Voluntary control over the autonomic nervous system is a superpower beyond the reach of most mere humans, yet a 23-year-old man from Germany appears to have acquired this remarkable ability. According to a case report in the International Journal of Psychophysiology, the man – known only as D.W – can dilate and constrict his pupils at will, thus achieving something that had been deemed scientifically impossible.
Normally, changes in pupil size occur automatically in response to fluctuations in light or as a result of arousal. As with other reflex actions, this process is entirely independent of conscious control, and can’t be manipulated through thought.
However, the study authors report that D.W is able to expand his pupils by up to 0.8 millimeters and contract them by 2.4 millimeters on command, and does so by “feeling and activating the pupillary musculature directly.” Speaking to Live Science, study author Christoph Strauch explained that this ability "is astonishing, as it was thought to be impossible."
In their write-up, the researchers explain that D.W first became aware of his unusual ability at the age of 16, when he tried to “relax” his eyeballs after a lengthy computer gaming session. A friend noticed that this caused the pupil of his left eye to become smaller than that of his right eye, and over the past seven years D.W has honed his technique.
The study authors explain that some people can alter their pupil size via “indirect methods” such as thinking about light or dark, yet after conducting a number of tests they conclude that D.W employs none of these, and is instead able to directly control the sphincter muscle in his eyes.
For example, intense mental concentration is known to produce an expansion of the pupil. However, previous research has shown that the most strenuous mental tasks only produce a maximum dilation of 0.5 millimeters, yet D.W is able to expand his pupils by considerably more than this, and demonstrated the ability to do so while at ease and chatting with the researchers. Furthermore, measurements of the electrical conductance of his skin suggested an absence of mental effort or arousal.
Shifting focus between near and far objects – a process known as accommodation – is another indirect method by which pupil size can be manipulated, yet eye-tracking tests confirmed that D.W used no such trick when adjusting his ocular openings. Amazingly, he was even able to constrict his pupils beyond the maximum degree typically observed when focusing on near objects, allowing him to improve his visual acuity and decrease the distance at which he was able to sharply focus.
Using functional magnetic resonance imaging (fMRI) to scan D.W’s brain while he adjusted his pupils, the study authors noted increased activity in the prefrontal cortex and adjacent motor areas, indicating voluntary muscle movement.
While this is the first recorded example of an individual deliberately controlling this particular reflex, Strauch says he has been contacted by several more people claiming to possess the same ability, and hopes to study the phenomenon in a wider subset of people in order to better understand it.