According to a case report, a German student aged 23 can shrink or enlarge his pupils upon request. This feat was previously believed impossible.
The eye's two tiny muscles that oppose each other act as puppeteers for each pupil (the dark central part of the eye). They dilate or enlarge the pupils in dark environments to allow in more light, and then constrict them in bright environments to reduce the light coming in.
This was believed to be an automatic process. When you walk into a darkened room, your pupils don't need to tell you to change their size. Other factors such as increased arousal can cause pupils to change their size.
It was known in the past that people could alter their pupil size by using indirect methods.
Researchers knew, for example, that the Sun can constrict pupils. However, the brain's ability to think about it, or even mentally calculate something, could cause them to dilate, Christoph Strauch, senior author and assistant professor at Utrecht University's experimental psychology department.
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However, no one believed it possible to alter pupil size by controlling it directly like a muscle until a student at Ulm University in Germany came across Strauch after he had taken one of his courses. Strauch was previously a doctoral student in psychology at Ulm University.
He was around 15-16 years old when the young man, identified by his initials in the case report, D.W., realized that he could alter the size of his pupils.
Strauch and his Ulm University colleagues were told by D.W. that he could 'tremble with my eyes' and that he had noticed that my pupils had become smaller. D.W. did not notice this until he was playing computer games for long periods.
D.W.'s eyes at different stages of dilation. (Eberhardt et al., IJP, 2021)
D.W. explained to the researchers that constricting the pupil felt like gripping, tensing a thing; making it bigger feels like fully releasing, relaxing your eye.
He would initially focus on an object in front or behind his pupil to change the size of his pupil. But, with practice, he was able to do this without having to concentrate on objects. According to him, he can change his pupil size by focusing on his eyes. He doesn't need to think about a bright or dark environment.
Strauch explained to Live Science that D.W. is different than other people who can change the size of their pupils. It's also amazing that he can feel the muscles of the pupils "is astounding, as it was thought impossible".
This is rare!
The researchers confirmed that D.W. had this ability through a series of tests. They also found no evidence that he was altering the size of his pupils in any way.
One test was to measure the electrical properties of skin. Researchers applied voltage to determine if he was stimulated by mental effort. This could have indirectly increased his pupil size. He wasn't.
D.W. was able to dilate his pupils to 0.09 inches (2.24 millimeters) and to constrict them to 0.03 inch (0.88mm) without using any indirect methods.
Furthermore, even at the nearest point where an object is visible in focus, the pupil can still be seen in focus even if it is not at its maximum (imagine holding a pencil up in front of your eyes, moving it closer to your face, and stopping just before it blurries). D.W. could also voluntarily constrict his pupil further.
D.W. was able to see objects more clearly than ever before by doing this.
The researchers used functional magnetic resonance imaging (fMRI) to scan the brain and found that certain brain regions were activated more frequently in the areas of volition. This is the ability to make decisions and act freely.
Although it is not possible to prove that D.W. was controlling his pupils directly, the researchers did find no evidence of him using indirect strategies.
Is it possible for others to learn this skill? Possibly, Strauch said. The team might be able to learn more from people with this ability by researching them.
Strauch said that researchers may be able to understand and describe the phenomenon if they study more people who might have it.
He said that "quite a few people have reached out to me who think they might be capable of doing the same thing, which is really cool."
These findings were published online in the International Journal of Psychophysiology on August 12, 2012.
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Live Science originally published this article. You can read the original article here.