On the vision and proprioception question, the systems interact strongly to build awareness of ones location and orientation. But proprioception is an independent sense and can be tested with a blindfold or such to discriminate.
I figured my spacial awareness and balance were completely shot when I was kid. It wasn't until I learned Tai Chi in college that I realized that vision was the only issue. Being able to split that awareness let me develop those senses. I still can't catch a ball, but I no longer fall over if I stand on one leg.
