Reacquisition following extinction in appetitive conditioning

14 Pages·2010·1.71 MB·English

AnimalLearning& Behavior
1996,24(4),423-436
Reacquisition following extinction
in appetitive conditioning
SEANT. RICKERandMARKE.BOUTON
UniversityofVermont, Burlington, Vermont
Infourexperimentsutilizinganappetitiveconditioningpreparation,reacquisitionofconditioned
respondingwasfound to occurboth rapidlyandslowlyfollowing extinction. InExperiment1,ac
quisitionofrespondingtoatonethathadbeenconditionedandextinguishedoccurredmorerapidly
thanacquisitionineitheragroupthatreceivedequivalentexposuretothefoodunconditionedstim
ulusora "rest"controlgroup thatreceivedonlyexposuretothe apparatusinthefirsttwophases.
However, reacquisitionwas impairedrelativeto acquisitionina "learning-experienced"group that
hadpreviouslyreceivedconditioningandextinctionwithadifferentstimulus. Experiments2and3
producedsimilarresults, butalsofound thathighresponding duringreacquisitionwasconfinedto
trialsthatfollowedreinforced,ratherthannonreinforced,trials.Experiment4,inwhichveryfewini
tial conditioning trials were used, produced reacquisition that was slow compared with both
learning-experiencedandrestcontrols.Theresultsareconsistentwitharoleforsequentiallearning:
Reacquisitionisrapidwhenanimalshavelearnedthatreinforcedtrialssignalotherreinforcedtrials.
It is often assumed that reacquisition ofconditioned spontaneousrecoverytobepresentattheoutset.Itisalso
responding following extinction occurs more rapidly possiblethatreinstatement, whereunconditionedstimu
than acquisition witha novel conditionedstimulus (CS; lus (US) presentations in the samecontextas extinction
e.g., McAllister& McAllister, 1994).Theassumptionis restore responding to an extinguished CS (Bouton &
based, in large part, upon a number ofearly studies Bolles, 1979b; Bouton & Peck, 1989; Rescorla& Heth,
(Brogden, Lipman, & Culler, 1938; Finch & Culler, 1975),orevenrenewal,wheretestinganextinguishedCS
1935; Frey& Butler, 1977; Frey & Ross, 1968; Hilgard inadifferentcontextthanthatused inextinctionresults
& Marquis, 1935; Hoehler, Kirschenbaum, & Leonard, in increasedresponding (Bouton& Bolles, 1979a;Bou
1973; Konorski & Szwejkowska, 1950, 1952a, 1952b; ton&Ricker, 1994),couldhavebeenresponsibleforthe
Smith & Gormezano, 1965; Szwejkowska, 1950). In high levelofrespondingobserved.Earlystudiesofreac
these experiments, responding during reconditioning of quisition often used massed conditioning and recondi
the CS was comparedwith responding during the origi tioning trials. With trials spaced closely together, it is
nalconditioningphaseinthesameanimals. Rapidreap possible that stimulus aftereffects ofthe US could have
pearance ofthe conditioned response after extinction providedacontextforrenewalofconditionedresponding
wastakenasevidencethattheCSretainssomeexcitatory (Bouton,Rosengard,Achenbach,Peck,&Brooks, 1993).
strengthfollowingextinction,andthatthisstrengthtrans Early studies had not controlled for any ofthese effects
fers positively to the reacquisition phase. The CS was (forargument, seeBouton, 1986).
seenasstartingwithagreaterassociativestrengthduring In contrast, clear evidence ofslow reacquisition has
reacquisitionthanduring conditioning. been obtained in the conditioned emotional response
TheideathattheCSsurvivesextinctionwithsomeex (CER) procedure (Bouton, 1986; Bouton & Swartzen
citation is clearly consistent with a variety ofevidence truber, 1989). Intheseexperiments,attemptsweremade
(e.g., Bouton, 199I, 1993). However, as Bouton (1986) to minimize recovery effects that might complicate in
pointed out, numerous difficulties exist in interpreting terpretationofreconditioning.Thegeneralprocedurein
theliteratureonreacquisition.Thehighlevelofrespond volvedgivingonegroupconditioning,extinction,andre
ingobtainedduringreacquisitioninstudiespriorto 1986 conditioningphaseswithoneCS,andcomparingtherate
oftencouldhavebeenduemerelytospontaneousrecov ofacquisition in the final phase with that ofa control
ery. That is, in many early experiments, reacquisition group that received conditioningwith a novel CS atthe
began after a time interval that would have permitted sametime.(Thesewerethefirstexperimentstocompare
acquisition in an extinguished CS with acquisition ofa
novel CS pairedwith the US atasimilarpointintheex
ThisresearchwassupportedbyGrantIBN-9209454fromtheNa periment.)Bouton(1986)useda"rest"control,whichre
tionalScienceFoundation.Experiments Iand2werepartofathesis ceivedexposuretotheapparatusbutnoPavlovianevents
submittedbythefirstauthorinpartialfulfillmentoftherequirements
during the first two phases. Bouton and Swartzentruber
ofthemaster'sdegreeattheUniversityofVermont.Correspondence
(1989) useda"learning-experienced"control,whichre
shouldbedirectedtoM. E. Bouton,DepartmentofPsychology,Uni
versityofVermont, Burlington,VT05405. ceivedconditioningandextinctionofadifferentCSdur-
423 Copyright 1996Psychonomic Society, Inc.
424 RICKERAND BOUTON
ing the first two phases. The basic finding was that, moreextinctionshouldproducetheresultwhen lessex
givenenoughextinctiontrials, conditioning in the third tinctionshouldbemorelikelytodoso(e.g.,Kehoe, 1988).
phaseproceededmoreslowlyforthegroupthatreceived Given that reacquisition can occur both rapidly and
conditioning with the extinguished CS than for groups slowly,ouroverallgoalwastodeterminewhatconditions
thatreceivedanovelCS. Boutoninterpretedthesefind produce the two results. One possibility, suggested by
ings as indicating that, following extinction, a memory Napieretal. (1992),is thatdifferentconditioningprepa
ofthat phase exists which interferes with subsequent rationshaveintrinsicdifferencesthatyieldrapidorslow
conditioning. reacquisition. Ourinitial goal, then, was to characterize
Slow,ratherthan fast, reacquisitionhasalsobeenob reacquisition in a preparation that had not been studied
tained in taste-aversion learning. Forexample, Danguir before.Wechoseanappetitiveconditioningmethodthat
and Nicolaidis (1977) found extremely slow reacquisi is widely used in the conditioning literature (e.g., Ball
tion;theirresultssuggestedthatanaversiontosaccharin eine& Dickinson, 1991; Bouton& Ricker, 1994; Dela
couldnotberelearnedfollowing extinction. Incontrast, mater, 1995; Farwell & Ayres, 1979; Hall & Channell,
Revusky and Coombes (1979) found that reacquisition 1985; Kaye & Mackintosh, 1990; Pearce & Redhead,
.did occur. Itwas rapidcomparedtoacquisition inarest 1995):Food pellets served as the US, and the rat's en
control group butcomparable in rate to acquisition in a tries into the magazine to which the pellets were deliv
learning-experiencedcontrolgroup(Revusky& Coombes, eredservedasthe conditionedresponse. Themagazine
1979,Experiment1).Morerecentstudies(Hart,Bourne, entryresponseisoftendescribedasaPavlovianCR,but
& Schachtman, 1995)have foundreacquisitionto occur sinceobtainingthepelletisdirectlycontingentonthere
more slowlythan acquisition in a learning-experienced sponse,theresponsepresumablyalsohas an instrumen
group. tal component. Indeed, when magazine approach is put.
The results obtained with CER and taste-aversion on an omission schedule (so that responding on a trial
learning contrast sharply with data recently reported in leadstotheomissionofareinforcerthatisotherwisede
the rabbit nictitating membrane response (NMR) para livered; Holland, 1979), the response is acquired and
digm (Napier, Macrae, & Kehoe, 1992). In a series of maintained (suggesting some Pavlovian control) but is
four experiments, Napieret al. addressed the criticisms alsoweakerthanthatinacontrolgroupthatreceivesthe
offeredbyBouton(1986) concerningpreviousresearch sameCS-USpairingswithouttheomissioncontingency
withthismethod. However,evenaftercontrollingforre (suggesting an instrumental component). As an instru
instatement, renewal, and spontaneous recovery, they mental response, magazine entry is probably best de
consistently found reacquisition to occur rapidly when scribed as a partially reinforced discriminated operant;
compared with a rest control. Rapid reacquisition oc manymagazineentriesgo unreinforcedduring boththe
curredwhetherextinctionconsistedofCS-alonepresen CS and the intertrial interval. The complexity ofthe
tations or explicitly unpaired CS and US presentations magazine-entryresponsewillrequiresomecautioninin
(rulingoutrenewalbyUSpresentationsasamechanism terpretation. Butthere now appearto be many similari
in the final phase). Rapid reacquisition also occurred ties between instrumental and Pavlovian learning (e.g.,
whentheCSwassubjectedtoproceduresthatcouldhave Mackintosh, 1983; Rescorla, 1987). And reacquisition
givenitan inhibitoryvalueinthe secondphase, suchas after instrumental extinction, like Pavlovian extinction,
feature-negativeanddifferentialconditioning.Theeffect isoftenassumedtooccurrapidly(e.g.,Bullock& Smith,
persisted despite a large number ofextinction trials 1953).
(three times the number required to eliminate sponta The present experiments obtained results suggesting
neous recovery). Reinstatement tests also produced no that both slow and rapid reacquisition can occur in the
evidence that US-alone presentations reinstated extin magazine-entry preparation. They also identified se
guishedrespondingintheNMRparadigm(NapieretaI., quentiallearning(e.g., Capaldi, 1994)as avariablethat
1992, Experiment 1). Napier et a!. interpreted their re contributestowhichoftheseresults isobtained. During
sults with a model that formally captured the idea that conditioning, reinforced trials may be associated with
residual excitatorystrengthwasavailableto groups that other reinforced trials. When reinforced trials are pre
had been through conditioning and extinction (Kehoe, sentedfollowing extinction,theymayrenewresponding
1988). onsubsequenttrials. .
A recent fear-conditioning study has also found evi
dence consistentwithrapidreacquisition(McAllister& EXPERIMENT1
McAllister, 1994).Usingtheacquireddrivemethod(ac
quisition ofa hurdle-jumping response to escape fear We designed Experiment 1as an initial investigation
conditionedto contextual cues), McAllisterand McAl ofreacquisition in our appetitive conditioning prepara
listerfoundthatreconditioningoffearfollowing 30hof tion. In Experiment 1A, we examined the rate ofreac
extinctionexposuretothecontextoccurredmorerapidly quisitioninagroupthathadreceivedconditioningandex
thandidconditioninginagroupanalogoustoarestcon tinctionwithatoneCS(GroupR)relativetoconditioning
tro!. However,theresultwasnotobtainedinthreeearlier inseveralcontrolgroups.Thefirstofthesewasalearning
experiments that used less extinction (McAllister & experienced control similar to the one used by Bouton
McAllister, 1994, Experiments 1-3). Itisnot clearwhy andSwartzentruber(1989); thisgroupreceivedaniden-
REACQUISITIONAFTEREXTINCTION 425
tical treatment with a different CS (a light-offstimulus) againbaitedwith4pelletseach.Duringthesession,thesubjects
during conditioningandextinction(Group L). Asecond weretrainedto approachandeatfromthe foodcupuponactiva
controlreceivedequivalentexposuretotheUSduringthe tionofthefeedermechanism.Approximately25pelletswerede
liveredduringeachsession.
conditioning phase but no pairings ofthe US with any
Conditioning. Thesubjectsthenreceived6daysofcondition
stimulus(GroupU). Thelastgroup(GroupC)wasarest
ing.Oneachday,therewasone90-minsession.ForGroupsRand
control that received no stimulus presentations during
L, thissessionconsistedofeightpairingsofthe 30-secCS with
theconditioningorextinctionphases(cf. Bouton, 1986; thefoodUS,withameanintertrialinterval(IT!)of10min(short
NapieretaI., 1992). Duringa final reacquisitionphase, estIT!= 9min).Throughout,theoffsetoftheCScoincidedwith
allgroupsreceivedtone-foodpairings.InExperiment1B, the onsetoftheUS. ForGroup Rthe CS wasthetone (T),while
wedoubledthenumberofextinctiontrialsandcompared for Group L the CS was the lightoff(L). Group Ureceivedthe
same eight US presentations but no CS. Group C was merely
areacquisitiongroupwithalearning-experiencedcontrol.
placedintheapparatusfortheentire90min;nostimuliwerepre
sented.OnDayI,thefirstsessionforeachgroupstartedwithtwo
ExperimentlA nonreinforcedpresentationseachofTandLaloneinthesequence
TLTL,withameanIT!ofImin.
Method
Extinction. Followingconditioning, the rats received 10ses
Subjects. The subjects were 32 male Wistar rats bredat the
sionsofextinction. Allsessionswere90min indurationandoc
UniversityofYermont.Theywereapproximately 120daysoldat
curredonconsecutivedays.ForGroupsRandL,the30-secCSwas
the startofthe experimentand were individuallyhoused insus
presentedeighttimesalonewithameanIT!of10minduringeach
pended stainless steel cages in a room maintainedon an 18:6-h
session. The CSs presentedwere the same as those used during
light:dark cycle. The experimentwas conductedon consecutive
conditioning. GroupsUandCwerebothplacedintheapparatus
daysduringthelightportionofthecycle.Theratswerefood de
for the 90-min session, but no stimuli were presented. Nofood
privedto80%oftheirfree-feedingweightsandmaintainedatthat
waspresentedduringthisphase.
levelthroughouttheexperiment.
Reacquisition. Followingextinction, the rats received four
Apparatus.TwosetsoffourSkinnerboxes, housed insound
moresessionsofconditioning. All fourgroups receivedone90
attenuation chambers and located in two separate rooms, were
min session aday in which the 30-sec tone CS was pairedwith
used. Thesetwosetsofboxeshaveprovideddifferentcontextsin
foodeighttimes,withameanITIof10min.
otherstudies,butwerenotsousedinthepresentexperiment.Each
boxinone setmeasured 26 x25 x 19cm. Thefront, back,and Dataanalysis.Conditionedrespondingwasmeasuredbymeans
ofan elevation score ofthe form e= c- p, where c represents
onesidewallweremadeofaluminum;theceilingandotherside
thenumberofmagazineentriesmadeduringthe30-secCSandp
wall were made ofclear plastic. The floor consisted oftubular
representsthenumberofmagazineentriesmadeduringthe30sec
steelbars 16mmindiameter,spaced3.2cmcentertocenter,and
immediatelyprecedingthe CS. Elevationscoreswere calculated
mountedperpendiculartothefrontwall.Onthefrontwallofeach
foreachtrialandthenconvertedtofour-trialblockaveragesprior
box, Icmabovethe floor, wasarecessed4 x 4cmfoodcup. A
toanalysis.Thesescoreswerethenanalyzedbymeansofamixed
2.5 x 2.5cmleverprotrudedfrom the front wall5cmabovethe
design analysis ofvariance (ANOYA), with group as a between
floor and I cm to the right ofthe food cup. The subjects were
subjects factor and blockas a repeated measure. An identical
placedintheboxesthroughadoorintherightwall.
ANOYAwasusedtoanalyzerespondingduringthepre-CSperiod
Each box in the second set measured 24 x 22 x 18 cm. The
(prescores).Arejectioncriterionofp<.05wasusedthroughout.
front and back walls were aluminum, while the ceiling andside
Posthoccomparisonswereconductedusingttestswithapooled
wallswereclearplasticwithverticalblackstripes2cmwideand
errortermandaBonferroniadjustmentforTypeIerrorrate.
2.5 cmapart. Thefloorconsistedofstainlesssteel bars3mm in
diameter, spaced 1.5cmfrom centertocenter,andmountedpar
alleltothe front wall. Onthe frontwallofeachbox, Icmabove Results
thefloorandcentered3.5cmfromtherightwall,wasarecessed Conditioningproceededuneventfully, withGroups R
4 X 4 cm food cup. A4 x I cm lever protruded from the front and L reaching asymptote by Day 5. The data are sum
wall5cmabovethefloorand6cmtotheleftofthefoodcup.The marized on the left side ofFigure 1. A group X block
subjectswereplacedintheboxesthroughtheceiling.
ANaYAontheconditioningdatarevealedonlyasignif
Inbothsetsofboxes,illuminationwasprovidedbytwo7.5-W icantmaineffectofblock [F(II,154) =7.11]; respond
white incandescent bulbs mounted on the ceilingsofthe sound
ing tendedto increaseoverblocks. Neitherthe mainef
attenuationchambers,25cmabovethefloor. TwoCSswereused
inthisstudy. Onewasthe 30-secpresentationofa3000-Hztone fect ofgroup [F(l,14) = 1.22] nor the group X block
(80dBre20,uN/M2[AJ)providedbyageneratorwiredtoidenti interaction[F(11,154) = 1.16]approachedsignificance.
calspeakersmountedineachchamber25cmabovetheboxfloor. Extinction proceededuneventfullyas well (rightpor
Background noise was 65 dB. The other CS consisted ofthe
tionofFigure 1).Agroup XblockANaYAcarriedouton
30-secoffsetofthehouselights, whichproducedcompletedark
the datarevealedonlyasignificantmaineffectofblock
ness.TheUSconsistedoftwo45-mgfoodpellets(Traditionalfor
mula, P.1.Noyes, Lancaster,NH) delivered0.2secapart. Maga [F(l9,266) = 15.43].Neitherthemaineffectofgroupnor
zine entries were detected by photocells mounted within the the group X blockinteractionweresignificant(Fs < 1).
magazines,justbehindtheplaneofthewalloftheSkinnerboxes. Groupcomparisonsduringreacquisition.Thedata
Theapparatuswas controlledbycomputerequipmentlocatedin for each group during the reacquisition phase are pre
anadjacentroom. sented in the top panel ofFigure 2. All groups acquired
Procedure.Pretraining.Eachsubjectfirstreceived30minof
conditionedrespondingatthistime.GroupsRandLap
exposuretotheboxitwasassignedtoforthedurationoftheex
peared to differ, with Group R responding somewhat
periment. Foodcups were baitedwith4food pelletspriorto the
startofeachexposuresession.Onthe followingday, subjectsre more on early trial blocks and somewhat less on later
ceivedone30-minsessionofmagazinetraining. Foodcupswere ones. Groups Uand Cwere both somewhat slowerthan
426 RICKER ANDBOVTON
6
• GroupR
---0-- GroupL
5
4
~
0
u
(/)
c:: 3
0
';j
'"
:>
~0 2
0+---"-""---"-""--"T-""--"T-..,.---:;:'--.!j'---r-D--rLJ-r-"'--r--;'"
o 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
4-TrialBlocks
Figure 1.Meanelevationscoresduringconditioningand extinctionin Experi
mentIA.
Groups RandLinacquiring responding, with GroupV Conditioningversusreconditioning.Theupperpanel
beingslowest. Agroup X blockANOVArevealedasig ofFigure 3 shows Group R's performance in both the
nificant main effect ofblock [F(7,196) = 12.28] and a original conditioning phase (Phase 1) and during re
significantgroup X blockinteraction[F(21,196) = 2.88]. acquisition(Phase3).Awithin-subjectcomparisonofper
Themaineffectofgroupwasnotsignificant[F(3,28) = formance inthesephasescancomplementourbetween
2.78]. subjects analysis of reacquisition, although it does
The interaction suggests that group differences ex confoundconditioninghistoryoftheCSwithothervari
isted only on certain trial blocks. Therefore, a series of ables, such as prior experience with the reinforcer, the
fiveunplannedcomparisonswereconductedwithanad apparatus, and the food-deprivation schedule. As Fig
justmentforerrorrate(which seta =.01). Thesecom ure3suggests,respondingwasclearlygreaterduringre
parisons compared Group R with each ofthe control conditioning. A within-subject phase X block ANOVA
groups separatelyontheblockswhere the largestgroup revealed a significant main effect ofphase [F(l,7) =
differences appeared, and similarly compared Group L 16.73].TheANOVAalsorevealedasignificantmainef
with each ofthe other controls. Group R did not differ fectofblock[F(7,49) = 4.86]andasignificantphase X
significantlyfromGroupLonBlock7[t(78) = - 2.11], blockinteraction [F(7,49) = 5.41].
where the largest difference between these two groups AsimilarANOVAonprescoresrevealedasignificant
appeared. However, Group R responded significantly maineffectofblock[F(7,49) =2.53].Prescoresincreased
morethanGroupV onBlock4 [t(78) = 3.13]andmore slightlyoverblocks,regardlessofphase. The main effect
than Group C on Block 3 [t(78) = 2.77]. Group L also ofphase approached significance, but was not reliable
respondedmorethanGroupV [t(78) = 2.88]andGroupC [F(I,7) =5.15,p = .06], and the phase X block inter
[t(78) = 2.68] onBlock5. action was not significant [F(7,49) = 1.00]. Mean pre
AlthoughGroupsRandLfailedtodifferintheprevi scoreswere 1.34and 1.71 duringconditioningandreac
ous analysis, previous CER and taste-aversion experi quisition, respectively.
mentsthatfound slowreacquisitionhadcomparedanal
ogous groups by themselves. Therefore, an additional
ExperimentIB
analysis was conductedusing onlythese two groups. A
Method
group X block ANOVA revealed a significant main ef
Subjectsand Apparatus. Thesubjectswere 16male Wistar
fectofblock[F(7,98) = 6.98]andasignificantgroup X
ratsofthesamestockasthoseusedinExperiment IA.Theywere
block interaction [F(7,98) =2.55]. The main effect of
approximately 160 days old at the start ofthe experiment, and
group was not significant (F< 1). The interaction sug werehousedandmaintainedasinExperiment IA.Onesubjectin
gests thatacquisitionproceededdifferentlyinGroupsR GroupLbecamesickduringthecourseoftheexperimentandwas
andL.However,thelargestdifferencebetweenthegroups removed, leaving7subjectsinthatgroup. Theapparatuswasthe
(Block 7)was notreliable [t(42) = -2.00]. sameasthatusedinExperiment IA.
Procedure.Pretraining. Boxexposureandmagazinetraining
TheANOVAcarriedoutonprescoresrevealednosig
werecarriedoutas inExperiment IA. Approximately28pellets
nificant effects [largest F(7,196) = 1.87]. Mean pre weredeliveredduringeachmagazinetrainingsession.
scores forthereacquisitionphasewere 1.71, 1.33, 1.38, Conditioning. Following magazine training, the subjects re
and 1.29forGroups R, L,V, andC,respectively. ceived eight sessions ofconditioning. Each rat received two
REACQUISITIONAFTEREXTINCTION 427
• Group R; the mean elevation scores for the phase were
GroupR
Experiment IA ---0--- GroupL 0.63 and0.33 forGroupsLandR,respectively. Agroup
10 ---e-- GroupU X block ANOVA revealed a significant main effect of
9 ---l:J.--- Groupe group [F(1,13) =4.72] and a significantmain effectof
block [F(39,507) = 6.42]. The interaction was not sig
8
nificant (F < 1). Although Group L appeared to extin
guishmoreslowly,thisdifferencehaddisappearedbythe
lastfour sessions, whereGroups LandRhadmeanele
vation scores of0.14 and 0.17, respectively. Four un
planned comparisons (at a = .0125) between the two
groupsonthefirstblockofeachofthelastfoursessions
revealedno significantdifferences [ts(405)< 1].
Groupcomparisonduringreacquisition.Thefocal
datafrom reacquisitionare presentedinthe lowerpanel
O+---r--r----,;----,.---r--,---,----,
o 2 3 4 5 6 7 8 ofFigure2.Duringthisphase,bothgroupsreceivedcon
4-Trial Blocks ditioningwiththe tone. Thegroups initiallydidnotdif
Experiment IB fer, but Group Rshowed less responding than Group L
10 overblocks. This descriptionwasconfirmedbystatisti
9 cal analysis. A group X block ANOVA revealed a sig
8 nificantmaineffectofblock [F(ll,143) = 11.93]anda
significant group X block interaction [F(11,143) =
3.33]. The main effect ofgroup was not significant
[F(1,13) =2.33]. Comparisons(ata = .0167) between
groupsonBlocks7, 11,and 12,wherethelargestgroup
Experiment IA
• GroupR 10
---0-- GroupL
o~-r--r--r-.--r--r-!;:=;::=;::=;::=;==;I"' 9
o 2 3 4 5 6 7 8 9 10 11 12 8
4-Trial Blocks
Figure2. Meanelevation scoresduringreacquisition in Ex
perimentslA(upperpanel)and1B(lowerpanel).
90-minsessionsoneachday. Eachsessioncontainedeight pair
•
ingsofthe30-secCSwiththefoodUS,withameanITIof10min. Phase I
•
ForGroupR,theCS wasT;forGroupL,itwas L.OnDay 1,the Phase3
firstsessionforeachgroupstartedwithtwopresentationseachof o+--,--.---r----,-=r==;:==::;==;_-'
Tand Lalone in thesequenceTLTL, withamean ITIof1min. o 2 3 4 5 6 7 8
Extinction.Followingconditioning,theratsreceived20sessions 4-Trial Blocks
ofextinction.Asinconditioning,thereweretwo90-minsessions
oneachday. In each session, the 30-secCS was presentedeight Experiment IB
timesalonewithameanITIof10min. Atotalof160extinction 10
trialsweregiven.TheCSspresentedwerethesameasthoseused 9
during conditioning. No food was presented during this phase.
8
Reacquisition.Followingextinction,theratsreceivedsixmore
7
sessions ofconditioning. Bothgroups receivedtwo 90-min ses 0
Cl6
sionsadayinwhichthe30-sectoneCSwaspairedwithfoodeight u
times, withamean ITI of10min. Dataanalysis wascarriedout "'5
.gC
asinExperiment I. 4
~3
Results ioil2
Conditioningproceededuneventfully;duringthefinal
1 • Phase I
four-trialblockofacquisition,GroupsRandLhadmean o • Phase3
elevationscoresof5.28and5.14,respectively.Agroup X -1 +--,--.--,-r--r-..,...--r'==r=r==;==;==;---'
blockANOVArevealedonlyasignificantmaineffectof o 2 3 4 5 6 7 8 9 10 11 12
block [F(15,195) = 10.55]. Neither the main effect of 4-Trial Blocks
group[F(l,13) = 2.56]northeinteraction[F(15,195) =
Figure3.AcomparisonofmeanelevationscoresforGroupR
1.52] were significant. During extinction, responding duringconditioningandreacquisitioninExperimentslA(upper
appeared to extinguish more slowly in Group Lthan in panel)and1B(lowerpanel).
428 RICKERAND BOUTON
differencesappeared,revealedlessrespondinginGroupR AccordingtoBouton's(1993)retrievalview,presentation
thaninGroupLonBlock7[t(35) = -2.68]andBlock II ofnonreinforced trials during reacquisition might help
[t(35) = -2.53] but not on Block 12 [t(35) = -2.50]. retrieveamemoryofextinctionforareacquisitiongroup
TheANOVA onprescoresrevealedonlyasignificant andthus causereacquisitionto occurslowly.
main effect ofblock [F(11,143) =3.67]; responding This analysis resembles Capaldi's (e.g., 1994) well
during the pre-CS period increased somewhat and then developedsequentialtheory. Itimpliesthatthe outcome
decreasedoverblocks.Allothereffectswerenotsignifi ofagiventrialcanserveasasignal(orretrievalcue)for
cant(Fs< 1).Meanprescoresforthereacquisitionphase theoutcomeofthenexttrial. Thus,duringconditioning,
were 1.27and0.90 for Groups RandL, respectively. reinforcedtrials mightcometo signalthatthe next trial
Conditioningversusreconditioning.Thelowerpanel will be reinforced, while during extinction nonrein
ofFigure 3presents a comparison ofGroup R's perfor forced trialsmightcometosignalthatthe nexttrial will
manceduringreacquisitionandtheoriginalconditioning benonreinforced. This viewimpliesaparticularpattern
phase. A phase X block ANOVA revealed a significant ofresponding during reacquisition with partial rein
maineffectofphase[F(l,7) = 12.09],asignificantmain forcement. Following conditioning and extinction, re
effect of block [F(11,77) = 7.80], and a significant spondingonatrialafterareinforcedtrialshouldbehigh,
phase X block interaction [F(11,77) = 2.46]. Again, whilerespondingfollowing anonreinforcedtrial should
conditioning occurred more rapidly in the reacquisition below. Sincereacquisitionwasconductedwithapartial
phasethanintheoriginalconditioningphase. reinforcement procedure in this experiment, we could
A similar ANOVA on prescores revealed no signifi test this prediction. A retrieval view emphasizing the
canteffects [largestF(lI,77) = 1.19]. roleofprevioustrialspredictsmorerespondingafterre
inforcedthanafternonreinforcedtrials.
Discussion We used a learning-naive control similarto Group U
The results ofExperiments lA and IB indicate that in Experiment lA (as opposed to Group C) so that the
reacquisitionintheappetitivemethodcanberapidwhen control would have had equal exposure to the US. This
comparedwith"learning-naive"controls(GroupsUand groupalsoreceivedconditioninginthethirdphasewith
C inExperiment lA)andwiththe originalconditioning a partial reinforcement procedure. Here one might also
phase. However,inExperiment 1B,performanceduring expecthigherresponding on trials following reinforced
reacquisitionwasimpairedrelativetothatinGroup L, a trials,ifonlybecauseassociativestrengthmightincrease
learning-experiencedcontrol(arelatedgroup X session aftereachCS-USpairing.Clearly,anysequentiallearn
interactionwasobtainedinExperiment lA).GroupLit ing effect in a reacquisition group would have to be
selfappearedtoshowa"learning-to-Iearn"effectanalo greaterthanthatobservedinGroupU.
gous to that previously observed in NMR conditioning Wealsoperformedacontextswitchfollowing USex
(e.g.,Kehoe& Holt, 1984;Kehoe,Morrow,& Holt, 1984). posure in order to reduce possible blocking by context
That is, previous conditioning (andextinction)with the conditioning (e.g., Randich, 1981). There is some evi
light-offCS facilitated conditioning with the tone rela dence to suggest that this occurred in Experiment 1A,
tivetolearning-naivecontrols. Somewhatparadoxically, because inthe final phase Group Uappeared to acquire
alearning-to-learneffectwaslessevidentinareacquisi conditioned responding more slowly than Group C, the
tiongroupthathadreceivedallthreephaseswiththesame controlthathadnotreceivedUS exposure inPhase I.
CS. That result might implicate an interference mecha
nism inadditiontothe learning-to-Iearnmechanism. Method
AlthoughthefactthatGroupRwaslowerinrespond Subjects
ingthanGroupLlaterinthephaseindicatessomeinter Thesubjectswere 16male Wistarrats from thesamestockas
ference by prior conditioning and extinction with the inthepreviousexperiments,andwere maintainedandhousedas
sameCS,itisworthnotingthat, inCER,theinterference before.Theywere approximately 100days oldatthestartofthe
experiment.
effectisobservedstartingearlyinreacquisition. Instead
ofacquiringrespondingmoreslowly,GroupRappeared
Apparatus
to approach a lower asymptote (see especially Experi
Theapparatuswasthesameas in Experiments IAand IB,ex
ment IB).Theoriesthatpredictslowreacquisitionwould ceptthatadishcontaining 10mlof'Heinzdistilledwhitevinegar
actually expect group differences to occur early, rather (H.1.HeinzCo.,Pittsburgh)wasplacedineachsound-attenuation
than late, in the phase (Bouton, 1993; Pearce & Hall, chamberofthefirst setofboxesinordertoprovideadistinctive
1980;Wagner, 1981). scentcue; adish containing IgofVick's Vaporub(Richardson
Vicks, Inc., Shelton, CT) was similarlyplaced in each sound
attenuationchamberofthesecondsetofboxes.Inthepresentex
EXPERIMENT2 periment, the two sets ofboxes, which provided the different
contexts,werefullycounterbalanced.
In Experiment 2, we conducted reacquisition with a
Procedure
partialreinforcementprocedurethatintermixednonrein
Pretraining.Boxexposureandmagazinetrainingwerecarried
forcedtrialsamongthereinforcedtrials.Thissortofpro
outas in Experiment I, with the exceptionthat each subject re
cedure was used by Bouton (1986) and Bouton and ceivedone session in Context A(the conditioning context) and
Swartzentruber(1989),whoobtainedslowreacquisition. oneinContextB(theUSexposurecontext).Sessionsindifferent
REACQUISITIONAFTEREXTINCTION 429
contextswereconductedonthesameday,althoughboxexposure main effect ofgroup [F(1,14) < 1] nor the interaction
and magazine training were conductedon separate days, as be [F(lI,154) = 1.10]wassignificant.Prescoresincreased
fore. Approximately20pelletsweredeliveredduringeachofthe somewhat and then decreased over blocks, but did not
magazinetrainingsessions.
differ between groups. Mean prescores were 1.64 and
Conditioning.Thesubjectsthenreceived8daysofcondition
1.55 forGroups RandU, respectively.
ing. On each day, there were two 90-min sessions, one in Con
Figure 5presents the responding by Groups Rand U
textAandoneinContextB.ForGroupR, sessionsinContextA
consistedofeight pairingsofthe 30-sectone CS with the food on trials that followed reinforced versus nonreinforced
US, with a mean ITI of10min. Sessions in Context B for this trials. Agroup X trialtype X sessionANOVAwascon
groupconsistedonlyofexposuretotheapparatus. ForGroupU, ducted on the elevation scores. The ANOVA revealeda
sessions in Context A consisted ofexposure to the apparatus, significantmaineffectofgroup [F(l,14) = 7.20],asig
whilesessionsinContextBconsistedofeightpresentationsofthe nificant maineffectofsession [F(5,70) = 12.59],anda
USalone,withamean IT!of10min. As in theprecedingexper
iments,onDay I allsessionsstartedwithtwopresentationsofthe significantgroup X sessioninteraction[F(5,70) =3.23]
tonealone,withameanIT!ofImin,sothatconditioningbegan (these effects correspond to the preceding analysis of
withanonnovelCSinallgroups.GroupRreceivedsessionsinthe reacquisition). In addition, there was asignificantmain
orderABBA, while Group U receivedthem in the orderBAAB. effectoftrialtype[F(l,14) =5.48]and,mostimportantly,
Extinction. Followingconditioning,the rats received 20ses a significant trial type X group interaction [F(I,14) =
sionsofextinctioninContextA.Thereweretwo90-minsessions
17.62]. While responding overall was higher following
in Context A each day. ForGroup R, each session consistedof
reinforced than following nonreinforced trials, this ef
eightpresentationsofthetonealone, withamean IT!of10min.
ForGroupU,thesesessionsconsistedonlyofexposuretotheap fect was confined to Group R. The session X trial type
paratus.Nofoodwaspresentedduringthisphase. interaction was significant [F(5,70) =2.70], but more
Reacquisition. Followingextinction,theratsreceived3more importantly,thesession X trialtype X groupinteraction
days(sixsessions)ofconditioninginContextA. Bothgroupsre was also significant [F(5,70) = 2.37]. Initially, for
ceivedtwo90-minsessionsadayinwhichthe30-sectoneCSwas
Group R only, responding was higher following rein
pairedwithfood fourtimesandpresentedalonefourtimes,with
forcedtrialsthanfollowingnonreinforcedtrials,but,over
ameanITIof10min. Twotrialsequenceswereusedoverthesix
sessions, this difference disappeared. This was con
sessions. Inone sequence,reinforced(R)andnonreinforced(N)
trialsalternated(i.e.,RNRNRNRN); intheothersequence,trials firmed with simple comparisons (at ex = .0125). In
semialternated(i.e., RNRRNNRN). Theorderofpresentationof GroupRthereweresignificantdifferencesbetweentrial
the two sequences was ASSAAS, where A refers to alternating types duringthefirsttwosessions [ts(82)>4.44],butin
andSreferstosemialternating. Group Uthere werenosuchdifferences(ts < 1).
A similar analysis was conducted on prescores. The
Results
ANOVA revealed significant main effects only ofses
By the endofconditioning, rats in Group Rwere re sion [F(5,70) = 5.63J and trial type [F(I,14) =5.77J.
spondingwell tothe CS;themeanelevationscoreinthe Responding during the preperiodwas somewhathigher
lastfour-trial blockwas 7.72. Aone-wayrepeatedmea followingreinforcedtrialsthanfollowingnonreinforced
sures ANOVA was conducted for Group R, and it re trials,wheretherespectivemeanswere1.74and1.54for
vealed a significant main effect of four-trial block Group Rand 1.81 and 1.28 for Group U. The fact that
[F(l5,105) = 4.21]. Extinction also proceeded without thiseffectdidnotvarywithgroup[group X trialtypein
incident,withrats inGroupRshowinglittleornospon teraction, F(l,14) = 1.15] is interesting, given that the
taneous recovery by Day 4. By the last session ofex
tinction, Groups Rand Uhad meanelevation scores of
0.00 and -1.88, respectively. Atrial-block ANOVA re 10
vealed a significant main effect ofblock [F(39,273) = • GroupR
9
7.71]. ---.-- GroupU
Reacquisition data are presented in Figure 4. During 8
reacquisition,GroupsRandUinitiallydidnotdiffer,but 7
overtrials, Rresponded more than U. Agroup X block .<.U. .
ANOVA carried out on elevation scores revealed a sig u0 6
nificantmaineffectofgroup [F(l,14) =7.20],asignif C'" 5 ,"'--
.g
niciafinctamntaignroeuffpecXtobflbolcokckin[tFer(alcIt,i1o5n4)[F=(II8,.11504],)an=d3a.4si5g] . ~<>U 4 ,.--.-... ",,
~
AlthoughrespondingoverallwashigherinGroup R,the 3
... I "
groupsdidnotdifferinitiallyandtowardtheendofreac 2 .--.....-." ,'eI
quisition. This was confirmed with four post hoc com
parisons (at ex = .0125). On Block 1, Groups Rand U
didnot differ [t(44) =0.53]. However, on Blocks6and 0
10,theydid [ts(44) ~ 3.44]. ByBlock 12,the groups no 0 2 3 4 6 8 9 10 11 12
longerdiffered [t(44) = 1.86]. 4-Trial Blocks
TheANOVAonprescoresrevealedonlyasignificant
Figure4. Meanelevationscoresduring reacquisition in Ex
main effect ofblock [F(lI,154) = 3.13]. Neither the periment2.
430 RICKERAND BOUTON
this idea, itdoes appearthattherapid reacquisition ob
• GroupR(r)
10 served in the present method is initially restricted to
--0-- GroupR(n)
trials thatfollow reinforcedtrials, as a retrieval view or
9
---e-- GroupD(r)
sequentialtheorypredicts.
8 ---0-- GroupD(n)
EXPERIMENT3
OnepurposeofExperiment3was to replicate these
quential learning effect observed in Experiment 2. An
other purpose was to further explore the learning-to
learneffectthatwasobservedinExperiment 1A. Inthat
experiment, conditioning and extinction with the light
2 offCSfacilitatedconditioningofthetoneCSinthefinal
phase. This sort ofresult is captured by the model pre
sentedby Kehoe (1988), which states that conditioning
o-t----r---,---,,....---.,.----.----. andextinctionwithanystimulusresultsinresidualexci
o 2 3 4 5 6 tation which may transfer to reconditioning or condi
Session tioning ofanother stimulus. An alternative possibility,
however, is thatthe sequential learningeffectidentified
Figure5.Meanelevationscoresduringreacquisition in Ex
periment2.HeredataforGroupsRandUarebrokendowninto in Experiment 2 may contribute to this result as well.
trialsfoUowingreinforcedtrials(r)andtrialsfoUowingnonrein Followingconditioning,theoccurrenceoftheUS might
forcedtrials(n).
potentiallyserveasageneralsignalofreinforcement,re
gardless ofthe identity ofthe CS. Ifso, we might like
wiseobserveenhancedrespondingfollowing reinforced
elevationscoresdidvarywithgrouponthesetrials. This
trialsinalearning-experiencedcontrolgroup. InExper
suggests that the aftereffects ofa reinforced trial were
iment 3, we therefore compared responding on trials
experiencedinbothgroups (higherprescores), butonly
afterreinforced andnonreinforced trials in Phase 3 ina
inGroupRdidareinforcedtrialsignalreinforcementon
learning-experiencedcontrol (Group L),a reacquisition
thenexttrial.
group,andarestcontrol.
Discussion Method
Reacquisitionagainoccurredrapidlycomparedwitha Subjects
learning-naive control, even when a partial, ratherthan Thesubjectswere24femaleWistarratsobtainedfromCharles
continuous, reinforcement procedure was used. How River,Canada.(TheratsinExperiments IA-Band2werederived
ever, closer analysis revealed that high responding in fromthisstock.)Theywereapproximately90daysoldatthestart
oftheexperimentandwerehousedandmaintainedasbefore.Dur
Group R was initially confinedto trials following rein
ingthecourseoftheexperiment,3oftheanimalsbecamesick(I
forced, rather than nonreinforced, trials. This result is
from eachgroup) and were removed, leaving 7 animals in each
consistent with a retrieval view, especially one empha group.
sizingtheretrievalroleofindividualtrials(e.g.,Capaldi,
1994). The fact thatthese differences in responding did Apparatus
not lastbeyondthe first two sessions maybe due to the Theapparatus was the same as that in Experiments I and 2,
withtheexceptionthatthetwoNoyesfoodpelletsthatservedas
change incontingenciesbetweenreinforced andnonre
theUSweredelivered0.4secapart.
inforced trials and the trial types that followed them.
That is, during reacquisition, nonreinforced trials now
Procedure
tended to signal reinforced trials and reinforced trials Pretraining.Boxexposureandmagazinetrainingwerecarried
tendedtosignalnonreinforcedtrials,reversingwhatmight outasinExperiments Iand2.Approximately 18pelletswerede
have been learned during extinction and conditioning. liveredduringeachofthemagazinetrainingsessions.
Responding following nonreinforced trials was not Conditioning. Thesubjectsreceivedeightsessionsofcondi
tioning,oneperday.ForGroupR,thesessionsconsistedofeight
lowerinGroup Rthan inGroup U. Thiscouldpresenta
pairingsofthe30-sectonewiththe(oodUS,withamean ITIof
problemfortheretrievalview. If, forGroup R,nonrein
10min. ForGroupL, thesessionsconsistedofeightpairingsof
forced trials were signaling nonreinforcement on the the 30-seclightoffwiththeUS, with amean ITIof10min. For
nexttrial,thenrespondingfollowingnonreinforcedtrials GroupC,thesesessionsconsistedonlyofexposuretotheappara
shouldhavebeenlowerinthisgroupthaninGroupU,for tus; no stimuliwere presented. Forall groups, the first session
whomnosuchsignalingshouldoccur.Onepossibilityis startedwithtwononreinforcedpresentationseachofthetoneand
lightoff,intheorderTLTL.
thatifretrievalofanextinctionmemoryismoresuscep
Extinction. Following conditioning,the rats received 20 ses
tible to retrieval failure (Bouton, 1993), itmay bemore
sions ofextinction, I perday. ForGroup R, these sessions con
difficult to retrieve the memory ofnonreinforcement sistedofeightpresentationsofthetonealonewithameanITIof
thanofreinforcementinGroupR.Whateverthemeritof 10min.ForGroupL,thesessionsconsistedofeightpresentations
REACQUISITION AFTEREXTINCTION 431
ofthelightoffalonewithameanIT!of10min.GroupCreceived •
GroupR
onlyexposuretotheapparatusduringthesesessions.Nofoodwas 10
presentedduringthisphase. ---0-- GroupL
Reacquisition. Followingextinction, the rats received three 9 ---/).-- Groupe ~~....o
0,
moresessionsofconditioning,again oneperday. Forallgroups,
8 I , ,"
thetonewaspairedwithfoodfourtimesandwaspresentedalone I ,
I ' ,..(]-----o'
four times with amean IT! of 10 min during these sessions. In 7 II " ,
eachsession, reinforcedandnonreinforcedtrials alternated(i.e., 8~ II
RNRNRNRN). '" 6 II
§ 5 II
I
Results .~ I
i) 4 oI
Conditioningproceededuneventfully, with Groups R G3
and Lreaching mean elevation scores of5.93 and 5.75, 3
respectively,duringthefinal four-trial block.Agroup X 2
four-trial block ANOVA revealeda significantmain ef
fect onlyofblock [F(15,210) == 2.09]. Neitherthemain
effect of group nor the interaction were significant o-i---,---,---,---..,.---..,.----,
[F(1,14) == 1.97andF(15,21O) == 0.93, respectively]. o 2 3 4 5 6
4-Trial Blocks
Extinction proceeded uneventfully as well, with rats
showinglittleornorespondingbySession7. Agroup X Figure6. Meanelevationscoresduring reacquisition in Ex
blockANOVArevealedasignificantmaineffectonlyof periment3.
block [F(39,468) == 1.58]. Neither the main effect of
group northe interactionweresignificant(Fs < I).
Thedatafrom reacquisitionarepresentedinFigure6. separately,usingthe errorterms from the overallanaly
During reacquisition, Group Ronce again acquired re sis.ForGroupR,thisanalysisrevealedbothmaineffects
sponding more rapidly than Group C but more slowly ofsession [F(2,36) == 9.60] and trial type [F(1,18) ==
thanGroupL.Agroup X blockANOVArevealedamain 7.14]. ForGroups LandC, however, there were no sig
effect ofgroup [F(2,18) == 5.17] and a main effect of nificant effects in these analyses [largest F(1,18) ==
block [F(5,90) == 9.57]. The interactionwas notsignifi 3.89]. Furthercontrasts inGroup Lon Sessions I and2
cant [F(10,90) == 1.15]. The main effect ofgroup was revealed no differences in responding following rein
explored with unplanned comparisons (at a == .017). forced versusnonreinforcedtrials [ts(24) ~ 1.36].Thus,
These comparisons revealed that Group R showed less GroupR,butneitherGroupLnorGroupC,gaveevidence
overall responding than Group L [t(18) == -3.19], that ofthesequentiallearningeffect.Theideathatfacilitated
Group R showed more responding than Group C responding in Group L was more than a result ofse
[t(18) == 4.64], andthatGroup Lshowedmorerespond quential learning was further supported by ANOVAs
ing than Group C [t(18) == 7.83]. Although responding comparing the groups' responding after reinforced and
inGroup Lseemsunusually high atthe outset, the first nonreinforcedtrials. RespondingwasgreaterinGroupL
trial elevation score in this group wasonly -0.29. thaninGroupCfollowingbothreinforced[t(18) == 3.15]
TheANOVAonprescoresrevealedasignificantmain and nonreinforced [t(18) > 2.74] trials; facilitation was
effect only of block [F(5,90) == 3.82]. Prescores in not dependenton trial type. Incontrast, there was more
creasedslightlyandthendecreasedoverblocks.Neither responding inGroup Rthan inGroup Cfollowing rein
themaineffectofgroupnorthe interactionweresignifi forcedtrials[t(18) == 2.14,.025<p<.05]butnotfollow
cant[F(2,18) == 1.24andF(10,90) == 0.96,respectively]. ing nonreinforced trials [t(18) == 1.34]. The facilitation
MeanprescoresforGroups R, L, andCwere 1.86,2.91, effect for Group R, but not Group L, was thus demon
and 2.15,respectively. strablyconfinedtotrialsfollowing reinforcedtrials.
Figure 7 presents responding ofeach group on the A group X trial type X session ANOVA on the pre
trialsfollowingreinforcedversusnonreinforcedtrials. A scores revealed a significant main effect of session
group X trial type X session ANOVA revealed signifi [F(2,36) == 4.75]. However, the three-way interaction
cantmaineffectsofgroupandsessionas intheprevious was also significant [F(4,36) == 2.80]. No other effects
analysis [F(2,18) == 5.17 and F(2,36) == 11.06, respec weresignificantinthisanalysis[largestF(4,36) == 1.56].
tively]. The interaction ofthese factors was not signifi Following reinforced trials, mean prescores for Groups
cant [F(4,36) == 1.39]. There was a significantmainef R, L, andCwere 1.64,2.63,and 1.75,respectively; fol
fect of trial type [F(l,18) == 11.46], indicating that lowing nonreinforced trials, they were 2.07, 3.19, and'
responding was higher overall on trials following rein 2.15, respectively. The three-way interaction suggests
forcedtrials.Noneoftheinteractionsinvolvingtrialtype that differences in trial types existed for some groups
weresignificant(Fs ~ 1.22). onlyon some sessions. Therefore, separatetrial type X
Because we had an a priori interest in which ofthe session ANOVAs were carriedout for eachgroup sepa
groups showed differentiation between trial types, trial rately,asintheanalysisofelevationscores.Theonlysig
type X sessionANOVAswereconductedforeachgroup nificanteffectswereamaineffectofsessionforGroupL
432 RICKERAND BOUTON
10
9
• GroupR(r)
8
--i:}- GroupR(n)
7
o ---e-- GroupL (r)
o15 6 ---0-- GroupL (n)
'"
§ 5 ..................... GroupC(r)
.~
> 4 ...._...f:s.......- GroupC(n)
.,!:l.
>Ll 3
2
O+----""T""----,----.......----,
o 2 3
Session
Figure7.MeanelevationscoresduringreacquisitioninExperiment3.Heredata
arebrokendownintotrialsfollowingreinforcedtrials(r)andtrialsfollowingnon
reinforcedtrials(n).
[F(2,36) = 4.64] and a trial type X session interaction bothnonreinforcedandreinforcedtrialsclearlyindicates
forGroupC[F(2,36) = 4.95].TheinteractioninGroupC that the learning-to-Iearn effect was not restricted to
was further exploredusing simple comparisons (ata = trialsfollowingreinforcedtrials.Therefore,thelearning
.017). Theserevealedonlya smallnonsignificanteffect to-learneffectevidentinthispreparationcannotbecom
oftrialtypeonSession3[t(31) = -2.05,p =.05].There pletelyattributedto sequentiallearning.
fore, itcanbeconcludedthatthere were noproblematic
differences inprescores. EXPERIMENT4
Discussion Thepurposeofthe final experimentwastotakealast
As in the previous experiments, reacquisition again lookatwhetherreacquisitioncouldoccurslowlyrelative
occurred rapidly as compared with the learning-naive to alearning-naive control inthis conditioningprepara..
control (Group C) but was slow as compared with the tion. We decided to take advantage ofan implication of
learning-experiencedcontrol (Group L). In this experi thesequentiallearningviewsuggestedbyExperiments2
ment, the interference effectappearedearly in the third and 3. Specifically, ifrapidreacquisition was due inpart
phase,aswouldbeexpectedgiventheresultsofprevious to reinforced trials' signaling further reinforced trials,
studies(Bouton, 1986;Bouton&Swartzentruber, 1989). thenonewaytoreducethefacilitativeeffect,andthuscre
This result is again consistent with the idea that two ateanopportunitytoviewtheinterferenceeffect,mightbe
mechanisms influence reacquisition rate: a savings to drastically reduce the number ofconditioning trials.
mechanism that allows groups that have been through With fewer conditioning trials, there would be fewer
conditioningandextinctionwithanyCStorespondmore occasions for the animals to associate reinforced trials
inPhase3thangroupsthathavenot,andaninterference withotherreinforcedtrials,andthusreacquisitionmight
mechanismthatproduceslessofthiseffectinareacqui actuallyoccurslowlyascomparedwithalearning-naive
sition group than in a learning-experienced control control.
group. It is interesting to note that previous experiments
While responding was greater on trials following re showing slow reacquisition in CER and taste aversion
inforced trials than on trials following nonreinforced haveinvolvedveryfewconditioningtrials(eightinCER,
trials, further analyses determined that this effect was and one-two in taste aversion). In Experiment 4 we
confinedtoGroupR.Thisresultreplicatesthemainresult therefore conducted conditioning with only eight trials.
ofExperiment 2, and continues to suggestthat sequen Toobtainconditioningwiththismethodinsofewtrials,
tial learning plays a role in producing rapid reacquisi we increasedthe magnitudeofthe food US from two to
tion. Incontrast,Group L didnotshowareliablediffer five 45-mg food pellets and increased the ITIs from 10
entiation. Itis possible that the present experimentwas to 20 min. Trial-spacing parameters were identical to
notpowerful enough to detect an effectthat might have those ofBouton and Swartzentruber(1989) in the CER
existed in Group L; there was a clearnumerical trend in preparation. We hoped that by using only eight condi
thedata. However,thefactthatGroupI:srespondingwas tioning trials, acquisition ofsequential learning would
significantly facilitated relative to Group C's following be minimized for Group R and reacquisition would