“Imagine a girl called Mary. She is a brilliant neuroscientist and a world expert on colour vision. But because she grew up entirely in a black and white room, she has never actually seen any colours. Many black and white books and TV programmes have taught her all there is to know about colour vision. Mary knows facts like the structure of our eyes and the exact wavelengths of light that stimulate our retinas when we look at a light blue sky.
One day, Mary escapes her monochrome room, and as she walks through the grey city streets, she sees a red apple for the first time.
What changes upon Mary’s encounter with the red apple? Has Mary learnt anything new about the colour red upon seeing the colour for the first time?”
What Did Mary Know? by Marina Gerner.