harmless and also useless.


(2) New attachments or linkages of stimulus and response occur in two forms, which are called "substitute stimulus" and "substitute response".

[Footnote: The writer hopes that no confusion will be caused by his use of several words to express this same meaning. "Attachment of stimulus and response", "linkage of stimulus and response", "connection between stimulus and response", and "bond between stimulus and response", all mean exactly the same; but sometimes one and sometimes another seems to bring the meaning more vividly to mind.]

(a) Substitute stimulus refers to the case where the natural response is not itself modified, but becomes attached to another stimulus than the one that originally aroused it. This new linkage can sometimes be established by simply giving the original stimulus and the substitute stimulus at the same time, and doing so repeatedly, as in the conditioned reflex experiment.

(b) Substitute response refers to the case where the stimulus remaining as it originally was, a new reaction is attached to it in place of the original response. The conditions under which this takes place are more complex than those that give the substitute stimulus. A tendency towards some goal must first be aroused, and then blocked by the failure of the original response to lead to the goal. The dammed-up tendency then facilitates other responses, and gives trial and error behavior, till some one of the trial responses leads to the goal; and this successful response is gradually substituted for the original response, and becomes firmly attached to the situation and tendency.

(3) New combinations of responses occur, giving higher motor units.

Human Learning

To compare human and animal learning, and notice in what ways the human is superior, cannot but throw light on the whole problem of the process of learning. It is obvious {312} that man learns more quickly than the animals, that he acquires more numerous reactions, and a much greater variety of reactions; but the important question is how he does this, and how his learning process is superior.

We must first notice that all the forms of learning displayed by the animal are present also in the human being. Negative adaptation is important in human life, and the conditioned reflex is important, as has already been suggested. Without negative adaptation, the adult would be compelled to attend to everything that aroused the child's curiosity, to shrink from everything that frightened the child, to laugh at everything that amused the child. The conditioned reflex type of learning accounts for a host of acquired likes and dislikes. Why does the adult feel disgust at the mere sight of the garbage pail or the mere name of cod liver oil? Because these inoffensive visual and auditory stimuli have been associated, or paired, with odors and tastes that naturally aroused disgust.

The signal experiment is duplicated thousands of times in the education of every human being. He learns the meaning of signs and slight indications; that is, he learns to recognize important facts by aid of signs that are of themselves unimportant. We shall have much to say on this matter in a later chapter on perception. Man learns signs more readily than such an animal as the rat, in part because the human being is naturally more responsive to visual and auditory stimuli. Yet the human being often has trouble in learning to read the signs aright. He assumes that a bright morning means good weather all day, till, often disappointed, he learns to take account of less obvious signs of the weather. Corrected for saying, "You and me did it", he adopts the plan of always saying "you and I", but finds that this quite unaccountably brings ridicule on him at times, so that gradually he may come to say the one or the {313} other according to obscure signs furnished by the structure of the particular sentence. The process of learning to respond to obscure signs seems to be about as follows: something goes wrong, the individual is brought to a halt by the bad results of his action, he then sees some element in the situation that he had previously overlooked, responds to this element, gets good results, and so—perhaps after a long series of trials—comes finally to govern his action by what seemed at first utterly insignificant.

Trial and error learning, though often spoken of as characteristically "animal", is common enough in human beings. Man learns by impulsively doing in some instances, by rational analysis in others. He would be at a decided disadvantage if he could not learn by trial and error, since often the thing he has to manage is very difficult of rational analysis. Much motor skill, as in driving a nail, is acquired by "doing the best you can", getting into trouble, varying your procedure, and gradually "getting the hang of the thing", without ever clearly seeing what are the conditions of success.

Human Compared With Animal Learning

Fairly direct comparisons have been made between human and animal learning of mazes and puzzles. In the maze, the human subject has an initial advantage from knowing he is in a maze and has to master it, while the rat knows no more than that he is in a strange place, to be explored with caution on the odd chance that it may contain something eatable, or something dangerous. But, after once reaching the food box, the rat begins to put on speed in his movements, and within a few trials is racing through the maze faster than the adult man, though not so fast as a child. Adults are more circumspect and dignified, they make less speed, cover less distance, but also make fewer false moves {314} and finish in less time. That is in the early trials; adults do not hold their advantage long, since children and even rats also reach complete mastery of a simple maze in ten or fifteen trials.

The chief point of superiority of adults to human children, and of these to animals, can be seen in the adjacent table. It is in the first trial that the superiority of the adults shows most clearly. They get a better start, and adapt themselves to the situation more promptly. Their better start is due to (1) better understanding of the situation at the outset, (2) more plan, (3) less tendency to "go off on a tangent", i.e., to respond impulsively to every opening, without considering or looking ahead. The adult has more inhibition, the child more activity and responsiveness; the adult's inhibition stands him in good stead at the outset, but the child's activity enables him to catch up shortly in so simple a problem as this little maze.


(From Hicks and Carr)

Trial No. Rats Children Adults

1 53 35 10 2 45 9 15 3 30 18 5 4 22 11 2 5 11 9 6 6 8 13 4 7 9 6 2 8 4 6 2 9 9 5 1 10 3 5 1 11 4 1 0 12 5 0 1 13 4 1 1 14 4 0 1 15 4 1 1 16 2 0 1 17 1 0 1

The table reads that, on the first trial in the maze, the rats averaged 53 errors, the children 35 errors, and the adults 10 errors, and so on. An "error" consisted in entering a blind alley or in turning back on {315} the course. The subjects tested consisted of 23 rats, five children varying in age from 8 to 18 years, and four graduate students of psychology. The human maze was much larger than those used for the rats, but roughly about the same in complexity. Since rats are known to make little use of their eyes in learning a maze, the human subjects were blindfolded. The rats were rewarded by food, the others simply by the satisfaction of success.

The puzzle boxes used in experiments on animal learning are too simple for human adults, but mechanical puzzles present problems of sufficient difficulty. The experimenter hands the subject a totally unfamiliar puzzle, and notes the time required by the subject to take it apart; and this is repeated in a series of trials till mastery is complete. In addition to taking the time, the experimenter observes the subject's way of reacting, and the subject endeavors at the end of each trial to record what he has himself observed of the course of events.

The human subject's behavior in his first trial with a puzzle is often quite of the trial and error sort. He manipulates impulsively; seeing a possible opening he responds to it, and meeting a check he backs off and tries something else. Often he tries the same line of attack time and time again, always failing; and his final success, in the first trial, is often accidental and mystifying to himself.

On the second trial, he may still be at a loss, and proceed as before; but usually he has noticed one or two facts that help him. He is most likely to have noticed where he was in the puzzle when his accidental success occurred; for it appears that locations are about the easiest facts to learn for men as well as animals. In the course of a few trials, also, the human subject notices that some lines of attack are useless, and therefore eliminates them. After a time he may "see into" the puzzle more or less clearly, though sometimes he gets a practical mastery of the handling of the puzzle, while still obliged to confess that he does not understand it at all.


Insight, when it does occur, is of great value. Insight into the general principle of the puzzle leads to a better general plan of attack, and insight into the detailed difficulties of manipulation leads to smoother and defter handling. The human "learning curve" (see Figure 50) often shows a prolonged stretch of no improvement, followed by an abrupt change to quicker work; and the subject's introspections show that 76 per cent, or more of these sudden improvements followed immediately after some fresh insight into the puzzle.

The value of insight appears in another way when the subject, after mastering one puzzle, is handed another involving the same principle in a changed form. If he has seen the principle of the first puzzle, he is likely to carry over this knowledge to the second, and master this readily; {317} but if he has simply acquired motor skill with the first puzzle, without any insight into its principle, he may have as hard a time with the second as if he had never seen the first.

Learning by Observation

"We learn by doing" is a true proverb, in the sense that we acquire a reaction by making just that reaction. We must make a reaction in order to get it really in hand, so that the proverb might be strengthened to read, "To learn, we must do". But we should make it false if we strengthened it still further and said "We learn only by doing". For human beings, at least, learn also by observing.

The "insight" just spoken of consists in observing some fact—often some relationship—and the value of insight in hastening the process of learning is a proof that we learn by observation as well as by actual manipulation. To be sure, observation needs to be followed by manipulation in order to give practical mastery of a thing, but manipulation without observation means slow learning and often yields nothing that can be carried over to a different situation.

Learning by observation is typically human. The adult's superiority in tackling a maze may be summed up by saying that he observes more than the child—much more than the animal—and governs his behavior by his observations. The enormous human superiority in learning a simple puzzle, of the sort used in experiments on animals, arises from seeing at once the key to the situation.

A chimpanzee—one of the most intelligent of animals—was tested with a simple puzzle box, to be opened from outside by turning a button that prevented the door from opening. The device was so simple that you would expect the animal to see into it at once. A banana was put into the box and the door fastened with the button. The {318} chimpanzee quickly found the door, and quickly found the button, which he proceeded to pull about with one hand while pulling the door with the other. Without much delay, he had the button turned and the door open. After about three trials, he had a practical mastery of the puzzle, showing thus considerable superiority over the cat, who would more likely have required twelve or fifteen trials to learn the trick. But now a second button was put on a few inches from the first, both being just alike and operating in the same way. The chimpanzee paid no attention to this second button, but turned the first one as before, and when the door failed to open, kept on turning the first button, opening it and closing it and always tugging at the door. After a time, he did shift to the second button, but as he had left the first one closed, his manipulation of the second was futile. It was a long, hard job for him to learn to operate both buttons correctly; and the experiment proved that he did not observe how the button kept the door from opening, but only that the button was the thing to work with in opening the door. At one time, indeed, in order to force him to deal with the second button, the first one was removed, but he still went to the place where it had been and fingered about there. What he had observed was chiefly the place to work at in order to open the door. We must grant that animals observe locations, but most of their learning is by doing and not by observing.

Here is another experiment designed to test the ability of animals to learn by observation. The experimenter takes two cats, one having mastered a certain puzzle box, the other not, and places the untrained cat where it can watch the trained one do its trick. The trained cat performs repeatedly for the other's benefit, and is then taken away and the untrained cat put into the puzzle box. But he has derived no benefit from what has gone on before his eyes, and must learn by trial {319} and error, the same as any other cat; he does not even learn any more quickly than he otherwise would have done.

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