The findings may help explain why social exclusion is often linked to aggression – which sometimes boils over dramatically, as in the case of school shootings, for example.

"Prior case studies show the majority of school shooters have experienced chronic peer rejection," said the study's lead author, C. Nathan DeWall, Ph.D., from the University of Kentucky. "And while not everyone who feels rejected reacts violently, we found they tend to act out aggressively in other ways. We wanted to help explain psychologically why this happens." A full report of the study appears in the January issue of the Journal of Personality and Social Psychology, published by the American Psychological Association.

DeWall conducted four separate experiments with 190 participants, all college students.

In one experiment, 30 participants completed a personality test and were given bogus feedback about the results. A third of the participants, the excluded group, were told their personalities would mean they would probably end up alone later in life. The rest of the participants, the control group, were either told they would have many lasting and meaningful relationships or were given no feedback at all.

All participants were then instructed to read a personal essay supposedly written by another participant, whom they did not know. The essay was about an event in which the author's actions could be perceived as either assertive or hostile and the participants rated their impression of the author's actions. They were also told that the author was up for a research assistant position and were asked whether they thought the author would be a good candidate, based on what they had read.

Participants who were told they were going to have a lonely life perceived the author's actions as significantly more hostile and gave a much more negative evaluation than those in the control groups. The authors also note that the participants' moods did not seem to differ among the different groups, which led them to conclude that the participants' emotional response to their personality results did not play a role in how they performed in the experiments.

In another experiment, 32 students underwent the same bogus personality evaluation and rated the same essay from the previous experiment. Again, some were told they would lead a lonely life while others were assigned to the control groups. This time, participants were led to believe they were playing a reaction-time computer game with another person in the lab whom they could not see and had never met. During the game, the loser of each trial was forced to listen to a blast of white noise through headphones. The participants could set the noise's intensity level and duration.

Those who were told they were going to have a lonely life blasted a higher level of the painful noise than those in the control groups. "Across all experiments, the participants who experienced some form of social rejection acted in similar ways," said DeWall. "This suggests these people feel betrayed by others. In turn, they see otherwise neutral actions as hostile and behave badly towards others."

Prior research has examined whether emotions play a role in this type of aggression, but this study's researchers say their findings do not support this idea. "Excluded people see the world through blood-colored glasses and it is our hope that this research can lead to a better understanding of why rejection causes aggression and what we can do to prevent such unwanted and harmful behavior," said DeWall.

Note: If no author is given, the source is cited instead.

• Psychology
• Social Psychology
• Anger Management
• Borderline Personality Disorder
• Behavior
• Relationships

• Milgram experiment
• Cognitive dissonance
• Illusion of control
• Social psychology
• Self-esteem
• Self-awareness