Novelty of Contextual Cues in Taste Aversion Learning

Animal Learning & Behavior 1982,10 (2), 229-232 Novelty of contextualcues in taste aversion learning

ELIZABETH M. KURZ and DAVID A. LEVITSKY Cornell University, Ithaca, New York

The purpose of this experiment was to test the theory of Lubow, Rifkin, and Alek (1976) con cerning the effects of stimulus preexposure on later learning. This hypothesis predicts that con ditioning willoccur faster when either the stimulus or the testing environment is novel relative to the other than when the stimulus and the environment are equally novel or equally familiar. The theory was tested in a taste aversion conditioning paradigm in which groups of rats were presented with either the familiar (preexposed) solution or the novel nonpreexposed solution, in either the familiar or the novel environment. Conditioning was affected by the novelty of both the stimulus and the environment, with novel stimuli enhancing learning and novel environ ments retarding it. However, no interaction between stimulus and environmental novelty was evident, and thus Lubow's hypothesis was not confirmed.

There is little question of the powerful effect of new, SnEn. Latent learning or perceptual learning is stimulus preexposure on subsequent tests of learning defined by more rapid learning by the experimental in animals. However, there is a problem in our un group, SrEn, than by the controls, SnEn. derstanding of why stimulus preexposure in cer These procedural differences led Lubow and his tain circumstances leads to slower learning, as in la associates to suggest that stimulus preexposure re tent inhibition (Lubow, 1973), and in other situations sults in faster, stronger learning when, during testing, leads to an increase in the rate of learning, for exam either the stimulus or the environment is novel rela ple, perceptual learning (Hall, 1980; Tees, 1976) or tive to the other. Situations which do not contain this latent learning (Kimble, 1961). contrast in the level of novelty (SrEr or SnEn> should In an attempt to explain this paradox, Lubow and produce slower, weaker learning. Lubowet al. (1976) his associates (Lubow, Rifkin, & Alek, 1976) sug obtained supporting evidence for this hypothesis in gested a fundamental methodological distinction be two discrimination experiments which used approach tween latent inhibition and perceptual (stimulus) responses as a measure of learning. In one of these learning experiments. In the typical latent inhibition experiments, rats were trained to approach a familiar experiment, the experimental groups are taken out of or novel odor for food reinforcement in a modified their home cages and exposed to the test stimulus in Y-maze. The other experiment used an identical de the test environment. Thus, this group becomes fa sign, with children as subjects. It is interesting to note miliar with both the stimulus and the environment, that these results also support Wagner's (1976, 1978) SrEr. The control group is also exposed to the test ap learning model involving the effect of contextual cues paratus, but is not exposed to the test stimulus. Dur on conditioning. ing testing, therefore, this group receives a novel The purpose ofthe present investigation was to test stimulus in a familiar environment, SnEr. Latent in Lubow's hypothesis of stimulus preexposure, using a hibition is defined by more rapid learning of a prob conditioned taste aversion paradigm. In the present lem by the control group, SnEr, than by the experi study, both the novelty of a flavored solution and the mentals, SrEr. novelty of the testing environment (context) were On the other hand, in the typical perceptual learn manipulated, and their effect on a conditioned taste ing experiment, the experimental group is exposed to aversion to the flavor were examined. If the hypoth and becomes familiar with the test stimuli in their esis ofLubow et al. (1976) was correct, a novel-tasting home cages, but are tested in a new environment, solution should produce strong conditioning in a fa SrEn. The control group in these experiments receives miliar environment (SnEr>SrEr)but weak condition no such stimulus preexposure and, thus, during test ing in a novel environment (SrEn>SnEn>. ing, both the stimuli and the test environment are METHOD

Research supported in part by Orant BNS 7812S31 from the Na Subjects tional Science Foundation and from Hatch funds, The authors are The subjects were 80 male Long-Evans hooded rats approx associated with the Department or Psychology and the Division or imately 6 weeks old and weighing 135-222 g at the beginning or the Nutritional Sciences. Cornell University, Ithaca, New York 148S3. experiment. They were housed singlyunder a reversed lighting cycle

Table I Experimental Design (vanilla or anise flavor) or the kind of cage (solid Stimulus and Environ- metal or wire mesh) to which the rats were exposed Phase Days ment Conditions on the test days. Therefore, in all subsequent analy ses, the data were summed over these factors. 1. Preexposure 1-14 SrEr II. Conditioning 15 SrEr, SrEn' SnEr, SnEn Table 2 shows the overall intake of the flavored III. Rest 16 SrEr solution on the 2 test days, broken down by treat IV. Conditioning 17 SrEr, SrEn' SnEr. SnEn ments (SfEn, SnEn, etc.). The data were analyzed in V. Testing 18-19 SrEr, SrEn' SnEr, SnEn terms of absolute intake; however, the same pattern Note-S = stimulus, E = environment; [ = familiar, n = novel. of results was evident when the data were expressed as the percentage of the total fluid consumed as the (12 h light, 12 h dark). All subjects had ad-lib access to Purina test solution. A 2 x 4 ANOVA revealed a significant Lab Chow throughout the experiment, and 12 h access per day effect of treatment [F(3,76)=3.33, p < .OS, two (during the dark half of their cycle)to water andlor another fluid, tailed] and a marginally significant decrease in intake depending on the experimental procedure. between the first and second test days [F(l ,76)= 3.08, Procedure .10 > P > .OS, two-tailed], but no significant inter The basic sequence of events is shown in Table I. The first action. phase of the experiment, the preexposure phase, ran from Day I to The comparison of the test-day data with preex Day 14 of the experiment. For this phase, each animal was as signed randomly to one of the two types of environment (a 24 x posure intake demonstrates that all groups except the 18x 18 em cage made of wire mesh or solid metal) and to one of SfEn showed a significant depression in intake on the two stimuli (vanilla or anise solution, .2010 v/v), such that the the first test day, indicating strong conditioning. four resulting groups had 20subjects each. During the preexposure Comparing the flavored solution intake from the period, each animal had access to a bottle of tap water and a bottle first test day with the average intake over the last 3 of its assigned solution for the 12-h fluid-access period each day. Fluid intakes and body weights were recorded daily. preexposure days, the following results were ob For the first conditioning session, on Day IS of the experiment, tained: for SfEf, t(19)=2.94, P < .01; for SnEf' t(19) each of the four major groups of the preexposure period was di =3.9S, p < .002; for SnEn, t(19)= 3.22, p < .OOS; for vided into four subgroups (n = S in each subgroup) corresponding SfEn, t(19)= .490, n.s. to the four groups in Table I. For example, of the group that had been preexposed to the vanilla solution in wire-mesh cages, five The next major analysis performed on the data ex animals were conditioned with the vanilla solution in the same amined the overall effects of familiar or novel stimuli mesh cages (StEr), another five were so conditioned in a novel solid and familiar or novel environments on intake of the metal cage (SrEn>. In the conditioning procedure itself, each ani flavored solutions on the first test day. The results of mal was given access to the appropriately flavored solution alone the analysis are presented in Figure 1. As indicated for Y2 h in the appropriate type of cage. It was then injected intra peritoneally with 2 cc/iOO g body weight of a .IS M lithium by a significant main effect of stimulus novelty/ chloride (LiCI) solution and returned to its home cage, where it re familiarity [F(1,76)=4.89, p < .OS], it is clear that a ceived tap water only for the remainder of the usual 12-h period. novel stimulus significantly enhances conditioning. On the following day, the animals remained in their home cages This is in agreement with observations made by and received the same fluids they had received on Day 14. The second conditioning session on Day 17 of the experiment followed others (e.g., Kalat & Rozin, 1973; Revusky & Bedarf, exactly the same procedure as the one just described. All animals 1967;Siegel, 1974).' received the same treatment (SrEr, SrEn' SnEr. SnEJ on Day 17 The most important point, however, is that the they had received on Day IS. Two conditioning sessions were em data clearly fail to confirm Lubow's hypothesis con ployed to ensure an observable conditioning effect, given the fact cerning the latent inhibition and perceptual learning that a stimulus other than a taste (i.e., a novel environment) was being manipulated as a possible conditioned stimulus (CS). It has effects. It should be recalled that Lubow's hypothesis been reported (e.g., Mitchell, Kirschbaum, &: Perry, 1975) that predicts better conditioning resulting from a novel when using an exteroceptive CS with LiCI as the unconditioned stimulus presented in a familiar environment. On the stimulus (US), more than one conditioning trial may be neces other hand, in a novel environment better condition sary. For the testing days, which immediately followed the second ing should occur with familiar stimuli. The data indi conditioning day, each animal was exposed to the environment and cate that conditioning was enhanced in a familiar en- to the flavor it had experienced during conditioning. It was given a bottle of plain tap water and a bottle of the appropriately flavored Table 2 solution. Its intake from both bottles was recorded after I. 2, 3, 4, Mean Intake of Flavored Solution S, 6, 8, 10, and 12 h on the first test day (Day 18). The animals were reexposed to the testing situation on Day 19, and their in Intake (in Mi11iliters) takes of water and of the solution were recorded after 12 h of Baseline Test Day 1 Test Day 2 access. Treat- ment Mean SE Mean SE Mean SE RESULTS AND DISCUSSION SrEr 11.2 .939 6.3 1.54 4.9 1.56 SrEn 10.5 .760 11.3 2.50 7.6 1.83 A preliminary analysis of variance (ANOVA) SnEr 11.2 1.01 4.3 1.32 2.8 .917 11.4 .986 6.4 1.49 4.6 showed no significant effects of the kind of solution SnEn 1.40 CONTEXTUAL CUESIN TASTE AVERSION 231

other factor, such as distraction by novel stimuli, 11 11 must be operating in this situation. 10- 10- The relationships between novelty, context, and conditioning are addressed in a theory recently pro 9 9 f- - f- ..... posed by Wagner (1976, 1978). This theory suggests a 8 (in part) that contextual or environmental cues can be associated with particular conditioned stimuli (CSs) 7 1 § such that when the contextual cues are presented, 6 6 they can activate the memory of the associated CS w - I- and "prime" it into short-term memory (STM). :lI::: - S- - j! 5 When the memory of the CS is represented in STM, it ~ 4 4 is "expected," according to Wagner's theory, and therefore cannot support strong conditioning. On the 3- 3 other hand, if an animal is presented with a previ 2 2- ously exposed stimulus in a novel context (or any context other than that in which the stimulus was ex 1· 1· posed), the stimulus should be unexpected and thereby be able to promote strong conditioning. old new old new Similarly, if a novel (unexpected) stimulus is pre STIMULUS ENVIRONMENT sented in a familiar context, conditioning should also Figure 1. Mean Intake (with standard error) of the flavored so occur. In the present experiment, Wagner's theory lution In milliliters on the first test day, presented as a function of would predict strong conditioning in both the SnEf the stimulus conditions (on the left) and environmental conditions and the SfEn conditions. Our failure to obtain condi (on the right). tioning in the latter group casts some doubt on the general applicability of Wagner's theory. vironment [F(1,76) =4.61, p < .05], but, as indicated The present results clearly support the emphasis by a lack of statistical interaction between the stim placed by both Lubow and Wagner on the impor ulus and environmental factors [F(1,76) = .478, n.s.], tance of contextual cues in conditioning. However, the enhancing effect of a novel stimulus on condi these results also imply that the particular manner tioning occurred to about the same degree in both through which contextual cues may affect condition novel and familiar environments. Neither the stim ing may be dependent upon the specific learning ulus nor the environmental factors interacted with problem confronting the organism. the test days factor, indicating that the same pattern of results occurred on both test days. It should be noted that conditioning was poorer in REFERENCES a novel environment than in a familiar one. One ex BARKER, L. M. CS duration, amount, and concentration effects planation may lie in the fact that during conditioning in conditioning taste aversions. Learning and Motivation, 1976, sessions, the animals in novel environments con 7,265-273. sumed less than did the rats in familiar environments; BOLLES. R. C., & RAPP, H. M. Readiness to eat and drink: Effect in the novel environments, an average of 5.01 ml of of stimulus conditions. Journal of Comparative and Physio the flavored solutions were consumed, compared logicalPsychology, 1965,60,93-97. BOND, N., & DIGIUSTO, E. Amount of solution drunk is a factor with 6.97 ml in the familiar environments. A similar in the establishment of taste aversions. Animal Learning & effect of novel environments on consummatory be Behavior, 1975,3,81-84. havior has been noted by others (Bolles & Rapp, HALL, G. Exposure learning in animals. Psychological Bulletin, 1965; Moll, 1959; Welker, 1959). Moreover, it is 1980,88,535-550. KALAT, J. W., & ROZIN, P. "Learned safety" as a mechanism in known that the strength of a taste aversion is a direct long-delay taste aversion in the rat. Journal of Comparative function of the amount of fluid consumed during and Physiological Psychology, 1973,83,198-207. conditioning (Barker, 1976; Bond & DiGiusto, 1975). KIMBLE, G. A. Hi/gard and Marquis' conditioning and learning. However, the correlation between conditioning New York: Appleton-Century-Crofts, 1961. day intake and test day intake in our data is ap LUBOW, R. E. Latent inhibition. Psychological Bulletin, 1973, 79,398-407. proximately .26, which implies that variations in in LUBOW, R. E., RIFKIN, B., & ALEK, M. The context effect: The take during the conditioning sessions account for relationship between stimulus preexposure and environmental only 70/0 of the variance in test day intake. This anal preexposure determines subsequent learning. Journal ofExperi ysis, therefore, suggests that the disruptive effect of mental Psychology: Animal Behavior Processes, 1976,2,38-47. MITCHELL, D., KIRSCHBAUM, E. H., & PERRY, R. L. Effects of novel environments on taste aversion learning is neophobia and habituation on the poison-induced avoidance of greater than can be accounted for merely by the dif exteroceptive stimuli in the rat. Journal of Experimental Psy ferences in fluid intake during conditioning. Some chology: AnimalBehavior Processes, 1975, 104, 47-55. 232 KURZ AND LEVITSKY

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