Pallazzo said:
Now, how does one see "nothing"? It is a logical paradox to say that one sees nothing.
It certainly is not. A logical paradox is something which directly contradicts itself.
If one sees nothing, then what is the experience of "nothing"?
Nothing. No experience whatsoever.
To say that being blind is like seeing with the back of our heads disregards the fact that even when the eye-organ is damaged, we still have a visual cortex.
It disregards nothing. Blindness doesn't necessarily always trace back to damage to the eye, and even if it does, that doesn't mean the visual cortex would somehow be active and recognizing patterns (that's what neurons do) in no signal input at all. No signal is not the same as blackness. Look at something through the blind spot in your eye, and you'll see nothing. Not black, just nothing. You do have visual cortex for that part, but that piece of visual cortex simply continues whatever pattern it can recognize in nearby regions. People with long-term retina damage report a similar phenomenon.
If you've never seen anything at all anywhere in your visual cortex, there are no patterns to recognize, no signal to analyze, and therefore nothing to compare "black" to. The concept of black would never have even obtained a set of neurons in your frontal lobes to identify it, because there's nothing to discriminate it against. Instead, in blind people, that piece of cortex is either adapted and repurposed for other things (like touch) or simply not used at all (in which case it does not generate any perception, because it has never produced any signal to train the rest of the brain to pay attention to it in any way).
When we sleep we still "see" perfectly well in a dream.
Because you've seen things before. Dreams are based on random combinations of things you've experienced -- patterns that have meaning to you. You never hear anyone speak (at least, not correctly) in a language you don't understand in a dream, for example, because that language is not known to your mind. Similarly, the patterns of stimuli we describe as vision are not available to someone blind from birth. People blind from birth don't normally see things in a dream. We would know because they can talk about their experiences, and they don't usually describe experiencing some unknown sense when dreaming.
These are generalizations, obviously. Some blind people might see something sometimes. But there's no reason to expect them to in general.
