You touch on an interesting idea I've been pondering to myself about conscience and the "soul" in that it is the result of our 5 senses.
A man that's blind can count with sound.
A man that's blind and deaf can count by touch.
A blind, deaf man with no nerve system can count different smells.
A man that can't see, hear, touch, smell or taste doesn't exist to himself but we know he exists because we have those senses.
It can still be said that even if all senses are lost after birth, he may still have thought because he once used those senses to retain memory. Without any senses from birth he would have no internal voice to construct a thought and is just a fleshy rock.