Atlanta, GA, USA. The human senses comprise a facial recognition system that predates computer applications by millions of years. This is a critical human social skill which enables us to form relationships and interact appropriately with others.

Our facial recognition is so good, we can penetrate disguises and identify the all but the most expert of imposters with a high degree of reliability. Research at the Yerkes National Primate Research Center at Emory University indicates the ability to perform this skill probably evolved some 30 million or more years ago in an ancestor common to humans and rhesus monkeys.

A study in Current Biology demonstrates for the first time that rhesus monkeys and humans share a specific perceptual mechanism, called configural perception, for discriminating among the numerous faces they encounter on a daily basis.

"Because faces share so many features in common – eyes, nose, mouth, etc. – the simple detection of the collection of these features alone would not permit us to tell many faces apart," Dr. Hampton noted. "It's our ability to perceive small changes in the relations among the features that enables us to distinguish thousands of faces and recognize those we know," he explained.

Hampton and his research team used a perceptual illusion called the Thatcher Effect. The phenomenon occurs when it becomes difficult to detect local feature changes. In this case, an upright face is turned upside down.

The effect is named after British former Prime Minister Margaret Thatcher (the subject of the most famous demonstration) by Peter Thompson at the University of York in 1980.

The distorted view of an upside down face is thought due to psychological processes that have evolved to specifically deal with upright faces. The faces seem unique despite the fact that they are very similar because of our sensitivity to the configuration individual features on the face (e.g.,, eyes, nose and mouth). Once upside down, even minor differences tend to escape detection.

To determine if rhesus monkeys use configural perception to recognize other monkeys, researchers presented images of six different monkeys to four 4-year-old rhesus macaque monkeys raised for two to three years in large social groups at the Yerkes Research Center.

The Thatcher Effect. Why does this image appear normal when viewed upside down, but clearly shows that it is distorted when right-side up? It is a phenomenon known as the Thatcher effect.

Click Pic for Details

The researchers "thatcherized" the images of faces by positioning the eyes and mouths upside down relative to the rest of each face. The researchers presented monkeys with normal images of each face upside down and right side up until the monkeys were bored and ceased looking at the pictures.

The monkeys then viewed the thatcherized faces.

In the upright position, the monkeys were surprised by the distorted features and began looking at the pictures again.

In contrast, when the faces were upside down, they were not at all surprised and treated the faces as if nothing had been done to them.

This is similar to the human response to the Thatcher Effect, which shows that when the eyes and mouth are rotated and distorted. 

Humans surprisingly process the upside-down version of the image more as a collection of features and with less emphasis on the relations among the features.

As a result, the face appears fairly normal despite being thatcherized. However, when viewed right side up, humans say the image looks awkward or grotesque, demonstrating they clearly see the eyes and mouth have been rotated.

"This study advances our understanding of social processes critical for a healthy and successful social life in primates. Early primates apparently solved the problem of recognizing each others' faces in this way well before humans arrived on the planet," Dr. Hampton concluded.

Some people who have experienced a brain injury or illness develop a disorder where face processing is impaired (prosopagnosia. Studies of such conditions confirm the existence of processes that analyse facial structures and suggest a basis for measuring the degree of disability imposed by varying levels of damage severity.

CitationThatcher Effect in Monkeys Demonstrates Conservation of Face Perception across Primates. Ikuma Adachi, Dina P. Chou, Robert R. Hampton. Current Biology (25 June 2009). doi: 10.1016/j.cub.2009.05.067

Summary

Accurate recognition of individuals is a foundation of social cognition. The remarkable ability of humans to distinguish among thousands of similar faces depends on sensitivity to unique configurations of facial features, including subtle differences in the relative placement of the eyes and mouth. Determining whether similar perceptual processes underlie individual recognition in nonhuman primates is important for both the study of cognitive evolution and the appropriate use of primate models in social cognition research. In humans, some of the best evidence for a keen sensitivity to the configuration of features in faces comes from the Thatcher effect. This effect shows that it is difficult to detect changes in the orientation of the eyes and mouth in an image of an inverted face, even though identical changes are unmistakable in an upright face. Here, we demonstrate for the first time that a nonhuman primate species also exhibits the Thatcher effect. This direct evidence of configural face perception in monkeys, collected under testing conditions that closely parallel those used with humans, indicates that perceptual mechanisms for individual recognition have been conserved through primate cognitive evolution.

Keywords: sysneuro.

The TS-Si News Service is a collaborative effort by TS-Si.org editors, contributors, and corresponding institutions. Sources can include the cited individuals and organizations, as well as TS-Si.org staff contributions. Articles and news reports do not necessarily convey official positions of TS-Si, its partners, or affiliates. We welcome your comments. Use the form below to leave a public comment or send private correspondence via the TS-Si Contact Page. We will not divulge any personal details or place you on a mailing list without your permission.


TS-Si is dedicated to the acceptance, medical treatment, and legal protection of individuals correcting the misalignment of their brains and their anatomical sex, while supporting their transition into society as hormonally reconstituted and surgically corrected citizens.

Tweet

Comments (0)

Subscribe to this comment's feed

Show/hide comments

Show/hide comment form

Name

Email

Website

Title

Comment

smaller | bigger

I have read and agree to the Terms of Usage.

Add Comment