Study: Unconscious mind can do math, parse language

Our unconscious minds may be far more capable than we usually give them credit for: According to a study published Monday in the Proceedings of the National Academy of Sciences, people can do multi-step math problems in their heads without being consciously aware that they’re doing math at all. The same goes for correctly parsing multi-word phrases.

It has long been taken for granted that consciousness is required to complete such tasks. While scientists have shown that people can do simple things like add 2+2 and process single words without realizing it, researchers have generally believed that anything more complicated than that would require our conscious attention.

Myriad experimental techniques exist to disrupt conscious perception for a brief time — including what’s called “masking,” in which a visual image is presented directly after a target, leading to an inability to consciously perceive the target. For example, if the number five were presented directly before a mask, you would never know you saw the five, even though you may have perceived it unconsciously.

Many studies have shown that masked stimuli can still impact decision-making and response times, which is how we know they can be perceived at all. Here’s an example: In one study, subjects were shown a number and asked to determine whether or not it was a prime number. But before they did so, they were shown a masked math equation for a brief time, such as “2+2=,” which they did not consciously perceive. Nonetheless, if the number they were evaluating for “primeness” was the same as the answer to the masked math problem, they were much faster at telling whether it was prime. This shows that, at some level, the subject’s brain solved the problem. The same has been shown to be true for the perception of single words.


But what about more complex math problems, or even multi-word English phrases? How far can our unconscious go?

That question has traditionally been very difficult to answer because the techniques used to disrupt conscious perception only worked for a brief time. But the new study, carried out by a team from Hebrew University in Jerusalem, utilized a recently developed approach called Continuous Flash Suppression, or CFS, which can disrupt perception for seconds at a time. It works by showing the target stimulus to one eye — say, a multi-word phrase or a math problem — while showing a series of colorful images to the other eye.

During CFS, the distraction caused by the flashing colorful images lasts for a while, but not forever. The researchers first used this trick to test whether people were able to perceive phrases unconsciously. While flashing the CFS images to one eye, they showed people a phrase that either made sense or didn’t—for example, “I ironed coffee” versus “I made coffee” — in the upper or lower parts of the screen. They told the subjects to look for an English phrase and push a button indicating its location.

If conscious perception was required to understand the phrase, the content of the phrase should have had no difference on reaction time — a measure of when the phrase “popped” into consciousness. But instead, the researchers found that the subjects perceived phrases that didn’t make sense much sooner than ones that did, evidence that they were processing the words even before they were conscious of them.

They then tried something slightly different to test the mathematical abilities of the unconscious brain. While showing the same flashing images to one eye, they presented three-number math equations, such as “9-5-1=” to the other eye for between one and two seconds. They then showed the subjects a single number, and asked them to pronounce it. Though subjects reported no conscious awareness of the equation, they were much faster at pronouncing numbers that were the CFS-masked equation’s solution.

Taken together, these experiments present compelling evidence that conscious awareness is not required for tasks as complex as understanding words put together to make phrases, or math problems that include multiple steps.

Or, as the researchers write in their study, “These results suggest that the modal view of consciousness and the unconscious, a view that ties together (our unique) consciousness with (humanly unique) capacities, should be significantly updated.”

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