Nor do they know whether other vertebrate species, or even nonvertebrate animals with camera eyes such as octopuses, might perceive the same illusion as we do. The researchers don’t yet know why a minority seem unsusceptible to the ‘expanding hole’ illusion. For black holes, but not for colored holes, the stronger individual participants subjectively rated their perception of the illusion, the more their pupil diameter tended to change. The researchers also found that black holes promoted strong reflex dilations of the participants’ pupils, while colored holes prompted their pupils to constrict. Among those who did perceive an expansion, the subjective strength of the illusion differed markedly. 14% of participants didn’t perceive any illusory expansion when the hole was black, while 20% didn’t if the hole was in color. The illusion appeared most effective when the hole was black. As controls, the participants were shown ‘scrambled’ versions of the expanding hole image, with equal luminance and colors, but without any pattern.
While participants gazed at the image, the researchers measured their eye movements and their pupils’ unconscious constrictions and dilations. On a screen they presented variations of the ‘expanding hole’ image to 50 women and men with normal vision, asking them to rate subjectively how strongly they perceived the illusion. Laeng and colleagues explored how the color of the hole (besides black: blue, cyan, green, magenta, red, yellow, or white) and of the surrounding dots affect how strongly we mentally and physiologically react to the illusion. The illusion of the expanding hole prompts a corresponding dilation of the pupil, as it would happen if darkness really increased,” said Laeng.
“Here we show based on the new ‘expanding hole’ illusion that that the pupil reacts to how we perceive light – even if this ‘light’ is imaginary like in the illusion – and not just to the amount of light energy that actually enters the eye. Pupil reflex depends on perception, not necessarily reality In the new study, published in Frontiers in Human Neuroscience, Laeng and colleagues show that the ‘expanding hole’ illusion is so good at deceiving our brain that it even prompts a dilation reflex of the pupils to let in more light, just as would happen if we were really moving into a dark area. Optical illusions aren’t mere gimmicks 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 roundabout way than a photometer device, which simply registers the amount of photonic energy. Do you perceive that the central black hole is expanding, as if you’re moving into a dark environment, or falling into a hole? If so, you’re not alone: a new study shows that this ‘expanding hole’ illusion, which is new to science, is perceived by approximately 86% of people.ĭr Bruno Laeng, a professor at the Department of Psychology of the University of Oslo and the study’s first author, said: “The ‘expanding hole’ is a highly dynamic illusion: The circular smear or shadow gradient of the central black hole evokes a marked impression of optic flow, as if the observer were heading forward into a hole or tunnel.” By Mischa Dijkstra, Frontiers science writerĪn illusion new to science shows that the pupillary light reflex, which controls the width of the pupil in anticipation of expected changes in light, depends on the perceived environment rather than the physical reality.