Interva l be tween preexposure and test de termi nes the magn i tude of l a tent i nh i b i t i on : Imp l i ca t i ons for an i nter ference account

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1 An i ma l l xarn i ng & 1 i r l w i ' i nr 1994, 21!2, i, 18R-194 Interva l be tween preexposure and test de termi nes the magn i tude of l a tent i nh i b i t i on : Imp l i ca t i ons for an i nter ference account LUIS AGUADO Un i uers i dad Comp l uterese de Madr i d, Madr i d, Spa i n and MICHELLE SYMON l l S and GEOFFREY HALL, Un i vers i ty of York, York, Eng l and The e f fec t of a re tent i on i nterva l on l a tent i nh i b i t i on was stud i ed i n three exper i ments by us i ng ra ts ard the cond i t i oned taste-avers i on procedure, In Exper i ment 1, we der r i orcst ra ted an appar - ent l oss of l a tent i nh i b i t i on ( i e, a st rengthen i ng of the avers i on) i n preexposed sub j ec ts tha t exper i enced a re tent i on i nterva l of 12 days be tween cond i t i on i ng and the test In Exper i ment, 2, we found no e f fec t of th i s re tent i on i nterva l on the hab i tua t i on of neophob i a produced by the phase of exposure to the f l avor, In Exper i ment 3, we showed tha t i nterpos i ng a re tent i on i nter - va l be tween preexposure and cond i t i on i ng produced e f fec ts exac t l y comparab l e to those seen i n Exper i ment 1 The i mp l i ca t i ons of these resu l ts for r i va l theor i es of l a tent i nh i b i t i on, as an acqu i s i t i on de f i c i t or as a case of i nter ference a t re t r i eva l, are d i scussed La tent i nh i b i t i on i s the re tarda t i on of cond i t i on i ng observed when the to-be-cond i t i oned st imu lus (CS) is preexposed before the cond i t i on i ng phase (Lubow, 1973), Th i s e f fec t has usua l l y been thought of as re f l ec t i ng an acqu i s i t i on de f i c i t, var i ous l y a t t r i buted to a decrease i n the assoc i ab i l i ty of the st i mu l us (Mack i ntosh, 1975 ; Pearce & Ha l l, 1980), the cond i t i on i ng of i na t tent i on ( I ubow, We i ner, & Schnur, l 9$1), or reduced process i ng of the st i mu l us caused by pr i mi ng by the context i n wh i ch i t has been exposed (Wagner, 1976) For al l these theor i es, the reduced CR (cond i t i oned response) observed af ter cond i t i on i ng w i th a preexposed st i mu l us i s assumed to re f l ec t a weak under l y i ng assoc i a t i on I t i s poss i b l e, however, tha t l a tent i nh i b i t i on mi ght be the resu l t, i n who l e or i n par t, not of an acqu i s i t i on de f i c i t, but of a fa i l ure of re t r i eva l For examp l e, Bouton (1991) and Kraemer and Rober ts (1984) have suggested that the preexposure and cond i t i on i ng exper i ences genera te i ndependent memor i es, and tha t a l though the assoc i a t i on of the preexposed st i m- u l us w i th the US (uncond i t i oned st i mu l us) i s per fec t l y we l l establ i shed, the memory of the pr cxpasure exper i ence i nter feres w i th i ts re t r i eva l a t the t i me of test i ng Suppor t for the inter ference account has been sought in at tempts to show that cer ta in procedures can act as This research was suppor ted 6y a grant ( ram the Spanish M ini s l eno de Educat ion y Ciencia (Eslancias de Invest igadores en Cent ros de Invest i gac i on I : xt ran j cros) to the f i rst author, and by a grant f rom the U K Sc i ence and Eng i neer i ng Research Counc i l to the th i rd author We thank Char lot te HonardL f i r her helpful rommen l s Address cor respondence to G Hal l, nepachnent of Psychology, Universi ty of York, YOI SIJp Eng l and " re i n i ndcrs " tha t w i l l promote the re t r i eva l of one memory over another Thus, Kxsprow, Ca t terson, Schacht - man, and M i l l er (1984) found tha t rccxpos i ng an an i ma l to the US be fore the test phase of a l atent inhibi t ion exper i ment resu l ted i n a more v i gorous CR, a resu l t they interpreted as suggest i ng that the remi nder t reatment cou l d at tenuate the inter fer ing ef fects of the preexposure phase and ensure express i on of the CS- US assoc i at ion establ i shed dur i ng cond i t i on i ng A converse e f fec t, re i nstatement of l atent inhibi t ion, has been recent l y repor ted by Ack i l, Carman, Bakner, and R i cc i o (1992) These authors found that a l though preexposure to sucrose 10 days before taste-avers i on cond i t i on i ng d i d not reduce the st rength of the acqu i red avers i on, a " remi nder " presentat i on of sucrose the day be fore cond i t i on i ng restored the e f fec ts of precxposure, that is, l atent inhibi t ion was found under these cond i t i ons Such a re i nstatement of l a tent i nh i b i t i on mi ght be expec ted i f this remi nder t reatment were ab l e to reac t i va te the memory of the preexposure phase of the procedure A second l i ne of ev i dence, and one tha t forms the fetus of the present exper i ments, comes f rom stud i es of the e f - fec ts of i mpos i ng a l ong re tent i on i nterva l be tween cond i t i on i ng and test i ng i n a l a tent i nh i b i t i on procedure Us i ng the cond i t i oned taste-avers ion procedure, Kracmer and Rober ts (1984) found tha t, i n some cond i t i ons of t ra i n- i ng, the avers i on to the CS i n the preexposed an i ma l s was st ronger when the test was g i ven 21 days a f ter cond i t i oni ng ra ther than on the day fo l l ow i ng cond i t i on i ng Th i s resu l t i s not to be expec ted nn the bas i s of the not i on tha t l a tent i nh i b i t i on i s an acqu i s i t i on de f i c i t a weak assoc i - a t i on present i mmed i a te l y a f ter cond i t i on i ng wou l d not Copyr i ght 1994 Psychonomi c Soc i e ty, Inc 189

2 RETENTION INTERVAL IN LATENT INHIBITION 189 he expec ted to grow st ronger w i th the passage of t i me Kraenter and Rober ts propose, rather, that the CS- US assoc i at ion is we l l formed, even af ter latent inhibi t ion t raini ng, and i s not i nf l uenced substant i a l l y by the re tent i on interna l But the inter fer ing memory produced by preexposure becomes, i t is suggested, l ess ef fect i ve over the course of the retent ion interva l, w i th the resul t that the l a tent i nh i b i t i on e f fec t i s no l onger ev i dent a f ter 21 days G i ven i ts potent i a l theore t i ca l i mpor tance, we thought i t wor thwh i l e, as our f i rst exper i ment, to a t tempt to conf i rm the re l i ab i l i ty of the e f fec t repor ted by Kraemer and Rober ts (1984), and a l so, by i nt roduc i ng a number of procedura l mod i f i cauons, to extend i ts genera l i ty In Exper i ments 2 and 3, we i n i t i a te an ana l ys i s of the mechan i sms respons i b l e for the e f fec t seen i n Exper i ment 1 Exper i ntent Z was des i gned to ru l e out (he poss i b i l i ty tha t the retent ion interva l mi ght have i ts ef fect by v i r tue of i ts inf luence on the rat ' s neophoh i c response to f l avor st i mu l i, In Exper i ment 3, we tested an i mp l i ca t i on of the inter ference interpretat ion of the retent ion interva l e f fec t - tha t the cr i t i ca l i nterva l i n produc i ng an a t tenuat ion of l atent inhibi t ion i s that be tween preexposure and test, and tha t the i nterva l be tween the cond i t i on i ng t r i a l and the test i s i mma ter i a l EXPERIMENT l In prev i ous stud i es of the a t tenua t i on of l a tent i nh i b i - t i on i n f l avor -avers i on cond i t i on i ng, an e f fec t of the cond i t i on i ng- to- test i nterva l has been demonst ra ted on l y under a rest r i c ted se t of cond i t i ons In par t i cu l ar, a re l i - ab l e e f fec t has been observed on l y when the f l avor used as the CS has been somewha t d i f ferent f rom tha t presented dur i ng preexposure (Kraemer & Ossenkopp, 1986 ; Kracmer & Robot s, 1984 ; Kraemer & Spear, 1992) Demonst ra t i ons of the e f fec t w i th the same f l avor i n both phases are l ess secure Bakncr, St rahen, Nordeen, and R i cc i a (199! ) were successfu l us i ng sucrose as the f l avor, as were Kraemer and Rober ts and Kraemer, Hof fmann, and Spear (1988) us i ng choco l a te mi l k Kraemer and Ossenkopp, however, found per fect retent ion of the l atent inhibi t ion e f fec t when choco l a te mi l k was used for both phases an a t tenua t i on was found on l y when preexposure was to sacchar i n and cond i t i on i ng was w i th choco l a te mi l k We do not know why the retent ion interva l ef fect shou l d show such sens i t i v i ty to the na ture of the f l avors used, and we were keen to de termi ne i f we cou l d obta i n the e f fec t w i th our standard t ra i n i ng procedures w i th the f l avor (sacchar i n) tha t we have rout i ne l y used i n our prev i ous work on l a tent i nh i b i t i on, and by us i ng the same f l avor both i n preexposure and as the CS, Fo l l ow i ng Kracmer and Rober l s (1984), the re tent i on i nterva l s ( the i nterva l s be tween cond i t i on i ng and the test ) most of ten used i n stud i es of the a t tenua t i on of l a tent i n- hibi t ion have been 1 day and 21 days In the present exper i ment, we reduced the l onger interva l to 12 days because the resu l ts of l 3akoer e t a l (1991) ind i ca te l i t t le e f fec t of extend i ng the i nterna l beyond th i s po i nt We a l so i ncreased the shor ter interva l to 2 days We have found, i n p i l ot work, tha t an i nfec t i on of l i th i um ch l or i de (L i Ci ), the US emp l oyed in the present exper i ments, produces t rans i ent changes in the rat ' s read iness to consume f luids There i s a pronounced suppress i on of wa ter consumpt i on for severa l hours fo l l ow i ng i n j ec t i on, wh i ch i s some t i mes fo l l owed by a compensa tory i ncrease i n consumpt i on on the fo l l ow i ng day Var i a t i ons of th i s sar i mi ght make i t d i f f i cu l t to obta i n an accura te measure of the st rength of a cond i t i oned avers i on when the test i s g i ven w i th i n 24 h of cond i t i on i ng But our p i l ot work has shown tha t consumpt i on of wa fer re turns to norma l l eve l s when an i n- terva l of 4$ h i s a l l owed to e l apse fo l l ow i ng an L i CI i n j ec t i on A fur ther, mi nor procedura l mod i f i ca t i on was tha t i n our exper i ment, the sub j ec ts were g i ven a f i xed and l i m- i ted amount of f luid on each tr ial of preexposure and cond i t i on i ng Al l the an i ma l s consumed a!1 the f l u i d on each presentat i on, so exposure to the f l our was equ i va l ent i n a l l t ra i n i ng cond i t i ons We were thus ab l e to avo i d the prob l ems noted by Bakner et al (1991) in the i r Exper i - ment 1 (hut not in the i r Exper i ment 2), in wh i ch there were substant i a l d i f ferences among the groups in the amounts of f l u i d consumed dur i ng t ra i n i ng The exper i menta l des i gn i nc l uded four groups Two groups (Pre-2 and Pre-12) rece i ved preexposure to sacchar i n be fore a cond i t i on i ng t r i a l i n wh i ch consumpt i on of th i s f l avor was fo l l owed by L i C! - i nduced i l l ness The st rength of the avers i on genera ted by th i s t rea tment was tasted e i ther 2 or 12 days a f ter the cond i t i on i ng day We hoped to show a st ronger avers i on in Group Pre-12 than i n Group Pre-2 I t i s of theore t i ca l i mpor tance to show that any such ef fect of retent ion interva l is rest r i cted to sub j ec ts tha t rece i ved the i n i t i a l l a tent i nh i b i t i on t ra i n i ng (And there i s ev i dence tha t, i n some c i rcumstances, the measured st rength of an avers i on can i ncrease over a retent ion interva l, even in subj ects that have had no preexposure ; e g, Ba tse l l & Best, 1992 ) Accord i ng l y, we i nc l uded cont ro l groups, Cont -2 and Conk-12, tha t d i d not rece i ve preexpasure, but exper i enced the shor t and l ong re tent i on i nterva l s be tween cond i t i on i ng and the test These two groups shou l d not di f fer 9n the i r test per for - mance i f the retent ion interva l has i ts ef fects sol e l y by ac t i ng on the memory estab i shed by st i mu l us preexposure Me thod Subj ects and Apparatus, The subjects were 32 ma l e Lister hooded ra ts, w i th a mean we i ght of 500 g a t the star t of the exper i - ment The an i ma l s were housed i nd i v i dua l l y w i th cont i nuous access to food i n a colony room that a l so served as the test room F luids were administered at room temperature in a 50-ni l plast ic cent r i fuge tube w i th a rubber stopper f i t ted w i th a stainless steel dr ink ing spout In thi s and the fol low ing exper iments, the test f lavor was a so l ut i on of 0 I k sod i um sacchar i n, and i l l ness was i nduced by a 1(F% body-we ight int raper i toneal inject ion of 0 3 M I ici Procedure Before the preexposure phase, the anima l s were subjected f i r 4 days to a water -depr ivat ion schedul e consist ing of two dai ly 30-min per iods of f ree access to water, separated by a 7-h i nterva l These dr i nk i ng per i ods took p l ace a t 1100 and 1800 h!n subsequent phases of the exper iment, f lavored solut ions were presented dur i ng the f i rst of these per i ods ; the an i ma l s cont i nued to rece ive water dur ing the second per iod throughout the exper iment

3 190 AGUADO, SYMONDS, AND HALL Dur i ng the morn i ng dr i nk i ng per i od of each of the three preexposure days, the an i ma l s i n Groups Pre-2 and Pre- l 2 were of fered 10 ml of the sacchar i n so l ut i on for 30 mi n The sub j ec ts i n the cont rot groups rece i ved 10 ml of water in these sess i ons On the next condi t ioning day, al l rece ived access to 10 ml of sacchar in for 30 mi n, fo l l owed i mmed i a te l y by an i n j ec t i on of L i CI A recovery day fo l l owed, i n wh i ch the an i ma l s had access to wa ter for the usua l two 30-mi n per i ods The test cons i sted of three da i l y sess i ons i n wh i ch the an i ma l s were a l l owed f ree access to the sacchar i n so l u- t ion for 30 mi n For Groups Pre-2 and Copt -2, the ors[ test was g i ven nn the day a f ter the recovery day For Groups Pre-12 and font - l2, an interval of 12 days intervened between condi t ioning and the f i rst test session Tra ining for these groups was begun 10 days be fore the star t of t ra i n i ng for the groups g i ven the 2-day re tent ion interval so as to a l low the test tr ials (or al l the subjects to fal l on the same days Dur i ng the l ast 5 days of the re tent i on i nterva l for the 12-day groups ( the days cor responding to the preexposure, condi t ioning, and recovery sessions for Groups Pre-2 and Cont -2), the schedu l e of wa ter admi n i st ra t i on was ma tched to tha t de termi n i ng the presentat ion of f luids to 2-day groups Thus, al l the groups w i re equated in leve l of depr i va t ion at the t ime of test ing Resu l ts ant i l l i seuss i on F i gure 1 presents the mean amounts or test so l ut i on consurned by each group on each of the 3 test days Al l showed an ini t ial avers i on that dec l i ned to some extent over the course of the ext i nc t i on test, but more i mpor tant i s the c l ear d i f ference be tween the two preexpased groups ; Group Pre-12 showed less consumpt i on than Group Pre-2 The nonprcexposed cont ro l groups showed l ower l eve l s of consumpt i on, cons i stent w i th the suggest i on tha t l atent inhibi t ion occur red in the preexposed groups There we t no s i gn tha t i mpos i ng a re tent i on i nterva l i ncreased the s i ze of the measured avers i on i n the an i ma l s tha t were not g i ven l a tent i nh i b i t i on t ra i n i ng There was l i t t l e d i f - ference be tween the two cont ro l groups, but the avers i on was, i f anyth i ng, s l i ght l y more l marked i n Group Cont -2 than in Group Copt 'E l 5 n n 0 s i o s n i v` - Tr ials - -~`_ CON7' -2 ^- } - ' - PRE-2 cor rtaz ~- PRE-12 F igure 1 Mean sacchar in consumpt ion aver the three test tr ials i n Exper iment 1 "Pre " groups rece ived preexpasure to the sacchar i n be fore the cond i t i on i ng t r i a l ; "Cont groups d i d not For one pa i r of groups, the interval between condi t ioning and the f i rst test t r i a l was 2 days ; for the other pa i r of groups, the i nterva l was 12 days An ana l ys i s of var i ance (ANNA) was per formed nn the consumpt i on data f rom the test days, w i th interva l, preexposure cond i t i on, and t r i a l s as the fac tors Th i s ana l - ys i s y i e l ded s i gn i f i cant i nterac t i ons be tween i nterva l and preexposure cond i t i on [x ' (1,28) = 4 11, p = OS] and between precxposure cond i t i on and t r i a l s [F(2,Sb) = 6 49, >> c 05] The three-way interact ion of interva l x preexposure x t r i a l s was not s i gn i f i cant (F = 1 15), Pa i r - w i se compar i sons among the group means us i ng Duncan ' s test were made in order to de termi ne the source of the i nterac t i on be tween i nterva l and preexposure cond i t i on These repea l ed s i gn i f i cant d i f ferences be tween Groups Pre- 2 and Pre-12 (p C 05), Pre-2 and Cont -2 (p < O1), and Pre-12 and Cont -12 (p c D5) Th i s exper i ment conf i rmed tha t, a l though the l a tent i n- h i b i t i on e f fec t i s not abo l i shed comp l e te l y (a t l east w i th the 12-day i nterva l used here), the magn i tude of a cond i - t i oned taste avers i on w i l l i ncrease over a re tent i on i nter - va l i n an i ma l s g i ven pr i or l a tent i nh i b i t i on t ra i n i ng Thus, these resu l ts extend the genera l i ty of the e f fec t tha t was ini t ial ly repor ted by Kraemer and Rober ts (1984), and make c l ear tha t i t can be found not on l y when d i f ferent f l avors are used for preexposure ar i a cond i t i on i ng (e g, Kraemer & Ossenkopp, 1986), but a l so when the same f l avor is used in both phases We cannot account for the fa i l ure of Kraemer and Robots (1984, Exper i ment 3) to f ind the ef fect in groups that, l ike our preexposed subj ec ts, were g i ven three prcexposure sess i ons w i th 0 1 sacchar i n fo l l owed by cond i t i on i ng w i th th i s same f l avor The d i screpancy presumab l y ar i ses f rom some procedura l d i f ference be tween the i r exper i ment and ours, such as the i r use of scopo l ami ne ra ther than L i CI as the US, or the i r use of a cho i ce as opposed to a s i ng l e-bot t l e test There was no e f fec t of the re tent i on i nterva l on the aver - s ion shown by the nonpreexposed groups ; cer ta inl y there was no s i gn of any enhancement of the avers i on i n these groups (c f Ba tse l l & Best, 1992), and the s l i ght l oss of the avers i on i n Group Cont -12 was not stat i st i ca l l y re l i - ab l e (Th i s l ast resu l t accords w i th prev i ous f i nd i ngs tha t cond i t i oned taste avers i ons tend to be espec i a l l y res i stant to forge t t i ng ; e g, Brooksh i re & Brackb i l l, 1976 ; Co l by & Smi th, 1977 ) Taken as a who l e, th i s pa t tern of resu l ts i s cons i stent not on l y w i th the i nter ference theory ' s c l a i m tha t the precxposure exper i ence i s a t l east par t i a l l y forgot - ten or becomes l ess re t r i evab l e aver a re tent i on i nterva l, but a l so w i th a comp l ementary assumpt i on of th i s theory Both Kraemer and Rober ts (1984) and Hauton (1941) have suggested that memor i es of nonre i nforced exposure to a st i mu l us and of the assoc i a t i on be tween a st i mu l us and a mot i va t i ona l l y re l evant consequence are d i f ferent i a l l y sens i t i ve to the passage of t i me Spec i f i ca l l y, i t i s assumed tha t memor i es of s i gn i f i cant assoc i a t i ons are more res i s- tant than the memory of mere st i mu l us exposure In Exper i men i 1, the res i stance of s i gn i f i cant memor i es to for - ge t t i ng i s conf i rmed by the v i r tua l absence of a reduc t i on of the acqu i red avers i on i n the nanpreexposed group a f ter a retent ion interva l of 12 days

4 RETENTION INTERVAL IN LATENT INHIBITION 191 EXPERIMENT 2 The resu l ts of Exper i ment l conf i rmed tha t a re tent i on i nterva l w i l l i ncrease the magn i tude of a cond i t i oned taste avers i on i n sub j ec ts g i ven i n i t i a l l a tent i nh i b i t i on t ra i n- ing However, before accept i ng an interpretat ion of this e f fec t as be i ng due to forge t t i ng or a reduc t i on i n the ret r i cvab i l i ty of the preexposure exper i ence, an a l terna t i ve account shou l d he cons i dered One of the e f fec ts of repea ted exposure to a new f l avor i s the hab i tua t i on of the neophob i c reac t i on i n i t i a l l y e l i c i ted by i t, a process that is ref l ected in a progress i ve increase in consumpt i on of the f l avor A l though our procedures d i d not a l l ow us to observe any such e f fec t ( the sub j ec ts were a l l owed to consume a f i xed 10 ml of f l u i d on each t r i a l ), i t seems very l i ke l y tha t the t rea tment g i ven to our preexposed subj ects wou l d have produced a loss of neophob i a A rest i nterva l w i thout st i mu l a t i on a f ter hab i tuat ion t ra ining has of ten been found to resul t in spontaneouc recovery of a hab i tuated response (e g, Thnmpson & Spencer, 1966) and there is some ev i dence to suggest tha t such recovery can occur in the case of f l avor neophoh i a (e,g, Domj an, 1977) h i s poss i b l e, then, tha t for our preexposed groups tested af ter a l ong retent ion inter - va l, neophoh i a ini t ial ly lost dur i ng preexposure mi ght have returned over that interva l Then, decreased consumpt i on on the test wou l d not be the resu l t of an a t tenua t i on of l a tent i nh i b i t i on, but of recovery of neophob i a Kraemer and Rober ts (19$4), in the i r exper i ment 3, a t tempted to i nvest i ga te the poss i b l e ro l e of neophob i a by compar i ng consumpt i on of the test so l ut i on a f ter 1 or 21 days i n an i ma l s tha t had been exposed to the so l ut i on but tha t had oa t rece i ved an i n j ec t i on However, as Lubow (1989, p 185) has noted, the absence of a d i f ference between these cond i t i ons i s not enough to a l l ow us to asser t tha t the recovery of neophab i a p l ays no ro l e i n the e f fec t seen i n an i ma l s g i ven l a tent i nh i b i t i on t ra i n i ng I t mi ght we l l be tha t neophob i a i nduced by the L i CI i n j ec t i on i s wha t recovers dur i ng the retent ion interva l ; to exc l ude th i s fac tor requ i res a cont ro l cond i t i on i n wh i ch an i ma l s are not on l y exposed to the f l avor, taut a l so rece i ve an unpa i red i n j ec t i on Th i s poss i b i l i ty has been d i rec t l y eva l ua ted i n a study of the a t tenua t i on of l a tent i nh i b i t i on a f ter de l ayed test i ng i n the cond i t i oned en i cx i ona l response procedure Kracmer, Randa l l, and Carbary (1991, Exper i ment 2) found no ef - fec t of a 7-day re tent i on i nterva l on the suppress i on shown by subj ects that had f i rst rece i ved preexposure and then nonpa i red presentat i ons of l i ght and an e l ec t r i c shack They conc l uded tha t a recovery of uncond i t i oned suppress i on was not the cause of the apparent a t tenua t i on of l a- tent inhibi t ion they had found in the i r f i rst exper i ment In the present Exper i ment 3, we app l i ed a s i mi l ar l og i c to the cond i t i oned taste-avers i on parad i gm Two groups were f i rst preexposed to the sacchar i n solut ion and then rece i ved an L i CI i n j ec t i on unpa i red w i th the so l ut i on Consumpt i on of sacchar i n was tested i n one group a f ter 2 days ; i n the other, test i ng was de l ayed for 12 days 1f neophob i a recovers over the retent ion interva l, then the 12-day group shou l d consume l ess on test of the so l ut i on Such an out - come wou l d ser i ous l y undermi ne the s i gn i f i cance of the resu l ts of our prev i ous exper i ment as a demonst ra t i on of the a t tenua t i on of l a tent i nh i b i t i on w i th t i me, Me thod Subj ects The subjects were 16 ma l e Lister hooded rats, w i th a mean we ight of 500 g They were ma inta ined on the water - depr iva t ion schedu l e tha t was used in Exper iment 1 Procedure On the f i rst 3 exper i menta l days, a l l the an i ma l s were of fered the sacchar in solut ion under condi t ions ident ica l to those emp l oyed for the preexposed subjects 9n Exper iment I The pracedure emp l oyed on the fo l l ow i ng day was s i mi l ar to tha t used for condi t ioning in Exper iment i, except that the I ici inject ion occur red in the af ternoon rather than in the morn ing That is, al l the anima l s rece i ved 10 ml of the sacchar i n so l ut i on i n the morn i ng and, 7 h l a ter, had access to 10 ml of wa ter for 30 mi n fo l l owed by the L i CI inject ion The next day was a recovery day Test presentat ions of sacchar i n began for ha l f the an i ma l s (Group 2) on the day fo l l owing this recovery day ; far the rema inder (Group 12), a fur ther 11 days i ntervened be tween the recovery day and the stars of the test As in the prev ious exper iment, t ra in ing far the sub jects gi ven the longer retent ion interva l star ted ear l ier than t ra ining for those gi ven the shor ter interval, so that test ing mi ght occur on the sane days for both groups Procedura l de ta i l s not spec i f i ed here were the same as those descr ibed for Exper iment 1 Resu l ts and D i scuss i on F i gure 2 shows the mean amount of sacchar i n consumed by each group on the three test t r i a l s The on l y s ign of a d i f ference be tween the two groups was on Tr i a l i, i n wh i ch Group 2 drank s l i ght l y l ess than Gro i ns 12 Note, however, tha t th i s sma l l d i f ference was i n the d i rec t i on oppos i te f rom wha t wou l d have been expec ted had neophob i a recovered over the 12-day retent i on i nterva l An ANOVA was per formed on the resu l ts summar i zed i n the f i gure, w i th re tent i on i nterva l and t r i a l s E 0 20 IR 16 C i o z Tr ia ts F igure 2 Mean sacchar in consumpt ion over the three test tr ials in Exper iment 2 The subjects had rece ived preexposure to sacchar i n and an unpa i red i n j ec t i on of I,9CI e i ther 2 or 12 days be fore the f i rst l est t r i a l,

5 192 AGUADO, SYMONDS, AND HALL as fac tors, Th i s y i e l ded no s i gn i f i cant e f fec ts [ for the ma i n e f fec t of group, F C 1 ; for t r i a l s, F ' (2,28) = 2 $3 ; and for the group x t r ials interac t ion, F(2, 28) = 1 99] These resu l ts prov i de no ev i dence of recovery of neophob i a over a retent ion interva l of 12 days Apar t f rom the fac t tha t the i n j ec t i on was not pa i red w i th sacchar i n, the an i ma l s i n th i s exper i ment rece i ved exac t l y the same pa t tern of depr i va t i on, i n j ec t i on, and exposure to the test f l avor tha t was emp l oyed i n Exper i ment 1 I t i s d i f f i cu l t to argue, therefore, that the recovery of the avers i on obta ined in Exper i ment 1 cou l d be a consequence of the recovery of neophob i a EXPERIMENT 3 The i nterpre tat i on of the a t tenua t i on of l a tent i nh i b i t i on af ter a retent ion interva l of fered by inter ference theory rests on two ma i n assumpt i ons F i rst, i t i s assumed tha t i ndependent memor i es are estab l i shed by preexposure and cond i t i on i ng ; second, i t i s assumed tha t the memory estab l i shed by precxposure i s sens i t i ve to the e f fec ts of the re tent i on i nterva l, whereas tha t estab l i shed by cond i t i oning is not Th i s account can be app l i ed oat on l y to the case i n wh i ch there i s a l ong re tent i on i nterva l f rom cond i t i on i ng to test, but a l so to the comp l ementary case i n wh i ch a de l ay occurs be tween preexposure and cond i t i oni ng (w i th no de l ay be tween cond i t i on i ng and the test ) In this l at ter case, just as in the former, the ef fects of the precxposure t rea tment w i t! dec l i ne over the re tent i on i n- terva l and l a tent i nh i b i t i on shou l d aga i n be a t tenua ted In fact, prov i ded the interva l be tween preexposure and the test is the same, the at tenuat ion produced by the retent ion interva l shou l d he the same in the two cases These two cases di f fer both in the recency of the preexposure exper i ence a t the t i me of cond i t i on i ng and i n the prox i mi ty of the cond i t i on i ng phase to the test, but accord i ng to the theory be i ng cons i dered, ne i ther of these fac tors w i l l be of i mpor tance i n de termi n i ng the outcome The memory formed as a resu l t of the cond i t i on i ng exper i ence w i l l be t i e same i n both cases, as i t i s assumed tha t preexposure i s w i thout d i rec t e f fec t on acqu i s i t i on The ab i l i ty of th i s memory to i nf l uence test per formance w i l l a l so be the same i n the two cases, g i ven the assumpt i on tha t the memory of cond i t i on i ng i s i mperv i ous to the e f fec ts of a re tent i on i nterva l The cr i t i ca l fac tor i n determi n i ng the magn i tude of the CR observed i n the test sess i on w i l l be the ab i l i ty of the memory, formed dur i ng prcexposure, to inter fere, and this, in turn, w i l l depend so l e l y on the i nterva l be tween preexposure and test Thus, inter ference theory predi cts that l atent inhibi t ion shou l d be s i mi l ar l y a t tenua ted by a g i ven re tent i on i nterna l, whe ther the interva l occurs be tween preexposure and cond i t i on i ng or be tween cond i t i on i ng and test i ng The purpose of Exper i ment 3, there fore, was to a l l ow us to make a d i rec t compar i son of the e f fec ts of a tang cond i t i on i ng- to- test i nterva l and a l ong preexposure- tocond i k i on i ng i nterva l on l a tent i nh i b i t i on We expec ted to conf i rm our prev i ous resu l ts for the cond i t i on i ng- to- test interva l, and thus the ch i ef quest i on of interest was whe ther or not there wou l d be an equ i va l ent a t tenua t i on of the l a tent i nh i b i t i on e f fec t i n the l a t ter case Prev i ous stud i es i n the taste-avers i on parad i gm of the e f fec ts of i n- terpos i ng an i nterva l be tween preexposure and cond i t i oni ng have produced mi xed resu l ts Severa l have shown an a t tenua t i on of the l a tent i nh i b i t i on e f fec t i n these c i rcumstances (e g, Ack i l e t a l, 1492 ; E l k i ns & Hobbs, 1979 ; Kraemer & Rober ts, 1984, Exper i ment 4 ; Mc Intosh & Tarpy, 1977), but there have a l so been same fa i lures to obta i n such an a t tenua t i on (e g, Ka l a t & Roz i n, 1973 ; S i ege l, 1974), and on one occas i on a t tenua t i on occur red on l y when d i f ferent f l avors were used dur i ng prccxposure and cond i t i on i ng (Kraemer & Rober ts, 1984, Exper - i ment 4) I t i s not c l ear exac t l y wha t cond i t i ons must be me t for an a t tenua t i on of l a tent i nh i b i t i on to be found i n exper i ments of th i s sor t But g i ven tha t the t ra i n i ng procedures and parame ters used in the present Exper i ment 1 were e f fec t i ve i n produc i ng an a t tenua t i on of l a tent i nh i - b i t i on over the cond i t i on i ng- to- test i nterva l, i t fo l l ows f rom the inter ference account that they wi l l a l so be ef - fect i ve when the same interva l separates preexposure and cond i t i on i ng Me thod Subj ects The subjects were 24 ma l e E ister rats, w i th a mean ad- l i b we i ght of 430 g They were ma i nta i ned under the same condi t ions that were used in the prev ious exper iments Procedure The anima l s were divided into three groups of $ Al l three groups ( to 6e referred to as 5-1, I -S, and S-S) were exposed to the sacchar i n so l ut i on for 3 days be fore cond i t i on i ng ; they had access on each of these days to 10 ml of the solut ion for a per iod of 30 mi n In Group S-1 (shor t preexposure-condi t ioning interval, long condi t ion ing test interva l ), condi t ioning took pl ace on the day fo l l ow i ng the l ast preexposure day ; then there was an interval of I 1 days before the f i rst lest session For Group L-S, the condi t ioning tr ial occur red 10 days af ter the last preexposure session ; the test session occur red on the day af ter the post inject ion recovery day and thus occur red 2 days a f ter the cond i t i on i ng t r i a l These subjects exper i enced a long preexposura-condi t ior t ing interval and a shor t condi t ioning- test interva l For both groups, an inter - val of 12 days e l apsed f rom the last precxposure day to the f i rst test day Group S-S exper i enced cond i t i on i ng on the day a f ter the l ast preexposure sess i on and the test on the day fo l l ow i ng the recovery day ( i e, they rece i ved t ra i n i ng tha t was the same as tha t g i ven to the Pre-2 group of Exper i ment I ) They sewed as a cont ro l to a l l ow us to assess the extent of the measured avers ion when nei ther of the retent ion intervals was long The start of t raining for Group S-5 was de l ayed so that al l three groups came to the test on the same day As in theprev ious exper iments, al l the groups exper i enced the sane schedul e of access to f luids so as to ensure that depr ivat ion levels were equated for the test Any procedura l de ta i l s not spec i f i ed here were the same as those descr ibed far the prev ious exper iments Resu l ts and D i scuss i on F i gure 3 shows mean sacchar i n consumpt i on aver the three test t r ials for the three groups Group S-S shows the h i gh l eve l of consumpt i on tha t wou l d be expec ted f rom an i ma l s g i ven t ra i n i ng known to produce a power fu l l a- tent i nh i b i t i on e f fec t Both Groups L-S and S-1, show an

6 RETENTION INTERVAI 1N LATENT INHIBITION 193 E o o V Ip v '+ 2 Tea l s - -~- - S-5 -a- s-l i s s F i gure 3 Mean sacchar i n consumpt i on over the three test t r i a l s in Exper iment 3 Al l the subjects rece ived preexposure to sacchar i n and a cond i t i on i ng t r i a l For Groups S-S and S-S,, the i nterva l between preexposure and cond i t ion ing was shor t, whereat for Group L-S, the interval was long For Groups S-S and L-S, the interval be tween cond i t i on i ng and the l est was shor t, whereas for Group S, ( the interva l was long apparent a t tenua t i on of the l a tent i nh i b i t i on e f fec t, ant i do so to the same extent An ANNA per formed on the test scores w i th groups and t r i a l s as fac tors repea l ed s i gn i f i - cant ma i n e f fec ts of group (F(2,21) = 3 45, p =, 05] and t r i a l [F ' (2,42) = 27,99, p < 01], and no s i gn i f i cant i nter - ac t i on Pa i rw i se compar i sons (Duncan ' s test ) conduc ted on group means poo l ed over a l l three t r i a l s showed tha t Groups L-S and S-L both d i f fered s i gn i f i cant l y f rom Group S-S (p C OS), but not f rom each other These resul ts ( compar i ng Groups S-S and S-L) conf i rm the f i nd i ng of our prev i ous exper i ments- tha t l a tent inhibi t ion i s at tenuated when a retent ion interva l intervenes be tween cond i t i on i ng and the test, The compar i son of Groups S-S and i, -S shows tha t, w i th these t ra i n i ng procedures, the ef fects of preexposure are a l so at tenuated when a retent ion interva l intervenes be tween preexposure and cond i t i on i ng A compar i son of Groups S-L and I, -S shows tha t a 12-day i nterva l be tween preexposure and test - ing at tenuates l atent inhibi t ion to a comparab l e degree, whe ther the cond i t i on i ng ep i sode takes p l ace a t the beg i nn i ng or a t the end of tha t i nterva l As pred i c ted by the inter ference account, the recency of the preexposure exper i ence a t the t i me of cond i t i on i ng p l ays no rote i n determi n i ng the e f fec ts of prcexposure Ra ther, wha t counts i s the preexposu re- test interva l, the interva l over wh i ch the i nter fer i ng e f fec ts of the preexposure exper i ence are presumed to suf fer a toss F ina l l y, the fact that Groups I -S and S-L show a s i mi l ar degree of avers i on i n sp i te of the i r hav i ng exper i enced d i f ferent cond i t i on i ng- test i n- terva l s conf i rms the suggest i on tha t there i s no forge t t i ng of the cond i t i oned avers i on i tse l f, a t l east over the i nter - va l used in these exper i ments GENERAL DISCUSSION In our f i rst exper i ment, we found tha t there was a c l ear at tenuat ion of l atent inhibi t ion af ter a retent ion interva l be tween cond i t i on i ng and the test ; the an i ma l s g i ven cond i t ion ing w i thout any pr i or exposure to the CS showed no change i n the st rength of the avers i on over th i s i nter - va l These e f fec ts were found w i th a standard t ra i n i ng procedure in wh i ch the preexposed st i mu l us was the same as tha t used as the CS Exper i ment 2 a l l owed us to ru l e out changes i n neophob i a as a poss i b l e source of the e f - fec ts seen i n Exper i ment 1 I t was shown tha t neophob i a to the f l avor used as the CS in Exper i ment 1 d i d not recover dur i ng a 12-day retent ion interva l in an i ma l s rece i v i ng the same pa t tern of exposure to sacchar i n as the preexposed an i ma l s i n Exper i ment 1, but for wh i ch sacchar i n and the L i CI i n j ec t i on were unpa i red F i na l l y, i t was demonst ra ted i n Exper i ment 3 tha t an a t tenua t i on of l a tent i nh i b i t i on comparab l e to tha t seen i n Exper i ment I can be obta i ned when the re tent i on i nterva l i ntervenes between preexposure and cond i t i on i ng ra t ter than be tween cond i t i on i ng and test The cr i t i ca l de termi nant of these ef fects appears to be the l ength of the interva l be tween precxposure and the test Our resu l ts arc wha t wou l d be expec ted on the bas i s of a ret r i eva l inter ference theory of l atent inhibi t ion In i ts most bas i c form, this theory assumes that the preexposure and cond i t i on i ng ep i sodes are represented i ndependenf l y i n memory and tha t assoc i a t i on occurs norma l l y, even a f ter preexposure At the t i me of test i ng, the memory of preexposure i nter feres w i th re t r i eva l of the cond i - t i on i ng ep i sode and the st i mu l us thus e l i c i ts on l y a weak CR To accommoda te the e f fec ts of the re tent i on i nter - va l, i t is assumed that the memory of nonre i nforced exposure to the st i mu l us becomes l ess re t r i evab l e w i th t i me, so that af ter a long interva l i t w i l l no l onger be ab l e to i nter fere w i th re t r i eva l of the cond i t i on i ng ep i sode, the e f fec ts of wh i ch can then be fu l l y expressed The re tent i on i nterva l e f fec ts demonst ra ted i n our exper i ments pose a prob l em, however, for theor i es tha t i n- terpre t l a tent i nh i b i t i on as be i ng the resu l t of an acqu i s i - t i on de f i c i t Al though these theor i es can accept tha t an i nterva l be tween preexposure and cond i t i on i ng mi ght a1- l ow same forge t t i ng of t i e e f fec ts of preexposure, they cannot accommoda te the a t tenua t i on of the l a tent i nh i b i - t i on e f fec t produced by an i nterva l be tween cond i t i on i ng and the test There is nn reason, accord i ng to these theor i es, why the supposed l y weak assoc i a t i on l oaned when cond i t i on i ng i s car r i ed out i mmed i a te l y a f ter preexposure shou l d i ncrease i n st rength ever such a re tent i on i nterva l I t shou l d be acknow l edged tha t our resu l ts do not ent i re l y exc l ude the poss i b i l i ty tha t an acqu i s i t i on de f i c i t p l ays some ro l e i n l a tent i nh i b i t i on I t i s poss i b l e tha t preexposure mi ght both h i nder the acqu i s i t i on of assoc i a t i ve st rength and a l so estab l i sh a memory tha t i nter feres w i th the express i on of tha t st rength on test A hybr i d theory of th i s type has cer ta i n exp l ana tory advantages (see Ha i l, 1991) ; i n add i t i on, i t supp l i es a ready exp l ana t i on for the observat i on that even at long retent ion interva l s, the l atent i nh i b i t i on e f fec t l 5 not abo l i shed but mere l y a t tenua ted, but i f means the add i t i on of a ma j or new mechan i sm to theor i es tha t have h i ther to emp l oyed on l y the very s i m- p l est of pr i nc i p l es to dea l w i th re t r i eva l

7 194 AGUADO, SYMONpS, AND HALL Re t r i eva l i nter ference theory i s not i tse l f w i thout probl ems, however F i rst, there rema i ns some doubt about the genera l i ty of the at tenuat ion of l atent inhibi t ion af ter a re tent i on i nterva l As we have a l ready noted, most demonst ra t i ons have found th i s a t tenua t i on on l y i n wha t may be ca l l ed genera l i zed l a tent i nh i b i t i on, i n wh i ch d i f ferent st i mu l i are used dur i ng preexposure and cond i t i on i ng Al - though i n our exper i ments we have bean ab l e to obta i n the ef fect in the standard l atent inhibi t ion procedure, the reason why this has not been the case in some prev i ous repor ts (Kracmer & Ossenkopp, 1986 ; Kraemer & Spear, 1992) rema i ns unc l ear Fur ther, there i s l i t t l e ev i dence as ye t to demonst ra te the genera l i ty of these e f fec ts across exper i menta l parad i gms Apar t f rom cond i t i oned taste avers i on, a t tenua t i on of l a tent i nh i b i t i on aver a re tent i on i nterna l has been shown on l y w i th the cond i t i oned emot iona l response procedure (Kraemer et al, 1991) and the i mpac t of th i s demonst ra t i on i s du l l ed by the presence of d i f ferences be tween the precxposed and nonpreexposed groups i n the e f fec t of the d i f ferent re tent i on i nterva l s on base l i ne ac t i v i ty Whe ther the a t tenua t i on of l a tent i nh i - b i t i on a f ter a re tent i on i nterva l i s a genera l l earn i ng phenomenon rema i ns to be de termi ned A second concern ar i ses f rom the undeve l oped status of the re t r i eva l theory I t wou l d be he l pfu l, for i nstance, i f we had ava i l ab l e a prec i se spec i f i ca t i on of the na ture of the memory tha t i s he l d to be formed dur i ng preexposurc ; aga in, we have no c l ear statement about wha t changes take p l ace over a retent ion interna l, about why t i e memory of cond i t i on i ng appears to be i mmune to these ef fects, and about the exact nature of the inter ference process i tse l f These ma t ters need to be se t t l ed be fore a fu l l y sat i sfactory account of l atent inhibi t ion can be of fered None the l ess, i t rema i ns the case tha t our resu l ts are d i f f i - cu l t to exp l a i n i n terms of theor i es tha t a t t r i bute l a tent i n- h i b i t i on ent i re l y to an acqu i s i t i on de f i c i t And even i f i t i s accepted that there are reasons for reta ining cer ta in aspects of these theor i es (see, e g, Ha l l, 1991), i t seems l i ke l y tha t i t w i l l be necessary to comb i ne them i n some way w i th the proposa l tha t i nter ference a t re t r i eva l p l ays a ro l e i n genera t i ng the l a tent i nh i b i t i on e f fec t KF : FERFKCES ACKI1, I K, CARMAN, H M, BAKNFR, L, & RICC[0, D C (L992) Rein-statement of talent inhibi t ion fol low ing a reminder t reatment in a condi t ioned taste aversion paradigm Behaviora l & Neura l Biology, 58, BAKNFR, I, S7"ROF IFN, K, NORPFF N, M, & RICCJO, D C (1991) Postcor tdi t ioning recovery f rom the latent inhibi t ion ef fect in condi - t ioned taste aversion, Physiology & Behav ior, 50, 12b F3nTSH l l, W R, & Rest, M R (1992) Var ia t ions in the re tent ion of taste aversions : Evidence for retr ieval compet i t ion Anima l Learning & Behavior, 20, ouroN, M E (1991) Context and re t r i eva l i n ext i nc t i on and i n other exampl es of inter ference in simple associat ive learning In L W Daehowsk i & C F Flaher ty (Eds ), Current topics in anima l learning : Brain, enot inn and cogni t ion (pp 25-53) H l lcdale, NJ : Er lbaum BROOKSHIRE, K H, & S i uckirh, R M (1976), Format ion and retent i on of cond i t i oned taste avers i ons and UCS hab i tua t i on- Bu l l e t i n of the Psychonomi c Society, 7, $ Co[ -AY, J J,,a Snt i rx, N F (1477) The ef fect of three procedures (or e l imina t ing a cond i t ioned taste aversion in the ra t Learn ing Mot iva t ion, 8, 4(k4-A13, DoM i nw, M (1977) At tenuat ion and enhancement of neophob ' ta (or edible substances In L M Barker, M R Best, & NS Domj an (Eds ), Learning mechani sms in fnndselecr ion (pp, F51-180), Waco, TX: Bay- )or Un iversi ty Press Ei,Kixs, R L, & Hoass, S H (1979) Forget t ing, precondi t ioning CS fami l iar izat ion and taste aversion teaming: An anima l exper iment w i th i mp l i ca t i ons for a l coho l i sm t rea tment Behav i ora l Research & 7 i i er - apy, 17, F9&t t, G (1991) Perceptua l and associat ive learning Oxford : Cl arcndon KALnT, l w, & Roz I r+, P (1973) "Learned sa fety" as a mechan i sm in long-delay taste aversion in rats Jourrur l of Connotat i ve & Physi - ologi cal Psychology, 83, KASPAOW, W I, CATT6RSON, A, SCHACl i I 'MAN, T R, & MI I - I ER, R R (1984) At tenua t ion of la tent inh ibi t ion by postacqu isi t ion reminder Quar ter ly Journal of Fxper imenral Psychology, 368, 53-b3 KRAFMBR, P!, HQFFMANN, 1-1, & SPEAR, N E (1988) At tenua t i on of the CS-prcexposure ef fect af ter a retent ion interval in preweanl ing rate Ani rrw l Learning & Behavior, 16, IBS-190 : : KRAFMEA, P I, & OSSENKOPP, K -P (1986) The ef fects of f lavor preexposure and test interval on condi t ioned taste aversions in rats Bul let in of the Psyehonomi c Society, 24, KRAEMFR, P t, RANPAI, I, C K, & CARBARY, T 1 (1991) Re l ease f rom l a tent i nh i b i t i on w i th de l ayed test i ng An i r rut l l earn i ng & Behavior, 19, KRAFMER, P J, & RoerRrs, W A ( [4&i ) The inf luence of f lavor preexposure and test i nterval on condi t ioned taste aversions in the rat Learning & Mot ivat ion, 15, KRnaMSR, P J, & SPEAR, N E (1992) The ef fect of nonrc inforced st i mu l us exposure on the st rength of a cond i t i oned taste avers i on as a funct ion of retent ion interva l : Do latent inhibi t ion and ext inct ion involve a shared process? 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