The effect of nonnutritive satiation on the learning of a flavor preference by rats

On each day of training in Experiment 1, hungry rats were given one flavored saccharin solution followed by a differently flavored saccharin solution. The rats drank more of the first flavor during training, but preferred the second flavor in a subsequent choice test. In Experiment 2, the two flavored saccharin solutions were provided on alternate days, with one flavor being preceded by nothing and the other flavor by plain saccharin. The rats drank more of the flavor preceded by nothing during training, but preferred the other flavor in a subsequent choice test. These results suggest that a state of nonnutritive satiation can reinforce a flavor preference.     

The effects of taste extinction on ingestional potentiation in weanling rats

Four experiments investigated taste potentiation in weanling rats. In Experiment 1, the animals that drank a conditioning compound of denatonium and saccharin consumed significantly less on the test than controls that drank only saccharin during conditioning. This enhanced saccharin aversion was decremented by postconditioning extinction to denatonium in Experiment 2, and no generalization of saccharin aversions to the denatonium was observed in Experiment 3. Extinction of either saccharin or denatonium aversions after compound conditioning was shown in Experiment 4 to result in substantial decrements in aversions to the compound. The relationship of these outcomes to a multiple-association account of potentiation and to the role of discrimination processes in ingestional learning is discussed.     

Stimulus selection in discriminative taste-aversion learning in the rat

In three experiments, rats were presented compound solutions consisting of a common element, saccharin, mixed with one of two different flavor elements, cinnamon and wintergreen. Rats in the experimental groups consistently received a toxicosis-inducing injection following one compound solution but not following the other compound solution. Rats in the control groups received toxicosis-inducing injections half the time following each of the compound solutions. After training in each experiment, there were tests for conditioning to the saccharin alone. The experimental groups drank significantly more than the control groups, indicating that the aversion to the partially reinforced saccharin in isolation was less when the different flavor cues were more highly correlated with reinforcement. In Experiment III, there was also a test for conditioning to the cinnamon or wintergreen flavor alone. The experimental group drank significantly less of the continuously reinforced flavor than the control group did of the partially reinforced flavor. These results are similar to those reported within more traditional conditioning paradigms.     

Taste aversion learning and schedule-induced polydipsia in rats

Experiment 1 sought to determine whether schedule-induced drinking could be abolished by means of a taste aversion. Polydipsic rats were given access to a .4% saccharin solution while they were exposed to an intermittent food schedule. Immediately after the session, they received an intraperitoneal injection of either lithium chloride or sodium chloride. Following a recovery day with water in the experimental chamber, the animals were again exposed to the saccharin solution. The poisoned animals (lithium chloride) drank very little saccharin compared to the control animals (sodium chloride), indicating that they had learned a taste aversion in only one conditioning trial. Experiment 2 established that polydipsic rats can learn a taste aversion despite a long delay between schedule-induced saccharin consumption and poisoning, and that the delay gradient displayed by polydipsic rats is similar to that observed in thirst-motivated rats.     

The effect of drug habituation before and after taste aversion learning in rats

In Experiment I, rats received eight habituation injections of either lithium chloride (LiCl) or sodium chloride (NaCl), then two aversion training trials in which access to saccharin solution was followed by LiCl injections, and finally eight extinction trials with saccharin but no injections. The rats habituated to LiCl showed less aversion to saccharin during training and extinction. In Experiment II, rats received two aversion training trials, then eight habituation trials to either LiCl or NaCl, then eight extinction trials, four more aversion training trials, and eight more extinction trials. The rats habituated to LiCl did not differ during the first extinction period from those habituated to NaCl, but showed less aversion to saccharin during the second training and extinction periods. Consequently, habituation to LiCl reduces the learning of an aversion to saccharin but does not reduce the performance of a previously learned aversion.     

Amount of solution drunk is a factor in the establishment of taste aversion

Experiment I demonstrated that the strength of a rat’s aversion to saccharin is a direct function of the amount of saccharin it consumed prior to poisoning. Using Kalat and Rozin’s (1973) procedure, Experiment II showed that results consistent with a “learned-safety” theory of taste aversion appear to depend on whether rats drink most saccharin on their first or second exposure to the solution prior to poisoning. Experiment III demonstrated that when animals drank equal amounts of saccharin solution on each of two exposures prior to poisoning, evidence strongly confirming the “learned-safety” theory was obtained. These experiments together demonstrate the importance of amount of solution drunk in the determination of taste aversion.     

The effect of a retention interval on habituation of the neophobic response

In three experiments, water-deprived rats were preexposed to a novel saccharin solution. The neophobic response to this flavor was then assessed in a choice test involving saccharin and water, administered either immediately or 24 h after preexposure. Subjects displayed a significantly greater preference for saccharin at the 24-h test than at the immediate test (Experiments 2 and 3). This “incubation” effect was eliminated if the subjects were more water-deprived at the delayed test than at the immediate test (Experiment 1), and enhanced if the amount of saccharin consumed during preexposure was increased (Experiment 3). Possible ways in which current theories of habituation might be amended in order to accommodate this finding are discussed.     

Injected flavor as a CS in the conditioned aversion preparation

Three experiments were conducted to determine the effectiveness of intravenous (IV) flavor injections in the formation of conditioned taste aversions and in the attenuation of neophobia. In Experiment 1, two groups of rats were permitted to drink either a .1% saccharin solution or tap water followed immediately by IV injections of lithium chloride (LiCl), and two more groups were given IV injections of a 2% saccharin solution followed immediately by IV injections of either LiCl or distilled water. Injected flavor did not serve as an effective CS for the conditioning of an aversion to .1% saccharin. The second experiment employed a two-bottle procedure to detect attenuation of neophobia using the injected-flavor technique. It was found that, whether saccharin had been injected intravenously (2%), injected intraperitoneally (2% IP), or orally consumed (.1%), neophobia for .5% saccharin was attenuated equally relative to controls. CS-US intervals were manipulated in the final experiment such that IP injections of 2% saccharin solution were followed 0–480 min later by IP injections of LiCl. In this case, it was shown that injected flavor (2% saccharin) could act as an effective CS if the US was delayed (optimally about 120 min) and when the test solution was .1% saccharin. The delay gradient found in Experiment 3 was interpreted as a generalization gradient where optimum conditioning was displayed at the point where the concentration of saccharin circulating in the animal at the time of illness onset most closely matched the concentration of the test solution.     

Conditioned taste aversion in Philippine rice rats (R. r. mindanensis): Comparisons among drugs,dosages, modes of administration,and sexes

The effects of select drugs, dosages, and modes of administration upon learned taste aversions were compared among groups of wild-caught male and female Philippine rice rats (R. r. mindanensis). Experiment 1 compared two-choice saccharin aversions for 28 days among groups intubated with copper sulfate, cyclophosphamide, lithium chloride, red squill, sodium chloride (control), or deionized water (control). Main results were that 375 mg/kg lithium chloride produced the greatest sustained aversions, whereas 198 mg/kg cyclophosphamide and 210 mg/kg red squill produced moderate aversions, with males showing more resistance to extinction than females. Experiment 2 compared saccharin aversion among matched groups of male and female rats that received low (36 mg/kg), moderate (105 mg/kg), or high (368 mg/kg) dosages of lithium by gavage, ip injection, or ingestion. Sex differences in rates of extinction were found for the ingestion and injection-dosed rats, but no sex difference was again found for rats dosed by gavage. A significant mode × day interaction indicated that extinction progressed more rapidly for rats dosed by gavage. For all modes of administration, high dosages yielded intense 28-day aversion, moderate dosages produced intermediate 3–5 day aversion, and low dosages caused no aversion.     

Lack of reacquisition in learned taste aversions

Following ingestion of either water (Experiment 1) or saccharin (Experiment 2), experimental groups of rats were poisoned with lithium chloride and acquired an aversion to the ingested fluid. This aversion gradually extinguished and, in both experiments, was not reacquired when fluid intake was again followed by poisoning. These results are in marked contrast to usual findings of very rapid relearning following extinction with conditioning preparations other than taste-aversion learning.     

Carbohydrate-induced stimulation of saccharin intake: Yoked controls

Dilute, intragastric infusions of carbohydrate stimulate saccharin intake. To determine whether this effect is due to an associative process, a yoked control was employed. One group of rats was trained in the conventional fashion: they received carbohydrate (maltodextrin) infusions whenever they drank saccharin. Whenever these rats were infused with carbohydrate, yoked rats were infused with the same amount of carbohydrate. In an experiment in which saccharin was available continuously, carbohydrate infusions stimulated saccharin intake in conventionally trained rats but not in yoked rats. In a subsequent experiment, in which rats were offered saccharin for only 2.5 h/day, carbohydrate infusions stimulated intake in conventionally trained and in yoked rats. However, when these rats were switched to continuous saccharin availability, saccharin intake declined in yoked rats but remained elevated in conventionally trained rats. Thus, carbohydrate infusions stimulate saccharin intake via an associative process.     

The interaction of conditioned taste aversions and schedule-induced polydipsia: Effects of repeated conditioning trials

In Experiment 1, rats poisoned following schedule-induced saccharin consumption showed a moderate reduction in the schedule-induced consumption of saccharin. With repeated poisoning, schedule-induced saccharin polydipsia was markedly reduced. Acquisition of conditioned aversion under the schedule-induced procedure was significantly slower than acquisition under water deprivation. In addition, recovery of consumption of the previously poisoned solution during extinction was more rapid under schedule-induced polydipsia. Experiment 2 revealed that schedule-induced polydipsia was less sensitive to suppression by conditioned aversions than a prandial drinking condition in which subjects were equally food deprived but were given a mass feeding instead of spaced pellet deliveries, suggesting that the relative insensitivity of schedule-induced polydipsia to conditioned taste aversions is not simply a function of different levels of food deprivation. This relative insensitivity is offered as a partial basis for the occurrence and maintenance of schedule-induced alcohol polydipsia.     

Impact of brief or extended extinction of a taste aversion on inhibitory associations: Evidence from summation,retardation, and preference tests

In five conditioned taste aversion experiments with rats, summation, retardation, and preference tests were used to assess the effects of extinguishing a conditioned saccharin aversion for three or nine trials. In Experiment 1, a summation test showed that saccharin aversion extinguished over nine trials reduced the aversion to a merely conditioned flavor (vinegar), whereas three saccharin extinction trials did not subsequently influence the vinegar aversion. Experiment 2 clarified that result, with unpaired controls equated on flavor exposure prior to testing; the results with those controls suggested that the flavor extinguished for nine trials produced generalization decrement during testing. In Experiment 3, the saccharin aversion reconditioned slowly after nine extinction trials, but not after three. Those results suggested the development of latent inhibition after more than three extinction trials. Preference tests comparing saccharin consumption with a concurrently available fluid (water in Experiment 4, saline in Experiment 5) showed that the preference for saccharin was greater after nine extinction trials than after three. However, saccharin preference after nine extinction trials was not greater, as compared with that for either latent inhibition controls (Experiments 4 and 5) or a control given equated exposures to saccharin and trained to drink saline at a high rate prior to testing (Experiment 5). Concerns about whether conditioned inhibition has been demonstrated in any flavor aversion procedure are discussed. Our findings help explain both successes and failures in demonstrating postextinction conditioned response recovery effects reported in the conditioned taste aversion literature, and they can be explained using a memory interference account.     

Anticipation of incentive gain

In four experiments, the once daily availability of saccharin (.15%) preceded the availability of sucrose (32% or 2%). Experiment 1 showed that the intake of saccharin was reduced when it preceded 32% sucrose but not when it preceded 2% sucrose, as compared with saccharin-alone conditions. Experiment 2 showed that less saccharin was consumed when the saccharin preceded sucrose by 5 min than when there was a 30-min intersolution interval. Experiment 3 replicated this finding and showed that the presentation of the two solutions through the same or different access holes in the apparatus was not relevant to the result. Experiment 4 showed that there was an inverse relationship between saccharin intake and the length of the intersolution interval in the range of 1 to 30 min. These data were interpreted to indicate that the animals learn the predictive relationship between the saccharin and sucrose solutions and that the intake of the saccharin is reduced by an anticipatory contrast mechanism—a mechanism that may have restricted temporal parameters.     

Poison avoidance and patch (location) selection in rats

Thirsty rats were tested on a four-armed radial maze with three water locations and one distinctive taste location (saccharin). Rats that were injected with lithium chloride after drinking a novel saccharin solution visited the saccharin location less than did unpoisoned animals, primarily during the later portions of the test sessions. When saccharin was moved to a different location, previously poisoned rats rapidly avoided the new saccharin location and increased visits to the original saccharin location, now rebaited with water. A similar pattern of learned avoidance and approach was obtained in Experiment 2 with three water locations and one vacant location (no water). These results indicate that: (1) sampling the contents of alternative patches mediates both learning to avoid the location of an aversive substance and returning to a newly viable patch, and (2) avoiding the location of a novel substance after a single poisoning occurs because the location does not contain an edible substance, not because of an aversion conditioned to environmental cues.     

Extinction of a saccharin—lithium association: Assessment by consumption and taste reactivity

Extinction of a conditioned palatability shift preceded extinction of conditioned taste avoidance whether rats were tested using a within-subjects design or a between-subjects design. In each of two experiments, consumption of 0.1% saccharin was paired with either 20 ml/kg of 0.15 M LiCl or equivolume physiological saline on a single trial. In Experiment 1, on each of 10 extinction trials, rats were given a taste reactivity test immediately prior to a consumption test. In Experiment 2, half of the rats were extinguished by taste reactivity testing and half of the rats were extinguished by a consumption test on each of 10 extinction trials. In both experiments, the aversive reactions of gaping and passive dripping were extinguished in a single trial and the suppression of ingestive reactions was extinguished in 2 trials; however, extinction of taste avoidance required 4–5 trials. These results suggest that rats continue to avoid a lithium-paired flavor even when they do not have an aversion to the taste.     

Variable processing of flavors in rat STM

Hooded Lister rats exhibited less neophobia towards (i.e., drank more of) a novel fluid (3% lemon or 5% sucrose) on a 10-min test if given a 6-min exposure to that fluid 6 h earlier. Presentation of a distractor (1.26% coffee) immediately after preexposure to the test solution enhanced neophobia habituation to lemon (Experiment 1), but disrupted habituation to sucrose (Experiment 3). This bidirectional distractor effect was not due to distractor-induced change in the hedonic value of the preexposed test flavor (Experiment 4). Evidence was obtained (Experiment 5) indicating that the rat perceives lemon to be more similar to coffee than is sucrose. It is suggested that when test flavor and distractor are dissimilar, processing of the distractor denies the preexposed test flavor sufficient processing in STM to allow encoding of information about that flavor in LTM. Consequently, the rat responds to a subsequent presentation of the test flavor as it would to a novel stimulus. When test flavor and distractor are similar, however, the distractor elicits less processing in STM (cf. Wagner, 1976) and is therefore less able to disrupt STM processing of the preexposed test flavor. The resultant loss of neophobia to the test flavor resulting from encoding of information about that flavor in LTM may then be augmented by generalization of attenuated neophobia to the distractor. Consistent with this analysis, coffee was shown to suffer more proactive interference when preceded by lemon than when preceded by sucrose (Experiment 6).     

Specificity of cue to consequence in aversion learning in the rat: Control for US-induced differential orientations

In four experiments, each using a single conditioning trial, rats avoided a light more than a saccharin solution after these stimuli had been paired with footshock, whereas saccharin was avoided more than the light after these stimuli had been paired with lithium injection. The use of a single conditioning trial precludes possible US-induced differential orientations from influencing which stimuli will be associated on the conditioning trial. This cue-consequence specificity effect was obtained even when subjects conditioned with lithium received a non-contingent footshock prior to the test session, and when subjects conditioned with footshock received a noncontingent lithium injection before testing (Experiments 2–4). Weak aversions to the light in rats given a light-lithium pairing and noncontingent footshock and to the saccharin in subjects that received a saccharin-footshock pairing and noncontingent lithium administration were obtained in Experiment 2. However, these weak aversions were not obtained when subjects were given three nonreinforced exposures to the test chamber before the test session (Experiments 3 and 4). These results indicate that US-induced differential orientations do not mediate the cue-consequence effect in aversion learning.     

Anticipatory contrast as a measure of time horizons in the rat: Some methodological determinants

In three experiments, the time horizon over which the rat evaluates alternative feeding sources was investigated. The time horizon was measured by the suppression of intake of one incentive (a 0.15% saccharin solution) when a preferred alternative incentive (a 32% sucrose solution) was available but delayed. In Experiment 1, we found a direct function between the amount of saccharin intake and the delay time before access to 32% sucrose. Compared with intake for a saccharin-only control, saccharin intake was suppressed before 4-min and 16-min sucrose delays, but not before a 32-min delay. Because previous work (Flaherty & Checke, 1982) had reported suppression before a delay of nearly 32 min, in the subsequent experiments we examined factors that might account for this difference. In Experiment 2, we found that saccharin intake was suppressed before a 32-min delay interval when saccharin and sucrose solutions were presented in a bright-novel test environment but not when the same solutions were presented in the home cage. In Experiment 3, we found that the time between testing and subsequent postsession feeding could also affect the suppression of saccharin intake. Saccharin intake was suppressed when access to 32% sucrose was delayed by 32 min and the test situation was followed by immediate postsession feeding, but not when postsession feeding was delayed by 90 min. These results thus extend estimates of the rat’s time horizon to at least 32 min, but indicate that the effective time horizon can vary, depending on the test situation.     

Food deprivation and conditioned flavor preferences based on sweetened and unsweetened foods

In four experiments, rats’ preferences for flavors consumed under high deprivation versus low deprivation were measured. In Experiment 1, rats preferred flavors received in unsweetened food under high deprivation to flavors received in unsweetened food under low deprivation. This preference did not vary with amount of food used to deliver the flavors (1-g vs. 16-g wet mash). Sweetening the food (0.10% saccharin) eliminated this preference when 16 g of mash was received, but not when 1 g of mash was received (Experiments 2 and 3). Sweetening the mash even more (0.15% saccharin) eliminated the preference when 1 g of mash was received, as well as when 20 g of mash was received. We suggested that the reinforcing value of sweetness is reduced by increasing deprivation level.