The Stimulus-Response Fallacy in Psychology

L. L. Thurstone
Bureau of Public Personnel Administration, Washington

In psychology we talk very much about the stimulus and the response. I am almost inclined to believe that no other words in psychological terminology occur more often. About these two terms we have come to take for granted a point of view for psychological analysis, the validity of which I want here to question. By the stimulus-response formula in psychological writing I mean the assumption that mental life is essentially determined by stimuli and that our actions are in the nature of replies to the stimuli. We write and talk as though the stimuli were primarily provocative of mental life and of our actions. When we meet any mental phenomenon which is to be explained we look first for a stimulus. If we find one we assume that the first requirement of a scientific explanation has been met. If we cannot find a stimulus which is obviously responsible for the present mental state, or for the present overt act, we rest convinced nevertheless that some stimulus in our past is now finding expression in us. We must. have a stimulus for otherwise we cannot psychologize.

A mental phenomenon is to be explained. It is very simple. What was the stimulus? Describe it. What was the muscular response? Describe it objectively. What happened between these two things? There were `bonds' between them, and `pathways,' and 'grooves,'-and `processes' took place, and there were `connections' in the nervous system. That settles it, and the event is psychologically explained. In order to make our teaching clear we draw three lines on the blackboard with `fuzzy' ends to represent neurones and synapses. Our amateurish neurology is passed out as a scientific discussion of mental life, when there is really nothing

( 355) mental about any of these things, the physical stimulus, the muscular response, and the blackboard neurones.

In Figure 1, I have represented this stimulus-response

figure 1

psychology in a simple diagrammatic way. A stimulus hits us. The mind consists of the so-called bonds and pathways, and out comes the response. When we see a muscular adjustment we point to a known, or unknown, stimulus which has found its way transformed through bonds and pathways into conduct. It would hardly be fair to say that we are always as totally unmindful of the mental in our mental science as my simple diagram would indicate, but I am calling in question the stimulus-response formula which is explicit or implied in much of our psychological writing. To relegate habitually our mental life into the unmental stimulus-response categories is a procedure that carries the appearance of science in its terminology but it is often indicative of a superficial and unsympathetic understanding of mental life.

In Figure 2, I have represented the function which, it

figure 2

seems to me, the stimulus really serves. Let us start the causal sequence with the person himself. Who and what is he? What is he trying to do? What kind of satisfaction is he trying to attain? What are the large types of self expres-

(356) -sion that are especially characteristic of him? What are the drives in him that are expressing themselves in his present conduct? Let us consider the stimuli as merely the environmental facts in terms of which he expresses himself. In the mental the diagram I have represented the causal sequence as starting with the dynamic living self. Self expression is defined into particular actions at the terminal end of the diagram. The environment, the stimulus, is causally intermediate . The stimulus determines the detailed manner in which a drive or purpose expresses itself on any particular occasion.

In the last analysis the datum for psychology is the dynamic living self and the energy groups into which it may be divided. We may refer to this datum as the will to live, or we may call it the life impulse, or the vitality of the organism, or we may discover it to be the energy released by metabolism. We may be able to subdivide our will to live into large energy groups which manifest themselves in conduct more or less independently. These energy groups would be our innate, dynamic, and more or less distinct sources of conduct, and we might come to call them drives, motives, instincts, determining tendencies, or any other words that represent that which we as individuals innately really are, that which characterizes us as persons with individually preferred forms of life.

With our interest thus centered on the dynamic aspects of the living person himself, we are in a position of good perspective from which to study the manner in which he utilizes the stimuli of his environment, the manner in which he goes about hunting for the stimuli that the environment does not immediately give the manner in which his dynamic self finds overt expression through and by the stimuli that by chance happen to be available, and his compromises with substitute stimuli which in other moments lie would reject as. inadequate. The stimulus is not primarily provocative of living, of mental life. We, ourselves, are.

If we consider the causal sequence of Figure 2 we have first the presence of drives, tendencies, or motives in us. These conscious or unconscious motives become in the second phase

(357) of the sequence more and more defined through the stimuli of the environment, and they issue in the third phase of the sequence in overt action. Let us call this sequence a psychological act. An overt act is then merely the terminal end of a psychological act. The stimulus may be defined materially as any physical event in the environment, but psychologically the stimulus would be defined as a motive that is being formed. The complete formulation of a motive is an overt act. Hence the stimulus is a motive that is partly formed, but not yet completely formed into overt action. This represents briefly the causal sequence which should he the fundamental concern of psychology.

One of the basic problems in psychology is necessarily the classification of actions and their incomplete forms which constitute conscious life. There are at least six different bases by which actions may be classified. The simplest of these is that of direct similarity of the overt acts themselves. To pick up a fork and to pick up a fountain pen are two acts that are closely similar and they may for certain narrow purposes be classified together. Psychologically two such actions are totally different in two respects. The mental antecedents of the two overt acts are totally different, and the consequences and immediate satisfactions are also different. If we compare the two psychological acts that are involved we find that they converge at one point only, namely, at the point where the motives or purposes issue into overt expression. Before and after this point the two acts and their consequences cannot be classified together. From the standpoint of the psychologist it is a trivial circumstance that the two psychological acts happen to terminate in the same muscle groups.

We may proceed in either direction, through the antecedents or through the consequences of the act, in order to discover other basses for classifying action. Let us go to the antecedents first. If two psychological acts are similar in the mental antecedents of the overt acts, the two resulting actions may for that reason be classified together. Suppose that you discover that some information should be given to another

( 358) man. This is a mental state and it is therefore unfinished action. The resulting overt formulation of the psychological act may take various forms. You may reach for the telephone, or you may put on your hat and coat and walk out. These two seen forms of behavior are, of course, different in appearance, but there was a point. in the mental antecedents of two such possible actions at which they would be identical, namely, that stage in the formulation of behavior at which it is merely the realization that some information should be conveyed. Two widely different overt acts may, then, have converged; and they may have been identical, at some mental antecedent stage. We see that if we define the psychological act as the whole course of events from a purpose or motive, through its imaginal form, through the overt expression, to the consequences and satisfactions to the actor, we have numerous points at. which different psychological acts may be treated as identical even though they differ widely at other stages.

Two acts may be declared to be in the same category because of the fact that they converge and are identical at the point were the stimulus appears. The stimulus for the exteroceptors constitutes a relatively late and rather completely formulated phase of the psychological act. The stimulus for the interoceptors constitutes an earlier and less definitely formulated phase of behavior. It often happens that a stimulus for the interoceptors is the first conscious presence of the unfinished behavior which completes itself in a hunt for suitable stimulation of the exteroceptors. These latter stimuli in turn complete themselves as ordinary percepts in overt action and resulting satisfaction or a continued hunt for more stimuli. Two psychological acts may be declared to belong in the same category because of the similarity of the internal or external stimuli by which the several lines of unfinished behavior converge or are identical.

A more important and fundamental basis of classification would be the possible identity of several types of behavior at their energy source. It may be possible to discover that the total energy of the organism, which is derived from its metabolism, is divisible into energy groups. It is not impossible

( 359) to imagine that in one organism much of the energy may turn to digestive functions with resulting keen interest and satisfaction in food. In another organism a relatively smaller proportion of the energy which it accumulates is turned into this direction. There may well be individual differences in the division of the total energy of the organism into the several groups which constitute the source of its life impulses. In a similar manner organisms of the same species may differ in the relative proportion of their total energy which normally goes into the sex functions. In the human it is also conceivable that there are individual differences in the proportions of energy which normally seek expression in aggressive and self-assertive behavior, in sex life, in digestion, in locomotion, in gregarious conduct, and so on. It may well be that the different behavior of the prize fighter and the scholar converge as identical in that early phase of their conduct in which both seek social approval. Both may be so absorbed in the immediate details of what they are doing that they do not consciously realize the identity of the source of their labors.

It is in these energy sources of conduct that we shall find the distinctions between instincts. Instincts can never be defined in terms of the stimuli by which we happen to express ourselves; nor can they ever be defined in terms of particular behavior on particular occasions. The futility of the instinct category in psychology is caused by the fact that we have been looking for a specific stimulus on which to attach a specific instinctive response. The sex instinct, for example, should be defined so as to include the total range of possible human conduct, and the total range of human stimuli. The only point in the great variety of behavior at which the psychological acts belonging to an instinct are identical is at the energy source.

If, instead of proceeding from the overt act toward the mental and the unconscious antecedents, we follow the psychological acts into their consequences, we find still additional points at which they may converge. Two psychological acts may be totally different but they may conceivably have similar immediate consequences as objectively determined.

( 360) Such a fact would be a legitimate basis of classification. The subjective variant of the above classification on the basis of immediate consequences is to group together those psychological acts which yield for the actor the same types of satisfaction.

Still another basis for classifying actions together is the degree to which they may be substituted with equal satisfaction to the actor. This is one of the most useful explanatory devices in psychology.

I have listed a number of stages in the development of psychological acts in which they may be identical or similar. If we start with action at its source and follow the stages through which it becomes formulated into conduct, and the consequent satisfactions, we shall have a table as follows:


(I) Energy source
(2) Reduced threshold for stimuli
(3) Deliberate ideation
(4) The internal stimulus
(5) Imaginal hunt for external stimuli
(6) Overt hunt for external stimuli
(7) The external stimulus
(8) The consummatory overt act
(9) Overt consequences of the act
(10) Satisfaction to the actor, and quiescence at the energy source

(I) The energy source is the dissatisfaction in the physiological, mental, and social conditions which provokes action. These physical and mental conditions cover such wants as the satisfaction of hunger, bodily comfort, sex, social approval, social power. A state of dissatisfaction in any one of the instinct conditions is the starting point for action which is maintained until satisfaction is attained. Two actions belong in the same instinct category if they can by conditioning be readily substituted for each other. Two actions belong in different instinct categories if they can only by prolonged conditioning be substituted for each other. It may be that

(361) the instinct sources of behavior are not truly energy groups but only physiological and mental conditions which make demands on the total energy supply of the organism for random or purposive behavior until conditions of satisfaction are attained.

(2) Lowered threshold for stimuli. When an instinct condition is in a state of dissatisfaction there results a lowered threshold for relevant stimuli long before the appearance of conscious need, desire, or purpose. At five o'clock in the afternoon we are normally more easily tempted by the smell of a good steak than immediately after lunch, but in the absence of the external stimulus we may be entirely unaware of the lowered sensory and interest threshold. The instinct condition by its lower threshold has already started to determine the ultimate behavior before any conscious or external indices appear. The behavior is already on its course of formulation before the internal or external stimulus appears.

(3) Deliberate ideation. In a dissatisfaction which has not yet become sufficiently acute to be conscious in sensory form, and in which the actor is not himself aware of the lowered interest threshold, the expected behavior appears in imaginal form. Biologically the purpose of ideation is to prepare for action. The actor himself may not be aware of the fact that his thinking has its source in some state of incompleteness or dissatisfaction in the physical or social self. Since the need is not urgent or explicitly conscious, the actor's thinking is correspondingly calm and deliberate.

(4) The internal stimulus is parallel to the stage of deliberate ideation in the formulation of behavior, but it represents, in those instinct conditions where it normally takes part, a more definitely specified form of the behavior than the ideation which precedes or accompanies it.

(5) Imaginal hunt for the external stimulus represents a later and more complete formulation of behavior than free -moving purposeless thought and its relatives in internal stimuli. At this stage of the definition of conduct we have the expected experience in conscious form, and it has taken sufficient definition to be introspectively recognized as purpo-

( 362) -sive. It is in reality an imaginal hunt for those suitable stimuli which, if found, would lead to consummatory action. It is purposive imaginal preparation for expected experience. Expected conduct is now beginning to take sufficient cognitive form to be the subject of imaginal trial and error choice. This is realistic thinking which is purposive, as contrasted with autistic thinking which is less definitely purposive. Both forms of thinking are driven by instinct conditions.

(6) Overt hunt for external stimuli is merely carrying the purposive thinking into action in the hope of finding the imaginally expected stimuli. These overt actions may be directed immediately toward the significant stimulus, or they may be random in the nature of overt trial and error. It happens not infrequently that an instinct condition leads to overt random search without any conscious purpose, and without any definite conscious realization of the nature of the satisfaction that is sought.

(7) The external stimulus represents a rather late stage in the formulation of behavior. The psychological act is almost completed at the appearance of the external stimulus. The meaning of the stimulus is the expected satisfaction of the instinct condition for which the organism is ready. Most of the external stimuli are consciously sought, hunted for. The external stimuli which appear suddenly, such as danger signals, have as their meaning the maintenance of bodily integrity, a condition which by the mere fact of living the organism is in constant readiness to maintain. It should be noted, however, that the great majority of external stimuli are not met fortuitously. We actually hunt for most of our stimuli.

(8) The consummatory overt act is the terminal of what I have called the psychological act.

(9) The overt consequences of the act are in most cases practically parallel with the consummatory act and with the satisfactions to the actor.

(10) Satisfaction to the actor. It should be noted that the beginning of this sequence and the end of it are closely related in that both are concerned with the degree of satisfaction of

( 363) the physical and mental instinct conditions. Behavior starts in dissatisfaction and it terminates in satisfaction. It is in this sense that we can speak of a reflex circuit rather than the reflex arc. We have traced the psychological sequence by which behavior is formed. The mental antecedents of behavior constitute in fact behavior in the process of being particularized.

Every scientific problem is a search for the functional relation between two variables. In psychology we have two systems of variables that are to be related; namely, the motives or drives on the one hand and their overt expressions on the other. Instead of selecting these two systems of variables we more often attempt to express action as a function of the stimulus. Since the stimulus is a partly defined motive or drive there is no doubt frequently a relation between the stimulus and the overt act, but it is not nearly so fundamental for the understanding of mind, human nature, and conduct as is the relation between the drive at its source and its overt expression. The particular stimulus in any experiment may not be the one which the momentarily dominant motive cares to select for its expression.

Let us consider a typical illustration. I have said that we are in the habit of describing action as a function of the stimulus. We place before a subject a tachistoscope and he sees nonsense syllables. He tries over and over again until he has learned them. Out of this psychological experiment comes the scientific deduction that, other things being equal, he remembers best those syllables which are at the end of the list and which he saw last. He tends to remember also quite well those syllables that he saw first, before the novelty wore off. He does not remember so well the syllables in the middle of the list. This is a scientific experiment in which we state the relationship between two variables. The answers of the subject are described as a function of the stimulating nonsense. But how about incentives? The most important factor is whether or not he cares about our nonsense syllables. This factor of interest and effort overshadows entirely the small effects of the arrangement of the syllables. The experiment

(364) is scientifically quite legitimate but it is trivial relative to the factors that are most important for mental life.

We recognize of course this fact, that incentives are more important than the arrangement of the syllables on the page in predicting the recall. But since the incentives are not really measured, we have been content to describe the relations that we can measure. Well and good. This would not be subject to criticism if it were not for the fact that we have come to forget the individual person altogether. Experiments of this type have come to be the rule and we have taken for granted that psychology is primarily concerned with the incidental relation between the response and the response-modifying stimulus. We have gone so far as to assert that psychology studies the stimulus-response relation, and we have forgotten the person himself who may or may not want to do the responding.

I suggest that we dethrone the stimulus. He is only nominally the ruler of psychology. The real ruler of the domain which psychology studies is the individual and his motives, desires, wants, ambitions, cravings, aspirations. The stimulus is merely the more or less accidental fact in the environment which becomes a stimulus only when it serves as a tool for somebody's purposes. When it does not serve as a tool for getting us what we want, it is no longer a stimulus. It is not a cause. It is simply a means by which we achieve our own ends, not those of the stimulus. The psychological act which is the central subject-matter of psychology becomes then the course of events, primarily mental, which intervene between the motive and the successful neutralization or satisfaction of that motive. The stimulus appears somewhere between the provocative and overt terminals of the psychological act. Mental life consists primarily in the approximate formulation of the motives leading toward overt expression. To the extent that mental life is of a relatively high order these approximate formulations of the motives become more and more tentative, deliberate, inhibited, delayed, and subject to choice before precipitating into their final overt form.

This point of view that I am recommending is not so

( 365) radical as it might at first sight appear. What I am recommending is after all merely a shift of emphasis diagrammatically represented in Figure 3. In that figure the upper line


Fig. 3.

represents the causal chain tacitly followed by psychology as it is now usually written. This chain of events starts with the stimulus as the fundamental datum for psychological inquiry. From the stimulus as a source we trace the mental events to the response. Between these two terminals we place the characteristics of the individual in the form of modifying mental sets, predispositions, irritability, instincts, habits. We admit that the individual does enter into the causal chain but only as a modifier of the stimulus-response series. When we talk about instincts, for example, we look first of all for a suitable stimulus which can be given the credit for starting the instinctive behavior. The stimulus is assumed to be the absolutely essential starting point for an instinctive act. At the other end of the causal chain we set down the characteristic behavior which is brought about by the particular stimulus. Between these two events we assume that the individual himself has something to say but only as a modifier of the fundamental stimulus-response relation.

In the second line of Figure 3, I have represented the individual and the stimulus as exchanging their places. The individual is in this second representation assumed to be the starting point for that which he himself does. The stimulus takes the secondary role of modifier. The primary formula is then to be found in the motive-expression relation. The expression of the motive is, of course, markedly affected by the stimuli which are now to be considered as the momentary circumstances of the environment. I am simply shifting the stimulus to the secondary role of a modifier, and I am promoting the individual and his life impulses to the first rank of cause as far as psychology is concerned.

Let us consider an illustration. Consider the instinctive

( 366) adjustments of retaliation for an insult. The insult would be described as a stimulus. Your defense would be described as a response. If you have lately been on the defensive as regards your position, professional status, financial security, or health, your motive of self defense or self preservation would have a low threshold. A trivial remark from an insignificant source might be sufficient to arouse defensive conduct on your part such as a fist blow, loss of temper, loud self-assertative talk, sullenness, or a bossy manner toward associates. If you have lately enjoyed a feeling of relative security with reference to your social, professional, financial, and physical self, the threshold for this defensive behavior would be so high that the trivial remark would be passed unnoticed. If you do reply to it, one would of course say that the insulting remark came first, and that your reply came afterward. But such a stimulus-response analysis of the situation would be superficial. It would not be the remark that drove you on to defend yourself. The stimulus is only an environmental fact which determines partly how you express what is already in you. It is psychologically much more interesting to discover the tendencies that seek expression than to describe conduct as merely replies to stimuli.

Suppose that you are stalled on a country road on account of an engine which has been maltreated. There were surely stimuli that preceded your inspection of the engine. That which makes you do things to that engine is not primarily the stimuli from the engine it is your desire to go. The stimuli are simply environmental facts which modify the expression of your desire to get there.

It may well be that our stimulus-response habits in psychological discussion came about because of the obvious fact that the stimulus often precedes conscious solution, and this in turn often precedes the overt act. The insulting remark no doubt preceded your back-talk; the engine balked before you looked for the trouble. That is all true, but your unsatisfied , desire for security was active as an unlocalized irritability before the insulting remark was made, and your desire to keep on going was being actively satisfied before the engine

( 367) balked. The facts of apparent temporal sequence should not blind us to the major causal factors of mental life.

This point of view is not limited to the interpretation of the human mind. It applies as well to the behavior of the lower organisms. We are too often inclined to look upon the animal mind as consisting of nothing but reflexes acting in response to the stimuli that happen to strike it.

Let me quote from Jennings.[1] "Activity does not require present external stimulation. A first and essential point for the understanding of behavior is that activity occurs in organisms without present specific external stimulation. The normal condition of Paramecium is an active one, with its cilia in rapid motion; it is only under special conditions that it can be brought partly to rest. Vorticella, as Hodge and Aikins showed, is at all times active, never resting. The same is true of most other infusoria and, in perhaps a less marked degree, of many other organisms. Even if external movements are suspended at times, internal activities continue. The organism is activity, and its activities may be spontaneous, so far as present external stimuli are concerned. . . . The spontaneous activity, of course, depends finally on external conditions, in the same sense that the existence of the organism depends on external conditions. Reaction by selection of excess movements depends largely on the fact that the movement itself is not directly produced by the stimulus. The movement is due, as we have seen, to the internal energy of the organism. . . . The energy for the motion comes from within and is merely released by the action of the stimulus. It is important to remember, if the behavior is to be understood, that energy, and often impulse to movement, come from within, and that when they are released by the stimulus, this is merely what James has called `trigger action."'

I will, of course, admit that the life impulses depend on the environment. So does the very life of the organism. The life impulses may be derived from the metabolism of the organism, and this is in turn contingent on what the environ-

(368) -ment gives. That is all true. But I should insist that psychology begin with the life impulse as its datum and that it be concerned with the mental routes by which the impulse expresses itself. It is up to the biologist to tell us the course of events by which the environment gives us our vitality. It is up to the physiologist to tell us about the physical routes by which the life impulse expresses itself.

The life impulse has, then, a history leading back to past stimuli but the sequence from these stimuli to the accretion of vitality is a biological rather than a psychological problem. Except for some division of the task one could readily find one's self arguing in a circle as to what it is that starts the whole business, the life impulse}or the stimulus. I prefer to consider mental life as an irreversible process beginning with the life impulse and terminating in the overt act. The stimulus may be thought of as a means for specifying the approximate act which is mental. Present overt action, and the approximate actions which constitute mental life, can only very roughly be stated in terms of the individual's stimulus-history.

The shift of emphasis that I am recommending would probably result in a more comprehensive and sympathetic understanding of mental life and human nature. It may also prove to be more serviceable to the related social sciences, and more illuminating to common sense.


My main thesis is that conduct originates in the organism itself and not in the environment in the form of a stimulus. Instead of analyzing behavior in the form of stimulus-response we should analyze it as the expression of cravings that originate in the organism and find particular modes of satisfaction in the stimuli that happen to be available.

All mental life may be looked upon as incomplete behavior which is in the process of being formed. The first phase in the expression of a craving is the lowering of the thresholds? for stimuli that are relevant. Phantasy consists in cravings which have no available stimuli for their expression. Purpo-

( 369) -sive thinking is the more restricted imaginal anticipation of satisfying experience. Imagination is the anticipatory hunt for suitable stimuli through which a craving may be satisfied. Perception is the discovery of the suitable stimulus which is often anticipated imaginally. The appearance of the stimulus is one of the last events in the expression of impulses in conduct. The stimulus is not the starting point for behavior.


  1. Jennings, 'Behavior of the Lower Organisms,' Chapters 16 and 18

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