Picture the following, and prepare to be amazed. You're walking across a college campus when a stranger asks you for directions. While you're talking to him, two men pass between you carrying a wooden door. You feel a moment's irritation, but they move on and you carry on describing the route. When you've finished, the stranger informs you that you've just taken part in "a psychology experiment. "Did you notice anything change after the two men passed with the door?" he asks. "No," you reply uneasily. He then explains that the man who initially approached you walked off behind the door, leaving him in his place. The first man now comes up to join you. Looking at them standing side by side, you notice that the two are of different height and build, are dressed differently, have different haircuts and different voices. It sounds impossible, but when Daniel Simons, a psychologist at Harvard University, and his colleague Daniel Levin of Kent State University in Ohio actually did this experiment, they found that fully 50 per cent of those who took part failed to notice the substitution. The subjects had succumbed to what is called change blindness. Taken with a glut of recent experimental results, this phenomenon suggests we see far less than we think we do.
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