Why does Thatcher Illusion arise and what can it tell us about face processing?

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Why does Thatcher Illusion arise and
what can it tell us about face processing?

Topics on face recognition processing were always interested by psychologists.

Recognition is defined as the approaches to information stored in memory and here, face

recognition involves how people interpret faces. Facial recognition begins with simple

patterns (i.e. eyes, nose, mouth etc) that are combined in a known configuration to make

a recognisable face. Since we normally perceive faces as a whole (Bartlett & Searcy, 1993;

Rossion & Boremanse, 2008, Tanaka & Farah, 1993), and in an upright orientation (Rock,

1973); illusions may occur when we try to perceive inverted faces.

Rock in 1973 demonstrated that the perceived form depends on the orientation of a

stimulus in the world coordinates. The common view to see an object in its upright

orientation would render us difficulty to perceive its upside-down form. This inversion effect

is much larger for faces than for any other object categories, and this phenomenon was

known as the ‘Face Inversion Effect’ (Yin, 1969). 


   
Thatcher Illusion, which is one of the most powerful face inversion illusions in face

recognition, was introduced by Thompson in 1980. It was named because Margaret

Thatcher’s face was first used to demonstrate the effect. It was found that people would

perceive individual features on inverted face but hardly perceive the face as a whole. Thus

people were not surprise when shown an edited image with inverted eyes and mouth when

the image was inverted; however they found it odd once the edited picture with inverted eyes

and mouth is in an upright orientation. The Thatcher illusion explains the face inversion

effect and nonetheless, it also tells us some crucial ideas on how human processes face

recognition.


It was believed that faces are perceived both “featurally” and holistically. Thatcher

illusion indicated that when faces are inverted, it would be more difficult for us to interpret

the expression and identity. Therefore we will not find thatcherized faces (i.e. images of faces

with inverted eyes and mouths) look grotesque when they are inverted since we focus on

individual features rather than the faces holistically. Thatcherized images however would be

alarming when they are shown in normal orientation, in which people usually perceive faces

as a whole.

This paper will first focus on discussing the face inversion effect, and then illustrate the

demonstration and causes of Thatcher Illusion, and finally elaborate the explanation on how

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the Thatcher Illusion relates to face recognition processing.  

Face inversion effect


The face inversion effect was introduced by Yin in 1969 and was defined as the larger

decrease in face recognition performance than for other mono-oriented objects when they

are presented upside down. Since people are used to the way they perceive a form, for

example seeing faces in an upright orientation, recognition of an ...

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