Smile

A woman smiling.

A smile is a facial expression formed by flexing the muscles near both ends of the mouth ^[1]. The smile can also be found around the eyes (See 'Duchenne smile' below). Among humans, it is customarily an expression denoting pleasure, happiness, or amusement, but can also be an involuntary expression of anxiety, in which case it is known as a grimace. Cross-cultural studies have shown that smiling is a means of communicating emotions throughout the world.^[2] But there are large difference between different cultures.^[3] A smile can be spontaneous or artificial (when people feel obliged to smile). Happiness is most often the motivating cause of a smile. Among animals, the exposure of teeth, which may bear a resemblance to a smile, is often used as a threat or warning display—known as a snarl—or a sign of submission. In chimpanzees, it can also be a sign of fear. The study of smiles is a part of gelotology, psychology, and linguistics, comprising various theories of affect, humor, and laughter.^[4]

Dimples

A man smiling, with dimples.

Cheek dimples are visible indentations of the skin, caused by underlying flesh, which form on some people's cheeks, especially when they smile. Dimples are genetically inherited and are a dominant trait.^[5] Dimples on each cheek are a relatively common occurrence for people with dimples. A rarer form is the single dimple, which occurs on one side of the face only. Anatomically, dimples may be caused by variations in the structure of the facial muscle known as zygomaticus major. Specifically, the presence of a double or bifid zygomaticus major muscle may explain the formation of cheek dimples.^[6] This bifid variation of the muscle originates as a single structure from the zygomatic bone. As it travels anteriorly, it then divides with a superior bundle that inserts in the typical position above the corner of the mouth. An inferior bundle inserts below the corner of the mouth.

Duchenne smile

Although many different types of smiles have been identified and studied, researchers (e.g. Freitas-Magalhaes) have devoted particular attention to an anatomical distinction first recognized by French physician Guillaume Duchenne. While conducting research on the physiology of facial expressions in the mid-nineteenth century, Duchenne identified two distinct types of smiles. A Duchenne smile involves contraction of both the zygomatic major muscle (which raises the corners of the mouth) and the orbicularis oculi muscle (which raises the cheeks and forms crow's feet around the eyes). A non-Duchenne smile involves only the zygomatic major muscle.^[7] Many researchers believe that Duchenne smiles indicate genuine spontaneous emotions since most people cannot voluntarily contract the outer portion of the orbicularis oculi muscle.^[8]

See also

• Emoticon
• Emotion
• Emotional labor
• Facial Action Coding System
• Frown
• Facial expression
• Laughter
• Smiley
• Social psychology

References

1. ↑ Freitas-Magalhães, A., & Castro, E. (2009). The Neuropsychophysiological Construction of the Human Smile. In A. Freitas-Magalhães (Ed.), Emotional Expression: The Brain and The Face (pp.1-18). Porto: University Fernando Pessoa Press. ISBN 978-989-643-034-4..
2. ↑ Carroll E. Izard (1971). The Face of Emotion, New York: Appleton-Century-Croft.
3. ↑ http://www.articlealley.com/article_112402_35.html
4. ↑ Freitas-Magalhães, A. (2006). The Psychology of Human Smile. Oporto: University Fernando Pessoa Press.
5. ↑ Singapore Science Centre: ScienceNet|Life Sciences|Genetics/ Reproduction
6. ↑ http://www3.interscience.wiley.com/cgi-bin/abstract/78395/
7. ↑ Duchenne, Guillaume (1990). The Mechanism of Human Facial Expression. New York: Cambridge University Press. (Original work published 1862).
8. ↑ Ekman, P., Friesen, W. V., and O'Sullivan, M. (1988). "Smiles when lying". Journal of Personality and Social Psychology, 54, pp. 414–420.

Further reading

• Conniff, R. (2007). What's behind a smile? Smithsonian Magazine, 38,46-53.
• Miller, Professor George A., et al. Overview for "smile." Retrieved 12 December 2003 from this page.
• Ottenheimer, H.J. (2006). The anthropology of language: An introduction to linguistic anthropology. Belmont, CA: Thomson Wadsworh.
• Ekman, P., Davidson, R.J., & Friesen, W.V. (1990). The Duchenne smile: Emotional expression and brain psysiology II. Journal of Personality and Social Psychology, 58, 342-353. Cited in: Russell and Fernandez-Dols, eds. (1997).
• Russell and Fernandez-Dols, eds. (1997). The Psychology of Facial Expression. Cambridge. ISBN 0521587964.
• Messinger, D. & Fogel, A. (2007). The interactive development of social smiling. In Robert Kail (ed.), Advances in Child Development and Behavior, 35, 327-366. Oxford: Elsevier. Retrieved 25 June 2010 from [1]

External links

• BBC News: Scanner shows unborn babies smile