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Does love make your pupils dilate?

The eyes' romantic depiction as the "windows to the soul" isn't just the stuff of whimsical verse. Sure, the word pupil comes from the Latin for "little doll," referencing how those storied orbs produce miniature, doll-like reflections of people in their sightline, much like shiny sunglasses lenses [source: Merriam-Webster]. But the vacillating openings at the center of our irises indeed mirror more than what's on the outside.

The mechanism of pupil constriction and dilation is regulated by the autonomic nervous system, which is also responsible for other uncontrollable reactions like goose bumps and heart rates. Inside the eyeball, the dilator and the sphincter muscles play the iris tissue like an accordion to the tune of light [source: Swaminathan]. Then again, the sun isn't the only thing orchestrating when the pupils open and shut. Humans' inborn fight or flight response, triggered by the parasympathetic nervous system -- a subset of the autonomic nervous system -- also manifests in our irises. When fear strikes, as Charles Darwin first proposed in the 1870s, the pupils expand to heightened attention and focus [source: Stern, Ray and Quigley]. About a century later, scientists discovered that pupils also pop when we experience emotions on the sunnier end of the spectrum.

In a 1965 Scientific American magazine article, psychologist Eckhard Hess described an intriguing experiment [source: Stern, Ray and Quigley]. While showing his research assistant James Polt a series of photographs, Hess tracked changes in the diameter of Polt's pupil size. Lo and behold, Polt's pupils enlarged most dramatically when a picture of a nude woman flashed before his eyes, leading Hess to hypothesize that sexual arousal stimulates the pupils [source: Andreassi]. Further experimentation found heterosexual people's pupils dilated when staring at opposite-sex nudes, whereas homosexual participants exhibited that pupillary response when looking at same-sex nudes, offering further confirmation of a link between sexual interest and dilation [source: Andreassi].

Additionally, the researchers noticed a compelling clue about how the eyes may influence physical attraction. Not only do pupils dilate in response to titillating material, but people also rate faces with saucer-like pupils as more attractive than those looking back with fuller irises [source: Murphy].

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How Pupils Advertise Attraction

Italian women in the Middle Ages were a step ahead of science. Recognizing the beauty endowed by wide-open pupils, they would dilate their own eyes with belladonna [source: Gowin]. (Incidentally, the word "belladonna" means "beautiful woman" in Italian.) Unfortunately, the plant secreted not only the chemical atropine, which draws back the irises, but also a toxin that would deteriorate these women's eyesight and possibly poison them [source: Swaminathan].

Although belladonna wasn't an optimal dilating agent, the come-hither effect of large pupils was a scientifically valid assumption. In 1965, pupillometry pioneer and psychologist Eckhardt Hess asked men to compare the attractiveness of images of women with average-sized pupils to drawings in which the women's pupil sizes were enhanced. Consistently, men ranked the doe-eyed gazes as prettier, since the subtle ocular opening unconsciously signals sexual attraction on the woman's part [source: Tombs and Silverman]. In response to attraction, the brain secretes norepinephrine, which then flexes the eyeball's dilator muscles [source: Murphy]. Therefore, men may unwittingly read pupil dilation as an advertisement of interest.

Studying women's preferences for male pupil sizes wasn't so predictable, however. A 2002 study at York University identified medium-sized pupils as most appealing to many female participants [source: Tombs and Silverman]. Whereas men seek out the maximum sexual attraction, as hinted at by women's fully dilated pupils, the same isn't true of women seeking men, probably because unbridled sexual attraction in males has greater chance of fostering overly aggressive or violent behavior [source: Tombs and Silverman]. Medium pupils, on the other hand, indicate interest but not blinding lust.

But, as implied earlier, that evolutionary principle doesn't hold true for all women all the time. Those looking for short-term mating options who tend to date "bad boys" may be more drawn to fully expanded pupils, research has affirmed [source: Tombs and Silverman]. Monthly menstrual cycles also appear to hold sway over female pupil preferences. During the follicular phase, which culminates with ovulation, desire for doe-eyes peaks [source: Caryl et al].

In other words, the more physiologically primed for sex they are, the more males and females both innately keep an eye out for dilated pupils. Given that evolutionary phenomenon, the eyes are less the windows to one's soul than the windows to his or her bedroom.

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Lots More Information

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Sources

  • Andresassi, John L. "Psychophysiology: human behavior and physiological responses." Psychology Press. 2000. (Jan. 31, 2012) http://books.google.com/books?id=FYFEwh2b-ZoC&dq=chapter+12+pupillary+response+and+behavior&source=gbs_navlinks_s
  • Caryl, Peter G. "Women's preference for male pupil size: Effects of conception risk, sociosexuality and relationship status." Personality and Individual Differences. March 2009. (Jan. 31, 2012) http://www.sciencedirect.com/science/article/pii/S0191886908004509
  • Gowin, Joshua. "Beauty Is in the Eye." Psychology Today. July 08, 2010. (Jan. 31, 2012) http://www.psychologytoday.com/blog/you-illuminated/201007/beauty-is-in-the-eye
  • Merriam-Webster. "Pupil." The Merriam-Webster New Book of Word Histories. Merriam-Webster, Inc. 1991. (Jan. 31, 2012) http://books.google.com/books?id=IrcZEZ1bOJsC&dq=pupils+latin+little+girl&source=gbs_navlinks_s
  • Miller, Allan S. and Kanazawa, Satoshi. "Ten Politically Incorrect Truths About Human Nature." Psychology Today. July 01, 2007. (Jan. 31, 2012) http://www.psychologytoday.com/articles/200706/ten-politically-incorrect-truths-about-human-nature
  • Murphy, Cheryl. "Learning the Look of Love: In Your Eyes, the Light the Heat." Scientific American. Nov. 01, 2011. (Jan. 31, 2012) http://blogs.scientificamerican.com/guest-blog/2011/11/01/learning-the-look-of-love-in-your-eyes-the-light-the-heat/
  • Stern, Robert Morris; Ray, William J.; and Quigley, Karen S. "Psychophysiological Recording." Oxford University Press. 2001. (Jan. 31, 2012) http://books.google.com/books?id=9WmvzrkZdv8C&dq=hess+attraction-dilation+hypothesis&source=gbs_navlinks_s
  • Swaminathan, Nikhil. "How did they find the chemical that dilates your pupils?" Scientific American. Feb. 25, 2008. (Jan. 31, 2012) http://www.scientificamerican.com/article.cfm?id=experts-chemical-pupil-dilate
  • Tombs, Selena and Silverman, Irwin. "Pupillometry: A sexual selection approach." Evolution and Human Behavior. April 23, 2004. (Jan. 31, 2012) http://boileddown.me/storage/pupil.pdf