OPERANT BEHAVIOR1 - Stoastoa.usp.br/vahs/files/1/16172/Skinner, B. F. Operant...OPERANT BEHAVIOR1 B. F. SKINNER Harvard University W E are interested in the behavior of an organism

OPERANT BEHAVIOR1

B. F. SKINNER

Harvard University

WE are interested in the behavior of anorganism because of its effects on theenvironment. (One effect on the social

environment is, of course, the arousal of our inter-est.) Some effects seem to throw light on the be-havior which produces them, but their explanatoryrole has been clouded by the fact that they followthe behavior and, therefore, raise the specter ofteleology.

An attempt has been made to solve the problemby creating a cpntemporary_ûxmgate of a giveneffect. A quality or property of purpose is assignedto behavior to bring "what the organism is behav-ing for" into the effective present, or the organismis said to behave in a given way because it intendsto achieve, or expects to have, a given effect, or itsbehavior is characterized as possessing utility to theextent that it maximizes or minimizes certain ef-fects. The teleological problem is, of course, notsolved until we have answered certain questions:What gives an action its purpose, what leads anorganism to expect to have an effect, how is utilityrepresented in behavior?

The answers to such questions are eventually tobe found in past instances in which similar behaviorhas been effective. The original problem can besolved directly in the same way. Thorndike's Lawof Effect was a step in that direction: The approxi-mately simultaneous occurrence of a response andcertain environmental events (usually generated byit) changes the responding organism, increasing theprobability that responses of the same sort willoccur again. The response itself has passed intohistory and is not altered.

By emphasizing a-daange-in-th&jjrganism, Thorn-dike's principle made it possible to include the ef-fects of action among the causes of future actionwithout using concepts like purpose, intention, ex-pectancy, or utility. Up to that time, the onlydemonstrable causes of behavior had been anteced-ent stimuli. The range of the eliciting stimulus

1A chapter in Werner Honig (Ed.), Operant Behaviorand Psychology. New York: Appleton-CenUuy-Crofts, tobe published.

was later to be extended by Pavlovian conditioning,and the concept could be broadened to includethe releasers of the ethologists, but only a smallpart of behavior caj^Jp^jDredicted--er--t:ontrolled' Vsimply by identifying or majiirjiulating stimuli. TheLa"w~6T Effect added an important new class of vari-ables of which behavior could be shown to be afunction.

Thorndike's solution was probably suggested byDarwin's treatment of phylogenetic purpose. Be-fore Darwin, the purpose of a well developed eyemight have been said to be to permit the organismto see better. The principle of natural selectionmoved "seeing better" from the future into the îfpast: Organisms with well developed eyes were de-

Ascended from those which had been able to see bet-ter and had therefore produced more descendants.Thorndike was closer to the principle of naturalselection than the above statement of his law. Hedid not need to say that a response which had beenfollowed by a certain kind of consequence was morelikely to occur again but simply that it was not lesslikely. It eventually held the field because re-sponses which failed to have such effects tended,like less favored species, to disappear.

Thorndike was concerned with how animalssolved problems rather than with the concept ofpurpose, and his Law of Effect did not end pur-posive formulations. The devices used for thestudy of behavior during the next quarter of a cen-tury continued to emphasize an intentional relationbetween behavior and its consequences. The rela-tion was represented spatially. In mazes, runways,and open fields, for example, organisms ran towardtheir goals. In discrimination apparatuses they•crrosirffie' door which led to food. They escapedfrom the dangerous side of shuttle boxes or pulledaway from sources of dangerous stimulation. Theydrew objects toward them with rakes or strings.The experimenter could see the purpose of an ac-tion in the spatial relation of the organism and theobjects toward which it was moving or from-whichit was receding. It was even asserted that the or-ganism itself should see a purposive relationship in

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some such form in order to behave effectively.Kb'hler, for example, criticized Thorndike on justthis score.

The spatial representation of purpose, expectancy,or intention obscured one of the most importantfeatures of the relation emphasized by Thorndike.The process he identified remained unexplored for30 years, and during that time was confused withrote habit formation and with various .formulationsof Eavlovian- conditioning. In the late 1920s, how-ever, the consequences of behavior began to bestudied with devices of another sort. Pavlov'stechnique for the study of conditioned reflexes con-tributed to their development, even though Pavlovhimself was not primarily concerned with conse-quences as such. In his basic studies, indeed, itmight be said that the organism did not receivefood for doing anything; the salivation elicited bythe conditioned stimulus did not produce the foodwhich followed. The experimental design, how-ever, called for food to be introduced at a givenmoment automatically. Once the procedure wasfamiliar, it was no great step to arrange devices inwhich a response _ "produced" food in a similarfashion. Ivanov-Smolensky (192 71), one of Pavlov'sassociates, studied an experimental arrangement,close to Thorndike, in which a child squeezed arubber bulb and delivered candy into his mouth.Miller and Konorski (1928) devised an apparatusin which a shock to the foot of a dog elicited flexionof the leg, and the resulting movement was followedby the presentation of food; the leg eventuallyflexed even when the foot was not shocked. InAmerica D. K. Adams (1929) used a similar ar-rangement with cats, and in England Grindley(1932) with guinea pigs. The essential featuresmay be seen in an apparatus in which depressionof a lever operates a food dispenser (Skinner,1932). Pressing a lever is not a natural or un-conditioned way of getting food. The responseproduces food only in the sense that food followsit—a Humean version of causality. Behavior isnevertheless altered. The consequences of actionchange the organism regardless of how or why theyfollow. The connection need not be functional ororganic—as, indeed, it was not in Thorndike's ex-periment.

PRACTICAL ADVANTAGES

These early devices were not designed to elimi-nate spatial representations of purpose, but they all

did so, and the fact had far-reaching consequences.Some of these were practical. The experimentercould choose a response which was convenientlyrecorded, or one which the organism could executerapidly and without fatigue for long periods oftime, or one which minimized the peculiarities ofa species and thus furthered a comparison betweenspecies with respect to properties not primarily re-lated to the topography of behavior. In particular,it was possible to choose a response which was rela-tively free of extraneous variables and not likely tobe confused with responses elicited or evoked bythem. When a shuttle box, for example, is used tostudy the effect of the postponement or terminationof a shock, the behavior affected (running or jump-ing from one side to the other) is topographicallysimilar to unconditioned responses to the shock,such as startle or jumping into the air, and to moreelaborate patterns of escape from a space in whichshocks have been received. It may also resembleresponse of both these sorts conditioned in thePavlovian manner and elicited by the warningstimuli. The inevitable confusion can be avoidedby making the postponement or termination of ashock contingent on an arbitrary response, such aspressing a lever in the Sidman arrangement, whichis not otherwise related to the variables at issue(Sidman, 1953).

A response which is only temporally related toits consequences could also be conveniently studiedwith automatic equipment. Instruments were de-veloped which permitted the investigator to con-duct many experiments simultaneously, particu-larly when unskilled technical help was available.It is true that automatic mazes and discriminationboxes had been or were soon to be built, but mostmodern programing and recording equipment canbe traced to research on responses with arbitrarilyarranged consequences for the very good reasonthat the conditions are easily instrumented. Theavailability of automatic equipment has helped tostandardize experiments and has facilitated thestudy of relations between responses and conse-quences too complex to be arranged by hand orfollowed by eye.

Another practical result was terminological. Theconcept of the .reflex .made no reference to the con-sequences "of a response. Reflexes were often ob-viously "adaptive," but this was primarily a phylo-genetic effect. The term "ppermit" was introducedto distinguish between reflexes and responses op-

OPERANT BEHAVIOR 505

erating directly on the environment (Skinner,1937). The alternative term "instrumental" sug-gests the use of tools. To say that a rat "uses alever to obtain food" has purposive overtones, andwhere nothing can be identified as an instrument,it is often said that the organism "uses a response"to gain an effect. For example, verbal behavior isinterpreted as "the use of words," although theimplication that words exist as things apart frombehavior unnecessarily complicates an analysis(Skinner, 19S7). Another change was from "re-ward" to "reinforcement." Reward suggests com-pensation for behaving in a given way, often insome sort of contractual arrangement. Reinforce-ment in. its, etymological_sejnse_..designalea.. simply(the strengthening of a response. It_refers_.tO-simi-lar eyentsjnjây.liman-conditioningy-^where-r-ewardis inappropriate. These changes in terminology

ave not automatically eliminated purposive ex-(such as, "The pigeon was reinforced for

pecking the key"), but a given instance can usu-ally be rephrased. Comparable teleological expres-sions are common in other sciences, as Bernatowicz(1958) has pointed out.

OF RESPONDING AS A DATUM

A more important result of studying an arbitraryconnection between a response and its consequences,together with the simplified procedures which thenbecome available, has been to emphasize rate ofresponding as a property of behavior. Earlier de-vices were almost always used to study responsesfrom trial to trial, where rate of responding wascontrolled by the experimenter and hence obscuredas a datum. When the organism can respond atany time, its rate of responding varies in manysubtle ways over a wide range. Changes in ratecomprise a vast and previously largely unsuspectedsubject matter. (The changes are made conspicu-ous with a cumulative recorder, the ubiquity ofwhich in the study of operant behavior is no acci-dent. In a cumulative record, rate and changes inrate are visible at a glance over substantial pe-riods of time. The "on-line" record permits theexperimenter to note changes as they occur andtake appropriate steps.)

Rate of responding is important because it isespecially relevant to the principal task of a scien-tific analysis. Behavior is often interesting becauseof what might be called its character. Animalscourt their mates, build living quarters, care for

their young, forage for food, defend territories, andso on, in many fascinating ways. These are worthstudying, but the inherent drama can divert atten-tion from another task. Even when reduced togeneral principles, a narrative account of how ani-mals behave must be supplemented by a considera-tion of why. What is required is an analysis ofthe ronditicms~ which -governJtoejarpbability that agiven response will occur at a., given time. Rate of ,responding is by no means to be equated with/^MxJ *probability of responding, as frequency theories ofprobability and comparable problems in physicshave shown. Many investigators prefer to treatrate of responding as a datum in its own right.'Eventually, however, the prediction and control ofbehavior call for an evaluation of the probabilitythat a response will be emitted. The study of rateof responding is a step in that direction.

Rate of responding is one of those aspects of asubject matter which do not attract attention fortheir own sake and which undergo intensive studyonly when their usefulness as a dependent variablehas been discovered. Other sciences have passedthrough comparable stages. The elements and com-pounds studied by the chemist also have fascinat-ing characters—they exist in many colors, textures,and states of aggregation and undergo surprisingtransmutations when heated, dissolved, combined,and so on. These are the characteristics whichnaturally first attract attention. They were, forexample, the principal concern of the alchemists.In contrast, the mere weight of a given quantity ofa substance is of little interest in its own right.Yet it was only when the weights of substances en-tering into reactions were found to obey certainlaws that chemistry moved into its modern phase.Combining weight became important because ofwhat could be done with it. Rate of respondinghas emerged as a basic datum in a science of be-havior for similar reasons—and, hopefully, withcomparable results.

Rate of responding djffen5_|ro,in the measures de-rived from earlier devices and procedures, such asthe time required to complete a task or the effortexpended or the number of errors-made in doingso, and the two kinds of data have led to differentconceptions of behavior as a scientific subject mat-ter. We like to believe that basic processes areorderly, continuous, and significant, but the dataobtained from mazes, memory drums, shuttle boxes,and so on, vary "noisily" from trial to trial and


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depend for their dimensions on particular tasksand apparatuses. Orderly and significant processesare therefore sought elsewhere—in some mental,physiological, or merely conceptual inner systemwhich by its nature is neither directly observed in,nor accurately represented on any given occasionby, the performance of an organism. There is nocomparable inner system in an operant analysis.Changes in rate of responding are directly ob-

served, they have dimensions appropriate to a.scientific formulation, and undex---skillful _experi-mental control they-show the uniformity expectedof biological processes in general. Those accus-tomed to the older formulation have nevertheless

ij; found them difficult to accept as an alternative sub-ject for analysis.

BEHAVIORAL PROCESSES

One difficulty is that changes in rate do notclosely resemble the behavioral processes inferredfrom earlier measures. A few examples may becited from the field of learning. By arranging areinforcing- consequence, we--increase the rate atwhich a response occurs; by eliminating the conse-quence, we decrease the rate. These are the proc-esses of operant conditioning and extinction. Topo-graphical properties of the response depend on thecontingencies. The force with which a lever ispressed, for example, is related to the force re-quired to operate the food dispenser. An initialmoderate force can be increased indefinitely, withinphysiological limits, by progressively requiringgreater forces. A complex topography can be"shaped" with a series of changing contingencies,called a program, each stage of which evokes aresponse and also prepares the organism to respondat a later stage. A shaping program can be me-chanically prescribed in advance, but the process ismost easily demonstrated when the experimenterimprovises contingencies as he goes.

The behaviors evoked by mazes, puzzle boxes,memory drums, and so on, are also shaped, but al-most always without specific programing of con-tingencies. The organism is usually exposed atonce to a set of /emi«aL£Qntingencies, for whichit possesses ho adequate behavior. Responses oc-cur, however—the rat explores the maze, the sub-ject guesses at the next nonsense syllable—andsome of these may be reinforced in ways whichlead at last to a terminal performance. What can

we conclude from the series of stages throughwhich this comes about?

Such data are usually plotted in so-called learn-ing curves showing, let us say, the times requiredto complete a task or the number of errors madein doing so, by trials. These are facts and in somesense quantifiable. From such a curve we maypredict within limits how another organism willbehave in similar circumstances. But the shape ofthe curve tells us little or nothing about_tlie-^proc-esses of conditioning and extinction- revealed in anoperant analysis. It merely describes the rathercrude overall effects of adventitious contingencies,and it often tells us more about the apparatus-orprocedure than about the organism. ^

Similar discrepancies appear in the analysis ofstimuli. In so-called stimulus-response theories, astimulus is broadly defined as something which cus-tomarily precedes a response—the eliciting stimulusin a conditioned reflex, the "cue" to more complexbehavior, or even an internal "drive state." Theterm is little more than a synonym for cause, andvarious relations between cause and effect are usu-ally not distinguished. The stimulus control of anoperant, on the other hand, has been carefully ana-lyzed. Although we can shape the topography ofa response without identifying or manipulating anyanterior stimulus, stimuli enter into a more com-plex type of contingency in which a response is re-inforced in the presence of a stimulus and is there-fore more likely to be emitted in its presence. Therelations among the three terms in this contingency—stimulus, response, and reinforcement—comprisea substantial field for investigation.

One property of the control acquired by a stimu-lus when a response is reinforced in its presence isshown in the so-called stimulus generalization gradi-ent. Hypothetical gradients in mental, neurologi-cal, or conceptual inner systems have been dis-cussed for years, but thanks to the work of Gutt-man (1963) and his students, and others, behavioralgradients are now directly observed. A pigeon, re-inforced when it pecks a circular key of a givencolor and size, will peck keys of other shapes,colors, or sizes at lower rates depending upon thedifferences in the properties. When the responseis reinforced in the presence of one property andextinguished in the presence of others—the well-known process of discrimination—a very sensitiveand powerful control is established. In a class-

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room demonstration a response is brought underthe control of a red as against a green key. Solong as the key is green, no response is made;when it turns red, the pigeon pecks it immediately.The power of the stimulus can be dramaticallyshown by changing from red to green just as thepigeon's beak moves toward the key. The peck-ing response will be interrup.t£fUn_jni4-air, eventhough stopping probably requires more energythan following through. Stimulus control can alsobe shaped by changing relevant stimuli in a pro-gram which leads the organism into subtle dis-criminations, often without "errors," as Terrace(1963) has recently shown. Very little of this isseen in traditional studies of sensory learning, how-ever. In using a classical multiple-choice appa-ratus, for example, the organism is exposed at onceto a set of terminal contingencies. Its progress to-ward an appropriate performance is represented ina curve showing, say, the number of errors madeor the times required to reach a criterion, over aseries of trials, but the dimensions of these meas-ures are again arbitrary, and the behavior is ob-viously the product of shifting. largely^_adverrtr-

jMuj__CQntingencies. ,,QClassical studies of Warning have emphasized the

process of acquisition, presumably because one caneasily see that an organism is doing something newor is responding to a new stimulus, but reinforce-ment is also responsible for the fact that an organ-ism goes on responding long after its behavior hasbeen acquired. The fact has usually been at-tributed to motivational variables, but an experi-mental analysis has shown that various schedulesof intermittent reinforcement are usually involved.The nature or quantity of reinforcement is oftenmuch less important than the schedule on which itis received. Programing is again important, formany schedules can take effect only when the or-ganism has passed through intervening contingen-cies. To take a very simple example—an appa-ratus which reinforces every hundredth responsewill have no effect at all if 100 responses are neveremitted, but by reinforcing every second, thenevery fifth, then every tenth response, and so on,waiting until the behavior is well developed at eachstage, we can bring the organism under the con-trol of the more demanding schedule. The patho-logical gambler and the dedicated scientist bothshow terminal behavior resulting from a special

history of reinforcement on a related ("variable-jratio") schedule—a history which society attemptsto prevent in the former case and encourage in thelatter.

The history which brings a complex terminalschedule into control is not, of course, visible inthe terminal performance. A scientist once bor-rowed an apparatus to demonstrate the use of amultiple fixed-interval fixed-ratio schedule in as-sessing the effects of certain drugs. When one ofthe pigeons lent with the apparatus was acciden-tally killed, he purchased another, put it into theapparatus, and was surprised to find that nothinghappened^'^vTe make the same mistake when weattempt to explain conspicuous effects of reinforce- M ,7 fment on human behavior by examining only currentschedulesT^ 01 /', f

Comptex terminal contingencies involving multi-ple stimuli and responses, in sequential or concur-rent arrangements, are often called problems. Anorganism is said to have solved such a problemwhen it comes under the control of the terminalcontingencies. Its capacity to respond appropri-ately under such contingencies must, however, bedistinguished from its capacity to reach themthrough a given series of intervening stages.Whether an organism can solve a problem in thissense is-as_mucbL a qaesfcien-of-the-program through ^, .which it passes—and the skill of the programmer f. ',who constructed it—as_o.l any so-called problem '-,,-,,,,solving ability. Whether an organism "can solve a .probTemTwithout the help of a prepared program v,^ ,., ,,depends on the behavior initially available and the y' /-<more or less accidental contingencies which follow/-;-' •»from it. Apparent differences in problem solvingability among species or among organisms of dif-ferent ages or other properties within a speciesmust be interpreted accordingly. Solving a prob-lem, like learning, is again often attributed to aninnec sysiem, although the supposed inner proc- ,,esses, like the facts they explain, are more complex.Those committed to sequestered faculties andthought processes are not likely to feel at home inan analysis of the behavior itself and may, there-fore, find it inacceptable as an alternative enter-prise.

STATISTICS

Another difficulty is methodological. Processestaking place in some inner system can usually be

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investigated only with "statistics." If learning isnever accurately represented in one performance,performances must be averaged. If statementsabout the inner system cannot be directly con-firmed, hypotheses must be set up, and theoremsdeduced and tested, following established practicesin logic and scientific method. If some propertiesof the inner system are meaningful only with re-spect to larger sets of facts, a procedure such asfactor analysis may be needed. It is not surpris-ing that research on this pattern has come to bejudged by the sophistication of its statistical andlogical techniques. Confidence in an experiment isproportional to the number of subjects studied, anexperiment is good only if properly "designed,"and results are significant only at a level deter-mined by special tests.

Much of this is lacking in the experimentalanalysis of behavior, where experiments are usuallyperformed on a few subjects, curves representingbehavioral processes are seldom averaged, the be-havior attributed to complex mental activity is ana-lyzed directly, and so on. The simpler procedureis possible because rate of responding and changesin rate can be directLy_ja]jserved, especially whenrepresented in cumulative records. The effect issimilar to increasing the resolving power of a micro-scope: A new subject matter is suddenly open todirect inspection. Statistical methods are unneces-sary. When an organism is showing a stable orslowly changing performance, it is for most pur-poses idle to stop to evaluate the confidence withwhich the next stage can be predicted. When avariable is changed and the effect on performanceobserved, it is for most purposes idle to prove sta-tistically that a change has indeed occurred. (It issometimes said in such a case that the organism is"used as its own control," but the expression, bor-rowed from a basically different methodology, ispotentially troublesome.) Much can be done in thestudy of behavior with methods of observation nomore sophisticated than those available to Fara-day, say, with his magnets, wires, and cells. Even-tually the investigator may move on to peripheralareas where indirect methods become necessary, butuntil then he must forego the prestige which at-taches to traditional statistical methods.

Some traditional uses must also be questioned.Learning curves remain inadequate no matter howsmooth they are made by averaging cases. Sta-

tistical techniques may eliminate noise, but the di-mensions are still faulty. A curve which enablesus to predict the performance of another organismdoes not therefore represent a basic process. More-over, curves which report changes in variables hav-ing satisfactory dimensions can often not be aver-aged. The idiosyncracies in a cumulative record donot necessarily show caprice on the part of the or-ganism or faulty technique on the part of the ex-perimenter. The complex system we call an organ-ism has an elaborate and largely unknown historywhich endows it with a certain individuality. Notwo organisms embark upon an experiment in pre-cisely the same condition nor are they affected inthe same way by the contingencies in an experi-mental space. (Most contingencies would not berepresentative if they were precisely controlled,and in any case are effective only in combinationwith the behavior which the organism brings to theexperiment.) Statistical techniques cannot elimi-nate this kind of individuality; they can only ob-scure and falsify it. An averaged curve seldomcorrectly represents any of the cases contributingto it (Sidman, 1960).

An analysis which recognizes the individuality ofthe organism is particularly valuable when contact ismade with other disciplines such as neurology, psy-chopharmacology, and psychotherapy, where idio-syncratic sets of variables must also be considered.The rigor of the analysis is not necessarily threat-ened. Operant methods make their own use ofGrand Numbers: Instead of studying l.,Q_QQ--rats""for1 hour each,._or.,,lQ_Q, rats for 10 hours each, the in-vestigator is likely to Siydy 1 rat for LOJXLJipurs.The procedure is not only appropriateto an enter-prise which recognizes individuality, it is at leastequally efficient in its use of equipment and of theinvestigator's time and energy. The ultimate testof uniformity or reproducibility is not to be foundin method but in the degree of control achieved, atest which the experimental analysis of behaviorusually passes easily.

The study of operant behavior also seldom fol-lows the "design of experiments" prescribed bystatisticians. A prior design in which variables aredistributed, for example, in a Latin square may bea severe handicap. When effects on behavior canbe immediately observed, it is most efficient to ex-plore relevant variables by manipulating them in animprovised and rapidly changing design. Similar

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practices have been responsible for the greater partof modern science. This is not, however, the tenorof R. A. Fisher's Design of Experiments, which, asLancelot Hogben (19S7) has said, gives the reader

the impression that recourse to statistical methods is pre-requisite to the design of experiments of any sort whatever.In that event, the whole creation of experimental scientistsfrom Gilbert and Hooke to J. J. Thomson and Morganhas been groaning and travailing in fruitless pain together;and the biologist of today has nothing to learn from well-tried methods which have led to the spectacular advancesof the several branches of experimental science during thelast three centuries [p. 29].

Statistics, like logic and scientific methodology ingeneral, emphasizes the verbal behavior of the_scj-entist: How reliable are his measures, how signifi-cant are the differences he reports, how confidentcan we be that what he says is true? His nonver-bal behavior is much less easily codified and ana-lyzed. In such considerations, what the scientistdoes takes second place to what he says. Yet thea priori manipulation of variables, guided by di-rectly observed effects, is superior to the a posteriorianalysis of covariation in many ways. It leadsmore rapidly to prediction and control and to prac-tical recombinations of variables in the study ofcomplex cases. Eventually, of course, the experi-menter must behave verbally. He must describewhat he has done and what he has seen, and hemust conduct his research with this obligation inmind. But a compulsive preoccupation with va-lidity or îgnificance^niay• T5erTnifntear to other,equally-impor-tanLohligations. ~f /f tJ^>

A nonstatistical strategy may also be recom-mended for its effect on the behavior of the in-vestigator, who is perhaps as strongly reinforcedduring a successful experiment as the organism hestudies. The contingencies to which he is sub-mitted largely determine whether he will continuein similar work. Statistical techniques often injecta destructive delay betweeiLlhe_cc>Bdirct of an ex-periniejiL_and the discovery of_the^-sigatficance' ofthe data—a fatal violation of a fundamental prin-ciple of reinforcement. The exceptional zeal whichhas often been noted in students of operant behav-ior is possibly attributable to the immediacy oftheir results.

THE CIRCUMVENTION OF AN OPERANT ANALYSIS

By accepting changes in rate of responding asbasic behavioral processes and by emphasizing en-

vironmental variables which can be manipulatedwith the help of automatic equipment, research onoperant behavior has been greatly simplified. Butit has not been made easy. Technical advanceshave been offset by the demand for incrjasjngjigor,by the probkrns_jvhjcJb~aJise ̂isnHatJLiime, an(j by the attack on more and morecomplex^rrangement5_qf interrelatedjjperants. Be-havior — human or otherwise — remains an extremelydiffiajlt__subjficL-Bifttter. It is not surprising thatpractices which seem to circumvent or simplify anoperant analysis are common. In particular, vertial

between subject and experimenter

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is widely used in lieu of the explicit arrangementof contingencies of reinforcement and the objectiverecording of behavior. The practice goes back tothe study of mental life and is still favored by psy-chologists who formulate their subject matter inmental terms, but it survives as if it were a_labor^ ̂ U ,'\

^saviag-deviee in many essentially behavioristic for- , <--mulations.

The manipulation of independent variables ap-pears to be circumvented when, instead of exposingan organism to a set of contingencies, the con-tingencies are simply described in "instructions."Instead of shaping a response, the subject is toldto respond in a given way. A history of reinforce-ment or punishment is replaced by a promise orthreat: "Movement of the lever will sometimes op-erate a coin dispenser" or ". . . deliver a shock toyour leg." A schedule of positive or negative rein-forcement is described rather than imposed: "Everyresponse to the right lever postpones the shock butincreases the number of responses to the left leverrequired to operate the coin dispenser." Insteadof bringing the behavior under the control of astimulus, the subject is told to behave as if a dis-crimination had been established: "Start when thelight goes on, stop when it goes off." Thus in-structed, the subject is asked either to behave ap-propriately or to describe behavior he might emitunder such circumstances. The scope of the verbalsubstitute can be estimated by considering how anonverbal organism, human or otherwise, could besimilarly "instructed."

Descriptions of contingencies are, of course, ofteneffective. Hypothetical consequences are commonlyused for practical purposes ("Will you do the jobif I pay^you $50?" or "How would you feel aboutgoing if I told you that X would be there?"), and


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the subject is worth studying. Verbal instructionmay be defended when the resulting behavior is notthe primary object of interest; for example, the ex-perimenter may show a subject how to operate apiece of equipment rather than shape his behaviorthrough reinforcement so long as he is not con-cerned with the acquisition of the response butwith what happens to it later. ^Verbal communica-tion is not, however, a substitute, for the arrange-ment and manipulation of variable^! ' ^

There is no reason why a description of contin-gencies of reinforcement should have the same ef-fect as exposure to the contingencies. A subjectcan seldom accurately describejthe way in which hehas_a^±uallyJlBE£iEîffT5rced. Even when he hasbeen trained to identify a few simple contingencies,

f;'' 'hej^nnot-ihen. describe a ne,w__c.Qn,tinge,ncy, particu-larly when it is complex. We can scarcely expecthim, therefore, to react appropriately to descrip-tions by the experimenter. Moreover, the verbalcontingencies between subject and experimentermust be taken into account. Instructions must insome way promise___or ^threaten xortsequejices not

_ êrniane-tQjhe-«5Epmincnt if the subject is to fol-low them.

The other major task in an operant analysis mayseem to be circumvented when, instead of record-ing behavior so that rate or probability of responsecan be observed or inferred, the experimenter sim-ply asks the subject to evaluate his tendency to re-spond or to express his preference for respondingin one way rather than another. The subject may

....do so by describ,ingîs_"intenJ;i0ns'J--er__it.plans^.,prby reporting "expectations" regarding the conse-quences of an action. Such behavior may be worth

f, ^ investigating, but it is not a substitute for the be-havior observed in an operant analysis. Only inthe simplest cases can a person correctly describehis ongoing behavior. The difficulty is not lin-guistic, for he may be given an operandum and per-mitted to "model" the behavior—for example, togenerate a cumulative record. It is practically im-possible to construct a curve closely resembling thecurve one would generate if actually exposed to aspecified set of contingencies, or even a curve onehas already generated when so exposed. Changesin rate of responding are.'not easy to__dfiscribe.

^They necessarily take place m time, and even a' ' second observer cannot "see" them until they have

been reduced to graphic form. The subject's ownbehavior presents other difficulties, which are notovercome by permitting him to be less specific. Ifwe ask him to say simply whether he will be moreor less likely to respond or will respond more orless rapidly, we have increased his chances of beingright only by asking him to say less. Any report,no matter how specific, is also subject to the verbalcontingencies which induce him to describe his be-havior and possibly by similar contingencies else-where which may classify his behavior, for exam-ple, as right or wrong.

Verbal substitutes for arranged or observed vari-ables may be used at different points in an investi-gation: Contingencies may be described and thesubject's behavior then actually observed, the sub-ject may be exposed to a set of contingencies andthen asked to evaluate the nature or probability ofhis responses, and so on. Similar practices areused to evaluate the reinforcing or aversive proper-ties of a given event or procedure, to predict theoutcome of several variables operating at once, andso on, and are subject to the same criticism.

To those interested primarily in mental processes,verbal communication may not be an attemptedcircumvention or shortcut. -jQnjth_e contrary, anoperant analy_sjs_jria;y_ seem to be the long jwayaromid. The position is sometimes defended by in-sisting that the student of behavior always beginswith an interest in mental life—possibly his own—and designs his experiments essentially to test hy-potheses about it. Whatever the case may oncehave been, operant research has long since passedthe point at which the experimenter can be guidedby considering possible effects of variables on him-self. The introspective vocabulary used in circum-venting an experimental analysis is hopelessly in-adequate for the kinds of facts currently under in-vestigation. If one field is to borrow from theother, the debt will henceforth almost certainly bein the other dixectipn: From the study of the be- J»'[ n <*•RaVioT'oTother organisms, the experimenter is mostlikely to come to understand himself. In sometheories of knowledge, introspective observationsmay be regarded as primary data, but in an analy-sis of behavior they are a form of theorizing whichis not required or necessarily helpful (Skinner,1963).

/A


FORMAL ANALYSES OF CONTINGENCIESOF REINFORCEMENT

The consequences of action and their effects onbehavior also enter into theories of probability,decision making, conflict, and games. The classicalurn containing a given proportion of black andwhite balls may, like other sample spaces, be ana-lyzed without reference to behavior, but it wouldbe of little interest if the consequences of drawingeither a black or white ball were not in some wayreinforcing. (There has always been a close con-nection between probability theory and jambling,where every play is punishecTlo the'extent of itscost and some plays are also reinforced.) Prob-ability theory also often takes into account the factthat this reinforcement will occur on an intermit-tent schedule, and that as a consequence the drawerwill experience a given subjective or felt probabil-ity, or exhibit a given probability of drawing again.

The probability that the drawer will draw againis usually assumed to be related to the probabilityfunction of the sample space. A relation is im-plied when it is said that a subject who has suffi-cient knowledge about a given system, possibly in-ferred from his experience with it, can behave "ra-tionally." A relation is also implied when it isargued that irrational behavior requires explana-tion. For example, the fact that intermittenl_re-inforcement raises the probability of respondingabdve the value generated when all responses arereinforced has recently occasioned surprise (Law-rence & Festinger, 1962), Any such relation is, ofcourse, an empirical fact, to be determined experi-mentally. Standard operant equipment can be usedto set up contingencies of reinforcement which havethe effect of classical sample spaces. A schedulecould, if necessary, be programed by actually draw-ing balls from an urn. An organism can then beexposed to the schedule and the effect on its be-havior observed. In such a procedure the statusof the probability function of the sample space (theschedule of reinforcement arranged by the pro-graming equipment) is clear. The probability thatthe organism will respond at a given time is in-ferred from its rate.

The relation between the two probabilities iscomplicated by the fact that rate of responding un-der a given schedule depends, as we have seen, onprevious exposure to the schedule. When intro-duced into an experimenfar"spacT for the first time,

an organism may be said to show a certain "priorprobability" of responding—the so-called operaTrtlevel. A first response is or is not reinforced, andthe rate rises or falls accordingly. This brief his-tory contributes to what is now a different situa-tion. When the organism responds again and isagain possibly reinforced, the situation changes stillmore substantially. A given set of contingenciesyields a performance which combines with the pro-graming equipment to generate other contingencieswhich in turn generate other performances, andso on.

Many of these interactions between behavior andprograming equipment have been carefully studied.Under a variable-interval schedule of reinforcement,for example, the organism often responds at anearly constant rate for long periods of time. Allreinforcements therefore occur when it is respond-ing at that rate, although this_cpndition_is not speci-fied by the equipment. The rate becomes a dis-criminative and, in turn, a reinforcing stimulus,which opposes any change to a different rate—suchas would otherwise be induced by, say, a psycho-pharmacological agent. As another example, whenonly the first response after the passage of a fixedinterval of time is reinforced, the organism comesto exhibit a fairly stable performance in which thenumber of responses emitted during an interval ap-proaches constancy. The organism is then beingreinforced not only after a constant interval of timebut after emitting a. constant number.- of—responses.The latter condition, which is 'not specified by theequipment, is characteristic of a fixed-ratio sched-ule, and it generates a much higher rate of respond-ing. As rapid responding breaks through, the sta-bility of the fixed-interval performance is destroyed,the number of responses per reinforcement is nolonger constant and a stable interval performanceis restored, as another cycle begins (Ferster & Skin-ner, 19S7).

A third example is closer to probability theory.A schedule in which a response is reinforced uponcompletion of an appreciable fixed or variable num-ber of responses must often be reached through aprogram, as we have seen. The number must firstbe small, but the schedule favors reinforcementwhen the organism is responding at a high rate,and it is soon possible to/-stretch" the requirjj.rrj.ent.When a hungry rat is reinforced with food for run-ning in a wheel, the required distance can be in-


creased until more energy is consumed than is avail-able in the food received (Skinner, 1938). The be-havior of the gambler, which almost always showsa similar "negative utility," is the result of thesame kind of stretchingr The variable-ratio sched-ules inherent in gambling systems maintain behav-ior only after a history of reinforcement in whichbehavior has combined with the programing equip-ment to generate certain powerful terminal contin-gencies.

In summary, a scheduling system has no effectuntil an organism is exposed to it, and it then nolonger fully determines the contingencies. Stillother interactions between equipment and perform-ance arise when a second response is introduced inorder to study choice or decision making. Sup-pose, for example, that a subject may press eitherof two keys, A and B, on which reinforcementsare independently scheduled. The performance oneither key can be accounted for only by examiningthe combined action of equipment and earlier per-formances on both keys. For example, if reinforce-ments are programed on interval schedules, re-sponding to A after B is more likely to be rein-forced than responding to B after B since the equip-ment may have set up a reinforcement on A whilea response was being made to B. The behavior ofchanging from A to B or from B to A may be fa-vored to the point at which the performance be-comes a simple alternation (Skinner, 1950). Thisyields the same rate on both keys, even though theschedules may be substantially different. The in-teraction may be corrected with a "change-over de-lay" in which, for example, a response to B is notreinforced if a response to A has been made duringthe preceding second, or in which the first responseto either key after changing over is never rein-forced (Herrnstein, 1961). The contingencies onthe two levers are nevertheless still subject to otherinteractions. (A word of caution: By manipulatingthe change-over delay and other characteristics ofthe schedules it may be possible to generate ratesof responding on the two keys which would be pre-dicted from ^me_ hypothesis of rationality or util-._.

r ity. It is tempting to regard these as optimal con-ditions and possibly to stop the research when they

have been discovered.)Interactions between performance and program-

ing system are still more complex if the perform-ance changes the system, as in the so-called "ad-justing" and "interlocking" schedules (Ferster &

Skinner, 19S7). Many examples are to be found inthe theory of games and conflict, where the behav-ior of onejorganism alters the contingencies affect-ing 'another, and vice versa. The rules of any gamecan be represented by programing equipment whichis subject to modification by the performances ofthe players, but the actual contingencies of rein-forcement are still more complex, for they includeconditions not specified by the equipment but gen-erated by the earlier performances of all parties.

(That there is a limitation inherent in formalanalyses is suggested by the fact that mathemati-cal inquiries into probability, decision making, con-flict, and games confine themselves almost exclu-sively to ratio schedules. The contingencies de-fined in sample spaces and rules practically alwaysspecify reinforcement as a function of a number ofresponses, a restraint traceable perhaps to prac-tical issues involving winning, losing, and ultimateutility. Yet the interactions between equipmentand performance are the same when reinforcementis scheduled by clocks or speedometers rather thanby counters, and the same processes are involved,as an experimental analysis has abundantly shown.)

The formal properties of sample spaces, like thevarious conditions under which choices are made,games played, or conflicts resolved, may be ana-lyzed without taking behavior into account or, atmost, by assuming selected performances. Thoseinterested primarily in a formal analysis are likelyto approach behavior, if at all, by setting up hy-potheses. The research which follows has the na-ture of hypothesis testing and is wasteful if thedata collected lose their value when a hypothesishas been disproved or abandoned for other reasons.An experimental analysis of the behavior gener-ated by the contingencies in sample spaces may beconducted without guessing at the results. ^- •

THE USE OF FORMAL ANALYSES

Formal analyses of contingencies of reinforce-ment are related to behavior in another way whenthey are used as guides. The behavior of a personwho has calculated his chances, compared alterna- ; ,tives, or considered the consequences of a move isdifferent from, and usually more effective than, thebehavior of one who has merely been exposed tothe unanalyzed contingencies. The formal analysisfunctions as a discriminative stimulus. When sucha stimulus is perfectly correlated with reinforce-

OPEEANT BEHAVIOR 513

ment, the behavior under its control is maximallyreinforced. On an interval schedule and in the ab-sence of related stimuli, an organism emits unrein-forced or "wasted" responses, but if the apparatuspresents a conspicuous stimulus whenever a rein-forcement becomes available, the organism even-tually responds only in the presence of that stimu-lus and no responses are wasted. Clocks providestimuli of this sort in connection with events oc-curring on interval schedules and are built andused for just that reason. Stimuli less closely cor-related with reinforcement yield lesser improve-ments in efficiency. If a given setting on a clockcannot be_ sharply-discriminated, for example, someresponses will be emitted prior to "the time to re-spond" and some potentially effective responsesmay be delayed, but performance is neverthelessimproved. A speedometer serves a similar func-tion when reinforcement depends on a given rateof responding.

Formal analyses of sample spaces serve the samefunction as imprecise clocks and speedometers.Not every response under their control is rein-forced, but there is still a net gain. When a manlearns to play poker under the contingencies ar-ranged by the cards and rules, his sampling of thepossible contingencies is necessarily limited, evenin prolonged play. He will play a more successfulgame, and after a much shorter history, if he con-sults a table showing his chances of success in mak-ing given plays. The contingencies in poker alsodepend upon the behavior of other players, andprior stimuli correlated with that behavior aretherefore also useful. They are particularly im-portant in such a game as chess.._Chess playingmay be shaped by the unanalyzed contingenciesgenerated by the rules of the game and by the per-formances of opponents, but a player will play abetter game, after a shorter history, if he can con-sult standard gambits, defenses, end games, and soon, which show some of the likely consequences ofgiven moves.

A stimulus commonly correlated with reinforce-ment and hence useful in improving efficiency is therecord left by previous behavior. When a manfinds his way from one place to another, he mayleave traces which prove useful when he goes thatway again. He wears a path which supplementsthe change taking place in his behavior and mayeven be useful to others who have not gone thatway before. A path need not be constructed be-

cause it serves this function, but the advantagesgained may reinforce the explicit leaving of traces.A trail is "blazed," for example, precisely becauseit is more easily followed. Comparable reinforcingadvantages have led men to construct pictures andverbal descriptions of paths.

Many proverbs and maxims are crude descrip-tions of contingencies of social or nonsocial rein-forcement, and those who observe them come un-der a more effective control of their environment.Rules of grammar and spelling bring certain verbalcontingencies of reinforcement more forcefully intoplay. Society codifies its ethical, legal, and re-ligious practices so that by following a code the in-dividual may emit behavior appropriate to socialcontingencies without having been directly exposedto them. Scientific laws serve a similar functionin guiding the behavior of scientists.

A person could, of course, construct rules ofgrammar and spelling, maxims for effective per-sonal conduct, tables of probabilities in the gameshe plays, and scientific laws for his own use, butsociety usually analyzes the predictable contin-gencies for him. He constructs comparable stimulifor himself when he makes resolutions, announcesintentions, states expectations, and formulatesplans. The stimuli thus generated control his be-havior most effectively when they are external,conspicuous, and durable—when the resolution isposted or the plan actually drafted in visible form—but they are also useful when created upon oc-casion, as by recalling the resolution or reviewingthe plan. The gain from any such discriminativestimulus depends upon the extent to which it cor-rectly represents the contingencies which led to itsconstruction.

Discriminative stimuli which improve the effi-ciency of behavior under given contingencies of re-inforcement are important, but they must not beconfused with the contingencies themselves, northeir effects with the effects of those contingencies.The behavior of the poker player who evaluates hischances before making a given play merely resem-bles that of the player whose behavior has beenshaped by prolonged exposure to the game. Thebehavior of one who speaks correctly by applyingthe rules of a grammar merely resembles the be-havior of one who speaks correctly from long ex-perience in a verbal community. The efficiencymay be the same, but_the controlling variables aredifferent and the b~ehaviors are therefore different.


Nothing which could be called following a plan orapplying a rule is observed when behavior is aproduct of the contingencies alone. To say that"the child who learns a language has in some senseconstructed the grammar for himself" (Chomsky,1959) is as misleading as to say that a dog whichhas learned to catch a ball has in some sense con-structed the relevant part of the science of me-chanics. Rules can be extracted from the rein-forcing contingencies in both cases, and once inexistence they may be used as guides. The directeffect of the contingencies is of a different nature.

The distinction bears on two points already made.In the first place, the instructions used in circum-venting an operant analysis also have the status ofprior stimuli associated with hypothetical or realcontingencies of reinforcement, but behavior in re-sponse to them is not^the_behavior_generaled byexposure to the contingencies—themselves evenwhen, on rare "occasions, the two are similar.When subjects report that they understand in-structions and hence know what to expect, it doesnot follow that comparable reportable states aregenerated by the contingencies themselves. In thesecond place—to return at last to the point withwhich this paper began—when a man explicitlystates his purpose in acting in a given way he may,indeed, be constructing a "contemporary surrogateof future consequences" which will affect subse-quent behavior, possibly in useful ways. It doesnot follow, however, that the._b.ghavior generatedby the consequences alone, js-under the- control ofany comparable pjrior_stirnulus, such as a felt pur-pose or intention.

THE CONTINGENCIES OF REINFORCEMENT

The Law of Effect specifies a simple temporalorder of response and consequence—the relationimplied by the term operant. The contingenciesof reinforcement currently under investigation aremuch more complex. Reinforcement may be con-tingent, not only on the occurrence of a response,but on special features of its topography, on thepresence of prior stimuli, and on scheduling sys-tems. An adequate analysis must also reach intothe traditional fields of motivation and emotion todetermine what is reinforcing and under what con-ditions. Interrelated systems of operants raiseother problems.

The techniques of an experimental analysis havefortunately remained commensurate with the in-

creasing complexity of the subject. Rate of re-sponding has come to be examined over a muchwider range and in much greater detail. Cumula-tive records have been supplemented by distribu-tions of interresponse times and, very recently, by"on-line" computer processing. Better measures oftopographical properties have become available. In-dependent variables have been effectively controlledover a wider range and in more complex patterns.Arrangements of operants resembling many of thebehaviors attributed to higher mental processeshave been successfully constructed and studied.

The experimental space has been improved. Briefdaily experimental periods have given way to con-tinuous observation for many hours, days, weeks,or even months. More of the behavior exhibited inthe experimental space has been controlled, re-corded, and analyzed. Total control of the envi-ronment from birth is within range. As in thestudy of animal behavior in general, the hundredsof thousands of extant species arc still far fromadequately sampled, but problems of instrumenta-tion have been solved for a fairly wide range ofanatomical and behavioral differences.

The contingencies of reinforcement which defineoperant behavior are important in the analysis ofvariables of other sorts. The stimulus control ofbehavior is central to a kind of nonverbal psycho-physics, where interest may be primarily in the ac-tion of receptor mechanisms. Operant techniquesarc important in defining the behavioral effectsof physiological variables—surgical, electrical, andchemical—in specifying what aspects of behaviorare to be attributed to hereditary endowment, intracing features of mature behavior to early envi-ronment, and so on. They are important in clari-fying the nature of defective, retarded, or psychoticbehavior. As Lindsley (1963) has pointed out, theimportant thing about a psychotic is often not whathe is doing but whatjie is not doing, and in such acase it is important to be able to predict normalperformances under standard conditions.

Contingencies of reinforcement are also valuablein interpreting behavior not easily submitted to alaboratory analysis. Verbal behavior, for exam-ple, can be defined just in terms of its contingen-cies: Its special characteristics are derived from thefact that reinforcement is mediated by other organ-isms. In education the.-instructional programing ofreinforcement is the raison d'etre of teaching ma-


chines, the future of which is much brighter thancurrent activities may suggest. It is too early topredict the effect of comparable analyses in otherbranches of the social sciences—for example, eco-nomics and government—but if the history ofphysical technology is any guide, the knowledgeand skills derived from an experimental analysiswill become increasingly important.

In short, in the field of human behavior as awhole, the contingencies of reinforcement which de-fine operant behavior are widespread if not ubiqui-tous. Those who are sensitive to this fact aresometimes embarrassed by the frequency with whichthey see reinforcement everywhere, as Marxists seeclass struggle or Freudians the Oedipus relation.Yet the fact is that reinforcement is extraordinarilyimportant. That is why it is reassuring to recallthat its place was once takenJryjhe concept of jnir-pose; no one is likely jp_object to a_search_for pur-pose in every_Juiirian act. The difference is that we

-ape^nCwTn a position to search effectively. In itsvery brief history, the study of operant behaviorhas clarified the nature of the relation between be-havior and its consequences and has devised tech-niques which apply the methods of a natural sci-ence to its investigation.

REFERENCES

ADAMS, D. K. Experimental studies of adaptive behaviorin cats. Comp. Psychol. Monogr., 1929, 6(1, Whole No.2 7 ) .

BERNATOWICZ, A. I. Teleology in science teaching. Science,1958, 128, 1402-1405.

CHOMSKY, N. Review of Skinner's Verbal behavior. Lan-guage, 1959, 35, 26-58.

FERSTER, C. B., & SKINNER, B. F. Schedules of reinforce-ment. New York: Appleton-Century-Crofts, 1957.

GRINDLEY, G. C. The formation of a simple habit in guineapigs. Brit. J. Psychol, 1932, 23, 127-147.

GUTTMAN, N. Laws of behavior and facts of perception.In S. Koch (Ed.), Psychology: A study of a science.Vol. S. New York: McGraw-Hill, 1963. Pp. 114-178.

HERRNSTEIN, R. J. Relative and absolute strength of re-sponse as a function of frequency of reinforcement. /.exp. Anal. Behav., 1961, 4, 267-272.

HOOBEN, L. Statistical theory. London: Norton, 1957.IVANOV-SMOLENSKY, A. G. On methods of examining con-

ditioned food reflexes in children and in mental disorders.Brain, 1927, 50, 138-141.

LAWRENCE, D. H., & FESTINGER, L. Deterrents and rein-forcement. Stanford, Calif.: Stanford Univer. Press,1962.

LINDSLEY, O. R. Direct measurement and functional defi-nition of vocal hallucinatory symptoms. J. nerv. ment.Dis., 1963, 136, 293-297.

MILLER, S., & KONORSKI, J. Sur une forme parliculiere desreflexes conditionnels. CR Soc. Biol., Paris, 1928, 99,1155-1157.

SIDMAN, M. Avoidance conditioning with brief shock andno exteroccptive warning signal. Science, 1953, 118, 157-158.

SIDMAN, M. Tactics of scientific research. New York:Basic Books, 1960.

SKINNER, B. F. Drive and reflex strength: II. J. gen. Psy-chol,, 1932, 6, 38-48.

SKINNER, B. F. Two types of conditioned reflex: A replyto Konorski and Miller. J. gen. Psychol., 1937, 16, 272-279.

SKINNER, B. F. Behavior of organisms. New York: Ap-pleton-Century-Crofts, 1938.

SKINNER, B. F. Are theories of learning necessary? Psy-chol. Rev., 1950, 57, 193-216.

SKINNER, B. F. Verbal behavior. New York: Appleton-Century-Crofts, 1957.

SKINNER, B. F. Behaviorism at fifty. Science, 1963, 134,566-602.

TERRACE, H. S. Discrimination learning with and without"errors." /. exp. Anal. Behav., 1963, 6, 1-27.

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OPERANT BEHAVIOR1 - Stoastoa.usp.br/vahs/files/1/16172/Skinner, B. F. Operant...OPERANT BEHAVIOR1 B. F. SKINNER Harvard University W E are interested in the behavior of an organism