I’ve read that imagination (in the sense of conjuring mental imagery) is a spectrum, and I’ve encountered a test which some but not all phantasic people fail.
I don’t recall the details enough to pose it directly, but I think I do recall enough to reinvent the test:
Ask the subject to visualize a 3x3 grid of letters.
Provide the information required to construct the visualization in an unusual order, for example top-to-bottom right-to-left for people not accustomed to that layout.
Ask them to read the 3-letter word in each row.
Test details guessed above may not properly recreate the ability to distinguish levels of imagery. My hazy memory says the words might be top-to-bottom? Or the order of providing the letters might matter?
Someone actually seeing the image you’ve requested they construct would be able to trivially read off three words. …but someone without mental imagery or with insufficient mental imagery may fail.
I recall discovering that I really can’t imagine more than about 2 letters at a time before adding additional detail to my mental visual workspace forces the loss of something else. That seems pretty poor, and tracks with my inability to imagine human faces—my theory is that a specific face requires more details to distinguish it from other faces than the maximum amount of detail I can visualize.
Yes, red and green seem subjectively very different—but only to conscious attention. A green object amid many red objects (or vice versa) does not grab my attention in the way that, e.g. a yellow object might.
When shown a patch of red-or-green in a lab setting, I see “Red” or “Green” seemingly at random.
If shown a red patch next to a green patch in a lab, I’ll see one “Red” and one “Green”, but it’s about 50:50 as to whether they’ll be switched or not. How does that work? I have no hypotheses that aren’t very low confidence. It seems as much a mystery to me as I infer it seems mysterious to you.