According to the effect, old impressions may be less powerful than new ones.

You’ll never get a second chance to make a great first impression.” We’ve all heard that an interviewer, or a stranger at a party, will form an impression of you, your character, your personality — an impression that is nearly indelible — all within the first 60 seconds of meeting you.

Or wait, is it 30 seconds? Twenty?

Two or three?

Forget whatever figure you may have heard. Not to intimidate you, if you happen to be preparing for a job or grad school interview, or a blind date, but new research shows that you may need to have your act together in the blink of an eye.

A series of experiments by Princeton psychologists Janine Willis and Alexander Todorov reveal that all it takes is a tenth of a second to form an impression of a stranger from their face, and that longer exposures don’t significantly alter those impressions (although they might boost your confidence in your judgments). Their research is presented in their article “First Impressions,” in the July issue of Psychological Science.

Like it or not, judgments based on facial appearance play a powerful role in how we treat others, and how we get treated. Psychologists have long known that attractive people get better outcomes in practically all walks of life. People with “mature” faces receive more severe judicial outcomes than “baby-faced” people. And having a face that looks competent (as opposed to trustworthy or likeable) may matter a lot in whether a person gets elected to public office.

Willis and Todorov conducted separate experiments to study judgments from facial appearance, each focusing on a different trait: attractiveness, likeability, competence, trustworthiness, and aggressiveness. Participants were shown photographs of unfamiliar faces for 100 milliseconds (1/10 of a second), 500 milliseconds (half a second), or 1,000 milliseconds (a full second), and were immediately asked to judge the faces for the trait in question (e.g., “Is this person competent?”). Response time was measured. Participants were then asked to rate their confidence in making their judgments.

Participants’ judgments were compared with ratings of the same photographs given by another group of participants in a preliminary study, in which there were no time constraints for judging the personality traits of the faces. (In that preliminary study, there was strong agreement among the various participants about the traits of the people in the photographs.)

For all five of the traits studied, judgments made after the briefest exposure (1/10 of a second) were highly correlated with judgments made without time constraints; and increased exposure time (1/2 or a full second) didn’t increase the correlation. Response times also revealed that participants made their judgments as quickly (if not more quickly) after seeing a face for 1/10 of a second as they did if given a longer glimpse.

Longer exposure times did increase confidence in judgments and facilitated more differentiated trait impressions (that is, less correlation between the different traits for a given person).

All the correlations between judgments made after a 1/10-second glimpse and judgments made without time constraints were high, but of all the traits, trustworthiness was the one with the highest correlation. Along with attractiveness, this was also the trait that participants were able to assess most quickly. The authors suggest, based on evolutionary psychology, that an accelerated and accurate ability to judge trustworthiness in others may have evolved as an important survival mechanism.

But before you rest secure in the knowledge that at least you have a whole 1/10 of a second to make that great first impression at your next job interview, the authors acknowledge that future research may well close that window even smaller. Other researchers recently revealed in Psychological Science that objects are categorized as soon as they are perceived; something similar, Willis and Todorov suggest, may be true of certain trait judgments.

It may be that, to impress a prospective employer with your competence and trustworthiness, or a prospective mate with your attractiveness, you can do it in, well, no time. That may be a good or bad thing, depending.

What are the three main factors that influence interpretation of behavior?

Which of the following factors may influence your perceptions?

What is the first stage of perception in communication?

When initial negative perceptions lead us to view later interactions as negative?