< Gesichtserkennung auf den ersten Blick

Recognition at first sight

Max Planck scientists investigate the way faces are recognized


The Thatcher illusion. Graphics: Christoph Dahl / Max Planck Institute for Biological CyberneticsTübingen, June 24th, 2010. Each day, we meet a multitude of people: the nice waitress in the coffee shop around the corner, the bus driver, or the colleagues at the office. Without the ability to recognize faces at first sight, we would not be able to distinguish or identify these people. Monkeys also possess the ability to differentiate faces of group members efficiently by extracting the relevant information about the individual directly from the face. With the help of the so-called Thatcher illusion, scientists of the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, have examined how people and macaque monkeys recognize faces and how this information is processed by the brain. They found out that both species perceive the faces of their kin quickly and efficiently, whereas faces of the other species are processed in a different way.   


"From an early age on we are accustomed to the faces of other humans: a long nose, the curve of the lips or shape of the eyebrows. We learn to recognize the small differences which contribute to the overall, individual appearance", explains Christoph Dahl, researcher at the Max Planck Institute. “The situation is similar in monkeys. They learn to recognize the features of their conspecifics and can identity every group member quickly. In our study, we found that for humans as well as for macaque monkeys, this principle only works with individuals of their own kind", says Dahl. Even though the recognition of conspecific faces is achieved by means of so-called holistic processing, the separate parts such as mouth, nose and eyes as well as the facial proportions are still important. "Although we look at the eyes first, our neural functions still process the whole picture", Christoph Dahl describes the processing mechanisms behind the facial recognition.  

With the help of the Thatcher illusion the scientists have examined face processing in macaque monkeys and humans. Local changes in facial features are hardly noticeable when the whole face is upside down, but strikingly grotesque when the face is upright. "The faces in which the eyes and the mouth were rotated 180 degrees look grotesque - but only if we see them the right side up. Upside-down the differences between a normal face and a ‘thatcherized’ face are hardly recognizable", explains Christian Wallraven, one of the involved scientists. This striking effect can be explained by the lack of processing capabilities for locally rotated facial features when the face is turned upside down. The holistic processing mechanisms allow the recognition of fine changes in the arrangement of the separate facial parts. If the whole face is rotated 180 degrees, this ability is lost.  

Interestingly, the study found that the usual face processing mechanism not only are disrupted for inverted faces but also for faces of foreign species: the scientists discovered that the Thatcher illusion in macaque monkeys only works for the faces of their conspecifics, while they paid no special attention to the extremely grotesque human faces. Conversely, for humans the manipulated monkey faces remained inconspicuous. "It must have been of great advantage for us as well as for our evolutionary ancestors, the monkeys, to fine-tune recognition processing to faces of our species by developing similar holistic processing strategies," Wallraven sums up. Holistic processing therefore allows us to recognize our own kind at first sight.

Original publication:
Dahl C. D., Logothetis N. K., Bülthoff H. H, Wallraven C., The Thatcher illusion in humans and monkeys. Proc. R. Soc. B (2010) doi: 10.1098/rspb.2010.0438  

More Information:
Is this a stranger or an acquaintance?
Have We Met Before? - Patterns of Facial Recognition

Contact:

Dr. Christoph Dahl
Phone: +49 (0)7071 601-610
E-mail: christoph.dahl(at)tuebingen.mpg.de
 
Christian Wallraven
Phone: +49 (0)7071 601-1717
E-Mail: christian.wallraven(at)tuebingen.mpg.de  

Stephanie Bertenbreiter (Public Relations)
Phone: +49 (0)7071 601-472
E-mail: presse(at)tuebingen.mpg.de  

The Max Planck Institute for Biological Cybernetics works in the elucidation of cognitive processes. It employs about 325 people from more than 40 countries and is located at the Max Planck Campus in Tübingen, Germany. The Max Planck Institute for Biological Cybernetics is one of 80 research institutes that the Max Planck Society for the Advancement of Science maintains in Germany.


The Thatcher illusion: Local changes in facial features are hardly noticeable when the whole face is inverted (rotated 180°), but strikingly grotesque when the face is upright. In the Diagram two faces of an individual are presented. One picture is normal, while the seems grotesque by an upright presentation, but not if the faces are rotated 180°. Moreover, this illusion disappears if faces of another species are manipulated in the same way (see monkey faces). Graphics: Christoph Dahl / Max Planck Institute for Biological Cybernetics

The Thatcher illusion: Local changes in facial features are hardly noticeable when the whole face is inverted (rotated 180°), but strikingly grotesque when the face is upright. In the Diagram two faces of an individual are presented. One picture is normal, while the seems grotesque by an upright presentation, but not if the faces are rotated 180°. Moreover, this illusion disappears if faces of another species are manipulated in the same way (see monkey faces). Graphics: Christoph Dahl / Max Planck Institute for Biological Cybernetics