Contextual control of fluid consumption: The effects of context extinction

Learning and Motivation 36 (2005) 297–311

www.elsevier.com/locate/l&m

Contextual control of Xuid consumption: The eVects of context extinction�

Madonna Murphy, Darlene M. Skinner¤

Department of Psychology, Memorial University of Newfoundland, St. John’s, NL, Canada A1B 3X9

Received 20 August 2004; received in revised form 28 October 2004Available online 19 December 2004

Abstract

Rats were trained on a conditional discrimination task in which saccharin was paired withLiCl in one context but paired with saline in another context. Rats drank less saccharin in thedanger context than in the safe context, and consumption in the home cage was intermediateto consumption in the two training contexts. Rats also avoided the danger context on a choicetest. After discrimination training, rats were given extinction trials with the danger contextalone (Experiment 1 and 2) or with the danger context + water (Experiment 2). Extinction tri-als with the context + water abolished contextual control over saccharin consumption but notthe avoidance of the danger context on the choice test. Extinction trials with the context aloneabolished avoidance of the danger context but not contextual control over saccharin consump-tion. These data suggest that occasion setting, not simple context conditioning, is the mecha-nism by which contextual cues modulate Xuid consumption. 2004 Elsevier Inc. All rights reserved.

Contextual cues have been shown to control the expression of conditioned tasteaversions (López & Cantora, 2003; Loy, Alvarez, Rey, & López, 1993; Nakajima,Kobayashi, & Imada, 1995; Puente, Cannon, Best, & Carrell, 1988; Skinner, God-dard, & Holland, 1998; Skinner, Martin, Pridgar, & van der Kooy, 1994). While

� This study was supported by a grant from the Natural Sciences and Engineering Research Council ofCanada to DMS.

* Corresponding author. Fax: +1 709 737 2430.E-mail address: [email protected] (D.M. Skinner).

0023-9690/$ - see front matter 2004 Elsevier Inc. All rights reserved.doi:10.1016/j.lmot.2004.11.002

mailto: [email protected]

mailto: [email protected]

298 M. Murphy, D.M. Skinner / Learning and Motivation 36 (2005) 297–311

many studies report that consumption of a particular Xuid is suppressed in one con-text but not in another, there are diVering views as to the mechanism of this contex-tual control. One view is that the context is another cue that enters into a Pavlovianassociation with the US. This association then sums with the associative strength ofthe Xavor presented in the context (López & Cantora, 2003; Loy et al., 1993). A sec-ond view is that the control over responding by contextual cues is similar to occa-sion setting with more discrete cues (Boakes, Westbrook, Elliott, & Swinbourne,1997; Holland, 1992; Skinner et al., 1994). In occasion setting, the conditional cue, orfeature, tells the animal when to respond to an explicit CS. For example, in positiveoccasion setting, the CS is not reinforced when presented alone but is reinforcedwhen it is preceded by the feature (F¡CS+/CS¡). Occasion setting is thought to beindependent of simple excitatory conditioning to the feature cue (Holland, 1983,1992).

Skinner et al. (1994) argued that contextual control over Xuid consumption wassimilar to occasion setting. In that study, saccharin was paired with LiCl in one con-text but paired with saline in a second context. During the acquisition phase, ratssuppressed consumption of saccharin in the Wrst context relative to the second con-text. The performance of this conditional group was compared to a control groupthat received pairings of one context with LiCl and pairings of a second context withsaline. On a Xuid ‘transfer’ test, rats in both groups were given a novel Xuid in the twotraining contexts. Only the conditional group suppressed consumption of Xuids inthe context paired with LiCl. Data such as these have previously been argued to sup-port the notion of simple conditioning to the context (i.e., the formation of a context–LiCl direct association). However, Skinner et al. argued against this account becausethe control group, given direct context–LiCl pairings, did not show suppression ofXuid consumption in the context paired with LiCl. Both groups avoided the contextassociated with LiCl on a place choice test. These data suggest that a context–LiClassociation is not suYcient to exert contextual control over Xuid consumption. Inaddition, Skinner, Clarke, and van der Kooy (2000) showed that rats with amygdalalesions acquired the conditional discrimination task but did not show the avoidanceof the danger context on a choice test. Thus, the aversive properties of the context donot appear to be necessary for contextual control over Xuid consumption.

Extinction procedures have also been used to distinguish between simple Pavlov-ian conditioning and occasion setting. Extinction of an occasion setter, by present-ing it alone, reduces responding to that cue but does little to the cue’s ability tomodulate responding to another target CS (Holland, 1992). Skinner et al. (1994)found that presenting the contextual cues in the absence of the US (but in the pres-ence of a water bottle) abolished the occasion setting ability of the context but notthe aversion to the context as measured by a place choice test. This pattern of resultsis opposite that seen with more traditional occasion setting paradigms and mayhave been due to the presence of the drinking response during extinction. Theextinction procedure was identical to training except for the Xuid used (water versussaccharin). Skinner et al. argued that contextual cues modulate a drinking response,rather than the taste of the saccharin, and so the extinction procedure involvedpresentation of the occasion setter in the presence of an appropriate response

M. Murphy, D.M. Skinner / Learning and Motivation 36 (2005) 297–311 299

(i.e., drinking). Rescorla (1986) has shown that a cue’s occasion setting ability can beextinguished if the occasion setter is unreinforced in the presence of an appropriatetarget.

The present study was designed to determine if the aversive properties of the con-text could be extinguished without extinguishing the occasion setting properties ofthe context. In Experiment 1, the context was presented alone in the absence of thedrinking response. In Experiment 2, the two extinction procedures were compared.Many previous studies have used one or both of these extinction procedures but haveused a consumption test and/or indirect blocking tests to measure aversion to thecontext (López & Cantora, 2003; Loy et al., 1993; Nakajima et al., 1995). Here wedirectly measure aversion to the context using a place choice test.

Experiment 1

We have previously suggested that contextual control over Xuid consumption isan example of the type of modulation seen in occasion setting and is not due to sim-ple context conditioning (Skinner et al., 1994; Skinner et al., 2000). The present exper-iment attempted to test this idea by using an extinction procedure similar to that usedin more traditional occasion setting procedures (Holland, 1992). Although we previ-ously extinguished the contexts in the presence of a water bottle (Skinner et al., 1994),in the present experiment the danger context was presented in the absence of a drink-ing response. Conditioning to the context was assessed pre- and post-extinction by aplace choice test.

The present study also made use of a modulation test (Bouton & Swartzentruber,1986) which is typically not used with the taste aversion paradigm. Bouton andSwartzentruber (1986) paired an auditory cue with shock in one context and gave thesame tone without the shock in a second context. They showed that responding to theauditory cue in a neutral context was intermediate to responding to the auditory cuein the two training contexts, suggesting that both contexts played a role in the modu-lation of responding to the target CS. After completion of discrimination training inExperiment 1, the saccharin was presented in the home cage. While the home cagewas not novel, it was associatively neutral since saccharin was never given in thehome cage. In addition, using the home cage reduced the likelihood of neophobiathat might be present with a novel environment.

Method

SubjectsTen, experimentally naive, male Long–Evans rats, weighing 350–400 g at the

beginning of the experiment, were used as subjects. The rats were housed individuallyin clear plastic cages (44 cm £ 22 cm £ 20 cm) with wood chip bedding. The rats weremaintained on a 12-h light/dark cycle, with lights on at 07:00, in a room kept at atemperature of 20 § 2 °C. Food was available ad lib. Rats were placed on a waterdeprivation schedule, consisting of 60 min access to tap water each day between 1400


and 1500, commencing 1 week prior to discrimination training. All training and test-ing took place between 09:30 and 11:00 each day.

ApparatusFor the context discrimination training, wooden boxes, measuring 41 cm £

41 cm £ 38 cm, were used. Half the boxes had white walls and a wire mesh Xoor cov-ered with wood chips. The remainder had black walls and a black plexiglass Xoorthat was wiped with a 2% acetic acid solution before each trial. Holes were drilled inone side of the boxes (approximately 7 cm above the Xoor) to allow the spout of thebottles to protrude inside the box. Bottles were attached to the outside of the boxwith a wire spring. The place choice box was divided into three chambers; a neutralgrey zone divided the two contexts used during the discrimination training. The doseof LiCl (60 mg/kg dissolved in 3 ml saline) and saline (0.9% NaCl) remained constantthroughout both experiments. A 0.1% saccharin solution served as the trainingXavor.

ProcedureAll rats were trained on a conditional contextual discrimination task. The acquisi-

tion phase of the experiment was divided into danger and safe days. On danger days,the rats were placed in a novel context 15 min prior to 15-min access to a novel sac-charin solution in the context. Removal of the saccharin solution was followed by ani.p. injection of LiCl, and rats were returned to the home cage. On safe days, rats wereplaced in a second novel context 15 min prior to 15-min access to the same saccharinsolution in the context. Saccharin removal was followed by an i.p. injection of physi-ological saline and rats were returned to the home cage. The white box served as thedanger context for half the rats in each group and the black box served as the dangercontext for the remaining rats.

This phase of the experiment started with 3 safe days to overcome any neophobia tothe saccharin solution prior to the Wrst danger day. There were a total of 12 dangerdays with a varying number of safe days after each one. These extra safe days weregiven to all subjects to increase consumption in rats that developed a taste aversion.For the purpose of statistical analysis, the discrimination phase was divided into 12cycles, consisting of a danger day followed by a safe day. One day after the end of thediscrimination phase, animals were given a 15min test with saccharin in the home cage.

Place choice testAfter the saccharin test in the home cage, rats were given a place test to assess

acquisition of a Pavlovian aversion to the context associated with LiCl. The test pro-cedure consisted of placing a rat in a neutral gray zone between the black and whitecontexts used during training. The amount of time spent in each of the two contextswas recorded in seconds for a 10-min period. Since the contextual cues were counter-balanced (half the rats had the black box as the LiCl-paired context and half had theblack box as the saline-paired context) we did not measure the initial preference ofthe individual rats prior to training. However, considerable previous work usingidentical contextual cues has shown that naive rats, on average, show a 50:50 split of


their time in the two contexts on a place choice test (Bechara & van der Kooy, 1992;Mucha, van der Kooy, O’Shaughnessy, & Bucenieks, 1982).

Context extinctionUpon completion of the place choice test, animals were given Wve 1-h extinction

trials in the danger context over a 5-day period. Animals were placed in the dangercontext for Wve 60-min trials. No Xuids were given in the context and no injectionswere given upon removal from the context.

Place choice testAfter the context extinction phase the animals were given a second place choice

test identical to the Wrst test.

Discrimination retention testAfter the place test, animals were given a discrimination retention test consisting

of a safe day and a danger day. Half the rats were placed in the safe context on theWrst day and the other half were placed in the danger context. The following daythe rats were placed in the alternate context. No injections were given on the reten-tion test. All other aspects of the test were the same as those in discriminationtraining.

Results

Context discrimination trainingAll animals acquired the context discrimination over the 12 cycles, consuming less

saccharin in the danger context than in the safe context (see Fig. 1). A 2 £ 2(Cycles £ Days) ANOVA revealed a main eVect of Days (F (1, 108) D 5.66, p < .05)and a Cycles£ Days interaction (F (11, 108) D 16.75), reXecting acquisition of the dis-crimination. Consumption of the saccharin solution in the home cage was intermedi-ate to consumption in the safe and danger contexts (Fig. 2A). A one-way ANOVAcomparing saccharin consumption on the last danger and safe day and in the homecage revealed a signiWcant eVect of context (F (2,18) D 44.09, p < .05). Follow-up New-man–Keuls tests revealed that consumption in the home cage was signiWcantly lessthan consumption in the safe context (p < .05) but signiWcantly greater than con-sumption in the danger context (p < .05).

Place choice testsIn addition to acquiring contextual control over saccharin consumption, animals

showed an avoidance of the danger context on the Wrst place test. A one-wayANOVA on time spent in the two compartments revealed a signiWcant eVect of con-text (F (1, 9) D 30.28, p < .05), conWrming that animals spent more time in the safecompartment than in the danger compartment (Fig. 2B).

When the second place test was administered, after the extinction phase, animalsno longer showed an avoidance of the danger context (Fig. 2D). A one-way ANOVAon time spent in the two compartments revealed no signiWcant eVect (F (1,9) D 0.73,


p > .05). A two-way ANOVA (Test £ Context) comparing performance on the twotests revealed a signiWcant Test £ Context interaction (F (1,18) D 11.65, p < .05). Fol-low-up Newman–Keuls tests revealed that time spent in the safe context was signiW-cantly greater than time spent in the danger context on the Wrst test (p < .05) but noton the second test (p > .05).

Discrimination retention testThe subsequent discrimination retention cycle revealed that discriminative control

over saccharin consumption was not abolished. A one-way ANOVA on consump-tion during the retention cycle revealed a signiWcant eVect of context (F (1,9) D 5.41,p < .05), conWrming that the animals still consumed signiWcantly less in the dangercontext than in the safe context (Fig. 2C). A two-way ANOVA (Test £ Context) com-paring performance on the retention cycle to the last cycle of discrimination trainingrevealed a signiWcant Test £ Context interaction (F (1, 18) D 11.58, p < .05). Follow-upNewman–Keuls tests revealed that consumption on the two safe days did not diVer(p > .05) but that consumption on the second danger day was higher than on the Wrstdanger day (p < .05). Thus, while the animals drank less in the danger context than inthe safe context on the retention test, this diVerence was not as big as during the lastcycle of discrimination training.

Discussion

The results from Experiment 1 suggest that contextual control over Xuid con-sumption may be due to an occasion setting mechanism. The pattern of results wascomparable to what is seen using more traditional occasion setting procedures.

Fig. 1. Mean saccharin consumption (ml) over 12 cycles of context discrimination training by rats inExperiment 1. Each cycle consists of a danger day (D) followed by a safe day (S). The extra safe days arenot included in the Wgure.


Bouton and Swartzentruber (1986) have argued that with contextual modulation thelevel of responding to a target CS in a neutral context should be intermediate toresponding levels in the safe and danger contexts. Indeed, consumption of saccharinin the home cage was higher than in the danger context but lower than in the safecontext. However, the home cage was probably not neutral in the present experimentsince animals experienced the eVects of LiCl in the home cage on danger days. Thus,the intermediate consumption in the home cage might also be explained by a summa-tion account.

In addition, unlike a previous study (Skinner et al., 1994), extinction in the pres-ent study was closer to what is typically observed in other occasion setting para-digms. The aversive properties of the context were abolished but contextual controlover consumption was only attenuated. The pattern of extinction results are inter-esting and do not appear to be due to the order of the tests. More extinction was

Fig. 2. (A) Mean (+SEM) saccharin consumption (ml) on the last two days of discrimination training andin the home cage by rats in Experiment 1. (B) Mean (+SEM) time (s) spent in the two training contexts onthe place choice test given after discrimination training. (C) Mean (+SEM) saccharin consumption in thedanger and safe contexts after context extinction. (D) Mean (+SEM) time (s) spent in the two trainingcontexts on the place choice test given after context extinction.


evident using the place test, which was given Wrst. Less extinction was evident onthe discrimination retention test. Since this test was given after the place choicetest, there was more opportunity for further extinction to occur. Some of theattenuation of the contextual control over saccharin consumption may have beendue to the fact that there was no retraining after saccharin was given in the homecage.

Experiment 2

In Experiment 1, extinction of the danger context, by presenting it alone in theabsence of a drinking response, abolished the aversive properties of the context butonly attenuated contextual control over saccharin consumption. We previouslyreported that context extinction abolished the occasion setting properties of the con-text but left intact the aversive properties of the context, as measured using a choicetest (Skinner et al., 1994). In the earlier study, the contextual cues were presented witha water bottle. In the present experiment, we directly compared the two extinctionprocedures by giving one group of rats unreinforced exposures to the danger contextin the absence of a drinking response and another group unreinforced exposures tothe danger context in the presence of the drinking response.

Method

SubjectsSixteen, experimentally naive, male Long–Evans rats, weighing 238–283 g at the

beginning the experiment, were used as subjects. The rats were maintained as in theprevious experiment.

ProcedureRats were assigned to two groups of 8 rats each based on body weight. Both

groups were treated identically until the extinction phase (see below). All ratswere trained on the contextual discrimination task used in Experiment 1. Theacquisition phase was again divided into danger and safe days. On danger days,the rats were placed in a novel context 15 min prior to 15-min access to a novelsaccharin solution followed by an i.p. injection of LiCl. On safe days, rats wereplaced in a second novel context 15 min prior to 15-min access to the same saccha-rin solution followed by an i.p. injection of physiological saline. The training con-texts, the dose of LiCl and the concentration of the saccharin were the same as inExperiment 1.

This phase of the experiment started with 3 safe days to overcome any neophobiato the saccharin solution prior to the Wrst danger day. There were a total of 14 dangerdays with a varying number of safe days after each one. For the purpose of statisticalanalysis, the discrimination phase was divided into 14 cycles, consisting of a dangerday followed by a safe day. At the end of the discrimination phase, animals weregiven a 15-min test with saccharin in the home cage, as in Experiment 1.


Place choice testAfter the saccharin test in the home cage, all rats were given a place choice test to

assess acquisition of a Pavlovian aversion to the context associated with LiCl. Thetest was identical to that in the previous experiment.

Context extinctionUpon completion of the place choice test, animals were given one of two extinc-

tion procedures. Rats in Group Box were exposed to the danger context alone, with-out any Xuid, for ten 30-min trials. Rats in Group Box-W were also give ten 30-minextinction trials but were exposed to the danger context for 15 min prior to 15-minaccess to tap water in the danger context. The context extinction procedure waschanged in this experiment, from Wve 60-min trials to ten 30-min trials, to moreclosely mimic training conditions. Due to experimenter error, consumption of waterwas not measured on the Wrst extinction trial. By the second extinction trial, con-sumption of water by rats in group Box-W was high (mean D 14.7 ml; by the lastextinction trial, rats consumed a mean of 15.8 ml of water).

Place choice testAfter the context extinction phase, the animals were given a second place choice

test identical to the Wrst test.

Discrimination retention testAfter the place test, animals were given a discrimination retention test consisting

of a safe day and a danger day. Half the rats were placed in the safe context on theWrst day and the other half were placed in the danger context. The following daythe rats were placed in the alternate context. No injections were given on theretention test. All other aspects of the test were the same as discriminationtraining.

Results

Context discrimination trainingAll animals acquired the context discrimination over the 14 cycles, consuming less

saccharin in the danger context than in the safe context. Because there were no diVer-ences between the groups during the acquisition phase, the groups were combined forinitial analyses. A one-way ANOVA on the last cycle revealed a signiWcant eVect ofcontext (F (1,15) D 123.14, p < .05), conWrming that the rats drank signiWcantly less inthe danger context (2.2 § 0.5 ml) than in the safe context (14.0 § 0.9 ml). As in Experi-ment 1, consumption of the saccharin solution in the home cage (9.9 § 0.9 ml) wasintermediate to consumption in the safe and danger contexts. A one-way ANOVAcomparing saccharin consumption on the last danger and safe day and in the homecage revealed a signiWcant eVect of context (F (2,30) D 74.66, p < .05). Follow-up New-man–Keuls tests revealed that consumption in the home cage was signiWcantly lessthan consumption in the safe context (p < .05) but signiWcantly greater than con-sumption in the danger context (p < .05).


Place choice testIn addition to showing diVerential saccharin consumption in the two training

contexts, animals showed an avoidance of the danger context on the Wrst place test.A one-way ANOVA on time spent in the two compartments revealed a signiWcanteVect of context (F (1, 15) D 33.08, p < .05), conWrming that animals spent more timein the safe compartment (309.7 § 11.4 s) than in the danger compartment(195.8 § 10.0 s).

Performance on the second place test depended on the treatment the animalsreceived during the extinction phase. Animals in Group Box, that were put in thedanger context without access to Xuid during extinction, did not show an avoidanceof the danger context (F (1,7) D 0.39, p > .05). A two-way ANOVA (Test £ Context)comparing performance on the two place choice tests revealed a signiWcantTest £ Context interaction (F (1,14) D 5.97, p < .05). Animals in Group Box showedan avoidance of the danger context on the place choice test given before extinction(Fig. 3B) but did not show this avoidance after extinction (Fig. 3D). Animals inGroup Box-W, that were put in the danger context with access to tap water duringextinction, continued to show an avoidance of the danger context (F (1,7) D 7.06,p < .05). A two-way ANOVA (Test £ Context) comparing performance on the twotests revealed a signiWcant eVect of Test (F (1, 14) D 9.10, p < .05), and Context(F (1, 14) D 18.68, p < .05), but no signiWcant interaction. As seen in Fig. 4, rats inGroup Box-W spent more time in the safe context than in the danger context on boththe Wrst place choice test (Fig. 4B) and on the second test (Fig. 4D).

Discrimination retention testPerformance on the subsequent discrimination retention cycle also depended on

the treatment the animals received during the extinction phase. Animals in GroupBox, that were put in the danger context without access to Xuid during extinction,consumed signiWcantly less saccharin in the danger context than in the safe contexton the retention test (F (1, 7) D 9.90, p < .05). A two-way ANOVA (Test £ Context)comparing performance on the last cycle of discrimination acquisition and on theretention test revealed a signiWcant Test £ Context interaction (F (1, 14) D 13.55,p < .05). Follow-up Newman–Keuls tests revealed that consumption on the two safedays did not diVer (p > .05) but that consumption on the second danger daywas higher than on the Wrst danger day (p < .05). Thus, while the animals drankless in the danger context than in the safe context on the retention test (Fig. 3C),this diVerence was not as big as during the last cycle of discrimination training (seeFig. 3A).

Animals in Group Box-W, that were put in the danger context with access to tapwater during extinction, did not consume less saccharin in the danger context than inthe safe context (F (1, 7) D .008, p > .05). A two-way ANOVA (Test £ Context) com-paring performance on the last cycle of discrimination acquisition and on the reten-tion test revealed a signiWcant Test £ Context interaction (F (1,14) D 8.88, p < .05).Follow-up Newman–Keuls tests revealed a signiWcant diVerence between consump-tion in the safe and danger contexts during the last cycle of training (p < .05; Fig. 4A)but not during the retention test (p > .05; see Fig. 4C).


Discussion

The results from Experiment 2 replicated those from Experiment 1 and also repli-cated the Wndings of an earlier study (Skinner et al., 1994). During extinction, Skinneret al. (1994) gave rats presentations of both the safe and danger contexts with a waterbottle. In the present experiment, rats were only given presentations of the dangercontext with water. However, both procedures produced the same pattern of results.If contextual cues are extinguished in the presence of a drinking response, thencontextual control over consumption is abolished. If contextual cues are extinguishedin the absence of a drinking response then the aversive properties of the context are

Fig. 3. (A) Mean (+SEM) saccharin consumption (ml) on the last two days of discrimination training byGroup Box rats in Experiment 2. (B) Mean (+SEM) time (s) spent in the two training contexts onthe place choice test given after discrimination training. (C) Mean (+SEM) saccharin consumption in thedanger and safe contexts after context extinction. (D) Mean (+SEM) time (s) spent in the two trainingcontexts on the place choice test given after context extinction.


abolished but the contextual control over consumption is not abolished. Bothextinction procedures provide evidence for a dissociation between the occasion set-ting function and the simple aversive properties of contextual cues. The Wnding thatsaccharin consumption in the home cage was intermediate to consumption in the safeand danger contexts replicates the Wnding from Experiment 1 and suggests that bothcontexts participate in the modulation of saccharin consumption.

Since the avoidance of the danger context on the place preference test depends ona direct association between the context and LiCl, one could argue that it should belost under both types of extinction. However, the presence of the water bottle (or thedrinking response) blocks the extinction of the Pavlovian properties of the context.This was the case in the present study and in the Skinner et al. (1994) study. While

Fig. 4. (A) Mean (+SEM) saccharin consumption (ml) on the last two days of discrimination training byGroup Box-W rats in Experiment 2. (B) Mean (+SEM) time (s) spent in the two training contexts on theplace choice test given after discrimination training. (C) Mean (+SEM) saccharin consumption in the dan-ger and safe contexts after context extinction. (D) Mean (+SEM) time (s) spent in the two training con-texts on the place choice test given after context extinction.


both simple conditioning to the context and occasion setting are acquired at thesame time, the associations may be stored in separate memory systems (Holland,1989). Presentations of a water bottle during extinction accesses the ‘higher-order’memory system and we see extinction of the occasion setting properties of the con-text. Presentations of the context alone only have access to the simple conditioningsystem. The pattern of extinction results might have been diVerent with moreextinction trials. Presentations of the danger context with a water bottle resulted insuperior extinction of the occasion setting properties of the context. Increasedextinction trials might also have abolished the Pavlovian aversion to the context.Likewise presentations of the danger context alone resulted in superior extinctionof the Pavlovian aversion to the context. With more trials, we might also have seenextinction of occasion setting with this treatment. It should be noted that theoccasion setting properties of the context were attenuated by context alonepresentations.

General discussion

It has been known for some time that taste aversions can be put under the controlof discriminative stimuli, such as contextual cues (Puente et al., 1988; Skinner et al.,1994). The present experiment conWrmed that contextual cues can control the expres-sion of a taste aversion. All rats suppressed consumption of saccharin in the dangercontext relative to the safe context. Skinner et al. (1994) argued that this contextualcontrol over taste aversions is an example of occasion setting. The present study pro-vided some support for this notion. Consumption of saccharin in the home cage wasintermediate to consumption in the safe and danger contexts. Bouton and Swartz-entruber (1986) have argued that this suggests both contexts are playing a role in themodulation of responding to the CS. In addition to acquiring contextual control oversaccharin consumption, animals showed an avoidance of the danger context on theWrst place test. This suggests that simple Pavlovian conditioning and occasion settingcan be acquired simultaneously (Skinner et al., 1994). Despite the fact that both areacquired simultaneously, they can be distinguished through extinction. Animals thatreceived tap water in the danger context during extinction still showed an avoidanceof the danger context on a place choice test. Animals that did not receive tap water inthe danger context during extinction no longer showed an avoidance of the dangercontext on this second place test. For animals that received tap water during theextinction phase, the retention test revealed that discriminative control over saccha-rin consumption was abolished. For animals that did not receive tap water during theextinction phase, the retention test revealed that discriminative control over saccha-rin consumption was not abolished.

Previous work has shown that extinction of an occasion setter results in a reduc-tion in responding to the cue itself but little eVect is seen on the cue’s occasion set-ting properties. Skinner et al. (1994) showed the opposite pattern of results: theyshowed extinction of the occasion setting properties of contextual cues while thesimple conditioning to the context was maintained. The diVerence between these


two extinction procedures is that previous studies did not extinguish the occasionsetter in the presence of an appropriate target cue (i.e., Holland, 1983, 1992),whereas Skinner et al. (1994) extinguished the contextual cues in the presence of anappropriate target (i.e., water/drinking response). In the present study, both proce-dures were used. If the danger context was extinguished by presenting it alone, thesimple aversion was abolished but the context still suppressed consumption of sac-charin. This pattern supports previous Wndings (Holland, 1983, 1992). If the dangercontext was extinguished by presenting the context with the water bottle, the sim-ple aversion remained while the occasion setting properties of the context wereabolished. This diVerential extinction eVect seems to support the occasion settingview. Rescorla (1986) found that the critical feature in extinguishing occasion set-ting was the non-reinforcement in the presence of an excitatory stimulus. This Wnd-ing can explain the results of the present study and the results found by Skinneret al. (1994). In these experiments the danger context was non-reinforced in thepresence of an appropriate target, the tap water (or the drinking response). Sincethe tap water was present at a time when the danger context was non-reinforced,the danger context lost its occasion setting ability but retained its Pavlovianassociations.

While the present results, and previous Wndings, support an occasion setting mech-anism for contextual control over taste aversions, others have proposed diVerentmechanisms to explain these results. The summational explanation suggests that theexcitatory strength of the LiCl-paired context sums with the excitatory strength ofthe Xavor to produce a stronger reduction in Xuid consumption (López & Cantora,2003; Loy et al., 1993). Loy et al. (1993) found that extinction of the contextual cuesin the presence of a water bottle reduced contextual control over Xuid consumption.This is consistent with the results of the present experiment in that the group thatreceived the tap water during extinction also showed a reduction in contextual con-trol over saccharin consumption. Because other experiments have shown that extinc-tion does not decrease the conditional control over responding to target stimuli(Bouton & Swartzentruber, 1986; Holland, 1983, 1992; Rescorla, 1985, 1986),Loy et al. (1993) concluded that their data support the summational view ratherthan the occasion setting view.

As in the present study, Nakajima et al. (1995) employed two extinction proce-dures: presentation of the contexts alone and presentation of the contexts with water.Rats that received contextual cues with water during extinction showed a reductionin contextual control over sucrose consumption, but it was not eliminated. Rats thatreceived the context alone during extinction maintained contextual control over thesucrose consumption. They concluded that the reduction in contextual control overXuid consumption in the group that received water during extinction supports thesummational view but the fact that this contextual control was maintained in thegroup that received the context alone during extinction supports the occasion settingview. We suggest that one mechanism is suYcient to explain both Wndings. If oneassumes that contextual cues modulate a drinking response, rather than thepalatability of a speciWc Xavor, both sets of extinction results support the occasionsetting view.


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Contextual control of fluid consumption: The effects of context extinction

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