Science And Human Behavior

B.F Skinner

• Publisher: Free Press
• Year: 2012
• ISBN:
  9781476716152
• Topic: Psychology
• Subtopic: Behaviorism
• Index: Psychology

The psychology classic—a detailed study of scientific theories of human nature and the possible ways in which human behavior can be predicted and controlled— from one of the most influential behaviorists of the twentieth century and the author of Walden Two. "This is an important book, exceptionally well written, and logically consistent with the basic premise of the unitary nature of science. Many students of society and culture would take violent issue with most of the things that Skinner has to say, but even those who disagree most will find this a stimulating book." —Samuel M. Strong, The American Journal of Sociology "This is a remarkable book—remarkable in that it presents a strong, consistent, and all but exhaustive case for a natural science of human behavior…It ought to be…valuable for those whose preferences lie with, as well as those whose preferences stand against, a behavioristic approach to human activity." —Harry Prosch, Ethics

SECTION II

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THE ANALYSIS OF BEHAVIOR

CHAPTER IV

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REFLEXES AND CONDITIONED REFLEXES

MAN A MACHINE

Behavior is a primary characteristic of living things. We almost identify it with life itself. Anything which moves is likely to be called alive—especially when the movement has direction or acts to alter the environment. Movement adds verisimilitude to any model of an organism. The puppet comes to life when it moves, and idols which move or breathe smoke are especially awe-inspiring. Robots and other mechanical creatures entertain us just because they move. And there is significance in the etymology of the animated cartoon.

Machines seem alive simply because they are in motion. The fascination of the steam shovel is legendary. Less familiar machines may actually be frightening. We may feel that it is only primitive people who mistake them for living creatures today, but at one time they were unfamiliar to everyone. When Wordsworth and Coleridge once passed a steam engine, Wordsworth observed that it was scarcely possible to divest oneself of the impression that it had life and volition. “Yes,” said Coleridge, “it is a giant with one idea.”

A mechanical toy which imitated human behavior led to the theory of what we now call reflex action. In the first part of the seventeenth century certain moving figures were commonly installed in private and public gardens as sources of amusement. They were operated hydraulically. A young lady walking through a garden might step upon a small concealed platform. This would open a valve, water would flow into a piston, and a threatening figure would swing out from the bushes to frighten her. René Descartes knew how these figures worked, and he also knew how much they seemed like living creatures. He considered the possibility that the hydraulic system which explained the one might also explain the other. A muscle swells when it moves a limb—perhaps it is being inflated by a fluid coming along the nerves from the brain. The nerves which stretch from the surface of the body into the brain may be the strings which open the valves.

Descartes did not assert that the human organism always operates in this way. He favored the explanation in the case of animals, but he reserved a sphere of action for the “rational soul”—perhaps under religious pressure. It was not long before the additional step was taken, however, which produced the full-fledged doctrine of “man a machine.” The doctrine did not owe its popularity to its plausibility—there was no reliable support for Descartes’s theory—but rather to its shocking metaphysical and theoretical implications.

Since that time two things have happened: machines have become more lifelike, and living organisms have been found to be more like machines. Contemporary machines are not only more complex, they are deliberately designed to operate in ways which resemble human behavior. “Almost human” contrivances are a common part of our daily experience. Doors see us coming and open to receive us. Elevators remember our commands and stop at the correct floor. Mechanical hands lift imperfect items off a conveyor belt. Others write messages of fair legibility. Mechanical or electric calculators solve equations too difficult or too time-consuming for human mathematicians. Man has, in short, created the machine in his own image. And as a result, the living organism has lost some of its uniqueness. We are much less awed by machines than our ancestors were and less likely to endow the giant with even one idea. At the same time, we have discovered more about how the living organism works and are better able to see its machine-like properties.

REFLEX ACTION

Descartes had taken an important step in suggesting that some of the spontaneity of living creatures was only apparent and that behavior could sometimes be traced to action from without. The first clear-cut evidence that he had correctly surmised the possibility of external control came two centuries later in the discovery that the tail of a salamander would move when part of it was touched or pierced, even though the tail had been severed from the body. Facts of this sort are now familiar, and we have long since adapted our beliefs to take them into account. At the time the discovery was made, however, it created great excitement. It was felt to be a serious threat to prevailing theories of the inner agents responsible for behavior. If the movement of the amputated tail could be controlled by external forces, was its behavior when attached to the salamander of a different nature? If not, what about the inner causes which had hitherto been used to account for it? It was seriously suggested as an answer that the “will” must be coexistent with the body and that some part of it must invest any amputated part. But the fact remained that an external event had been identified which could be substituted, as in Descartes’s daring hypothesis, for the inner explanation.

The external agent came to be called a stimulus. The behavior controlled by it came to be called a response. Together they comprised what was called a reflex—on the theory that the disturbance caused by the stimulus passed to the central nervous system and was “reflected” back to the muscles. It was soon found that similar external causes could be demonstrated in the behavior of larger portions of the organism—for example, in the body of a frog, cat, or dog in which the spinal cord had been severed at the neck. Reflexes including parts of the brain were soon added, and it is now common knowledge that in the intact organism many kinds of stimulation lead to almost inevitable reactions of the same reflex nature. Many characteristics of the relation have been studied quantitatively. The time which elapses between stimulus and response (the “latency”) has been measured precisely. The magnitude of the response has been studied as a function of the intensity of the stimulus. Other conditions of the organism have been found to be important in completing the account—for example, a reflex may be “fatigued” by repeated rapid elicitation.

The reflex was at first closely identified with hypothetical neural events in the so-called “reflex arc.” A surgical division of the organism was a necessary entering wedge, for it provided a simple and dramatic method of analyzing behavior. But surgical analysis became unnecessary as soon as the principle of the stimulus was understood and as soon as techniques were discovered for handling complex arrangements of variables in other ways. By eliminating some conditions, holding others constant, and varying others in an orderly manner, basic lawful relations could be established without dissection and could be expressed without neurological theories.

The extension of the principle of the reflex to include behavior involving more and more of the organism was made only in the face of vigorous opposition. The reflex nature of the spinal animal was challenged by proponents of a “spinal will.” The evidence they offered in support of a residual inner cause consisted of behavior which apparently could not be explained wholly in terms of stimuli. When higher parts of the nervous system were added, and when the principle was eventually extended to the intact organism, the same pattern of resistance was followed. But arguments for spontaneity, and for the explanatory entities which spontaneity seems to demand, are of such form that they must retreat before the accumulating facts. Spontaneity is negative evidence; it points to the weakness of a current scientific explanation, but does not in itself prove an alternative version. By its very nature, spontaneity must yield ground as a scientific analysis is able to advance. As more and more of the behavior of the organism has come to be explained in terms of stimuli, the territory held by inner explanations has been reduced. The “will” has retreated up the spinal cord, through the lower and then the higher parts of the brain, and finally, with the conditioned reflex, has escaped through the front of the head. At each stage, some part of the control of the organism has passed from a hypothetical inner entity to the external environment.

THE RANGE OF REFLEX ACTION

A certain part of behavior, then, is elicited by stimuli, and our prediction of that behavior is especially precise. When we flash a light in the eye of a normal subject, the pupil contracts. When he sips lemon juice, saliva is secreted. When we raise the temperature of the room to a certain point, the small blood vessels in his skin enlarge, blood is brought nearer to the skin, and he “turns red.” We use these relations for many practical purposes. When it is necessary to induce vomiting, we employ a suitable stimulus—an irritating fluid or a finger in the throat. The actress who must cry real tears resorts to onion juice on her handkerchief.

As these examples suggest, many reflex responses are executed by the “smooth muscles” (for example, the muscles in the walls of the blood vessels) and the glands. These structures are particularly concerned with the internal economy of the organism. They are most likely to be of interest in a science of behavior in the emotional reflexes to be discussed in Chapter X. Other reflexes use the “striped muscles” which move the skeletal frame of the organism. The “knee jerk” and other reflexes which the physician uses for diagnostic purposes are examples. We maintain our posture, either when standing still or moving about, with the aid of a complex network of such reflexes.

In spite of the importance suggested by these examples, it is still true that if we were to assemble all the behavior which falls into the pattern of the simple reflex, we should have only a very small fraction of the total behavior of the organism. This is not what early investigators in the field expected. We now see that the principle of the reflex was overworked. The exhilarating discovery of the stimulus led to exaggerated claims. It is neither plausible nor expedient to conceive of the organism as a complicated jack-in-the-box with a long list of tricks, each of which may be evoked by pressing the proper button. The greater part of the behavior of the intact organism is not under this primitive sort of stimulus control. The environment affects the organism in many ways which are not conveniently classed as “stimuli,” and even in the field of stimulation only a small part of the forces acting upon the organism elicit responses in the invariable manner of reflex action. To ignore the principle of the reflex entirely, however, would be equally unwarranted.

CONDITIONED REFLEXES

The reflex became a more important instrument of analysis when it was shown that novel relations between stimuli and responses could be established during the lifetime of the individual by a process first studied by the Russian physiologist, I. P. Pavlov. H. G. Wells once compared Pavlov with another of his distinguished contemporaries, George Bernard Shaw. He considered the relative importance to society of the quiet laboratory worker and the skillful propagandist and expressed his opinion by describing a hypothetical situation: if these two men were drowning and only one life preserver were available, he would throw it to Pavlov.

Evidently Shaw was not pleased, and, after what appears to have been a hasty glance at Pavlov’s work, retaliated. His book, The Adventures of the Black Girl in Her Search for God, describes a girl’s experiences in a jungle of ideas. The jungle is inhabited by many prophets, some of them ancient and some as modern as an “elderly myop” who bears a close resemblance to Pavlov. The black girl encounters Pavlov just after she has been frightened by a fearful roar from the prophet Micah. She pulls herself up in her flight and exclaims:

“What am I running away from? I’m not afraid of that dear noisy old man.”

“Your fears and hopes are only fancies” said a voice close to her, proceeding from a very shortsighted elderly man in spectacles who was sitting on a gnarled log. “In running away you were acting on a conditioned reflex. It is quite simple. Having lived among lions you have from your childhood associated the sound of a roar with deadly danger. Hence your precipitate flight when that superstitious old jackass brayed at you. This remarkable discovery cost me twenty-five years of devoted research, during which I cut out the brains of innumerable dogs, and observed their spittle by making holes in their cheeks for them to salivate through instead of through their tongues. The whole scientific world is prostrate at my feet in admiration of this colossal achievement and gratitude for the light it has shed on the great problems of human conduct.”

“Why didn’t you ask me?” said the black girl. “I could have told you in twenty-five seconds without hurting those poor dogs.”

“Your ignorance and presumption are unspeakable” said the old myop. “The fact was known of course to every child; but it had never been proved experimentally in the laboratory; and therefore it was not scientifically known at all. It reached me as an unskilled conjecture: I handed it on as science. Have you ever performed an experiment, may I ask?”

“Several” said the black girl. “I will perform one now. Do you know what you are sitting on?”

“I am sitting on a log grey with age, and covered with an uncomfortable rugged bark” said the myop.

“You are mistaken” said the black girl. “You are sitting on a sleeping crocodile.”

With a yell which Micah himself might have envied, the myop rose and fled frantically to a neighboring tree, up which he climbed catlike with an agility which in so elderly a gentleman was quite superhuman.

“Come down” said the black girl. “You ought to know that crocodiles are only to be found near rivers. I was only trying an experiment. Come down.”

But the elderly myop is unable to come down and begs the girl to perform another experiment.

“I will” said the black girl. “There is a tree snake smelling at the back of your neck.”

The myop was on the ground in a jiffy.¹

It is clear that Shaw has caught the spirit of a science of behavior. The black girl is undeniably a good behavioral engineer. In two very neat examples of stimulus control she induces clearcut responses in the elderly myop. (His behavior does not, as we shall see later, exemplify the simple reflex, conditioned or otherwise.) But if the author is fully aware of the potentialities of the practical control of behavior, he is not so strong on theory, for the passage exemplifies a common misunderstanding regarding the achievement of science.

The facts of science are seldom entirely unknown “to every child.” A child who can catch a ball knows a good deal about trajectories. It may take science a long time to calculate the position of a ball at a given moment any more exactly than the child must “calculate” it in order to catch it. When Count Rumford, while boring cannon in the military arsenal in Munich, demonstrated that he could produce any desired amount of heat without combustion, he changed the course of scientific thinking about the causes of heat; but he had discovered nothing which was not already known to the savage who kindles a fire with a spinning stick or the man who warms his hands on a frosty morning by rubbing them together vigorously.

The difference between an unskilled conjecture and a scientific fact is not simply a difference in evidence. It had long been known that a child might cry before it was hurt or that a fox might salivate upon seeing a bunch of grapes. What Pavlov added can be understood most clearly by considering his history. Originally he was interested in the process of digestion, and he studied the conditions under which digestive juices were secreted. Various chemical substances in the mouth or in the stomach resulted in the reflex action of the digestive glands. Pavlov’s work was sufficiently outstanding to receive the Nobel Prize, but it was by no means complete. He was handicapped by a certain unexplained secretion. Although food in the mouth might elicit a flow of saliva, saliva often flowed abundantly when the mouth was empty. We should not be surprised to learn that this was called “psychic secretion.” It was explained in terms which “any child could understand.” Perhaps the dog was “thinking about food.” Perhaps the sight of the experimenter preparing for the next experiment “reminded” the dog of the food it had received in earlier experiments. But these explanations did nothing to bring the unpredictable salivation within the compass of a rigorous account of digestion.

Pavlov’s first step was to control conditions so that “psychic secretion” largely disappeared. He designed a room in which contact between dog and experimenter was reduced to a minimum. The room was made as free as possible from incidental stimuli. The dog could not hear the sound of footsteps in neighboring rooms or smell accidental odors in the ventilating system. Pavlov then built up a “psychic secretion” step by step. In place of the complicated stimulus of an experimenter preparing a syringe or filling a dish with food, he introduced controllable stimuli which could be easily described in physical terms. In place of the accidental occasions upon which stimulation might precede or accompany food, Pavlov arranged precise schedules in which controllable stimuli and food were presented in certain orders. Without influencing the dog in any other way, he could sound a tone and insert food into the dog’s mouth. In this way he was able to show that the tone acquired its ability to elicit secretion, and he was also able to follow the process through which this came about. Once in possession of these facts, he could then give a satisfactory account of all secretion. He had replaced the “psyche” of psychic secretion with certain objective facts in the recent history of the organism.

The process of conditioning, as Pavlov reported it in his book Conditioned Reflexes, is a process of stimulus substitution. A previously neutral stimulus acquires the power to elicit a response which was originally elicited by another stimulus. The change occurs when the neutral stimulus is followed or “reinforced” by the effective stimulus. Pavlov studied the effect of the interval of time elapsing between stimulus and reinforcement. He investigated the extent to which various properties of stimuli could acquire control. He also studied the converse process, in which the conditioned stimulus loses its power to evoke the response when it is no longer reinforced—a process which he called “extinction.”

The quantitative properties which he discovered are by no means “known to every child.” And they are important. The most efficient use of conditioned reflexes in the practical control of behavior often requires quantitative information. A satisfactory theory makes the same demands. In dispossessing explanatory fictions, for example, we cannot be sure that an event of the sort implied by “psychic secretion” is not occasionally responsible until we can predict the exact amount of secretion at any given time. Only a quantitative description will make sure that there is no additional mental process in which the dog “associates the sound of the tone with the idea of food” or in which it salivates because it “expects” food to appear. Pavlov could dispense with concepts of this sort only when he could give a complete quantitative account of salivation in terms of the stimulus, the response, and the history of conditioning.

Pavlov, as a physiologist, was interested in how the stimulus was converted into neural processes and in how other processes carried the effect through the nervous system to the muscles and glands. The subtitle of his book is An Investigation of the Physiological Activity of the Cerebral Cortex. The “physiological activity” was inferential. We may suppose, however, that comparable processes will eventually be described in terms appropriate to neural even...