PSYCHOPHYSIOLOGY ^°^- 1̂ ' No. 4Copyright ® 1977 by The Socirty for Psychophysiological Research Printed in U.S.A.

First Interval Skin Conductance Responses:Conditioned or Orienting Responses?

WILLIAM F . PROKASY

Umversity of Utah

ABSTRACT

This paper was concerned primarily with whether or not the first interval respimse in classicalskin conductance conditioning can be interpreted as a response which occurs at least in part as aconsequence of the pairing of, or contingency between, a conditioned stimulus and an uncondi-tioned stimulus. Based on a context in which classical conditioning is seen strictly as a method ofinquiry, not as a process, the problems of various control procedures were discussed. It was con-cluded that with a simple conditioning paradigm the data available to date are sufficiently con-founded with differential habituation rates in control-experimental group comparisons that it isdifficult to conclude with assurance that the first-interval response does refiect the contingency be-tween the conditioned stimulus and the unconditioned stimulus. In spite of possible confoundingfactors, the data obtained in differential conditioning experiments permit the conclusion tbat tbefirst interval response does refiect stimulus pairing.

DESCRIPTORS: Classical conditioning. Skin conductance conditioning. First interval re-sponses. Control procedures. Stimulus contingencies.

This paper is designed to address four questions val of 5.0 or more sec. Although the SIR is germaneof relevance to classical skin conductance response to aspects of the questions raised for this series of(SCR) conditioning: 1) Is the first-interval SCR a papers, the major concern is with the FIR. It is wellreinstated, or sensitized, orienting response, and, if known (see, e.g., Graham, 1973; Kimmel, 1973)so, how does one decide that conditioning has oc- that SCRs occur within the FIR latency range tocurred; 2) for simple conditioning, what are appro- virtually any discretely-presented signal and thatpriate control operations to permit the inference of they habituate upon repeated presentations of thatconditioning; 3) for differential conditioning, what signal. It is also well laiown (see, e.g., Prokasy &are appropriate control operations to permit the in- Kumpfer, 1973, pp. 174-176) that SCR perform-ference of conditioning; and 4) can the first-interval ance to a CS rises rapidly (within 1 to 5 trials)SCR be interpreted to reflect exclusively habitua- to a peak and then decreases over trials. Since thetion phenomena without any necessary implication typical method of determining whether or not SCRsthat CS-US pairing per se has had a differential reflect simple conditioning involves a contrast inperformance impact? performance between a control group which receives

The first-interval response (FIR), or orienting habituation experience with both CS and US and anresponse, is an SCR which occurs approximately experimental group which receives CS-US pairing,1.0 to 3.5 sec after the onset of a signal. It is given the performance decline it is not surprisingcalled "FIR" because there are circumstances in that questions have been raised about the extent towhich responses occur to a signal but with latencies which the FIR reflects largely, or at all, the effectsgreater than 3.5 sec (see, e.g., Prokasy & Kumpfer, of a conditioning arrangement.1973, pp. 162-165). One such response, a second- rn. r-i • i r^ J-*. • n J .interval response (SIR), for example, occurs in a ^he Classical Conditioning Paradigmlatency range of 3.5 to 6 sec after signal onset when Before dealing with the four questions, it will bea conditioned stimulus (CS) and an unconditioned useful to outline the context from which classicalstimulus (US) are paired with an interstimulus inter- conditioning is viewed. The context derives from a

position taken some years ago (Prokasy, 1965, pp.r - . , J u KT »• IT • •,» f IV* »I 208-212) to the effect that classical conditioningThis research was supported by National Institute of Mental . ' ^ . r™ •

Health research grant MH 15353. ^̂ ^̂ ^^ ^^^^ ^^ ^ ^^^ of operations. These operationsAddress requests for reprints to: William F. Prokasy, 205 specify a relationship between two or more Stimuli:

SpencerHall, University ofUtah, Salt Lake City, Utah 84112. The conditional likelihood of the second of two

360

July, 1977 SKIN CONDUCTANCE RESPONSES 361

events is greater during or immediately following acquired without any evidence of having been re-the first of two events than at any other time. This warded; that a response to a neutral cue has beencontingency between two stimuli contrasts with that acquired which i s . . . indistinguishable from thewhich characterizes the method of instmmental UCR; or that one aspect of an observed behavioralconditioning: The critical contingency is between change is similar to an attribute of the UCR [p.an experimenter-selected response and the conse- 208]." Broadly speaking, the words have generallyquences of that response for the subject. A third been employed simultaneously to refer to a set oflaboratory method of some relevance for present laboratory operations and to a restricted range ofpurposes is that of habituation. In its usual applica- behavioral change occurring when the second of thetion the subject is presented a number of times with two stimuli is clearly appetitive or aversive anda selected stimulus. The only contingencies in that when the behavior measured to the first of the twosituation are those which characterize the distiibu- stimuli is (or is assumed to be) highly similar to tiiattion of the stimulus events over time (e.g., at a fixed elicited by the second of the two stimuli. Theoriesinterval of, say, 15 sec or a variable interval averag- of behavior change associated with the conditioninging, say, 40 sec). method have usually been assessed by taking as a

Each of the three sets of operations is, then, a dependent variable the subset of behavior which islaboratory tool, or method of inquiry. As such, each most similar to that (presumed to be) elicited by theamplifies for the observer some characteristics of a US.behaving system and is relatively insensitive to As employed in the present context the wordsothers. Thus, the classical conditioning paradigm "classical conditioning" emphasize the set of lab-involves, for example, pairs of stimulus presenta- oratory operations but do not place a restriction ontions which are not subject-regulated. This provides the nature of the stimuli or on the classes of responsean opportunity to observe behavioral changes which measured. The only requirement for determiningare less dependent upon the consequences of the be- whether or not a response has been "conditioned''havior itself. The same is tme for the method of is that the behavioral change assessed be one whichhabituation except that the contingency between is a unique consequence of the pairing of, or con-two experimenter-controlled stimuli does not exist, tingency between, stimuli. Since many changes canThe method of instmmental conditioning, on the occur in the presence of a CS, and since theseother hand, amplifies, relatively, behavior changes changes do not necessarily constitute a subset of thewhich are in part a result of response-contingent response pattem observed to the US, the emphasisoutcomes. on operations and their consequences does not place

Viewing the three sets of operations as methods, any a priori restrictions on what is to be measured oreach of which permits an experimenter to raise, and on what a theory of selected behavioral changes ob-presumably answer, theoretical and empirical ques- served during conditioning must be. For example,tions about living organisms, means that, as meth- one may well be interested in an account of theods, they are not to be confused with processes, acquisition of a response to the CS which is similarThus, the method of classical conditioning is not to in form to that elicited by the US. Such an approachbe confused with speculations about the kinds of emphasizes selecting a response which meets cer-effect that contingentiy-related stimuli may have tain a priori theoretical criteria in order to examineupon the subject, theories to account for behavioral response integration and acquisition. On the otherchanges resulting from the contingency, or an as- hand, one may be interested in what informationsumption that a "fundamental" unit of behavior is is abstracted from the pairing of stimuli and how itbeing assessed. Similarly, there is no requirement is recalled and employed in subsequent trials orthat the response to one signal (say, the first) needs settings. Under these circumstances, the responseto be the same as that to the other (say, the second), selected for measurement is not particularly critical,or that performance changes to the first must in- providedthattheindexof change employed in mea-volve an increasing response strength, or that either surement is one which is demonstrably a uniquestimulus event, first or second, must be relatively result of the conditioning paradigm,neutral or relatively non-neutral. Thus, when the method is employed the theoreti-

Since classical conditioning is seen as a method, cal and/or empirical objectives can be quite diverse,some language problems must be addressed. As The common element is the conditioning paradigm,noted earlier (Prokasy, 1965) the words "classical and the behavioral restriction is then only to ttiatconditioning'' have been employed to mean ' 'that behavior which can be indexed as a unique outcomean organism has associated two temporally-related of the CS-US pairing (or contingency). From thisextemal events; that a response has been acquired to definitional point of view, to say that a subjecta CS which in no way interferes with, or alters, has been "conditioned" is to say no more than thatthe reception of the UCS; that a response has been the subject has been exposed to the conditioning

362 WILLIAM F. PROKASY Vol. 14, No. 4

paradigm and tiiat some change in behavioral mea- fleet the contingency. The focus is on whether orsures reflects tiiat fact. To ask whether or not a not current FIR data reflect the CS-US correlation.response can be conditioned means, in the present „ . . . . ^v-s ^ »«.„»«»«-,.

*1 . *u 4. 1 u *u .. il Reinstated Onentmg Responsescontext, no more than to ask whether or not changes ^ "̂in that response are a consequence of the CS-US One of tiie questions posed had to do with whetiierrelationship. Stated differently, an investigator may or not the FIR changes (in frequency and/or ampli-use the conditioning paradigm to study, for example, tude) observed across conditioning trials can bethe leaming of a class of contingencies or the acqui- treated as habituation of a reinstated orienting re-sition of a class of response. It should be under- sponse. The answer to this depends strictly uponstood that this implies neither that the method is the whether or not the FIR changes are, at least in part,only one which might be employed nor that, when a unique consequence of the CS-US contingency. Ifemployed, its use results only in those effects of the FBR. changes are at least partly a function of theinterest to the investigator. contingency, then to that extent it is insuflficient to

It will be noted that this approach makes no dis- treat the initial acquisition of the FIR with the intro-tinction between CS and US on the basis of qualita- duction of CS-US trials as a reinstated orientingtive or quantitative characteristics. The labels will response.beretainedforconvenience, but, within the present This view requires some amplification. First,definitional framework, apply only to the first (i.e., there is the empirical question of whether or notthe CS) and tiie second (i.e., the US) of two stimuli FIR topography and latency is the same witii condi-presented in either a delay or a trace conditioning tioning operations as with habituation operationsparadigm. (i.e., the introduction of and repetition of a single

The classical conditioning paradigm can be spec- stimulus). In other words, given that the responseified in the form of conditional likelihoods between occurs, does it have the characteristics of an orient-stimuli or as conditional likelihoods of stimuli per ing response? Though a systematic examination hasunit time (see Prokasy, 1%5, pp. 209-212). As one not been made, what we do know suggests that theexample, suppose a typical 50% reinforcement FIR occurring with conditioning operations is tiieschedule is employed with an interstimulus interval same as that occurring with habituation operationsof 1 sec and an average intertrial interval of 30 sec and that, by inference, the effector output is thewith an intertrial interval range of 25 to 35 sec. The same. Assuming this to be the case is not, however,conditional likelihood of the US given the CS is a sufficient condition for concluding that the FIRthen .5; the conditional likelihood of the US occur- observed with the introduction of CS-US pairing isring exactly 1 sec following CS onset, given a paired a reinstated orienting response. It is still necessarytrial, is 1.0; the conditional likelihood of either a to consider the locus of control.CS or a US occurring other than in the range of time If, given appropriate control operations (see sec-from 25 to 35 sec following the preceding trials is tion on simple conditioning), the FIR occurs with0.0; and the conditional likelihood of tiie US in the identical topography and latency, but with greaterabsence of the CS is 0.0. The point to tiiis de- frequency, witii the conditioning paradigm tiianscription is that subjects are presented witii more witii the typical habituation paradigm, tiien it can-information tiian the simple fact that there is a CS- not be labeled as a reinstated orienting response.US contingency. Given the array of contingencies This is because the source of control is at least inavailable with tiie method of classical conditioning, part a CS-US contingency and is something otherit is not surprising tiiat subjects not only learn about than tiie return of an orienting response to tiie CS.tiiem but reflect tiiem to some extent in tiie condi- Thus, even tiiough the responses in habituation andtioning measures. We know, for example, tiiat conditioning paradigms may look alike, tiie sourcesclassically conditioned responses do reflect sudden of control can be different and they ought not,shifts in intertrial interval as well as trial-by-trial tiierefore (in tiie absence of a tiieory which permitseffects of variations around the average intertrial that deduction), be treated as the same,interval (Prokasy, 1965, pp. 211-212). There is a sense in which an impasse is reached.

Out of the array of contingencies, the one of however. It is possible to interpret the differencesinterest for present purposes is the CS-US contin- in FIR (whetiier in frequency, latency, or topo-gency. Does tiie FIR in any way indicate that tiie graphy) between the conditioning and the controlsubject has learned that contingency? Note that the operations also to be a difference in relative strengthfailure of the FIR to exhibit a contingency effect of orienting responses. For example, it may be ar-does not permit the inference that the subject does gued (see Stem & Walrath, 1977) that the differ-not have the information, nor does it permit the ence itself reflects a difference in the stimulus com-inference that altemative measures would not re- plex to which the subject is responding. Since the

July, 1977 SKIN CONDUCTANCE RESPONSES 363

nature of tiie functional stimulus is changed withpairing, the difference associated with the pairingis merely the kind of difference in responding whichcan occur between any two arbitrarily selected stim-uli and is not in any sense special simply becausethe stimulus complex to which the subject has beenexposed involves CS-US pairing. Assuming thatthere are no systematic differences in FIR topo-graphy, latency and frequency which do not charac-terize differences between other arbitrarily-selectedstimuli, such an interpretation is really an empiricaldefinition with no more or less substantive valuethan the empirical position taken in this paper to theeffect that any uniqueness associated with pairingis, by definition, evidence of a conditioning effect.No further gain, given the definitional overlap, canbe made in the absence of theoretical development.

Acknowledging the definitional problem, how-ever, does not eliminate two points which should beemphasized. The first is that even if the FIRs ob-served in conditioning and habituation paradigmsare the same, this in itself is an insufficient basisupon which to argue that the FIR is not influenced atleast in part uniquely by the CS-US contingency.Specifically, to identify a conditioning effect doesnot require that the measured response have a uniqueeffector output. The second is that, in the absenceof a theory, there is no reason to exclude as aconditioning effect differences in the rates at whichFIRs decrease in frequency and/or amplitude. If thesource of control for the differential rates is the CS-US contingency, then that is sufficient to define aconditioning effect. Even if decreases in FIR rateand amplitude are, by some other definition, inter-preted to be orienting responses, then one can ac-knowledge that there are combinations of stimuluscircumstances and response measurement which donot permit differentiation of habituation and condi-tioning effects. Such a state of affairs is uncomfort-able, but in no way forces the abandonment of adistinction between the effects of conditioning andhabituation operations.

Simple Conditioning

The typical control for simple SCR conditioningis to have a group of subjects receive the same num-ber of CSs and USs as does the experimental group,but to have these stimuli presented in an unpre-dictable, unpaired, sequence. Thus, if the experi-mental group receives 40 paired CS-US trials withan average intertrial interval of 50 sec and a range ofvariation from 40 to 60 sec, the control group wouldtypically receive 40 CSs and 40 USs presented in arandom order at an average intertrial interval of 25sec and a range of intertrial interval from 20 to 30sec. As summarized elsewhere (Prokasy & Kump-

fer, 1973, pp. 174-194), a contrast between suchcontrol and experimental groups clearly permits tiieconclusion that the CS-US contingency results indifferential FIR performance. The usual contrast isbetween two functions of decreasing relative fre-quency or magnitude: The rate of habituation to theCS is faster in the control than in the experimentalgroup.

As observed elsewhere (Prokasy, 1965, p. 211)there are biases in the comparison between experi-mental and control groups. The principal bias is thatin the control group the conditional likelihood of aUS occurring during or shortly after a CS is zerowhile in the experimental group that likelihood isvery high and is usually zero in the absence of theCS. When contrasting just those two groups it is notpossible to know whether the difference is attribut-able to the conditional likelihood being greater thanchance in the experimental group or to its being atzero in the control group, or both. The alternativeis to contrast with the experimental group a controlgroup in which the conditional likelihood of a US isthe same both in the presence and absence of theCS, i.e., one in which the occurrence of the CSprovides no information about the US. The severalattempts to contrast such experimental and controlgroups to date have not been definitive (see Furedy,Poulos, & Schiffmann, 1975a, 1975b; and Prokasy,1975a, 1975b), but it is probably safe to concludethat, by confining die measurement to the FIR, ifthe traditional and tiie random control groups resultin differences in FIR outcome, the differences arenot great. Thus, for present purposes it is probablysafe to assume that conclusions about the FIR madeon the basis of one control group generalize to theother control.

Having noted that the traditional and the condi-tional likelihood controls very likely result in, atmost, limited FIR differences does not eliminatethe problem of controls for the experimental group.More than simply a difference in the conditionallikelihood of a US given the CS exists between con-trol and tiie experimental groups. Contrasting tiietraditional control group and tiie experimentalgroups, consider the experimental arrangement de-scribed in the first paragraph of this section. Theexperimental group has a "dead" space of a mini-mum of 40 sec between stimulus presentations,while the control group has a "dead" space of amaximum of 30 sec between stimulus presentations.Thus, the conditional likelihood of an event as afunction of time differs between the two groups:For the control group the conditional likelihood ofeither a CS or a US presented in isolation is 1.0 inthe range of 20 or 40 sec following the last stimuluspresented, and is zero otherwise, while for the con-

364 WILLIAM F. PROKASY Vol. 14, No. 4

ditioning group the likelihood of a CS-US pairedtrial occurring between 40 and 60 sec after the lasttrial is unity, and is zero otherwise. There is littledoubt that differential distributions of events overtime affect rates of habituation (e.g., Graham,1973), but the extent to which differences betweenexperimental and control groups are a function ofdifferential habituation rates is unknown.

I am unaware of any way in which this problemcan be solved by a direct comparison of two groups.That is, any empirically-based control group willdiffer from the experimental group in more than justthe CS-US contingency: The dismption of that con-tingency produces other contingency differences.One way to approach the problem is to conduct aseries of experiments in which the contingencies aresystematically modified in comparing control andexperimental groups on the assumption that if, withvarious altemative contingencies added and sub-tracted, there remains evidence of FIR conditioningthrough the contrasts, th6n one might be able to getaround the interpretive constraint implicit in themultiple ways that the control and experimentalgroups differ.

We have made one such attempt at manipulatingcontingencies.* As noted above, a clear interpre-tation that the FIR, in a simple conditioning para-digm, reflects in part the CS-US contingency can-not be made because the experimental and controlgroups differ in the distribution of stimulus eventsover time in the session, this difference very possi-bly introducing differential habituation rates. Infor-mation can be obtained on the extent to whichdifferential habituation rates complicate interpreta-tion by providing a baseline for comparison whichbiases against an habituation interpretation. To thisend, three groups of subjects were employed. Theexperimental, or conditioning, group received 40CS-US trials at an interstimulus interval of 6 sec andan average intertrial interval of 50 sec. It differedfrom the typical conditioning group in that both theCS and tiie US were, for half of tiie subjects, 95 dBand, for the other half of the subjects, 115 dB .2-secbursts of white noise. Thus the CS and the US wereof the same modality and intensity, an atypicalarrangement in which the CS is identified only bythe fact that it is the first of two stimuli occurringin relatively close proximity.

The atypical CS-US arrangement considerablysimplifies comparisons with control groups by vir-tue of having but a single stimulus. The condition-ing group. Group E, received a total of 80 burstsof white noise. The first control. Group CI, alsoreceived 80 bursts of white noise, but these were

'The research described is part of a larger study conductedin collaboration with Charles Spurr, William Williams, andCraig Clark.

distributed at an average intertrial interval of 25 sec.Group CI conforms in contingencies to the typicalcontrol group in that it received the same totalnumber of stimulations as did Group E and that notwo stimulus presentations occurred in close tem-poral proximity to one another (i.e., the minimumtime between stimuli was 20 sec). The second con-trol. Group C2, in a sense controlled for trial units.It received a total of 40 bursts of white noise, thesebeing presented at an average intertrial interval of50 sec (i.e., the same average intertrial intervalbetween pairs of stimuli in Group E). Half of tiiesubjects in both control groups received a 115 dB,tiie other half a 95 dB, stimulus.

TTie reasoning behind the introduction of GroupC2 is that, if anything, it will exhibit a slowerhabituation rate than will Group E. This is becauseGroup E is receiving twice as many total stimuli(though presented in pairs) in the same span of time.Groups CI and C2 are both habituation groups inthat each receives a series of unpaired stimuli, withthe average intertrial interval in Group C2 twice thatof CI. Any FIR performance differences betweenthese two groups would reflect habituation rates as afunction of intertrial interval.

Table 1 presents mean FIR probability for thethree pairs of groups, the pairs differing only in thatone subgroup of each pair of groups received a 95 dBsignal, the other a 115 dB signal. As expected (andconfirming prior findings by Prokasy, Williams, &Clark, 1975), for both stimulus intensity levelsGroup E performance was reliably greater thanGroup CI performance. This contrast is one whichinvestigators typically employ to infer that there isa CS-US contingency effect on the FIR. Consider,however. Group C2 performance. It exceeds, as ex-pected. Group CI performance, but does not differreliably from Group E performance.

Since the difference between Groups CI and C2is not attributable to a CS-US contingency, thedifference between Groups CI and E cannot clearlybe attributed to a CS-US contingency. To concludeunequivocally that the FIR reflects the CS-US con-tingency would require that Group C2 performancealso be reliably less than Group E performance. Tobe sure, this is a conservative test because Group C2

Mean

Groups

ECIC2

TABLE 1

response probability for groups E, CI, and C2

Mean Response Probabilities

95 dB Signal

.789

.651

.759

115 dB Signal

.883

.808

.925

July, 1977 SKIN CONDUCTANCE RESPONSES 365

performance, if anything, will exhibit a somewhatfaster rate of habituation than will Group E. It isconceivable, therefore, that the equivalent perform-ances of Groups C2 and E reflect a CS-US contin-gency, but there is no way witii present informationto determine that. The current approach which biasesagainst detecting a CS-US contingency permits theconclusion of a contingency effect only if it is strongenough for Group E to overcome the habituationbias and yield a greater performance than that ob-tained in Group C2. Since that did not happen,we are in no position to infer a contingency effect.This conservative test, together with the clear dif-ferences between Groups Cl and C2, does serve,however, to emphasize that the conventional con-trast between experimental and control groups (i.e.,analogous to Groups E and Cl) is not sufficient topermit an unequivocal statement that the CS-UScontingency is reflected in the FIR during simpleconditioning.

There is one independent variable manipulationin simple conditioning which appears at first to pro-vide a case for permitting the inference of a CS-UScontingency effect: the interstimulus interval. Theavailable data on the interstimulus interval havebeen summarized by Prokasy and Kumpfer (1973,pp. 176-181). In simple conditioning the typicalresult is that FIR responding first increases and thendecreases as the interstimulus interval is increasedfrom 0.0 through 5.0 sec. In view of the fact thatthere is an interstimulus interval effect even thoughtiie CS-US contingency (otiier tiian tiie CS-US delayinterval) remains the same, and because the controlgroup function has a slope of zero, one might wellconclude that there is a contingency effect and thatits impact varies as a function of tiie interstimulusinterval. One possible confounding factor in thisconclusion is the existence of SIRs. With longerinterstimulus intervals, SIRs are observed. Withshorter ones, the SIR might exist but be sufficientlyreduced in latency to fall in the FIR latency range.Such additivity is implied, for example, in the workof Ohman (1972). In addition, the omission of tiieUS at short interstimulus intervals can produce an"omission" response or a perceptual disparity re-sponse (see, e.g., Grings, I960), eitiier of whichcould inflate responding at short interstimulus inter-vals (see, also, Badia & Defran, 1970). This is notto argue that tiie contingency effect does not existbut to point out that the extent to which it doesexist is difficult to know because of the potentialconfounding of other known phenomena.

The basic question posed for tiiis section wastwofold: Does tiie FIR reflect a CS-US contingencyin simple conditioning, and what are the propercontrols for simple conditioning? Conventionalcomparisons of control and experimental groups

have resulted in the conclusion that the FIR doesreflect a contingency. The present data, however,suggest that differential habituation rates are a con-founding factor in the traditional contrast and that,therefore, the CS-US contingency effect has notbeen clearly demonstrated. It is to be emphasizedthat this conclusion applies only to the FIR, thesubject of this series of papers, and not to the SIRor to modifications in the UCR, both of which seemto reflect a contingency effect.

In the absence of a well-formulated theory whichspecifies a control, it appears that there is no easyanswer to what constitutes a proper control for per-mitting the inference that the FIR in simple con-ditioning reflects a CS-US contingency. It appears,rather, that a system control is necessary: a seriesof manipulations which systematically determinesthe contribution of the myriad of contingenciespresent with the conditioning operations. The onestep described above does not eliminate differentialhabituation rates, independent of the CS-US con-tingency, from accounting for the results. Furtherrelated studies, particularly ones which involve dif-ferent CS and US modalities and intensities, wouldbe useful.

Differential Conditioning

The typical differential conditioning paradigminvolves two CSs: a CS-I- which is paired with theUS, and a CS— which is never paired with the US.Stated in different language, the conditional likeli-hood of tiie US given the onset of the CS-f- is 1.0;the conditional likelihood of the US given the onsetof the CS— is 0.0; and the conditional likelihood oftiie US given neitiier CS-I- nor C S - is also 0.0.As summarized by Prokasy and Kumpfer (1973,pp. 173-194), it is clear that FIR perfonnance toCS+ exceeds that to C S - .

Because it is a within-subject assessment, the dif-ferential perfonnance to CS-I- and CS— is stronglyindicative of the influence of the CS-h-US contin-gency. Given time-related phenomena such as ha-bituation, reinstatement of ORs, and recovery fromUS presentation, it should be observed that thetypical differential conditioning schedule may pro-duce biases in the contrast between CS+ and CS—perfonnance. Altiiough half of the trials are CS+and the remaining half CS—, the sequence of CS-f-and C S - trials is not usually random: Restrictionsare placed on the number of CS -I- or CS - trials per-mitted to occur in succession, and frequently thetrials are so blocked as to produce an equal numberof each within a subset of the total number of trials.To illustrate, a schedule of 24 CS+ and 24 C S -trials might be administered. A typical restrictionwould be to assure that no more than 3 CS 4- or CS—trials occurred in a row and that each block of 8

366 WILLIAM F. PROKASY Vol. 14. No. 4

trialscontainedexactly4CS+andCS-trials.This over the initial training trials (see, e.g., Grings,arrangement implies that the conditional likelihood 1973; Grings, Schell, & Carey, 1973).of, say, a CS + following a CS + (or a CS - follow- To tum to tiie basic question, that of what the ^ -ing a CS-) is less than .5 and that the likelihood propdate control operations are in differential con-drops to zero following (should it occur) the third ditioning, I think it can be concluded that a contrastCS+ (CS-) in a row. Such an arrangement poten- in performances to CS- and CS+ is a sufficienttially provides another cue to the subject as to the condition. Ideally the two stimuli would be presentedlikelihood of the next trial being reinforced or not in a strictly random order (i.e., generated with areinforced, but this isn't a cue which attenuates a random number generator in which the conditionalconditioning interpretation of the CS+-CS—- per- likelihood of a CS+ following a CS+ equalled thatformance difference. However, that sequence of of a CS- following a CS- which, in tum, equalsCS H-CS - trials also produces a bias in the amount .5); however, the data available to date do indicateof time elapsing between the onset of one of the two that whatever biases exist in the sequence of stimuliCSs and the last occurrence of the US. The bias is do not result in differential reinstatement of orient-that the average amount of time elq)sing between ing responses or differential rates of habituation inthe last US and tiie next CS+ is greater than that a way which precludes concluding that the subjectbetween tiie last US and the next C S - . To tiie is, in fact, responding to the CS+-US contingency,extent that there are US-correlated effects such as »» L. . ^ J . . •reinstatement of an orienting response or recovery Habituation vs Conditooningfrom any US-induced suppression, a bias would The final question raised is whetiier or not FIRsexist to produce a higher FIR performance to CS+ can be interpreted to reflect exclusively habituationthan to CS—. phenomena witiiout any necessary implication that

To date the available data to help determine if a CS-US contingency has had a unique impact. Thesuch sequential effects exist are limited. If tiie ef- answer to tiiis question is ratiier straightforwardfects described do exist, then we would expect to based upon the preceding questions. For simplesee certain sequential effects develop with succes- conditioning it is possible to interpret the availablesive occurrences of CS+ and C S - . Consider a se- data in terms of habituation phenomena providedquence of CS+ trials in the middle of a differential tiiat the interstimulus interval function is in tumconditioning session. Since the first of the CS+s interpreted to be a function incorporating in variousnecessarily occurs following a CS— trial, then one degrees multiple responses,might expect two factors to contribute to elevated For differential conditioning the evidence isresponding: tiie switch to a CS+ and a more ex- much stronger tiiat the FIR does reflect a CS+-UStended time since the last US. With successive contingency. Although there are admittedly poten-CS+s, one would tiien expect a decline in response tial biasing sources in the typical sequence of CS+-probability. The same two factors, if present, would CS- trials, tiiese biases do not operate in a wayoperate differently with a succession of CS-s: The which precludes an inference of a conditioningswitch from a CS+ to a CS— trial would produce effect.elevation, but the shorter duration of time since the While I think that the question of whether or notlast US would result in reduced responding. With a specific CS-US contingency is manifest in FIRsuccessive CS-s one would tiien expect increased performance can be addressed empirically, at arecovery from any US suppression and decreases more general level I believe that trying to accountwith habituadon to interact with one another. In for conditioning performance in the language of ha-view of the known sizable decreases associated with bituation or vice versa is a restrictive way to under-successive instances of the same stimulus, the re- stand what the organism is doing. Whether a singlesuiting function would be expected to decrease stimulus is presented successively with an identi-across a CS— sequence. The only available data fied intertrial interval distribution, or whether mul-are those of Williams (1975). He found tiiat tiie tiple stimuli (as CSs and USs) are presented, tiieCS+ and CS— sequence functions were essentially subject is exposed to a number of contingencies,flat and parallel with a constant difference between Whether one or more stimuli are presented willthem, the CS + function being greater than the CS — determine which classes of contingency are ampli-function. Such an outcome does suggest that the fied for, as mentioned early in the paper, any par-possible biases in the non-random schedule are not ticular experimental arrangement tends to amplifyof sufficient magnitude to preclude the inference some phenomena and to be insensitive to others. Tothat there is FIR conditioning to the CS +. Further the extent that there are contingencies in common tosupport for that inference comes from tiie fact that the method of classical conditioning and the metiiodthe acquisition curves for CS+ and CS— diverge of habituation, functional overlap can be expected.

July, 1977 SKIN CONDUCTANCE RESPONSES 367

Whetiier or not the observed behavioral changeseither in common or unique to the paradigms con-form to a priori theoretical notions of what con-ditioning or habituation should be is not as importantas recognizing that there are multiple contingency

effects possible with both paradigms and that onlythrough a systematic manipulation of those contin-gencies will it be possible to understand what flieeffects of each are.

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(Manuscript received June 15, 1976; accq)ted for publication December 29, 1976)