b. f. skinner - a case history in scientific method (1956)

A CASE HISTORY IN SCIENTIFIC METHOD1

B. F. SKINNER

Harvard University

IT has been said that college teaching is the onlyprofession for which there is no professionaltraining, and it is commonly argued that this is

because our graduate schools train scholars andscientists rather than teachers. We are more con-cerned with the discovery of knowledge than withits dissemination. But can we justify ourselvesquite so easily? It is a bold thing to say that weknow how to train a man to be a scientist. Scien-tific thinking is the most complex and probably themost subtle of all human activities. Do we actuallyknow how to shape up such behavior, or do wesimply mean that some of the people who attendour graduate schools eventually become scientists?

Except for a laboratory course which acquaintsthe student with standard apparatus and stand-ard procedures, the only explicit training in scien-tific method generally received by a young psy-chologist is a course in statistics—not the intro-ductory course, which is often required of so manykinds of students that it is scarcely scientific atall, but an advanced course which includes "modelbuilding," "theory construction," and "experimen-tal design." But it is a mistake to identifyscientific practice with the formalized construc-tions of statistics and scientific method. Thesedisciplines have their place, but it does not coin-cide with the place of scientific research. Theyoffer a method of science but not, as is so oftenimplied, the method. As formal disciplines theyarose very late in the history of science, and moslof the facts of science have been discovered withouttheir aid. It takes a great deal of skill to fit Fara-day with his wires and magnets into the picturewhich statistics gives us of scientific thinking. Andmost current scientific practice would be equallyrefractory, especially in the important initial stages.It is no wonder that the laboratory scientist ispuzzled and often dismayed when he discovers howhis behavior has been reconstructed in the formalanalyses of scientific method. He is likely to pro-

1 Address of the President at the Eastern PsychologicalAssociation meetings in Philadelphia, April 1955.

test that this is not at all a fair representation ofwhat he does.

But his protest is not likely to be heard. Forthe prestige of statistics and scientific methodologyis enormous. Much of it is borrowed from the highrepute of mathematics and logic, but much of itderives from the flourishing state of the art itself.Some statisticians are professional people employedby scientific and commercial enterprises. Some areteachers and pure researchers who give their col-leagues the same kind of service for nothing—orat most a note of acknowledgement. Many arezealous people who, with the best of intentions, areanxious to show the nonstatistical scientist how hecan do his job more efficiently and assess his resultsmore accurately. There are strong professionalsocieties devoted to the advancement of statistics,and hundreds of technical books and journals arepublished annually.

Against this, the practicing scientist has verylittle to offer. He cannot refer the young psycholo-gist to a book which will tell him how to find outall there is to know about a subject matter, how tohave the good hunch which will lead him to devisea suitable piece of apparatus, how to develop anefficient experimental routine, how to abandon anunprofitable line of attack, how to move on mostrapidly to later stages of his research. The workhabits which have become second nature to himhave not been formalized by anyone, and lie mayfeel that they possibly never will be. As Richter(5) has pointed out, "Some of the most importantdiscoveries have been made without any plan ofresearch," and "there are researchers who do notwork on a verbal plane, who cannot put into wordswhat they are doing."

If we are interested in perpetuating the practicesresponsible for the present corpus of scientificknowledge, we must keep in mind that some veryimportant parts of the scientific process do not nowlend themselves to mathematical, logical, or anyother formal treatment. We do not know enoughabout human behavior to know how the scientistdoes what he does. Although statisticians and

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99? THE AMERICAN PSYCHOLOGIST

melhodologists may seem to tell us, or at leastimply, how the mind works—how problems arise,how hypotheses are formed, deductions made, andcrucial experiments designed—we as psychologistsare in a position to remind them that they do nothave methods appropriate to the empirical observa-tion or the functional analysis of such data. Theseare aspects of human behavior, and no one knowsbetter than we how little can at the moment besaid about them.

Some day we shall be better able to express thedistinction between empirical analysis and formalreconstruction, for we shall have an alternative ac-count of the behavior of Man Thinking. Suchan account will not only plausibly reconstruct whata particular scientist did in any given case, it willpermit us to evaluate practices and, I believe, toteach scientific thinking. But that day is somelittle distance in the future. Meanwhile we canonly fall back on examples.

Some time ago the director of Project A of theAmerican Psychological Association asked me todescribe my activities as a research psychologist.I went through a trunkful of old notes and recordsand, for my pains, reread some of my earlier publi-cations. This has made me all the more aware ofthe contrast between the reconstructions of for-malized scientific method and at least one case ofactual practice. Instead of amplifying the pointsI have just made by resorting to a generalized ac-count which is not available, I should like to discuss

FIG. i.

FIG. 2.

a case history. It is not one of the case historieswe should most like to have, but what it lacks inimportance is perhaps somewhat offset by accessi-bility. I therefore ask you to imagine that youare all clinical psychologists—a task which becomeseasier and easier as the years go by—while I sitacross the desk from you or stretch out upon thiscomfortable leather couch.

The first thing I can remember happened whenI was only twenty-two years old. Shortly after Ihad graduated from college Bertrand Russell pub-lished a series of articles in the old Dial magazineon the epistemology of John B. Watson's Be-haviorism. I had had no psychology as an under-graduate but I had had a lot of biology, and two ofthe books which my biology professor had put intomy hands were Loeb's Physiology of the Brain andthe newly published Oxford edition of Pavlov'sConditioned Reflexes. And now here was Russellextrapolating the principles of an objective formula-tion of behavior to the problem of knowledge!Many years later when I told Lord Russell that hisarticles were responsible for my interest in behavior,he could only exclaim, "Good Heavens! I hadalways supposed that those articles had demolishedBehaviorism!" But at any rate he had taken Wat-son seriously, and so did I.

When I arrived at Harvard for graduate study,the' air was not exactly ful l of behavior, but WalterHunter was coming in once a week from Clark Uni-versity to give a seminar, and Fred Keller, also agraduate student, was an expert in both the tech-nical details and the sophistry of Behaviorism.

A CASE HISTORY IN SCIENTIFIC METHOD 223

Many a time he saved me as I sank into the quick-sands of an amateurish discussion of "What is animage?" or "Where is red?" I soon came into con-tact with W. J. Crozier, who had studied underLoeb. It had been said of Loeb, and might havebeen said of Crozier, that he "resented the nervoussystem." Whether this was true or not, the factwas that both these men talked about animal be-havior without mentioning the nervous system andwith surprising success. So far as I was concerned,they cancelled out the physiological theorizing ofPavlov and Sherrington and thus clarified what re-mained of the work of these men as the beginningsof an independent science of behavior. My doctoralthesis was in part an operational analysis of Sher-rington's synapse, in which behavioral laws weresubstituted for supposed states of the central nerv-ous system.

But the part of my thesis at issue here was ex-perimental. So far as I can see, I began simply bylooking for lawful processes in the behavior of theintact organism. Pavlov had shown the way; butI could not then, as I cannot now, move without ajolt from salivary reflexes to the important businessof the organism in everyday life. Sherrington andMagnus had found order in surgical segments of theorganism. Could not something of the same sortbe found, to use Loeb's phrase, in "the organism asa whole"? I had the clue from Pavlov: controlyour conditions and you will see order.

It is not surprising that my first gadget was asilent release box, operated by compressed air anddesigned to eliminate disturbances when introducinga rat into an apparatus. I used this first in study-ing the way a rat adapted to a novel stimulus. Ibuilt a soundproofed box containing a specially

FIG. 3.

FIG. 4.

structured space. A rat was released, pneumatically,at the far end of a darkened tunnel from which itemerged in exploratory fashion into a well-lightedarea. To accentuate its progress and to facilitaterecording, the tunnel was placed at the top of aflight of steps, something like a functional Parthe-non (Figure 1). The rat would peek out from thetunnel, perhaps glancing suspiciously at the one-way window through which I was watching it, thenstretch itself cautiously down the steps. A softclick (carefully calibrated, of course) would causeit to pull back into the tunnel and remain there forsome time. But repeated clicks had less and lessof an effect. I recorded the rat's advances andretreats by moving a pen back and forth across amoving paper tape.

The major result of this experiment was thatsome of my rats had babies. I began to watchyoung rats. I saw them right themselves and crawlabout very much like the decerebrate or thalamiccats and rabbits of Magnus. So I set about study-ing the postural reflexes of young rats. Here was afirst principle not formally recognized by scientificmethodologists: When you run onto something in-teresting, drop everything else and study it, I toreup the Parthenon and started over.

If you hold a young rat on one hand and pull itgently by the tail, it will resist you by pulling for-ward and then, with a sudden sharp spring whichusually disengages its tail, it will leap out into space.

224 THE AMERICAN PSYCHOLOGIST

FIG. S.

I decided to study this behavior quantitatively. Ibuilt a light platform covered with cloth and mountedit on tightly stretched piano wires (Figure 2 ) , Herewas a version of Sherringon's torsion-wire myograph,originally designed to record the isometric contrac-tion of the tibialis anticus of a cat, but here adaptedto the response of a whole organism. When thetail of the young rat was gently pulled, the ratclung to the cloth floor and tugged forward. Byamplifying the fine movements of the platform, itwas possible to get a good kymograph record of thetremor in this motion and then, as the pull againstthe tail was increased, of the desperate spring intothe air (Figure 3).

Now, baby rats have very little future, except asadult rats. Their behavior is literally infantile andcannot be usefully extrapolated to everyday life.But if this technique would work with a baby, whynot try it on a mature rat? To avoid attachinganything to the rat, it should be possible to record,not a pull against the substrate, but the ballisticthrust exerted as the rat runs forward or suddenlystops in response to my calibrated click. So, in-voking the first principle of scientific practice again,I threw away the piano-wire platform, and built arunway, eight feet long. This was constructed oflight wood, in the form of a U girder, mountedrigidly on vertical glass plates, the elasticity ofwhich permitted a very slight longitudinal move-ment (Figure 4). The runway became the floor ofa long tunnel, not shown, at one end of which Iplaced my soundless release box and at the other

end myself, prepared to reinforce the rat for com-ing down the runway by giving it a bit of wet mash,to sound a click from time to time when it hadreached the middle of the runway, and to harvestkymograph records of the vibrations of the sub-strate.

Now for a second unformalized principle ofscientific practice: Some ways of doing researchare easier than others. I got tired of carrying therat back to the other end of the runway. A backalley was therefore added (Figure 5). Now therat could eat a bit of mash at point C, go downthe back alley A, around the end as shown, and backhome by runway B. The experimenter at E couldcollect records from the kymograph at D in com-fort. In this way a great many records were madeof the forces exerted against the substratum as ratsran down the alley and occasionally stopped deadin their tracks as a click sounded (Figure 6).

There was one annoying detail, however. Therat would often wait an inordinately long time at Cbefore starting down the back alley on the nextrun. There seemed to be no explanation for this.When I timed these delays with a stop watch, how-ever, and plotted them, they seemed to show orderlychanges (Figure 7) . This was, of course, the kindof thing I was looking for. I forgot all about themovements of the substratum and began to run"rats for the sake of the delay measurements alone.But there was now no reason why the runway hadto be eight feet long and, as the second principlecame into play again, I saw no reason why the ratcould not deliver its own reinforcement.

A new apparatus was built. In Figure 8 we seethe rat eating a piece of food just after completinga run. It produced the food by its own action. Asit ran down the back alley A to the far end of therectangular runway, its weight caused the wholerunway to tilt slightly on the axis C and this move-ment turned the wooden disc D, permitting a pieceof food in one of the holes around its perimeter todrop through a funnel into a food dish. The foodwas pearl barley, the only kind I could find in thegrocery stores in reasonably uniform pieces. Therat had only to complete its journey by coming

FIG. 6.


down the home stretch B to enjoy its reward. Theexperimenter was able to enjoy his reward at thesame time, for he had only to load the magazine,put in a rat, and relax. Each tilt was recorded ona slowly moving kymograph.

A third imformalized principle of scientific prac-tice: Some people are lucky. The disc of woodfrom which I had fashioned the food magazine wastaken from a store room of discarded apparatus.It happened to have a central spindle, which for-tunately I had not bothered to cut off. One day itoccurred to me that if I wound a string around thespindle and allowed it to unwind as the magazinewas emptied (Figure 9), I would get a differentkind of record. Instead of a mere report of theof the up-and-down movement of the runway, as aseries of pips as in a polygraph, I would get a curve.And I knew that science made great use of curves,although, so far as I could discover, very little ofpips on a polygram. The difference between theold type of record at A (Figure 10) and the new atB may not seem great, but as it turned out thecurve revealed things in the rate of responding, andin changes in that rate, which would certainly other-wise have been missed. By allowing the string tounwind rather than to wind, I had got my curvein an awkward Cartesian quadrant, but that waseasily remedied. Psychologists have adopted cumu-lative curves only very slowly, but I think it is fairto say that they have become an indispensable toolfor certain purposes of analysis.

Eventually, of course, the runway was seen to

eFIG. 9.

be unnecessary. The rat could simply reach intoa covered tray for pieces of food, and each move-ment of the cover could operate a solenoid to movea pen one step in a cumulative curve. The firstmajor change in rate observed in this way was dueto ingestion. Curves showing how the rate of eat-ing declined with the time of eating comprised theother part of my thesis. But a refinement wasneeded. The behavior of the rat in pushing openthe door was not a normal part of the ingestive be-havior of Rattus rattus. The act was obviouslylearned but its status as part, of the final performancewas not clear. It seemed wise to add an initialconditioned response connected with ingestion in aquite arbitrary way. I chose the first device whichcame to hand — a horizontal bar or lever placedwhere it could be conveniently depressed by the ratto close a switch which operated a magnetic maga-zine, Ingestion curves obtained with this initialresponse in the chain were found to have the sameproperties as those without it.

Now, as soon as you begin to complicate an ap-paratus, you necessarily invoke a fourth principleof scientific practice: Apparatuses sometimes breakdown. I had only to wait for the food magazineto jam to get an extinction curve. At first I treatedthis as a defect and hastened to remedy the dif-

B

FIG. 10.


FIG. 11.

ficulty. But eventually, of course, I deliberatelydisconnected the magazine. I can easily recall theexcitement of that first complete extinction curve(Figure 11). I had made contact with Pavlov atlast! Here was a curve uncorrupted by the physio-logical process of ingestion. It was an orderlychange due to nothing more than a special con-tingency of reinforcement. It was pure behavior!I am not saying that I would not have got aroundto extinction curves without a breakdown in theapparatus; Pavlov had given too strong a lead inthat direction. But it is still no exaggeration tosay that some of the most interesting and surprisingresults have turned up first because of similar ac-cidents. Foolproof apparatus is no doubt highlydesirable, but Charles Ferster and I in recently re-viewing the data from a five-year program of re-search found many occasions to congratulate our-selves on the fallibility of relays and vacuum tubes.

I then built four soundproofed ventilated boxes,each containing a lever and a food magazine andsupplied with a cumulative recorder, and was on myway to an intensive study of conditioned reflexes inskeletal behavior. I would reinforce every responsefor several days and then extinguish for a day ortwo, varying the number of reinforcements, theamount of previous magazine training, and so on.

At this point I made my first use of the deductivemethod. I had long since given up pearl barley astoo unbalanced a diet for steady use. A neighbor-hood druggist had shown me his pill machine, andI had had one made along the same lines (Figure12). It consisted of a fluted brass bed across whichone laid a long cylinder of stiff paste (in my case aMacCollum formula for an adequate rat diet).A similarly fluted cutter was then lowered onto thecylinder and rolled slowly back and forth, convert-ing the paste into about a dozen spherical pellets.These were dried for a day or so before use. Theprocedure was painstaking and laborious. Eightrats eating a hundred pellets each per day couldeasily keep up with production. One pleasantSaturday afternoon I surveyed my supply of drypellets, and, appealing to certain elemental theorems

in arithmetic, deduced that unless I spent the rest ofthat afternoon and evening at the pill machine, thesupply would be exhausted by ten-thirty Mondaymorning.

Since I do not wish to deprecate the hypothetico-deductive method, I am glad to testify here to itsusefulness. It led me to apply our second principleof unformalized scientific method and to ask myselfwhy every press of the lever had to be reinforced.I was not then aware of what had happened at theBrown laboratories, as Harold Schlosberg later toldthe story. A graduate student had been given thetask of running a cat through a difficult discrimina-tion experiment. One Sunday the student foundthe supply of cat food exhausted. The stores wereclosed and so, with a beautiful faith in the fre-quency-theory of learning, he ran the cat as usualand took it back to its living cage unrewarded.Schlosberg reports that the cat howled its protestcontinuously for nearly forty-eight hours. Unawareof this I decided to reinforce a response only onceevery minute and to allow all other responses to gounreinforced. There were two results: (a) mysupply of pellets lasted almost indefinitely and (b)each rat stabilized at a fairly constant rate ofresponding.

Now, a steady state was something I was familiarwith from physical chemistry, and I therefore em-barked upon the study of periodic reinforcement.I soon found that the constant rate at which therat stabilized depended upon how hungry it was.Hungry rat, high rate; less hungry rat, lower rate.At that time I was bothered by the practical prob-lem of controlling food deprivation. I was work-ing half time at the Medical School (on chronaxieof subordination!) and could not maintain a goodschedule in working with the rats. The rate ofresponding under periodic reinforcement suggesteda scheme for keeping a rat at a constant level ofdeprivation. The argument went like this: Sup-

Fio. 12.


pose you reinforce the rat, not at the end of agiven period, but when it has completed the numberof responses ordinarily emitted in that period. Andsuppose you use substantial pellets of food andgive the rat continuous access to the lever. Then,except for periods when the rat sleeps, it shouldoperate the lever at a constant rate around theclock. For, whenever it grows slightly hungrier, itwill work faster, get food faster, and become lesshungry, while whenever it grows slightly less hun-gry, it will respond at a lower rate, get less food,and grow hungrier. By setting the reinforcement ata given number of responses it should even be pos-sible to hold the rat at any given level of depriva-tion. I visualized a machine with a dial which onecould set to make available, at any time of day ornight, a rat in a given state of deprivation. Ofcourse, nothing of the sort happens. This is "fixed-ratio" rather than "fixed-interval" reinforcementand, as I soon found out, it produces a very differ-ent type of performance, This is an example of a.fifth unformalized principle of scientific practice,but one which has at least been named. WalterCannon described it with a word invented byHorace Walpole: serendipity—the art of finding onething while looking for something else.

This account of my scientific behavior up to thepoint at which I published my results in a bookcalled The Behavior oj Organisms is as exact inletter and spirit as I can now make it. The notes,data, and publications which I have examined donot show that I ever behaved in the manner ofMan Thinking as described by John Stuart Millor John Dewey or in reconstructions of scientificbehavior by other philosophers of science. I neverfaced a Problem which was more than the eternalproblem of finding order. I never attacked a prob-lem by constructing a Hypothesis. I never deducedTheorems or submitted them to ExperimentalCheck. So far as I can see, I had no preconceivedModel of behavior—certainly not a physiologicalor mentalistic one, and, I believe, not a conceptualone. The "reflex reserve" was an abortive, thoughoperational, concept which was retracted a year orso after publication in a paper at the Philadelphiameeting of the APA. It lived up to my opinion oftheories in general by proving utterly worthless insuggesting further experiments. Of course, I wasworking on a basic Assumption—that there wasorder in behavior if I could only discover it—butsuch an assumption is not to be confused with the

hypotheses of deductive theory. It is also truethat I exercised a certain Selection of Facts but notbecause of relevance to theory but because one factwas more orderly than another. If I engaged inExperimental Design at all, it was simply to com-plete or extend some evidence of order already ob-served.

Most of the experiments described in The Be-havior oj Organisms were done with groups of fourrats. A fairly common reaction to the book wasthat such groups were too small. How did I knowthat other groups of four rats would do the samething? Keller, in defending the book, counteredwith the charge that groups of four were too big.Unfortunately, however, I allowed myself to bepersuaded of the contrary. This was due in part tomy association at the University of Minnesota withW. T. Heron. Through him I came into close con-tact for the first time with traditional animal psy-chology. Heron was interested in inherited mazebehavior, inherited activity, and certain drugs—theeffects of which could then be detected only throughthe use of fairly large groups. We did an experi-ment together on the effect of starvation on the rateof pressing a lever and started the new era with agroup of sixteen rats. But we had only four boxes,and this was so inconvenient that Heron appliedfor a grant and built a battery of twenty-fourlever-boxes and cumulative recorders. I suppliedan attachment which would record, not only themean performance of all twenty-four rats in a singleaveraged curve, but mean curves for four sub-groups of twelve rats each and four subgroups ofsix rats each (3). We thus provided for the de-sign of experiments according to the principles ofR. A. Fisher, which were then coming into vogue.We had, so to speak, mechanized the latin square.

With this apparatus Heron and I published astudy of extinction in maze-bright and maze-dullrats using ninety-jive subjects. Later I publishedmean extinction curves for groups of twenty-four,and W. K. Estes and I did our work on anxietywith groups of the same size, But although Heronand I could properly voice the hope that "the pos-sibility of using large groups of animals greatlyimproves upon the method as previously reported,since tests of significance are provided for andproperties of behavior not apparent in single casesmay be more easily detected," in actual practicethat is not what happened. The experiments Ihave just mentioned are almost all we have to


show for this elaborate battery of boxes. Un-doubtedly more work could be done with it andwould have its place, but something had happenedto the natural growth of the method. You cannoteasily make a change in the conditions of an ex-periment when twenty-four apparatuses have to bealtered. Any gain in rigor is more than matchedby a loss in flexibility. We were forced to confineourselves to processes which could be studied withthe baselines already developed in earlier work.We could not move on to the discovery of otherprocesses or even to a more refined analysis ofthose we were working with. No matter howsignificant might be the relations we actually dem-onstrated, our statistical Leviathan had swumaground. The art of the method had stuck at aparticular stage of its development.

Another accident rescued me from mechanizedstatistics and brought me back to an even moreintensive concentration on the single case. In es-sence, I suddenly found myself face to face withthe engineering problem of the animal trainer.When you have the responsibility of making ab-solutely sure that a given organism will engage ina given sort of behavior at a given time, youquickly grow impatient with theories of learning.Principles, hypotheses, theorems, satisfactory proofat the .OS level of significance that behavior at achoice point shows the effect of secondary rein-forcement—nothing could be more irrelevant. Noone goes to the circus to see the average dog jumpthrough a hoop significantly oftener than untraineddogs raised under the same circumstances, or tosee an. elephant demonstrate a principle of behavior.

Perhaps I can illustrate this without giving aidand comfort to the enemy by describing a Russiandevice which the Germans found quite formidable.The Russians used dogs to blow up tanks. A dogwas trained to hide behind a tree or wall in lowbrush or other cover. As a tank approached andpassed, the dog ran swiftly alongside it, and a smallmagnetic mine attached to the dog's back was suf-ficient to cripple the tank or set it afire. The dog,of course, had to be replaced.

Now I ask you to consider some of the technicalproblems which the psychologist faces in prepar-ing a dog for such an act of unintentional heroism.The dog must wait behind the tree for an indefinitelength of time. Very well, it must therefore beintermittently reinforced for waiting. But whatschedule will achieve the highest probability of

waiting? If the reinforcement is to be food, whatis the absolutely optimal schedule of deprivationconsistent with the health of the dog? The dogmust run to the tank—that can be arranged byreinforcing it with a practice tank—but it muststart instantly if it is to overtake a swift tank, andhow do you differentially reinforce short reactiontimes, especially in counteracting the reinforcementfor sitting and waiting? The dog must react onlyto tanks, not to a refugee driving his oxcart alongthe road, but what are the defining properties of atank so far as a dog is concerned?

I think it can be said that a functional analysisproved adequate in its technological application.Manipulation of environmental conditions alonemade possible a wholly unexpected practical control.Behavior could be shaped up according to specifica-tions and maintained indefinitely almost at will.One behavioral technologist who worked with me atthe time (Keller Breland) is now specializing inthe production of behavior as a salable commodityand has described this new profession in the Ameri-can Psychologist (2).

There are many useful applications within psy-chology itself. Ratliff and Blough have recentlyconditioned pigeons to serve as psychophysical ob-servers. In their experiment a pigeon may adjustone of two spots of light until the two are equallybright or it may hold a spot of light at the absolutethreshold during dark adaptation. The techniqueswhich they have developed to induce pigeons to dothis are only indirectly related to the point of theirexperiments and hence exemplify the application ofa behavioral science (4). The field in which abetter technology of behavior is perhaps mosturgently needed is education. I cannot describehere the applications which are now possible, butperhaps I can indicate my enthusiasm by hazardingthe guess that educational techniques at all agelevels are on the threshold of revolutionary changes.

The effect of a behavioral technology on scien-tific practice is the issue here. Faced with prac-tical problems in behavior, you necessarily empha-size the refinement of experimental variables. Asa result, some of the standard procedures of sta-tistics appear to be circumvented. Let me il-lustrate. Suppose that measurements have beenmade on two groups of subjects differing in somedetail of experimental treatment. Means and stand-ard deviations for the two groups are determined,and any difference due to the treatment is evalu-


ated. If the difference is in the expected directionbut is not statistically significant, the almost uni-versal recommendation would be to study largergroups. But our experience with practical controlsuggests that we may reduce the troublesome varia-bility by changing the conditions of the experi-ment, By discovering, elaborating, and fully ex-ploiting every relevant variable, we may eliminatein advance of measurement the individual differ-ences which obscure the difference under analysis.This will achieve the same result as increasing thesize of groups, and it will almost certainly yield abonus in the discovery of new variables whichwould not have been identified in the statisticaltreatment.

The same may be said of smooth curves. In ourstudy of anxiety, Estes and I published severalcurves, the reasonable smoothness of which wasobtained by averaging the performances of 12 ratsfor each curve. The individual curves publishedat that time show that the mean curves do notfaithfully represent the behavior of any one rat.They show a certain tendency toward a change inslope which supported the point we were making,and they may have appeared to justify averagingfor that reason.

But an alternative method would have been toexplore the individual case until an equally smoothcurve could be obtained. This would have meant,not only rejecting the temptation to producesmoothness by averaging cases, but manipulatingall relevant conditions as we later learned to manip-ulate them for practical purposes. The individualcurves which we published at that time do notpoint to the need for larger groups but for im-provement in experimental technique. Here, forexample, is a curve the smoothness of which ischaracteristic of current practice. Such curveswere shown in the making in a demonstrationwhich Ferster and I arranged at the Clevelandmeeting of the American Psychological Association(Figure 13). Here, in a single organism, three dif-ferent schedules of reinforcement are yielding cor-responding performances with great uniformityunder appropriate stimuli alternating at random,One does not reach this kind of order through theapplication of statistical methods.

In The Behavior of Organisms I was content todeal with the over-all slopes and curvature of cumu-lative curves and could make only a rough classifi-cation of the properties of behavior shown by the

FIG. 13.

finer grain. The grain has now been improved.The resolving power of the microscope has beenincreased manyfold, and we can see fundamentalprocesses of behavior in sharper and sharper detail.In choosing rate of responding as a basic datumand in recording this conveniently in a cumulativecurve, we make important temporal aspects of be-havior visible. Once this has happened, our scien-tific practice is reduced to simple looking. A newworld is opened to inspection. We use such curvesas we use a microscope, X-ray camera, or telescope.This is well exemplified by recent extensions of themethod. These are no longer part of my case his-tory, but perhaps you will permit me to consultyou about what some critics have described as afolie a deux or group neurosis.

An early application of the method to the be-havior of avoidance and escape was made byKeller in studying the light aversion of the rat.This was brilliantly extended by Murray Sidmanin his shock-avoidance experiments. It is no longernecessary to describe avoidance and escape by ap-peal to "principles," for we may watch the be-havior develop when we have arranged the propercontingencies of reinforcement, as we later watchit change as these contingencies are changed.

Hunt and Brady have extended the use of astable rate in the study of anxiety-producing stimuliand have shown that the depression in rate iseliminated by electroconvulsive shock and by othermeasures which are effective in reducing anxietyin human patients. O. R. Lindsley has found the


same thing for dogs, using insulin-shock therapyand sedatives. Brady has refined the method byexploring the relevance of various schedules of re-inforcement in tracing the return of the conditioneddepression after treatment. In these experimentsyou see the effect of a treatment as directly as yousee the constriction of a capillary under the micro-scope.

Early work with rats on caffeine and Benzedrinehas been extended by Lindsley with dogs. A specialtechnique for evaluating several effects of a drug ina single short experimental period yields a recordof behavior which can be read as a specialist readsan electrocardiogram. Dr. Peter Dews of the De-partment of Pharmacology at the Harvard MedicalSchool is investigating dose-response curves and thetypes and effects of various drugs, using pigeons assubjects. In the Psychological Laboratories atHarvard additional work on drugs is being carriedout by Morse, Herrnstein, and Marshall, and thetechnique is being adopted by drug manufacturers.There could scarcely be a better demonstration ofthe experimental treatment of variability. In asingle experimental session with a single organismone observes the onset, duration, and decline ofthe effects of a drug.

The direct observation of defective behavior isparticularly important. Clinical or experimentaldamage to an organism is characteristically unique.Hence the value of a method which permits thedirect observation of the behavior of the individual.Lindsley has studied the effects of near-lethal ir-radiation, and the effects of prolonged anesthesiaand anoxia are currently being examined by ThomasLohr in cooperation with Dr. Henry Beecher ofthe Massachusetts General Hospital. The tech-nique is being applied to neurological variables in

FIG. 14.

the monkey by Dr. Karl Pribram at the HartfordInstitute. The pattern of such research is simple:establish the behavior in which you are interested,submit the organism to a particular treatment, andthen look again at the behavior. An excellentexample of the use of experimental control in thestudy of motivation is some work on obesity byJ. E. Anliker in collaboration with Dr. Jean Mayerof the Harvard School of Public Health, whereabnormalities of ingestive behavior in several typesof obese mice can be compared by direct inspection.

There is perhaps no field in which behavior iscustomarily described more indirectly than psy-chiatry. In an experiment at the MassachusettsState Hospital, under the sponsorship of Dr. HarrySolomon and myself, 0. R. Lindsley is carrying outan extensive program which might be characterizedas a quantitative study of the temporal propertiesof psychotic behavior. Here again it is a questionof making certain characteristics of the behaviorvisible.

The extent to which we can eliminate sources ofvariability before measurement is shown by a re-sult which has an unexpected significance for com-parative psychology and the study of individualdifferences. Figure 14 shows tracings of threecurves which report behavior in response to a mul-tiple fixed-interval fixed-ratio schedule. The hatchesmark reinforcements. Separating them in somecases are short, steep lines showing a high constantrate on a fixed-ratio schedule and, in others, some-what longer "scallops" showing a smooth accelera-tion as the organism shifts from a very low ratejust after reinforcement to a higher rate at the endof the fixed interval. The values of the intervalsand ratios, the states of deprivation, and the ex-posures to the schedules were different in the threecases, but except for these details the curves arequite similar. Now, one of them was made by apigeon in some experiments by Ferster and me, onewas made by a rat in an experiment on anoxiaby Lohr, and the third was made by a monkey inKarl Pribram's laboratory at the Hartford Insti-tute. Pigeon, rat, monkey, which is which? Itdoesn't matter. Of course, these three species havebehavioral repertoires which are as different astheir anatomies. But once you have allowed fordifferences in the ways in which they make con-tact with the environment, and in the ways inwhich they act upon the environment, what remainsof their behavior shows astonishingly similar prop-


erties. Mice, cats, dogs, and human children couldhave added other curves to this figure. And whenorganisms which differ as widely as this neverthe-less show similar properties of behavior, differencesbetween members of the same species may beviewed more hopefully. Difficult problems ofidiosyncrasy or individuality will always arise asproducts of biological and cultural processes, butit is the very business of the experimental analysisof behavior to devise techniques which reduce theireffects except when they are explicitly under in-vestigation.

We are within reach of a science of the indi-vidual. This will be achieved, not by resorting tosome special theory of knowledge in which intuitionor understanding takes the place of observation andanalysis, but through an increasing grasp of rele-vant conditions to produce order in the individualcase.

A second consequence of an improved technologyis the effect upon behavior theory. As I have pointedout elsewhere, it is the function of learning theoryto create an imaginary world of law and order andthus to console us for the disorder we observe inbehavior itself. Scores on a T maze or jumpingstand hop about from trial to trial almost capri-ciously. Therefore we argue that if learning is, aswe hope, a continuous and orderly process, it mustbe occurring in some other system of dimensions—perhaps in the nervous system, or in the mind, or ina conceptual model of behavior. Both the sta-tistical treatment of group means and the averagingof curves encourage the belief that we are some-how going behind the individual case to an other-wise inaccessible, but more fundamental, process.The whole tenor of our paper on anxiety, for ex-ample, was to imply that the change we observedwas not necessarily a property of behavior, but ofsome theoretical state of the organism ("anxiety")which was merely reflected in a slight modificationof performance.

When we have achieved a practical control overthe organism, theories of behavior lose their point.In representing and managing relevant variables, aconceptual model is useless; we come to grips withbehavior itself. When behavior shows order andconsistency, we are much less likely to be concernedwith physiological or mentalistic causes. A datumemerges which takes the place of theoretical fantasy.In the experimental analysis of behavior we addressourselves to a subject matter which is not only

\0 20 30 30 SO 6OM I N U T IT 4 /w SARK

FIG. IS.

manifestly the behavior of an individual and henceaccessible without the usual statistical aids but also"objective" and "actual" without recourse to de-ductive theorizing.

Statistical techniques serve a useful function,but they have acquired a purely honorific statuswhich may be troublesome. Their presence orabsence has become a shibboleth to be used in dis-tinguishing between good and bad work. Becausemeasures of behavior have been highly variable, wehave come to trust only results obtained from largenumbers of subjects. Because some workers haveintentionally or unconsciously reported or>\y selectedfavorable instances, we have come to put a highvalue on research which is planned in advance andreported in its entirety. Because measures havebehaved capriciously, we have come to value skill-ful deductive theories which restore order. Butalthough large groups, planned experiments, andvalid theorizing are associated with significant scien-tific results, it does not follow that nothing can beachieved in their absence. Here are two briefexamples of the choice before us.

How can we determine the course of dark adap-tation in a pigeon? We move a pigeon from abright light to a dark room. What happens?Presumably the bird is able to see fainter andfainter patches of light as the process of adaptationtakes place, but how can we follow this process?One way would be to set up a discrimination ap-paratus in which choices would be made at specificintervals after the beginning of dark adaptation.The test patches of light could be varied over awide range, and the percentages of correct choicesat each value would enable us eventually to locatethe threshold fairly accurately. But hundreds of


observations would be needed to establish only afew points on the curve and to prove that theseshow an actual change in sensitivity. In the ex-periment by Blough already mentioned, the pigeonholds a spot of light close to the threshold through-out the experimental period. A single curve, suchas the one sketched in Figure IS, yields as muchinformation as hundreds of readings, together withthe means and standard deviations derived f romthem. The information is more accurate becauseit applies to a single organism in a single experi-mental session. Yet many psychologists who wouldaccept the first as a finished experiment becauseof the tables of means and standard deviationswould boggle at the second or call it a preliminarystudy. The direct evidence of one's senses in ob-serving a process of behavior is not trusted.

As another example, consider the behavior of sev-eral types of obese mice. Do they all suffer froma single abnormality in their eating behavior or arethere differences? One might attempt to answerthis with some such measure of hunger as an ob-struction apparatus. The numbers of crossings ofa grid to get to food, counted after different periodsof free access to food, would be the data. Largenumbers of readings would be needed, and the re-sulting mean values would possibly not describe thebehavior of any one mouse in any experimentalperiod. A much better picture may be obtainedwith one mouse of each kind in single experimentalsessions, as Anliker has shown (1). In an experi-ment reported roughly in Figure 16, each mousewas reinforced with a small piece of food after com-pleting a short "ratio" of responses. The hypo-thalamic-obese mouse shows an exaggerated butotherwise normal ingestion curve. The hereditary-obese mouse eats slowly but for an indefinite lengthof time and with little change in rate. The gokl-

Fio. 17.

poisoned obese mouse shows a sharp oscillation be-tween periods of very rapid responding and noresponding at all. These three individual curvescontain more information than could probably everbe generated with measures requiring statisticaltreatment, yet they will be viewed with suspicion bymany psychologists because they are single cases.

It is perhaps natural that psychologists shouldawaken only slowly to the possibility that be-havioral processes may be directly observed, orthat they should only gradually put the older sta-tistical and theoretical techniques in their properperspective. But it is time to insist that sciencedoes not progress by carefully designed steps called"experiments" each of which has a well-definedbeginning and end. Science is a continuous and oftena disorderly and accidental process. We shall not dothe young psychologist any favor if we agree to re-construct our practices to fit the pattern demandedby current scientific methodology. What the statis-tician means by the design of experiments is designwhich yields the kind of data to which his tech-niques are applicable. He does not mean the be-havior of the scientist in his laboratory devisingresearch for his own immediate and possibly in-scrutable purposes.

The organism whose behavior is most extensivelymodified and most completely controlled in re-search of the sort I have described is the experi-menter himself. The point was well made by acartoonist in the Columbia Jester (Figure 17).The caption read: "Boy, have I got this guy condi-tioned! Every time I press the bar down he dropsin a piece of food." The subjects we study rein-force us much more effectively than we reinforcethem. I have been telling you simply how I havebeen conditioned to behave. And of course it is amistake to argue too much from one case history.My behavior would not have been shaped as it


was were it not for personal characteristics whichall psychologists fortunately do not share. Freudhas had something to say about the motivation ofscientists and has given us some insight into thetype of person who achieves the fullest satisfactionfrom precise experimental design and the intricaciesof deductive systems. Such a person tends to bemore concerned with his success as a scientist thanwith his subject matter, as is shown by the factthat he often assumes the role of a roving am-bassador. If this seems unfair, let me hasten tocharacterize my own motivation in equally unflat-tering terms. Several years ago I spent a pleasantsummer writing a novel called Wolden Two. Oneof the characters, Frazier, said many things whichI was not yet ready to say myself. Among themwas this:

I have only one important characteristic, Burris: I'm stub-born. I've had only one idea in my life—a true idee fixe. . . to put it as bluntly as possible, the idea of having myown way. "Control" expresses it, I think. The control ofhuman behavior, Burris. In my early experimental days itwas a frenzied, selfish desire to dominate. I remember therage I used to feel when a prediction went awry. I couldhave shouted at the subjects of my experiments, "Behave,damn you, behave as you ought!" Eventually I realizedthat the subjects were always right. They always behavedas they ought. It was I who was wrong. I had made abad prediction.

(In fairness to Frazier and the rest of myself, Iwant to add his next remark: "And what a strangediscovery for a would-be tyrant, that the only ef-

fective technique of control is unselfish." Fraziermeans, of course, positive reinforcement.)

We have no more reason to say that all psy-chologists should behave as I have behaved thanthat they should all behave like R. A. Fisher. Thescientist, like any organism, is the product of aunique history. The practices which he finds mostappropriate will depend in part upon this history.Fortunately, personal idiosyncrasies usually leavea negligible mark on science as public property.They are important only when we are concernedwith the encouragement of scientists and the prose-cution of research. When we have at last an ade-quate empirical account of the behavior of ManThinking, we shall understand all this. Until then,it may be best not to try to fit all scientists into anysingle mold.

REFERENCES

1. ANLIKER, J. E. Personal communication.2. BRELAND, K., & BRELAND, MARION. A field of applied

animal psychology. Amer. Psychologist, 1951, 6, 202-204.

3. HERON, VV. T., & SKINNER, B. F. An apparatus for thestudy of behavior. Psychol, Rec., 1939, 3, 166-176.

4. RATLUT, F., & BIOUGH, D. S. Behavioral studies ofvisual processes in the pigeon. Report of ContractNSori-07663, Psychological Laboratories, HarvardUniversity, September 1954.

5. RICHTER, C. P. Free research versus design research.Science, 1953, 118, 91-93.

Received May 16, 1955.

b. f. skinner - a case history in scientific method (1956)

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