A scotoma is a blind spot, or area of reduced vision;[1] the grey square at the top left of the image represents an artificial scotoma, which is filled in by the twinkling background after staring at the centre of the image for a few seconds.

The phenomenon was first studied in detail by the psychologists Vilayanur S. Ramachandran and Richard L. Gregory , and reported in a letter to the journal Nature in 1991.[1] In it they reported that the “filling in” seen in the illusion is an active process that may involve the creation of a neural representation of the surround, rather than merely ignoring the absence of information from the scotoma.[2]

Fixing your gaze on the centre of the image for a few seconds will result in the square being replaced by the twinkling dots

See also

  • Troxler effectPerceptual illusion in which an image in peripheral vision disappears.

References

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Bibliography

Colman, Andrew M. “Scotoma.” A Dictionary of Psychology, Online, Oxford University Press, 2009, https://www.oxfordreference.com/view/10.1093/acref/9780199534067.001.0001/acref-9780199534067-e-7319.
Ramachandran, V. S., and R. L. Gregory. “Perceptual Filling in of Artificially Induced Scotomas in Human Vision.” Nature, vol. 350, no. 6320, 1991, pp. 699–702, https://doi.org/https://doi.org/10.1038/350699a0.