Question Corner Science

Why do patterns and colours appear when we close our eyes?

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Joshna Joshy, Thrissur, Kerala



Closed eye visualisation or photopsias or phosphenes is an entoptic phenomenon in which bursts of bright colours appear all across field of vision when eyes are closed or when one is in a dark room. Phosphenes come in 15 categories such as triangles, stars, spirals, spots, amorphous blobs, etc. As a part of normal cellular function, atoms in the retina absorb and emit tiny particles of photons and optic nerve relays these light signals to the brain, which then decide whether it is real image or just a phosphene.



When a reconstructed image does not make sense, the brain will quickly label the image as a phosphene. Even in the absence of photons, the neurons in the thalamus, visual cortex and retina are always active, and these neurons will spontaneously fire. This will again activate other visual neurons and so on. Depending on where a phosphene originates, it would take on a variety of shapes, patterns and colours.



The frequency and duration of colour patterns will differ depending on which part of the visual system the neurons are acting up in. In addition to the spontaneous generation of phosphene, these can be generated as a result of mechanical stimulation, metabolic stimulation, magnetic or electrical stimulations. Certain drugs such as psilocybin, LSD etc., low blood pressure, low oxygenation , lack of glucose are most common causes of metabolic stimulation.



Dr. SAINUDEEN PATTAZHY



Environmental Scientist and Chief Editor, Journal of Scientific Research and Reviews, Kollam, Kerala. Mobile: 9447243002



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Printable version | Nov 21, 2019 3:43:50 PM | https://www.thehindu.com/sci-tech/science/why-do-patterns-and-colours-appear-when-we-close-our-eyes/article7411361.ece

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