Thatcher effect

The Thatcher illusion or the Thatcher effect is a perceptual phenomenon in which it is difficult to detect localized changes in a face if that face is rotated by 180 ° ( upside down ), while these changes very clearly perceived when the face is presented correctly. This illusion is named after the former British Prime Minister Margaret Thatcher, whose photograph of Dr. Peter Thompson, a professor at the University of York, England was used in 1980 to demonstrate this illusion.

Description

The effect can be demonstrated by two originally identical photographs, both of which are rotated by 180 °, ie standing on your head. The second photograph is changed in such a manner that both the eyes and the mouth are present is rotated again by 180 ° within the image. At first glance, the two photographs do not differ, only if images are in the correct direction, you notice the grotesque change.

It is believed that this illusion is caused by the specific psychological processes that take place in the human visual perception and a role there, particularly in inverted faces (which rarely or never occur in nature ). Faces are unique, although many see faces in the basic pattern very similar. It is hypothesized that humans from birth specific operations to face discrimination developed, both on the configuration of the face ( spatial arrangement of facial components;? Eg standing, the eyes close or far apart as far as the mouth below the nose? ) as well as on the details of the face ( eg, What shape have lips? Are earlobe before? ) based. If a face is rotated 180 °, but the configuration detection is disturbed ( the facial components are not where they belong ), and in consequence also to fine tune the detail recognition.

This illusion does not occur in people who have certain forms of prosopagnosia, a cognitive disorder, in which the visual perception does not proceed normally, usually after brain injuries or diseases diagnosed.