A new optical illusion may trick most of us into perceiving an expanding black hole, according to new research reports.
The image is completely static, but the researchers say it gives people “a growing sense of darkness, as if they were entering a space devoid of light.”
The illusory forward motion is probably our mind’s way of preparing us for a change of scenery. By predicting a shift from bright to dark, our visual system can adapt much faster to potentially perilous conditions, the researchers suggest.
“Just as glare can dazzle, being in darkness is likely risky when navigating the dark environment,” the authors write in their new paper.
“Although, as in any illusion, this expanding virtual darkness comes at the expense of truthfulness, since the observer is neither advancing nor entering dark space, such a cost is likely to be less severe than s ‘there were no corrections when an observer actually stepped into a dark space.
The first study to analyze this optical illusion explored how the color of the hole and surrounding dots affect our mental and physiological responses.
To do this, a group of 50 participants with normal vision were presented with “expanding hole” images of different colors on a screen. In the series, they were also shown blurred versions of the illusion with no discernible pattern of light or color.
The illusion of forward movement was more effective when the hole was black. When the hole was of this shadow, 86% of participants felt that darkness was heading their way.
Tracking the participants’ eye movements revealed that their pupils unconsciously dilated at the sight of the black hole.
During this time, if the hole was white, their pupils contracted only slightly.
“Here we show, based on the new “expanding hole” illusion, that the pupil reacts to the way we perceive light – even if this “light” is imaginary as in the illusion – and not only to the amount of light energy that actually enters the eye,” says psychologist Bruno Laeng from the University of Oslo in Norway.
“The expanding hole illusion causes a corresponding dilation of the pupil, as would occur if the darkness really increased.”
The authors do not know why 14% of the group did not perceive illusory expansion when the hole was black. But even among those who perceived the illusion, the strength of the sensation varied.
The people who felt the illusion the most were also those whose pupil diameter changed the most.
“Our results show that the pupil dilation or contraction reflex is not a closed-loop mechanism, like a photocell opening a door, impervious to any information other than the actual amount of light stimulating the photoreceptor,” says Laeng. .
“On the contrary, the eye adapts to perceived and even imagined light, not simply to physical energy.”
The authors have a hypothesis as to why the eye can do this. When the central region is black, our pupils are probably preparing us for a change in luminance in the near future.
Instead of seeing the information that is presented directly in front of us, the visual neural network predicts how that information will change in the future, generating “an illusory ‘outward expansion’ of the central ‘hole’ region”.
If the brain did not, it would have taken milliseconds longer for the new visual information to reach higher brain processes. If it took our pupils that long to dilate, we might not be able to navigate the dark as efficiently.
The authors now want to test whether other animals are also fooled by the illusion to better understand how the human visual system evolved.
The study was published in Frontiers of Human Neuroscience.