See caption
Focus on the cross for a few seconds, and the surrounding colours seem to vanish.
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The Troxler effect, also known as Troxler fading, is a perceptual illusion named after the Swiss-German philosopher and physician Ignaz Paul Vitalis Troxler (1780–1866), in which an image in peripheral vision disappears when a central stimulus is fixated with a steady gaze.[1]

The effect has been attributed to the adaptation of neurons perceiving stimuli in the visual system, but the phenomenon introduces a paradox into how we see the world:[2]

… our visual system has a built-in paradox – we must fix our gaze to inspect the minute details of our world, but if we were to fixate perfectly, the entire world would fade from view.[2]

Because the Troxler effect involves not just the loss of the presence of something in peripheral vision, but a filling-in of the background to replace it, it has been suggested that it involves both the retina and the visual cortex, the former neuronally adapting, and the latter filling in for the lack of information being received from the retina.[3]

See also

  • Artificial scotomaPerceptual illusion in which an artificial blind spot is filled in by a twinkling background.

References

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Bibliography

Colman, A. “Troxler Effect.” A Dictionary of Psychology, Online, Oxford University Press, 2014, https://www.oxfordreference.com/view/10.1093/acref/9780199657681.001.0001/acref-9780199657681-e-8602.
Hsieh, P. J., and P. U. Tse. “Illusory Colour Mixing upon Perceptual Fading and Filling-in Does Not Result in Forbidden Colours.” Vision Research, vol. 46, no. 14, 2006, pp. 2251–58, https://doi.org/doi:10.1016/j.visres.2005.11.030.
Martinez-Conde, Susana, et al. “The Role of Fixational Eye Movements in Visual Perception.” Nature Reviews Neuroscience, vol. 5, no. 23, 2004, pp. 229–40, https://doi.org/doi:10.1038/nrn1348.