Summary: The highly dynamic new expanding hole optical illusion can be seen by 86% of people. The illusion is so good at tricking the brain that it causes the pupils to dilate, as if we were entering a dark room.
Look at this picture. Do you perceive the central black hole expanding as if you are moving into a dark environment or falling into a hole?
You are not alone: a new study shows that this scientifically new illusion of the “expanding hole” is perceived by approx. 86% of people.
dr Bruno Laeng, professor at the University of Oslo’s Department of Psychology and first author of the study, said: “The ‘expanding hole’ is a highly dynamic illusion: the circular spot or shadow gradient of the central black hole evokes a distinct impression of optical flow, as if the viewer were to enter a hole or tunnel.”
Optical illusions are not a gimmick without scientific interest: researchers in the field of psychosociology study them to better understand the complex processes our visual system uses to anticipate and make sense of the visual world – in a far more circumstantial way than a photometer device that simply registers the amount of photonic energy.
In the new study, published in Frontiers in human neuroscienceLaeng and colleagues show that the expanding hole illusion is so good at fooling our brain that it even triggers a dilation reflex of the pupils to let in more light, just like what would happen if we were really moving into a dark area .
The pupillary reflex depends on perception, not necessarily on reality
“Here we use the new ‘expansion hole’ illusion to show that the pupil reacts to how we perceive light – even if this ‘light’ is imaginary as in the illusion – and not just to the light energy that actually enters the eye.
The illusion of the expanding hole results in a corresponding dilation of the pupil, as would happen if darkness really increased,” Laeng said.
Laeng and colleagues studied how the color of the hole (besides black: blue, cyan, green, magenta, red, yellow or white) and the surrounding dots affect how strongly we react mentally and physiologically to the illusion.
On a screen, they presented variations of the “stretchy hole” image to 50 women and men with normal vision and asked them to subjectively rate how strongly they perceived the illusion.
As the participants looked at the image, the researchers measured their eye movements and the unconscious constrictions and dilations of their pupils.
As controls, participants were shown “scrambled” versions of the expanding hole pattern, with equal luminance and colors but without any pattern.
The illusion appeared most effective when the hole was black. 14% of the participants did not perceive any illusory expansion when the hole was black, while 20% did not when the hole was colored. For those who perceived expansion, the subjective strength of the illusion differed markedly.
The researchers also found that black holes promoted strong reflex dilations in the participants’ pupils, while colored holes caused their pupils to contract. With black holes, but not with colored holes, the stronger individual participants rated their subjective perception of the illusion, the more their pupil diameter tended to change.
minority not susceptible
Researchers don’t yet know why a minority seem unresponsive to the “expanding hole” illusion. Nor do they know if other vertebrate species, or even camera-eyed invertebrates like octopuses, could perceive the same illusion as we do.
“Our results show that the pupil dilation or contraction reflex is not a closed mechanism, like a photocell opening a door, opaque to information other than the actual amount of light stimulating the photoreceptor. Rather, the eye adapts to perceived and even imagined light, not just physical energy. Future studies could uncover other types of physiological or physical changes that may shed light on how illusions work,” Laeng concluded.
About this news from research on visual neuroscience and optical illusion
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Picture: The image is attributed to Laeng, Nabil and Kitaoka
Original research: Open access.
“The eye pupil adapts to illusory dilating holes” by Laeng, Nabil and Kitaoka. Frontiers in human neuroscience
The pupil of the eye adapts to illusory dilating holes
Some static patterns evoke the perception of an illusory expanding central region or “hole”.
We asked observers to rate the magnitude of black hole illusory movement, or expansion, and they predicted the degree of pupil dilation measured with an eye tracker.
On the other hand, if the “holes” were colored (also white), i.e. emitted light, these patterns narrowed the pupils, but the subjective dimensions were also weaker in comparison to the black holes.
The rates of change in pupil diameters were significantly associated with the illusory motion phenomenology only for the black holes.
These findings can be explained within a present-time perception report on visual illusions, in which both illusory movement and pupil adjustments represent compensatory mechanisms for next-moment perception, based on shared experiences with the ecological laws of light.