Soundpainting is the live composing sign language created in 1974 by New York composer Walter Thompson for musicians, dancers, actors, poets and visual artists. Soundpainting demands that artists step away from what is familiar and predictable and commit to each expressive act without knowing where it will lead. The soundpainter asks each member of the Orchestra to perform as she or he is normally accustomed but goes further, stretching the genre boundaries of their "instrument", for example, musicians may be called upon to laugh, actors to sing, and dancers to speak.
You can have a better idea if you have the chance of attending a soundpainting live performance.
For the next scheduled soundpainting events around the world : http://www.soundpainting.com/schedule/