I wondered for a bit what would happen if we did some split brain experiments on sign language speakers.
I think the results might be a bit different. It may also give some insight to what parts of sign language are deeply linguistic.
Supposedly the left brain handles most of language processing, and the right brain has very minimal language abillity. 
But intuitively it also seems like hand gestures can be made without
tapping into language. I don't know where I would find people to run these experiments on but it would be interesting.