Another group was allowed to deliberate — they were asked to think carefully about which candidate was more competent, and make a well-thought-out decision.
The deliberation group did worse than both of the snap judgment groups in predicting the winner of the election.
"These findings confirm that a significant portion of electoral judgments — and, therefore, choices — are not based on rational, deliberative assessments of the most important factors, such as a candidate's record and policy positions," said Jack Glaser, assistant professor at the Goldman School of Public Policy at the University of California at Berkeley. "Rather, they are, to a substantial degree, based on inferences made from superficial characteristics of candidates."
Previous research in this field has yielded some clues as to how people can make such snap judgments.
"[It] was an extremely small amount of time, but humans are experts in face processing," Little said. "Humans are fascinated by faces, and we have specialized brain mechanisms to process them."
In a study published earlier this year, Little and other U.K. researchers at the University of Stirling and the University of Liverpool found that differences in facial shapes alone could predict who won or lost in major elections.
In addition, they found that changing the context from wartime to peacetime, in hypothetical votes, led to dramatically different voter preferences.
During hypothetical wartime, voters preferred computerized faces that were more "masculine," while during peacetime voters preferred faces that were more "feminine."
"We found that individuals changed their opinion of who they would vote for based on context; dominant faces in a time of war, more friendly appearing faces in a time of peace," said Little.
"In this sense, there is no absolute right choice of leader — leaders might be selected according to the task that lies before them, and appearance may then interact with conscious or unconscious decisions about context."
Candidates may already innately understand some of the human nature behind this study. According to the psychologists who read the study, it may even explain some of the more amusing aspects of running for office.
"The burden needs to be placed on the voter, the campaigns and the media to provide good information about candidates so people can make choices based on substance, and not physical appearance," said Glaser. "And until that happens, we can keep expecting candidates to spend $200 on their haircuts — that's the rational thing for them to do in this environment."