Researchers have discovered an optical illusion that can deceive the brain and dilate pupils in humans.
If true, this means that you, like most people, have a brain that may even think you are entering a tunnel or falling into a deep hole, in order to adjust your eyes accordingly.
When you view this image, do you see the dark spot in the center appearing to expand?
As part of a study led by Professor Bruno Laeng from the University of Oslo, a total of 50 adult participants with normal vision (31 females, 19 males) were asked to look at the optical illusion “expanding hole”.
These individuals were shown 26 versions of this illusion, featuring different color combinations and dots. The simplest combination, displayed above—with a black spot and dots on a white background—generated the strongest response, with about 86% of participants reporting that they perceived the hole was expanding.
The response occurred regardless of the observer’s location, even if they were looking at the illusion in a well-lit room where pupil adjustment was unnecessary. The researchers believe that this illusion demonstrates how our brains compensate for the processing time needed to visually perceive the world around us in real-time, and that certain involuntary reflexes are not necessarily controlled by physical reality.
Asahi Illusion.
Another image illustrating this phenomenon is the “Asahi” illusion by Akiyoshi Kitaoka regarding brightness. Our brains perceive the white in the center of the illusion as much brighter than the white surrounding it, while in reality, both have the same RGB values and the brightness of the image is entirely uniform. Researchers also found that the pupils of subjects would constrict when observing this illusion, even though the lighting in their physical environment remained unchanged.
It is believed that this illusion triggers a response because the brain is trying to protect the retina from sudden bright light, which not only can temporarily impair our vision but also has the potential to harm the retina. The center of the Asahi illusion is not brighter than the surrounding white areas, but the arrangement of shapes and the gradient from dark to light creates a perceptual correlation with walking through a dense forest where sunlight occasionally breaks through the leaves. Although the observer is not actually at risk of looking at the sun, this is something that the brain predicts will occur, and the pupils respond accordingly.
In the case of the deep hole illusion, researchers found that the pupils of observers dilate when looking at the image, as their brains perceive that they are moving towards a space significantly darker than their current environment. The brain compensates by preparing the eyes to gather more light. The illusion of the deep hole appears to move forward partly due to the blurred edges of the black spot, creating the appearance of blurry motion. This is why observers perceive the dark spot as growing, similar to what one would see when approaching a dark cave.
However, a question arises: at any given moment, what we think we are actually seeing may just be an educated guess that our brains are making about what we might see in 100 milliseconds from now. Moreover, those educated guesses may unintentionally trigger physical responses. Another intriguing aspect is that only about 86% of the participants in the study exhibited pupil dilation responses, while the remaining 14% did not. What makes those individuals different, and does that put them at a disadvantage when navigating the world?
The researchers state that this discovery could help them gain a better understanding of the ways in which the human visual system perceives the surrounding world.
The study has been published in the journal Frontiers in Human Neuroscience.
