Laura Camacho explains how this optical illusion works:
The image above does not move. The hole doesn’t get bigger, it doesn’t expand, nor is there suddenly greater darkness. It is an optical illusion, and it is one of the protagonists of research recently published in the journal Fronteirs in human neuroscience. The experiment consisted of showing this image and others of the same style, but with different colors, and the reactions to these stimuli show that, although they are not real images, but rather illusory images, the human body reacts to them . In this case, and through an eye tracker, scientists have shown how the pupils change when observing these illusory images. When the hole is black, evoking greater darkness, the pupils dilate, just as when entering a dark room. On the other hand, when the central hole is colored, including white, suggesting an expansion of light, people’s pupils contracted. In the first case, the dilation occurred monotonically, while with the colored holes the pupils initially contracted upon contact with the image, but then showed fewer changes. Furthermore, the subjective expansions were weaker compared to black holes.
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