Cognitive Overload

Back in the 1970’s, 3 friends clubbed together to buy themselves a TV for the house they shared. Each of them managed to save £10 for the TV so out they went. Eventually they came across a shop that had, in the window, an excellent model with 3 preset channel buttons plus 1 spare. It was colour-ready and had a wood-effect cabinet. It was also on sale for £25 – within the three friends’ budget. They went into the shop and soon found the shop assistant and told him that they wanted the TV in the window. The assistant talked them through all of the features and them took their money – 3 £10 notes. As he went to the till to get their change he thought “I could tell them that there’s been a mistake and the TV is really £27 – then I could pocket the extra £2 and no-one would know!” Taking 5 £1 notes out of the till he returns to the 3 friends and tells them the bad news. They are so pleased with the TV that they accept anyway. The assistant gets his £2 and they leave the shop with the TV.

Each of the friends paid £9 making a total of £27. Add on the £2 that the shop assistant pocketed and you have £29 – the big question is: what happened to the extra one pound note?

This is a classic mental puzzle that a few people will have solved immediately but most won’t get it until the trick is explained.

There’s an old audio/radio engineering term: “Signal-to-Noise Ratio” (SNR) – A rough translation is the difference between the amount of stuff should be coming through and the amount of other stuff that just gets in the way. – If there’s too much crackle and hiss then you can’t hear the music. When this happens in a human brain it’s known as ‘Cognitive Overload’.

In the puzzle at the beginning there was so much mental noise being generated by all those numeric details that it was difficult to see where the missing £1 went – If you’re still struggling; it didn’t go anywhere. The three friends went in with £30, paid £27 and came away with a TV and £3 change – the little mathematical summary at the end of the story is just nonsense designed to overload our brains.

It’s possible to perform this sort of thing visually too – if an interface or web page is cluttered, has too many links or too many choices, then users may miss the key message or target – they may even turn off all together.

As humans we crave choice but faced with too many choices the SNR rises to the point where we are incapable of choosing – cognitive overload.

A simplified page should lead to more click through as users are more able to process the few choices that they are presented with. A simplified interface should lead to greater user satisfaction with the product as they make fewer mistakes with less cognitive background noise to deal with.


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