Several reports have cited it as “the expanding hole” illusion. This dynamic illusion consists of black dots, which are like small elliptical balls, over a white background. There is a black patch with no defined outline exactly at the centre of the image. This hazy black patch, seems like a hole, and keeps on expanding when you fix your eyes on it.
Reports say that though it is clearly seen that the black hole in the middle of the image keeps on expanding till we gaze at it, 20% of the people do not perceive this expansion. This stark difference between the observers calls for attention towards a proper understanding of the mechanism behind how this illusion works.
What do people see in the illusion
As explained before, most people see that the black patch or the black hole keeps expanding as we stare at the image. The black hole creates an illusion of a hollow dark matter which spreads continuously over the white background engulfing the black elliptical balls into it.
However, others who do not perceive the above illusion see it as a black patch of ink. These illusion resilient individuals do not perceive the expansion.
What do researchers say about the illusion
The researchers have explained that the change rates of pupil diameters are significantly related to the illusory motion.
“At the root of these bright/dark illusions is the fact that, in general, the perception of light is not straightforwardly related to physical parameters; hence, the visual system relies on ecological regularities or constraints to generate perceptual hypotheses that, in most instances, achieve pragmatically the behavioral success of vision,” says a research report explaining this optical illusion. The May 2022, study is published in Frontiers in Human Neuroscience.
“Typically, when looking at the pattern below, observers’ subjective reports are characterized by the perception of a gradually expanding central region, occurring over a span of several seconds,” the researchers have said and have added that close to 20% of the participants who were involved in the study did not perceive the illusory expansion.
The study was done on 50 people with normal vision. The participants were asked to rate the magnitudes of illusory motion or expansion of black holes, and these predicted the degree of dilation of the pupil, measured with an eye tracker.
People with more changes in their pupil diameter rated the intensity of illusion as high. Those who did not perceive any change did not have any change in the pupil diameter.
The researchers have concluded that the dilation or constriction of the pupils is not just guided by our surroundings, it is also directed by our own imagination and perception.