With the 2008 presidential election only a year away, the merits of each candidate are becoming a common topic of conversation. But how do our brains, after hearing so many different opinions, gauge the popularity of each one? New research findings suggest that we judge a viewpoint's prevalence by how familiar it is—regardless of whether we have heard it five times from one person or once each from five different people.

Kimberlee Weaver, a psychologist at Virginia Polytechnic University, and her colleagues gave volunteers records of opinions from a fictional focus group that had supposedly met to discuss the preservation of open space in New Jersey. In some cases, multiple people expressed the viewpoints; in others, the same person repeated an opinion many times. Based on these records, they asked the subjects to estimate how the focus group, and the population in general, felt about the matter.

The study participants rated an opinion as popular if it had been expressed several times—even if only one person had said it. The researchers’ follow-up experiments suggested that the opinion's familiarity was the most important factor in whether subjects considered it to be common.

“People are not always good at inferring what other people think,” Weaver says. The ability to gauge the sentiment of a crowd is vital for good social decision making, and for the most part evolution has honed our skills of perception. But our psychological mechanisms are sometimes subject to constraints—and this phenomenon is a perfect example. According to Weaver, these types of miscalculations could sway our own opinions and perceptions of reality, leading us to unintentionally make decisions influenced by a mentally amplified vocal minority.