Pupillometry: How the Eye’s Pupil Size Reveals More Than Just Emotions

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Pupillometry: How the Eye’s Pupil Size Reveals More Than Just Emotions

dilation or constricting of pupils is not only caused by the amount of light or attraction but also several other factors/ Photo By Przemyslaw Koch via 123RF


The pupil, which is defined by Science Daily as “an opening in the middle of an iris”, used to be only known to dilate and constrict depending on the presence or absence of light. Later, its dilation was discovered to be a sign of attraction or interest towards a person or object. Usually, the dilation of a person’s pupils was mostly associated with falling in love.

Recent studies have shown that the dilation or constricting of pupils is not only caused by the amount of light or attraction but also several other factors. For example, it may happen when women are looking at baby photos or when a hungry person looks at an appetizing meal.

What Is Pupillary Reflex?

Pupillary reflex is what happens when the pupil size increases or decreases because of the involuntary contraction and dilation of the iris. The eye does this to be able to regulate how much light gets in.

What is Pupillometrics?

The Body Language Expert describes pupillometrics as the study of the pupil size to determine a person’s emotion. In 1975, Eckhard Hess, a biopsychologist from the University of Chicago, established this field of study. He said that one evening, while being in bed next to his wife, he was leafing through a book with “strikingly beautiful" animal pictures. His wife had noticed the largeness of his pupils and told him that maybe the light was too dim. As a response, he told her that there was plenty of light in the room. Curious about this phenomenon, he decided to investigate how pupils dilate even with the abundance of light.

The day after that, he decided to make his lab assistant, James Polt, the first subject of his study. He showed him various pictures of landscapes and a photo of a pin-up girl. He held the pictures up to his head so that he would not be able to see the photos. Upon flashing the pin-up girl picture, he noticed that Polt’s eyes dilated. After this experiment, the two researchers started a deeper exploration on pupillometrics.

What Does Pupil Dilation Indicate?

Pupil diliation and contractions are shown to be indicators not only of emotions but also a person's thinking skills, focus and if they are going to make a decision. These are what pupil sizes indicate:

Fear or surprise

According to The Body Language Expert, the body’s natural adrenaline response or fight or flight mode, which is caused by triggering the autonomic nervous system’s sympathetic branch, can make the pupils dilate. Conversely, the pupils contracts when the body is in the relax or digest mode, which is caused by the stimulation of the parasympathetic system.

Sexual  interest

When an individual deems someone attractive, their pupils tend to increase in size. This is also sometimes called “bedroom eyes”  due to its association with sexual attraction. As a result, dilated pupils are also perceived to be appealing. This was shown by the studies conducted by Hess and his colleagues on men, women and homosexual men.

Researchers from the University of Edinburgh also discovered that ovulating women preferred pictures of men with large pupils over those with medium-sized or small pupils. They concluded that women who were starting their menstrual cycle link the dilation of pupils to sexual interest. In contrast to this, when someone gets turned off by an individual, their pupils constrict.


pupillometrics as the study of the pupil size to determine a person’s emotion/ Photo By Ghenadii Boiko via 123RF



Large pupils indicate that an individual likes what they are seeing. When someone looks at a person or object they love, this makes their pupils grow in size.

How hard a task is

Daniel Kahneman, a Princeton University psychologist says that pupils indicate how much mental effort is exerted in a very precise way.  This was revealed after he made participants both recite and recall a series of seven digits. When numbers were shown, he observed how their pupils gradually and steadily increased.  In a similar manner, when the subjects were told to recall numbers from their memory, their pupils gradually decreased.

In another research he conducted, he made the participants answer multiplication problems.  Kahneman said that he could tell if a person had given up on answering a multiplication problem by watching the contraction of their pupil.

Another study also reinforces Kahneman’s concept. The research showed that when smart individuals or those who scored higher on Scholastic Aptitude tests, are assigned to do cognitive tasks, their pupils dilated less than those who had lower scores.

A person’s decision timing

In 2010, Wolfgang Einhauser-Treyer, a neurophysicist, found in his study that pupil sizes are related to an individual’s decision timing. In his experiment, he asked participants to press a button every ten seconds. A second before they would be pressing the button, he noticed how their pupils would dilate.


When an individual looks at an object from afar, their objects dilate. On the other hand, when a person looks at a nearby object, their pupils contract.


pupillometry has been contributed much to psychology studies despite its limitations/ Photo By Robert Przybysz via 123RF


The Future of Pupillometry

Since the discovery of pupillometry, many people have taken an interest on how it can be used for business, dating and in the military. A study investigated how it could help a person determine another individual’s motives and feelings. Another research investigated if it could help classify sexual orientation. In the military, a study was carried out to see if it could help detect homosexuality in the civil service employees as an attempt to eliminate gays and lesbians among them. Still, another research was conducted to see if the dilation of pupils could indicate a consumer’s interest in a TV advertisement. However, all these studies failed.

Pupillometry has been contributed much to psychology studies despite its limitations, Steinhauer, a psychology researcher says. He attributes it to the eyes being observable and them being able to give a sign of a person’s sensitive emotional, sensory, and cognitive response.

Indeed, pupillometry has helped in examining  many psychological conditions. It has been used to determine if a person has schizophrenia, if an individual is introverted, if they have racial bias, if they can be diagnosed with autism or depression, if a person is sexually interested, and to be able to identify if a person has good moral judgment.



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