Concession: vision is harder to think about than most sensations, because it seems so tightly bound to reality. Easy to think that what’s on the back of your retina is the world.
On this point I like to think about gorgeous photographs of nebulae, which have been taken with infra-red telescopes.
How can I see them if they are infra-red? The photographers simply adjust the wavelengths into the range that I can perceive, so I get to see the beauty of the nebula as though I could see into the infrared spectrum.
The fact that you can slide red into yellow into blue just by adjusting the wavelength of light should make it immediately apparent that there is no substantive difference between red, yellow, or blue—only very slight differences in wavelength. We have evolved three types of cones that each respond to a specific slice of the electromagnetic spectrum (it is quite narrow for each), and these are represented as entirely different things in our mind for the purpose of distinguishing between them.
So long as your cones and my cones are working equally well, and our visual cortex is functioning equally well, it’s almost a certainty that blue, yellow, and red look exactly the same in my mind as they do in yours. This is because the electrical and chemical signals will be identical, and they will be processed in the same manner for each of us. It would be a great surprise to discover they “seemed” different.
Many birds, it’s worth noting, have a fourth type of cone that captures a slice of EM radiation in the ultraviolet, because most flowers reflect into the UV spectrum, while most other things do not. This makes distinguishing flowers from non-flowers significantly easier for the birds who feed on them (and the flowers who rely on the birds for pollination).
On this point I like to think about gorgeous photographs of nebulae, which have been taken with infra-red telescopes.
How can I see them if they are infra-red? The photographers simply adjust the wavelengths into the range that I can perceive, so I get to see the beauty of the nebula as though I could see into the infrared spectrum.
The fact that you can slide red into yellow into blue just by adjusting the wavelength of light should make it immediately apparent that there is no substantive difference between red, yellow, or blue—only very slight differences in wavelength. We have evolved three types of cones that each respond to a specific slice of the electromagnetic spectrum (it is quite narrow for each), and these are represented as entirely different things in our mind for the purpose of distinguishing between them.
So long as your cones and my cones are working equally well, and our visual cortex is functioning equally well, it’s almost a certainty that blue, yellow, and red look exactly the same in my mind as they do in yours. This is because the electrical and chemical signals will be identical, and they will be processed in the same manner for each of us. It would be a great surprise to discover they “seemed” different.
Many birds, it’s worth noting, have a fourth type of cone that captures a slice of EM radiation in the ultraviolet, because most flowers reflect into the UV spectrum, while most other things do not. This makes distinguishing flowers from non-flowers significantly easier for the birds who feed on them (and the flowers who rely on the birds for pollination).