eli5: What’s the thing happening when you see bright colours, while holding your hands over your eyes while they’re shut?

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eli5: What’s the thing happening when you see bright colours, while holding your hands over your eyes while they’re shut?

In: Biology
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Phosphenes are produced by pressure on the eye, which translates into various patterns by the optic nerve.

Sensory cells become excited when they detect things. When they are excited, they send messages to the brain.

In the eye, there are sensory cells called rods and cones, which become excited by light. Rods work better in the dark; when they are excited, they send signals that tells the brain ‘there’s light here!’ Cones work better in bright lighting; when they are excited, they send signals that tell the brain ‘there’s color here!’

Rods and cones are excited by light from the outside world, but some can also be excited by pressure. When you close your eyes and press on them, you excite some of the rods and cones, which send the same signals to the brain as they usually would: ‘I can see light!’ and ‘I can see colour!’

The weird things you see when you close your eyes and press on them don’t exist in the outside world. It’s just your brain’s way of making sense of the weird signals that it’s receiving.

If you’re seeing these colours without pressing on the eyes, though, then it’s probably just your brain making stuff up because it’s bored by the lack of messages coming from your rods and cones. Brains are weird like that.