First impressions are powerful and are formed in all sorts of social settings, from job interviews and first dates to court rooms and classrooms. We regularly make snap judgments about others, deciding whether people are trustworthy, confident, extraverted, likable, and more. Although we have all heard the old adage, “don’t judge a book by its cover,” we do just that. And at the same time that we are judging others, we in turn communicate a great deal of information about ourselves – often unwittingly – that others use to size us up.

It is no surprise that complete strangers engage in a process of mutual evaluation, or that people form impressions quite quickly, and in many cases, quite accurately. One of the first studies to demonstrate this fact was conducted in 1966 by Warren Norman and Lou Goldberg, who had college students rate their classmates’ personalities on the very first day of class, before they had a chance to interact. Students were also asked to rate their own personalities. Two surprising findings emerged from that study: First, classmates tended to agree in their assessments of others; if one classmate rated a peer as dependable or extraverted, it was likely that other classmates rated that individual as dependable or extraverted too.

The second and more noteworthy finding was that students’ first impressions of their classmates tended to align with their classmates’ own self-assessments. Thus, if a person was rated as sociable by his classmates, it was quite likely that he had independently rated himself as sociable as well. These data, and those from similar studies, suggest that we are adept in rapidly and accurately evaluating some personality traits, or at the very least that we are quick to discern the way others see themselves.

Just how low can we go? If we can accurately size up a fellow student in the first few moments of class, without any significant interaction, how little information do we need in order to make these assessments? Is body language enough? What about facial expressions, clothing, or mannerisms? From the shoes we wear and the way we stand to the songs we like and the way we walk, researchers have examined what our behaviors and our preferences convey to others. In many instances it seems we need to catch only the smallest detail about a person to form an accurate impression, but of course we can get it wrong.

Nalini Ambady and Robert Rosenthal led the quest to understand the limits of impression formation, and in a series of studies they demonstrated that observers make accurate personality and competency judgments using very “thin slices of behavior.” In their experiments, undergraduate raters watched brief, 30-sec video clips of teachers in the classroom, and evaluated the teachers on thirteen different variables, including likability, competence, warmth, honesty, and optimism. Notably, the audio on these video clips was removed, so that raters made their evaluations exclusively on the basis of non-verbal cues. Not only were the judgments of the teachers fairly consistent across raters, but they were also fairly accurate.

These appraisals, rendered after only half a minute of observation, were reliably predictive of the evaluation scores given to the teachers by students whom they had instructed for a full semester. In subsequent studies Ambady and Rosenthal examined judgments rendered after only ten seconds, and then after a mere two seconds. Even when given only two seconds of silent video, the raters made judgments that correlated reliably with end-of-semester evaluations made by the teachers' own students.

Two seconds of silent video may indeed seem like a very thin slice of behavior upon which to base an impression, but researchers have demonstrated that we can do well with far less. More recent investigations have demonstrated that a simple photograph of our favorite shoes provides enough data for strangers to judge our age, gender, income and attachment anxiety, and that a list of our top ten favorite songs reveals how agreeable and emotional stable we are.

But what if we reduce the information available to a mere series of dots, strung together to form a stick figure that depicts movement but nothing else? John Thoresen, Quoc Vuong, and Anthony Atkinson addressed this question in a series of experiments where participants judged personality traits on the basis of body movements alone. The scientists first videotaped male and female volunteers as they walked roughly 25 feet. From these videos, they created stick-figure depictions of each walker, eliminating all information about age, attractiveness, weight, clothing, race, and gender. The only information available to observers was the gait of the walker, conveyed in the form of a two-dimensional stick-figure.

Participants in these studies rated each stick-figure walker on six trait scales: adventurousness, extraversion, neuroticism, trustworthiness, warmth, and approachability. Two questions were addressed: First, were the impressions about the stick-figure walkers consistent across raters? Second, were they accurate?

Raters were in fact fairly reliable in their judgments: if one rater judged a walker to be adventurous and extraverted, it is likely that other raters did too. Despite the consensus in ratings, though, the impressions were not correct. The trait judgments made by raters did not align with the walkers' self-reports.

These findings are a bit puzzling. If the raters were wrong, why were their impressions so similar? What information were raters using to make their judgments that lead to such consistency? Thoresen and colleagues speculated that the raters may have tried to glean other (unseen) physical characteristics of the stick-figure walkers like gender, age, or health, and may have used those intuitions as the basis for their personality judgments. To test this possibility, Thoresen and colleagues thus asked new groups of raters to view the stick-figure walkers and guess various physical characteristics of the stick-figure walkers, like gender, attractiveness, age, and excitability.

Raters were again very consistent in their judgments: If one rater perceived a stick-figure walker as male or attractive, it was very likely that the other raters did. For some physical characteristics (e.g., gender) raters were both consistent and also fairly accurate, but for others (e.g., age), raters agreed with each other but were not correct in their assessments. Regardless of the accuracy of these judgments, the assessments of physical characteristics like gender and attractiveness reliably predicted the perceived personality traits for each stick-figure walker. For example, walkers perceived as masculine were also perceived as emotionally stable, those perceived as attractive were also considered approachable, and those perceived as calm were also viewed as warm.

The findings suggest that in the absence of good information, viewers glean what they can from a situation and use that information to form impressions about personality traits. Even though trait judgments that are derived from minimal detail (like gait) are likely to be wrong, there is an odd consistency in those errant judgments. People seem to rely on common factors when forming impressions, and reach similar, albeit inaccurate, conclusions when information is scarce.

Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist at the Boston Globe. He can be reached at garethideas AT gmail.com or Twitter @garethideas.