(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 apt.i.tudes" may work together to give success in some special line of work.

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REFERENCES

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 ill.u.s.trated article by Rudolph Pintner, in the _Psychological Review_ for 1918, Vol. 25, pp. 286-296.

For a study of one of the special apt.i.tudes, see C. E. Seash.o.r.e'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.

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CHAPTER XIII

LEARNING AND HABIT FORMATION

THE DEPENDENCE OF ACQUIRED REACTIONS UPON INSTINCT AND REFLEX ACTION, AND THE MODIFICATION OF NATIVE REACTIONS BY EXPERIENCE AND TRAINING.

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 a.s.sociation" 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 pa.s.sing 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 ill.u.s.trated 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 p.r.i.c.ked 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 _subst.i.tute stimulus_ that calls out the same response as the pin p.r.i.c.k. 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 p.r.i.c.ked, 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 _subst.i.tute response_ is another modification to be placed alongside of the subst.i.tute 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 coordinations. 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 ill.u.s.trate simultaneous coordination, and there is also a serial coordination, 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 pa.s.ses 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 subst.i.tute stimuli. Amus.e.m.e.nt 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 s.e.x 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 subst.i.tute 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."