Daniel Gilbert, in Stumbling On Happiness:
And it isn't just the subtle changes we miss. Even dramatic changes to the appearance of a scene are sometimes overlooked. In an experiment taken straight from the pages of Candid Camera, researchers arranged for a researcher to approach pedestrians on a college campus and ask for directions to a particular building. While the pedestrian and the researcher conferred over the researcher's map, two construction workers, each holding one end of a large door, rudely cut between them, temporarily obstructing the pedestrian's view of the researcher. As the construction workers passed, the original researcher crouched down behind the door and walked off with the construction workers, while a new researcher, who had been hiding behind the door all along, took his place and picked up the conversation. The original and substitute researchers were of different heights and builds and had noticeably different voices, haircuts, and clothing. You would have no trouble telling them apart if they were standing side by side. So what did the Good Samaritans who had stopped to help a lost tourist make of this switcheroo? Not much. In fact, most of the pedestrians failed to notice—failed to notice that the person to whom they were talking had suddenly been transformed into an entirely new individual.