Taste-Aversion Learning Research Paper

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In taste-aversion learning, an organism consumes a substance and experiences a nausea-inducing event. When this organism subsequently reencounters the edible substance, it will consume significantly less of it, especially when compared to controls that experienced the edible, but not the illness. Hence, the organism learns a taste aversion. Thus, taste-aversion learning is highly adaptive because it enables the foraging organism to identify potential sources of illness and learn to avoid them in the future. Considering its adaptive value, it is not surprising that evidence of taste-aversion learning has been shown across the entire animal kingdom including mammals, birds, reptiles, amphibians, fish, and insects. It is worth noting that the terms flavor-aversion learning and taste-aversion learning are used interchangeably, but technically, these terms are different. Taste-aversion learning should refer specifically to situations in which the edible has only a taste component, whereas flavor-aversion learning refers to situations in which the edible has both taste and odor components. Thus, most taste-aversion learning situations are more accurately flavor-aversion learning situations.

Taste-aversion learning is a form of classical conditioning (see Classical Conditioning, Chapter 33 in this volume) in which the edible is the conditioned stimulus (CS) and the illness-inducing stimulus or event is the unconditioned stimulus (US). Illness would be the unconditioned response (UCR), and either illness or an unwillingness to consume the edible could be the conditioned response (CR). As we will see in the Theory section, taste-aversion learning has often been viewed as somewhat different from other forms of classical conditioning. One example of this proposed difference is that in most forms of classical conditioning, the CS is a relatively neutral cue that elicits a weak response at best. Yet, in taste-aversion learning, the CS is often a food substance that could serve as a US. Moreover, this food substance can have reinforcing properties for the hungry or thirsty organism, so that taste-aversion learning may appear to be a counter-conditioning procedure in which an appetitive substance is now a signal for aversive consequences.

Methods

Conditioning

The most common taste-aversion experiments utilize rats as subjects because they readily learn taste aversions, are easily domesticated, can be housed in large numbers, are relatively inexpensive, and do not vomit. In these experiments, the rat drinks a flavored solution, such as sweet saccharin. For optimal conditioning, it is important to limit the amount of solution (5 to 10 ml) and the time of exposure to the solution (5 to 10 min) because increasing exposure to the CS will decrease the strength of the taste aversion. The choice of the CS flavor is less important for optimal conditioning because profound aversions occur with tastes that are sweet (e.g., saccharin), sour (e.g., hydrochloric acid), bitter (e.g., denatonium), and salty (e.g., saline).

Similarly, taste aversions occur with a wide range of USs. Although the most common experimental means to induce illness is an intraperatoneal injection (to the stomach) of the mild emetic lithium chloride, taste aversions occur with a range of illness-inducing agents including irradiation (e.g., Garcia, Kimeldorf, & Koelling, 1955; Smith & Roll, 1967) and rotational stimulation (e.g., Batsell & Pritchett, 1995; Braun & Mcintosh, 1973). Regardless of the type of illness-inducing US, aversion strength increases along with the intensity of the US.

As in other classical conditioning experiments, an important experimental variable is the CS-US interval (i.e., the amount of time that elapses between termination of the CS and presentation of the US). interestingly, the strongest taste aversions appear to be produced when the CS-US interval is a shorter time period, such as 15 minutes; however, reliable taste aversions can occur with backward conditioning (Barker, Smith, & Suarez, 1977) and extended CS-US intervals (e.g., Garcia, Ervin, & Koelling, 1966). Examination of taste-aversion learning with a long CS-US interval has been a key theoretical issue in the study of taste-aversion learning, and it will be addressed in the Theory section.

Testing

There are several testing procedures that insure accurate detection of a taste aversion. First, testing can occur at any period following the initial taste and illness pairing, but early tests may be compromised. For example, nauseous organisms will reduce their consumption of even familiar and preferred edibles, so tests conducted while the rat is still recovering from illness would confound detection of a taste aversion. Furthermore, research has shown that taste aversions may be artificially weak up to 24 hours following conditioning due to nonassociative issues (e.g., Batsell & Best, 1992), but aversion strength stabilizes by 48 hours after conditioning (Batsell & Best, 1994). Therefore, a retention interval of three or more days will allow for accurate recording of the taste aversion.

Second, the experimenter should consider the benefits of using either a one-bottle or a two-bottle test. In the typical one-bottle test, the deprived rat is given limited access to the target solution (e.g., a 10-minute or 20-minute exposure). This test essentially pits the rat’s thirst and motivation to consume liquid against its unwillingness to consume the target solution. The rat’s consumption of the target fluid is a reflection of aversion strength. Past experiments have confirmed that this test is an effective means of recording taste aversions, and it is particularly suited when comparing groups that have aversions of differential strength (Batsell & Best, 1993). Conversely, the two-bottle test is a choice test in which the rat is given simultaneous access to the target solution in one bottle and a different flavor in a second bottle. in this test, the aversion is the percentage of the target fluid consumed relative to the total amount consumed. The two-bottle test is particularly suited for the detection of very weak aversions (e.g., Dragoin, R. T. McCleary, & G. E. McCleary, 1971; Grote & Brown, 1971). One consideration that is crucial to the interpretation of the two-bottle test is the choice of the comparison flavor. if the comparison flavor is water or a familiar, preferred flavor, the test may be biased by preference for the comparison flavor rather than an aversion to the target fluid. As a result, between-group differences in aversion strength are obscured. Similarly, if the comparison flavor is novel, the rat’s natural unwillingness to consume a novel substance (neophobia) may compromise the validity of the test. Therefore, the experimenter’s choice of the comparison flavor is a critical decision that can influence the accuracy of the two-bottle test.

Third, although the consumption test is the most common test, Grill and Norgren’s (1978) taste reactivity test can also provide valuable data. in this test, the experimenter records the organism’s response to the edible, often via videotape, and notes characteristic disgust responses. Some of these characteristic disgust responses would include gaping (the organism extends its tongue out of its mouth), chin rubbing (the organism vigorously paws at its mouth), and head shaking (the organism moves its head side to side). It is worth noting that some researchers make the distinction between taste aversion and taste avoidance (e.g., Parker, 2003). The behavior most commonly used as evidence of flavor-aversion learning is consumption of the edible, but Parker and others use the term taste avoidance for these scenarios in which the organism avoids consumption of the edible. Instead, they use the term taste aversion to refer to the set of negative behaviors from the taste reactivity test that provide evidence that the organism now dislikes the edible.

Theory

John Garcia and the Advent of Taste-Aversion Learning Research

The demonstration of taste-aversion learning across the animal kingdom suggests that the phenomenon is millions of years old, but the development of a laboratory preparation to investigate taste-aversion learning did not originate until the 1950s with the work of John Garcia and his colleagues. Garcia’s academic journey is as fascinating as his research accomplishments. Garcia was the child of Hispanic migrant workers, who earned their living following the fruit seasons throughout California. Thus, the young Garcia grew up in the fields of California, observing the behavior of the family’s pets and natural wildlife. This “real-world” education was in sharp contrast to his more formal elementary education. Because Garcia primarily spoke Spanish, he had difficulty adapting to the English classroom, and his third-grade teacher remarked that he would never amount to much (Garcia, n.d.). Later, Garcia served in World War II, and was able to attend college on the recently created G.I. Bill. He chose to attend the University of California, Berkeley, where he advanced to complete his graduate studies in the lab of E. C. Tolman. To appreciate Garcia’s unique perspective, it is helpful to recall that the predominant theoretical psychological perspective during the late 1940s was neobehaviorism. As such, an animal like the rat was viewed as a machine of habits and twitches, shaped by any events that it encountered. Onto this theoretical landscape, Garcia brought his background of observing animals in their natural habitat as they faced ecological pressures.

After Garcia earned his graduate degree in 1950, he worked for the U.S. Navy, and it was here that he began taste-aversion learning research. In the early preparations, Garcia, Kimelolorf, and Koelling (1955) used radiation to induce illness. In this preparation, rats drank a highly preferred saccharin solution or water while confined in the experimental chamber. Rats were then exposed to one of two radiation conditions for a 6-hour period; the 30-r group (r = roentgen, which is a measure of radiation) received 5.0 r/hr whereas the 57-r group received a stronger 9.5 r/hr exposure. Control groups also drank water or saccharin, but a lead shield protected them from radiation. Two-bottle testing commenced two days later as rats were given a choice of water or saccharin in their home cage. The control rats continued to show the high preference for saccharin that they displayed before conditioning (86 percent preference of saccharin over water). On the initial tests, the 30-r group showed a 35 percent preference for saccharin and the 57-r group’s saccharin preference was less than 5 percent. These data were the first to demonstrate empirically that an illness-inducing agent could produce a dramatic decrease in consumption of a preferred flavor. Interestingly, Garcia et al. extended testing up to 60 days after the single conditioning trial, and despite these multiple exposures to saccharin during testing, Group 57-r never returned to their preconditioning saccharin preference level. Indeed, the saccharin preference level of Group 57-r hovered around 70 percent for the 10 days of testing. These data confirm the long-lasting nature of taste-aversion learning and its relative resistance to extinction.

Over the next 30 years, Garcia would continue to be at the forefront of taste-aversion research while working at the University of California, Los Angeles. During this time, he would examine phenomena such as cue-to-consequence learning, long-delay learning, and potentiation, all of which created intellectual commotion because they were not anticipated by previous research. Nonetheless, in each case, Garcia’s findings were replicated, and even if his theoretical treatments did not always stand the test of time and future work, his initial contributions stimulated considerable research and thought.

Is Taste-Aversion Learning A Unique Form Of Learning?

In the late 1960s and early 1970s, Garcia’s research motivated many researchers to conduct taste-aversion research to replicate and extend his novel findings. Indeed, from a historical standpoint, one could reasonably conclude that the 1970s and the early 1980s were the heyday of taste-aversion research, as the leading learning journals included many taste-aversion learning articles and many definitive collections appeared (Barker, Best, & Domjan, 1977; Braveman & Bronstein, 1985).

Cue-to-Consequence Learning

To appreciate the historical import of the introduction of cue-to-consequence learning, one must consider the prevailing mindset in the 1960s. At this time, a concept known as the general process theory of learning provided a theoretical framework to explain most learning phenomena. According to this theory, the nervous system of living organisms was designed to learn that basic stimuli (CS) could signal the presence or absence of biologically significant events (the US)—a statement that would be accepted by almost all researchers today. Yet in the 1960s, this proposition would have included within this readiness to learn that any neutral stimulus such as a light, tone, or taste could be equally effective as a CS, and any biologically significant stimulus such as a shock or illness could be equally effective as a US. Hence, assuming that the relative intensities of the CSs and USs were equal, any combination of these stimuli should produce equivalent levels of learning.

Garcia and Koelling (1966) tested this hypothesis in an experiment that is often referred to as the “bright-noisy water experiment.” In this experiment, they used two types of CSs (taste and audiovisual cues) and two types of USs (shock and sickness). The rats were allowed to drink at a spout that contained a flavored liquid (saccharin); when the rat’s tongue touched the spout it activated the flash of a light along with a clicking sound (i.e., bright-and-noisy water). After the animals had consumed the liquid, half of each group received an injection of poison while the other half received shock. For testing, the taste component was separated from the audiovisual component so the rats were tested either for their aversion to drinking the taste of saccharin or to drinking water in the presence of the light and noise. The rats that experienced the illness US drank significantly less of the taste CS than of water in the presence of the light and tone. In contrast, the rats that experienced the shock US drank significantly less of the water in the presence of the light and noise than of the saccharin taste. This novel finding was in direct conflict with the general process theory of learning: Certain cues were better associated with certain consequences (e.g., taste with illness, audiovisual cues with shock), hence cue-to-consequence learning. In light of the influence of this work on learning theory, an interesting historical footnote is that Garcia and Koelling had a difficult time publishing this research; in fact, they submitted the manuscript to multiple academic journals before it was accepted for publication (Garcia, n.d.).

Thus, Garcia and Koelling (1966) demonstrated the principle of cue-to-consequence learning in that certain combinations of stimuli are more easily associated than other combinations (taste with illness better than taste with shock). Garcia and Koelling argued that cue-to-consequence learning reflects a genetic predisposition for the selective association of certain combinations of CSs and USs. It is important to note that pairing a taste with shock can produce an effective taste aversion, but it is not as effective as pairing taste with illness. Later work from other labs replicated the basic cue-to-consequence finding (Domjan & Wilson, 1972). For a period of time it was thought that this effect was specific to tasteaversion conditioning; however, the presence of selective associations occur in fear learning (e.g., Ohman & Mineka, 2001) and in instrumental conditioning (e.g., LoLordo & Droungas, 1989).

One-Trial Learning and Long-Delay Learning

The most common preparations for studying classical conditioning (i.e., fear conditioning, autoshaping, eyeblink conditioning) all share similar procedural constraints in that they require multiple CS-US pairings to elicit a CR, and extending the CS-US interval—even if it is only a matter of seconds—is sufficient to weaken learning. In contrast, reliable taste aversions are produced after only a single conditioning trial and after extended CS-US intervals (e.g., Garcia, Ervin, & Koelling, 1966). Garcia’s work in long-delay learning spurred much subsequent research. For example, Smith and Roll (1967) conducted saccharin radiation conditioning, but they varied the delay interval between saccharin consumption and radiation exposure (i.e., the CS-US interval), including delays of 0.0 hour, 0.5 hour, 1 hour, 2 hour, 3 hour, 6 hour, 12 hour, and 24 hour. Saccharin preference testing occurred one day later. Reliable taste aversions occurred even with a 6-hour or 12hour delay imposed between taste consumption and illness induction. Although the initial interpretation was that one-trial learning and long-delay learning may be unique to taste-aversion learning, subsequent research has confirmed that one-trial learning can be observed in other preparations, and that animals can learn across extended CS-US intervals if interfering stimuli are kept at a minimum (for a review, see Bouton, 2006).

Synergistic Conditioning

In 1927 Pavlov described the effect of pairing a weaker CS and a stronger CS with a single US. During testing, Pavlov observed that learning was significantly stronger to the stronger CS than the weaker CS. In fact, learning to the weaker CS was significantly less than if only the weak CS was paired with the US. Pavlov coined the term “overshadowing” to describe this outcome as the presence of the strong CS competed with the weak CS to decrease learning to the latter stimulus. Evidence of overshadowing has since been reported in different classical conditioning preparations (e.g., Mackintosh, 1976).

In the late 1960s and early 1970s, research in other areas of classical conditioning was providing evidence of the rules of associative learning—in particular, the rules that may operate during compound conditioning. Leon Kamin introduced another example of competitive conditioning in 1969 when he reported the results of blocking in fear-conditioning experiments. In these experiments one CS (a tone) was presented with an aversive US (shock) for multiple trials. In the second conditioning phase, the pretrained CS (tone) and a novel CS (a light) now signaled the shock US. During testing, Kamin observed a strong fear CR to the pretrained tone, but no fear response to the light. He concluded that the pretraining of tone-shock prevented or “blocked” learning to the light because the light presented no new information. Overshadowing and blocking both suggest that cues compete with one another for associative strength; this finding led theorists to incorporate rules of competitive conditioning into formal models of associative learning (cf. Rescorla & Wagner, 1972).

Once again, Garcia’s work would present a finding that would challenge the assumption that cues must compete with one another. In 1979 Rusinak, Hankins, Garcia, and Brett published a series of experiments that demonstrated a new learning phenomenon, taste-potentiated odor aversion (TPOA). In these studies, the experimental group drank a strong taste plus a weak odor compound prior to illness induction, whereas the control group was given only the weak odor-illness pairing. During odor testing, the experimental group had a significantly stronger odor aversion than the control group. In other words, instead of the strong taste overshadowing the weak odor, the presence of the taste strengthened or “potentiated” the odor aversion. The phenomenon of TPOA immediately attracted the attention of researchers because it was in direct opposition to the principles of competitive conditioning, and thus it refuted predictions derived from formal models of learning.

Subsequent research replicated TPOA and established that it was the opposite of overshadowing and an example of synergistic conditioning, in which the presence of multiple cues do not compete for, but enhance, learning to other cues. In consideration that TPOA was the opposite of the competitive conditioning effect of overshadowing, it was speculated that a synergistic conditioning opposite to blocking could also exist, but it was 20 years before the reliability of such an effect was reported (Batsell & Batson, 1999; Batsell, Paschall, Gleason, & Batson, 2001; Batson & Batsell, 2000). In the first set of these studies (Batson & Batsell), experimental rats were pretrained with odor-illness in Phase 1 before they were given a pairing of taste plus odor-illness in Phase 2. This design is procedurally the same as Kamin’s blocking design. Compared to rats that had only the taste plus odor-illness pairing, the experimental rats displayed a significantly stronger taste aversion, a surprising outcome because models that incorporate competitive conditioning would have predicted blocking of the taste aversion. In a later set of studies, Batsell et al. reported the phenomenon was symmetrical because taste pretraining before taste plus odor-illness conditioning produced a significantly stronger odor aversion. The authors have used the term “augmentation” to describe the symmetrical synergistic conditioning effect obtained in the blocking design. Although there are different theoretical interpretations of synergistic conditioning (Durlach & Rescorla, 1980; Garcia, Lasiter, Bermudez-Rattoni, & Deems, 1985), the exact mechanism underlying TPOA and augmentation remains to be determined (Batsell & Paschall, in press).

Applications

Taste-aversion research is a fertile area that has generated countless experiments to understand basic associative learning principles, and these findings have also been applied to many human conditions. In the following sections, I will review how results from taste-aversion research have been applied to human food rejection, chemotherapy treatment, and alcohol-aversion therapy.

Taste-Aversion Learning and Human food Rejection

Lab-based investigations of taste-aversion learning have also led to studies of food rejection in humans—many of which involve variations of taste-aversion learning—but some broader distinctions are necessary. An organism’s rejection of a food can be unlearned or learned. Dislike, for example, is the organism’s unlearned rejection of an edible based on its taste, odor, or texture (Rozin & Fallon, 1980). There are multiple types of learned food rejection, and the most commonly studied form of learned food rejection in both humans and nonhumans is taste-aversion learning. With humans, a number of retrospective surveys (e.g., Garb & Stunkard, 1974; Logue, 1985; Logue, Ophir, & Strauss, 1981) confirm that taste aversions are learned through classical conditioning. The use of retrospective questionnaires has involved a large population completing a survey related to food rejection, illness experience, food type, and so on. The results of these questionnaires confirm that taste-aversion learning is quite common, with the percentage of individuals reporting at least one taste aversion varying from a low of 38 percent (Garb & Stunkard) to a high of 84 percent (de Silva & Rachman, 1987). Moreover, the results have consistently indicated that these food aversions are produced via classical conditioning, and they show the aforementioned predominant features of taste-aversion learning such as long-delay learning, one-trial learning, and persistence across time (e.g., Garb & Stunkard; Logue, 1985; Logue et al., 1981; de Silva & Rachman).

Although taste-aversion learning due to classical conditioning is the most commonly studied form of food rejection, there are other types of learned food rejections in humans. Rozin and Fallon (1980) identified three other types of food rejection in humans: inappropriate, danger, and disgust. First, inappropriate food rejection occurs when a food is rejected because it has no nutritional value and is inorganic (e.g., sand). Second, food rejection may also be due to danger, when the individual learns the negative consequences of ingestion (i.e., poisonous mush-rooms). Third, a taste rejection based on disgust occurs when the individual learns the nature or origin of the edible, and then refuses to consume it (e.g., learning that a consumed food was not chicken, but snake). Disgust and danger rejections share a common feature in that they are produced by ideational or cognitive factors, often in the absence of nausea.

At present, there have been only a few investigations of the cognitive factors that mediate food rejections (e.g., Batsell & A. S. Brown, 1998; Rozin, 1986). For example, Rozin reported that the pairing of a taste with a disgust-eliciting stimulus produces food rejection. In his analysis of one-trial shifts in taste preference, Rozin reported that 26.5 percent of taste dislikes were mediated by disgust. More recently, Batsell and A. S. Brown reported the results of a retrospective questionnaire that also identified cognitive factors in taste-aversion learning. Categories of these cognitive aversions included disgust, negative information, or forced consumption. Subsequent research confirmed the forced-consumption scenario was a unique situation that introduced a social/power dynamic with a to-be-consumed edible that may have been disliked or disgusting (Batsell, A. S. Brown, Ansfield, & Paschall, 2002). The crucial components of the forced-consumption scenario, as identified by the participants, were that (a) they were forced to do something against their will and (b) their protests went unheeded. Thus, the investigation of forced consumption shows the intertwining of social interaction, cognitive processes, food, and aversive consequences.

Chemotherapy and Treatment

As stated earlier, taste-aversion learning provides the foraging animal with an effective adaptation to prevent repeated samplings of poisonous foods. The effectiveness of this mechanism is evident in that a single experience with taste and illness is often sufficient for humans or animals to stop eating the tainted edible. Yet, in some modern situations, the advantage of taste-aversion learning actually becomes a disadvantage. The most dramatic contemporary example is the use of chemotherapy to treat cancer. Most common chemotherapy treatments often produce the side effect of pronounced illness, which may last hours or days after treatment. Research has reported that cancer patients identify nausea and vomiting as the most distressing side effect of treatment (e.g., Boakes, Tarrier, Barnes, & Tattersall, 1993). Even though the illness side effects have been greatly diminished by the advent of antinausea medication, many of the medications are inconsistent, and taste-aversion learning requires only one opportunity to occur.

Posttreatment Vomiting and Nausea

Technically, researchers in this area have identified two different illness periods that can influence the cancer patient’s eating habits. The first is posttreatment vomiting and nausea (PVN), the nausea from the treatment itself (i.e., PVN is the unconditioned or unlearned response to the US of treatment). Obviously, any foods eaten before chemotherapy treatment or during this nausea period are possible targets for taste-aversion learning. In 1978 I. L. Bernstein conducted research to determine if gastrointestinal (GI) toxic chemotherapy produced taste aversions in humans. In this study, she tested whether children undergoing chemotherapy treatment would develop an aversion to a unique ice cream flavor. Children in the experimental group (CS-US) ate Mapletoff ice cream (a combination of black walnut and maple flavor extracts) before GI toxic chemotherapy, whereas the children in the control group (US alone) did not eat the ice cream before chemotherapy treatment. Testing occurred either two or four weeks later. During testing, group CS-US showed a significantly lower preference for the Mapletoff ice cream (21 percent) compared to group US alone (67 percent). The fact that group US alone did not show a weakened preference for the Mapletoff ice cream confirmed that the decreased consumption of group CS-US was a learned aversion specific to ice cream and not a generalized decrease in consumption because of malaise, which both groups experienced. One important side note to this research is that I. L. Bernstein noted that many of the participants were well aware that the illness they experienced arose from their treatment sessions; nonetheless, they still learned powerful associations between ice cream and illness.

In consideration of the central role of taste-aversion learning to these deleterious side effects, much research has been initiated to lessen this suffering of cancer patients. One successful application of the logic of taste-aversion learning research to chemotherapy research is the introduction of a scapegoat flavor (I. L. Bernstein, Webster, & I. D. Bernstein, 1982). The logic of the scapegoat technique arose from previous research that showed if Taste A and Taste B are presented in series before illness (Taste A— Taste B—’illness), the aversion to the more contiguous Taste B will be significantly stronger than the less contiguous Taste A (e.g., Revusky, Parker, & Coombes, 1977). I. L. Bernstein et al. were aware that many patients would consume their normal diet before experiencing their chemotherapy treatment, so even though a long delay may be present between eating and illness, long-delay learning is a hallmark of taste-aversion learning. Instead, they examined the effects of having the patient eat a novel food that was not part of his or her regular diet immediately before chemotherapy treatment. In this way, the patient’s regular meal would be the distant Taste A and the scapegoat flavor would be the recent, novel Taste B. Three groups of children participated in this experiment. The control group was untreated, the experimental group had their normal diet before chemotherapy, and the scapegoat group was given the Mapletoff ice cream immediately before chemotherapy treatment. The dependent variable of interest was the number of aversions that developed to foods from the child’s diet. Not surprisingly, the control group developed few food aversions as a result of their placebo treatment. The experimental group reported the highest number of food aversions that developed because of their chemotherapy treatment. Importantly, the scapegoat group reported significantly fewer taste aversions to their normal diet than the experimental group, and the number reported by the scapegoat group was not significantly higher than the control group. Thus, the use of the interfering scapegoat technique is an effective means to protect the cancer patient’s normal diet.

Anticipatory Vomiting and Nausea

Anticipatory vomiting and nausea (AVN), the learned-aversion response resulting from chemotherapy treatment, occurs after the patient has experienced at least one bout of illness-producing treatment. Then, when they reencounter some of the cues that were experienced with illness, these cues will elicit nausea and vomiting CRs. The incidence rate of AVN has varied in a number of different studies; however, Morrow and Dobkin (1988) surveyed the literature and reported a median of 33 percent of patients experience AVN. Patients have reported a variety of cues can trigger AVN; the most common triggers of AVN, in order, were odors, “no particular event” and places/contexts (Boakes et al., 1993).

Linda Parker, on the basis of past taste-aversion research, has developed an animal model of AVN that may prove invaluable in generating new behavioral treatments for this disorder (e.g., Parker, Kwiatkowska, & Mechoulam, 2005). In Parker’s model, she uses the musk shrew because it reliably shows vomiting and retching (pronounced opening of the mouth) in response to lithium-induced illness (recall that rats do not vomit). These shrews learn that a neutral cue, such as a context, can serve as a signal for illness. After three pairings of context-illness, returning the shrew to this context reliably increases retching behavior. Next, this model helps identify drugs that could reduce context-induced illness. Interestingly, Parker et al. found that the antiemetic drug ondansetron, which is effective in reducing PVN, had no effect on reducing conditioned retching responses. Encouragingly, cannabidiol (a nonintoxicating cannibinoid that occurs in marijuana) was very successful in eliminating the conditioned retching responses that are analogous to AVN. Both the mechanism of this effect and its ultimate applicability to reducing AVN in the human population remain to be determined, but the potential is promising.

Alcohol Aversion Therapy

In the Chemotherapy and Treatment section, it is clear how a medical treatment inadvertently activates taste-aversion learning, which produces a side effect that interferes with cancer treatment. The next application, alcohol aversion therapy, involves a situation in which the treatment involves direct activation of taste-aversion learning to facilitate treatment. The use of emetics to decrease alcohol consumption is actually quite old; in 1789 the pioneer American psychiatrist Benjamin Rush reported poisoning a drunkard’s rum to force him off the drink.

Baker and Cannon (1979) provided one of the better case studies detailing the effectiveness of illness-inducing or emetic treatment for alcoholism. In this case, a male alcoholic drank the oral emetic syrup of ipecac along with his favorite liquor. Over the next 20 minutes, the alcoholic alternated between drinking alcohol, water, and regurgitating. After this 20-minute period, the patient was given a small amount of beer that contained potassium antimony tartrate to prolong the nausea. At this time, the patient was instructed to think of all the problems drinking had caused him. This conditioning procedure was repeated five times. Immediately after treatment, the patient’s intake of alcohol decreased by 50 percent, and the patient’s negative feelings toward alcohol increased. The experimenters monitored the patient’s postdischarge drinking status and outpatient adjustment for nine months. For the first three months, the patient drank no alcohol at all. During the next four months, he drank on 29 days, he drank only beer, and he never consumed more than three beers a day. The patient reported that even though he drank beer, both wine and hard liquor remained unappealing. Eventually, the patient did fall off the wagon.

Although the evidence from this case study is suggestive of the effectiveness of alcohol-aversion therapy, a later study was even more convincing. Cannon, Baker, and Wehl (1981) randomly assigned male alcoholic volunteers to three treatment conditions: (a) emetic aversion therapy, (b) shock aversion therapy, and (c) control, which received no aversion therapy. All patients also participated in a multifaceted alcoholism inpatient program (e.g., group, individual, marital, and family therapy; assertion training; relaxation training; alcohol education; Alcoholics Anonymous; etc.). The emetic aversion treatment consisted of 5 sessions in which a variety of alcoholic flavors were followed by nausea and vomiting. The shock aversion treatment consisted of 10 sessions, in each of which the patient experienced a variety of alcoholic flavors paired with variable-intensity electric shocks. Control patients received neither aversion treatment. During testing, each alcoholic participated in a taste test that evaluated behaviors consistent with conditioned taste aversions: (a) moving the glass away from the face in disgust after sniffing but before sipping; (b) grimacing; (c) gagging, choking, or coughing; and (d) pushing the drink away after sipping. The observers also made a subjective appraisal of whether the patient appeared to dislike each drink.

The results showed that emetic aversion, but not shock aversion, produced pronounced aversion to alcohol across all measures. Compared with the control group, alcoholics who received emetic aversion conditioning exhibited greater increases in heart rate to alcohol flavors, drank less during the taste test, reported more negative attitudes toward alcohol, and showed more overt behavioral signs of aversion during the taste test. This study is important in demonstrating that emetic aversion conditioning established conditioned aversion reactions to alcohol at post-treatment. The greater efficacy of emetic aversion treatment over shock aversion treatment was not surprising because this naturalistic experiment was conceptually similar to the cue-to-consequence experiment that demonstrated that taste-illness conditioning produced significantly stronger taste aversions than taste-shock conditioning (Garcia & Koelling, 1966).

It is worth noting that despite these positive reports there remains considerable debate about the effectiveness of emetic aversion conditioning as a treatment for alcoholism. Emetic aversion therapy is a treatment that requires highly trained personnel, sufficient time to implement, and a true commitment from the patient because the treatment is intense. The results from the well-controlled studies have shown emetic aversion therapy can be successful in producing short-term behavior change, and if the patient wants to curb his or her alcoholism, it is a valuable tool in helping him or her do so. Yet, like any form of taste-aversion learning, just as the organism can learn an aversion, it can also learn to extinguish that aversion. Therefore, if the patient is not highly motivated to change his or her alcoholic tendencies (or he or she is highly motivated to return to a life of alcoholism), he or she will be able to extinguish the alcohol aversions learned via emetic aversion conditioning after a number of months.

Summary

Since John Garcia’s initial research over 50 years ago, experimental investigations have revealed the robust and highly adaptive nature of taste-aversion learning with a wide range of species, stimuli, and conditions. An overview of this research reveals two overarching contributions from this work. First, as detailed in the Theory section, taste-aversion learning research has often identified phenomena that represent a challenge to existing learning theories or a departure from other types of classical conditioning. As a result, these findings have motivated considerable research and expanded the scope of theories of associative learning. Second, as detailed in the Applications section, the insight from the research has a number of practical benefits to humans. It will be interesting to see the developments produced by the next 50 years of taste-aversion research.

References:

Baker, T. B., & Cannon, D. S. (1979). Taste aversion therapy with alcoholics: Techniques and evidence of a conditioned response. Behaviour Research and Therapy, 17, 229-242.
Barker, L. M., Best, M. R., & Domjan, M. (1977). Learning mechanisms in food selection. Waco, TX: Baylor University Press.
Barker, L. M., Smith, J. C., & Suarez, E. M. (1977). “Sickness” and the backward conditioning of taste aversions. In L. M. Barker, M. R. Best, & M. Domjan (Eds.), Learning mechanisms in food selection. Waco, TX: Baylor University Press.
Batsell, W. R., Jr., & Batson, J. D. (1999). Augmentation of taste conditioning by a preconditioned odor. Journal of Experimental Psychology: Animal Behavior Processes, 25, 374-388.
Batsell, W. R., Jr., & Best, M. R. (1992). Variations in the retention of taste aversions: Evidence for retrieval competition. Animal Learning & Behavior, 20, 146-159.
Batsell, W. R., Jr., & Best, M. R. (1993). One bottle too many? Method of testing determines the detection of overshadowing and retention of taste aversions. Animal Learning & Behavior, 21, 154-158.
Batsell, W. R., Jr., & Best, M. R. (1994). The role of US novelty in retention interval effects in single-element taste-aversion learning. Animal Learning & Behavior, 22, 332-340.
Batsell, W. R., Jr., & Brown, A. S. (1998). Human flavor-aversion learning: A comparison of traditional aversions and cognitive aversions. Learning and Motivation, 29, 383-396.
Batsell, W. R., Jr., Brown, A. S., Ansfield, M. E., & Paschall, G. Y. (2002). “You will eat all of that!” A retrospective analysis of forced consumption episodes. Appetite, 38, 211-219.
Batsell, W. R., Jr., & Paschall, G. Y. (in press). Mechanism of compound conditioning in flavor-aversion conditioning. In S. Reilly & T. Schachtman (Eds.), Conditioned taste aversion: Behavioral and neural processes. Oxford, UK: Oxford University Press.
Batsell, W. R., Jr., Paschall, G. Y., Gleason, D. I., & Batson, J. D. (2001). Taste preconditioning augments odor-aversion learning. Journal of Experimental Psychology: Animal Behavior Processes, 27, 30-47.
Batsell, W. R., Jr., & Pritchett, K. P. (1995). Retention of rotationally induced taste aversions. Physiology & Behavior, 58, 815-818.
Bernstein, I. L. (1978). Learned taste aversions in children receiving chemotherapy. Science, 200, 1302-1303.
Bernstein, I. L., Webster, M. M., & Bernstein, I. D. (1982). Food aversions in children receiving chemotherapy for cancer. Cancer, 50, 2961-2963.
Boakes, R. A., Tarrier, N., Barnes, B. W., & Tattersall, M. H. N. (1993). Prevalence of anticipatory nausea and other side-effects in cancer patients receiving chemotherapy. European Journal of Cancer, 29A, 866-870.
Bouton, M. E. (2006). Learning and behavior: A contemporary synthesis. Sunderland, MA: Sinauer Associates.
Braun, J. J., & McIntosh, H., Jr. (1973). Learned taste aversions induced by rotational stimulation. Physiological Psychology, 1, 301-304.
Broberg, D. J., & Bernstein, I. L. (1987). Candy as a scapegoat in the prevention of food aversions in children receiving chemotherapy. Cancer, 60, 2344-2347.
Cannon, D. S., Baker, T. B., & Wehl, C. K. (1981). Emetic and electric shock alcohol aversion therapy: Six- and twelvemonth follow-up. Journal of Consulting and Clinical Psychology, 49, 360-368.
Domjan, M. (1980). Ingestional aversion learning: Unique and general processes. In J. S. Rosenblatt, R. A. Hinde, C. Beer, & M. C. Busnel (Eds.), Advances in the study of behavior (Vol. 11, pp. 275-336). New York: Academic Press.
Domjan, M., & Wilson, N. E. (1972). Specificity of cue to consequence in aversion learning in the rat. Psychonomic Science, 26, 143-145.
Dragoin, W., McCleary, G. E., & McCleary, P. (1971). A comparison of two methods of measuring conditioned taste aversions. Behavior Research Methods & Instrumentation, 3, 309-310.
Durlach, P. J., & Rescorla, R. A. (1980). Potentiation rather than overshadowing in flavor-aversion learning: An analysis in terms of within-compound associations. Journal of Experimental Psychology: Animal Behavior Processes, 6, 175-187.
Garb, J. L., & Stunkard, A. J. (1974). Taste aversions in man. American Journal of Psychiatry, 131, 1204-1207.
Garcia, J. (n.d.). From nino to scientist: The trip of my life. Part I. Childhood: 1917-1932. Unpublished manuscript.
Garcia, J., Ervin, F. R., & Koelling, R. A. (1966). Learning with prolonged delay of reinforcement. Psychonomic Science, 5, 121-122.
Garcia, J., Kimeldorf, D. J., & Koelling, R. A. (1955). A conditioned aversion towards saccharin resulting from exposure to gamma radiation. Science, 122, 157-158.
Garcia, J., & Koelling, R. A. (1966). Relation of cue to consequence in avoidance learning. Psychonomic Science, 4, 123-124.
Garcia, J., Lasiter, P. S., Bermudez-Rattoni, F., & Deems, D. A. (1985). A general theory of aversion learning. In N. S. Braveman & P. Bronstein (Eds.), Experimental assessments and clinical applications of conditioned food aversions, Annals of the New York Academy of Sciences (Vol. 443, pp. 8-21). New York: New York Academy of Sciences.
Grill, H. C., & Norgren, R. (1978). The taste reactivity test: I. Mimetic responses to gustatory stimuli in neurologically normal rats. Brain Research, 143, 263-279.
Grote, F. W., Jr., & Brown, R. T. (1971). Conditioned taste aversions: Two-stimulus tests are more sensitive than one-stimulus tests. Behavior Research Methods & Instrumentation, 3, 311-312.
Kamin, L. J. (1969). Predictability, surprise, attention, and conditioning. In B. A. Campbell & R. M. Church, (Eds.). Punishment and aversive behavior (pp. 279-296). New York: Appleton-Century-Crofts.
Logue, A. W. (1979). Taste aversion and the generality of the laws of learning. Psychological Bulletin, 86, 276-296.
Logue, A. W. (1985). Conditioned food aversion learning in humans. In N. S. Braveman & P. Bronstein (Eds.), Experimental assessments and clinical applications of conditioned food aversions, Annals of the New York Academy of Sciences (Vol. 443, pp. 316-329). New York: New York Academy of Sciences.
Logue, A. W., Ophir, I., & Strauss, K. E. (1981). The acquisition of taste aversions in humans. Behaviour Research & Therapy 19, 319-333.
LoLordo, V. M., & Droungas, A. (1989). Selective associations and adaptive specializations: Taste aversions and phobias. In S.B. Klein & R. Mowrer (Eds.), Contemporary learning theories: Instrumental conditioning theory and the impact of biological constraints on learning (pp. 145-179). Hillsdale, NJ: Erlbaum.
Mackintosh, N. J. (1976). Overshadowing and stimulus intensity. Animal Learning & Behavior, 4, 186-192.
Morrow, G. R., & Dobkin, P. L. (1988). Anticipatory nausea and vomiting in cancer patients undergoing chemotherapy treatment: Prevalence, etiology and behavioral interventions. Clinical Psychology Review, 8, 517-556.
Ohman, A., & Mineka, S. (2001). Fears, phobias, and preparedness: Toward an evolved module of fear and fear learning. Psychological Review, 108, 483-522.
Parker, L. A. (2003). Taste avoidance and taste aversion: Evidence for two different processes. Learning & Behavior, 31, 165-172.
Parker, L. A., Kwiatkowska, M., & Mechoulam, R. (2005). Delta-9-tetrahydrocannabinol and cannibidiol, but not ondansetron, interfere with conditioned retching reactions elicited by a lithium-paired context in Suncusmurinus: An animal model of anticipatory nausea and vomiting. Physiology & Behavior, 87, 66-71.
Pavlov, I. P. (1927). Conditioned reflexes. London: Oxford University Press.
Reilly, S., & Schachtman, T. R. (in press). Conditioned taste aversion: Behavioral and neural processes. Oxford, UK: Oxford University Press.
Rescorla, R. A., & Wagner, A. R. (1972). A theory of Pavlovian conditioning: Variations in the effectiveness of reinforcement and nonreinforcement. In A. H. Black & W. F. Prokasy (Eds.), Classical conditioning II: Current research and theories (pp. 64-99). New York: Appleton-Century-Crofts.
Revusky, S., Parker, L. A., & Coombes, S. (1977). Flavor aversion learning: Extinction of the aversion to an interfering flavor after conditioning does not affect the aversion to the reference flavor. Behavioral Biology, 19, 503-508.
Riley, A., & Freeman, K. (2006). Conditioned taste aversions: An annotated bibliography. Retrieved 2006, from http://www .CTALearning.com
Rozin, P. (1986). One-trial acquired likes and dislikes in humans: Disgust as a US, food predominance, and negative learning predominance. Learning and Motivation, 17, 180-189.
Rozin, P., & Fallon, A. E. (1980). The psychological categorization of foods and non-foods: A preliminary taxonomy of food rejections. Appetite, 1, 193-201.
Rusiniak, K. W., Hankins, W. G., Garcia, J., & Brett, L. P. (1979). Flavor-illness aversions: Potentiation of odor by taste in rats. Behavioral & Neural Biology, 25, 1-17.
de Silva, P., & Rachman, S. (1987). Human food aversions: Nature and acquisition. Behaviour Research & Therapy, 25, 457-468.
Smith, J. C., & Roll, D. L. (1967). Trace conditioning with X-rays as an aversive stimulus. Psychonomic Science, 9, 11-12.