What is nine plus six, plus eight? You may not realise it, but you already know the answer. It seems that we unconsciously perform more complicated feats of reasoning than previously thought 鈥� including reading and basic mathematics. The discovery raises questions about the necessity of consciousness for abstract thought, and supports the idea that maths might not be an exclusively human trait.
Previous studies have shown that we can subliminally process single words and numbers. To identify whether we can unconsciously perform more complicated processing, at the Hebrew University of Jerusalem, Israel, and his colleagues used a technique called continuous flash suppression.
The technique works by presenting a volunteer鈥檚 left eye with a stimulus 鈥� a mathematical sum, say 鈥� for a short period of time, while bombarding the right eye with rapidly changing colourful shapes. The volunteer鈥檚 awareness is dominated by what the right eye sees, so they remain unconscious of what is presented to the left eye.
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In the team鈥檚 first experiment, a three-part calculation was flashed to the left eye. This was immediately followed by one number being presented to both eyes, which the volunteer had to say as fast as possible. When the number was the same as the answer to the sum, people were quicker to announce it, suggesting that they had subconsciously worked out the answer, and primed themselves with that number.
In the second experiment, participants were subliminally shown a sensible or nonsensical sentence such as 鈥淚 drank the coffee鈥� or 鈥淚 ironed the coffee鈥�. The sentences were presented to the left eye until the people highlighted that they had become aware of any of the words in the sentence. People noticed words in sentences that didn鈥檛 make sense more quickly than in those that did, which suggests that the sentences had been unconsciously processed.
鈥淵ou鈥檙e integrating information from lots of different places,鈥� says Hassin. 鈥淧eople thought you needed consciousness for this.鈥�
鈥淭his study provides convincing evidence that people can perform complex rule-based operations unconsciously,鈥� says at the University of Bordeaux, France. 鈥淭his could change the way we think about how our brains work and what reason is.鈥�
Since arithmetic and reading might work at a level below conscious awareness, the study adds support to the idea that such reasoning may not be a uniquely human trait. 鈥淭his is consistent with the idea of there being a continuum between animal and human reasoning,鈥� says Ric.
Journal reference: , DOI: 10.1073/pnas.1211645109
