Solomon Opponent Process 1980

The Opponent-Process Theory ofAcquired Motivation

The Costs of Pleasure and the Benefits of Pain

RICHARD L. SOLOMON University of Pennsylvania

ABSTRACT: When an unconditioned stimulus, areinforcer, or an innate releaser is repeatedly presentedto human or animal subjects, three major affectivephenomena are often observed. First, one often seesaffective or hedonic contrast. Second, frequent repeti-tion of the unconditioned stimulus, reinforcer, or innatereleaser often gives rise to affective or hedonic habitu-ation (tolerance). Finally, after frequent repetition ofthese stimuli, a withdrawal or abstinence syndromeoften emerges directly following stimulus termination.These affective dynamics of organismically importantstimuli generate new motives, new opportunities forreinforcing and energizing operant behaviors, based onthe hedonic attributes of withdrawal or abstinencesyndromes. This article describes the opponent-processtheory of such new or experientially produced motivesand discusses recent research testing the theory. Thetheory attempts to account for such diverse acquiredmotives as drug addiction, love, affection and socialattachment, and cravings for sensory and aesthetic ex-periences (cases in which the initial reinforcers are posi-tive) and for such acquired motives as parachuting, jog-ging and "marathoning," sauna bathing, and a variety ofself-administered, aversive stimuli like electric shocks(cases in which the initial reinforcers are negative).The empirical laws governing the establishment of thesenew motives are described. Crucial variables includethe quality, intensity, and duration of each stimuluspresentation and the time intervals between presenta-

This article is derived from a Distinguished InvitedAddress delivered by the author at the April 1978 meet-ing of the Eastern Psychological Association.

This research was supported by Grant MH-29187 fromthe U.S. Public Health Service, National Institute ofMental Health. I wish to thank the many wonderfulyoung scientists who have contributed to my researchseminar and taught me so much. They know who theyare.

Requests for reprints should be sent to Richard L.Solomon, Department of Psychology, University of Penn-sylvania, 3813-1S Walnut Street T3, Philadelphia, Penn-sylvania 19104.

Vol. 35, No. 8, 691-712

tions (interreinforcement intervals). The theory alsogives a plausible account of the development of addic-tive behaviors, whether initiated by pleasurable or byaversive events.

How strange would appear to be this thingthat men call pleasure! And how curiouslyit is related to what is thought to be itsopposite, pain! The two will never be foundtogether in a man, and yet if you seek theone and obtain it, you are almost boundalways to get the other as well, just as thoughthey were both attached to one and the samehead. . . . Wherever the one is found, theother follows up behind. So, in my case,since I had pain in my leg as a result of thefetters, pleasure seems to have come to followit up.

—Plato, Phaedo

Acquired motives can be as powerful as innateones. They can become the focus for the majorbehaviors of an organism, even at the expense ofinnate needs. A heroin addict, for example, mayspend the better part of each day in drug-seekingbehavior, may ignore food, liquid, and sexual in-centives, and may abandon normal societal obli-gations. The heroin motive is acquired only be-cause certain experiences have occurred; it is notinnate. We tend to think of such addictions aspathological, but they are not. One thesis ofthis article is that most acquired motives, such aslove, social attachments, food-taste cravings,thrill seeking, and needs for achievement, power,and affiliation, obey the empirical laws for theaddictions. I develop a theory that explains whythis is so and describe recent research testing thetheory.

When Miller (1951) wrote his important essayon "learnable drives and rewards," the concept ofacquired motivation was an associative one. Byprocesses of Pavlovian conditioning, by means of

AMERICAN PSYCHOLOGIST • AUGUST 1980 • 691Copyright 1980 by the American Psychological Association, Inc.

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contingencies between conditioned stimuli (CSs)and unconditioned stimuli (UCSs), previously neu-tral 'stimuli could acquire some of the attributesof UGSs. Some UCSs had drive properties, somehad reward properties, and the CSs acquired theappropriate properties—either to motivate or ener-gize behaviors or to reinforce specific behaviorsselectively. The stimuli rendered no longer neu-tral by such conditioning were called either ac-quired drive stimuli or conditioned reinforcers(secondary reinforcers), depending on the attri-butes of their UCSs. In a real sense, no newdrives or incentives were created, but new stimuli,once neutral, could now elicit drivelike effects orrewardlike effects. The related phenomena weresometimes called "derived motives" (Bolles &Moot, 1971; D'Amato, 1974). The derived mo-tives were thus believed to be a consequence ofassociative or conditioning processes.

In a similar vein, Freud and the neo-Freudiansconsidered acquired motives to be derived frominnate needs, and associative processes were thefocus of clinical attention. The search in thiscase was not for CSs but for symbols, though theunderlying ideas were the same (Hall & Lindzey,1957). People were driven by, or rewarded by,symbols that were derived from the dynamics ofthe libido, the innate needs of the organism.

The phenomenon of addiction does not easily fitthe old associative-process theories about derivedmotives. My argument is that many new motivesare of the addictive type, not necessarily of thederived type, and that associative processes, thoughoften occurring in these cases, are neither neces-sary nor sufficient to produce the addictive be-haviors. The clearest case is, of course, opiateaddiction, in which one sees the emergence of apowerful new motive characterized by drug crav-ing and abstinence agony. Such phenomena donot appear to require either Pavlovian condition-ing or symbol formation for their establishment.Furthermore, I believe that the addictive type ofacquired motive is representative of many, if notmost, of the acquired motives that are the majorfeatures of human behavior in a social context.My arguments, therefore, pertain to social psy-chology and developmental psychology as well asto personality theory.

I start with some very dogmatic claims, but Ibelieve they are right. In every case of acquiredmotivation, affective or hedonic processes are in-volved; whenever one identifies an acquired mo-

tive, one can, in every case I have found, describeor measure three affective or hedonic phenomena.These are (a) affective or hedonic contrast, (b)affective or hedonic habituation (tolerance), and(c) affective or hedonic withdrawal (abstinence)syndromes.

Empirical Generalizations

AFFECTIVE CONTRAST

Following is an example of affective, emotional, orhedonic contrast that occurs when a positive rein-forcer is presented and removed. A powerful,species-specific unconditioned stimulus is pre-sented to a laboratory animal. In this particularcase, a moving mother duck is presented to a 5-hour-old duckling for the first time in its life.The duckling becomes excited, stumbles in thegeneral direction of the mother, and moves itshead quickly so that the mother is kept in sight.After 1 minute elapses, the mother is removed.Then, with a latency of 5-10 seconds, the ducklingshows agitated head movements and energetic,seemingly random locomotor activity and emits arepetitive, high-pitched sound referred to as dis~tress calling. These distress calls persist for sev-eral minutes and then cease.

One can show that the introduction of the mov-ing mother duck functions as a positive reinforcer(see Hoffman, Searle, Toffey, & Kozma, 1966;Hoffman, Stratton, Newby, & Barrett, 1970) be-cause the shaping of an arbitrary operanf occursif the presentation of the moving mother is con-tingent upon the occurrences of that operant. Inopposite fashion, the removal of the mother nega-tively reinforces any already established operants,and, indeed, even species-specific, instinctive be-havior chains can be weakened by this procedure(see Hoffman, Stratton, & Newby, 1969). There-fore, one can infer that the presentation of thereinforcer engenders a pleasant or desirable he-donic state but that the termination of the rein-forcer results in an aversive or unpleasant hedonicstate that finally ceases after several minutes ofstimulus absence. This affect sequence (baselinestate -» State A-^ State B —» baseline state) char-acterizes hedonic or affective contrast. State Aand State B appear to be in a contrasting relationto each other with regard to their reinforcingproperties.

Affective contrast engendered by positive rein-forcers occurs in a variety of settings. It seems

692 • AUGUST 1980 "AMERICAN PSYCHOLOGIST

to be the rule, not the exception. A few years ago,I became curious about the generality of affectivecontrast in humans. With the assistance of Reu-ben Kron, I carried out a brief, incomplete ex-periment in the baby nursery of Philadelphia Gen-eral Hospital. I presented a nursing bottle toseveral sleeping babies who were about 12 hoursold. Such babies usually are not hungry or thirstybecause they are still digesting a large quantity ofamniotic fluid. However, if one wiggles a nursingnipple into their mouths, they wake up and suck,ingesting some of the nutrient (especially if it issweet). When I allowed them to suck for 1 minuteand then withdrew the nipple, the obvious ofcourse occurred: The babies started crying with alatency of 5-10 seconds, cried for several minutes,and then went back to sleep. The babies wouldnot have cried at that time had I not introducedthe nipple and withdrawn it.- Affective contrastcan therefore occur whether or not the positivereinforcer or UCS is "needed" at the time. Inthis experiment, one can infer that the babieswent from baseline state -» State A —> State B —>baseline state. Stimulus termination precipitatedboth the ducklings and the infants into an aversivestate, one in which they would not have 'been hadthe positive reinforcer or UCS not been introducedand withdrawn. Indeed, it is possible that neitherduckling nor infant could ever have experiencedtheir particular affective State B during the pres-ence of any known variety of direct stimulation.

Next is an example of affective or hedonic con-trast that occurs when a negative reinforcer ispresented and then removed. It comes from Ep-stein's (1967) report of work on the emotionalreactions of military parachutists. During theirfirst free-fall, before the parachute opens, militaryparachutists may experience terror: They mayyell, pupils dilated, eyes bulging, bodies curledforward and stiff, heart racing and breathing ir-regular. After they land safely, they may walkaround with a stunned and stony-faced expressionfor a few minutes, and then they usually smile,chatter, and gesticulate, being very socially activeand appearing to be elated. Here again, one seesthe affect sequence: baseline state—* State A-»State B -» baseline state.

Or, consider the following example, quoted froman article on the effects of being struck bylightning:

My interest in this subject was aroused when my neigh-bor's son was struck by lightning as he was returning

from a golf course. He was thrown to the ground. Hisshorts were torn to shreds and he was burned across histhighs. When his companion sat him up, he screamed"I'm dead, I'm dead." His legs were numb arid blueand he could not move. By the time he reached thenearest hospital he was euphoric. (Taussig, 1969, p. 306)

Need I say more? Well, perhaps. It is possiblethat neither Epstein's nor Taussig's behavioral de-scription is decisively convincing to the reader.Therefore, my next example is semiphysiologicaland may thus be, to some, more acceptable. Weput laboratory dogs in a Pavlov harness and pre-

' sented a frightening shock to their hind feet,measuring the unconditioned heart rate changes(Church, LoLordo, Overmier, Solomon, & Turner,1966). The shock lasted 10 seconds.

.Figure 1 shows the heart rate reaction during theonset, maintenance, and termination of the shock,as well as during the minutes following shock ter-mination. The upper panel shows the large heart

BASELINE

0 2.5 55 75 Td.O

Time After Shock Onset (Sec)

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Figure 1. The unconditioned heart rate response indogs during a 10-second shock (ma. = milliampere)to the hind paws (upper panel) and after the shockis terminated (lower panel). (Note the change inscale for the ordinate in the lower panel. Adaptedfrom Church, LoLordo, Overmier, Solomon, and Tur-ner, 1966.)

AMERICAN PSYCHOLOGIST • AUGUST 1980 • 693

rate increase that occurred when the shock went on.This increase reached a peak after about S secondsof shock, and the rate then declined, even while theshock was still on. The lower panel shows the heartrate changes that occurred directly after the 10-second shock was terminated. Heart rate firstdecreased to a level below the original baseline andthen recovered slowly to the original baseline. Therate did not simply decline from its peak leveldirectly back to the baseline. Assuming, of course,,that heart rate changes measure affective changes,one can infer affective contrast in this example.

Of the four instances I have given of affectivecontrast, the heart rate data (Church et.al., 1966)will serve as our general guide. However, datafrom color vision (Hurvich & Jameson, 1974) pro-vide an important analogy. Turn on a relativelypure red light and keep it on for 30 seconds. Atfirst the red appears to the observer to be rich andsaturated. As the seconds go by, however, the red-ness seems to decrease, as though one had mixedwhite light with the red. Now turn the red lightoff. The observer experiences a green afterimagethat peaks in saturation immediately and thenslowly dies away until the greenness is undetectable.Many data sources suggest that there is probably asimilar or analogous standard pattern of affectivedynamics for hedonic stimuli.

This standard pattern is idealized in Figure 2;it contains five distinctive features. First, when thestimulation begins, there is a rapid departure frombaseline affect, which peaks within a few seconds(State A). Next, the affect intensity or magnitude

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TIMEFigure 2. The standard pattern of affective dynam-

ics. Note the five labeled distinctive features of thecomplex affective outcome produced by a simplesquare-wave stimulus input. (From "An Opponent-Process Theory of Motivation: I. Temporal Dynamicsof Affect" by R. L. Solomon and J. D. Corbit, Psycho-logical Review, 1974, 81, 119-145. Copyright 1974 bythe American Psychological Association. Reprinted bypermission.)

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Figure 3. The heart rate response of a "veteran"laboratory dog to shocks to its hind feet. (Note thevirtual absence of an acceleratory phase in response toshock onset and the exaggerated deceleratory responseafter shock is terminated. Adapted from Katcher etal., 1969.)

starts to decline, even while the precipitating stim-ulus is still present. The decreased State A affectthen approaches a relatively steady level. Whenthe stimulus event is terminated, there is a quick,phasic decrease in the affect level until the baselineis crossed, and then a new, contrasting affectivestate (State B) emerges, which quickly approachesa peak and then slowly decreases in magnitude untilthe original affective baseline is reestablished.There is no overshoot into State A after State B hasslowly died away. This pattern is assumed to be aconsequence of either pleasurable or aversive rein-forcers, releasers, or UCSs.

AFFECTIVE HABITUATION

In the example I gave of dogs having their hind feetshocked and heart rates measured, it was easy toobserve a contrast effect, and the habituation pro-cess was unambiguous. The heart rate slowedafter its initial acceleration, even while the UCSwas still there. Furthermore, as shown in Figure 1,the contrast effect was evidenced in the comparisonbetween the 4-mA and 8-mA shock conditions. Thepeak of the on response to 4 mA was of a lower

694 • AUGUST 1980 • AMERICAN PSYCHOLOGIST

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dynamics produced by a relatively novel uncon-ditioned stimulus.

amplitude than that for 8 mA. More important,the peak of the after-reaction showed a greaterdeparture from baseline for 8 mA than for 4 mA.This is the symmetry one would expect for contrastphenomena. However, it turns out that this initialsymmetry is misleading. It is characteristic onlyof the nonhabituated subject. The habituated sub-ject not only fails to show a contrast effect butalso shows an asymmetrical reverse. This is illus-trated in Figure 3, which shows the heart rate of a"veteran" laboratory dog after it had receivedhundreds of shocks over a period of many days(see Katcher et al., 1969). The increase in heartrate at shock onset was very small, yet the decreasein heart rate after the shock was terminated wasvery large, and the time required for return to base-line heart rate was relatively long. As far as theheart was concerned, the dog had become "used to"or "tolerant of" shocks to its hind feet. From thisone can infer that affective tolerance or habituationoccurred to some extent.

In general, when a UCS of medium intensity isrepeated many times within relatively short periodsof time, the affective reaction to that UCS oftendiminishes (see Kimmel, 1971). This generaliza-tion is meant to apply to either positive or negativereinforcers, to UCSs or releasers of either an extero-ceptive or an interoceptive (drugs, chemicals) sort.(For a review, see Randich & LoLordo, 1979.)

AFFECTIVE WITHDRAWAL SYNDROMES

In Figure 3 one can see that the veteran dog, whichhad received a large number of frightening shocks,no longer showed much cardiac arousal when shocks

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TIMEFigure 5. The standard pattern of affective

dynamics produced by a familiar, frequently re-peated unconditioned stimulus.

were present. Furthermore, the deceleration ofheart rate below the baseline is of greater magnitudethan it was during the first few shocks received. Inaddition, this after-UCS reaction is of quite longduration relative to that seen in Figure 2. Theemergence of a long-lasting, high-amplitude affec-tive after-reaction is one characteristic consequenceof a frequently repeated UCS.

It is now possible to portray the standard pat-terns of affective dynamics for two conditions—one in which the UCS event is new and one inwhich the UCS event has been repeated many times.Figures 4 and 5 show the habituation effectoccurring during a UCS and the enhancement orelaboration of the withdrawal syndrome occurringafter UCS termination, both a consequence ofrepeated stimulations.

The phenomena illustrated in Figures 4 and 5occur in a wide variety of situations for a verylarge number of UCSs. In Tables 1-4, I presentbut a few of the. examples available from theexperimental psychology laboratory, the psycho-logical clinic, and the arena of everyday life. Thestudents in my research seminar have over a periodof years called to my attention over SO suchexamples of the three highly correlated effects ofan often repeated UCS: (a) The affective reactionto the onset and maintenance of the UCS willgradually decline; (b) the affective after-reactionwill grow in intensity and duration; and (c) adistinctive affective quality of the after-reaction willoften emerge, and it will appear to be hedonicallyopposite to that quality which was engendered bythe onset and maintenance of the UCS during thefirst few presentations.


Tables 1-4 are arranged to contrast the affectiveevents that take place during presentations of areinforcer on early trials with those that take placeafter many repetitions of the reinforcer. They arealso arranged to point out the typical affects thatoccur before, during, and after each presentationof a particular reinforcer.

Before I discuss particulars concerning the proto-types in Tables 1-4, the relationship of the general-izations (derived from these tables) about thedynamics of affect, on the one hand, to the general-izations about the motivation concept^ on the other,needs to be mentioned. What do the laws of affecthave to do with motivation? Put very simply, fora large set of acquired motives, the laws of affectare the laws of acquired motives. The reasonsfor this are fairly simple. Repetition of a reinforcerchanges the hedonic or reinforcing potency of thatreinforcer and results in the emergence of a newreinforcer, which occurs after the termination of theoriginal reinforcer. The new reinforcer has ahedonic quality opposite to that ,of the original rein-forcer's onset. So new pr acquired motives arisefrom the dynamics of affect, as shown in Tables1-4.

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Some Prototypes of AcquiredMotivation

Table 1 outlines the affective dynamics in opiaieuse. The first few self-doses of an opiate (if thedosage is the right size) produce a potent pleasurecalled the "rush," followed by a less intense stateof euphoria. This effect can be shown in people(Wikler, 19S3), in monkeys (Deneau, Yanagita, &Seevers, 1969), and in rats (Kumar, Steinberg, &Stolerman, 1968), using various objective behavioralindices. The rush has been characterized by peopleas an intense sexual pleasure felt "all over the body,all at once." When the drug dose loses its effect

TABLE 1

Changes in Affect Before, During, and After EachStimulation (Self-Dosing With Opiates) for the FirstFew Experiences and After Many Experiences

Period

BeforeDuringAfter

First few

Resting^stateRush, euphoriaCraving

. Resting state

After many

CravingContentmentAbstinence-agonyCraving

because of metabolic destruction, the user goes intoa state of mild discomfort with both physiologicaland psychological aspects. The physiological aspectincludes runny eyes and nose, abdominal pains,clammy skin, and muscular malaise. The psycho-logical aspect is called craving and refers to an aver-sive state. Most organisms will perform an operantif it will get rid of an aversive state. Thus, drugusers tend to redose because this is the surest andquickest way to get rid of the physiological andpsychological aspects of withdrawal aversiveness.A slower way is merely to let time go by becausethe withdrawal aversiveness will slowly die away;but this method is less preferred.

The first few self-doses produce a pattern ofmotivational influences highly correlated, with thestandard pattern of affect dynamics shown inFigure 2. The onset and maintenance of the opiatefirst produce a peak of State A (the rush), followedby a decline in intensity (euphoria), the first signof habituation. Drug-event onset functions as apositive reinforcer. Then, after the drug "wearsoff," State B, an aversive craving state called thewithdrawal syndrome, emerges. Finally, the aver-siveness disappears with the passage of time. Insuch a case, there are two motivational events cap-able of reinforcing operants: the onset of State Aand the removal of State B. . .

If self-doses are frequently repeated, however,two correlated changes in affect then occur: (a)The rush is no longer experienced and euphoria isoften absent (loss of euphoria); and (b) the with-drawal syndrome becomes much more intense, bothphysiologically and psychologically, and its durationlengthens dramatically. Thus, the positive rein-forcer loses some of its power, but the negativereinforcer gains power and lasts longer. This effectis shown in the right-hand column of Table 1,under the heading After Many. Thus, the motiva-tion in drug use changes gradually, with successivedoses, from positive to aversive control. The usernot only becomes drug tolerant but also becomesmore intolerant of drug termination or absence.

In Table 1, the reinforcer is positive, and theacquired or new motivational state (State B) isaversive. The same generalization holds for Table 2.

Table 2 describes the behavior of ducklings whenthey are first exposed to a powerful innate rein-forcer—a moving mother surrogate. They show ahigh level of excitement and increased locomotion,and their eye movements follow the moving object.When the reinforcer is removed, duration of distresscalling is related to prior exposure duration, thus


TABLE 2

Changes in Affect Before, During, and After EachStimulation (Social Attachment in Ducklings) forthe First Few Experiences and After ManyExperiences

Period

BeforeDuringAfter

First few

ContentmentExcitementDistress .Contentment

After many

Some distressFollowingIntense distressSome distress

demonstrating the contrast effect (Eiserer & Hoff-man, 1973). After many exposures, the excitementlevel declines during an exposure period, but afterstimulus termination, the intensity and duration ofdistress calling increase. Sometimes, after manyrepeated exposures to a mother surrogate, the duck-ling emits distress calls sporadically during severaldays of the mother's absence, though this behavioreventually ceases (see Hoffman, Eiserer, Ratner, &Pickering, 1974). Presentation of the mother sur-rogate has been shown to be a positive reinforcer(Hoffman & Ratner, 1973), and removal of themother surrogate has been shown to function as anegative reinforcer. A new source of aversivenessis thus added to the ducklings' existence (Hoffmanet al., 1969). This new motivational problemwould never arise for the ducklings if they neversaw a mother surrogate.

In Tables 1 and 2, the reinforcer is positive, andthe acquired motivational state (State B) is aversive.In contrast, in Tables 3 and 4, the reinforcer isaversive, and the acquired motivational state (StateB) is positive.

Table 3 describes the affective events that occuras a consequence of sauna bathing. The air isvery hot, and during the first few repetitions thetypical bather reports painful burning sensationsand unpleasant affect, even fear. A short-lastingfeeling of relief is reported after the session is

TABLE 3

Changes in Affect Before, During, and After EachStimulation (Sauna Bathing) for the First FewExperiences and After Many Experiences

Period

BeforeDuringAfter

First few

Resting statePain, burningReliefResting state

After many

Resting stateHot, excitingExhilarationResting state

over. Unless some extraneous motivation comingfrom social pressures,/ beliefs about health, andso on is provided, the bathing sessions are notlikely to be repeated because their A state isaversive. However, if the behavior is repeated,two changes occur: The aversiveness of each ses-sion gradually declines, and a withdrawal syn-drome emerges and intensifies. The withdrawalsyndrome is characterized by sauna bathers as"exhilaration" and "a sense of well-being." ThisB- state usually lasts from 1-2 hours in a well-habituated sauna bather. The sauna bather, byrepeated exposures to a previously aversive stimu-lus pattern, now has a new source of pleasure; anacquired motive system has emerged.

Table 4 shows the pattern of affective changesfor military parachutists (Epstein, 1967). Dur-ing the first free-fall (before the parachute opens),even the bravest men show a fearful reaction.Their eyes may bulge, their lips retract, theymay yell, their bodies curl forward, and theirautonomic nervous systems are in a high state ofexcitation. There may even be involuntary uri-nation. After they have landed safely, they gothrough a short period during which they lookstunned and stony faced and do not talk much.Then, after a few minutes, they begin to chatterand enter into lively social interaction with peers.The after-reaction appears to last about 10 minutes.After many parachute jumps, the signs of affec-tive habituation are clear, and the fearful reactionis usually undetectable. Instead, the parachutistslook tense, eager, or excited, and during the free-

, fall they report a "thrill." After a safe landing,there is evidence of a withdrawal syndrome. Theactivity level is very high, with leaping, shouting,rapidly shifting social interactions, voluble talk,and general euphoria. This period, often describedas exhilaration, decreases slowly in time, but oftenlasts for 2-3 hours. Indeed, I was once told by

TABLE 4

Changes in Affect Before, During, and After EachStimulation (Free-Fail in Military Parachuting)for the First Few Experiences and After ManyExperiences

Period

BeforeDuringAfter

First few

AnxietyTerrorReliefResting state

After many

EagernessThrillExhilarationResting state


a sport parachutist (who was also a psychiatrist)that his "high" lasted 8 hours. A new, positivesource of reinforcement is now available, one thatcould never have eventuated without repeated self-exposures to an initially frightening situation towhich the subject then becomes accustomed.

The four prototypes described above are a fairsample of the different kinds of UCS that elicitaffective, emotional, or hedonic reactions and thatshow the phenomena of (a) initial affective con-trast; (b) affective habituation, or tolerance tothe presencexof the UCS; (c) the emergence ofan affective withdrawal syndrome; and (d) a re-lation of affective oppositeness or reinforcer oppo-siteness between the states characteristic of thepresence and absence of the UCS. A satisfactorytheory is needed to account for these phenomena.

It is important to work out a useful theorybecause many instances of acquired motivationseem to fit the characteristics illustrated in Tables1-4. First there are the drug UCSs, many ofwhich produce an addictive cycle in which the druguser self-doses in order to terminate or preventthe aversive withdrawal syndrome. Such self-dosing then produces more tolerance to the drugand a more intense and longer lasting withdrawalor abstinence syndrome. Drugs such as opiates,alcohol, barbiturates, amphetamines, and bromidesseem to reproduce well the four phenomena I have'emphasized above. Then there are the aversive,nondrug exteroceptive and interoceptive UCSs.Many of these appear to be capable of producingtolerance, a pleasurable withdrawal syndrome, andnew operant behaviors reinforced by the with-drawal syndrome affect (i.e., a new, acquired mo-tive system). Some examples are "marathoning"(Milvy, 1977), jogging (Booth, Note 1), variousfeats of daring that are initially frightening, vari-ous disgusting stimuli (e.g., human anatomy class),various irritating stimuli such as tobacco smoke,and even some painful stimuli produced in sports.Certainly, hard work might be an example. Agreat deal of empirical investigation is needed toascertain just which UCSs, reinforcers, or releas-ers, originally aversive and functioning as nega-tive reinforcers, lead to the development of anew, positive reinforcer. Finally, there are thepleasurable UCSs, reinforcers, and releasers. Manyof these seem to be subject to habituation ortolerance, and they can, after much repetition,generate an aversive withdrawal syndrome.

Such syndromes can then energize the develop-

ment of escape and avoidance behaviors and thusconstitute an acquired motive system. I believethat many of the most pleasurable reinforcers inlife fit the present description: love, social attach-ments, power and competence, achievement andrecognition, and aesthetic pleasures. In everydayuse are many terms for the withdrawal syndromesbased on such reinforcers: loneliness, grief, sor-row, disappointment, and cravings for love, power,beauty, or sensory experiences (e.g., taste crav-ings) . We do not yet know how many of thesemotivational influences demonstrate the phenom-ena I have pointed out. I suspect that most ofthem do, which leads to' further interest in atheory that would, in principle, account for suchacquired motives.

The Opponent-Process Theory ofAcquired Motivation

It turns out that the simplest, yet quite satisfac-tory, theoretical model for all of the affective orhedonic dynamics I have described is an affect-control system with a single negative feedbackloop. It is an opponent-process theory, similarto many already described by physiologists andpsychologists (see Hurvich & Jameson, 1974).1

The theory assumes that for some reason thebrains of all mammals are organized to oppose orsuppress many types of emotional arousals orhedonic processes, whether they are pleasurableor aversive, whether they have been generated bypositive or by negative reinforcers. The opposingaffective or hedonic processes are automaticallyset in motion by those stimulus patterns that psy-

1'The opponent-process theory is new, though it hasbeen a central topic of my research seminar since 1970.It was described at the Psychonomic Society in 1972 andin several later articles (Hoffman & Solomon, 1974; Solo-mon, 1977a; Solomon, 1977b; Solomon & Corbit, 1973;Solomon & Corbit, 1974; Starr, 1978). The theory waselaborated and sharpened by John D. Corbit and HowardS. Hoffman and was reviewed by D'Amato (1974). Ithas recently been applied to job satisfaction (Landy,1978), to fear conditioning (LaBarbera & Caul, 1976a,1976b), to cigarette smoking (Pomerleau, 1979; Ternes,1977), to fear-inhibitory associations (Maier, Rappaport,& Wheatley, 1976), to tonic immobility reactions (Berns& Bell, 1979), to tolerance to opiates (Siegel, Hinson, &Krank, 1978),. to gastric ulcer formation (Desiderato, Mac-Kinnon, & Hissom, 1974), to opiate addiction (Wikler,1973), to sucrose preference (Cohen, Note 2), to eating(Cantor & Wilson, Note 3), to peer separations in monkeys(Suomi, Mineka, & Delizio, in press), to addiction to jogging(Booth, Note 1), and to habituation to test anxiety incollege students (Craig & Siegel, 1980).


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chologists or ethologists have shown, through de-fining experiments, to function as Pavlovian UCSs,operant reinforcers, or innate releasers.

All primary affective or hedonic processes elic-ited by UCSs, reinforcers, or innate releasers arepostulated to correlate closely in magnitude withthe stimulus intensity, quality, and duration ofthe reinforcer. These primary processes are phasicand are sensitive to small stimulus changes. Theyare stable, unconditioned reactions, which in thetheory are called a processes. For example, asnake (UCS) elicits a reflex fear reaction (UCR)in a monkey. Or, the taste of chocolate syrup(UCS) elicits salivation (UCS) or excitement(UCR) and a pleasure state (UCR) in a child.

The primary process, the a process, in turnarouses a b process that functions to oppose andsuppress the affective or hedonic state initiallygenerated by the onset of the a process. The bprocess drags down the strength of an A state.The b process (the opponent process) is postulatedto be (a) of sluggish latency, (b) inertial, or slowto build to its asymptote, and (c) slow to decayafter the stimulus input (UCS) has been termi-nated and the a process (UCR) has stopped. Be-cause the b process is an opponent process, itsaffective or hedonic quality must be opposite tothat of the a process. The implications of such asimple assumption are far-reaching, as one will see.

The affective or hedonic state of the organism atany moment is postulated to be the difference,without regard to sign, between the magnitude ofthe a process and the magnitude of the b process.The b process has a negative sign because it op-poses the a process. The state rule is simple:(a) If |a — b shows a > b, then the organism isin State A, and (b) if \a — b\ shows b > a, thenthe organism is in State B. Furthermore, if beingin State A is positively reinforcing (pleasant, de-sirable), then being in State B will be negativelyreinforcing (aversive, undesirable), and vice versa.

The affect-processing system, reflecting the op-ponent-process assumptions made so far, is shownin Figure 6. First, there is a cognitive-perceptualevent representing the UCS, reinforcer, or innatereleaser. For illustrative purposes, assume thatthe subject is a cat and that the incoming signalis categorical—a dog. The dog can be depictedas a square-wave input. One of its side effects isthe arousal of an a process, a primary affective orhedonic process. In this case, the a process is afear reaction pattern. The occurrence of thisreaction pattern then results in arousal of a bprocess, the opponent process. It has an affectiveor hedonic sign opposite in quality to that of thea process. At this point, one can only guess atwhat the quality of the opponent really is. Asone sees shortly, its quality is only revealed when


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the categorical stimulus event is terminated, justas in the case of a color stimulus whose opponentcolor is revealed when the stimulus is turned off.

The magnitudes and qualities of the a processand b process are fed to a summator that com-putes a— b\ for any moment. The summator de-termines whether the subject is in State A orState B as well as the quality and intensity ofthose states. At UCS onset, most a processes aremore intense than their opposing b process, whichas I have indicated, has a slow buildup relative tothat of the a process. However, the slow buildupof the b process produces a gradual decrease inthe amplitude of the A state even while the UCS,the dog, is still present. The cat looks less fearfulas time goes by and appears to grow "accus-tomed" to the dog's presence.

When the dog goes away, there is no categoricalstimulus to maintain the a process, and so itquickly subsides to zero. The b process, how-ever, being sluggish and slow to decay, continuesfor some time. The peak of quality and intensityof the B state reveals itself directly after UCStermination, when the a process decreases to zero.The B state then slowly decays or subsides. Thecat may look relieved or relaxed, may show a typi-cal feline after-reaction of pleasure, and thenslowly returns to equanimity.

The processing system deduces several featuresin Figures 1 and 2, the standard pattern of affec-tive dynamics. v However, an additional assump-tion is needed before the system can generate the

effects of many repeated presentations, as shownin Figures 3 and 5 and in the right-hand columnsof Tables 1-4. The model must be able to pro-duce the habituation effect as well as a new,strong withdrawal syndrome. It can do so if onepostulates that b processes are strengthened by useand weakened by disuse. How this would workin the processing model is shown in Figure 7,which compares b processes and the resultantaffective states during the first few UCS presenta-tions and after many UCS presentations. Thegrowth of the strength of the b process with re-peated presentations of the UCS has two conse-quences: (a) The sum a — b\ during the onsetand presence of the,UCS is decreased, but (b) thesum a — b \ right after cessation of the UCS isincreased. This fits the present empirical gen-eralizations quite well.

New Experiments Pertinent to theOpponent-Process Theory

It is one matter to organize empirical generaliza-tions about the dynamics of affect into a coherenttheory of acquired motivation. It is quite an-other matter to test new deductions from such atheory and to find new problems and questionsinspired by that theory. Such a challenge hasbeen exciting. In the past five years, hiembers ofmy research seminar have pushed experimentationin several directions in an attempt to refute thetheory, to see where revisions are needed, and to


explore the generality of the theory. At the sametime, in other laboratories, several new findingshave been used to test the validity of deductionsfrom the theory. In addition, several other find-ings, although not initially intended to test thetheory, have served this purpose. It appears thatthe concept of opponent process or compensatoryprocess (see Siegel, 1977) is now in vogue.

The experiments can be classified as follows:(a) the growth of opponent processes in socialattachment; (b) the modulation of ongoing aver-sive affect by introduction of events that produceeither A states or B states (here one question iswhether A states and B states are really oppo-sites); (c) the conditioning of A states and Bstates; and (d) the role of endorphins in theopponent processes for aversive events. I startWith our social attachment experiments becausethese have taught us a great deal about opponentprocesses.

Growth of social attachment (imprinting) inducklings. Imprinting has been characterized asan all-or-nothing, irreversible, innate learning eventof surprising suddenness (Lorenz, 1935). It oc-curs when a newly hatched precocial bird such asthe chick or duckling is first exposed to a movingobject (or mother surrogate or mother). Thehatchling becomes excited, looking at the movingobject and often staggering toward it. There-after, the hatchling develops more and moreskilled locomotor behavior and stays close to, orfollows after, the moving object.

A striking feature of imprinting is the affectivereaction of a duckling when, the imprinting objectis suddenly removed. The animal at first ex-hibits a double take, a perceptual, startle with avery short latency. It then becomes very active,appearing to be searching for the lost object.Finally, after a 5-10-second latency, it emitshigh-pitched cries, or distress calls. These dis-tress calls can vary in the frequency with whichthey occur in time and in duration (Hoffman et al.,1974). They have been used as an index of de-gree of social attachment, much in the same waythat severity and duration of opiate withdrawalsymptoms have been used to index the degree ofphysiological and psychological dependence onheroin or morphine. If one assumes that dis-tress calls are an index of a b process, an opponentcaused by the presentation of a highly reinforcingor innate releasing stimulus, then certain phe-nomena should occur.

First, the presentation and removal of an im-N

printing object should have opposite reinforcingeffects. This is so. Hoffman et al. (1966) showedthat arbitrary operants could be shaped by pre-sentations of an imprinting object. Furthermore,Hoffman et al. (1969) showed that removal of theimprinting object functioned effectively in a pun-ishment contingency to weaken an arbitrary op-erant. Second, rather than being all-or-none, or"released," imprinting should instead develop grad-ually in strength as the b process is exercised byuse; and it should wane in strength as the bprocess is weakened by disuse.

After planning sessions with members of myseminar, the research group at Bryn Mawr (Hoff-man et al., 1974) designed and conducted the firstexperiment on the growth of an aversive opponentprocess in imprinting. They showed that with 1-minute exposures alternated with 1-minute re-movals of an imprinting stimulus, the amount ofdistress calling per unit of time gradually in-creased. The findings presented in Figure 8 dem-onstrate that the opponent process in imprintingis strengthened by use. One is thus led, as othershave been, to question the all-or-none character-ization of the imprinting process based on the dis-tress-calling measure (see Scott, 1972, pp. 198-200). Furthermore, one can now safely assume

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Figure 8. The growth of the opponent process(indexed by intensity of distress calling) for the actionof an imprinting unconditioned stimulus. This growthfunction was produced by alternating 1-minute presen-tations of the unconditioned stimulus with 1-minuteabsences of it. (From "Development of DistressVocalization During Withdrawal of an ImprintingStimulus" by H. S. Hoffman, L. A. Eiserer, A. M.Ratner, and V. L. Pickering, Journal of Comparativeand Physiological Psychology, 1974, 86, 563-568.Copyright 1974 by the American Psychological Asso-ciation. Reprinted by permission.)


that "following" behavior is not what is "released"in the imprinting process. Instead, the releasedbehavior is an affective reaction, an innate a pro-cess with positive reinforcement attributes. Onecan use this a process to shape arbitrary operants.Indeed, so-called following behavior itself mayfunction as an operant. Hoffman et al. (1970)actually taught ducklings to go away from theimprinting object in order to bring about pre-sentations of the imprinting object. If followingbehavior were released, this would not have beeneasy to do.

At the time the Hoffman et al. (1974) workwas being planned, we did not know whether theopponent process for imprinting could be weakenedby disuse. Lorenz was impressed by the "irre-versible" characteristics of imprinting and there-fore thought it was quite different from ordinarylearning. However, the opponent-process modeldeduces that the strength of social attachment,

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Figure 9. The growth of the opponent process(indexed by intensity of distress calling) for the actionof an imprinting unconditioned stimulus (UCS) as afunction of the temporal pattern of presentations andabsences of the imprinting UCS. (Note that the totalfamiliarity of all four groups with the UCS was thesame [6 minutes], although the groups differed in theirtime intervals between exposures [see text]. Adaptedfrom Starr, 1978.)

indexed by 6-process magnitude, ought to declinewith disuse. Starr (1978) carried out in our lab-oratory the appropriate experiment to test thedisuse postulate. He subjected four separategroups of ducklings to imprinting procedures. Thegroups were equal in their total familiarity withthe imprinting object: At the end of the experi-ment every animal had been in the presence ofa mother surrogate for a total of 6 minutes. How-ever, the groups differed in their time intervalsbetween exposures (their disuse'time). Group1-1 received twelve 30-second exposures to themother surrogate with 1-minute intervals betweenpresentations. Group 1-2 received twelve 30-sec-ond exposures with 2-minute intervals betweenpresentations. Group 1-5 received twelve 30-sec-ond exposures with 5-minute intervals betweenpresentations. Finally, a control group, 1-0, re-ceived 6 minutes of continuous exposure (or 0minutes between presentations).

The number of seconds of distress calling dur-ing a standard 1-minute observation period occur-ring right after each removal of the mother surro-gate was recorded for each group. Figure 9 showsthat the time interval between presentations ofthe imprinting stimulus was a very powerful vari-able in determining the rate and asymptote ofthe growth of distress calling. The data for Starr'sGroup 1-1 were quite similar to those recorded byHoffman and his colleagues at Bryn Mawr for1-minute exposures and 1-minute intervals be-tween exposures (Figure 8). Their distress callingincreased to an asymptote at which about threefourths of the time was occupied by distress calls.Starr's Group 1-2 showed some growth of distresscalling, but its asymptote was significantly lowerthan that for Group 1-1. It is in Group 1-5 thatone discovers a crucial result: The repetition ofexposures to the mother surrogate produced nogrowth of distress calling over and above that levelseen after the first exposure and separation.

It could be argued that the interstimulus inter-val had an associative function. The repetition of"imprinting stimulus present" —» "imprinting stim-ulus gone" may have increased the magnitude ofdistress calling by making the short presence ofthe imprinting object a signal for its subsequentremoval. Or it could be argued that distresscalling functioned as an operant during the separa-tion interval and was reinforced by presentationof the imprinting object on 11 occasions. Fur-thermore, following this line of reasoning, the 5-


minute interstimulus interval group (I-S) sufferedlonger delays of reinforcement for distress callingthan did Group 1-2 or Group 1-1. Associationtheory has a vast capacity to adapt itself to newsettings! (Moreover, because I am a typical as-sociation theorist, it is hard for me to abandonthese nice old habits of thought.)

However, such interpretations cannot accountfor the results obtained for the control group(1-0), which received 6 minutes of continuousexposure to the imprinting object before the objectwas removed for the first time. This groupshowed the same magnitude of distress calling(about three fourths of the 1-minute observationinterval was occupied by calls) during the firstdisappearance of the imprinting stimulus as didGroup 1-1 after 12 repeated presentations and dis-appearances. The operant contingency, thoughpossible in Group 1-1, was precluded in Group 1-0,and yet the distress-calling index of attachmentwas the same for these two groups. The condi-tioning argument seems weak here. Thus, myconclusion is that the interstimulus interval is acritical variable in the strengthening of the bprocess. Disuse, or prolonged absence of the UCSor releaser, weakens the b process between stimu-lations. During the stimulations themselves, theb process is strengthened.

From the above experiment, Starr (1978) in-duced the concept of the critical decay durationof the opponent.process. The critical decay dura-tion is that disuse time just adequate to allow theweakening of the opponent process to its original,innate reaction level. If reinforcing stimuli arepresented at interstimulus intervals greater thanthe critical decay duration, then the opponentprocess will fail to grow. In Starr's experiment,the critical decay duration must have been be-tween 2 and 5 minutes.

Starr discovered something else: a savings effectin the already strengthened opponent process.When he separated ducklings from their imprintingstimulus for several days, so that distress callingceased, he found that the restrengthening of theopponent process by repeated exposures to theimprinting object took less time and fewer ex-posures than did the original exposures. A similarphenomenon, called savings, is often found in thereconditioning of reflexes and emotional reactions.Evidently, even though an opponent-process sys-tem has been weakened by disuse, some uniqueresidues, or traces of past exercise of the opponent

process, remain and facilitate the restrengtheningof the temporarily dormant system. Such a phe-nomenon is not unexpected. In alcohol addiction,for example, the abstainer is warned that onedrink may be disastrous, and the reason is thesavings principle. The reexercise of alcohol's op-ponent-process system strengthens the withdrawalsyndrome very rapidly and sets up the special con-ditions for resumption of the addictive cycle.Cigarette smokers report the same phenomenon:Readdiction to nicotine takes place much morerapidly than does the initial addiction. The lawsof social attachment may be identical to those fordrug addiction. This was hinted at in the com-parisons among Tables 1-4. However, the simi-larities are now extended to the fine, parametricdetails of opponent-process functioning.

Finally, Starr (1978) found that an enhance-ment of the quality of stimulation could producean increase in the critical decay duration of theb process. When ducklings were exposed to animprinting object that made honking noises, theopponent process was strengthened rapidly, evenwith interstimulus intervals longer than the 5minutes used in Starr's first experiment. A generallaw for- the strengthening of b processes, derivedfrom Starr's imprinting experiments, might bestated as follows: Opponent processes are strength-ened by use and approach asymptotes havingvalues that are a direct function of the quality,intensity, and duration of each exposure and an in-verse function of the interstimulus interval. It is,of course, possible that this law governs mostnonassociative behavioral changes.

A science of opponent-process augmentation andweakening is now developing. It takes little imagi-nation to see how Starr's data and concepts canbe applied to drug dose frequency, quality, andsize or, for that matter, to any of the phenomenalisted in Tables 1-4. His ideas have considerableanalytical power, and it is now possible to under-stand some of the conditions leading to either thestrengthening or the weakening of opponent pro-cesses of all types and, consequently, to thestrengthening and weakening, of many experien-tially acquired, new motivation systems.

Whether the general law for strengthening bprocesses does in fact apply to all cases exempli-fied in Tables 1-4 will have to be empiricallyverified. Steven Seaman, working in my labora-tory/ has started a series of experiments to testthe application of this law to the growth of toler-


ance and the magnitude of the abstinence syn-drome for morphine in rats. He is trying toquantify the critical decay duration of the bprocess for varying dosages and durations. Inprinciple, it should be possible to quantify thecritical decay duration for any opponent-processsystem as a function of prior stimulation param-eters. In such experiments, the phenomena ofhabituation (in opponent-process terms, \a — b\)and withdrawal syndrome intensity and duration(the B state) would be the two major dependentvariables. The analysis would be equally appli-cable to positive and negative reinforcers. Al-though Starr's (1978) work concerned a powerfulpositive reinfbrcer, in principle it should be justas feasible to assess the strengthening of the bprocess for a negative reinforcer (e.g., heat, cold,sight of an enemy predator, long-distance running,weight lifting, shocks, free-falls, etc.).

Modulation of ongoing affect by the precipita-tion of A states and B states: The oppositenessconcept in opponent-process theory. In none ofour research reported so far have we quantita-tively demonstrated that a processes and b pro-cesses are motivational, hedonic, affective, or emo-tional opposites, although oppositeness has beeninferred in Tables 1-4. Two undergraduates,Peter Berns and Laura Bell, working with Starrand me, developed a test of oppositeness by usingchicks. The respondent, affective behavior base-line they used was the "tonic immobility" reaction(Gallup, 1977). This reaction—a chick remainingmotionless for relatively long periods of time—is induced by seizing the chick, holding it firmlyuntil it stops struggling, and then placing it ona flat surface on its side or back. The reactionduration is partly controlled by fear-evoking stim-uli and fear-suppressing stimuli. The reaction ispart of the prey-predator affect system of theyoung chick, and Gallup has presented convincingevidence that fear is the major mediator of theimmobility reaction. Pretreatments with shocks,Pavlovian fear CSs, and models of natural preda-tors, for example, all result in longer durations oftonic immobility. On the other hand, tranquilizerslike Pacitran result in significantly shortened tonicimmobility reactions. Finally, adrenalin injec-tions prolong the tonic immobility reaction, whilechlorpromazine shortens it. It seems safe to con-clude, as did Gallup, that the duration of an in-duced tonic immobility reaction in the young chickis a reasonable correlate of fear intensity or, at

least, an index of the intensity of some relativelylong-lasting and aversive affective or emotionalstate.

The strategy of Berns and Bell (1979) wassimple. First, they induced tonic immobility inlarge numbers of chicks to obtain an index of fearderived from their particular way of handling thechicks in our laboratory setting. Mean immobilitydurations for several groups of chicks varied from

^37 seconds to 45 seconds, a reasonably narrowrange. Next, Berns and Bell measured the dura-tion of the tonic immobility reaction when immo-bility was induced in the presence of an imprint-ing object (mother surrogate) that had previouslybeen present for 70 minutes. Finally, the experi-menters induced the tonic immobility reactionright after the familiar imprinting object had beenremoved.

The results are shown in Figure 10. The pres-ence of the imprinting object resulted in a sig-nificantly shortened tonic immobility reaction,whereas the removal of the imprinting objectlengthened the duration of the reaction. If oneassumes that the baseline affect for the immobilityreaction is an aversive state, then one can con-

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Figure 10. The duration of the tonic immobilityreaction in chicks as a function of the presence of andremoval ,of the imprinting unconditioned stimulus(UCS), (IS ON means the imprinting UCS is present;IS OFF means the imprinting UCS has just been re-moved. The control condition is the immobility dura-tion for nonimprinted chicks. Duration is in seconds.Adapted from Berns and Bell, 1979.)


elude that presence of the imprinting object de-creased the aversiveness and that removal ofthe imprinting object enhanced the aversiveness.Presentation of an innate reinforcer or releaserhas thus been shown to produce an affective resultopposite to that produced by the removal of thereinforcer, and vice versa. This is the sense ofoppositeness that is inherent in the opponent-process theory of motivation.

The paradigm used by Berns and Bell is pat-terned after the typical conditioned emotional re-sponse (CER) experiment, but includes a respon-dent, species-specific reaction as the baseline ratherthan the usual free-operant baseline. In principle,by using this technique it should be possible toquantify all five major distinctive features of thestandard pattern of affective dynamics (see Figure2) for any given reinforcer against a respondentbaseline.

The Berns and Bell technique is not the onlyone available to us, however. There is the stan-dard CER paradigm that usually measures theeffectiveness of a UCS, a CS+, or a CS~ in modu-lating an ongoing, reliable, and steady rate ofoperant responding. This method can be used totest many deductions from the opponent-processmodel. According to the present theoretical argu-ment, there should be a period directly followingthe termination of an aversive event (as long asthe subject has been habituated to that event)during which the affective after-reaction has posi-tive reinforcement properties. This positive re-inforcement effect, like any b process, shouldquickly peak and then decay in time. It should bemeasurable by its effect on either aversively con-trolled or appetitively controlled operant behavior.

Using the CER technique, LaBarbera and Caul(1976a, 1976b) have carried out a program ofresearch designed to assess opponent processes en-gendered by aversive stimuli. Their findings areencouraging. In one experiment, food-deprivedrats pressed a lever to obtain food. During each1-hour session, four test trials were run. Eachtrial consisted of pairing a CS+ with a shock of.75-mA intensity and ,5-second duration. How-ever, on three of these four trials the CS+ was pre-ceded by a ,5-second shock of .25, .50, or .75 mA.The four trials were at least 14 minutes apart.The rate of appetitive responding to obtain foodwas greater in the presence of the CS+ when it hadbeen preceded by shock, and the highest rate wasproduced 'by a .75-mA preshock. Furthermore,

there was a pronounced habituation effect over thedays of testing, with the .75-mA shock producingthe most rapid habituation.

LaBarbera and Caul (1976a) interpreted theirfindings to mean that a postshock b process of apleasurably reinforcing type dilutes the suppress-ing power (fear-eliciting power) of the CS+ pre-sentation, thus allowing more appetitive behaviorto occur. In addition, they assumed that the bprocess was strengthened by exercise. To confirmsuch an interpretation, however, one would haveto carry out their experiment with spaced versusmassed shock trials and a between-groups design.

In another experiment, LaBarbera and Caul(1976b) showed a decrement in what they calleddistress induced by an aversive event when thatevent occurred during the period directly followingthe termination of another aversive event thathad repeatedly been experienced. Rats licked forwater, and the CER technique was used. The ratsshowed less suppression of drinking in response toa given CS* for shock if that CS+ was preceded byanother CS+ for shock. The authors stated, "Theresults are compatible with the opponent-processtheory and suggest the presence of a positivehedonic afterreaction to an aversive event whichreduced distress to a following aversive event"(LaBarbera & Caul, 1976a, p. 485).

This result suggests that b processes, thoughinteracting with a-process arousers, retain theirintegrity in time and are not destroyed, discharged,or terminated when a processes are superimposedon them in time. This is, of course, what onewould expect based on the observations of mili-tary parachutists, who experience a long period ofexhilaration after a free-fall is terminated. Theexhilaration has been reported to persist (Epstein,1967), even through subsequent odious tasks. Theinverse of this would be the persistence of opiatecraving during opiate withdrawal; the cravingseems to permeate all concurrent activities andhedonic events. Therefore, b processes, if theyare derived from aversive a processes, can providea relatively enduring source of positive hedonictone following the removal of the aversive rein-forcer. Fear thus has its positive consequences.

The opponent-process theory maintains (1) thatthe reinforcing properties of a given b processmust be correlated with the magnitude of an Astate because the state rule is a — b\; (2) thatchanges in the magnitude of State A must be cor-related with changes in the magnitude of State B;


and (3) that such changes are nonassociative innature, coming about only because of the repeti-tion of a reinforcer. Starr's (1978) experimentwith ducklings demonstrated the changes in theB state with repetition of the reinforcer, but therewas no A-state measure during the presence ofthe reinforcer. Distress calling indexed only theB state.

A recent series of experiments by Overmier,Payne, Brackbill, Linder, and Lawry (1979),however, offers powerful support for the threepoints listed above. Overmier et al. used the CERparadigm and measured the effects of a CS+ forshock on a free-operant, shock-avoidance responsebaseline, using dogs as subjects. In Experiment 1,they showed the decline in magnitude of the CERwhen 300, as compared with 18, reinforced trialswere run. Then, in Experiment 2, they showedthis decline in the potency of the CS+, of the UCS,or of both to be nonassociative in nature. Theirevidence is striking. All subjects received 300reinforcements, but each of three groups receivedthe reinforcements in different sequences: (a) 18CS+-UCS pairings, followed by 282 UCS-alonetrials and then a test for the CER power of theCS+; (b) 282 UCS-alone trials, followed by 18CS+-UCS trials and then a test for the CER prop-erties of the CS+; and (c) 282 UCS-alone trialsrandomly intermixed with 18 CS-UCS trials, fol-

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exper.1values

Figure 11. The fear-ajrousing power of a CS+ (con-ditioned stimulus) measured by percentage of changein avoidance response rate. (Data are from Overmier,Payne; Brackbill, Linder, and Lawry, 1979. Shownhere is the fact that the CS4" is most potent when pairedonly 18 times with the US [unconditioned stimulus].With 300 US presentations, the CS+ becomes signifi-cantly weaker. This is so whether the USs occur aspart of pairings or as US-alone events. Therefore, thehabituation effect is most likely a nonassociative one.)

lowed by the CS* test. The experimenters hadpreviously determined, with another group of dogs,that 18 CS-UCS trials produced a sizable CER:The avoidance operant rate increased (more fear)75 % when the CS+ was tested during the operantbehavior. However, in all three of the experi-mental treatments with 300 presentations of thereinforcer, the CER-eliciting power of the CS*was negligible. The results of Experiment 2 areshown in Figure 11. Also illustrated in Figure 11is the finding from Experiment 1 that 300 CS-UCS pairings produced no greater CER-elicitationpower of the CS+ than did the three tested com-binations of 282 UCS-alone trials plus 18 CS-UCStrials. One can therefore conclude, as did Over-mier et al., that the habituation to the UCS wasa consequence of nonassociative processes and thatthe habituation effect significantly lowered theCER power of the CS+. Presentations of the UCSalone were sufficient to bring this about.

With Experiments 1 and 2, Overmier et al.showed that A-state magnitude is considerablysmaller after 300 reinforcements than it is after18 reinforcements and that this difference is dueto nonassociative processes not dependent on pair-ings or contingencies. However, even though Point3 was substantiated, Points 1 and 2 still remaineduntested.

In their third experiment, Overmier et al. (1979)used a backward-conditioning paradigm to estab-lish a CS~ for their CER test. In the backward-conditioning paradigm, the CS- is presented oneach conditioning trial immediately after the UCSis terminated (after the shock goes off). Pre-sumably, if the CS~ occurs only a few secondsafter UCS termination, each CS" presentation thencoincides in time with the peak of the B state.In the present case, the experimenters used a 10-second CS that began just as the UCS terminated,thus "blanketing" the time interval during whichthe peak of the B state is inferred to occur. Theycompared two modes of establishing a CS~ with300 trials: one in which the CS~ was presentedonly on the first, 40 trials, followed by 260 trialsof UCS alone, and one in which the UCSs alonewere given on the first 260 trials, followed by 40trials on which the CS" was presented.

The CER data are given in Figure 12. The CS~for the first mode showed a slightly excitatoryproperty, causing an avoidance response rate in-crease of about 1-5%. The CS~ for the secondmode, established on the 40 trials after 260 UCS-


c v +25 -"~

•sa&1<B--=a 8 -25

-50 -

Backward conditioning

ICS-

establishedon first 40

CS-

establishedon last 40

Figure 12. Data from Overmier, Payne, Brackbill,Linder, and Lawry, 1979. (The fear-inhibiting powerof a backward-conditioned CS- [conditioned stimulus]is much greater when it has been paired with the last40 terminations of shocks in a, 300-trial sequence thanit is when it has been paired with the first 40 shockterminations. Indeed, the first 40 shocks produce aslightly excitatory CS. Therefore, it is likely that theestablishment of the fear-inhibitory powers of a back-ward CS~ depends on habituation to the unconditionedstimulus already having occurred.)

alone trials had already occurred, produced asignificant decrease of about 40%. I am mostinterested in the comparison of the two modesbecause they test Points 1 and 2 above, whichrelate the magnitude of State A to the magnitudeof State B. These experimental findings showthat 260 UCS-alone presentations occurring priorto 40 backward conditionings of the CS' make thatCS~ an avoidance response suppressor or a fearinhibitor. In contrast, the 40 backward-condi-tioning trials yielded an excitatory CS". One canconclude here that a backward CS" is dependenton a strengthened b process for its fear-inhibitingeffect. Furthermore, such a fear-inhibiting CS",depending in theory on a strengthened b process,can only be established after habituation to theUCS has occurred. In Overmier et al.'s Experi-ment 2, the 300 presentations of the UCS wereshown to produce much habituation. Points 1 and2 have therefore been substantiated.

The demonstrated relationship between the de-cline in A-state amplitude and the augmentationof B-state amplitude gives firm support to thetentative impressions drawn from Tables 1-4.How general such opponent-process laws may beis not known. If they are general, then military

parachutists should not be able to experience ex-hilaration after a jump until they are habituatedto the jump itself; and opiate users should not beable to experience strong craving and a with-drawal syndrome until there is some developmentof affective tolerance to the opiate. A widevariety of empirical tests on positive and negativereinforcers are needed before one can safely con-clude that the b process is unitary and that thestate rule is really |a — b\.

The conditioning 0} A states and B states. Al-though the growth of the b process has been postu-lated to be a nonassociative process, this doesnot rule out the action of Pavlovian associativeprocesses in producing conditioned A states andB states whenever the proper requirements forthose processes have been met. The conditioningof A states is now not problematical. For example,one can condition fear reactions by presenting aneutral CS a few seconds prior to the presentationof a fear-evoking UCS. The CS acquires aver-sive, affect-arousing properties. The conditioningof B states is not as certain, but the evidence isaccumulating that such does occur. The Over-mier et al. (1979) findings are certainly suggestiveof B-state conditioning. Their backward-condi-tioning paradigm is appropriate for the investi-gation of conditioned B states because it placesthe occurrence of the CS near the postulated peakof the B state occurring right after the terminationof the UCS.

Moscovitch and LoLordo (1968) have shownthat a backward CS in a fear-conditioning experi-ment can acquire fear-inhibiting properties. Itcan subtract from a baseline fear level and soappears to elicit a conditioned opponent to condi-tioned fear. More recently, Maier, Rappaport,and Wheatley (1976) have shown that the tem-poral placement of the backward CS is importantin determining how powerful a fear-inhibiting ef-fect can be governed by the backward CS". Theypresented tone CSs to rats either 3 seconds or 30seconds following terminations of the shock UCSs.The tone at 3 seconds showed a fear-inhibitingproperty, but the tone at 30 seconds did not. Thisresult suggests that backward CSs need to be nearthe peak of the B state to acquire conditionedcontrol over that B state. It also suggests thatCSs do not become conditioned to B states if suchstates are dying out or weak.

The backward-conditioning paradigm is not theonly one capable of producing putative condi-


tioned B states, Siegel (1975, 1976, 1977; Siegel,Hinson, & Krank, 1978) has been able to showconditioning of tolerance for doses of morphine inrats to specific signals for drug administration.Tolerance to morphine was measured by rats' re-actions to a hot plate. When the rats were exposedto the hot plate in an environment like that exist-ing when they had received their morphine shots,they were more tolerant to morphine than whenthey were tested in a dissimilar environment.Siegel inferred that in such a case a "compensa-tory process" has been conditioned to environ-mental cues. Siegel's compensatory process ob-viously shares attributes with a, b process for theaffect aroused by morphine.

Yet this conclusion raises both theoretical andmethodological problems. Why should the b pro-cess in Siegel's experiments have been morestrongly conditioned than the a process? Afterall,, the environmental cues preceded and over-lapped with the morphine injection, so they shouldhave elicited conditional a-process elements. The"needle-freak" phenomenon in opiate users stronglysuggests that a processes can become conditionedto environmental cues. Why didn't Siegel's ratsbecome "needle freaks" and show conditioned opi-atelike reactions when they were tested with asaline injection? They showed a conditioned"opiate-opponent" reaction instead and were hy-peralgesic on the hot plate rather than analgesic.Was there some special feature of Siegel's (1977)procedure, that gave precedence to 6-process con-ditioning? Some temporal relationship in the ex-periment, for example? The dosage of morphine?We do'not know, but we are now starting to ex-periment with morphine tolerance with these ques-tions in mind. We would like to tease apart theassociative and nonassociative components of tol-erance.

The puzzling aspects of Siegel's findings arefurther highlighted by other findings. For example,infants born of opiate-addicted or opiate-maintainedmothers show a high degree of tolerance to pare-goric, and they go through a devastating with-drawal syndrome. Siegel's conditioning principlestrongly suggests that because the postnatal worldis so different from the prenatal world, the newbornshould be nontolerant to paregoric. These ques-tions about tolerance remain unanswered, but theymust be answered if the generality of the opponent-process theory is to be tested adequately.

Role of endorphins in the opponent processes foraversive UCSs. The relatively recent discoverythat the brain synthesizes and secretes opiatelikesubstances gives added meaning to the concept ofb process for aversive stimuli. These substances,called endorphins, are secreted when certain en-vironmental stresses are imposed on animals. Per-haps, in special cases, they are the major substratefor a b process, and if so their presence would beresponsible for the development of .affective toler-ance to selected aversive events. In the Sum \a — b\,b would then be endorphin amount. The opponent-process theory generates several imporant deduc-tions about the action of endorphins when they are

'secreted as a consequence of an aversive UCS: (a)The injection of the opiate antagonist, naloxone,should be able to reduce the b process to zero, (b)Reducing the b process to zero should destroytolerance to an aversive UCS. (c) Reducing the bprocess to zero and keeping it at zero should preventthe growth of the b process with repeated UCSpresentations, (d) Reducing the b process to zerofollowing UCS termination should suddenly termi-nate a B state.

These deductions are empirically testable. Thereare, even now, hints in reported research that someare correct. In my laboratory, Ehrman, Josephson,Schull, and Sparich (Note 4) have shown that thepower of an aversive UCS to establish a conditionedreaction to a CS+ can be strongly affected by aninjection of naloxone. As Overmier et al. (1979)have shown, the constant repetition of an aversiveUCS will result in a decrease in the effectivenessof that UCS (tolerance or habituation) in rein-forcing an association between it and a CS+. How-ever, if one administers naloxone after many UCSpresentations, subsequent pairings of a CS withthat UCS will be highly effective in strengtheningthe CS-UCS association, according to the findingsof Ehrman et al. Furthermore, one can usenaloxone to heighten the rat's reaction to heatapplied to the tail (Bernston & Walker, 1977). Asimilar process occurs in human reaction to shocks(Buchsbaum, Davis, & Buriney, 1977).

There are, however, many negative findings. Forexample, formalin-induced pain is not enhanced byinjections of naloxone (North, 1978). Further-more, naloxone does not alter human reports ofpain when the cold pressor test is used to producethe pain. Some comments are in order here.According to the opponent-process model, naloxoneshould be most dramatic in causing changes only


when the b process is already very large because ofrepetition (when tolerance is strong). In this case,the quantity a — b\ could theoretically be restoredto \a — b | = a, from \a — b \ of some small value,if naloxone were administered and if the b processwere, indeed, an endorphin process. Therefore, anexperiment on pain thresholds may not addressthis point. The affective reactions of humansubjects (to the cold pressor test) would only beenhanced by naloxone if they were already wellhabituated to the cold pressor test. The opponent-process model tells one how to do such an experi-ment in a more decisive way:. Use highly tolerantsubjects, then administer naloxone. Schull (Note5) is carrying out such an experiment for hisdissertation in our laboratory.

The deductions I have listed suggest some experi-ments that might be dramatic in their outcomes.For example, suppose a sauna bather (see Table 3)is thoroughly affectively habituated to the heat.Suppose that the b process includes a great amountof endorphin secretion. Naloxone should then dothree things: (a) It should "break" the habituation,throwing the bather back into his or her affectivelyintolerant condition; (b) it should prevent exhil-aration from being experienced when the bath isover; and (c) if the naloxone is injected during theexhilaration period, it should suddenly terminatethe exhilaration. These expectations could betested, and analogous expectations could be testedin parachutists or in marathon runners. By now,the reader can well deduce the outcomes of manynaloxone experiments, but how would they actuallycome out? "

Discussion

Prediction of experimental outcomes. How hasthe theory fared in predicting experimental out-comes? Almost too well. Well enough at least tomake me very suspicious! Every experiment gen-erated by the model has failed to refute the model,even though the experiments have been designed tobe capable of doing so. To me, this is quitethreatening. We are now living through an eraof behavior theory in which very few modestexplanatory schemes are being generated to accountfor rather limited experiments. The minimodel ispreferred to the grand, all-encompassing models ofthe past, partly because those grand models ulti-mately become impossible to refute. The opponent-process theory is quite encompassing. Although itdoes not claim to account for all phenomena of

acquired motivation, it certainly does try to accountfor many. Perhaps it overexplains. I am not sure.But there are advantages to the theory. In teach-ing the subject of acquired motivation to bothundergraduates and graduates, the existence of theopponent-process theory saves me time in exposi-tion, orders large arrays of data in a tight andunambiguous fashion, and generates many newquestions. A few of those questions have beenanswered. However, much is left to be done. Itwould make my life simpler were the theory to beunequivocally refuted by a fine experiment. Untilthat time arrives, however, I think the theory isseminal enough to warrant an intensive effort atempirical testing. The early stages of that programare under way.

Social philosophy. Another feature of theopponent-process theory warrants comment. It isobviously a puritan's theory. It argues for theexistence of psychological mechanisms for the auto-matic or autonomic control of affect, such thatrepeated pleasures lose a lot of their pleasantnessand make one potentially capable of new sourcesof suffering; in the same vein, repeated aversiveevents lose a lot of their unpleasantness and makeone potentially capable of new sources of pleasure.The philosophical implications of such a theoryshould be obvious.

Psychosomatic medicine. Furthermore, the the-ory implies some striking things about pathology.If one assumes that the phasic a processes areusually negated by their b processes, then thechronic, long-lasting effects of repeated reinforcers,whether pleasant or aversive, should be the attri-butes of enduring b processes. Therefore, if a bprocess has physiological "costs," like any defen-sive system or immunological system, such costsshould be equally characteristic of pleasantness andunpleasantness. Thus, if the opponent processescan wear out, or become exhausted (a feature ofSelye's, 1950, stress adaptation theory), some un-fortunate physiological dislocations may ensue.

We have been taught to think of aversion andtrauma as the only affective sources of physiologicalstress. The opponent-process model implies thatoften repeated pleasures are just as fertile a sourceof physiological stress. Indeed, the model suggeststhat two major classes of physiological pathologyare derived from repeated reinforcers—one classfor aversive events and the other for pleasurableevents. Pleasure as stressful has somehow beenoverlooked in our treatises on "the effects of stresson " The stress hormone system of the


pituitary-adrenal axis has somehow become identi-fied with aversiveness and trauma. The opponent-process theory suggests a fresh look. Some physio-logical pathologies may be generated by overworkedb processes for pleasurable a processes. It mightbe worthwhile to look for them.

The opponent-process model strongly impliesthat physiological pathology precipitated by fre-quently repeated reinforcements is caused by the bprocess,for a particular reinforcer. Therefore, onewould expect the pathology to develop much morerapidly following the termination of the reinforcer,when the B state is "pure," than during the pres-ence of the reinforcer> when the quantity |a— b\may be very small. Desiderate, MacKinnon, andHisson (1974) reported findings strongly in agree-ment with this expectation. They subjected ratsto aversive stress by putting them in an avoidance-avoidance conflict, wherein one aversive stimulus(shock) was intermittent while the other (shock)was continuous. Each rat participated in a con-tinuous 8-hour session of this sort (a very exhaust-ing experience). The stomachs of one group ofrats~ were examined for ulcerative lesions immedi-ately after an 8-hour stress period, and thestomachs of a second group were examined follow-ing a 2-hour rest-and-safety period that followed a6-hour stress period. Rats in a third group, acontrol for aversiveness per se without a conflictfeature, received 6 hours of continuous shock andwere then given a 2-hour rest-and-safety period,after which their stomachs were examined. Theresults were quite clear. Conflict plus a rest periodyielded a mean of over nine lesions per stomach,whereas conflict without a rest yielded a mean ofonly a little over three lesions per stomach, eventhough the total number of hours (8) allowed forulcer development was the same for both groups.This is exactly what one would expect if the bprocess was the pathogenic agent. The opponent-process model tells us to look at event terminations,as well as event onsets, for clues to the developmentof experientially induced, physiological dislocationsor malfunctions.

The reinforcement concept. Similarly, the op-ponent-process theory tells us that the reinforce-ment concept probably is inadequate. When psy-chologists write about their Pavlovian conditioningprocedures, UCSs are either presented or not.When operant. conditioning procedures are de-scribed, reinforcers are either presented or not, arepresented in some scheduled way, or are presentedaccording to complex schedule sequences; When

behavior therapists use their reinforcers, they areeither presented or not. The opponent-processmodel tells us that reinforcers, in addition to theirpresence or absence and in addition to their sched-ule, have (a) an onset, (b) a maintenance or dura-tion interval, and (c) a posttermination interval.None of these three aspects is psychologicallyequivalent to any of the other two. Each of themcan be orthogonally manipulated. Furthermore,each of the three aspects changes dynamically withfrequent repetition. Thus, a reinforcer is notjust a reinforcer. It is a triad of affective influencesthat can change with repetition. Simple operation-ism is not sufficient for a fruitful reinforcementconcept. Theory is needed.

Summary

1 have presented the postulates of a new theory ofacquired motivation. These postulates can be sum-marized as follows:

1. Primary affect, or the hedonic attributes ofreinforcers, usually arouses affective opponentprocesses, the action of which is (a) the reductionof the hedonic .potency of the reinforcer and (b)the occurrence of opponent hedonic aftereffect.

2. Primary affect, or the hedonic attributes ofreinforcers, closely tracks the stimulus intensityproperties of the reinforcer over time. These arecalled a processes. In contrast, the opponenthedonic process does not track accurately. Instead,the opponent process has a long latency, a sluggishcourse of increase, and a sluggish course of decayafter the reinforcer is terminated. The opponentprocesses have a high inertia. They are called bprocesses.

3. The primary hedonic process aroused by onsetof a reinforcer remains unchanged when the rein-forcer is repeatedly presented. In contrast, theopponent hedonic process is strengthened by useand weakened by disuse.

4. Opponent hedonic processes are strengthenedby use if and only if they are aroused at inter-reinforcer time intervals less than the time intervalrequired to allow the opponent process to decay tosome near-neutral baseline value. This time inter-val is called the critical decay duration of theopponent process or b process.

I have detailed some of the sources of data thatled to the formulation of the present theory. Ihave described some current research instigated bythe theory or highly relevant to it: (a) the growthof social attachment in ducklings and chicks; (b)


the modulation of ongoing fear by the occurrenceof primary hedonic processes (a processes) andopponent processes (b processes); (c) the condi-tioning of primary affective states (A states) andopponent affective states (B states); and (d) therole of the endorphins in the opponent processes foraversive stimuli. Finally, I have discussed some ofthe systematic implications of the theory, its ade-quacies and inadequacies, and its role as a generatorof new questions.

REFERENCE NOTES

1. Booth, N. P. An opponent process theory of motiva-tion for jogging. Manuscript in preparation, 1979.

2. Cohen, P. S- The temporal dynamics of sucrose pref-erence in water-deprived rats. Paper presented at themeeting of the Psychonomic Society, November 1978.

3. Cantor, M. B., & Wilson, J. F. Applications of theopponent process view to schedule-induced eating. Paperpresented at the meeting of the Eastern PsychologicalAssociation, Washington, D.C., March-April 1978.

4. Ehfman, R. N., Josephson, P. J., Schull, J., & Sparich.C. An assessment of the behavioral effects of the endor-phin system within instrumental and classical condition-ing paradigms. Paper presented at the meeting of theEastern Psychological Association, Philadelphia, April1979.

5. Schull, J. Personal communication, January 1980.

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