Change Destiny thinks it's cool that optical illusions give us information about how our brains work. I do too.
F is interested in synesthesia. She wrote her informative speech about it last semester and sent me a copy. Here is an article in Scientific American about synesthesia.
F has a touch of it; I remember that when she was a little girl she told me one day about the characteristics of various numbers, the way she saw them. Various words make her feel one way or another. What were those three words you told me about, F? Spoon? Police? Can't think of the other.
And I have it too. I was in the band when I was in school, and I associated certain notes on my clarinet with colors. It's not that I saw the colors, it's that I knew what colors they were. And now, when I am in a dark room, if I hear a sound I see a flash of light. I thought at first that I must be flinching, that that was what caused the visual phenomonon, but I'm fairly sure now that that's not the case.
F also has the trait that sunlight makes her sneeze. We always used to laugh about that, because every Sunday when we left church at noon the sun was right in her face and she would inevitably start sneezing. Less funny is that full sunlight sometimes gives her a migraine. This all has to do with stimulation of the optic nerve having cross-effects in her brain. We've speculated as to whether there is a connection to synesthesia; don't know.