We feel that we are in control when our brains figure out puzzles or read words, says Tom Stafford, but a new experiment shows just how much work is going on underneath the surface of our conscious minds.

It is a common misconception that we know our own minds. As I move around the world, walking and talking, I experience myself thinking thoughts. "What shall I have for lunch?", I ask myself. Or I think, "I wonder why she did that?" and try and figure it out. It is natural to assume that this experience of myself is a complete report of my mind. It is natural, but wrong.

There's an under-mind, all psychologists agree – an unconscious which does a lot of the heavy lifting in the process of thinking. If I ask myself what is the capital of France the answer just comes to mind – Paris! If I decide to wiggle my fingers, they move back and forth in a complex pattern that I didn't consciously prepare, but which was delivered for my use by the unconscious.

The big debate in psychology is exactly what is done by the unconscious, and what requires conscious thought. Or to use the title of a notable paper on the topic, 'Is the unconscious smart or dumb?' One popular view is that the unconscious can prepare simple stimulus-response actions, deliver basic facts, recognise objects and carry out practised movements. Complex cognition involving planning, logical reasoning and combining ideas, on the other hand, requires conscious thought.

A recent experiment by a team from Israel scores points against this position. Ran Hassin and colleagues used a neat visual trick called Continuous Flash Suppression to put information into participants’ minds without them becoming consciously aware of it. It might sound painful, but in reality it’s actually quite simple. The technique takes advantage of the fact that we have two eyes and our brain usually attempts to fuse the two resulting images into a single coherent view of the world. Continuous Flash Suppression uses light-bending glasses to show people different images in each eye. One eye gets a rapid succession of brightly coloured squares which are so distracting that when genuine information is presented to the other eye, the person is not immediately consciously aware of it. In fact, it can take several seconds for something that is in theory perfectly visible to reach awareness (unless you close one eye to cut out the flashing squares, then you can see the 'suppressed' image immediately).

Hassin’s key experiment involved presenting arithmetic questions unconsciously. The questions would be things like "9 - 3 - 4 = " and they would be followed by the presentation, fully visible, of a target number that the participants were asked to read aloud as quickly as possible. The target number could either be the right answer to the arithmetic question (so, in this case, "2") or a wrong answer (for instance, "1"). The amazing result is that participants were significantly quicker to read the target number if it was the right answer rather than a wrong one. This shows that the equation had been processed and solved by their minds – even though they had no conscious awareness of it – meaning they were primed to read the right answer quicker than the wrong one.

The result suggests that the unconscious mind has more sophisticated capacities than many have thought. Unlike other tests of non-conscious processing, this wasn’t an automatic response to a stimulus – it required a precise answer following the rules of arithmetic, which you might have assumed would only come with deliberation. The report calls the technique used "a game changer in the study of the unconscious", arguing that "unconscious processes can perform every fundamental, basic-level function that conscious processes can perform".

These are strong claims, and the authors acknowledge that there is much work to do as we start to explore the power and reach of our unconscious minds. Like icebergs, most of the operation of our minds remains out of sight. Experiments like this give a glimpse below the surface.

If you have an everyday psychological phenomenon you'd like to see written about in these columns please get in touch @tomstafford or ideas@idiolect.org.uk.

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