Thatcher-Illusion

The Thatcher effect or Thatcher illusion is a phenomenon where it becomes difficult to detect local feature changes in an upside down face, despite identical changes being obvious in an upright face. It is named after British former Prime Minister Margaret Thatcher on whose photograph the effect has been most famously demonstrated. This was originally created by Peter Thompson, who is a senior lecturer at the University of York, England (Thompson, 1980).

The effect is illustrated by two originally identical photos [1], which are inverted. The second picture is obviously (and quite grotesquely) altered so that the eyes and mouth are vertically flipped, though the changes are not immediately obvious until the image is viewed in normal orientation.

This is thought to be due to specific psychological processes involved in face perception which are tuned especially to upright faces. Faces seem unique despite the fact that they are statistically very similar. It has been hypothesised that we develop specific processes to differentiate between faces that rely as much on the configuration (the structural relationship between individual features on the face) as the details of individual face features, such as the eyes, nose and mouth. When a face is upside down, the configural processing cannot take place, and so minor differences are more difficult to detect.

This effect is not present in people who have some forms of prosopagnosia, a disorder where face processing is impaired, usually acquired after brain injury or illness. This suggests that their specific brain injury may damage the process that analyses facial structures.

See also

• Face perception
• Prosopagnosia

External links

• Thatcher illusion demonstration

References

Original Article

• Thompson, P. (1980). Margaret Thatcher: A new illusion. Perception, 9(4), 483-484.

Further investigations on the Thatcher effect

-Recognition Times

• Sjoberg, W., & Windes, J. D. (1992). Recognition times for rotated normal and 'Thatcher' faces. Perceptual and Motor Skills, 75(3, Pt 2), 1176-1178.
• Stuerzel, F., & Spillmann, L. (2000). Thatcher illusion: dependence on angle of rotation. Perception, 29(8), 937-942.

-Developmental aspects

• Lewis, M. B. (2003). Thatcher's children: Development and the Thatcher illusion. Perception, 32(12), 1415-1421.
• Rouse, H., Donnelly, N., Hadwin, J. A., & Brown, T. (2004). Do children with autism perceive second-order relational features? The case of the Thatcher illusion. J Child Psychol Psychiatry, 45(7), 1246-1257.

-EEG

• Carbon, C. C., Schweinberger, S. R., Kaufmann, J. M., & Leder, H. (2005). The Thatcher Illusion seen by the brain: An event-related brain potentials study. Cognitive Brain Research, 24(3), 544-555.