At the Speed of the Unconscious Mind

This is the week when I get to introduce a new batch of students to the idea that our unconscious minds can make better decisions than our conscious ones (if you’re not an expert, anyway). Which may be even more important to know, given some new evidence about just how quickly our unconscious minds can process incoming information.

In one recent experiment, college students were asked to make a deceptively simple decision: two shapes would flash on the screen. If the shapes matched, the students should push a button; if the shapes were different, they should do nothing. If that sounds simple, consider that those shapes stayed on the screen for a total of only 200 milliseconds (ms), or 2/10ths of a second, just barely long enough to register that anything had been there at all.

But being able to tell same from different in 200 ms isn’t even the interesting part of the experiment. That part only existed to get students into the mindset of don’t press the button if the shapes didn’t match. Because mixed in with those 200 ms pairs were even faster pictures, no more than 33.3 ms long – that’s one third of one tenth of a second, and as far as the students consciously knew they had seen nothing, and were just being prompted to press the button to show that they were still paying attention. But even that tiny fraction of a second should be enough for the unconscious mind to see those pictures.

The key is, some of these “invisible” trials had two identical shapes (both squares, or both diamonds), and some had two different shapes (one of each). The idea was that if the students had consciously adopted the don’t press the button if the shapes didn’t match mindset, and the unconscious mind had not just seen the “invisible” shapes but noted that they didn’t match, then it might try to put the kibosh on the whole press-the-button action. It shouldn’t win, and everyone should still push the button…but they might be just a hair slower, due to that interference from the unconscious.

Indeed, reaction times were slower for the different, unseen shapes. The difference was statistically significant, but also very, very small; pressing the button after different invisible shapes was only 10 to 32 milliseconds slower than for the identical shapes (about the same amount of time the shapes were flashed on the screen to begin with). To keep this seemingly tiny difference in perspective, know that most people were responding to the shapes in less than 300 milliseconds to begin with, so the cost is about 5% of their reaction time, and not quite as minuscule as it may seem (that’s better than most interest rates, after all). Across two experiments, this suggests that a third of a tenth of a second is enough for our unconscious mind to not only perceive the shapes, but to process them enough to know if they are identical or different.

Now, this may not seem like much of a superpower; certainly it’s not enough to renew any interest in subliminal advertising and mind control – after all, everyone did actually press the button; the unconscious influence only barely slowed them down, and that few milliseconds might not make a difference to anyone. To me, though, this is an important step to validating “gut instinct”. Your unconscious mind can see something without you knowing you see it – an object, or perhaps a microexpression – and process it, in less time than it takes you to blink. Perhaps with a little more than 33.3 milliseconds, or with something more vital to survival than squares and diamonds, your unconscious can do more than slow your reaction time…it might prompt you to hesitate, or second-guess a decision, all without you consciously knowing why you do so. There’s still plenty of room left for guts to get involved in our minds, but this particular kind of instinct may actually be stemming from the more unreachable parts of our brains.
Lin Z, & Murray SO (2014). Unconscious processing of an abstract concept. Psychological Science, 25, 296-298. PMID: 24285433


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