Thatcher effect

The Thatcher effect or Thatcher illusion is a phenomenon where it becomes more difficult to detect local feature changes in an upside-down face, despite identical changes being obvious in an upright face. It is named after the then British prime minister Margaret Thatcher, on whose photograph the effect was first demonstrated. The effect was originally created in 1980 by Peter Thompson, professor of psychology at the University of York. Overview The effect is illustrated by two originally identical photos, which are inverted. The second picture is altered so that the eyes and mouth are vertically flipped, though the changes are not immediately obvious until the image is viewed upright. The Thatcher effect is thought to be due to specific psychological cognitive modules involved in face perception which are tuned especially to upright faces. Faces seem unique despite the fact that they are very similar. It has been...