An optical illusion new to science appears to most people as an expanding hole, despite being a static image. This extremely dynamic Illusion is so powerful at deceiving our brain that it induces a dilation reflex, causing our pupils to dilate and allow in more light in anticipation of heading into a dark location.
Take a look at the optical illusion above. Does the center black hole appear to be spreading as if you’re entering a dark environment or falling into a hole? If that’s the case, you’re not alone. According to a new survey, over 86 percent of respondents see the “growing hole” optical Illusion.
According to Dr. Bruno Laeng, “The expanding hole is a rapidly evolving one. The core black hole’s shadow gradient or circular smear creates a strong feeling of optic flow as if the viewer were moving forward into a tunnel or hole.” Dr. Bruno Laeng is the study’s first author and professor at the University of Oslo’s Department of Psychology.
Optical illusions aren’t just gimmicks; they’re also interesting from a scientific standpoint. Psychosociologists study them to understand better 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—in a far more indirect manner than a photometer device, which simply logs the amount of photonic energy.
Laeng and colleagues reveal in a new study published in Frontiers in Human Neuroscience that the “growing hole” optical illusion is so good at misleading our brain that it even causes a pupil dilation reflex to let in more light, exactly as it would if we were really moving into a dark place.
The pupil reaction is based on perception rather than actuality
Using the new ‘growing hole’ optical illusion, we show that the pupil reacts to how we perceive light rather than the quantity of light energy that actually reaches the eye. The Illusion of the enlarging hole causes the pupil to dilate in response as if the darkness actually increased, “Laeng said. The color of the hole (apart from black: white, yellow, magenta, green, cyan, or blue) and the surrounding dots affect how strongly we react psychologically and physiologically to the Illusion, according to Laeng and colleagues.
The researchers presented 50 women and men with variations of the “expanding hole” image on a screen. They asked the participants to rate subjectively how strongly they felt about the Illusion. The researchers tracked the individuals’ eye movements and the unconscious constrictions and dilations of their pupils while they stared at the image. The subjects were shown “scrambled” versions of the expanding image of the hole as research controls, with equal colors and brightness but no pattern.
The Illusion seemed most powerful when the hole was black. While fourteen percent of participants didn’t see any illusory expansion when the hole was black, 20 percent of the subjects didn’t notice any illusory expansion when the hole was in color. The subjective degree of the Illusion varied significantly among individuals who did perceive an expansion.
The researchers also discovered that black holes caused the subjects’ pupils to dilate reflexively, but colored holes caused their pupils to constrict. Individual participants’ pupil diameter tended to fluctuate in response to how strongly they subjectively judged the Illusion’s impression of black holes but not colored holes.
The researchers aren’t sure why certain people seem immune to the “growing hole” optical illusion. They also don’t know if other vertebrate species, or even non-vertebrate animals with camera eyes like octopuses, are aware of the Illusion.
“Our findings demonstrate that the pupil dilation or contraction reflex is not a closed-loop mechanism like a photocell opening a door that is resistant to any information other than the amount of light stimulating the photoreceptor. Rather than reacting to physical energy, the eye adjusts to perceived and even imagined light. Other forms of physiological or bodily changes that can ‘give light’ on how illusions function could be discovered in future studies, “Laeng concluded.
Feature image credit: Laeng B, Nabil S and Kitaoka A under CC BY 4.0