system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is it possible to visualize objects and colors with closed eyes just by thinking of them?

Sometimes if I think of color purple with my eyes closed I can see purple lines or if I think of any random color I am able to see that color when I close my eyes. I know that the color is not actually there but how am I able to see the exact same thing that I think of with my eyes closed? 

In the same way, while giving a test or an exam,sometimes you close the eyes to think of the answer and you are able to see relevant information that you have studied in front of your eyes. How does that happen?
gpt
Your are actually activating the visual processing part of the brain to do this.

Your eyes produce a stream of raw data that is then heavily edited by the brain to produce a coherent image.  The brain isn't simply relaying what the eyes see, it's photoshopping the hell out of the feed (see all the optical illusions for ways to trick the system).

All that real-time photoshopping power can also be used to generate an image with no eyeball input at all, but rather recalling the relevant information from memory.