Rescorla (1967).pdf

Psychological Review1967, Vol. 74, No. I. 71-80

PAVLOVIAN CONDITIONING AND ITS PROPERCONTROL PROCEDURES1

ROBERT A. RESCORLA *

University of Pennsylvania

The traditional control procedures for Pavlovian conditioning areexamined and each is found wanting. Some procedures introducenonassociative factors not present in the experimental procedurewhile others transform the excitatory, experimental CS-US con-tingency into an inhibitory contingency. An alternative controlprocedure is suggested in which there is no contingency whatsoeverbetween CS and US. This "truly random" control procedure leadsto a new conception of Pavlovian conditioning postulating that thecontingency between CS and US, rather than the pairing of CS andUS, is the important event in conditioning. The fruitfulness of thisnew conception of Pavlovian conditioning is illustrated by 2 ex-perimental results.

The operations performed to estab-lish Pavlovian conditioned reflexes re-quire that the presentation of an un-conditioned stimulus be contingentupon the occurrence of a conditionedstimulus. Students of conditioninghave regarded this contingency betweenCS and US as vital to the definition ofconditioning and have rejected changesin the organism not dependent uponthis contingency (such as sensitizationor pseudoconditioning) as not being"true" conditioning (i.e., associative).Therefore, in order to identify the ef-fects due uniquely to the contingencybetween CS and US, a variety of con-trol procedures have been developed.Each of these procedures attempts toretain some features of the Pavlovianconditioning situation while eliminatingthe CS-US contingency.

!The preparation of this paper and theexperimental work related to it were aidedby United States Public Health ServiceGrant MH-04202 and National ScienceFoundation Grant GB-2428 to Richard L.Solomon and by a National Science Founda-tion predoctoral fellowship to the author.The author would like to express his appre-ciation to Vincent M. LoLordo and RichardL. Solomon for their advice and criticism ofthe ideas presented in this paper.

2 Now at Yale University.

This paper argues that, in fact, noneof the conventional control proceduresfor nonassociative effects is adequate,either taken alone or in combination; itfurther argues that a new type of "ran-dom stimulus" control procedure doesenable one to identify the role of theCS-US contingency in Pavlovian con-ditioning.

TRADITIONAL CONTROL PROCEDURES

The conventional control proceduresfor Pavlovian conditioning are quitefamiliar, so they will be described onlybriefly. In all of these descriptions,we assume that the conditioning or con-trol treatment is administered, and thenall groups are tested with a single (un-reinforced) CS presentation. It is onlythe results of the test trial that are ofinterest. (Similar descriptions couldbe given when anticipatory CRs ratherthan test trial CRs are used as theindex of conditioning.)

The various control treatments whichare administered prior to the test trialin place of Pavlovian conditioning arelisted below together with examples oftheir use.

1. CS-alone control. In this pro-cedure a control subject (5") receives

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72 ROBERT A. RESCOELA

the same number of CS presentationsas does an experimental S; however,no US is administered. This control isdesigned to evaluate the effects offamiliarity with the CS and anychanges in the organism due solely tothat familiarity (Rodnick, 1937;Thompson & McConnell, 1955).

2. Novel CS control. In this pro-cedure, no CS is given prior to the testtrial. The test trial gives an estimateof the unconditioned effects of the CS(Rodnick, 1937; Wickens & Wickens,1940).

3. US-alone control. Repeated pres-entations of the US alone are made inorder to control for sensitization by, orhabituation to, the US (Notterman,Schoenfeld, & Bersh, 1952; Wickens &Wickens, 1940).

4. Explicitly unpaired control (some-times called the random control). Inthis procedure, 6" receives unpairedpresentations of CS and US. This canbe done in a variety of ways, but themost typical is presentation of both CSand US in the same session in randomorder but never close together in time(Bitterman, 1964; Harris, 1943).

5. Backward conditioning. The CSand US are paired, but the US is al-ways presented prior to the CS (Kalish,1954; Spence & Runquist, 1958).

6. Discriminative conditioning. Onestimulus (CS + ) is paired with theUS and the other (CS-) is not. Inthis way CS— receives a treatmentsimilar to that of CS+ except that thecontingency with the US is an "ex-plicitly unpaired" one. Differences be-tween the reactions to CS+ and CS —are taken to indicate Pavlovian condi-tioning (Solomon & Turner, 1962).

The very variety of control pro-cedures which have been developedattests to the inadequacy of any one.But it may be worthwhile to pointbriefly to the pitfalls of each procedurebecause some of these have not been

widely recognized. We take as thelogical criterion for an adequate con-trol procedure that it retain as manyfeatures as possible of the experimentalprocedure while excluding the CS-UScontingency. In general, each of thecontrol procedures, although attempt-ing to eliminate the CS-US contin-gency, can be shown to do considerablymore. The result is that a variety ofother differences, both associative andnonassociative, between experimentaland control procedures is confoundedwith the absence of the CS-US con-tingency. Some of the confoundingsare pointed out below.

1. CS-alone control. Quite obvi-ously, an 6" treated in this way doesnot have the same number of US ex-periences as the experimental S does;therefore, any differences between .9scan be attributed to this difference inexperience with the US. But worse,repeated CS presentations in the ab-sence of all USs may not lead to thesame rate of CS habituation as does re-peated CS presentation in a chamberin which the US also occurs.

2. Novel CS control. It is usefulto know the unconditioned propertiesof the CS, but it is not clear whatrelevance this has for identifying"true" Pavlovian conditioning. Theexperimental 5" has experienced the CSa large number of times prior to thetest trial and it is no longer novel tohim. Why compare him to an 5" forwhom the CS is novel? Comparisonwith a novel CS group allows one toassess the total change in reaction tothe CS produced by the conditioningprocedure but does not permit isola-tion of those changes due uniquely tothe occurrence of Pavlovian con-ditioning.

3. US-alone control. This pro-cedure has faults similar to those of thenovel CS procedure. An 5" with thisprocedure receives a novel CS at the

PAVLOVIAN CONDITIONING AND CONTROL PROCEDURES 73

time of test, while the experimental 5"receives a CS which it has experiencedmany times.

4. Explicitly unpaired control. Inmany ways this procedure comesclosest to being an appropriate control,and it has become increasingly popu-lar in recent years. However, it con-tains flaws which cannot be overlooked.Although it escapes the criticisms ofProcedures 1, 2, and 3, it, too, does notsimply remove the contingency be-tween CS and US; rather, it introducesinstead a new contingency, such thatthe US cannot follow the CS for someminimum time interval. Instead of theCS being a signal for the US, it canbecome a signal for the absence of theUS. Although this is an interestingprocedure in itself, it does not allowa comparison between two groups, onewith a CS-US contingency and onewithout it. We are, instead, in theposition of having two different CS-UScontingencies which may yield differentresults. How can we know whichgroup showed Pavlovian conditioning?

5. Backward conditioning. The rele-vance of this procedure rests upon theassumption that in Pavlovian condi-tioning not only the CS-US contin-gency but also their temporal order ofpresentation is important. It is notclear whether this should be takenas part of the definition of Pavlovianconditioning or as an empirical result.Nevertheless, some investigators havesuggested comparison with a backwardconditioning group to evaluate the tra-ditional experimental group. For thepurposes of analysis, let us assume thatthe CS and US do not overlap in thisprocedure. We then have a sequenceof events: US-CS . . . US-CS . . .US-CS . . . in conditioning. Thisprocedure produces the same difficultyas does the explicitly unpaired pro-cedure : The occurrence of the CS pre-dicts a period free from the US.

Again, presentation of the US is con-tingent upon CS occurrence but thecontingency is a negative one. Ofcourse, if the CS begins during the USin this procedure, CS occurrence pre-dicts the termination of the US, which,in turn, introduces another contin-gency and further complications. It isworth noting that Konorski (1948)considered the backward conditioningparadigm as the prime example of aninhibitory conditioning procedure.

6. Discriminative conditioning. Bynow it should be clear that this controlprocedure falls prey to the same criti-cisms as do Procedures 5 and 6. CS—is explicitly unpaired with the US.In fact, the discriminative condition-ing procedure can be viewed as thesimultaneous administration to thesame 5" of the experimental procedureand Control Procedure 4.

We can conclude that each of theproposed control procedures eitherconfounds some important nonassoci-ative change with the disruption of theCS-US contingency or changes thecontingency from a positive to a nega-tive one. Furthermore, there is noobvious way in which combined controlprocedures can be used to eliminateconfoundings. Therefore, we are inthe unfortunate position of being unableto evaluate "true" Pavlovian condition-ing by the use of any or all of the con-ventional control procedures.

AN ADEQUATE ALTERNATIVE

There is, however, a control pro-cedure which solves the problemsraised above. We shall call this pro-cedure the "truly random" control pro-cedure. In this procedure, both theCS and the US are presented to 5" butthere is no contingency whatsoever be-tween them. That is, the two eventsare programmed entirely randomly andindependently in such a way that some

74 ROBERT A. RESCORLA

"pairings" of CS and US may occurby chance alone. All CS and US oc-currences for the control group are thesame as for the experimental group ex-cept that the regular temporal contin-gency between CS and US is elimi-nated. The occurrence of the CS pro-vides no information about subsequentoccurrences of the US. This procedureis similar in conception to the explicitlyunpaired procedure, (4), except thatit eliminates the contingency of thatprocedure which allows the CS to sig-nal nonoccurrence of the US.8

There are a variety of ways of ar-ranging a truly random control condi-tion. Two major alternatives are: (a)Present the CS as in the experimentalgroup but randomly distribute USsthroughout the session; (&) conversely,present USs as in the experimentalgroup but randomly distribute CSs.Note that, in order for there to be nocontingency, the distributions must besuch that CS occurrences do not pre-dict the occurrence of USs at any timein the remainder of the session. If theCS predicts the occurrence of a US 30minutes later in the session, an ap-propriate random control condition hasnot been achieved.

Despite the apparent adequacy ofthese alternatives, they actually addother confoundings. In the usualPavlovian conditioning procedure, sev-eral time intervals other than theCS-US interval are kept relatively con-stant. Thus time intervals betweensuccessive CSs and successive USs areof some (relatively large) minimumvalue. Each of the two truly randomcontrols would violate one of these re-lations and thus introduce changesother than removal of the CS-UScontingency. Fortunately, this can beavoided if we depart from the tradi-

8 A similar control procedure has beensuggested by Jensen (1961) and by Prokasy(196S).

tional conditioning procedures and usea wide variety of intertrial intervals forthe experimental 5s. Then it is pos-sible to arrange truly random presenta-tions of CS and US for the control 5swhile preserving the inter-US and in-ter-CS intervals of the experimentalcondition. For instance, one could pro-gram CS-US pairings for the experi-mental group with a random-intervalprogrammer. Then a truly randomcontrol would be arranged by usingtwo independent random-interval pro-grammers with the same parameters asthat of the experimental group—oneto deliver CSs and one to deliver USs.

We do not wish to understate theimportance of a variety of nonassoci-ative factors which do occur in Pav-lovian conditioning. It is respect fortheir effects that leads to the advocacyof the truly random control for con-tingency-produced effects. One greatadvantage of the truly random con-trol is that it holds constant betweenthe experimental and control pro-cedures all of the factors extraneousto the CS-US contingency without de-manding that we be able to specify inadvance what factors might be oper-ating. In contrast, the customary con-trol procedures have often been de-veloped only to deal with one supposednonassociative factor.

It is also important to realize thatthe actual results obtained with thetruly random control procedure are ir-relevant to the present argument. Itmay be that in some conditioning situ-ations, 5s treated with the truly ran-dom control procedure will show strongchanges in behavior when the CS ispresented. This simply means thatimportant changes not dependent upona CS-US contingency occur in thissituation; effects due to that contin-gency still must be evaluated as devi-ations from the effects produced by thetruly random procedure.


Traditionally, the prime concern ofAmerican investigators has been theexcitatory processes, and the inade-quate conventional control procedureshave reflected this concern. As notedabove, many of these control proce-dures are biased toward the inhibitoryside because of the explicit nonpairingsof the CS and US. But the inhibitoryeffects of conditioning deserve atten-tion in their own right. Clearly, weneed an appropriate base conditionagainst which to compare both the in-hibitory and excitatory kinds of con-ditioning relations. The truly randomsequence of CSs and USs provides anunbiased control procedure for bothpositive and negative contingencies be-tween CS and US. In fact, if we aregoing to retain the conceptual terms"conditioned excitatory" and "condi-tioned inhibitory" stimuli, the trulyrandom control procedure will providea base line against which to define theseeffects.

In addition to serving as a controlcondition for Pavlovian conditioning,the truly random presentation of CSand US provides an unbiased extinc-tion procedure. To the degree thatour concern in extinction of PavlovianCRs is with how the animal loses itsassociative connection, simply removingthe US from the situation is an inap-propriate extinction procedure. Sim-ple removal of the US eliminates notonly the CS-US contingency but alsowhatever nonassociative effects the USmight have. However, using the trulyrandom presentation of CS and US asan extinction procedure permits exam-ination of the loss of contingency-de-pendent learning independently of theseother effects. Furthermore, the trulyrandom procedure serves as an un-biased procedure for extinction of bothexcitation and inhibition. If inhibitioncan be acquired it seems reasonablethat it can be extinguished. The truly

random presentation of CS and USis the most natural extinction pro-cedure for inhibitory as well as excita-tory effects.

OBJECTIONS TO THE "TRULY RAN-DOM" PROCEDURE: Two THEO-

RETICAL VIEWS OF CON-DITIONING

It seems certain that our argumentswill not be entirely convincing. Allconventional control procedures havea common feature: They never allowforward pairings of the control CS andUS. The reluctance which one mightfeel toward accepting a truly randomcontrol procedure stems in part fromthe close temporal pairings of CS andUS which will occur by chance in thatcondition. One may thus argue thatthe truly random control procedure it-self allows Pavlovian conditioning be-cause of those few chance trials whichpair CS and US; if so, it can hardlybe considered a "pure" control condi-tion. According to such an argument,the same processes may be operativein both the experimental and controlprocedures, but to a lesser degree inthe latter.

This objection runs deep and isworthy of extensive examination. Itrests upon an assumption, often notmade explicit, that the temporal pair-ing of CS and US is the sufficient con-dition for "true" Pavlovian condition-ing. It views Pavlovian conditioningas a one-sided affair in which condi-tioning is either absent or excitatory;the number of CS-US pairings de-termines the degree to which condition-ing is excitatory. It is this view whichdominates American notions of condi-tioning and which has been influentialin preventing inhibitory processes fromplaying a major role in our thinking.A good example of this position is theGuthrian claim that the reinforcing


event in Pavlovian conditioning is sim-ple contiguity between CS and US.From this point of view, a reasonablecontrol procedure for Pavlovian con-ditioning is one in which 5" "is nottaught that the US follows the CS."This has been interpreted to include thepossibly quite different learning that"the CS is not followed by the US."With this type of bias, it might bereasonable to conclude that the "ex-plicitly unpaired" and the discrimi-native conditioning procedure are ap-propriate controls for Pavlovian con-ditioning.

An alternative theoretical view ofPavlovian conditioning, and one whichhas not often been distinguished fromthat in the previous paragraph, is thatthe temporal contingency between CSand US is the relevant condition. Thenotion of contingency differs from thatof pairings in that the former includesnot only what is paired with the CSbut also what is not paired with the CS.Thus the truly random procedure con-tains no contingency between the CSand US, even though it does containsome chance CS-US pairings. Fromthis point of view the appropriate con-trol condition for Pavlovian condition-ing is one in which the animal is taughtthat "the CS is irrelevant to the US."Deviations from this base condition canbe either positive (CS is followed byUS) or negative (CS is followed byabsence of US). This view of condi-tioning has the advantage of separatingout, from the simple absence of condi-tioning, a conceptualized inhibitoryprocess which has a status equal tothat of excitatory processes. Intui-tively it seems clear that learning thatthe US does not follow the CS is dif-ferent from failing to learn that the USfollows the CS or learning that the CSis irrelevant to the US. In this sense,at least, the contingency view of con-ditioning, and the truly random control

procedure which it generates, is morein the spirit of Pavlovian theory.4

The idea of contingency used hereneeds explication. By it we mean thedegree of dependency which presenta-tion of the US has upon prior presen-tation of the CS. This is clearly afunction of the relative proportion ofUS events which occur during or atsome specified time following the CS.Thus, in the truly random condition nodependency exists, but in the standardPavlovian conditioning situation thedependence is complete. The controlcondition is brought closer to the ex-perimental condition as we increasethe proportion of USs occurring in thepresence of the CS. When, at theother extreme, all USs occur in the ab-sence of the CS, the inhibitory end ofthe continuum is reached. These pro-portions can be stated in terms of theprobability of a US occurring giventhe presence of a CS (or given that theCS occurred at some designated priortime), and the probability of a USoccurring given the absence of the CS(cf. Prokasy, 1965). The dimensionof contingency is then a function ofthese two probabilities; if Pavlovianconditioning is dependent upon thecontingency between CS and US, it,too, will be a function of these twoprobabilities. However, no attempt ismade here to specify a particular func-tion which relates these two probabili-ties to a continuum of contingencies."

4 It is worth pointing out that the argu-ment advanced in this paper has directanalogues for instrumental training. What-ever faults it might have, the yoked-controlprocedure was introduced precisely to de-termine what effects are uniquely due to in-strumental reinforcement contingencies. Sim-ilarly, the distinction between pairing andcontingency views has recently been ex-amined for operant conditioning by Premack(1965).

"These probabilities can be calculatedwhatever the number of CS and US events.If, for instance, there is only one CS-US


If two conditioning procedures havethe same probability of reinforcementin the absence of the CS, but have dif-ferent probabilities in the presence ofthe CS, they differ in what is usuallycalled the degree of partial reinforce-ment. Whether or not this affects thedegree of contingency depends uponthe function of these two probabilitiesthat we choose to describe degree ofcontingency. We suggest that the con-tingency dimension, rather than thenumber of CS-US pairings, is thetheoretically fruitful dimension in Pav-lovian conditioning.

As soon as one admits a symmetryof inhibition and excitation in thePavlovian conditioning situation, theCS-US pairing view of conditioningbegins to lose appeal. Pavlovian con-ditioning consists of a sequence of CSsand USs arranged in a particulartemporal pattern. Suppose, now, thatone is primarily interested not in ex-citatory processes but in inhibitoryprocesses, or in how an animal learnsthat the CS signals a period free fromthe US. From the point of view thatthe pairing of CS and US is the im-portant Pavlovian event, the truly ran-dom control procedure is inadequatefor a reason that is exactly the oppositeto what it was for excitatory condition-ing ; now it contains a number of non-pairings of CS and US. Therefore,from such a view we are forced toconclude that the symmetrical controlprocedure for the study of inhibitoryprocesses is to consistently pair CS andUS. This, it seems, is less thansensible.

It may also be argued that the trulyrandom control procedure does morepairing, there is a high degree of contingencysince the probability of a US following a CSis one and the probability of a US in theabsence of the CS is zero. However, itmay turn out empirically that with only afew CS and US events the relative impor-tance of single pairings is greater.

than simply remove the contingency ofPavlovian conditioning. It might, forinstance, introduce a new process of itsown such as increasing the likelihoodthat 5 will ignore or habituate to theCS since it bears no relation to the US.This is, of course, possible; but itmeans that the arrangement of a con-tingency affects the rate at which 6"comes to "ignore" a CS. Thus thisignoring of a CS is governed by itsassociative relation to the US and is aproper part of the development of aCR. From the point of view of thispaper, then, the truly random controlprocedure still provides the appropriatecontrol.

Another objection to the truly ran-dom control procedure rests again uponthe notion that the pairing of CS andUS is the significant event for Pavlo-vian conditioning. One can claim"what is random for the experimentermay not be random for S." Such anobjection argues that if we use thetruly random control, we should ar-range it so that the relation between theCS and US is phenomenally random.One suspects that, at least in part, thisobjection is based upon the notion ofpairing of CS and US. The statementimplies that even though CS and USare not related, .S will behave as if theCS predicts the US. Those who makethis claim are rarely concerned that 5will behave as if the CS predicts noUS!

It is, of course, possible that someprocess which normally produces Pav-lovian conditioning when the US ismade contingent upon the CS is opera-tive even when the CS and US arepresented in random fashion. Such aprocess might fail to operate only whenthere is a slight inhibitory, or onlywhen there is a slight excitatory, con-tingency between CS and US. In itsmost general form, this argument saysthat the limits of our operational pro-


cedures do not necessarily define thelimits of psychological processes in theorganism. It is difficult to disagree.On the other hand, this is not an ob-jection which applies uniquely to thetruly random control procedure. Forinstance, it applies also to the tradi-tional controls for Pavlovian condi-tioning: What is explicitly unpairedfor E may not be explicitly unpairedfor S. A solution to this problem re-quires an ability, which we do not yethave, to identify psychological proc-esses ; until we do, there is little choicebut to associate psychological processesin Pavlovian conditioning with experi-mental operations.

A major advantage of the contin-gency view of Pavlovian conditioningis that it provides a continuum of CS-US contingencies along which a zeropoint can be located. In the long run,the location of this zero with respectto process is not crucial; if we discoverthat the assumed correspondence be-tween experimental contingency andpsychological process is in error, itmay be that results can be brought intoline by relocating the point of "zerocontingency."

Two EXPERIMENTAL PREDICTIONS

The truly random control has ledto the consideration of two theoreticalviews of Pavlovian conditioning, thepairing view and the contingency view.The difference between these two theo-retical conceptions of Pavlovian condi-tioning is partly semantic. From ourpresent knowledge it is arbitrarywhether we wish to have a point of"zero" conditioning with deviations onboth sides or a zero point from whichdeviations can occur only in one direc-tion. On the other hand, the differ-ence is also partly empirical, and in thisframework the question is whether thenumber of CS-US pairings, or the rela-

tive probabilities of US in the presenceand absence of the CS, is the determinantof Pavlovian conditioning. A compre-hensive empirical answer to this ques-tion requires an extensive program ofresearch, but two specific predictionscan be extracted for illustrative pur-poses.

The area of most blatant disagree-ment between the two conceptions ofconditioning is the notion of inhibi-tion, (a) The pairing viewpoint failsto distinguish between 5"s failing tolearn and 5s learning that the CS andUS are explicitly unpaired. Experi-mentally, in accord with the pairingview, a CS which has been repeatedlypresented alone should not differ fromone which has been explicitly unpairedwith the US. (This simple statementof the prediction neglects the operationof such factors as sensitization whichwould produce more CRs in the ex-plicitly unpaired condition.) (&) Fromthe viewpoint that CS-US contingen-cies are the important determinants ofPavlovian conditioning, repeated CSpresentations may result in failure tocondition; but, explicitly unpairing CSand US should lead to the develop-ment of inhibitory phenomena. Thus,under some circumstances, the contin-gency viewpoint predicts a differencebetween the outcomes of these twotreatments and the pairing view doesnot. But it is important to note thatthe contingency approach only predictsthis difference when the CS is testedin the presence of some other excita-tory stimulus. Inhibitory effects canbe measured only when there is somelevel of excitation to be reduced.Again, at the risk of being pedantic, itis important not to confuse the ques-tion of the presence or absence of in-hibition with the question of the abilityto measure inhibitory effects.

The conditions for testing the em-pirical fruitfulness of the contingency


view were met in an experiment byRescorla and LoLordo (1965). Inthat experiment, two groups of dogswere trained on a Sidman avoidancetask. Both groups were then con-fined and given Pavlovian conditioningtreatments. While confined, one groupreceived repeated tone presentationswithout any shock USs, while the othergroup received tones and shocks ex-plicitly unpaired in the manner of Pro-cedure 4 above. Later presentation ofthese tonal stimuli during the Sidmanavoidance performance led to a sub-stantial reduction in avoidance rateduring the CS in the explicitly un-paired group and little change in rateduring the CS for the group that re-ceived only tones. Because previousexperiments supported the assumptionthat avoidance rate is in part a func-tion of the level of fear, these resultswere interpreted to indicate that ex-plicitly unpairing the CS and US ledto the development of Pavlovian inhibi-tory processes capable of reducing fear.Merely presenting the tones did notlead to this result. The outcome of thisexperiment is consistent with the theo-retical view that CS-US contingency,rather than simply CS-US pairing, de-termines the outcome of Pavlovian con-ditioning procedures.

The two contrasting views of Pavlo-vian conditioning also make differentialpredictions for the outcomes of excita-tory conditioning procedures. Supposethat we condition one group of SB witha type of truly random conditioningprocedure in which USs are deliveredon a variable interval schedule and CSsare randomly distributed throughoutthe session. A second (experimental)group receives the identical treatmentexcept that the preprogrammed USsare allowed to reach 6" only if theycome in a 30-second period following aCS onset. Thus, for this group aswitch permits the delivery of the in-

dependently programmed USs only fora period just after each CS. USswhich are programmed for the trulyrandom 5s during other periods of thesession never occur for the experi-mental group. The .5s in this experi-mental group receive at least as manyCS-US pairings as do -9s in the trulyrandom group, but USs can occur onlyfollowing CSs. If the number of CS-US pairings is important, then thisprocedure should produce results simi-lar to those of the truly random control.However, if the CS-US contingenciesare important, then a considerablygreater number of CRs should occur inthe experimental group.

This conditioning procedure wasused in a paradigm like that of theRescorla and LoLordo experiment(Rescorla, 1966). All dogs weretrained on a Sidman avoidance sched-ule. Then, separately, half of the ani-mals received the truly random con-trol treatment while the other halfreceived the modified treatment of theexperimental group described above.Shock was the US and tones served asCSs. After these conditioning treat-ments, the tones were presented dur-ing performance of the avoidance re-sponse. The CS of the truly randomgroup had little effect upon perform-ance, while the CS of the experimentalgroup showed marked fear-producingproperties, increasing the avoidance re-sponse rate. Again, this result sup-ports the view that the important di-mension in Pavlovian conditioning isthe CS-US contingency rather thanCS-US pairing.

These are but two examples of thekinds of experiments which the con-tingency view of Pavlovian condition-ing generates. The fact that the resultsof these experiments support the fruit-fulness of the contingency view sug-gests a program of research varyingthe relative probabilities which form


the basis of the CS-US contingencies.In this way we can explore the rela-tions between CS-US contingenciesand Pavlovian conditioning.

In summary, we have argued thatthe conventional control procedures forPavlovian conditioning are inadequatein a variety of ways. An alternativeprocedure, in which the CS and USbear no relation to each other, wasproposed. It was argued that the fail-ure previously to use this procedurestems from a particular, and probablyinadequate, conception of Pavlovianconditioning. Taking seriously thetruly random control procedure, weproposed an alternative theoretical viewof Pavlovian conditioning in which theCS-US contingency is important ratherthan the CS-US pairing. The empiri-cal usefulness of this alternative viewhas been illustrated.

REFERENCES

BITTERMAN, M. E. Classical conditioning inthe goldfish as a function of the CS-USinterval. Journal of Comparative andPhysiological Psychology, 1964, 58, 359-366.

HARRIS, J. D. Studies of nonassociativefactors inherent in conditioning. Compar-ative Psychological Monographs, 1943, 18(1, Whole No. 93).

JENSEN, D. D. Operationism and the ques-tion "Is this behavior learned or innate?"Behavior, 1961, 17, 1-8.

KALISH, H. I. Strength of fear as a func-tion of the number of acquisition and ex-tinction trials. Journal of ExperimentalPsychology, 1954, 47, 1-9.

KONORSKI, J. Conditioned reflexes andneuron organization. New York: Cam-bridge University Press, 1948.

NOTTERMAN, J. M., SCHOENFELD, W. N., &BERSH, P. J. Partial reinforcement andconditioned heart rate response in humansubjects. Science, 1952, 115, 77-79.

PREMACK, D. Reinforcement theory. In D.Levine (Ed.), Nebraska symposium onmotivation: 1965. Lincoln: University ofNebraska Press, 1965. Pp. 123-180.

PROKASY, W. F. Classical eyelid condi-tioning : Experimenter operations, task de-mands, and response shaping. In W. F.Prokasy (Ed.), Classical conditioning.New York: Appleton-Century-Crofts,1965.

RESCORLA, R. A. Predictability and numberof pairings in Pavlovian fear conditioning.Psychonomic Science, 1966, 4, 383-384.

RESCORLA, R. A., & LOLORDO, V. M. In-hibition of avoidance behavior. Journalof Comparative and Physiological Psy-chology, 1965, 59, 406-412.

RODNICK, E. H. Does the interval of delayof conditioned responses possess inhibitoryproperties? Journal of Experimental Psy-chology, 1937, 20, 507-527.

SOLOMON, R. L., & TURNER, L. H. Discrim-inative classical conditioning in dogs para-lyzed by curare can later control discrimi-native avoidance responses in the normalstate. Psychological Review, 1962, 69,202-219.

SPENCE, K. W., & RUNQUIST, W. N.Temporal effects of conditioned fear on theeyelid reflex. Journal of ExperimentalPsychology, 1958, 55, 613-616.

THOMPSON, R., & MCCONNELL, J. Classi-cal conditioning in the planarian, Dugesiadorotocephala. Journal of Comparative andPhysiological Psychology, 1955, 48, 65-68.

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(Received March 29, 1966)

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Rescorla (1967).pdf