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BiologicalConstraintsonClassicalConditioning 105was that the avoidance of the CS was an in-stance of sensitization. That is, perhaps afterbecoming ill, an animal is hesitant about in-gesting any sttbstance. This possibility hasbeen disproven in at least two ways. First,aversion to the CS is much greater in experi-mental groups (in which a specific taste is laterfollowed by poison) than in control groups(which are exposed only to the poison). Sec-ond, a taste aversion s specific to the CS; it isnot a seneral avoidance of all foods or allliquids.-It is now generally accepted that taste aver-sions can be acquired by animals of many dif-ferent specieswhen the CS-US interval is sev-eral hours long, and that this Iearning is notdependent on any aftertaste or other stimulusthat misht fill the delay between insestion andillness. "M"try writers have argued ihat such alearning ability is adaptive: If an animal in thewild eats a ooisonous food. it may not becomeill until many hours later. Creatures that havethe ability to associate heir illness with whatthey have previously eatenwill be able to avoidthat food in the future and thereby have a bet-ter chance of survival. Nonetheless, becausethe effective CS-US intervals are many timeslonger than in traditional experiments on clas-sical conditioning, some psychologists pro-posed that taste-aversion earning is a_ pecialtype of learning, one that does not obey theprinciple of contiguity. Thus, taste-aversionlearning was seenby some as an exception toone of the most basicprinciples of association.fu the next section shows,taste-aversion earn-inE was also involved in a second line of attackon-the general-principle approach.

Biological Preparednessin Taste-Aversion Learningfu alreadymentioned,a crucial assumptionunderlying most researchon classicalcondi-tioning iJ that the experimenter's. hoice ofstimuli, esponses,ndspecies f subjects rel-ativelyunimportant. Suppose,or example,anexperimenterwishes o test some hlpothesis

abbut earning using the salivaryconditioningpreparation.The subjectswill be dogs,and heUS- *itt be food powder, but what stimulus

shouldbe usedas he CS?According o whatSeligman ndHager(1972) alled he equioo-tentiality premise, it doesnot matter whatstimulus s used; he decisions entirelyarbi-trary. The following quotation from Pavlov(1928)documents is belief n the equipoten-tiality premise: "Any natural phenomenonchosenat will may be converted nto a condi-tional stimulus . . any visualstimulus,any de-sired sound,any odor, and the stimulationofanypart ofthe skin"(p.86).From the outset,we should dismissa verystrict interpretation of the equipotentialityoremise.t doesnot mean hat all stimuli andall responses ill result n equally apid lfarn-ins. Pavlovhimselfrecognizedhat differentCSswill conditionat diferent rates:A brightlight will acquire a CR more rapidly than adim light. Yet althoughstimuli (or responses)certainly differ in their conditionability, theequipotentialitypremisestates hat a stimulus(or response) hat is difficult to condition inone context should alsobe difficult to condi-tion in other contexts.For example, f a dimlight is a poor CS in a salivary onditioningex-periment, t shouldalsobe a poor CS in anbyeblink conditioning experiment._n short,the equipotentialitypremisestateshat a givenstimuluswill be an equally good (or equallybad)CS in all contexts.Although the simplicity of the equipoten-tiality premise might be appealing,a largeamount of evidence asshown hat it is incor-rect. Garciaand Koelling (1966)conductedanimportant experimentshowing hat_the sametwo stimuli can be differentially effective ndifferent contexts.Two groups of rats wereeachpresentedwith a compoundstimuluscon-sisting of both taste and audiovisualcompo-nentslEach rat receivedwater that had a dis-tinctive flavor,andwhenever he rat drank thewater, t waspresentedwith flashing ightsanda clickingnoiie.For onegroup' he procedureconsistedof typical taste-aversionearning:After drinking the water, a rat was injectedwith a poison,and t soonbecamell' For thesecond-group,herewasno poison; nstead,rat's paws were shockedwhenever t drank.Thus both groupsof animals eceivedpairingsof both tasie and audiovisualstimuli with an

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106 TheoriesndResearchn ClassicqlConditioninqaversive event, but the aversive event was ill-ness or one group and shock for the other.Garcia and Koellins wanted to determinehow strongly the two t'?es of stimuli (tasteand audiovisual) were associatedwith the twodifferent aversive consequences. To do so,they conducted extinction tests (no shock orpoison present) in which the taste and audiovi-sual stimuli were presented separately. Half ofthe subjects in each group first received theflavored water without the audiovisual stimu-lus, and their consumption was measured.Later, they were presented with plain water,but their drinking was now accompanied bythe audiovisual stimulus. To control for possi-ble sequenceeffects, he other half of the sub-jects received these stimuli in the oppositeorder.Fizure 5-6 shows the results of this experi-ment: For each group, the bar graphs show theamount of water consumed in each of the twotests,measuredas a percentageof that group'sconsumption in baseline tests conducted be-fore any poison or shock was presented.Thegroup that received poison showed a greateraversion to the taste stimulus than to the au-diovisual stimulus. However, exactly the oppo-site pattern was observed for the group thatreceived the shock. For these animals, con-sumption of the flavored water was almost thesame as in baseline, but consumption of wateraccomoanied bv the audiovisual stimulus de-..""r"d to less than 20 percent of its baselinelevel.

What can we conclude about the stimuliused in this experiment? Which was the betterstimulus, taste or the audiovisual stimulus?What was the more effective aversive event,shock or illness?The results shown in Figure5-6 imply that there is no simple answer tothese questions. Taste was a more effectivestimulus when the aversive event was poison,but the audiovisual stimulus was more effectivewhen the aversive event was shock. Garcia andhis colleagues therefore concluded that beforewe can predict the strength of a conditionedresponse, we must know something about therelationshipbetween the CS and the US. Theysuggest hat because f a rat's biological make-up, it has an innate tendenry to associate ll -nesswith the taste of the food it had previouslyeaten. The rat is much less likely to associateillness with visual or auditory stimuli that areDresent when a food is eaten. On the otherhand, the rat is more likely to associate apainful event like shock with external auditoryand visual stimuli than with a taste stimulus.Seligman (1970) suggested hat some CS-US associationsmight be called prepared as-sociations because the animal has an innatepropensity to form such associations quicklyand easily (for example, a taste-illnessassocia-tion). Other potential associations might becalled contraprepared associations, becauseeven after many pairings, a subject may havedifficulty forming an association between thetwo stimuli (such as taste and shock). In be-tween are unprepared associations-those

for which thesition, but whafter a modeGarcia and Ktion betweenshock may besociation. t ihave an innastrange flashishock to theassociate hespairings.It should tof preparedntiality premisdict how effenot enough tcbeen in othewhat US willpair is an exaor contraprepmatters furthethat the predican vary acromay be prediwith illness,coxon, Dragobehaviors ofness ollowedtinctive (sour(dark blue) ctasting and ddisplayed avethe blue colaversions botlwater, and theffective stimWilcoxonthe differenclated to theirfood in the ncellent sensepoor vision,at night. Quhave excellening for food.that are mostthe time of imost readilycation ofthis

_ 100o,6co a no v v@o(rg 6 0oo(gP + ooE z oC)q)

Audiovisual STasteCS

Poison ShockTypeof US

FIGURE 5-6 Results from the experiment ofGarcia and Koelling (1966). The first two barsshow the amount of rvater consumed in thepresence of two different CSs by the group forwhich ooison was the US. The second two barsshow the consumption by the group withshock as he US.

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Biologicalonstraintsn Classicalonditioning 1o7

for which the creaturehasno specialpre-dispo- creature's ifestyle in its natural environmentsition, but which ."" ;;;;;;hi"r, ui, r"r-ga may providecluesaboutwhich associationsreafter a moderare""#;;';;';ilo!.; il ril e*;;' unprepared,and contrapreparedor6rr.i, an dKoellingexperiment.he associa- thatcreature -^r:^^ c tho-rtcmnr:tion between the ,"Ji."i**f stimulus arid Another -implication is that attempting toshockmay b" u., "*"rrr'il""L?"" ""pt"p-"a "* g"n"r"lir" aboutpreparednessr ease f learn-sociation. t is hard to imaginewhy rats*ooid ing

fto- o"t 'pttiti to anothercan be a dan-have an innate predisposition o associate. gero,,s strategy' Note' however' that quailstrange lashing lg6t "t""JJ;kitg ,ootd -ltfr Eo"iJ at"ttof avtttiont to either the color orshockto the forepaw;il;;";;" "Uf" It i"". "f water, but that aversions o colorassociatehese wo r,jlJ"ji;il";;#;; a."J.p.a more easilY'Braveman 1977) de-pairings. 'rrurr

drtL!" '." ' "" r.riu",i a numberof siudies howingha tvari-' It Jhouldbe clear hat Seligman's oncept trr, -"--"1s, including rats and other ro-ofpreparednesss at oJJ, *i,tirtt. .qoipo,.I- ;;;.;;; developan iversion to the visualtiali* premir.. It i-pii", that in ord.'. to pr.- upp""t""." of a food or liquid' although sev-dict how effective p;;;i;;bS -iff b.'it i, eiil p.aitittgtof food and illnessmay be re-not enough o know h;;;#;.,t* irtir Cs n"r t"ir.ia In ihort,.althoughanimalsmay be pre-been in o.h", .o.r.."ii.'w" ;; ufro f."o* iirp"r.a to developavJrsions-to,=T,y: of onewhat US will be or"a'"rra *tt.th", thi, CS-;; t"tittty "t"aa[ry, aversionso stimuli of otheroair is an exampleof "-pr.prr"a, onp."o".Jd", -oa4iti"t t"t''bt learned' only with greater

5;':;ilpdrt'"J uttotltdon' To complicate difficultv';";; fri.th"., other experiments aveshown*t i ,ft. pt.aispositiono associateu'o sdmuli BiologicalPreparednesslun-t'urr''".tos diff.t.nt species'\lthoughrats it i tlu-,,,in teai'ningTii,l,i":::::il'"T*i-xi:TffJ::t.'."ffiir tuwith nimars,omef he est idencecoxon,Dragoin,andKral (lg7i).o-prt.d,h. fo. pt"p"t"dtt" i" human beings involvesbehaviors f ratsandbobwhiteqoail Mh"n li i i"*.i.uittion learnins'Peoplecan developanessollowed rrg"ruoit'-"i.rit ", had a dis- sffong aversion o a Food hat is followed bytinctive (sour) aste, , *"... *i,t, " dirtinci#" "i11"";;3,t"p" ir the illness ollows ingestionof(darkblue)"olor, or"ri";;-# ; both soui ,tt" r"i'a by severalhours' Basedon what youtastingand darkb1".. fu ;. ;oold .*p".t' ,ii, t "o* ,bo"t the pastand presenteatinghabitsdisplayed versions;;;h. ,;;;" u'.r.1oi.o of the humanspecier, hichstimulusmodalitythe biue color. ln contrast,quail developed do you-suspects

the most likely to be theaversionsoth to ,h;;;;;;.;;r"a .r-,"di"" i*rir-rr an'illness-inducedversiono certainwater,and he Ufo. .oto"r?", ".*"iLy rft. ;;;; ioodr? Logue, Ophir, and Strauss1981) usedeffective timulus or theseanimals'Wilcoxon and colleagues lpothesized hat ilg. ,tud.nts about any food aversions heythedifferenc.,"*'1".f;1;';fifidii;;g;: ;?shlh;; thatdevelopedsaresult f an ll-latedo th.i, ,.rp..iii. ;,h;d. ii obtrinirig F;.+" occurredftei hevate he ood'Offood in the natural ;;;;;t. Rats ru. .*"- the 65 percentwho reportedat leastone aver-cellentsenses f r"r*'"'ri'J;;il il r"l"tiu"ly 1i"", ai percentclaimed hat the tasteof thepoor vision,""d .h;;;;;lltlor"g. for fooh food wai now aversiveo them' Smallerper-atnisht.Q.,rit r"'tiffi;';:;;;i'r,.d ,hit ..n,rg", .claimedhev oundothersensoryhave-excellen."irirrrl#fi.n,n"v-"r"'i" t."i.it'- charaiteristicsof the food aversive: he smelling for food. It -"1;:,; ;;;r" thit thor" tti-"ii ;T ;h" food was aversive or 51 percent' thethat are most rmportanr or a given ,p""i"r*"a i"t*t" of the food for 32 percent' and thethe time of ingestio;'-. "fl-.frose'thaiaie riim of ,ft. food for only 26 percent'Thesemost readily "rro.iul"d *iah liln"rr. An lmpli- pJ...,,t"g"',suggest that peoplearemore srml-cationof this conclusions that an analysisf a iu, to ,"i, th"ri"to quail when it comes o the