But this may not be so, says a study published last month in the journal Psychological Science. It found that people are more likely to lie about themselves when under time pressure. “Asking people to respond quickly just makes them give you the answer you want to hear,” said John Protzko, the study’s first author and a postdoctoral scholar at the University of California, Santa Barbara.

This finding, now replicated five times (twice by Dr. Protzko’s team, three times by independent labs), could undermine one of the bedrock assumptions of pop psychology: that speedy responses, like those described in Malcolm Gladwell’s 2005 book “Blink,” can provide access to our hidden brains.

To test that notion, Dr. Protzko’s team randomly assigned 1,500 representative Americans to one of two groups. The “fast group” had to answer each of 10 questions within an 11-second time limit. The “slow group” got more time to reflect, as they had to wait at least 11 seconds before responding.

Both groups were given the same survey, a standardized test called the Social Desirability Scale, which measures the degree to which people describe themselves in socially acceptable terms. The scale includes personal statements such as “There have been times when I was quite jealous of the good fortune of others” and “I have never intensely disliked anyone.” By comparing an individual’s responses to these statements with the statistical average, researchers can capture how likely it is that they are fudging the truth to enhance their reputation.

Responses to these categorical statements were revealing. We expect people to show their hidden cards when buttonholed for a quick reaction. But the study found that we are about 30% more likely to lie about ourselves when rushed to respond. This result makes sense: In human societies, tit-for-tat-type exchanges grease the wheels of interpersonal interaction. Enhancing our reputations by presenting ourselves in the best possible light is the natural, quick and easy thing to do.

By contrast, defying social norms by admitting our faults takes not only more deliberation but also a more relaxed context—one often lacking in psychological research. People are more motivated to tell the unvarnished truth in non-judgmental environments than in the typical cinder-block, fluorescent-lit psychology lab, with a stopwatch ticking. If experimental psychology hopes to capture our true, unamplified selves, it may have to reproduce environments and time-frames that allow us to let our guard down.

As Dr. Protzko observed, many studies “assume that putting people under time pressure gives you access to a hidden part of the mind. But we’re finding that they’re just lying. They’re giving you the answer that makes them look best.” He adds, “When you make people answer quickly, everyone lies.”

The moral of the study? If you want the truth, you have to be willing to wait for it.