staddon y simmelag 1971 the superstition experiment a reexamination of its implications for the...

8/14/2019 Staddon y Simmelag 1971 the Superstition Experiment a Reexamination of Its Implications for the Principles of Ad

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Psychological Review1971, Vol.78, No. 1.3-43

THE "SUPERSTITION" EXPERIMENT:A R E E X A M I N A T I O N OF ITS IMPLICATIONS FOR THEPRINCIPLES OFAD APTIVE BEHAVIOR '

J. E. R. STADDON2 A N D V I R G I N I A L . SIMMELHAG3Duke University Scarborou gh College, Un iversity of Toronto

Replication and extension of Skinne r 's supersti t ion expe rimen t showedth e development of two k i nds of behavior at asymptote: interim activities(related to adjunct ive behavior) occurred just after food del ivery ; theterminal response (a discriminated opera nt) occurred toward the end ofth e interval and continued until food delive ry. These data suggest a viewof operant condi t ioning (the terminal response) in terms of two sets ofpr inc ip le s : pr inciples of behavioral variation that describe th e origins ofbehavior app ropriate to a si tuation, in advance of re in forcement ; andprinc iples of reinforcement that descr ibe the selective elimination of be-havior so produced. This approach was supported by (a) an account ofthe pa ral lels between the Law of Effect and evolution by means of naturalselection, ( f c ) it s abi l i ty to shed light on persistent problems in learning(e.g., continuity vs. noncontinuity, variabil i ty associated with extinction,the relationship between classical and instrumental conditioning, the con-troversy between behaviorist and cognitive approaches to learn ing) , and(c) its abil i ty to deal with a number of recent anomalies in the learningl i terature ( inst inct ive dr i f t , auto-shaping, and auto-main tenan ce) . Theinterim act ivi t ies were interpreted in terms of interactions among motiva-t ional systems, and this view was supported by a review of the literatureon adjunct ive behavior and by comparison with similar phenomena inethology (displace men t, redirection, and vacuum act iv i t ies) . Thepro-posed theoretical scheme represents a shift away from hypothetical "laws oflearning toward an in terpre t a t ion of behavioral change in t e rms of inter-action and compet i t ion among tendencies to act ion according to pr inciplesevolved in phylogeny.

The field of learning has undergone in- At times, one senses a widespread feeling ofdis-creasing fractionation in recent years. In- couragement about the prospects of ever gett ing, . , . i j * clear on the fundam entals of condi tioning. At tem ptsterest in miniature systems and exact to arrive atfirm dedsions abouf alternatfvetheories of local effects has grown_ to the formulations rarely prod uce incisive results. Everydetriment of any attempt at overall integra- finding seems capableofman y explan ations. Issuestion. Consequently, as one perceptive ob- become old,shopworn, and disappear wi thout aserverhasnoted: proper burial [Jenkins 197-107-1081Research was supported by grants from the The present article outlines an attempt toNational Insti tute ofMen tal Hea lth, United States redress this imbalance. It is organized

FL STunlverSTndteUnlT -ound the problem of"superstitious" be-sity of Toronto. The authors thank Nanc y K. havior, originated by Skinner some yearsInn is for advice and assistance. Janice Frank, agO; which plays a crucial part in the em-Irving Diamond, Carl Erickson, Richard Gil- . . , , ., ,. , , . . . ,bert , and Peter Klopfer kindly commented on Pmcal.and theoretical foundations ofCUr-earlier versions of this paper. A shorter version rent views of learning. Discussion of aof the experimental part of this work was pre- replication of Skinner's original experimentsented inpartial fulfi l lment of th erequirementsfor . . . ,, i j . - t . - i .th e MA degree at the University of Toronto leadstoan account of the relationships be-(Simmelhag, 1968). tween evolution and learning, and a system2Requests for reprints shouldbe sent to J. E. R. Of classification derived therefrom. TheStaddon, Department of Psychology, Duke Uni- , , . < . 1 . - 1 , rversity, Durham, North Carolina 27706. PaPerconcludeswitha theoretical accountof3Now at Duke Universi ty . "superstition" and some related phenomena.


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J. E. R. STADDONANDVIRGINIA L. S I M M E L H A GTHE SUPERSTITION EXPERIMENT

In his classic experiment on "supersti-tious" behavior, Skinner (1948) showedthat th e mere delivery of food to a hungryanimal is sufficient to produce operant con-ditioning. The pigeons in that experimentwere al lowed 5-second access to food every15 seconds, and food del ivery was independ-ent of their behavior. Nevertheless, ne arlyevery pigeon developed a recognizable formof stereotyped, superstitious behavior thatbecame temporally correlated with food de-livery as train ing progressed.Skinner's (1961) analysis of th i s phe-nomenon is a st raightforward appl icat ion ofthe Law of Effect:The con ditioning process is usua lly obvious. Thebird happens to be executing some response asthe hopper appears; as a result i t tends to repeatthis response. If the interval before th e nex tpresentat ion is not so great that extinct ion takesplace, a second "contingency" is probable. Th isstrengthens th e response still fu r ther and subse-quent re inforcement becomes more probable[p . 405].

Skinner's observations were quickly re -peated in a number of laboratories. Theapparent simplicity and reliability of thephenomenon, coupled with the plau sibil i tyof Skinner's interpretation of it, and themore excit ing attractions of work on re-inforcement schedulesthen developing, effec-tively stifled further study of this si tuation.However, both the experiment and his ex-plication played a crucial role in advancingSkinner's theoretical view of operant be-havior as the strengthening of unpredictablygenerated ("emitted") behavior by the auto-matic action of reinforcers.Two kindsofdata obtained inrecen t yearsraise new questions about "superstition"in this sense. First, experiments wi th t ime-related reinforcement schedules have shownthe development of so-called me diatingbehavior during the wai t ing period, whenth e an imal is not making th e reinforced re -sponse. Thus, on schedules which requirethe animalto spacehis responses a few sec-ondsapartiftheyare to be effectivein pro-ducing reinforcement (spaced-respondingschedules), pigeons often show activitiessuch as pacing and turn in g circles. Simi-

larly, on fixed-interval schedules, in whichth e first response t seconds after the pre-ceding re in forcement is effective in produc-in g reinforcement, pigeons m ayshow asimi-la r behavior during th e postreinforcement"pause" when they are not making the re-inforced response. Other species showactivities of this sort in the presence of ap-propriate environmental s t imul i ; for ex-ample, schedule-induced polydipsia, in whichrats reinforced with food on temporal rein-forcement schedules show excessive drinkingi f wa t e r is continuously available (Falk,1969). None of these activities is rein-forced, in the sense ofbeingcontiguouswi thfood del ivery,yet they are reliably producedin situations similar in many respec t s toSkin ne r's supe rsti t ion proc edu re. Possibly,therefore, some of the activities labeledsupersti t ious by Skinner , and attributed byhim to accidental reinforcement of spon-taneously occurring behavior, may insteadreflect th e same causal factors as thesemediating activit ies.Second, a number of experiments havedemonstrated the development of behaviorin operant condit ioning situations by a proc-ess m ore reminisce nt of Pavlovian (classi-cal) cond i t ioning than Law of Effect learn-in g as com mon ly understood. Breland andBreland (1961) reporte d a series of observa -tions showing that wi th con t inued operan ttraining, species-specific behavior will oftenemergeto disrup t ana pparen t ly wel l - learnedoperant response. In the cases they de-scribe, behavior closely linked to food (pre-sumably ref lect ingan instinct ive me chanism )began to occur in advance of food del ivery,in th e presence of previously neutral stimuli( instinctive dri ft ). Since these irrele-van t act ivit ies in terfere d with food deliveryby delayingthe occurrence of the reinforcedresponse, they cannot be exp la ined by theLaw of Effect . A descr ip t ion in t e rms ofst imulus substi tutiona principle usuallyassociated with Pavlovian condit ioningisbetter, al though sti l l not completely satis-factory. M ore recently, Brown and Jenk ins(1968) have shownthat hungry pigeons canbe t rained to peck a lighted response keysimply by i l lumina t ing the key for a fewseconds before food del ivery. Fewer than a


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SUPERSTITION EXPERIMENT A N D A D A P T I V E B E H A V I O Rhundred light-food pairings are usually suf-ficient tobring aboutk eypecking. The rela-tionship between this auto-shaping pro-cedure and Pavlovian condit ioning isfur theremphasized by an experiment reported byWilliams andW ill iams (1969). They foundthat auto-shaped key pecking is maintainedeven if the keypeck turnsoff the light on thekey and thus prevents food delivery on thatoccasion. All these experiments show th eoccurrence of food-related behaviors, inanticipation of food, under condit ions moreor less incompatible with the Law of Effect.The auto-shaping procedure is opera-t ionally identical to Pavlovian condit ioningwith short delay (the light-food interval inthese experiments is typically 8 seconds).Therefore th e eventual emergence of food-related behavior, in anticipation of food de-livery, is not altogether surprisingalthoughth e directed nature of key pecking has nocounterpart in principlesof conditioning thattake salivation as a model response. Thesupersti t ion si tuation is also equivalent to aPavlovian procedurein this case temporalconditioning, in which the UCS (food) issimply presented at regular intervals. Per-haps, therefore, prolonged exposure to thissituation will also lead to the em ergen ce offood-related behavior in anticipation of food.Possibly th e superstitious behavior describedby Skinner includes activit ies of this sort ,that occur in anticipation of food, as well asmediating activit ies that occur jus t after fooddelivery.The present experiment affords an op-portuni ty to test these ideas. It providescomparative dataon the effect of fixed versusvariable interfood intervals on supersti t iousresponding (Skinner used only fixed inter-vals), as well as allowing a comparison be-tween response-dependent and response-independen t fixed-interval schedules. Theexperiment also extends Skinner's work byrecording in some detail both th e kind andt ime of occurrence of superstitious activities.The emphasis is on the steady-state adapta-tion to the procedures, but some data on thecourse of development of superstition arepresented.We hope to show that careful study of thesupersti t ion si tuat ion makes necessary a re-

vision of Skinner's original interpretationand, by extension, requires a shift of empha-sis in our viewof adaptive behavior.Method

SubjectsSix pigeons were used: four white Carneaux,tw o with experimental experience (Birds 31 and29) and two experimentally naive (Birds 47 and49). Two other pigeons were of a local (Toronto,Ontario) breed and were experimentally naive(Birds 40 and 91). All the birds were main-ta ined at 80% of their free-feeding weightsthroughout.

ApparatusTw o standard Grason-Stadler operant condition-ingchamberswere used. The response keys werecovered with white cardboard except during th eresponse-dependent condition when one key was ex-posed and transi l luminated with white light. Datawere recorded by a clock, digital counters, and anevent recorder. Food delivery was controlledautomatically by relays and timers. Behaviorswere recorded via push buttons operated by anobserver. A tape recorder was used to recordcomments and corrections. Except for the pushbuttons and the tape recorder , a l l programmingand recording apparatus was located in a separate

room. White noise was present in the experi-menta l chamber and, together wi th th e noise ofth e vent i la t ing fan, served to mask extraneoussounds.Procedure

Three schedules of food del ivery were u s e d :(a) A response-independent fixed-interval (FI)schedule in which the food magazine was pre-sented at 12-second intervals , ( f c ) A response-indepen dent variable-interva l (V I) schedule inwhich th e food magazine was presented on theaverage every 8 seconds. The following sequenceof interreinforcement intervals was used, pro-grammed by a loop of 16-millimeter film withholes punched at appropria te intervals: 3, 6, 6,12, 9, 7, 3, 10, 21, 6, 5, 11, 8, 5, 3, 9, 7, 9, 5, 13,3, 8, 9, 4, 7, 12, 11, 3, 6, 5, and 9 seconds, (c ) Aresponse-dependent FI schedule in which food wasdelivered (reinforcement occurred) for the firstke y peck 12 seconds or more af ter the precedingreinforcement .Food delivery in volve d 2-second access to mixedgrain . Sessions ended afte r the sixty -fou rth fooddel ivery and the pigeons were run daily.

Habituation sessions. All the birds were givena number of daily 10-minute sessions when no foodwas delivered; the birds were simply placed in thechamber and their behavior observed and recorded.The birds received the following numbers of suchsessions: Bird 31, 3; Bird 29, 3; Bird 47, IS ;Bird 49 , 15 ; Bird 40, 7; Bird 91, 7. Note that th e


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J. E. R. S T A D D O N ANDV I R G I N I A L. S I M M E L H A Gexperimentally naive birds received more habitua-tion exposure.Response-independent training. Four of thepigeons were then given a number of sessions oneach of the two response-independent procedures,either FI followed by VI, or the reverse. Thebirds received th e procedures in the indicatedorder (number of sessions in parentheses) : Bird31: FI 12(26),VI 8 (111); Bird 29:VI 8 ( 2 6 ) ,FI 12 (109) ; Bird 47: VI 8 (36), FI 12 (36);Bird 49 : FI 12(37), VI 8 (36) .Response-dependent training. Two of the b i rdsalready trained on the response-independent pro-cedures were then switched to the response-dependent FI 12 for the fol lowing numbers ofsessions: Bird 31, 37; Bird 47 , 52. The twonaive birds (40 and 91), af ter their habituationsessions, were given on e session of response-inde-pendent FI 12 when th e food magazine operatedevery 12 seconds, bu t contained no grain. Thiswas to habituate these birds to the sound of themechanism. The next day these tw o birds wereplaced in the exper imental box with th e food maga-zine continuously available for 10 minutes . Thefo l lowing day the two birds were introduced toth e response-dependent FI 12-second schedule. Asmall piece ofblack tape wasplaced on the lightedresponse key, as an inducement to pecking, fo r th isfirst session only. All the birds pecked the keyduring the first session of the response-dependentprocedure. This rather elaborate key-training pro-cedure was designed both to prevent the experi-menter from shaping th e naive birds' behavior, andto avoid th e possibility of "superstitious" condi-t ioning, which migh t be entailed by some formof auto-shaping. Bird 40 received a total of 45sessions of the response-dependent FI 12-secondschedule, Bird 91 received 38.Response description an d scoring. Responsecategories were arrived at on the basis of initialobservation during th e habituation sessions andwere altered as necessary to accommodate newbehaviors. The names, descriptions, and nu m b e r sof the categories appear in Table 1. Responseswere scored (b y pushing th e appropriate button)in two ways, either discretely or continuously.If a response tended to occur in discrete units(e.g., pecking), then th e appropriate button w aspushed each time an instance of the responseoccurred. The observer was the same throughout(VLS), and the maximum recordable rate fordiscrete responses was 3-4 per second. A con-tinuous response is one which took an indefiniteamount of t ime (e.g., facing magazine wal l ) ; theappropriate button w as pressed throughout th eduration of a continuous response. Discrete re -sponses were pecking (wa ll , key, or floor) andquarter circles, all the rest were continuous re -sponses. In general, th e response categories weremutua l ly exclusive. The only exception is facingMagaz ine wal l (Ri), which a t var ious t imes oc -curred wi th Flapping wings ( R s ) , Moving alongmagazine wal l (R s) , a n d Pecking ( R ? ) .

ResultsThe data of interest in this experiment arethe kindand amount ofbehavior at differentpoints in timefollowing the delivery of food.

As training progressed, a systematic patterno f behavior as a function of postfood timebegan to emerge. The prope rties of thissteady-state pattern for VI and FI schedulesis discussed first, followed by a descriptiono f the changes that took place durin g acquisi-tion.Steady-State Behavior

In the steady state, th ebehavior developedunder both the FI and VI procedures fellreliably into two classes: (a ) The terminalresponse was the behavior that consistentlyoccurred jus t before food delivery. It be-gan 6-8 seconds after food delivery on theFI procedures, and about 2 seconds afterfood on the VI procedure, and usually con-tinued until food delivery, (b ) A numbero f activities usually preceded the terminalresponse in the interva l. These activities areprobably indistinguishable from what hasbeen terme d m ediating behavior, but we pre-fe r the more descriptive term interim activi-ties. These activities we re rarely con-tiguous with food.Figure 1shows the performance averagedacross three sessionsof steady-state respond-in g under all conditions for all the pigeons.The left-hand panels show the response-de-pendent FI schedule; the middle panels , theresponse-independent (superstitious) FIschedule; and the right-hand panels, the re-sponse-independent VI procedure, for thefour birds exposed to each. The graphsshow th e probabil i ty (relat ive frequency)with which each of the activities occurredduring each second of postfood time. Eachbird shows the clear division between termi-nal and interim activities already alluded to.Excluding R1; and the results fo r Bird 29on V I, Pecking (R7) was the terminal re-sponse for all the response-independent pro-cedures. For Bird2 9, the terminal responseHead in magazine (Ru) became an interimactivity following the shift from VI to FIand was replaced as terminal response byPecking. Pecking remain ed th e termina lresponse for this bird throughouta sequence


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'SUPERSTITION EXPERIMENT AND ADAPTIVE B E H A V I O RT A B L E 1

D E S C R I P T I O N O F O B S E R V E D A C T I V I T I E SResponse no. N a m e Descrip tion

R3R4

Re

Rr

Rs

R i o

RnRl2

R i s

R uRl5Rl6

MagazinewallPecking keyPeckingfloorJ circle

FlappingwingsWindow wall

Pecking

Movinga long magaz inewall

PreeningBeak to ceil ingHead inmagaz ineHead movemen t salong magazinewallDizzy mot ionPecking windowwal lHead to magazineLocomotion

An orientation response in which the bird's head andbody are directed toward the wall containing themagazine.Pecking move me nts directedat thekey.Pecking m ovemen ts directedat the floor.A responseinwhichacoun tof onecircle wouldbegivenfort u rn i ng90awayfrom facing th emagaz inewall,acountof two fort urn in g 180 away, three for270, and four for 360.Avigorousup anddown movemen tof theb ird's wings.An orientation response inwhich th ebird's head andbody are directed toward the door of the experi-mentalchambercontaining theobservationwindow.Peckin g movem ents directed toward some pointon themagazine wall.Thispoint general ly var ied betweenbirds and somet imes wi thin th e same bird a t d i f -ferent t imes.A side-stepping motion with breastbone close to themagazinewall ,a fewsteps to the left followed by afew steps to the right, etc. Somet imes accompa niedby (a) beak pointed up to ceiling, (6) hopping , c ) flapping wings.Any movement inwhich th e beak comesintocontactwiththe fea thers on the bird's body.The bird moves around the chamber in no par t iculardirect ionwith i ts beak directed u pw ard touching the

ceiling.A response in which at least the beak or more of thebird'shead is inserted into the magazine opening.The bird faces the magazinewall and moves i ts headfrom left to r ightand/or up and down.A response peeuliar to Bird 49 in which the head vi -brates rapidly from side to side. It was apparent lyrelated to, and al ternated wi th ,Pecking (Rr) .Peckingm ovements directed at thedoor withthe ob-servation w indow in i t .The bird turns it s head toward th emagaz ine .The bird walks about in no par t icular direct ion.

of response-independent procedures after theones reported here, lasting for a total inexcess of 90 sessions. A cu rious idiosyn -cratic head movement accompanied peckingby Bird 49 (R1 3 :Dizzy motion) on response-independent FI, although it disappeared fol-lowing th e switchto VI. The locusofPeck-ing on the magazine wal l differed from birdto bird and varied both across and withinsessionsfor somebirds. The stable featuresof this response were its topography and itsrestrict ion to the general area of the maga-zine wall. A variety of interim activit iesoccupied th e early parts of the FIs and theperiod wi th in 2 or 3 seconds after food on

the VI schedu le: Pecking floor (R3),icircles (R4), Flappingwings (RB ) , Movingalong magazine wall (R8), and Beak to ceil-in g (R10) were the most frequent . Theinter im activit ies were therefore more vari-able from bird to bird than was the terminalresponse.The pat tern of behavior characterist ic ofeach interval was little affected by whetheror not foodwas dependent on keypecking.The similari ty between the pat terns duringresponse-dependent and response-independ-ent FI is particularly striking for Bird 47,w ho w as switched directly from the re-sponse-independent to the response-depend-


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J. E. R. S T A D D O N ANDV I R G I N I A L. S I M M E L H A GR ESR - D EP.Fl RESR-INDER Fl R E S R - I N D E R V I

12 0 2 4 6 8 10 12 14 16 18

2 4 6 8 10 1 2 0 2 4 6 8 10 1 2 0 2 4 6 8 10 1 2 14 16 18

6 8 10 12 12 14 16 18 20S E C O N D I N IN T E R V A L

F I G . 1. Probability of each behavior as a function of postfood time for all birdsfor all three experimental conditions, averaged over three sessions of steady-stateresponding under each condition. (Each point gives the probability that a givenbehavior occurred in that second of postfood time. Data for theresponse-dependentcondition are averaged across 2-second blocks. Behaviors ( R ) are identified inTable J , )


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'SUPERSTITION EXPERIMENT AND A D A P T I V E B E H A V I O Rent procedure. Bird 31, for whom the re-sponse-independent and response-dependentFIs were separated by response-independentVI, shows more variation in the interimactivities under the two conditions. Bird s91 and 40, who were exposed only to theresponse-dependent FI, showa similar pat-tern of interim activities to the response-independent birds, although again there issome variationas to details. This similaritycannot be attributed to the procedure usedto shape key pecking (seeProcedure). Af terthe imposition of the key-pecking contin-gency, Bird 31 retained the old Pecking re-sponse as an interim activity restricted to aperiod in the interval just before key peck-ing. Bird 47 showed a similar effect of hisresponse-independent experience in that ahigh proportion of his key pecks failed todepress the key sufficiently to activate th eautomatic recording circuitry, although theywere recorded as key pecks by the observer.Overall, these data provide no evidence forsubstantial changes in the pattern oft e rmina lor interim activities traceableto the imposi-tion of a key-pecking requirement.The general pattern of termina l and in-terim activities during the response-inde-pendent VI schedulewas similarto the FIprocedures. Differences were restriction ofthe interim activities to the first 2 or 3 sec-onds ofpostfood time rathe r than to the first6 or 7 seconds (withoneexception,to bedis-cussed) , and the smaller number of interimactivities, in most cases. Un der both fixedand variable procedures, once the terminalresponse began in an interval, it continuedunti l food delivery. The excep tion is B ird47 who showed a drop in the probabilityofthe terminal response (Peckin g,R7) accom-panied by a transient increase in the interimactivity oficircles (R4) at the 14-15-second postfood time . A similar slight dropin the probability of Pecking, although notaccompanied by an interim activity,was alsoshown by Bird 31. These differences are re-lated to the properties of the VI schedule(see Discussion).Sequential Structure

Figure 2 indicates something of the se-quential structure of the behavior occupying

each interfood interval fo r each bird duringthe response-indepe ndent procedures. Thefigure summarizes the two to five behaviorsequencesthat account for most of the inter-vals during the three steady-state sessions.For simplicity, no account is taken either ofinterbehavior t imes or of the duration ofeach activity in this method of representa-tion. The most striking characte ristics ofthese sequences are: (a) that each birdshowed only a small number of typical se -quences (usually three or f o u r ) ; (& ) thatthe sequencingwas very rigid, so that al-though a given behavior might fail to occurduring a particular interval, it never occur-red out of sequencethis is indicated by theabsence of return arrows ("loops") inthese diagrams; and (c ) that the variabilityof the sequences was greatest early in theinterval and least at the end, in the periodjus t preceding food deliverythis is indi-cated by the absence of forks (ambiguoustransi t ions from one behavior to two or m oreothers, as in the diagram for Bird 31 whereR6 R5 or R6-R7 with approximatelyequal probability) late in the sequenceof be-haviors shown in the diagrams. This reg-ular sequen cing did not occur early in train-ing, as indicated in Figure 4, discussedbelow.An invitin g possibility raised by these reg-ular sequences is that this behavior may bedescribed by some kind of Markov chain(cf. Cane, 1961). Although the argumentcannot bepresented infull here,thisassump-tion cannot be sustained for a number ofreasons, the most important of which are(a) that th e durat ion of a bout of a givenactivity was shorter the later the activitybegan within an interval, and (& ) that th et ime between two successive activities wasshorter th e later in the interval the firstactivity ended. These and other considera-tions suggest that postfood t ime was themost impor tan t factor controlling both th eonset and offset of each activity in the se-quence.Acquisition

Figure 3 shows acquisition data fo r naiveBird 49, through and beyond the periodwhen his behavior became stable on re-


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10 J. E. R. S T A D D O N ANDV I R G I N I A L. S I M M E L H A GF I X E D I N T E R V A L V A R I A B L E I N T E R V A L

183/192 Intl.

.16 x l i m i n e i

2 qutoett179/192 loti.

169/192 Int..

^-*-R3-.21.32 /*-Vt^5~.io

.17

Bird 49 ; s s v . Cx..94** 1.0 3l.qulnc.i-*-R10 -R7 -rSf .* 176/192 Intl.

F I G . 2. Steady-state sequences : Sequential relationships among behaviors during th e lastthree sessions of each response-independent procedure for all four pigeons. (Fixed-interval ison the left , var iable- in terval on the right. Num bers give probabilities of the indicated transi-t ions. Number of di f fe rent sequences on which th e diagrams are based and number of intervals(out of 192) accounted for by these are indicated. "F" is food delivery, and behaviors (Ri)are ident if ied in Table 1. Note: probabilities at each "fork" do not always sum to 1.0because not every sequence is accounted for.)

spouse-independent FI. The graphs show(as a function of sessions) the probabilityof the various behaviors in each of thesix 2-second periods making up the FI.The most noteworthy characterist ic ofacqui-sition is the relatively sudden disappearanceof th e behaviorHead inm agazine, whichwasalmost the only behavior to occur duringthe first few sessions fo r Bird 49, in favorof the terminal response Pecking on maga-zine wall. For Bir d 49 this transit ion tookplace between the seventh and eighthses-sions of FI without any prior history ofpecking duri ng earl ier sessions. Once peck-in g became established as a termina l re-sponse, the only further change was a slowdecline in the probability of the responsedviring early parts of the interval (e.g., be-tween 3 and 8 seconds). The other birdsshowed similar results ontheir first exposureto the response- independen t p rocedure s ;for each bird, pecking on the magazinewal l

first occurred during the followingsessions:for Bird31, on the first FI session; Bird 29 ,twelfth session of FI following the switchfrom response- independent VI; Bird 4 7,twenty-e ighth session ofVI; Bird 49, eighthsession of FI. Thus, al though one of the ex-perienced birds pecked during the first re-sponse-independent session (31), the otherdid not unti l being switched to a differentschedule (29). Nobird shifted to a differentt e rmina l response once he began peck ing ;th e to ta l number of sessions of response-independen t experience (FI a nd VI) foreach of the four birds following th e onsetof pecking was as fol lows: Bird 31 , 140;Bird 29,96; Bi rd 47,45; Bird 49, 66. ForBird 29, the terminal response during theresponse-independent FI procedure (i .e.,be-fore th e onset of pecking) was Head inmagazine . As wi th the other birds, oncepeck ing appeared it was in f u l l strengthalmost immediately and further experience


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SUPERSTITION E X P E R I M E N T A N D A D A P T I V E B E H A V I O R 11_, i

o. p-o- ' o--< . .0 0 0V V

HEAD IN MA Go o PECKING MAG. WA LL

1/4 CIRCLES.10-12

i ' T I 4 ' i b i^ ' 2 6 2 ^ 3 0 35SESSIONS

FIG. 3. Deve lopment of the terminal response, (The graph shows, fo rBird 49 on the response- independent fixed-interval procedure, th e transitionf rom Head in magaz ine (Ru) to Pecking (R7) as terminal response, an dincludes one interim activity, i circles (R


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12 J. E. R. S T A D D O N ANDV I R G I N I A L. S I M M E L H A GFIXED- INTERVAL

Bird 31

19 sequences160/188tuts

Bird49

3 sequences161/192 Ints.

V A R I A B L E- IN T E R V A LBird 29

25 sequences179/192 Ints

4 sequences179/192 Ints

F I G . 4. Sequence data, in the same form asFigure 2, for the first three sessions under thefirst response-independent procedure to which eachbird was exposed. (Deta ils as inFigure 2.)had the effect merely of restricting it moreto the later parts of the interval.Figure 4 shows sequence data, in thesame form as Figure 2, for the first threesessions of the first response-independentschedule to which each bird was exposed.Approximately the same proportion of thetotal number of sequences observed within19 2 intervals is accounted for by thesedia-

grams as in the diagrams of Figure 2 forthe last three sessions. The data for thefirst three sessions are much more variable,showing repetitions of a behavior within aninterval and reversals of sequence; threeout of four birds show no single terminalresponse. Thus, the regularities app arentin Figure 2 are evidently a real effect oftraining and not simply an artifact of thismethod of representation.Discussion

The results of this experiment confirm th esuggestion that the "superstition" situationgenerally produces tw o distinct kinds of ac-t iv i ty : interim activities that occur at shortand intermediate postfood times, and theterminal response that begins later in theintervalandcontinues until food delivery. Itis not always clear from Skinner's originaldiscussion just which kind of behavior hewas observing. In one case, he briefly de-scribes an experiment in which th e interfoodinterval was 60 seconds, and the "super-stitious response (a well-defined hoppingstep from the right to the left foot ) wa sautomatical ly recorded. In this case, thebehavior was evidently a terminal response,since it occurred with increasing frequencythrough the in terva l :The bird does not respond immediately aftereating,but whe n 10 or IS or even 20 sec.have elapsedit begins to respond rapidly and continues untilthe reinforcement is received [Skinner, 1961,p.406].On other occasions, howe ver, Skinner mayhave been observing interim activities, as,in our experience, they are sometimes muchmore str iking than the terminal response,especially early in t ra ining when they mayinc lude act ions like jumping in the air,vigorous wing flapping, and idiosyncratichead and limb movements. W e have alsosometimes observed interim activities duringsessionsw hen therewas no obvious termin alresponse.Nature of the Terminal Response

The data from both FIand VI schedulesof food presentation in dicate that the prob-ability of the terminal response at differentpostfood t imes was a function of the prob-


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14 J. E. R. S T A D D O N ANDVIRGINIA L. S I M M E L H A GSpanier, 1968). They are related to moti-vational systems, since a number of activ-itiesfor example, polydipsia (excessivedrinking), pica (eat ing nonfood mate r ia l ) ,wheel running, and schedule-inducedaggres-sionmay occur more or less interchange-ably depending on the presence of appro-pria te s t imuli ; and animals wil l learn anoperant response in order to obtain an op-por tuni ty to engage in one of these activities(Falk, 1970).The interim activities in the present ex-per imen t appear to reflect th e same causalfactors as adjunctive behavior: they occura t t imes when re inforcement is not availableand the terminal response is not occurr ing ;they occur on both response-dependent andresponse-indep enden t schedules (cf. A zrin,Hutch inson , & Hake, 1966; Burks, 1970;Flory, 1969); and they occur on both FIand V I schedules. Ad junctive behavior re -quires appropriate stimuli (water for poly-dipsia, wood shavings for pica, etc.) towhichitis directed and by which it can be modified,within limits. Thisi sunlikelyto be acrucia ldifference, however, since appropriate stim-uli were not available in the present experi-m e n t (had water been available, schedule-induced drinking would a lmost certa inlyhave been observed in lieu of the interimactivi t ies ; cf. Shanab & Peterson, 1969),and behavior resembling inter im act ivi t ieshas occasionally been reported under condi-t ions when most animals show ad junc t ivebehavior, thus[this ra t] was a typica l in that it did not developpolydipsia . . . exhibiting instead a number ofstereotyped behaviors, l ike rearing and r u n n i n gto the corners of the experimenta l chamber, be-tween re inforcements [Keehn, 1970, pp. 164-167].Wereturnto atheoreticalaccountof interimand adjunctive behavior in the conc lud ingsection.A n analogy can be drawn be tween thete rmina l and interim activities here and theclassical dichotomy between consummatoryand appetitive behavior (Craig, 1918).Thus, pecking, the stable terminal response,is a food-elicited (consu mm atory) activityin pigeons, and the interim activities werequite variable ,as might beexpected of appe-titive behavior. M oreover, th e variabilityof

the sequences (as measured by the numberof "forks" in the sequence) was greatest atthebeginningof the sequence and decreasedtoward the end (cf . Figure 2). More orless unlearned sequences terminating in con-summatory acts show a similar reductionin variabil i ty toward the end of the sequence(e.g., M orris, 1958).In a similar vein, Falk (1970) has com-pared adju nc tive behavior with displace-m e n t activities (Tinbergen, 1952):In both adjunct ive behavior and displacement ac-t ivity situations, the interruption of a consumma-tory behavior in an intensely motivated animal in-duces th e occurrence of another behavior imme-diately fol lowing the interrupt ion [p. 305].

At the present stage of knowledge, thesecomparisons do little more than group to -gether a numberofpuzzling phenomena thatcannot as yet be convincingly explained,e i ther by ethological principles or by theLaw of Effect. We can choose either toaccept these behaviors as anomalies withinour present conceptual system, hoping thatfur ther research will show how to reconcilethem, or revise the system in a way that willaccommodate them more natural ly. Thefirst alternative is becoming increasinglyhard to main ta in , as it becomes clear thatthese behaviors are of wide occurrence, andas they continuetoresist at tempts toexplainthem in conven tional terms. Polydipsia isthe most widely studied adjunctive behavior,and Falk (1969) summarizes research re-sults as follows:It is not explicable in te rms of any a l tered stateof water balance initiated by the experimental con-ditions. It cannot be attributed to adventitiousreinforcing effects. Since it cannot be related toabnormal water losses, chronic internal stimulationaris ing from unusual s ta tes . . . or from in ju ryto the centra l nervous system, the overdrinkingwould be classified c l inica l ly as pr imary or psy-chogenic polydipsia [p . 587].A revision of the conceptual foundationsofoperant behavior, which will deal naturallywith these behaviors, as well as guide re-search into more profi table channels, seemscalled for.Development of the Terminal Response

The development of the terminal responseprovides some clues toward an alternative


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SUPERSTITION E X P E R I M E N T A N D A D A P T IV E B E H A V I O R 15conception. Changes in the termin al re-sponse throughout acquisition rule out anunqualif ied application of the Law of Effectas a description of the process. For ex-ample, three of the four birds made the re-sponse Head in magazine a t a higher f re-quency and for a larger fraction of the totalt ime than any other response, for the firstfew sessions of exposure to the superstitionprocedure (either FI or VI, depending onthe bird ). This behavior w as also the onemost often contiguous with the delivery offood. Yet during later sessions, it droppedout abruptly and was replaced by Pecking.Thus th e developmentofPeckingaste rmina lresponse resembles the findings of Williamsand Will iams and of Bre land and Bre land ,much more than i t does the s trengtheningof an emitted response, in Skinner ' s te rms ,by the automatic action of food as a rein-forcer. In all these cases, the presentationof food at a predictable time resulted, aftertraining,in theregular occurrence of afood-related behavior in antic ipat ion of food de-livery, qui te independent ly of the demandchara cteristics of the situation (i.e., thereinforcement schedule) . Given tha t foodis a stimulus that elicits pecking by pigeons,the appearance of pecking, in antic ipat ionoffood, in thepresent exper imentis an instanceof th e principleofst imu lus substi tut ion(Hil-ga rd & M arqu is , 1940). The stimulus is,of course, a temporal one (postfood time),and the situation is analogous, therefore, toPavlovian temporal condit ioning (Pavlov,1927), both operationally and in its con-formity to the substitution principle. There-fore, it is tempting to attribute the appear-ance of pec king to a classical con dition ingmechanism, and leave it at that.A number of considerations suggest thatthis explanation will not suffice, however:(a) The behavior of onebird (29) is a par-t ial exception. He showed a te rmina l re-sponse (Head in magaz ine) different fromPecking, although this response was meta-stable (Staddon, 1965), in the sense thatit was displaced by Pecking following aschedule shift. In addition, Skinner's resultsand informal observations in a number oflaboratories indicate that th e superstitionprocedure m ay generate behaviors other than

pecking that persist fo r considerable periodsof t ime . Presumably, man y of these be -haviorsare te rmina lresponses,in our sense,and, metastable or not, they cann ot be dis-missed in favor of a Pavlovian account of allt e rmina l responses in superstition situations.(b ) The results of Ra chlin (1969),who wasable to obtain spontaneous key pecking bymeans of the auto-shaping procedure ofBrownand Jenkins,butusingelectric shock-reduct ion ra ther than food as the reinforcer ,also complicate th e pic ture , s ince it is notclear that pecking iselicitedbyshock,as itis by food. The results of Sidman andFletcher (1968), w ho were able to autoshape key pushing in rhesus monkeys, arealso not readily explicable by stimulus sub-sti tution, ( c ) Will iams and Will iams(1969) note that the directed nature of thekey peck in the auto-shaping situation is notreadily acc omm odated w ithin a Pavlovianf r a m e w o r k :th e direc ted qual i ty of the induced pecking doesnot follow na tura l ly from respondent pr inc iples(see a lso Brown and Jenkins, 1968). It is un-clear, for example , why pecking would be directedat the key rather than the feeder, or indeed whyit would be d i rec ted anywhere at all [p. 519],A similar object ioncan be raised here, sinceth e terminal response ofpecking was alwaysdirected at the magaz inewal l , although it isimpor tan t to notice that this object ion ismore damaging to an interpretation in termsof classical conditioning than one couchedsimply in te rms of st imulus substi tut ion.(d ) Finally, there is the problem of theskeletal na tu re of pecking. Ever sinceSkinner ' s (1938) original suggestion, it hasbecome increasingly common to restrict theconcept of classical conditioning to auto-nomically me diated responses. Some cri-t ic isms of this convention are presented be-low, and Staddon (1970a) has arguedagainst theoperan t / respondent andemitted/elicited dichotomies. For the moment , le tit be said that the objection to the skeletalna ture of the response is only a problem foran interpreta t ionof the development of peck-ing in terms of classical conditioning, ast radi t ional ly conc eived. It does not conflictwith a s t im ulus substitut ion interpreta t ion.


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16 J. E. R. S T A D D O N ANDV I R G I N I A L. S I M M E L H A GIn summary,it is clear that whilethe prin-ciple of stimulus substitution describes thedevelopment of the terminal response in amajority of cases, and is more successfulthan an appeal to Pavlovian principlesmodeled on the salivation referenceexperi-ment , it is not adequate as a universalaccount. W e turn now to the possibilityofageneral schemeto deal with these anoma-lous facts.

E V O L U T I O N A N D L E A R N I N GObjectively considered, th e subject mat-ter of the psychology of animal learning-the behaviorof animalsis apart ofbiology.

This commonality does not extend to t e rmsand concepts, howeve r. Although th eethologists have investigated unlearned be-haviors in a variety of species, learning re -mains almost exclusively the possession ofpsychologists. Consequently, the theoreticalfoundations of the study of learning, such asthey are, have evolved almost independentlyof biology. It is now 15 years since V er-planck (1955) wrote: the structure of thetheory of unlearned behavior and that oflearned behavior must prove to be similarif not identical [p . 140]," but littleprogresstoward a unified set of concepts has beenmade. Yet the facts discussed in the pre-vious section seem to demand an interpreta-t ion within th e context of adaptive behavioras a whole.The principles of evolution by natural se-lection provide a unifying framework forbiology. Pfaffman (1970) has recentlycommen ted :I am impressed by the extent to which evolution,the genetic machinery, and biochemistry providefor biologists a com mon language and un ity oftheory that overrides the molecular versus orga-nismic debate within biology. In contrast , it isobvious that there is no unified theory of behaviorfor all students of behavior [p . 438].

These considerat ionsthe commonali tyofsubject matter between biology and animalpsychology, the probable co mm on basis oflearned and unlearned behavior, th e unifyingrole of evolutionary processes in biologyall suggest the application of evolu tiona ryprinciples to the psychology of learning inanimals . In recent years, several papers

have drawn at tent ion to the similarities be-tween evolution and learning (e.g., Breland& Bre land , 1966; Broadbent, 1961; Gilbert,1970; Herrnstein, 1964; Pringle, 1951;Skinner, 1966a, 1966b, 1969), but no ver-sion of the evolutionary approach has provedinfluential as yet. The main reasons forthis failure, perhaps, have been th e compara-tive effectiveness of tradit ional vers ions ofthe Law ofEffect in dealing with th e limitedphenomena of laboratory learning experi-ments and the lack of a substantial bodyoffacts clearly in conflict with accepted theory.To someextent, of course, the second factorreflects the firstalthough it would be cyni-cal to speculate that the kind of experimentspsychologists do are often such as to p re -clude data that might go beyond currenttheory. In any even t, neither of these rea-sons now holds true.The growing number of facts on auto-shaping, instinctive dr if t , adjunct ive, andsuperstitious behaviors are not readilyaccommodated within tradit ional views. Inaddit ion, th e his tory of the Law of Effectas a principle of acquisition (a s opposed toth esteady state, i.e., asy m pto te) has notbeena distinguished one. Little rem ain s of theimpressive edifice erected by Hull and hisfollowers on this base. We are no longerconcerned with the production of lea rn ingcurves, nor with the measurement of habitstrength or reaction poten tial. Hullia ntheory has proven effective neither in theelucidation of complex cases nor as an aidto the discovery of new phenomena . In -deed, th e opposite has general ly been true:new learning phenomena such as schedulesof re inforcement, learning, and reversal sets,etc. have typically been th e result ofuna idedcuriosi ty ra ther than the hypothetico-deduc-tive method, as exemplified by Hul l and hiss tudents . This represe nts a fai lure of Hul-lian theory ra ther than a genera l ind ic tm entof the hypothet ico-deduct ive method, whichhas proven every bit as powerful as Hul lbelieved it to bewhen usedby others (e.g.,Darwin, cf . Ghisel in, 1969). A similar ,although less sweeping, verdict must behanded down on stochastic learning theory,which represents perhaps the most d irecta t tempt to t r ans l a t e the L aw of Effect in to


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SUPERSTITION EXPERIMENT AND ADAPTIVE BEHAVIOR 17a quan titative principle of acquisition. W iththeexceptionofpredictionsabout thesteadystate, such as Estes' ingenious deductionofprobability matching (Estes, 1957), theearly promiseofthisapproachas a way ofunders tanding the behavior of individualanimals has not been fulfilled. It seems fairto saythatthe rashof theoretical elaborationthat has occupied the years since Thorndikefirst stated the Law of Effect has told usalmost nothing more about the moment-by-moment behavior of a single organism ina learning situation. Althoug h th e alterna-tive we will offer may be no better thanearlier views, it does accommodate theanomalies we have discussedand th e needfor some al ternat ive can hardly be ques-t ioned.The close analogy between the Law ofEffect and evolution suggests an approachthat m ay be a step towa rd the gene ral frame-work which the psychology of learning soobviously lacks. At the pre sen t stage ofknowledge, this approach is simply an anal-ogy, althougha compelling one, and cannotyet becalledanevolutionary theoryof learn-ing. However, it provides a beginningandmay lead to a truly evolutionary accountwhich can securely imbedthe study oflearn-ing in the broader field ofbiology.Behavioral Variation and Reinforcement

The Law of Effect, suitably modified totake account of advances sinceThorndike'soriginal formulation, can be stated so as toemphasize acquisition, or the steady state,and learning (e.g., S-R bonds ) , or per-formance. W e will take as a point of de-parture a neutral version of the law thatemphasizes performance in the steady state,as follows: If, in a given situation, a posi-tive correlation be imposed between someaspect of an animal's behavior and the de-livery of reinforc em en t, that behavior willgenerally cometo predominate inthat situa-tion. The term correlation is in tendedtoinclude cases of delay of reinforcement an dexperiments in which the response acts onth e rate of reinforcement direct ly (e.g.,Herrnstein &Hineline,1966; Keehn, 1970).This formulation does not take account ofmore complex s i tuat ions where more than

one behavior and more than on e correla-tionare involved (i.e., choice situations),asthese complications do not affect the presentargument . A discussion of three aspectsofthis law(a) the initial behavior in thesituation before reinforcement is introduced,( > ) th e process whereby this behavior istransformed into the dominant reinforcedbehavior, and (c) reinforcementfollows:(a) The behavior in a situation beforethe occurrence of reinforcement reflects anumber offactors, includingpast experiencein similar situations (transfer), motivation,stimulusfactors (e.g.,novel or sign stim uli),and others. We propose the label "prin-ciples of behavioral variation" for all suchfactors that originate behavior. These prin-ciples are analogous to Darwin's laws ofvariation, corresponding to the modern lawsof heredity and ontogeny that provide thephenotypes on which selection (analogousto the principles of reinforcement, see be-low) can act. Thus, th e term "variation"is intended to denote not mere variabili ty,bu t the organized production of novelty, inth e Darwinian sense.(b ) Transition from initial behavior tofinal behavior is the traditional problem oflearning theory and, as we have seen, isessentially unsolved at the level of the indi-vidual organism. However, it is at thispoint that th e analogy to the mechanismofna tura l selection becomes most apparent.Broadbent (1961) makes the parallel quitec lear :Since individual animals differ, and those withuseful characteristics [with respect to a particularniche] survive and pass them on to their children,we can expla in the de l ica te adjustment of eachanimal's shape to its surroundings without requir-in g a conscious purpose on the pa r t of the Polarbear to grow a wh ite coat. Equa lly each indi-vidual animal [under the Law of Effect] triesvarious actions and those become more commonwhich are followed by consummatory acts [i.e.,re inforcement] [p . 56].Thus, th e transition from initial to final be-havior can be viewed as the outcome of twoprocesses:a processthatgenerates behavior,and a process that selects (i.e., selectivelyeliminates) from the behavior so produced.Since thereis no reason to supposethat theprocess which generates behavior following


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18 J. E. R. S T A D D O N ANDV I R G I N I A L. S I M M E L H A Gthe first and subsequent reinforcements isdifferent inkindfrom the process that gener-ated the initial behavior (although thee f f e c t s will generally be different, see Ex-t inct ion, be low) , we can inc lude both underthe head ofprinciples ofbehavioral variation.W e propose the label principles of rein-forcement for the second, selective process.(c ) As we have seen, th e Darwinianprinciple of selection is analogous to theprocess that transforms initial behavior intofinal behavior the principles of re inforce-ment." The notion of re inforcement (moreexactly, the schedule ofre in forcem ent) i tselfis infact analogous to an earl ier concept,on ethat preceded evolution by na tura l selectionand can bederived from it: the Law ofCon-ditions of Existence, that is, the fact thatorganisms are adapted to a particular niche.This is apparent in the form of the state-men t s: The Polar bear has a white coatbecause it is adaptive in his environment.The pigeon pecks the key because he isreinforced for doing so. It is importantto emp hasize this d is t inct ion between rein-forcement and principles of reinforcement,and the analogous dis t inct ion between adap-tation to aniche and the process ofselectionby which adaptation comes about. In thecase of adapta t ion, the process of selectioninvolves differential reproduction, e i therthrough absence of a mate , infert i l i ty, ordeath before reproductive maturity. In thecase of reinforcement, the distinction is lessobvious, since th e principles of re inforce-men t refer to the laws by means of whichbehaviors that fail to yie ld re inforcementa reel iminated, ra ther than the simple fact thatreinforced behaviors generally predominateat the expenseof unreinforced behaviors .Thus, both evolution and lea rn ing can beregarded as the outcomeof two independentprocesses: a process of variation that gener-ates either phenotypes, in the caseof evolu-tion, or behavior, in the case of l e a rn ing ;and a process of selection that acts withinthe limits set by the first process. In bothcases, th e actual outcome of the total proc-ess is related to, but not identical with, th emateria l ac ted upon: phenotypes reproducemore or less successfully, but a gene pool isthe outcome ofselection; similarly, behaviors

are moreor less highlycorrelated with rein-forcement , but learning (i.e. , an alteration inmemory) results.The three aspects of this processvaria-t ion, select ion, and adap ta t ionhave re-ceived differing emphases at different times,depending on the prevail ing s ta te ofknowl-edge. Before Darwin, adapta t ion, in theform of the Law of Conditions ofExistence,was emp hasized, s ince the only explanationfor itthe design of the Creatorwas notscientifically fruitful . Following Darw in ,selection, both na tura l and artificial, re-ceived increased a t tent ion, in the absence offirm knowledge of the mechanism of varia-tion (i.e., inheritance). With the adventof M ende lian genetics, varia t ion has beenmost inte nsiv ely studied (this is one aspectof the molecular vs.organismic" debate re -ferred to by Pfa f fman) .In terms of this development, the studyof lea rn ing is at a relatively primitive level,since the Law ofEffect, although a great ad-vance over the level of understanding whichpreceded i t , simply represents theiden tifica-tion of env i ronmen ta l eventsreinforcerswith respect to which behavior is adaptive.Lacking is a c lea r unders tand ingof both se -lection (the principles of reinforcement)and varia t ion ( the principles of va r i a t ion ) .Space precludes exhaustive elaborationof all the implications of the classificatoryscheme we are suggesting. However, inorder to provide some context for ouraccount of the facts already discussed, itseems essential to briefly sum ma rize somepossible candidates fo r principles of varia-tion and re inforcement . It should be ob-vious that current knowledge does not per-mit the categories used to be ei ther exhaus-t ive or clear-cut.Principles of behavioral variation. 1.Transfer processes: One of the main sourcesof behavior in a new situation is obviouslypast experiencein similar situations. Trans-fe r has been most exhaustively studiedu n d e r the restricted conditions of verballearning (e.g., Tulving & Madigan , 1970),but the principles of me mory thus de-r ivedproact ive and retroactive interfer-ence, primacy and recency, retrieval factors,e tc .are presumablyof general applicability.


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SUPERSTITION E X P E R I M E N T A N D A D A P T IV E B E H A V I O R 19With few exceptions (e.g., Gonzales,Behrend, & Bi t te rman, 1967), these prin-ciples have been little used to interpretanimal learning experiments. Other prin -ciples of transfer are st imulus and responsegeneralization (induction) and what mightbe called compositional tran sfer, in whic hseveral past experiences are combined togenerate anovel behavior,as in insight learn-ing and other forms of subjective organiza-tion ofpast input .2. Stimulus subst i tu t ion: This principle,which is usually identified with Pavlovianconditioning, has already been discussed asa description of the origin of the terminalresponse of Pecking. It may also describethe origin of the metastable terminal re -sponseHeadinmagazine, since this responseis also elicited by food under these condi-tions, and the animal which showedthis re -sponse most persistently (Bird 29) had hadconsiderable experimental experience. Thedifference in the persistence ofHead in mag-azine in the case of this bird, as comparedwith others, cannot be explained in this wayand might reflect a difference inother trans-fer processes. The final dominanceof Peck-ing, in every case, may reflect a specialsusceptibility of consummatory responses toth e stimulus substitution principle,or the ac-tion of other transfer principles in this par-ticular situation in ways that are presentlyuncle ar. The ind efinite persistence of keypecking following only three peck-contingentreinforcements, found by Neuringer(1970b),tends to support the simpler con-clusion, as does the data of Wolin (1968),who reports a similarity between the to-pography of operant pecking for food orwater reinforcers, and the appropriate un-conditioned response. W e return later to ageneral discussion of this principle in rela-tiontothesedata (pp.33-34).3. Preparatory responses: This principleis also frequently associated with classicalconditioning, and in that sense is relatedto , and to some extent overlaps with, th estimulus substitution princip le. Thu s, someconditioned responses,suchassalivation, canbe equally well described by either principle.Others, also respondents (suchas heart rate,which increases following electric shock, but

usually decreases in anticipation of it [Zea-man & Smith, 1965]) may be classified aspreparatory responses. Skeletal responsesobserved in classical conditioning situationsare often preparatory in nature (see discus-sion ofclassical conditioning, below).4. Syntactic constraints:There are oftensequential constraints among behaviors, sothat a given behavior is determined by someproperty of the sequence of preceding be-haviors. Examples are spontaneous positionalternation observed in rats and other ro -dents, stimulus alternation observed in mon-keys on learning se t problems (e.g., Levine,1965),and sequential dependencies observedin most species which cause responses tooccur in runs rather than alternating ran-domly (e.g., position habits and other per-severative errors). Hum an language pro-vides the most developed example of syntac-tic constraints.5. Orienting responses: This category in -cludes all those transient behaviors, such asexploration, play, curiosity, etc., that exposeth e organism to new stimuli and providethepossibilityoftransfer tofuturesituations.6. Situation-specific and species-typicalresponses: Certain situations seem to callforth specific responses, which are oftentypical of the species rather than the indi-vidual and do not seem to depend in anyobvious way on any of the other principlesof variation such as transfer, etc. Examplesare the species-specific defen se reactions dis-cussed by Bolles (1970), which occur infear-producing situations, the tendency topeck bright objects shown by many birds(Breland &Breland, 1966), and the diggingshown by small rodents (Fantino & Cole,1968). Other examples are givenby Click-man andSroges (1966).Principles of reinforcement. Before thediscovery of the mechanism of inheritance,evolution could be explained only in termsof a goaladaptationand a means suf-ficient to reach that goalvariation andselection; th e generation-by-generation de-tails of the process were obscure: Ourignorance of the laws of variation is pro-found [Darwin, 1951, p. 170]." We areat present equally ignorant of the mecha-nisms of beha vioral varia tion. Since learn -


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20 J. E. R. S T A D D O N ANDV I R G I N I A L. S I M M E L H A Ging must usually involve constant interplaybetween variation and re in forcement ,we arenotyet in apositionto suggest anything spe-cific about the moment-by-moment detai ls ofth e process, either in its var iat ional or se-lective aspects. How eve r, just as Darwinwas able to say something about selectionby pointing out the adaptive role of variousstructures, so it is possible to learn some-thing about th e selective role of reinforce-men t by looking at steady-state adaptationsto fixed conditions of reinforcement, that is,re inforcement schedules. On this basis, wesuggest the following tentative generaliza-t ions about th e effects of re inforcement :1. Reinforcement acts directly onlyon thet e rmina l response; activities which occur atother times (interim activities, adjunctivebehavior, etc.) must be accounted for inother ways, to be discussed later. Thisassertion is perhaps closer to a definitionthan an empirical generalization, since it isequivalent to the assertion that the termina lresponse may, in general, be identified asthe act iv i ty occurr ing in closest proximity toreinforcement in the steady state. Identifi-cation is, of course, no problem incondit ion-ing situations that enforce a cont ingencybe-tween some proper ty of behavior and thedelivery of reinforcem ent. However , wewill show later that there is no empir ical orlogical basis for separating situations thatdo impose a contingency between responseand re in forcement from those that do not(see Classical Conditioning, be low) .2. Reinforcem ent acts only to el iminatebehaviors that are less directly correlatedwith reinforcem ent than others. This gener-alization, like the first, is also more like adefinit ion, since all that is observed (underconsistent conditions of re in forcement ) isth e even tua l p r edominance of one behaviorover otherswhich is consistent with eithera suppressive or a strengthening effect. A sSkinner (1966a) points out in a summaryof the Law of Effec t :Thornd ike w as closer to the princ iple of natura lselection than th e [usual] s ta tement of his law.He did not need to saythat a response which hadbeen followed by a certa in kind of consequencewas more likely to occur again but simply thatit was not less likely. It ev entu ally held the fieldbecause responses which failed to have such

effects tended, like less favored species, to dis-appear [p. 13].Unfor tuna te ly , Skinner , and most other be-haviorists, elected to follow Thorndike inconsidering reinforcement to have a positive,strengthening, or "stamping-in" effect. Oneof th e main purposes of the presen t paper isto suggest that this decision was a mistakeand has given rise to a n u m b e r ofproblemsand controversies that can be avoided if theeffects of re in forcementare considered to bepurely selective or suppressive.There are three kinds of argument which

, support a purely selective role for reinforce-\ment. The first, and most important ,is thatfthe overall conceptual scheme which results{is simpler and more easily related to bio-logical accountsof behavior than thealterna-t ive.The second point is that situations suchas extinction and shaping by successive ap-proximationsthat might seem torequireanactive role for reinforcement can be inter-7pretedin a way that doesnotrequire any-thing more than a selective effect. This

point is discussed later (see Extinction,be-l ow ) .The third point is that the superstitionand related exper iments suggest that the re-sponse contingency imposed by most rein-forcement schedules is not essential for theproduction of some terminal response, butonly for the selection of one response overothers, or for directing a response whichwould probab ly predominate in any caseas in key pecking by pigeons. Our fai lureto find a consistent difference in rate of ob-server-defined pecking between the response-dependen t and response- independen t condi -tions of the present superst i t ion exper imentsupports th is view, as does a recent f indingthat the cont ingency between electr ic shockand respondingis not necessary to the gener-ation of behavior maintained by intermit tentshock deliveryto squirrel monkeys (Hutch-inson, 1970; Stretch, personal com mu nica -t ion, 1970).The usual in terpretat ion of the fact thatthere is a terminal response in the supersti-tion situation, despite th e absence of re-sponse-contingency, is the notion of acci-dental strengthening of a response by con-


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22 J. E. R. S T A D D O N ANDV I R G I N I A L. S I M M E L H A Ggiven stimulus may be reinforcing at onetime, but not at another, requires the ideaof a state corresponding to each class ofreinforcers. The independent variable ofwhich the strength of most of these states isa function is deprivation with respect to theappropriate class of reinforcers (food de-privation for the hunger state, water fo rthirst,etc.). Thiswillnot d o formost nega-tive reinforcers (e.g., the removal of electricshock), however, since there is no obviouscounterpart to deprivation in this case. Itisalso unlikely that deprivation is the onlyindependent variable sufficient to alter thestrength of states associated with positivereinforcem ent. For example, evidence isdiscussed later in favor of reciprocal inhibi-tory interaction betweenstates as apossiblefactor in polydipsia and other adjunctive be-havior. Inte ract ions of this sort may alsoalter the strength of states for which thereis no deprivation requirement, as in audioanaesthesia (Licklider, 1961).Thus,one mayhope for a set of principlesof reinforcement that will deal both withthe proper classification of states and withthe interactions among them.The theoretical vocabulary of learning isfull of terms with an uneasy conceptual sta-tu s somewhere between explanation, defini-t ion, and category label. Thisterminology,which is not coherent or internally consist-ent, makes it difficult to approach particulartopics with an open min d. It is too easyto dismiss an experimental result as due toadventitious reinforcement or respondentconditioning without, in fact, having anyclear understanding of what ha s been said.Simply defining everything operationally isof little help in this situation, since a setof definitionsis not atheory. And a theory,in the sense of a system of concepts that isinternally consistent and coherent, is whatis required if we are to be sure, in particularcases, whether we really understand a phe-nomenonor are merely substituting onemystery for another, with the assistance ofan opaque vocabulary.W hat we are proposing is too primitive tobe called a theory in this sense. How eve r,it does offer a system of classification thatmakes it difficult to have the illusion of

understanding a phenomenon if compre-hension is really lacking. In the followingsection, some implicationsof this scheme areshown in three major areas:acquisition, ex-tinction, and classical conditioning. This isfollowed by a brief discussion of possibledifficulties of this approach. With the aidof this groundwork, it will then be easier toreturn to a general account of the supersti-tion and related experiments in the conclud-ing section.Acquisition

The numberof trials necessary for learn-ing is one of those perennial problems thatseems to defy resolution. Ap peal to data isnot conclusive because learning curves aresometimes incremental and sometimes step-like. Even in particular cases, theory is notconclusive either, since with sufficient in -genuity, theoretical accounts of both kindsof curve may be constructed on the basisof either one (or a few) tr ia l learningassumptions or incremental assumptions in-volving thresholds. W e turn now to thepossibility that the issue is a consequenceof the stamping-in view of reinforcementand becomes less urgent once that view ischallenged.A comm ent by Skinner (1953) on thenecessary and sufficient conditions for thedevelopment of superstition provides ani l lustration:In superstitious operant behavior . . . the processof conditioning ha s miscarried. Conditioningoffers tremendous advantages in equipping th eorganism with behavior which is effective in anovel environment, bu t there appears to be noway of preven ting the acquisition of non -advan ta-geous behavior through accident. Curiously, thisdifficulty must have increased as the process ofconditioning was accelerated in the course ofevolution. If, for example, three reinforcem entswere always required in order to change theprobability of a response, superstitious behaviorwould be unlikely. It is only because organismshave reached the point at which a single con-tingency makes a substantial change that theyare vulnerable to coincidences [pp. 86-87].

Even within the framework of the stamp-ing-in view, it is clear that the truth of thisstatement depends on a tacit assumptionthat responses will not generally occur morethan once unless followed by reinforcement.


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SUPERSTITION EXPERIMENT AND ADAPTIVE BEHAVIOR 23If a given response can be relied on to occurat least 20 t imes in succession, even withoutreinforcement , then 3-trial, or even 10-triallearning might wellb e sufficient toinsure it sacquisition un der the c onditions of the super-stition experiment. The assumption thatresponses w ill occur only once in the absenceof re inforcement is a strong assumptionabout syntact ic constra ints , in our terminol-ogy. M oreover, it is contradicted by the re-sults of the Wil l iams and Will iams s tudy(1969), which show indefini te persistenceof pecking in the absence of any contiguousre la t ionship between pecks and reinforce-men t . There is no reason to suppose that asimilar persistence is not characteristic ofother behaviors (e.g., position hab i t s ) , a l -though pecking may be more pers is tent thanmost. Thus, th e finding of superstitiousterminal responses, or of indefinite peckingfollowing just three response-contingent re-inforcements (Neuringer, 1970b), needimply nothing about the n u m b e r of trialsnecessary for learning.

These considerations suggest, as a mini-mum, the need to take varia t ion into accountin discussions of the speed of condition-ing, since rapid acquisition m ay either re -f lec t an unpersis tent response that is rea l lylearned rapidly, or a very persistent onethat may be learne d qu ite slowly. No in-ferences about speed of conditioning canbe drawn solely on the basis of speed ofacquisition wi thout informat ion about thef requency and pa t te rn of a given behaviorto be expected in a given s i tuat ion (whichmay inclu de predic table del ivery of re in-forcement ) in the absence of contiguity be-tween that behavior and re inforcem ent. Inpract ice , s ince information of the requiredsort is rarely, if ever, available, it seemswise to defe r the issue of speed of learningunt i l behavioral varia t ion has been muchmore thoroughly studied.4Thus , the moment -by-moment details con-cern ing th e effect of re inforcement remain

4Problem s of this sort are not solved by re-fe r r i ng to a hypothet ica l "operant level because(a) this level is often zero in the absence of ahistory of re inforcement in the s i tua t ion; (6) it isr a re ly cons tan t , as the te rm leve l i m p l i e s ; and(c ) th e problem of the origin of this level isthereby simply evaded.

uncerta in unti l much more is known aboutvaria t ion. In the meant ime it seems moreparsimonious and less likely to lead to fruit-less controversies about "speed of condition-ing, continuity versus noncontinuity, etc.to assume that the appearance of one be-havior , rather than another, at a certaint ime or place, rather than some other timeor place, always require s explanation inte rms of principles of variation, with onlyth e disappearance of behaviors being attrib-utable to the effects of reinforcement.This general approach is not novel. Itresembles both Harlow's (1959) account oflearning-set acquisition in terms of the pro-gressive elimination of error factors, andcertain versions of stimulus-sampling theory(Ne imark & Estes, 1967). In Harlow'sterms, as in ours, one-trial acquisition is aphenomenon that depends on the existenceof factors tha t make the correct behaviormuch more probable (and pers is tent) thanothers (i.e. , upon principles of varia t ion).In the learning-set case, these factors areembodied in the prior training procedure,which progressively selects for an initiallyweak behavior (the win stay, lose shift"strategy) at the expense of the initiallymuch stronger tendencies to approach par-ticular stimuli. A lengthy process ma y notbe essentia l , however, fo r principles of varia-tion inv olving insight ( compositional trans-fer, see above) may serve th e same func-t ion, if they are available to the animal .The important point is the shift of emphasisaway from the supposed efficacy of somestamping-in mechanism, the action of whichmust remain obscure in the absence ofknowledge about variation, to the principlesof varia t ion that determine the strength ofbehaviors in advance of contiguity with re -inforcement.5Extinction

Extinct ion is often used as a test fo r what is learned during a training pro-5Mem ory has not been separately discussed inthis account of acquisition because it is embodiedin most of the variational and selective processeswe have described. The argum ent of the presentsection suggests that a separate account of mem-or y may have to await advances in our knowledgeof these processes.


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24 J. E. R. S T A D D O N ANDV I R G I N I A L. S I M M E L H A Gcedure, as in generalization testing (Gutt-man &Kalish, 1956), and testing for con-trol by temporal factors (Ferster & Skin-ner, 1957; Staddon, 1970b). Under theseconditions, it is assumed that behavior isdetermined almostentirelyby transfer fromthe base-line condition. Providing the dif-ference between the extinction and trainingconditions is not too great, either in termsof environmental factors (the stimulus situa-tion is not too different) or temporal factors(the extinction is not prolonged), thisassumption can be just if ied by thereliabilityand predictability of the behavior usuallyobserved.

When these conditions are not satisfiedor when the training preceding extinctionhas notbeen protracted, this reliabilityis notusually found. On the contrary, extinctionunder these conditions is usually associatedwith an increase in the variability of be-havior (Antonitis, 1951; Millenson & Hur-witz, 1961). This increase in variability isexactly what would be expected if, as wehave suggested, reinforcement has a purelyselective effect: in these terms, traininginvolves a progressive reduction in vari-ability under th e selective action of rein-forcement (centripetal selection, see be-low), so that absence of reinforcement(extinction) represents a relaxation of se-lectionwith an attendant rise in vari-ability. We turn now to a brief accountof the effects of changes in the amount anddirection ofselection inevolution, whichmayshed some further light on the propertiesofbehavioral extinction.Darwin (1896) comments on the effectof domestication as follows:From a remote period to the present day, underclimates and circumstances as dif ferent as it ispossible to conceive, organic beings of all kinds,when domesticated or cultivated, have varied. . . .These facts, and innumerable others which couldbe added, indicate that a change of almost anykind in the conditions of life suffices to causevariabili ty . . . [Vol. 2, p.243].Although Darwin sometimes (erroneously)interpreted this observation as reflecting adirect effect of changed conditions on thereproductive system, it can be interpretedin modern terms as due to a relaxation of

selection. This is clear from the concept ofcentripetal selection (Haldane, 1959; Mayr,1963; Simpson, 1953), which refers to thefact that selection under wwchanging condi-tions, iflong continued, acts toweed out ex-tremes, rather than systematically to shiftpopulation characteristics in any particulardirection:When adaptation is keeping up , selection at anyon e time will be mainly in favor of the existingtype. . . . In such cases, the intensity of selec-tion tends to affect not the rate of change but theamount of variation [Simpson, 19S3, p. 147].Thus, a changein conditions will generallyinvolve a shift away from centripetal selec-tion, with its tendency to reduce variability,and will often lead, therefore, to increasedvariability. The most obvious example ofthe effects ofrelaxation of selectioninevolu-tion is degenerating or vestigial structures,tha t are no longer being selected f o r :It is so commonly true that degenerating struc-tures are highly variable that thismay beadvancedas an empirical evolutionary generalization [Simp-s o n , 1953, p. 75].

We have already noted that the onsetofvariability inextinction is often delayed. Asimilar delay in the effect ofchanged condi-t ions is often apparent in evolution, Darwin(1896) notes:W e have good grounds fo r believing that the in-fluence of changed conditions accumulates, so thatno effect is produced on a species until it has beenexposed during several generations to continuedcultivation or domestication. Universal experi-ence shows us that when new flowers are firstintroduced into our gardens they do not vary;but ultimately all, with th e rarest exceptions, varyto a greater or less extent [Vol. 2, p. 249].Similar delays have also been reported inexperiments on artificial selection (Mayr,1963). These delays seem to reflect whathas been termed "genetic inertia"or "gene-tic homeostasis" (Mayr, 1963), that is, thetendency for agene pool which is the resultof a long period of consistent selection toresist changes in the direction of selection.A similar mechanism in behavior mightaccount for the dependence ofvariability inextinction on the duration of the precedingtraining period, which was referred to ear-lier: The amountofvariabil i ty might be ex-


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SUPERSTITION EXPERIMENT A N D ADAPTIVE B E H A V I O R 25pected to be greater and its onset soonerfollowing a brief training period than afterone oflonger duration. Genetichomeostasisalso seems to beinvolvedin thephenomenonof reversion, to be discussed next.Not all the variation which occurs eitherin behavioral extinction, or following achange in the conditions of life in evolution,isw holly novel. A relatively commoneffect,for example, is the reappearance of whatDarwin terms "ancestral types, that is,phenotypes which predominated earlier inphylogeny but which have been selectedagainst m ore recen tly. Thisis thephenome-non of reversion which, because of hisignorance concerning heredity, Darwin(1896) found among the most myster iousof evolutionaryprocesses:B ut on the doctrine of reversion . . . the germ[germ plasm] becomes a far more marvellous ob-ject, for, besides the visible changes which it under-goes [i.e., phenotypicexpressions],we must believethat it is crowded with invisible characters, properto ... ancestors separated by hundreds or eventhousands of generations from the present time:and these characters, like those written on pape rwith invisible ink, li e ready to be evolved wheneverthe organisation is disturbed by certain knownor unknown conditions [Vol. 2, pp. 35-36].Thus, on e effect of a relaxation of selectionis a more or less transient increase in therelative influence of the distant past at theexpense of the immediate past. In be-havioral extinction, this should involve thereappearance of old (in the sense of pre-viously extinguished) behavior patterns;that is , t ransfer from conditions precedingthe training condition at the expense oftransfer from the training condition.* Inboth cases, evolution and behavior, the effectof the change in conditionsmay be expectedto depend on variables such as the magni-tude of the change and the time since thepreceding change.

8Other than clinical accounts of regression, wehave been able to find only one published report ofthis effectin an account describing shaping por-poises to show novel behaviors (Pryor, Haag,&O'Reilly, 1969). However, we have frequentlyobserved it while shaping pigeons: if a pigeon hasbeen trained in the past to perform a variety ofresponses, the increase in variability during ex-t inction of the most recently reinforced responsegenera l ly inc ludes the reappearance of earlier re -sponses.

The analogy from Darwin suggests thatany considerable change in conditions shouldincrease variability, yet a change in rein-forcement schedules that includes an in -crease in reinforcement rate is not usuallythought of as producing an increase in vari-ability. This apparent contradiction is re-solved by noting that an increase in rateof re inforcement , in addition to changingconditions, also increases the rate of selec-tion (since th e analogy assumes reinforce-ment to have a purely selective effect ) .Thus, variability may be briefly increased,bu t since the rapidity of selection is alsoincreased, the net effect may be small. Ananalogous (but impossible) phenomenon inevolution would be to decrease th e t imebe-tweengenerations at the same timethat con-ditions are changed. This would speed upthe attainment of a new equilibrium andminimize th e increaseinvariabili ty generallyassociated with changed environment.The increase in variabili ty due to extinc-tionis most direc tly put to use in the processof shaping by successive approximations.Frequent ly,following the first fewreinforce-ments delivered duringa"shaping"session,th e effect is simplyan increase in the rangeand vigor of behav ior. This change can beviewed as being due to the interruption ofeat ing (cf.Handler, 1964), however, ratherthan any direct strengthening effect ofrein-forcement (whichwe are questioning in anycase). In terms of the foregoing analysis,th e condit ionsfollowing the first reinforce-ment should be optimal for an increase invariabili ty: th e change is large (from con-t inuous eating to absence of food) and thetraining procedure is of short duration (the3-4-second eating bout), so that time sincethe prec edin g change is also short. As foodcontinues to be delivered intermittently, se-lection occurs and variability decreases.

We have been suggesting a purely selec-t ive (rather than s trengthening, stamping-in , or energizing) role for reinforcement.The present discussion suggests that suchanessentially passive role is compatible with anumber of phenomenaextinction, the acti-vat ing effects of isolated reinforcementsthat may appear to demand a more activerole for reinforcement. This com patibility


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26 J. E. R. S T A D D O N ANDVIRGINIA L. S I M M E L H A Gwas established by drawing attention tosimilar phenomena in evolution, where th epurely selective effect of the conditions oflife (analogous to the schedule of reinforce-ment) is unquestioned. However, no nec-essary identity between the genetic mecha-nism, which is responsible for the effect ofchanged conditions on variability in struc-ture , and whatever process is responsiblefor analogouseffects in behavior, is intended.Any process for the production of variationthat incorporates some latent memory ofpast adapta t ions is likely to show similareffects.Classical ConditioningOur scheme has strong implications fo rth e distinction betwe en classical (Pavlovia n,respondent) and instrumental (operan t )conditioning, to the extent that th e distinc-tion goes beyond procedural differences.Classical conditioning is often thought of asaparadigmaticinstance of theprimary proc-ess oflearn ing: The [learning] process ap-pears to be based entirely on temporal con-tiguity and to have classical conditioningas its behavioral prototype [Sheffield, 1965,p.321]." The salivation reference exp eri-ment can be interpreted as prototypical inat least two ways that are not always keptseparate. The first (which has some simi-larities to our position) is referred to bySheffieldthe notion that learning dependssolely on temporal relationships. Guth rie 'saphorism that th e animal "learns what hedoes" is a related idea. It is not easy tofind a definitive account of this position,but it mayperhaps be summarizedby sayingthat reinforcement or reward is simply nec-essary to ensure that some behavior occursin a conditioning situation. Principles in -volving temporal relationships (contiguity)then ensure that whatever occurs will trans-fe r from oneoccasion to the next.The second way in which classical con-ditioning is discussed as prototypical is int e rmsof the rulethat relates th e conditionedand unconditioned responses. Pavlov(1927) emphasized stimulus substitution asth e distinctive property of the si tuation: theresponse originallyelicited only by the UCSis later ma de to the CS, Subse que ntly, two

kinds of departure from this rule have beenpointed out: (a) Even in the salivationexperiment, there are other readily identifi-able components of the conditionedresponsethatdo not fit the stimulussubstitution rule.These prep aratory responses (Zen er, 1937)are largely, but not exclusively, skeletal(rather than au tonomic) . (b ) Even in thecase of salivation and other autonomic re-sponses, the CR is rarely identical to theUCR (i.e., a redintegrat ive response), sothat components of the UCR may bemissing from the CR. M ore serious aredifferences in direction of change be-tween CR and UCR, which may not evenbe consistent across individuals, as inheartrate and respiratory conditioning (M artin& Levey, 1969; Upton, 1929; Zeaman &Smith, 1965).

Partly because ofp roblems involving pre-paratory responses, classical conditioning hasincreasingly been restricted to autonomicallymediated responses. There were twobasesfor this restrict ion: th e apparen t difficulty ofconditioning skeletal responses by theopera-t ions of classical conditioning and accordingto the stimulus substitution principle (cf.Skinner, 1938, p . 115), and the supposedimpossibility of conditioning autonomic re-sponses via the Law ofEffect. This isclearfrom Kimble 's (1961) commen t :Obviously th e common expression, th e conditionedresponse, is mis leading, and probably

staddon y simmelag 1971 the superstition experiment a reexamination of its implications for the...

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