Possibly too late to be seen now, but I've been wodering about this too; for instance how do you talk about windows?
A blind person who has a sense of the size of a room, have they any idea that windows are transparent and have a view over a vast area of cityscape/fields/oceans/length of road/etc?
Standing on a hilltop or in a viewing tower, you can see people in the landscape, but too small to see their faces or identify them - still identifiable as people by shape and gait.
I often automatically turn to Google images for an idea of what something I'm unfamiliar with "is", having to revert to a dictionary and textual description would feel like a step backwards, and that's a very recent (last 5 years) development.
You could also ask if blind people are able to perceive vision in dreams. To which the answer, I believe, is that they simply cannot, due to the fact that their brains have no notion of a visual image.
'...dreaming is a gradual cognitive achievement that requires the development of visual and spatial skills and other forms of imagistic skills as well.'[1]
Those who've never seen, or who were blinded very early, have auditory dreams. (They dream in sounds.) Those who were blinded after the age of around seven -- when the ability to form mental images necessary for dreaming develops -- are able to dream in pictures.
I suspect we commonly underestimate blind people mental capacities.
One can argue that 'seeing' goes beyond the perception of lights and colors. It's also about shape, so I guess a blind person can perfectly 'visualize' a rectangle, a cube, etc. And probably do geometry, or even 3D-object rotations.
I read something recently by a blind guy who said that sometimes he perceived some amount of light in his dreams. This was because his blindness is not complete blindness. There are varying degrees of it. In his case, he could detect some light changes.
