Magic: Holding a card to your heart

by Paul Curzon, Queen Mary University of London

A volunteer chooses a card at random to predict how rich the person they marry will be. Without seeing what the chosen card is they hold it against their heart and link it to their one true love. Amazingly they choose the only Joker in the pack - they will marry a fool! Even more amazingly, on the table in a sealed envelope is the calling card of a Joker asking the volunteer to marry them. It just shows how easy it is for your heart to make a fool of you!

Magician's use lots of different techniques to make sure their tricks seem magical. One of the most important is misdirection. It involves making the audience miss things that are there to be seen. It's all about controlling their attention and the way magician's do it includes some lessons for designers of interactive systems.

For example, magicians often make use of the fact that we can easily be distracted by sounds. When someone talks we naturally look at their face, for example, and when we are looking at their face we don't see what the magician's hands are doing. They also make use of the fact that information coming in from our different senses can interfere and that we don't always perceive what is really out there, because of this confusion. Software engineers need to draw on the same cognitive science to design good multimodal systems. Magicians find combinations of effects that interfere so we make mistakes whereas software engineers have to find combinations that reinforce one another.