Social exclusion and aggression are often linked. People who behave aggressively are often excluded from groups. At the same time, social exclusion frequently causes increases in aggressive behavior. Rejection poses a serious and fundamental threat to human existence and meaning, and it seems logical that rejected people would behave in a way that would garner future acceptance. Against that line of reasoning, psychologists have amassed a large body of evidence confirming a causal path from social rejection to aggression (Buckley et al., 2004
; Kirkpatrick et al., 2002
; Twenge et al., 2001
; Warburton et al., 2006
). It is less clear, however, why
rejection causes aggression. Previous work has suggested that the link from exclusion to aggression cannot easily be explained by either motivation or emotion (e.g., Buckley et al., 2004
; Twenge et al., 2001
). One possibility is that rejection leads to increased activation of hostile cognitions, which in turn has consequences for aggressive treatment of others. The experiments reported here provide consistent support for this hypothesis.
Participants who experienced social exclusion, compared with socially accepted and control participants, showed substantial increases in hostility-related cognitive processes. This took the form of rating aggressive and ambiguous words as similar (Experiment 1a), completing word fragments with aggressive words (Experiment 1b), and rating the ambiguous actions of another person as hostile (Experiments 2-4). Hostile cognition was found only among participants who experienced or anticipated social exclusion. Among participants who anticipated interpersonal success but individual failure, no hostile cognitive bias emerged. Thus, social exclusion promoted a generalized cognitive tendency to perceive a broad range of information as antagonistic.
The second goal of the current investigation was to demonstrate that the hostile cognitive bias that accompanied social exclusion had implications for aggression. Replicating previous research, socially excluded participants were more aggressive; in addition, the hostile cognitive bias that followed the exclusion consistently predicted aggressive responding. In Experiments 2 and 3, the relationship between social exclusion and aggression was mediated by hostile cognition. Experiment 4 showed that the hostile cognition bias following social exclusion predicted aggression toward a third person who was not involved in the exclusion experience and with whom participants had no previous contact. The results from Experiment 4 demonstrated a crucial boundary condition to the effects observed in Experiments 2 and 3: the effect of hostile cognition in mediating the relationship between rejection and aggression was conditional upon the opportunity to perceive hostility in the target of aggression. When the hostile cognitive bias was directed toward the target of aggression (as in Experiments 2 and 3), hostile cognition mediated the rejection-aggression link. In contrast, when the hostile cognitive bias was directed at a person other than the target of aggression, hostile cognition was related to—but did not mediate—aggression toward another target. The implication is that hostile cognition plays a mechanistic role in the rejection-aggression link when that cognition is directed toward the target of aggression, whereas hostile cognition that is not directed toward the target of aggression relates to later aggression but is not independent of whether a person has been rejected.
How might the current findings be reconciled with other evidence suggesting desirable, prosocial responding following social exclusion? Past findings have shown that excluded people are eager to connect with potential sources of renewed affiliation, but only with individuals who appear to represent immediate and promising prospects for social acceptance (Maner, DeWall, Baumeister, & Schaller, 2007
). When others appear to be less promising in terms of the potential for social connection, excluded people behave in a relatively hostile manner (e.g., Twenge et al., 2001
). This depiction of the excluded person is consistent with the findings from the current experiments, in which the targets that excluded people perceived as hostile and toward whom excluded people behaved aggressively did not represent potential sources of social acceptance. Excluded people might not show such a strong hostile cognitive bias toward others for whom the likelihood of renewed affiliation was relatively high.
More broadly, writers dating back at least to Freud (1930)
have emphasized the idea that human social life depends on an implicit bargain. Individuals must restrain their impulses, sacrifice some of what they want, and effortfully bring their behavior into agreement with social standards; in exchange, they reap the rewards of belonging to the group. Recent work has begun to confirm that this bargain can break down on either side. Failing to control oneself and to behave in socially prescribed fashion leads to social exclusion, whether in the form of ostracism by childhood peers (Kupersmidt, Burchinal, & Patterson, 1995
; McDougall, Hymel, Vaillancourt, & Mercer, 2001
) or formal imprisonment as a criminal (Gottfredson & Hirschi, 1990
). Conversely, laboratory manipulations of social exclusion cause people to lose the will to regulate their behavior according to external standards (Baumeister, DeWall, Ciarocco, & Twenge, 2005
; DeWall, Baumeister, & Vohs, in press
; Oaten, Williams, Jones, & Zadro, in press
). Applied to the present investigation, these results suggest that social exclusion creates a sense that one has been betrayed by others, as one’s efforts to behave properly and seek acceptance have been met instead with rejection and exclusion. This sense of betrayal causes excluded people to perceive neutral information in the environment as relatively hostile, which then has consequences for their aggressive treatment of others.
Alternative Explanations, Limitations, and Future Directions
These results provide consistent evidence that social exclusion causes a hostile cognitive bias, which has direct implications for aggression. Despite the consistency and strength of these effects, there are several alternative explanations that deserve consideration. A first possibility is that social exclusion simply constitutes a form of bad news. If this is true, then participants who received any form of positive feedback should not show a hostile cognitive bias or aggressive behavior. The results from the Interpersonal Failure and Individual Failure conditions in Experiments 3 and 4 contradict this explanation. Interpersonal Failure participants were informed that they would have successful professional accomplishments later in life, but they would also experience difficulty having successful interpersonal relationships. Individual Failure participants anticipated a future marked by interpersonal success but possible professional failure. Although participants in the Interpersonal Failure condition received positive feedback regarding their future professional accomplishments, these participants showed a pronounced hostile cognitive bias and behaved quite aggressively. Social exclusion appears to be such a basic threat that it increases hostile cognitive biases and aggression even in the presence of anticipated professional success.
It is also possible that the effects of social exclusion on hostile cognition and aggression could be attributed to differences in emotional response. According to this perspective, social exclusion produces increased negative emotions, which in turn causes hostile cognition and aggression. In each experiment, participants completed the BMIS, which provided measurements of mood valence and arousal. Negative emotion and arousal have both played prominent roles in classic social psychological theories of aggression (Berkowitz, 1982
; Zillman, 1983
). It was still possible, however, that the BMIS may not have measured emotional responses that were theoretically relevant to aggressive responses. To address this possibility, we included the State Hostility Scale in Experiments 3 and 4 (Anderson et al., 1995
). However, these experiments provide no support for a mood mediation explanation. In all but one case, excluded participants did not report emotional states that differed from socially accepted and control participants. The only exception was Experiment 3, in which excluded participants reported somewhat less
hostile affect than non-excluded participants. Thus, the current findings suggest that hostile cognition is a far better predictor of aggression following social exclusion than negative emotion.
We hasten to add that the current investigation was limited in the number of emotions that were measured and the type of emotion measurement technique that was used. We did not test whether our social exclusion manipulations influenced the amount of shame participants felt nor did we include measures of shame proneness, both of which may have had implications for aggression (see Tangney, Wagner, Hill-Barlow, Marschall, & Gramzow, 1996
). Some prior work has shown that social exclusion does not increase shame (Twenge, Catanese, & Baumeister, 2003
, Experiment 1), but it is still possible that future work may benefit from considering state or trait shame as a potential mediator or moderator of the rejection-aggression link. Also, we relied solely on self-report measures of emotion. Using physiological measures (e.g., electroencephalogram, electromyography, functional magnetic resonance imaging) may have allowed for more fine-grained measurements of participants’ current emotional state compared to self-report measures. Prior work, for example, has shown that anger correlates with greater left than right frontal electroencephalographic activity (Harmon-Jones & Sigelman, 2001
). Although not all anger leads to aggression (Averill, 1982
), recent evidence indicates that this frontal cortical asymmetry can play a causal role in predicting aggressive behavior (Peterson, Shackman, & Harmon-Jones, 2008
). It is possible that asymmetrical frontal cortical activity or other physiological responses may play a mediating role in the rejection-aggression link (in addition to hostile cognition).
One might also question whether our manipulations provided sufficiently impactful forms of social rejection to produce the requisite emotional reactions. Possibly other, more direct forms of rejection would produce greater emotional distress than what we found (e.g., Gaertner, Iuzzini, & O’Mara, in press
; Twenge et al., 2001
). To be sure, we have used the terms rejection and social exclusion somewhat interchangeably, and the total set of manipulations used in these studies would be more precisely described as social exclusion rather than rejection per se. Only the procedure of Experiments 1a and 1b included a direct personal rejection of the participant, in the sense that the partner ostensibly decided not to interact with the participant after viewing the participant’s video. The other manipulations (e.g., bogus feedback predicting a lonesome future) might be regarded as not actual rejection per se.
There are however several arguments to be made in support of the present procedures. First, in the present studies and in other investigations that have used them, they have repeatedly produced large effects on behavior, so they are highly impactful, even though the impact may not include emotion. Second, the future alone manipulation has consistently produced results that parallel a direct and immediate group rejection manipulation (e.g., Twenge et al., 2001
). Third, as noted earlier, a meta-analysis combining results from many studies has found at best only a small average effect of exclusion on emotion (Blackhart et al., 2007
Fourth, another recent investigation by some of the present authors included a study in which some participants were asked to intuitively imagine how they would respond to the same “Future Alone” manipulation that was used here, and they predicted strong emotional distress — whereas those who actually experienced it reported no significant increase in distress. (Note: The effect size in our studies has been in the neighborhood of the .26 effect found in Blackhart et al.’s meta-analysis; that size effect simply fails to reach significance without very large samples.) If the lack of emotion were due to the weakness of this manipulation, then persons who imagine experiencing it ought to spot its weakness and say they would not feel upset. That is not what they say. Instead, people expect that this manipulation will be very upsetting, but in reality it turns out to be much less so. Moreover, this pattern is hardly unique to our manipulations and in fact conforms to what has repeatedly been shown in research on affective forecasting, which is that people predict strong, lasting emotional reactions when imagining a broad variety of events — but they experience much less emotion when these events actually occur (Wilson & Gilbert, 2003
In short, we cannot completely rule out that emotion might mediate between rejection and aggression in some other studies with other procedures, but we by now have ample evidence that multiple manipulations of social exclusion produce strong aggressive reactions without any sign of emotional mediation. We sympathize with those who may still advocate the emotional mediation theory, because it was our own initial hypothesis, but we have abandoned it after repeated failures. More generally, accumulating evidence has come to question the widespread assumption that emotion is the common mediator between situational events and behavioral responses (for review, see Baumeister, Vohs, DeWall, & Zhang, 2007; also Schwarz & Clore, 2007
). Emotion is undoubtedly a vitally important part of human functioning, but its functions may be other than the direct causation of behavior.
Future research may investigate how hostile cognitive biases develop and shape aggressive behavior within the context of close personal relationships. As is typical with much of the empirical work in the social exclusion literature, our studies were conducted with individuals who were unacquainted with each other before entering the laboratory. Of course, people often experience social exclusion within the context of longer lasting—and presumably more meaningful—relationships than the exclusion our participants experienced at the hands of a stranger. Experiencing social exclusion from close friends, family members, or a romantic relationship partner may promote a hostile cognitive bias and aggression, but such responding will likely depend on the importance of the relationship and the specific interpersonal domain that has been threatened (see Kirkpatrick & Ellis, 2001
). If someone experiences social exclusion from an important romantic relationship partner, for example, then the excluded person may perceive hostility and hence behave aggressively toward others who appear similar to the relationship partner and who represent no potential source of reconnection.
Another possible avenue for future inquiry may involve identifying other types of hostile cognition that play a role in promoting aggression following social exclusion. We found evidence of partial mediation in Experiment 3, which by definition indicates that other processes were involved in fostering aggressive responses to social exclusion. Also, we found no evidence that hostile cognition mediated the rejection-aggression link when the hostile cognition was not directed toward the target of aggression (Experiment 4). The current investigation measured accessibility of hostile cognition (Experiment 1a) and hostile attribution bias (Experiments 1b-4), but it is possible that other types of hostile cognition may have impacted the aggression we observed. One possibility is that social exclusion primes aggressive behavioral scripts. Scripts refer to concepts stored in memory that guide actions, plans, and social interactions (Schank & Abelson, 1977
). Social exclusion and aggressive behavioral scripts may be closely linked in memory, which would give rise to aggression when people experience social exclusion.
The current investigation sought to resolve the paradox of why socially excluded people behave aggressively. Although one might expect (and hope) that social exclusion would promote desirable and prosocial responses, an abundance of evidence suggests that social exclusion frequently results in aggression. Explanations based on motivational or emotional processes have been consistently discredited. Psychologists have therefore been left wondering what, if any, process may help to explain the link between social exclusion and aggression.
The current findings may offer a first step in resolving the mystery of processes that promote aggression following social exclusion: excluded people see the world through blood-colored glasses. Socially excluded people find words related to violence and aggression easily accessible and perceive others as antagonistic and hostile. Moreover, the activation of hostile cognition is directly related to the aggression that is so often observed in people who have been rejected. Though it is potentially disturbing to observe the relative ease with which rejected participants in our studies abandoned their normal inclination toward cooperative and prosocial behaviors, it is also encouraging to understand one reason why they became aggressive. It is our hope that the present findings lead to a better understanding of why rejection causes aggression and what measures can be taken to prevent such unwanted and harmful behavior.