The study, to be published in the May issue of the Journal of Experimental Social Psychology, found that participants given more powerful roles in two experiments attributed fewer uniquely human traits — characteristics that distinguish people from other animals — to their peers who were given less powerful roles.

“I think a lot of us have the intuition that some powerful people can be pretty dehumanizing,” said Jason Gwinn, a doctoral student in the Department of Psychology and Neuroscience and lead author of the study. “But our goal was to test if power, when randomly assigned to ordinary students, would have that effect. That would say something about power itself rather than about the sort of people who have the drive to take power.”

The researchers enlisted about 300 CU-Boulder students taking an introductory psychology course to participate in two experiments. In the first experiment, students were assigned to be either a manager or an assistant for a mock hiring task. The assistants were asked to review resumes for an open job and then list the strengths and weaknesses of each applicant. The managers then reviewed the list made by their assistants and made a final decision about whom to hire.

In the second experiment, participants were asked to play a game and were assigned to be either an allocator or a recipient. For the game, one allocator and one recipient were tasked with splitting a pot of money. The allocator, the higher-power role, made the first offer, suggesting how the money be split. If the recipient, the lower-power role, accepted the offer, both people received their share of the money. If the recipient declined the offer, neither person received any of the money.

At the end of each experiment, the participants were asked to rate each other on 40 traits. The result was that students in higher-power roles assigned fewer uniquely human traits to the students in lower-power roles than vice versa. Examples of traits considered to be more uniquely human, as defined and tested in a 2007 Australian study, include being ambitious, imaginative, frivolous and insecure. Examples of traits that are less uniquely human — those that could be used to describe a pet as well as a friend, for example — include being passive, timid, friendly and shy.

The question of whether power leads to dehumanization has part of its roots in the renowned Stanford Prison Experiment conducted in 1971. Twenty-four male students were randomly assigned to play the role of either inmate or guard in a mock prison in the basement of the Stanford psychology building. During the study, the guards were psychologically abusive to the prisoners, many of whom passively accepted the abuse, despite the fact that the participants knew that they were all students at the same elite university.

Though the guards were described as dehumanizing the prisoners, the term “dehumanization” was well defined at the time and the experiment was not designed to allow the researchers to confidently state that it was the increase in power that lead to the dehumanization. By contrast, Gwinn’s study, now available online, was designed specifically to test the relationship between power and dehumanization.

Gwinn cautions that the researchers cannot yet say whose perspective is being changed by the power differential imposed on participants in the CU study. It’s possible that being in a position of less power makes a person see those in power as more human rather than the other way around, or that both people are affected.

“We haven’t pinned down why this happens,” Gwinn said. “We don’t know whose perception is being affected.”

Charles Judd and Bernadette Park, both professors in CU-Boulder’s Department of Psychology and Neuroscience, co-authored the study.