Discussion 3

1 PSYCHOLOGY AND THE REFLEX

NATURE WITH its myriad phenomena assumes a unified aspect only in the rarest cases; in the majority of instances it exhibits a thoroughly com- posite character...; it is accordingly one of the duties of science to conceive phenomena as made up of sets of partial phenomena, and at first to study these partial phenomena in their purity.

P. Volkmann, Erkenntnistheoretische Grundziige der Naturwissenschaft, 1896

Preliminary The purpose of this text is threefold: (1) to acquaint you

with a number of well-established psychological principles; (2) to show you how these principles are related, one to the other; and (3) to suggest how you may apply them in the analysis of everyday human activity. In addition, we hope that you will draw from it some notion of where the frontiers of our science lie, of what important problems remain to be solved, and, perhaps, an idea of how you can help in further- ing their solution.

With certain matters of theory and practice commonly considered in elementary texts, we shall not be concerned. You will find in this book no chapters on the workings of the human nervous system, the structure and function of our sense organs, or the measurement of intelligence. These are interesting matters for advanced study, but they do not rightly belong within a text devoted to fundamental problems and basic principles of psychology.

For the general reader, there are excellent surveys and samplings of the various fields and problems of psychology, which provide a bird's-eye view of the science. For the ad-

S PRINCIPLES OF PSYCHOLOGY

vanced student, there are many books that deal exclusively with this or that area of specialized interest. The present text belongs within neither category. It aims simply to furnish the beginning student with a solid foundation and a trust- worthy framework for thinking about, or dealing with, human nature as he finds it in his daily life. And, needless to say, it should also prepare him for further, more intensive, study in our field.

As you make your way, step by step, through this book, you will notice certain outstanding characteristics of our approach. These may well be mentioned in advance, as a preparation for things to come. Our approach is biological, experimental, and systematic. Biological, in that our basic principles will often be drawn from the study of animal behavior, and will be found to apply at various evolutionary levels; experi- mental, in that these principles will be derived, not from casual observation or untested opinion, but from laboratory studies in which the important factors are isolated and varied in such a manner as to permit scientific lawfulness to be dis- covered; and systematic, in that the interrelation of experi- mental facts will be one of our major concerns.

The Subject Matter of Psychology Tentatively we may define psychology as the science of the

behavior of organisms. Such a simple statement, however, is both incomplete and misleading. Psychologists are not, as a rule, equally interested in the behavior of all organisms. Their attention is usually focussed primarily upon the human being and a few of his near-relations in the animal kingdom —for example, the rat, the cat, the dog, the monkey, and the chimpanzee. The comparative psychologist makes it his busi- ness to examine differences and similarities of behavior throughout the evolutionary scale. We, however, shall have little interest in the activities of animals markedly different from man, or in those infra-human activities which throw no light on human conduct.

PSYCHOLOGY AND THE REFLEX 3

Moreover, the psychologist studies behavior in its relation to environment. Behavior alone would hardly constitute the subject matter of a science. Imagine, for a moment, the sense- lessness of a motion-picture record of an organism's behavior from birth to death, with every indication of the world in which it lived carefully blotted out! Only when we begin to relate behavioral to environmental happenings does the possi- bility of a scientific psychology make its appearance.

Stimulus and Response But we must go still further. Behavior and environment are

unwieldy terms, too broad in their meaning to be very useful. As soon as we attempt to deal with either, we find ourselves risking What sort of behavior? What aspect of environment? This is but another way of saying that, whenever we try to describe either the behavior or the environment of an or- ganism, we are forced to break it down into parts. Analysis is essential to description, in our science as well as others.

Through analysis, psychologists have arrived at the concepts of stimulus and response. A stimulus may be provision- ally defined as "a part, or change in a part, of the environ- ment," and a response may be defined as "a part, or change in a part, of behavior." We shall recognize, however, that a stimulus cannot be defined independently of a response. An environmental event becomes a stimulus by virtue of the fact that it is followed by a response. Activities of our muscles and glands (the so-called bodily effectors) make up our re- sponses. These terms provide the specificity we desire and make a study of the environment-behavior relation feasible by giving us things to observe and to measure. Stimuli and responses are the basic units of our descriptions and provide the starting point for a science of behavior. We would not go far astray in asserting that modern psychology itself is essentially a stimulus-response psychology.

4 PRINCIPLES OF PSYCHOLOGY

The Reflex

Physiologists have supplied us with a very useful word with which to designate any specific stimulus-response relation- ship. The word is reflex, and, in the chapters to follow, we shall employ it frequently. For example, we shall speak of the salivary reflex when we refer to the fact that food, in the mouth of a hungry man, quickly evokes a flow of saliva. We shall even extend the use of the term to denote responses for which related stimuli are not clearly observable. Thus, we shall give the name reflex to the response made by a child in clapping his hands, even when we have no way of knowing exactly what stimuli are responsible for the act. But more of this later.

The Response Mechanism Between the stimulus and the response there are obviously

bodily happenings. It is well recognized today that stimuli affect sense organs (called receptors) and that sense organs, when excited, cause nerve impulses to be transmitted over nerve pathways to the brain or spinal cord and thence to the muscles and glands (effectors). This sequence of events results in those responses which we, as psychologists, are interested in relating to stimuli. The structures involved—the receptors, the nervous system, and the effectors— make up what is com- monly known as the response mechanism.

The detailed function of the response mechanism is of principal concern to the physiologist. He tells us that the receptors or sense organs are of three main types:

1. Exteroceptors, small structures within the eye, the ear, or the skin, which are excited by stimuli external to the organism.

2. Interoceptors, tiny organs which lie mainly within the alimentary tract, and which are excited by internal stimuli.

5. Proprioceptors, which are located within the muscles,

PSYCHOLOGY AND THE REFLEX 5

joints, and tendons, as well as the inner ear, and are excited, that is, stimulated, by movements of the body or its parts.

In line with this distinction, stimuli themselves are often described as exteroceptive, interoceptive, or proprioceptive. This gives us greater specificity than is conveyed merely by the word environment.

We are also told that the nervous system has subdivisions. One part of it, the somatic nervous system, serves primarily to transmit nerve impulses from the sense organs to those muscles of the body which are employed in walking, talk- ing, writing, and the like—responses which are highly spe- cific and of great importance in making changes in our environment. The other part, the autonomic nervous system, is essentially an extension of the somatic nervous system, but serves mainly for the conduction of nerve impulses to the glands and the so-called "smooth" muscles of our bodies —for example, the digestive glands and the muscles of the blood-vessel walls, the stomach, and the iris of the eye. The action of part of this autonomic system is extremely diffuse and is most conspicuously responsible for the widespread internal changes which occur in all of us when under strong emotion.

The Reflex Arc and the Reflex

Anatomists and physiologists have analyzed in detail the structure and function of the response mechanism. Their interest in filling the gap between stimulus and response has led them to the conception of a reflex arc, in order to dis- tinguish it from the observed relation of stimulus to response which we have called the reflex. The simplest conceivable chain of structures between our two end-terms, stimulus and response, is presumably one that includes (1) a receptor ele- ment (cells or cell groups in the sense-organ tissues), (2) a sensory or afferent nerve element (nerve cells or neurons) for conducting impulses to some nerve center in either the

6 PRINCIPLES OF PSYCHOLOGY

brain or the spinal cord, (3) a motor or efferent nerve element for conduction from nerve center to effector, and (4) the effector itself, a muscular or glandular element (muscle or gland cells) that accounts for the final response.

This chain or arc of structural elements—receptor cells, sensory and motor nerve cells, and effector cells—has some- times been called a reflex, and some theorists have maintained that it is the organic basis of the stimulus-response relation. We need not here examine the evidence for such an argument, which has often been disputed, but it is important that we make a clear distinction between the reflex as a relation actu- ally observed and the reflex as a hypothetical mechanism. Confusion will be avoided if we use reflex in the former case, and reflex arc in the latter.

The newcomer to psychology will gain little from further discussion of physiological matters. It is true that psychologists have long been interested in relating behavior to receptor, effector, and nervous-system function; and physiological psy- chology is today a thriving field of study for the advanced student. But as far as general principles of behavior are con- cerned, this area of investigation has not as yet been very helpful. It is, in fact, the case that our knowledge of the stimulus-response relation has more often preceded than fol- lowed our knowledge of its physiological counterpart.

Extension of the Reflex Concept The reflex, as well as the reflex-arc, concept grew up in

physiological science. Muscular movement, originally attrib- uted to supernatural forces and later ascribed to a power residing within the muscles themselves, was gradually recog- nized as due to the action of successively excited parts of the response mechanism. Also, the importance of an initiating stimulus was demonstrated, and it became clear that many animal reactions were a direct and almost inevitable result of stimulus presentation. Observation of such phenomena as the writhings of a decapitated lizard in response to mildly

PSYCHOLOGY AND THE REFLEX 7

injurious stimulation of its skin led to the search for stimuli to other reactions of operated animals, and soon disclosed a considerable number of comparable stimulus-response rela- tions. The advocates of scientific determinism were thus en- couraged to extend their researches into the realm of normal, intact animals and, eventually, to man himself. It became obvious that, regardless of the physiological activities in- volved, stimuli and responses were often associated in a defi- nite and openly observable cause-effect sequence. Lists of animal and human reflexes were compiled, and psychologists, as well as physiologists, turned to the task of further explora- tion and study.

By 1919, it was possible for John B. Watson, an American pioneer in the objective, natural-science approach to psychol- ogy, to suggest that the identification, enumeration, and classi- fication of stimulus-response relations was the principal concern of our science. In effect, he proposed a cataloguing of reflexes as basic to the prediction and control of human and infra-human behavior. In the furtherance of such a program, Watson himself made extensive observations on the 'unlearned' reactions of newly-born human infants to various simple forms of stimulation.

Watson's proposal is now deemed impracticable. Even if we assumed that the entire reflex repertory of a given organism might some day be determined (which is very unlikely in view of the effects of training and the extreme difficulty in identifying the stimuli for many common forms of response), we would still be unable to formulate general principles of the sort that we require. We need a dynamic, rather than a static, picture of the behavior of organisms. To describe proc- ess, not to inventory elements, is our major concern. A more productive approach has been one that takes for granted the basically reflex character of our behavior, selects a few ex- amples for observation, and examines their dynamic prop- erties in some detail. This is the approach that will be taken in the present text.

8 PRINCIPLES OF PSYCHOLOGY

Some Reflex Properties We begin our account with a few facts that are so simple

and ubiquitous that they might easily be overlooked. Yet they actually have the status of fundamental principles. They are readily demonstrable in any experimental situation where the intensity of a stimulus can be controlled and the magni- tude of a response can be measured, and they may also be crudely observed under the non-quantitative circumstances of everyday life.

Take, as an example, the scratch reflex of a spinal dog in the laboratory of a physiologist. In such an animal, a severed spinal cord permits movements of the hind legs which are free from any influence stimulating the fore part of the body. When a touch stimulus is applied to the dog's hind ribs, a rhythmic flexion and extension of the right hind leg will take place. This response resembles a normal dog's reaction to the bite of a flea, but since it is uncomplicated by the effect of any stimuli concurrently exciting the dog's eyes or ears, it has a somewhat artificial appearance. Nevertheless, it is easily elicited and very useful in illustrating properties of reflex action in general.

The Threshold or Limen One of the first facts that may be demonstrated with such

a reduced animal is that a stimulus must be of a certain in- tensity before it can elicit a response. The intensity just suffi- cient to excite is called a liminal or threshold intensity. Lesser intensities are called below-threshold or sub-liminal since, when applied singly, they never evoke a reaction. Correspond- ingly, greater intensities are called above-threshold or supra- liminal.

All of the elicited responses of organisms (either operated or intact) show this dependence upon stimulus level, and great effort has been expended throughout the past century in determining the liminal intensities of visual, tactual,

PSYCHOLOGY AND THE REFLEX 9

auditory, and other stimuli. Indeed, an entire field of re- search, psychophysics, has been oriented about such measure- ments. Workers in this field have dealt not only with absolute thresholds, the kind defined above, but also with difference thresholds, in which one studies the organism's capacity to detect differences in the intensity of stimuli that are at the outset well above absolute-threshold value.

We shall come back to thresholds later, in Chapter 5. At present, it is enough to note that many common observations point to their existence. When we raise a watch to our ear to hear the tick, when we find the first star in the evening sky, or when we observe the dimming of theatre lights, we are dealing with the fact of absolute or relative intensity limens. Other instances will quickly occur to anyone who thinks about the matter.

Latency

A short interval of time elapses between the application of a stimulus and the arousal of a response. This interval is called the latency or latent period. In the scratch reflex of the spinal dog, the interval may range from 140 ms. (milli- seconds ) to 500 ms. (half a second), depending upon the in- tensity of the stimulus employed. In such a reflex, strong stimuli reduce the latent period and weak ones lengthen it. Other reflexes may show a different range of latency values, but for any single reflex of this sort conditions may be so con- trolled as to produce a fairly constant value. This constancy is important since it gives us a measure of the effect of chang- ing the conditions.

Although this relation is quite dependable in such cases as that of the spinal dog's scratch reflex, there is another type of stimulus-response connection where changes in stimulus intensity are not so clearly reflected in alterations of latency. When the driver of a car responds to a green light by making the movements which set his car in motion, the latency of the response does not appear to be directly related to the

10 PRINCIPLES OF PSYCHOLOGY

intensity of the light. He starts up as quickly for a weak light as for a strong one. The process involved in such a case requires, as we shall see, its own explanatory treatment.

We shall return to the matter of latency in Chapter 5, when we discuss some experimental studies of reaction time—a. term that may already have suggested itself to you. We shall then see that latency and reaction time are not unrelated, the latter being a variation of the former. For the present, how- ever, the distinction should not be prematurely pressed.

Stimulus Intensity and Response Magnitude If the scratch reflex of our spinal dog is elicited by a barely

supra-liminal stimulus, the latency, as stated above, will be relatively long. This will not be the only effect observed. The flexion of the leg may be limited to a single short excur- sion or, at most, to two or three. If, now, the stimulus in- tensity is raised to a higher value, there will ensue an increase in both the amplitude and number of scratching movements. Within limits, the magnitude of the elicited response is de- pendent upon, that is, is a function of, the intensity of the stimulus.

As in the case of latency, however, the response magnitude is not always seen to bear such a neat relation to the stimulus variable. In a snake-infested cave, a faintly heard rattle may evoke as vigorous a reaction as the report of a revolver; in a tropical jungle, the hum of a mosquito may sometimes elicit as strong an emotional response as the roar of a near-by plane. Such observations point to other controlling factors, and the laboratory bears this out. A different, but nonetheless lawful, relation will occupy our attention later.

Reflex Strength There are properties of reflex action other than those just

described, and they too may be observed in the behavior of a spinal animal. We need not, however, consider them in this text, since we are here concerned with bare essentials, and

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FIG. I. Schematic tape records of three reflex properties. The height of a spike on the stimulus line indicates stimulus intensity; that on the response line, response magnitude. The distance between the stimulus and response spikes on the constant-speed tape gives the latency. The time line is made by an automatic marker which ticks off any desired unit of time. The broken threshold tape shows that the stimulations were very widely spaced to prevent possible summation of stimulus effects.

12 PRINCIPLES OF PSYCHOLOGY

we already have enough facts to take the next step in our thinking.

Returning to the scratch reflex again, let us ask ourselves a question. What happens to threshold, latency, and response magnitude when we apply a stimulus not once but many times and in fairly quick succession? A moment's thought may suggest the answer. The reflex undergoes fatigue. This shows itself on the observational level. The latency increases, the magnitude of successive 'scratchings' becomes less and less, and the stimulus intensity required for threshold excitation heightens appreciably. Moreover, these changes take place together.

Since other procedures or "experimental operations" than that of repeating stimulations will also produce concurrent changes in reflex properties, it will be useful to have a single term to denote such changes. Reflex strength has been sug- gested for this purpose and will be adopted here. We shall, then, speak of a strong reflex when there is a relatively low threshold of stimulation, a relatively short latency, and a relatively large magnitude of response. Conversely, a weak reflex will be considered as one with a high threshold, a long latency, and a small magnitude of response. Frequently, we shall take as our indicator or measure of strength either the latency or the response magnitude alone, without bothering to consider the related values of other properties.

It has already been mentioned, in passing, that the term reflex will often be applied in this book to responses which are not observably related to any stimuli. In such cases, where concepts like latency and threshold can have no meaning (since they depend upon a stimulus-response relation), we shall nevertheless speak of reflex strength. Frequency of occurrence will then become a very important measure of strength. Until we come to Chapter 3, however, this matter needs no further discussion.

PSYCHOLOGY AND THE REFLEX 1J

A Few Remarks So much by way of preliminaries. This is a short chapter,

but you should now be able to say something about (1) the general aim of this text; (2) the subject matter of psychology; (3) the concept of the reflex; (4) the nature of a few basic reflex properties; and (5) the meaning of reflex strength. All this is essential to your understanding of what will be treated in the pages to come. Each step in our exposition will depend upon what has gone before. Unless you have understood the earlier facts and principles, you will almost surely have trouble with the later. For this reason it will often be helpful for you to go over again a paragraph, a section, or a chapter previously read, in order to strengthen your foundation for the topic at hand or the topics to come.

It will also be wise, in reading the coming chapters, to divest yourself, as far as possible, from preconceptions con- cerning psychology. Our everyday language is shot through with purportedly psychological terms and concepts. Most of these are lacking in scientific significance, because they are either poorly defined or unrelated to anything else, and they will find no place in our account. You are asked here, as you would be in physics, chemistry, or biology, to learn a new language. The power of this language can be appreciated only by the one who applies it consistently and rigorously, avoiding the contamination of ill-defined or long-discarded terms.

NOTES

In the back of this book, along with the subject index, is an alphabet- ical list of some of the more important books and articles to which we have referred in preparing our chapters. We have adopted the practice of mentioning, in the text, authors' names and the dates of their publica- tions (e.g., Hilgard and Marquis, 1940). The complete reference is provided in our list—thus "HILGARD, E. R., and MARQUIS, D. G. (1940). Conditioning and learning. New York, Appleton-Century-Crofts, xi, 429 pp." After each reference you will find, in italics, the page numbers on which the contribution is cited in this text.

14 PRINCIPLES OF PSYCHOLOGY

The introduction to psychology provided by this book is something of a departure from the usual approach, and you may at some time be interested in comparing it with other texts. Three very popular elemen- tary accounts are those by Munn (1946), Ruch (1948), and Woodworth and Marquis (1947). Two other well-known books, by Garrett (1941) and by Crafts, Schneirla, Robinson, and Gilbert (1938), are often used as collateral reading in beginners' courses. Any one of these will give you a good idea of the range of topics to which students are usually exposed in their first course, but in none of them will you find a serious attempt to show how the topics are interrelated or integrated within a unified whole. Only a few authors have made an effort similar to ours (e.g., Muenzinger, 194s).

The systematic position portrayed in the present text is best described as reinforcement theory, which is the dominant viewpoint in modern behavior theory. Our own account leans heaviest on the work of B. F. Skinner (The behavior of organisms, 1938), but is not uninfluenced by other expositions—as found, for example, in the writings of E. L. Thorn- dike (1911, 193s) and the recent teachings of C. L. Hull (1943).

The student who does not mind reading something of a more tech- nical stripe than we offer may go to Skinner's book. There, in the first two chapters, he will find further discussion of such topics as the data of psychology, the need for analysis, the concept of the reflex, the structure of psychological theory, and related matters. The viewpoint in Hull's Principles of behavior (1943) provides a stimulating contrast.

Our systematic position has not kept us from looking at facts in other theoretical contexts. Good data are good data, regardless of theory, and we have been happy to draw upon the experimental findings of our colleagues whenever it seemed profitable, regardless of the viewpoint that guided their research. Therefore, if you are one who likes to "go to the original," do not be surprised if you occasionally find an article written in terms with which you are unfamiliar. If you can push aside the interpretations and discussions, and attend to the experimental procedures and results, you will see why we thought the article worth consideration. Later on, if your interest in psychology continues, you will be better able to evaluate the explanations and debated points.