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Take a look at this video. Were you fooled? Rewind to take a closer look at the first and second sets of cards and all should become clear.

This exploits 鈥渃hange blindness鈥� 鈥� our failure to notice clearly visible alterations to our surroundings. Vision researchers have long been fascinated by phenomena like these because of what they reveal about the workings of our brain.

Now, at the Institute of Neurosciences in Alicante, Spain, has used the card trick to reveal how we take in more visual information than we consciously notice. The results suggest that if you are not sure whether you recognise something or someone, you should pay attention to your gut instinct. Your subconscious may have registered the information after all.

Pick a card

Mart铆nez鈥檚 team posed as magicians to play the card trick on people in the street, and took in nine out of 10 passers-by. Afterwards they showed each participant two cards and asked which one had been in the first set of five.

The participants answered correctly about 80聽per cent of the time. If they really hadn鈥檛 been aware of the other four cards in the first set, their score should have been only 50聽per cent 鈥� no better than chance.

So even though the participants had no conscious awareness of having seen the card already 鈥� which is why the trick fooled them 鈥� in fact the information was in their short-term memory.

鈥淣one of the subjects consciously remembers the card, but when forced to choose between two options they performed much better than expected by chance,鈥� says Mart铆nez. 鈥淎ll the cards leave a trace in working memory for a brief period.鈥�

Until now it has been unclear if change blindness is the result of failure to create certain visual images or of failure to compare two consecutive scenes. This study suggests the latter explanation is correct.

Gut instinct

The subconscious process does not just work with magic shows. Mart铆nez鈥檚 team repeated the experiment with pictures of faces instead of playing cards and got just the same results. 鈥淭hat was unexpected,鈥� says Mart铆nez.

This could be useful to know. Imagine you are in a caf茅 wanting to pay your bill and you look for the waiter who initially took your drinks order. It may be hard to recognise them. 鈥淏ut when you鈥檙e forced to choose you get it right most of the time,鈥� says Mart铆nez. 鈥淲e should pay attention to our gut instincts. They reflect the contents of our unconscious memory.鈥�

鈥淐hange blindness comes from optimising the system to catch all the important material,鈥� says , a neuroscientist at Boston University who studies memory. 鈥淚t relies upon expectations of what is going to happen next. If something occurs that is seemingly unrelated it seems as if you don鈥檛 even notice it. But this study shows the visual areas actually accessed the information. It鈥檚 one step further in understanding how [the brain] works.鈥�

Blinded by chatter

The team also found it was possible to disrupt the subconscious memories, or access to them, by distracting the participants with irrelevant chat: participants were then less likely to answer correctly. 鈥淭he casual chit-chat used by magicians to distract audiences can interfere with the contents of the visual short-term memory,鈥� says Mart铆nez.

The study was presented this week at the in Washington聽DC.