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Bitter Taste Causes Hostility Christina Sagioglou and Tobias Greitemeyer Pers Soc Psychol Bull 2014 40: 1589 originally published online 1 October 2014 DOI: 10.1177/0146167214552792 The online version of this article can be found at: http://psp.sagepub.com/content/40/12/1589
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PSPXXX10.1177/0146167214552792Personality and Social Psychology BulletinSagioglou and Greitemeyer
Article Personality and Social Psychology Bulletin 2014, Vol. 40(12) 1589–1597 © 2014 by the Society for Personality and Social Psychology, Inc Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0146167214552792 pspb.sagepub.com
Bitter Taste Causes Hostility Christina Sagioglou1 and Tobias Greitemeyer1
Abstract The present research tested the novel hypothesis that bitter taste increases hostility. Theoretical background formed the intimate link of the taste-sensory system to the visceral system, with bitter intake typically eliciting a strong aversion response. Three experiments using differential bitter and control stimuli showed that hostile affect and behavior is increased by bitter taste experiences. Specifically, participants who consumed a bitter (vs. control) drink showed an increase in self-reported current hostility (Experiment 1), in hypothetical aggressive affect and hypothetical aggressive behavior (Experiment 2) and in actual hostile behavior assessed using a well-established method for non-physical laboratory aggression (Experiment 3). Furthermore, the effect occurred not only when participants were previously provoked (Experiments 2 and 3) but also when no provocation preceded (Experiment 1 and 3). Importantly, stimulus aversiveness and intensity did not influence the effects observed, ruling them out as explanations. Alternative interpretative frameworks and limitations are discussed. Keywords bitter taste, hostility, aggressive affect, taste–affect nexus, provocation Received May 27, 2014; revision accepted August 25, 2014
Introduction
The Taste–Psyche Nexus
The human diet includes a variety of bitter foods. Tea, chocolate, beer, and coffee are but few examples of foods that people enjoy despite—or even because of—their bitterness. Nonetheless, although humans have learned to relish bittertasting substances, social psychologists find that bitter intake leads to cognitive activation of survival-related concepts (Chen & Chang, 2012), suggesting that its close association with threat has not been eliminated. In fact, elimination seems unlikely considering the neuroanatomical overlap of the sense of taste with the visceral system (Scott, 1987, 2010). Importantly, different from the non-chemical senses, taste projects to subcortical areas associated with reinforcement, emotion, and autonomic processes (Scott, 1987). Perhaps it is this connection that forms the origin of several linguistic expressions relating bitterness to non-oral phenomena. In many languages, bitterness connotes negative emotional conditions. For example, having a bitter pill to swallow figuratively expresses a state in which an unpleasant fact has to be accepted, bitter fruits describe an unpleasant result, being bitter enemies implies extraordinary animosity between two parties, and crying bitter tears refers to intense grief and pain. Furthermore, bitterness is a synonym of hostility, antagonism, animosity, and antipathy (Bitterness, n.d.-a). Thus, what was originally a fundamental sensation now additionally describes abstract psychological phenomena such as personality characteristics or interpersonal relationships. In the studies reported here, we address whether it is conceivable that bitter taste has an impact on actual interpersonal hostility.
Looking at physiological behavioral studies, there is ample indirect evidence for this notion. From the first moment of postnatal life, flavor is the primary criterion by which humans decide on whether they consume a certain food or not (Drewnowski, 2001). This makes the sense of taste figure prominently in survival; not only because survival crucially depends on consumption of nutritious foods, but also because it depends on the rejection of potentially harmful foods (e.g., Fischer, Gilad, Man, & Pääbo, 2005). As contaminated, nonedible substances typically taste bitter (Matsunami & Amrein, 2003), bitter taste has evolved to be interpreted as an indicator of noxious, potentially life-threatening intake (e.g., Zhang et al., 2003), and rejecting bitterness has the highly adaptive value of repulsing poisonous substances (e.g., Glendinning, 1994). In fact, this interconnection led Chen and Chang (2012) to predict that bitter taste activates survival-related cognition. Early research found that neonates display a dramatic rejection response when administered bitter substances, while sweet substances elicited clear, but less drastic, pleasant responses (Steiner, 1979). Furthermore, human adults (e.g., Greimel, Macht, Krumhuber, & Ellgring, 2006), primates (Steiner, Glaser, Hawilo, & Berridge, 2001), and rats 1
University of Innsbruck, Austria
Corresponding Author: Christina Sagioglou, Institut für Psychologie, Universität Innsbruck, Innrain 52, Innsbruck 6020, Austria. Email: [email protected]
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(Grill & Norgren, 1978) show an immediate aversion response to bitterness. This common strong and innate reaction to oral stimuli and their instantaneous categorization as pleasant or unpleasant reflects a close association with fundamental hedonic principles (Dess, 1991). Although other sensual input is occasionally evaluated on hedonic dimensions (e.g., unpleasantness of a blinding light), gustation is almost unique in that it instantly classifies stimuli as good or bad (Dess, 1991). It has therefore been reasoned that early in mammalian evolution, gustation became linked to affect (Dess, 1991; Garcia & Hankins, 1975), a connection that has neuroanatomical foundations (Scott, 1987). Accordingly, the sense of taste has been empirically linked to a variety of psychological phenomena. If people watch a joy-inducing film clip, for example, they perceive a sweet drink to be more pleasant than after watching a sad film clip (Greimel et al., 2006). Interestingly, ratings of a bitter drink remained unaffected by these mood manipulations, revealing a robustness that might be linked to the adaptive value of detecting bitterness (Greimel et al., 2006). Other researchers find similar results insofar as a semantic priming for love led to higher sweetness ratings compared with a jealousy priming and neutral condition, but did not affect bitterness ratings (Chan, Tong, Tan, & Koh, 2013). Also non-induced, intrinsic emotional states such as depression or anxiety often show symptoms such as altered taste perception (Miller & Naylor, 1989), with anxiety leading to higher intensity ratings of bitter substances (DeMet et al., 1989; Platte, Herbert, Pauli, & Breslin, 2013). Similarly, being in a stress situation increases the sensitivity to bitterness in rats (Dess, 1992) and in humans (Dess & Edelheit, 1998). Recent research suggests that attention plays a crucial role in people’s taste experiences by showing that cognitive load causes alleviated taste intensity and increased consumption (van der Wal & van Dillen, 2013). Moreover, there is much evidence for the bidirectionality of the link between psychological states and taste experiences. Sweet intake was shown to reduce stress in rat pups and human infants (Blass, 1992) and to increase prosocial behavior and agreeableness (Meier, Moeller, Riemer-Peltz, & Robinson, 2012). Recent research demonstrated a connection between blood glucose levels and intimate partner violence: The lower participants’ glucose level, the more pins they stuck in a voodoo doll representing their spouse, and the more drastic the punishment in a competing game they played with their partner (Bushman, DeWall, Pond, & Hanus, 2014). The ties between taste and affect also touch on mother–child interactions (Mennella, Pepino, & Reed, 2005): Genetic differences in bitter-sensitive alleles caused those children with more bitter-sensitive alleles than their mothers to be seen as particularly emotional. This finding is highly congruent with research by Macht and Mueller (2007), who found that individuals with an increased sensitivity to bitterness show pronounced emotional reactivity.
Finally, several recent findings have linked taste to morality. For example, oral disgust as induced by bitter intake is likely to be the foundation of moral disgust (Chapman, Kim, Susskind, & Anderson, 2009). Furthermore, evoking oral disgust leads to harsher moral judgments (Eskine, Kacinik, & Prinz, 2011), which also works the other way around: Remembering being treated unfairly at work evokes a feeling of disgust, which then leads to stronger ratings of bitter tastes (Skarlicki, Hoegg, Aquino, & Nadisic, 2013).
The Present Research The findings reported above consistently emphasize the intimate relationship taste holds with the affective system. Specifically, bitterness appears to be closely associated with emotional reactivity and threat. If tasting bitter substances activates threat-related cognition, what are the specific emotional reactions to such stimuli? While researchers agree on the notion of a significant coherence of the affective and the taste system, the scope of the emotional consequences of bitter taste has not been extensively explored. Based on the high physiological potential of bitterness to evoke rejection in people, we hypothesized that bitter intake would not leave subsequent social interactions unaffected. Specifically, we reasoned that the rejection of the substance would elicit hostile behavioral tendencies in people, insofar as the activated hostility toward the intake would manifest itself in interpersonal hostility. That is, it would be applied in an unrelated context and to an uninvolved target. To examine this and related issues, three experiments were conducted. Experiment 1 provided an initial test of the hypothesis that bitter tastes causally affect perceived state hostility. Experiment 2 examined the link between bitter taste and hypothetical aggressive behavioral intention. Finally, Experiment 3 addressed the effects of bitter taste on actual aggressive behavior. Moreover, it examined whether provocation might moderate the link between bitter taste and aggressive behavior.
Experiment 1 Experiment 1 provided a first test of our hypothesis that bitter taste experiences are causally associated with hostility. After participants either drank a bitter or a sweet beverage state hostility was assessed. It was predicted that participants in the bitter taste condition would report stronger hostile affect than participants in the sweet taste condition.
Method Participants and design. Eighty students were recruited to participate in a short taste test. Five of them failed to complete our dependent measures and could therefore not be included in the analyses. This leaves 75 participants (MAge = 21.97, SD = 2.26), who were randomly assigned to a bitter taste (n = 38;
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Sagioglou and Greitemeyer 25 female) or a sweet taste condition (n = 37; 24 female). Materials and procedure. To create the respective taste experiences, two different beverages were prepared. As a bitter drink, gentian root tea was prepared according to the instructions on the package bought in a pharmacy. It contains the bitterest natural substance currently known (amarogentin; Aberham, Schwaiger, Stuppner, & Ganzera, 2007). As a control condition, a sweet water solution was prepared by dissolving white sugar in water. Participants were recruited to participate in a set of studies, one of which would be a taste test for which they would have to consume a small amount of liquid. No further information was given about the content of the questionnaire and none of the participants inquired. The drinks were administered at room temperature in 20 ml cups. Afterward, participants completed a questionnaire containing the State Hostility Scale (C. A. Anderson, Deuser, & DeNeve, 1995), drink-related control variables (e.g., intensity, aversiveness, and bitterness, on a scale from 1—not at all to 7—very much), some filler items, and demographic data. The State Hostility Scale includes several statements about one’s current mood (e.g., “I feel irritated,” “I feel friendly”) that are rated on a scale from 1 (strongly disagree) to 5 (strongly agree).
Results The manipulation check confirmed that participants in the bitter taste condition perceived their drink to be significantly bitterer (M = 6.58, SD = 1.13) than participants in the sweet taste condition (M = 1.41, SD = 0.80), t(73) = 22.85, p < .001, d = 5.29, 95% confidence interval (CI) = [4.72, 5.62]. To calculate our dependent variable, the positive mood items were reverse-scored. Next, all items were averaged into a mean hostility score (Cronbach’s α = .94), with higher values indicating stronger hostile mood. As predicted, participants who consumed a bitter beverage reported significantly more state hostility (M = 2.70, SD = 0.85) than participants who drank a sweet beverage (M = 1.89, SD = 0.51), F(1, 73) = 25.16, p < .001, η2 = .26, 95% CI = [0.49, 1.14].1 We also controlled for intensity and aversiveness of the drink. The bitter stimulus was rated as more intensive (M = 6.66, SD = 0.63) and as more aversive (M = 6.74, SD = 1.08) than was the sweet stimulus (M = 5.00, SD = 1.55; M = 4.89, SD = 1.37, respectively), F(1, 72) = 37.12, p < .001, η2 = .34, 95% CI = [1.12, 2.20], F(1, 73) = 41.99, p < .001, η2 = .37, 95% CI = [1.28, 2.41], respectively. Moreover, intensity, r(74) = .30, p = .009, and aversiveness of the drink, r(75) = .35, p = .002, were significantly associated with state hostility. However, an analysis of covariance revealed that neither did they form a significant covariate (both ps > .526), nor did including them (together or separately) change the pattern or 2 significance of our effect, F(1, 70) = 9.06, p = .004, η p = .12 when controlling for both at the same time. Admittedly, including these variables decreases the size of our effect 2 (from η2p = .26 to η p = .12), indicating that intensity and
aversiveness partially contribute to our effect. Importantly, however, the effect of taste experience on state hostility remained significant.
Discussion The results confirm our hypothesis that bitter taste evokes hostility. Importantly, the extent to which people liked the drink (i.e., the perceived aversiveness) and how intense the drink was perceived to be did not influence this effect. Thus, the bitter beverage led to increased hostility in a way that was independent of its aversiveness and intensity. What remains unclear, however, is whether bitterness elevated hostility, or sweetness alleviated it. Although in specific contexts sweetness increases leniency toward violence (Hellmann, Thoben, & Echterhoff, in press), there is also evidence for a negative correlation of glucose levels and aggression (Bushman et al., 2014; DeWall, Deckman, Gailliot, & Bushman, 2011). In the following experiments, we therefore tested bitterness against neutral taste manipulations.
Experiment 2 In Experiment 1, bitter taste was created with a drink that is not typically included in the human diet. In Experiment 2, we therefore wanted to test our bitter-aggression hypothesis by administering a more common, palatable bitter stimulus. We also adjusted the control condition to a neutral taste stimulus, that is, water, which has been administered in past research investigating the psychological effects of bitterness (e.g., Chen & Chang, 2012). Furthermore, we were interested in examining whether bitterness not only affected state hostility but also other aggression-related variables. Specifically, hypothetical aggressive affect as well as hypothetical aggressive behavioral intentions were assessed. It was anticipated that participants in the bitter taste condition would report more aggressive affect and behavioral intention.
Method Participants and design. Forty-four (MAge = 27.91, SD = 11.05) university students were recruited on campus and asked to participate in a set of studies. They were randomly assigned to either a bitter taste (n = 23; 10 female) or a neutral taste condition (n = 21; 11 female). Materials and procedure. Upon arrival at the lab, participants were told that they were to take part in two unrelated studies. The first part of our experiment was described as a taste test. Participants started by indicating demographic details and their mood (1 item; scale ranging from 1—very bad to 7— very good). Next, participants consumed either 20 ml of water2 or an equal amount of grapefruit juice (both at room temperature) and then answered a few questions about the drink (e.g., “How much did you like the drink?”) that included filler items. After completing the taste test, it was
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Table 1. Detailed APQ-12 Action Choices by Beverage Condition (Experiment 2).
Bitter drink Neutral drink
n (maximum = 276) M (SD) n (maximum = 252) M (SD)
No response
Avoid
Anger
Assertive behavior
Direct aggression
101 4.39 (1.75) 89 4.24 (2.32)
53 2.3 (1.74) 54 2.57 (1.96)
29 1.26 (1.05) 54 2.76 (1.87)
42 1.83 (1.30) 32 1.52 (1.72)
51 2.22 (2.19) 19 0.90 (1.48)
Note. APQ = Aggressive Provocation Questionnaire. n = Total number of times each action alternative was chosen across all scenarios and participants by drink condition. M = Mean times each action alternative was chosen across all 12 scenarios by drink condition.
declared as finished and our dependent measure was given to participants. To measure aggression-related emotions and behavioral tendencies, the Aggressive Provocation Questionnaire (APQ-12; O’Connor, Archer, & Wu, 2001) was used. The questionnaire consists of 12 vignettes that were validated to describe typical daily-life situations in which people may find themselves provoked and confronted with different action alternatives. For example, one of the vignettes reads, “You are in the cinema watching a movie. Behind you two lads are talking, laughing loudly and kicking the back of your seat all the time.” Afterward, participants rated how angry, frustrated, and irritated this situation would make them feel on 5-point scales. Thus, these three items asked for estimates of their hypothetical feelings in that situation. Next, participants were asked to imagine what they would do in this situation and select one of five potential actions. For each vignette, the options included an avoid response (e.g., “Move to another seat.”), no response (“Try to ignore them.”), an anger response (“Feel angry, and do nothing.”), assertive behavior (“Turn round and ask them to be quiet or to leave.”), and direct (physical or verbal) aggression (“Turn round and threaten to hit them if they do not keep quiet.”). These options were mutually exclusive, that is, one could choose only one of the five behaviors per vignette. If, for example, someone chose the option of direct aggression in all cases, it would be assigned the value 12, while the other behaviors would have the value 0. They were presented in different orders (see O’Connor et al., 2001, for the complete questionnaire). After completing all 12 vignettes, participants were thanked and debriefed.
Results APQ-12. The APQ-12 was scored according to O’Connor et al. (2001) by calculating mean scores for the emotional response subscales and by aggregating the number of times each action alternative was chosen across all vignettes. There were thus three mean scores, namely, anger (α = .80), frustration (α = .86), and irritation (α = .80) with higher values reflecting higher levels of each hypothetical affect, and five absolute scores, namely, avoid response, no response, anger response, assertive behavior, and direct aggression, potentially ranging from 0 to 12 each (see Table 1). A multivariate
analysis of variance revealed that drinking a bitter drink led to significantly more hypothetical feelings of anger (M = 3.71, SD = 0.54) than drinking a neutral drink (M = 3.35, SD 2 = 0.59), F(1, 42) = 1.49, p = .037, η p = .1, 95% CI = [0.02, 0.71]. Similarly, the bitter juice significantly increased imagined feelings of irritation (M = 3.43, SD = 0.50) compared with water (M = 2.87, SD = 0.67), F(1, 42) = 9.93, p = .003, η2p = .19, 95% CI = [0.20, 0.93], but feelings of frustration were not estimated significantly higher in the bitter drink condition. Furthermore, people who drank grapefruit juice chose the behavioral option of direct aggression significantly more often (M = 2.22, SD = 2.19) than did participants who drank water (M = 0.90, SD = 1.48), F(1, 42) = 5.31, p = .026, η2p = .11, 95% CI = [0.16, 2.46]. Drinking the bitter drink also led to significantly less anger responses (i.e., feeling angry, but doing nothing; M = 1.26, SD = 1.05) than drinking the neutral drink (M = 2.76, SD = 2.87), F(1, 42) = 11.02, p 2 = .002, η p = .21, 95% CI = [−2.41, −0.59], suggesting that when feeling angry, the option of acting out the anger was preferred over holding it back. This assumption is supported by a marginally significant difference between the number of times the anger option was chosen (M = 1.26, SD = 1.05) compared with the aggressive action option (M = 2.22, SD = 2.19) in the bitter condition, t(22) = 1.80, p = .086, d = 0.56. No significant differences were found for the other behavior categories depending on beverage condition (all ps > .512). Finally, neither overall mood (p = .640) nor liking of the drink (p = .806) differed significantly depending on beverage condition. Furthermore, all effects described above remained significant and without notable changes in effect size when controlling for these variables. Mediation analysis. As previous research and theorizing (e.g., C. A. Anderson & Bushman, 2002; Greitemeyer, Agthe, Turner, & Gschwendtner, 2012) suggest that differences in aggressive affect may account for effects on aggressive behavior, we further tested whether the increase in aggressive affect would (in part) account for the effect of beverage condition on hypothetical aggressive behavior intentions. As beverage condition significantly affected irritation and anger but not frustration, we composed a combined score of the former two (α = .89). Including this combined score as a dependent variable in an ANOVA showed that it is
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Sagioglou and Greitemeyer significantly affected by beverage condition, F(1, 42) = 8.02, 2 p = .007, η p = .16. In the following, we examined whether bitter taste would increase aggressive behavior intentions indirectly by increasing aggression-related affect. We therefore conducted mediational analysis through the PROCESS program of Hayes (2013). However, hypothetical aggressive affect did not form a significant mediating variable, as the 95% CI [−1.38, 0.05] included 0.
Discussion Results from our second experiment support our hypothesis that consuming a bitter drink evokes aggression-related affect and behavioral intention. Importantly, as in Experiment 1, how much participants liked the drink did not affect any of our dependent variables, which makes an overall valence effect unlikely; that is, participants reported more aggressive behavioral intentions in the bitter compared with the neutral condition, but this finding was not due to liking of the drink they consumed. Moreover, the effects observed appeared to be independent of mood; thus, a decrease in mood can similarly be ruled out as an explanation for our results. Finally, grapefruit juice was not only perceived to be bitterer, but also sweeter than water. In fact, the specific grapefruit juice used contained 9 g of sugar per 100 ml of juice compared with no sugar in the non-carbonated mineral water that was used. This strongly suggests that the results from the first experiment cannot be attributed solely to different levels of sweetness. Had that been the cause of our hostility effect, then grapefruit juice, compared with water, should have yielded either null effects or an opposite effect (cf. Bushman et al., 2014; DeWall et al., 2011). There are, however, certain limitations of Experiment 2 that we address in the final experiment.
Experiment 3 The main limitation of the previous experiments was in their lack of assessing actual aggressive behavior. Thus, in Experiment 3, we used a measure of aggressive behavior as opposed to hostile affective states and hypothetical behavior as in Experiments 1 and 2, respectively. Furthermore, Experiment 1 assessed unprovoked hostility, whereas Experiment 2 assessed provoked hostility. Because both experiments revealed similar data patterns, it appears that bitter taste experiences increase both unprovoked and provoked hostility. Nevertheless, we felt it an important endeavor to empirically address within one experiment whether provocation might moderate the link between bitter taste experiences and aggression.
Method Participants and design. One hundred sixty-four university students (MAge = 23.6, SD = 4.73) were recruited via the
university mailing list and flyers on campus by offering the chance to win an MP3 player. They were randomly assigned to a 2 (taste of drink: bitter vs. neutral) × 2 (provocation: yes vs. no) between-subjects design. Participants thus consumed either a bitter drink and were provoked (n = 38; 21 female) or not (n = 44; 24 female), or consumed a neutral drink and were provoked (n = 40; 23 female) or not (n = 42; 24 female). Materials and procedure. The bitter beverage was the same as the one used in Experiment 1. The control beverage was water. The drinks were served at room temperature in a shot glass (20 ml). As a behavioral measure of aggression, we adopted a commonly used procedure to measure non-physical aggression in a laboratory context (e.g., Berkowitz, 1970; Zillmann & Cantor, 1976). The specific procedure was very similar to the one used by Stucke and Baumeister (2006). All sessions were run individually. Upon arrival of the participant in the lab, one of the experimenters placed the drink in front of the participant on the desk and subsequently left the lab room. A second experimenter, who was blind to the condition of the beverage, entered and explained to the participant that he or she was to take part in a study on motor performance, taste, and creativity (the cover story was adopted from Eskine et al., 2011). Therefore, it would be important to consume the complete drink in a single motion as though it was a shot. After the drink was consumed, participants proceeded with the creativity test. The test was based on Guilford’s (1967) divergent thinking task and asked respondents to generate as many uses for a book as possible. After 2 min, the experimenter collected the test sheet. At this point, participants were either provoked or not. In the provocation condition, the experimenter said, “Oh, that isn’t many ideas!” In the no-provocation condition, the experimenter said nothing. The participant then filled in the ostensibly final questionnaire, which asked for demographic data and bitterness of the drink (7-point scale ranging from “not at all” to “very much”) and some drink-related filler items. Because aversiveness, intensity, and mood were not related to any of our measures in the previous experiments, these variables were not assessed in Experiment 3. After collecting this questionnaire, participants were told that the study was now finished, but that the university was currently evaluating research projects including personnel involved in these projects. In fact, this evaluation constituted our dependent measure. Each participant evaluated the experimenter regarding how capable and competent, how friendly and likable, and how good of a job he or she was doing (3 items; for example, “The experimenter appeared capable and competent”). Answers were rendered on 9-point scales ranging from 1—Completely disagree to 9— Completely agree. To support our cover story, the header of this evaluation sheet was different from the others used in the experiment. Specifically, it contained the official faculty header, a fake project number, and included a university envelope. Moreover, the first paragraph on the evaluation
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4.5
Neutral
Bitter
4
Evaluation of the experimenter
sheet informed participants that evaluation results were relevant for decisions about the future of the project and, importantly, of the employee (cf. Stucke & Baumeister, 2006). Participants then placed their evaluation in the envelope and dropped it in an urn that had been placed near the exit. Such a task has been successfully used in previous research (e.g., Bushman, Bonacci, Pedersen, Vasquez, & Miller, 2005; Greitemeyer, 2011; Greitemeyer & McLatchie, 2011; for a review, see Bushman & Anderson, 1998). Finally, participants were thanked for participation and thoroughly debriefed.
3.5 3 2.5 2 1.5 1 0.5
Results Results of the manipulation check indicated that our manipulation of bitter taste was successful. Participants who drank gentian root tea rated the beverage to taste significantly more bitter (M = 6.26, SD = 0.94) than did participants who drank water (M = 1.22, SD = 0.74), t(162) = 38.17, p < .001, d = 5.97. Next, we calculated a mean score from the three items that formed our dependent variable (α = .85) with higher values indicating more aggressive behavior, that is, worse evaluations of the experimenter. As predicted, participants who consumed a bitter beverage rated the experimenter to have performed worse (M = 2.85, SD = 1.51) than participants who drank water (M = 2.07, SD = 1.29). Similarly, participants who were provoked rated the experimenter worse (M = 3.17, SD = 1.52) than participants who were not provoked (M = 1.82, SD = 1.03). These differences in ratings turned out significant. A two-way analysis of variance revealed a significantly main effect of bitter taste, F(1, 160) = 17.57, p < 2 .001, η p = .09, 95% CI = [0.42, 1.18], and provocation, F(1, 160) = 51.17, p < .001, η2p = .24, 95% CI = [0.99, 1.75]. In contrast, the interaction was not significant, F(1, 160) = 2.47, 2 p = .201, η p = .01 (see Figure 1).
Discussion The results from Experiment 3 showed that bitter taste evokes aggressive behavior not only after being provoked but also without a preceding provocation. It conceptually replicated the findings from the first two experiments by demonstrating that tasting bitter substances increases hostile behavior. Importantly, we used an actual measure of nonphysical aggression, which allows us to conclude that the bitter-aggression effect may also have some actual behavioral consequences.
0
Provocation
No Provocation
Figure 1. Evaluations of the experimenter as a function of beverage condition and provocation, with higher values representing greater hostility (Experiment 3). Error bars indicate two standard errors of the mean.
experience, bitter taste experiences elevate hostility levels in people. Experiment 2 showed that also other aggressionrelated affect is intensified by bitter taste, namely, irritation and anger. Importantly, Experiment 2 confirmed that the bitter-aggression effect cannot be attributed to differential levels of sweetness, because the stimulus administered in this experiment was not only perceived as bitterer but also as sweeter than the control stimulus. This analysis is consistent with findings by Greimel et al. (2006), who found that ratings of a bitter–sweet drink remained unaffected by induced emotional states, just as a purely bitter drink did, but unlike a sweet drink. Furthermore, Experiments 2 and 3 demonstrated that bitter stimuli caused individuals to project their rejection onto targets that had little or no relation to the intake. Their aggressive tendencies were of little use with regard to the stimulus that elicited the aversion, but instead carried over to secondary contexts. Interestingly, even a bitter stimulus that is typically included in the human diet evoked aggression in people. This suggests that despite palatability, the bitter stimulus was interpreted as a threat to survival. From an evolutionary perspective, the present effect can thus be interpreted as a flight or fight response, albeit not only directed at the causal stimulus, but also at unrelated real-life and hypothetical targets.
General Discussion
How Has Bitter Taste Become Associated With Hostility?
Taken as a whole, the findings of three experiments provide converging evidence for the novel bitter-aggression hypothesis, which predicted that consuming bitter substances elicits aggressive affective and behavioral responses in people. Experiment 1 revealed that compared with a sweet taste
Our findings could equally logically be interpreted within a conceptual metaphor framework (Landau, Meier, & Keefer, 2010). As mentioned in the “Introduction” section, bitterness is a common metaphor for certain personality characteristics and emotions. Specifically, the term is often used to express
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Sagioglou and Greitemeyer emotions that are particularly painful with regard to the strength of their unpleasantness or because of preceding unfair treatment (Bitterness, n.d.-b). This includes expressions such as bitter enemies, referring to intense hostility, or bitter complaints, referring to harsh reproaches. According to Landau et al.’s (2010) metaphoric transfer strategy, manipulating psychological experiences should alter how subsequent information regarding a seemingly dissimilar, but metaphorically related concept is processed. Therefore, if bitter taste is used as a concrete experience for conceptualizing the more abstract concept of hostility, then manipulating bitter taste experience should lead to metaphor-consistent changes in the evaluation of hostility-related information (cf. Landau et al., 2010). Consistent with this logic, we find that the concrete experience of bitter taste leads people to report an increase in their current hostility and even behave in a metaphor-consistent manner. Importantly, no linguistic presentation is needed for the metaphor to unfold its impact (Landau et al., 2010). Instead, activating the experience directly (psychologically or bodily) suffices for co-activation of the metaphorically related, more abstract concept. Precisely which neural mechanisms underlie this effect remains for neuroscientific research to investigate. Increasing evidence points to neural pathways that were formed early in evolution due to their adaptive functionality and that are now reused for higher-order cognition (M. L. Anderson, 2010). This is comparable with the conceptualization of the mind as a scaffold (Williams, Huang, & Bargh, 2009), which describes a similar yet more circumscribed development from an embodied cognition perspective. A recent study provides neuroscientific evidence for a joint neural foundation of emotional warmth and physical warmth (Inagaki & Eisenberger, 2013). Even more so than the sense of touch, the sense of taste has been associated with cortical regions responsible for a variety of higher-order cognitive processes (e.g., Scott, 1987), rendering it likely that shared neural circuits lie at the core of the bitter-aggression effect. In addition, warmth and taste are prenatal experiences that comprise important adaptive information about the environment, and the hedonic dimensions associated with the different taste modalities were argued to be innate (Steiner, 1979). Taste and warmth thus involve neural pathways that have developed evolutionarily earlier and are likely to be involved in behavior acquired ontogenetically (M. L. Anderson, 2010; Williams et al., 2009).
Limitations Looked at separately, each of our experiments displays certain limitations. In the first experiment, the use of a sweet control group left it unclear whether sweetness decreases hostility while bitterness does not affect it at all, or whether it is actually bitter taste that is causing a rise in hostility. Moreover, as gentian root tea is an atypical beverage, conclusions regarding the generalizability of the bitter taste effect were clearly limited. The second experiment addressed these
caveats. To induce a bitter taste experience, a palatable, typical beverage that was both bitter and sweet was administered and compared with a neutral (instead of a sweet) control group. The results confirmed the hypothesis that it is, in fact, bitterness that increases hostility. Admittedly, as the sample size in our second experiment was rather small, this study is underpowered. In addition, the aggressive behavior exhibited remained hypothetical and was always a reaction to a preceding provocation. In the third experiment, these issues were approached by using a measure for actual non-physical aggressive behavior, by doubling cell size, and by investigating the potential moderating effect of provocation. Nevertheless, some inconclusive aspects remain, and future research should target these. For example, the selection of control groups is often challenging when investigating taste (cf. Greimel et al., 2006). Many palatable stimuli that can be found in general supermarkets differ on a range of variables (e.g., taste, consistency). Thus, the stimuli should be adjusted to avoid potentially confounding attributes. For example, a quinine solution, which tastes solely bitter, could be compared with a quinine solution with added sucrose (Gaudette & Pickering, 2013). Alternatively, besides sweet and neutral, further taste experiences such as sour or salty could be used as controls. This could shed light on the fundament of the effect. If our reasoning is correct, then other tastes that are not associated with life-threatening substances should not increase hostility if administered at a palatable level. Chen and Chang (2012) provide a first hint regarding this notion. In their study, bitter but not sour stimuli led to the activation of survival-related concepts. This suggests that although sour taste is often an indicator of spoilage (Liman, 2006), it does not implicitly signal a threat to survival.
Conclusion In sum, the results of the three experiments reported here provide convincing evidence for the hypothesis that tasting bitter substances provokes hostility-related affect and behavior in people. The present findings thereby extend previous research by showing that bitter taste influences not only our emotions but also human behavior. Specifically, the intake of a bitter substance caused participants to harm another person by attributing less competency and friendliness, features that are unrelated to the modality of bitterness. Importantly, this was also found for a palatable, common bitter stimulus, suggesting that even substances consumed in everyday life make people more hostile toward others. Compared with grapefruit juice that was consumed in our experiment, there are several bitter products that are notably more popular. Consider, for example, the popularity of beer, a drink that very often tastes bitter due to its hops content (Pusecker, Albert, & Bayer, 1999). While the notion that alcohol increases aggression has long been established (Bushman & Cooper, 1990), our research suggests that even non-alcoholic beer could lead to hostility.
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Previously, bitter taste had been experimentally linked to repulsion (e.g., Steiner, 1979), survival motivation (Chen & Chang, 2012), and was metaphorically associated with more abstract psychological phenomena including moral disgust (Chapman et al., 2009) and mental disorder (posttraumatic embitterment disorder; Linden, 2008). Although aggression is not a phenomenon typically associated with ingestion, the present research demonstrates that taste can increase aggressive behavior, thereby extending knowledge about the taste– affect nexus. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
Notes 1. In addition, we also tested for gender differences in all major analyses of the three experiments. As we neither predicted nor found gender effects, we abstained from reporting these analyses. 2. We conducted a posttest using the same stimuli as in the original experiment. This showed that the drinks differed significantly in bitterness. Participants who drank water rated the drink to be significantly less bitter (n = 26, M = 1.50, SD = 1.11) than participants who drank grapefruit juice (n = 34, M = 5.88, SD = 1.04), t(58) = −15.77, p < .001, d = 4.07, 95% CI = [3.83, 4.94]. Moreover, grapefruit juice was rated as sweeter (n = 34, M = 2.20, SD = 1.26) than water (n = 26, M = 1.27, SD = 0.72), t(58) = 3.59, p = .001, d = 1.06, 95% CI = [0.44, 1.55], an important difference that will be addressed in the “Discussion” section.
Supplemental Material The online supplemental material is available at http://pspb. sagepub.com/supplemental.
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Bitter Taste Causes Hostility Christina Sagioglou and Tobias Greitemeyer Pers Soc Psychol Bull 2014 40: 1589 originally published online 1 October 2014 DOI: 10.1177/0146167214552792 The online version of this article can be found at: http://psp.sagepub.com/content/40/12/1589
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PSPXXX10.1177/0146167214552792Personality and Social Psychology BulletinSagioglou and Greitemeyer
Article Personality and Social Psychology Bulletin 2014, Vol. 40(12) 1589–1597 © 2014 by the Society for Personality and Social Psychology, Inc Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0146167214552792 pspb.sagepub.com
Bitter Taste Causes Hostility Christina Sagioglou1 and Tobias Greitemeyer1
Abstract The present research tested the novel hypothesis that bitter taste increases hostility. Theoretical background formed the intimate link of the taste-sensory system to the visceral system, with bitter intake typically eliciting a strong aversion response. Three experiments using differential bitter and control stimuli showed that hostile affect and behavior is increased by bitter taste experiences. Specifically, participants who consumed a bitter (vs. control) drink showed an increase in self-reported current hostility (Experiment 1), in hypothetical aggressive affect and hypothetical aggressive behavior (Experiment 2) and in actual hostile behavior assessed using a well-established method for non-physical laboratory aggression (Experiment 3). Furthermore, the effect occurred not only when participants were previously provoked (Experiments 2 and 3) but also when no provocation preceded (Experiment 1 and 3). Importantly, stimulus aversiveness and intensity did not influence the effects observed, ruling them out as explanations. Alternative interpretative frameworks and limitations are discussed. Keywords bitter taste, hostility, aggressive affect, taste–affect nexus, provocation Received May 27, 2014; revision accepted August 25, 2014
Introduction
The Taste–Psyche Nexus
The human diet includes a variety of bitter foods. Tea, chocolate, beer, and coffee are but few examples of foods that people enjoy despite—or even because of—their bitterness. Nonetheless, although humans have learned to relish bittertasting substances, social psychologists find that bitter intake leads to cognitive activation of survival-related concepts (Chen & Chang, 2012), suggesting that its close association with threat has not been eliminated. In fact, elimination seems unlikely considering the neuroanatomical overlap of the sense of taste with the visceral system (Scott, 1987, 2010). Importantly, different from the non-chemical senses, taste projects to subcortical areas associated with reinforcement, emotion, and autonomic processes (Scott, 1987). Perhaps it is this connection that forms the origin of several linguistic expressions relating bitterness to non-oral phenomena. In many languages, bitterness connotes negative emotional conditions. For example, having a bitter pill to swallow figuratively expresses a state in which an unpleasant fact has to be accepted, bitter fruits describe an unpleasant result, being bitter enemies implies extraordinary animosity between two parties, and crying bitter tears refers to intense grief and pain. Furthermore, bitterness is a synonym of hostility, antagonism, animosity, and antipathy (Bitterness, n.d.-a). Thus, what was originally a fundamental sensation now additionally describes abstract psychological phenomena such as personality characteristics or interpersonal relationships. In the studies reported here, we address whether it is conceivable that bitter taste has an impact on actual interpersonal hostility.
Looking at physiological behavioral studies, there is ample indirect evidence for this notion. From the first moment of postnatal life, flavor is the primary criterion by which humans decide on whether they consume a certain food or not (Drewnowski, 2001). This makes the sense of taste figure prominently in survival; not only because survival crucially depends on consumption of nutritious foods, but also because it depends on the rejection of potentially harmful foods (e.g., Fischer, Gilad, Man, & Pääbo, 2005). As contaminated, nonedible substances typically taste bitter (Matsunami & Amrein, 2003), bitter taste has evolved to be interpreted as an indicator of noxious, potentially life-threatening intake (e.g., Zhang et al., 2003), and rejecting bitterness has the highly adaptive value of repulsing poisonous substances (e.g., Glendinning, 1994). In fact, this interconnection led Chen and Chang (2012) to predict that bitter taste activates survival-related cognition. Early research found that neonates display a dramatic rejection response when administered bitter substances, while sweet substances elicited clear, but less drastic, pleasant responses (Steiner, 1979). Furthermore, human adults (e.g., Greimel, Macht, Krumhuber, & Ellgring, 2006), primates (Steiner, Glaser, Hawilo, & Berridge, 2001), and rats 1
University of Innsbruck, Austria
Corresponding Author: Christina Sagioglou, Institut für Psychologie, Universität Innsbruck, Innrain 52, Innsbruck 6020, Austria. Email: [email protected]
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(Grill & Norgren, 1978) show an immediate aversion response to bitterness. This common strong and innate reaction to oral stimuli and their instantaneous categorization as pleasant or unpleasant reflects a close association with fundamental hedonic principles (Dess, 1991). Although other sensual input is occasionally evaluated on hedonic dimensions (e.g., unpleasantness of a blinding light), gustation is almost unique in that it instantly classifies stimuli as good or bad (Dess, 1991). It has therefore been reasoned that early in mammalian evolution, gustation became linked to affect (Dess, 1991; Garcia & Hankins, 1975), a connection that has neuroanatomical foundations (Scott, 1987). Accordingly, the sense of taste has been empirically linked to a variety of psychological phenomena. If people watch a joy-inducing film clip, for example, they perceive a sweet drink to be more pleasant than after watching a sad film clip (Greimel et al., 2006). Interestingly, ratings of a bitter drink remained unaffected by these mood manipulations, revealing a robustness that might be linked to the adaptive value of detecting bitterness (Greimel et al., 2006). Other researchers find similar results insofar as a semantic priming for love led to higher sweetness ratings compared with a jealousy priming and neutral condition, but did not affect bitterness ratings (Chan, Tong, Tan, & Koh, 2013). Also non-induced, intrinsic emotional states such as depression or anxiety often show symptoms such as altered taste perception (Miller & Naylor, 1989), with anxiety leading to higher intensity ratings of bitter substances (DeMet et al., 1989; Platte, Herbert, Pauli, & Breslin, 2013). Similarly, being in a stress situation increases the sensitivity to bitterness in rats (Dess, 1992) and in humans (Dess & Edelheit, 1998). Recent research suggests that attention plays a crucial role in people’s taste experiences by showing that cognitive load causes alleviated taste intensity and increased consumption (van der Wal & van Dillen, 2013). Moreover, there is much evidence for the bidirectionality of the link between psychological states and taste experiences. Sweet intake was shown to reduce stress in rat pups and human infants (Blass, 1992) and to increase prosocial behavior and agreeableness (Meier, Moeller, Riemer-Peltz, & Robinson, 2012). Recent research demonstrated a connection between blood glucose levels and intimate partner violence: The lower participants’ glucose level, the more pins they stuck in a voodoo doll representing their spouse, and the more drastic the punishment in a competing game they played with their partner (Bushman, DeWall, Pond, & Hanus, 2014). The ties between taste and affect also touch on mother–child interactions (Mennella, Pepino, & Reed, 2005): Genetic differences in bitter-sensitive alleles caused those children with more bitter-sensitive alleles than their mothers to be seen as particularly emotional. This finding is highly congruent with research by Macht and Mueller (2007), who found that individuals with an increased sensitivity to bitterness show pronounced emotional reactivity.
Finally, several recent findings have linked taste to morality. For example, oral disgust as induced by bitter intake is likely to be the foundation of moral disgust (Chapman, Kim, Susskind, & Anderson, 2009). Furthermore, evoking oral disgust leads to harsher moral judgments (Eskine, Kacinik, & Prinz, 2011), which also works the other way around: Remembering being treated unfairly at work evokes a feeling of disgust, which then leads to stronger ratings of bitter tastes (Skarlicki, Hoegg, Aquino, & Nadisic, 2013).
The Present Research The findings reported above consistently emphasize the intimate relationship taste holds with the affective system. Specifically, bitterness appears to be closely associated with emotional reactivity and threat. If tasting bitter substances activates threat-related cognition, what are the specific emotional reactions to such stimuli? While researchers agree on the notion of a significant coherence of the affective and the taste system, the scope of the emotional consequences of bitter taste has not been extensively explored. Based on the high physiological potential of bitterness to evoke rejection in people, we hypothesized that bitter intake would not leave subsequent social interactions unaffected. Specifically, we reasoned that the rejection of the substance would elicit hostile behavioral tendencies in people, insofar as the activated hostility toward the intake would manifest itself in interpersonal hostility. That is, it would be applied in an unrelated context and to an uninvolved target. To examine this and related issues, three experiments were conducted. Experiment 1 provided an initial test of the hypothesis that bitter tastes causally affect perceived state hostility. Experiment 2 examined the link between bitter taste and hypothetical aggressive behavioral intention. Finally, Experiment 3 addressed the effects of bitter taste on actual aggressive behavior. Moreover, it examined whether provocation might moderate the link between bitter taste and aggressive behavior.
Experiment 1 Experiment 1 provided a first test of our hypothesis that bitter taste experiences are causally associated with hostility. After participants either drank a bitter or a sweet beverage state hostility was assessed. It was predicted that participants in the bitter taste condition would report stronger hostile affect than participants in the sweet taste condition.
Method Participants and design. Eighty students were recruited to participate in a short taste test. Five of them failed to complete our dependent measures and could therefore not be included in the analyses. This leaves 75 participants (MAge = 21.97, SD = 2.26), who were randomly assigned to a bitter taste (n = 38;
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Sagioglou and Greitemeyer 25 female) or a sweet taste condition (n = 37; 24 female). Materials and procedure. To create the respective taste experiences, two different beverages were prepared. As a bitter drink, gentian root tea was prepared according to the instructions on the package bought in a pharmacy. It contains the bitterest natural substance currently known (amarogentin; Aberham, Schwaiger, Stuppner, & Ganzera, 2007). As a control condition, a sweet water solution was prepared by dissolving white sugar in water. Participants were recruited to participate in a set of studies, one of which would be a taste test for which they would have to consume a small amount of liquid. No further information was given about the content of the questionnaire and none of the participants inquired. The drinks were administered at room temperature in 20 ml cups. Afterward, participants completed a questionnaire containing the State Hostility Scale (C. A. Anderson, Deuser, & DeNeve, 1995), drink-related control variables (e.g., intensity, aversiveness, and bitterness, on a scale from 1—not at all to 7—very much), some filler items, and demographic data. The State Hostility Scale includes several statements about one’s current mood (e.g., “I feel irritated,” “I feel friendly”) that are rated on a scale from 1 (strongly disagree) to 5 (strongly agree).
Results The manipulation check confirmed that participants in the bitter taste condition perceived their drink to be significantly bitterer (M = 6.58, SD = 1.13) than participants in the sweet taste condition (M = 1.41, SD = 0.80), t(73) = 22.85, p < .001, d = 5.29, 95% confidence interval (CI) = [4.72, 5.62]. To calculate our dependent variable, the positive mood items were reverse-scored. Next, all items were averaged into a mean hostility score (Cronbach’s α = .94), with higher values indicating stronger hostile mood. As predicted, participants who consumed a bitter beverage reported significantly more state hostility (M = 2.70, SD = 0.85) than participants who drank a sweet beverage (M = 1.89, SD = 0.51), F(1, 73) = 25.16, p < .001, η2 = .26, 95% CI = [0.49, 1.14].1 We also controlled for intensity and aversiveness of the drink. The bitter stimulus was rated as more intensive (M = 6.66, SD = 0.63) and as more aversive (M = 6.74, SD = 1.08) than was the sweet stimulus (M = 5.00, SD = 1.55; M = 4.89, SD = 1.37, respectively), F(1, 72) = 37.12, p < .001, η2 = .34, 95% CI = [1.12, 2.20], F(1, 73) = 41.99, p < .001, η2 = .37, 95% CI = [1.28, 2.41], respectively. Moreover, intensity, r(74) = .30, p = .009, and aversiveness of the drink, r(75) = .35, p = .002, were significantly associated with state hostility. However, an analysis of covariance revealed that neither did they form a significant covariate (both ps > .526), nor did including them (together or separately) change the pattern or 2 significance of our effect, F(1, 70) = 9.06, p = .004, η p = .12 when controlling for both at the same time. Admittedly, including these variables decreases the size of our effect 2 (from η2p = .26 to η p = .12), indicating that intensity and
aversiveness partially contribute to our effect. Importantly, however, the effect of taste experience on state hostility remained significant.
Discussion The results confirm our hypothesis that bitter taste evokes hostility. Importantly, the extent to which people liked the drink (i.e., the perceived aversiveness) and how intense the drink was perceived to be did not influence this effect. Thus, the bitter beverage led to increased hostility in a way that was independent of its aversiveness and intensity. What remains unclear, however, is whether bitterness elevated hostility, or sweetness alleviated it. Although in specific contexts sweetness increases leniency toward violence (Hellmann, Thoben, & Echterhoff, in press), there is also evidence for a negative correlation of glucose levels and aggression (Bushman et al., 2014; DeWall, Deckman, Gailliot, & Bushman, 2011). In the following experiments, we therefore tested bitterness against neutral taste manipulations.
Experiment 2 In Experiment 1, bitter taste was created with a drink that is not typically included in the human diet. In Experiment 2, we therefore wanted to test our bitter-aggression hypothesis by administering a more common, palatable bitter stimulus. We also adjusted the control condition to a neutral taste stimulus, that is, water, which has been administered in past research investigating the psychological effects of bitterness (e.g., Chen & Chang, 2012). Furthermore, we were interested in examining whether bitterness not only affected state hostility but also other aggression-related variables. Specifically, hypothetical aggressive affect as well as hypothetical aggressive behavioral intentions were assessed. It was anticipated that participants in the bitter taste condition would report more aggressive affect and behavioral intention.
Method Participants and design. Forty-four (MAge = 27.91, SD = 11.05) university students were recruited on campus and asked to participate in a set of studies. They were randomly assigned to either a bitter taste (n = 23; 10 female) or a neutral taste condition (n = 21; 11 female). Materials and procedure. Upon arrival at the lab, participants were told that they were to take part in two unrelated studies. The first part of our experiment was described as a taste test. Participants started by indicating demographic details and their mood (1 item; scale ranging from 1—very bad to 7— very good). Next, participants consumed either 20 ml of water2 or an equal amount of grapefruit juice (both at room temperature) and then answered a few questions about the drink (e.g., “How much did you like the drink?”) that included filler items. After completing the taste test, it was
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Table 1. Detailed APQ-12 Action Choices by Beverage Condition (Experiment 2).
Bitter drink Neutral drink
n (maximum = 276) M (SD) n (maximum = 252) M (SD)
No response
Avoid
Anger
Assertive behavior
Direct aggression
101 4.39 (1.75) 89 4.24 (2.32)
53 2.3 (1.74) 54 2.57 (1.96)
29 1.26 (1.05) 54 2.76 (1.87)
42 1.83 (1.30) 32 1.52 (1.72)
51 2.22 (2.19) 19 0.90 (1.48)
Note. APQ = Aggressive Provocation Questionnaire. n = Total number of times each action alternative was chosen across all scenarios and participants by drink condition. M = Mean times each action alternative was chosen across all 12 scenarios by drink condition.
declared as finished and our dependent measure was given to participants. To measure aggression-related emotions and behavioral tendencies, the Aggressive Provocation Questionnaire (APQ-12; O’Connor, Archer, & Wu, 2001) was used. The questionnaire consists of 12 vignettes that were validated to describe typical daily-life situations in which people may find themselves provoked and confronted with different action alternatives. For example, one of the vignettes reads, “You are in the cinema watching a movie. Behind you two lads are talking, laughing loudly and kicking the back of your seat all the time.” Afterward, participants rated how angry, frustrated, and irritated this situation would make them feel on 5-point scales. Thus, these three items asked for estimates of their hypothetical feelings in that situation. Next, participants were asked to imagine what they would do in this situation and select one of five potential actions. For each vignette, the options included an avoid response (e.g., “Move to another seat.”), no response (“Try to ignore them.”), an anger response (“Feel angry, and do nothing.”), assertive behavior (“Turn round and ask them to be quiet or to leave.”), and direct (physical or verbal) aggression (“Turn round and threaten to hit them if they do not keep quiet.”). These options were mutually exclusive, that is, one could choose only one of the five behaviors per vignette. If, for example, someone chose the option of direct aggression in all cases, it would be assigned the value 12, while the other behaviors would have the value 0. They were presented in different orders (see O’Connor et al., 2001, for the complete questionnaire). After completing all 12 vignettes, participants were thanked and debriefed.
Results APQ-12. The APQ-12 was scored according to O’Connor et al. (2001) by calculating mean scores for the emotional response subscales and by aggregating the number of times each action alternative was chosen across all vignettes. There were thus three mean scores, namely, anger (α = .80), frustration (α = .86), and irritation (α = .80) with higher values reflecting higher levels of each hypothetical affect, and five absolute scores, namely, avoid response, no response, anger response, assertive behavior, and direct aggression, potentially ranging from 0 to 12 each (see Table 1). A multivariate
analysis of variance revealed that drinking a bitter drink led to significantly more hypothetical feelings of anger (M = 3.71, SD = 0.54) than drinking a neutral drink (M = 3.35, SD 2 = 0.59), F(1, 42) = 1.49, p = .037, η p = .1, 95% CI = [0.02, 0.71]. Similarly, the bitter juice significantly increased imagined feelings of irritation (M = 3.43, SD = 0.50) compared with water (M = 2.87, SD = 0.67), F(1, 42) = 9.93, p = .003, η2p = .19, 95% CI = [0.20, 0.93], but feelings of frustration were not estimated significantly higher in the bitter drink condition. Furthermore, people who drank grapefruit juice chose the behavioral option of direct aggression significantly more often (M = 2.22, SD = 2.19) than did participants who drank water (M = 0.90, SD = 1.48), F(1, 42) = 5.31, p = .026, η2p = .11, 95% CI = [0.16, 2.46]. Drinking the bitter drink also led to significantly less anger responses (i.e., feeling angry, but doing nothing; M = 1.26, SD = 1.05) than drinking the neutral drink (M = 2.76, SD = 2.87), F(1, 42) = 11.02, p 2 = .002, η p = .21, 95% CI = [−2.41, −0.59], suggesting that when feeling angry, the option of acting out the anger was preferred over holding it back. This assumption is supported by a marginally significant difference between the number of times the anger option was chosen (M = 1.26, SD = 1.05) compared with the aggressive action option (M = 2.22, SD = 2.19) in the bitter condition, t(22) = 1.80, p = .086, d = 0.56. No significant differences were found for the other behavior categories depending on beverage condition (all ps > .512). Finally, neither overall mood (p = .640) nor liking of the drink (p = .806) differed significantly depending on beverage condition. Furthermore, all effects described above remained significant and without notable changes in effect size when controlling for these variables. Mediation analysis. As previous research and theorizing (e.g., C. A. Anderson & Bushman, 2002; Greitemeyer, Agthe, Turner, & Gschwendtner, 2012) suggest that differences in aggressive affect may account for effects on aggressive behavior, we further tested whether the increase in aggressive affect would (in part) account for the effect of beverage condition on hypothetical aggressive behavior intentions. As beverage condition significantly affected irritation and anger but not frustration, we composed a combined score of the former two (α = .89). Including this combined score as a dependent variable in an ANOVA showed that it is
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Sagioglou and Greitemeyer significantly affected by beverage condition, F(1, 42) = 8.02, 2 p = .007, η p = .16. In the following, we examined whether bitter taste would increase aggressive behavior intentions indirectly by increasing aggression-related affect. We therefore conducted mediational analysis through the PROCESS program of Hayes (2013). However, hypothetical aggressive affect did not form a significant mediating variable, as the 95% CI [−1.38, 0.05] included 0.
Discussion Results from our second experiment support our hypothesis that consuming a bitter drink evokes aggression-related affect and behavioral intention. Importantly, as in Experiment 1, how much participants liked the drink did not affect any of our dependent variables, which makes an overall valence effect unlikely; that is, participants reported more aggressive behavioral intentions in the bitter compared with the neutral condition, but this finding was not due to liking of the drink they consumed. Moreover, the effects observed appeared to be independent of mood; thus, a decrease in mood can similarly be ruled out as an explanation for our results. Finally, grapefruit juice was not only perceived to be bitterer, but also sweeter than water. In fact, the specific grapefruit juice used contained 9 g of sugar per 100 ml of juice compared with no sugar in the non-carbonated mineral water that was used. This strongly suggests that the results from the first experiment cannot be attributed solely to different levels of sweetness. Had that been the cause of our hostility effect, then grapefruit juice, compared with water, should have yielded either null effects or an opposite effect (cf. Bushman et al., 2014; DeWall et al., 2011). There are, however, certain limitations of Experiment 2 that we address in the final experiment.
Experiment 3 The main limitation of the previous experiments was in their lack of assessing actual aggressive behavior. Thus, in Experiment 3, we used a measure of aggressive behavior as opposed to hostile affective states and hypothetical behavior as in Experiments 1 and 2, respectively. Furthermore, Experiment 1 assessed unprovoked hostility, whereas Experiment 2 assessed provoked hostility. Because both experiments revealed similar data patterns, it appears that bitter taste experiences increase both unprovoked and provoked hostility. Nevertheless, we felt it an important endeavor to empirically address within one experiment whether provocation might moderate the link between bitter taste experiences and aggression.
Method Participants and design. One hundred sixty-four university students (MAge = 23.6, SD = 4.73) were recruited via the
university mailing list and flyers on campus by offering the chance to win an MP3 player. They were randomly assigned to a 2 (taste of drink: bitter vs. neutral) × 2 (provocation: yes vs. no) between-subjects design. Participants thus consumed either a bitter drink and were provoked (n = 38; 21 female) or not (n = 44; 24 female), or consumed a neutral drink and were provoked (n = 40; 23 female) or not (n = 42; 24 female). Materials and procedure. The bitter beverage was the same as the one used in Experiment 1. The control beverage was water. The drinks were served at room temperature in a shot glass (20 ml). As a behavioral measure of aggression, we adopted a commonly used procedure to measure non-physical aggression in a laboratory context (e.g., Berkowitz, 1970; Zillmann & Cantor, 1976). The specific procedure was very similar to the one used by Stucke and Baumeister (2006). All sessions were run individually. Upon arrival of the participant in the lab, one of the experimenters placed the drink in front of the participant on the desk and subsequently left the lab room. A second experimenter, who was blind to the condition of the beverage, entered and explained to the participant that he or she was to take part in a study on motor performance, taste, and creativity (the cover story was adopted from Eskine et al., 2011). Therefore, it would be important to consume the complete drink in a single motion as though it was a shot. After the drink was consumed, participants proceeded with the creativity test. The test was based on Guilford’s (1967) divergent thinking task and asked respondents to generate as many uses for a book as possible. After 2 min, the experimenter collected the test sheet. At this point, participants were either provoked or not. In the provocation condition, the experimenter said, “Oh, that isn’t many ideas!” In the no-provocation condition, the experimenter said nothing. The participant then filled in the ostensibly final questionnaire, which asked for demographic data and bitterness of the drink (7-point scale ranging from “not at all” to “very much”) and some drink-related filler items. Because aversiveness, intensity, and mood were not related to any of our measures in the previous experiments, these variables were not assessed in Experiment 3. After collecting this questionnaire, participants were told that the study was now finished, but that the university was currently evaluating research projects including personnel involved in these projects. In fact, this evaluation constituted our dependent measure. Each participant evaluated the experimenter regarding how capable and competent, how friendly and likable, and how good of a job he or she was doing (3 items; for example, “The experimenter appeared capable and competent”). Answers were rendered on 9-point scales ranging from 1—Completely disagree to 9— Completely agree. To support our cover story, the header of this evaluation sheet was different from the others used in the experiment. Specifically, it contained the official faculty header, a fake project number, and included a university envelope. Moreover, the first paragraph on the evaluation
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4.5
Neutral
Bitter
4
Evaluation of the experimenter
sheet informed participants that evaluation results were relevant for decisions about the future of the project and, importantly, of the employee (cf. Stucke & Baumeister, 2006). Participants then placed their evaluation in the envelope and dropped it in an urn that had been placed near the exit. Such a task has been successfully used in previous research (e.g., Bushman, Bonacci, Pedersen, Vasquez, & Miller, 2005; Greitemeyer, 2011; Greitemeyer & McLatchie, 2011; for a review, see Bushman & Anderson, 1998). Finally, participants were thanked for participation and thoroughly debriefed.
3.5 3 2.5 2 1.5 1 0.5
Results Results of the manipulation check indicated that our manipulation of bitter taste was successful. Participants who drank gentian root tea rated the beverage to taste significantly more bitter (M = 6.26, SD = 0.94) than did participants who drank water (M = 1.22, SD = 0.74), t(162) = 38.17, p < .001, d = 5.97. Next, we calculated a mean score from the three items that formed our dependent variable (α = .85) with higher values indicating more aggressive behavior, that is, worse evaluations of the experimenter. As predicted, participants who consumed a bitter beverage rated the experimenter to have performed worse (M = 2.85, SD = 1.51) than participants who drank water (M = 2.07, SD = 1.29). Similarly, participants who were provoked rated the experimenter worse (M = 3.17, SD = 1.52) than participants who were not provoked (M = 1.82, SD = 1.03). These differences in ratings turned out significant. A two-way analysis of variance revealed a significantly main effect of bitter taste, F(1, 160) = 17.57, p < 2 .001, η p = .09, 95% CI = [0.42, 1.18], and provocation, F(1, 160) = 51.17, p < .001, η2p = .24, 95% CI = [0.99, 1.75]. In contrast, the interaction was not significant, F(1, 160) = 2.47, 2 p = .201, η p = .01 (see Figure 1).
Discussion The results from Experiment 3 showed that bitter taste evokes aggressive behavior not only after being provoked but also without a preceding provocation. It conceptually replicated the findings from the first two experiments by demonstrating that tasting bitter substances increases hostile behavior. Importantly, we used an actual measure of nonphysical aggression, which allows us to conclude that the bitter-aggression effect may also have some actual behavioral consequences.
0
Provocation
No Provocation
Figure 1. Evaluations of the experimenter as a function of beverage condition and provocation, with higher values representing greater hostility (Experiment 3). Error bars indicate two standard errors of the mean.
experience, bitter taste experiences elevate hostility levels in people. Experiment 2 showed that also other aggressionrelated affect is intensified by bitter taste, namely, irritation and anger. Importantly, Experiment 2 confirmed that the bitter-aggression effect cannot be attributed to differential levels of sweetness, because the stimulus administered in this experiment was not only perceived as bitterer but also as sweeter than the control stimulus. This analysis is consistent with findings by Greimel et al. (2006), who found that ratings of a bitter–sweet drink remained unaffected by induced emotional states, just as a purely bitter drink did, but unlike a sweet drink. Furthermore, Experiments 2 and 3 demonstrated that bitter stimuli caused individuals to project their rejection onto targets that had little or no relation to the intake. Their aggressive tendencies were of little use with regard to the stimulus that elicited the aversion, but instead carried over to secondary contexts. Interestingly, even a bitter stimulus that is typically included in the human diet evoked aggression in people. This suggests that despite palatability, the bitter stimulus was interpreted as a threat to survival. From an evolutionary perspective, the present effect can thus be interpreted as a flight or fight response, albeit not only directed at the causal stimulus, but also at unrelated real-life and hypothetical targets.
General Discussion
How Has Bitter Taste Become Associated With Hostility?
Taken as a whole, the findings of three experiments provide converging evidence for the novel bitter-aggression hypothesis, which predicted that consuming bitter substances elicits aggressive affective and behavioral responses in people. Experiment 1 revealed that compared with a sweet taste
Our findings could equally logically be interpreted within a conceptual metaphor framework (Landau, Meier, & Keefer, 2010). As mentioned in the “Introduction” section, bitterness is a common metaphor for certain personality characteristics and emotions. Specifically, the term is often used to express
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Sagioglou and Greitemeyer emotions that are particularly painful with regard to the strength of their unpleasantness or because of preceding unfair treatment (Bitterness, n.d.-b). This includes expressions such as bitter enemies, referring to intense hostility, or bitter complaints, referring to harsh reproaches. According to Landau et al.’s (2010) metaphoric transfer strategy, manipulating psychological experiences should alter how subsequent information regarding a seemingly dissimilar, but metaphorically related concept is processed. Therefore, if bitter taste is used as a concrete experience for conceptualizing the more abstract concept of hostility, then manipulating bitter taste experience should lead to metaphor-consistent changes in the evaluation of hostility-related information (cf. Landau et al., 2010). Consistent with this logic, we find that the concrete experience of bitter taste leads people to report an increase in their current hostility and even behave in a metaphor-consistent manner. Importantly, no linguistic presentation is needed for the metaphor to unfold its impact (Landau et al., 2010). Instead, activating the experience directly (psychologically or bodily) suffices for co-activation of the metaphorically related, more abstract concept. Precisely which neural mechanisms underlie this effect remains for neuroscientific research to investigate. Increasing evidence points to neural pathways that were formed early in evolution due to their adaptive functionality and that are now reused for higher-order cognition (M. L. Anderson, 2010). This is comparable with the conceptualization of the mind as a scaffold (Williams, Huang, & Bargh, 2009), which describes a similar yet more circumscribed development from an embodied cognition perspective. A recent study provides neuroscientific evidence for a joint neural foundation of emotional warmth and physical warmth (Inagaki & Eisenberger, 2013). Even more so than the sense of touch, the sense of taste has been associated with cortical regions responsible for a variety of higher-order cognitive processes (e.g., Scott, 1987), rendering it likely that shared neural circuits lie at the core of the bitter-aggression effect. In addition, warmth and taste are prenatal experiences that comprise important adaptive information about the environment, and the hedonic dimensions associated with the different taste modalities were argued to be innate (Steiner, 1979). Taste and warmth thus involve neural pathways that have developed evolutionarily earlier and are likely to be involved in behavior acquired ontogenetically (M. L. Anderson, 2010; Williams et al., 2009).
Limitations Looked at separately, each of our experiments displays certain limitations. In the first experiment, the use of a sweet control group left it unclear whether sweetness decreases hostility while bitterness does not affect it at all, or whether it is actually bitter taste that is causing a rise in hostility. Moreover, as gentian root tea is an atypical beverage, conclusions regarding the generalizability of the bitter taste effect were clearly limited. The second experiment addressed these
caveats. To induce a bitter taste experience, a palatable, typical beverage that was both bitter and sweet was administered and compared with a neutral (instead of a sweet) control group. The results confirmed the hypothesis that it is, in fact, bitterness that increases hostility. Admittedly, as the sample size in our second experiment was rather small, this study is underpowered. In addition, the aggressive behavior exhibited remained hypothetical and was always a reaction to a preceding provocation. In the third experiment, these issues were approached by using a measure for actual non-physical aggressive behavior, by doubling cell size, and by investigating the potential moderating effect of provocation. Nevertheless, some inconclusive aspects remain, and future research should target these. For example, the selection of control groups is often challenging when investigating taste (cf. Greimel et al., 2006). Many palatable stimuli that can be found in general supermarkets differ on a range of variables (e.g., taste, consistency). Thus, the stimuli should be adjusted to avoid potentially confounding attributes. For example, a quinine solution, which tastes solely bitter, could be compared with a quinine solution with added sucrose (Gaudette & Pickering, 2013). Alternatively, besides sweet and neutral, further taste experiences such as sour or salty could be used as controls. This could shed light on the fundament of the effect. If our reasoning is correct, then other tastes that are not associated with life-threatening substances should not increase hostility if administered at a palatable level. Chen and Chang (2012) provide a first hint regarding this notion. In their study, bitter but not sour stimuli led to the activation of survival-related concepts. This suggests that although sour taste is often an indicator of spoilage (Liman, 2006), it does not implicitly signal a threat to survival.
Conclusion In sum, the results of the three experiments reported here provide convincing evidence for the hypothesis that tasting bitter substances provokes hostility-related affect and behavior in people. The present findings thereby extend previous research by showing that bitter taste influences not only our emotions but also human behavior. Specifically, the intake of a bitter substance caused participants to harm another person by attributing less competency and friendliness, features that are unrelated to the modality of bitterness. Importantly, this was also found for a palatable, common bitter stimulus, suggesting that even substances consumed in everyday life make people more hostile toward others. Compared with grapefruit juice that was consumed in our experiment, there are several bitter products that are notably more popular. Consider, for example, the popularity of beer, a drink that very often tastes bitter due to its hops content (Pusecker, Albert, & Bayer, 1999). While the notion that alcohol increases aggression has long been established (Bushman & Cooper, 1990), our research suggests that even non-alcoholic beer could lead to hostility.
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Previously, bitter taste had been experimentally linked to repulsion (e.g., Steiner, 1979), survival motivation (Chen & Chang, 2012), and was metaphorically associated with more abstract psychological phenomena including moral disgust (Chapman et al., 2009) and mental disorder (posttraumatic embitterment disorder; Linden, 2008). Although aggression is not a phenomenon typically associated with ingestion, the present research demonstrates that taste can increase aggressive behavior, thereby extending knowledge about the taste– affect nexus. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
Notes 1. In addition, we also tested for gender differences in all major analyses of the three experiments. As we neither predicted nor found gender effects, we abstained from reporting these analyses. 2. We conducted a posttest using the same stimuli as in the original experiment. This showed that the drinks differed significantly in bitterness. Participants who drank water rated the drink to be significantly less bitter (n = 26, M = 1.50, SD = 1.11) than participants who drank grapefruit juice (n = 34, M = 5.88, SD = 1.04), t(58) = −15.77, p < .001, d = 4.07, 95% CI = [3.83, 4.94]. Moreover, grapefruit juice was rated as sweeter (n = 34, M = 2.20, SD = 1.26) than water (n = 26, M = 1.27, SD = 0.72), t(58) = 3.59, p = .001, d = 1.06, 95% CI = [0.44, 1.55], an important difference that will be addressed in the “Discussion” section.
Supplemental Material The online supplemental material is available at http://pspb. sagepub.com/supplemental.
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