Optical illusion is a new thing in science. It is an expanding hole for most people, although it is only a static image. This highly dynamic illusion is very effective in deceiving our brain. It induces an expansive reflex, which makes our pupils allow more light to enter, and makes us think that we have really entered a dark area.
Look at the picture above. Do you feel that the central black hole is expanding, as if you are entering a dark environment or falling into a hole? If so, you are definitely not the only one: a new study shows that about 86% of people will have this illusion of "enlarged hole", which is new in science.
Bruno Laeng, the first author of the research paper, pointed out: "the 'enlarged hole' is a highly dynamic illusion: the circular smear or shadow gradient of the central black hole evokes an obvious impression of optical flow, just as the observer is moving towards a hole or tunnel."
Optical illusions are not just gimmicks without scientific interest: researchers in the field of social psychology study them to better understand the complex processes that our visual system uses to predict and understand the visual world - in a more circuitous way than photometer devices, which simply record the amount of photon energy.
In this new study published in Frontiers in human neuroscience on may30,2022, Laeng and his colleagues showed that the "enlarged hole" illusion is very good at deceiving our brain, and it even makes the pupil dilate and reflect, so as to let more light enter.
Pupillary reflex depends on perception, not necessarily on reality
"Here, based on the new 'enlarged hole' illusion, we believe that the pupil reacts to how we perceive light - even if this' light 'is imaginary as in the illusion - and not just to the amount of light energy actually entering the eye," Laeng said. "The illusion of enlarged holes causes the pupil to dilate accordingly, just as it would happen if the darkness really increased."
Laeng and his colleagues explored how the color of the hole (except black: blue, cyan, green, magenta, red, yellow or white) and the surrounding dots affect our strong mental and physical response to hallucinations. On one screen, they showed 50 women and men with normal vision the changes in the "enlarged hole" image, and then asked them to subjectively evaluate their perception of the illusion. When participants stared at the image, the researchers measured their eye movements and the involuntary contraction and expansion of the pupils. As a control, the researchers showed the subjects a "scrambled" version of the enlarged hole image with the same brightness and color but without any pattern.
This illusion is most effective when the hole is black. When the hole was black, 14% of the participants did not feel any illusory expansion, while if the hole was colored, 20% of the participants did not feel it. The subjective intensity of hallucinations was significantly different among those who did feel expansion.
The researchers also found that black holes promoted the highly reflective expansion of participants' pupils, while colored holes caused their pupils to contract. For black holes rather than colored holes, the stronger the subjective evaluation of hallucinations by individual participants, the more inclined their pupil diameter is to change.
Few people are not easily affected
Researchers do not yet know why a minority of people seem insensitive to the illusion of an "enlarged hole". Nor do they know whether other vertebrate species, or even invertebrates with camera eyes such as octopus, perceive the same hallucinations as we do.
Laeng concludes: "Our research results show that the pupil dilation or contraction reflex is not a closed-loop mechanism. Just like the photocell opening the door, it is not affected by any other information except the actual amount of light stimulating the photoreceptor. On the contrary, the eye adjusts according to the perceived or even imagined light, not just based on physical energy. Future research may find other types of physiological or physical changes, which can To 'project' onto how the illusion works. "