We investigated whether the scientific data supports the common belief that a person’s pupils immediately dilate when looking at an object of adoration.
The human pupil, a round hole in the iris of the eye, changes size due to various branches of the autonomic nervous system. The sympathetic fibers, which originate from the spinal cord from the I-II thoracic to the II-IV lumbar segments, control the dilator muscle responsible for pupil expansion. This process typically occurs reflexively in response to external stimuli, such as a small amount of light falling on the retina, causing the pupil to expand after approximately 5 seconds. This reaction can increase the pupil diameter up to 8 mm. However, pupil dilation is not solely caused by changes in lighting. Pathologies and injuries of the eye or brain, reaction to pain, the use of certain drugs, including antidepressants, antihistamines, or atropine drops for eye examination, the use of recreational drugs or alcohol, and sexual arousal, can also affect pupil dilation.
In 1959, American psychologist Eckhard Hess became the first person to track the pupil’s response to an attractive object. He recorded the size of his assistant’s pupils while the assistant viewed various pictures. The greatest pupil dilation occurred when viewing an image of a pin-up girl, a visually attractive image created for mass reproduction and informal distribution. However, Hess only observed the response and did not conduct any additional experiments.
In 2007, the Department of Psychology at the University of Tromsø in Norway conducted a study on the connection between looking at an object of love and pupil dilation. Fourteen women were invited to view photographs of different men on a computer screen, including pictures of their loved ones, during three different phases of their menstrual cycle: the follicular phase (before the release of the egg), the ovulatory phase (during the release of the egg), and the luteal phase (after the release of the egg). The researchers used an infrared eye-tracking device to measure the size of the participants’ pupils. Half of the participants were taking oral contraceptives. The study found that only during the ovulatory phase, which lasts from 16 to 32 hours, did the participants’ pupils noticeably dilate when looking at their partners. This effect was observed only in women who were not taking hormonal medications.
In 2012, scientists turned their attention to male pupil reactions. A group of researchers from the Department of Human Development at Cornell University (USA) conducted a similar experiment in which they invited 325 men and women to participate. Before the experiment began, participants were asked to identify themselves as one of seven categories of sexual orientation on the Kinsey scale: completely heterosexual, predominantly heterosexual, bisexual with a predominance of heterosexuality, completely bisexual, bisexual with a predominance of homosexuality, predominantly homosexual, or completely homosexual. Each participant was then placed in a room with a monitor displaying a one-minute neutral video of a landscape, followed by a stimulating video in random order – a 30-second clip of a naked masturbating man or woman. The researchers measured the size of the volunteers’ pupils and asked them three questions about the person depicted: how physically attractive they found them, how arousing they found them, and how much they would like to date that person. After answering the questions, the participants were shown the neutral and stimulating videos again.
Scientists observed that both men and women experience pupil dilation while watching erotic videos. They also found that the degree of dilation generally corresponds with the participant’s declared sexual orientation, with bisexual men and heterosexual women showing the strongest reaction to a sexually stimulating stimulus. The researchers attribute the pupil dilation response to the release of dopamine and oxytocin, which are actively produced during preparation for intimacy.
Dutch scientists conducted a study in 2018 to investigate the relationship between pupil dilation and the level of trust in an interlocutor, and found that emotion-induced pupil dilation is not always exclusively related to sexual attraction. Participants watched short videos of people’s eyes, with varying pupil sizes, while being scanned using MRI. The study found that in response to an image of a person with dilated pupils, the brain areas responsible for trust were activated. Additionally, in real-life interactions, the pupils of interacting partners usually expand and contract synchronously, which can be interpreted as a demonstration of mutual trust.
The sympathetic fibers, which are a part of the sympathetic nervous system, play a primary role in the “emotional” dilation of the pupil on a physiological level. When the body experiences stress reactions or the release of certain hormones, these fibers are activated. When a person feels sympathy or sexual attraction towards someone, they experience a range of emotions from a psychological perspective, and physiologically, they are influenced by several hormones: adrenaline, oxytocin, and dopamine. These hormones cause the pupils to dilate when a person looks at a partner or an attractive person.
When a person looks at someone they find sexually attractive, their pupils do tend to dilate more frequently. However, it is crucial to note that this is specifically related to sexual arousal. It is challenging to connect pupil size to the feeling of being in love, particularly in long-term relationships, except for women who are not using oral contraceptives and only during a brief phase of the menstrual cycle (16-32 hours). It is essential to keep in mind that dilated pupils of a conversation partner do not always indicate romantic intentions. The size of the pupils can change due to lighting, medication intake, and individual health characteristics, and the level of trust between participants can also influence the dilation. Moreover, it is not possible to conclude that the absence of such a reaction indicates that the person is not attracted to you. Not everyone exhibits this reaction even when looking at their partner.
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