FIGURE 1.

The “Thatcher illusion ” (Thompson, 1980). We first see two more-or-less identical faces. However, when they are turned around 180° to their proper orientation, it turns out that one face had been manipulated. These abnormal physical details had previously been perceptually obscured behind the meaningful experience of seeing a replication of the left-hand image. (This figure was first published in Thompson, P. “Margaret Thatcher: a new illusion” Perception, 1980, 9, pp. 483–484, reproduced by kind permission of Pion Ltd, London. Website: http://www.perceptionweb.com).