Brian, I couldn't respond to your post, so I just made a new post...

The way I envision what you are talking about is a space that is completely quiet unless affected. Not unlike an instrument, it could be played. Just a few examples of what I am talking about: Rain on a tin roof, Gravel only makes sound in response to a footstep, a halway with a very hard flooring so that somebody's approach is made known long before you see them...

I guess I'm stating the obvious, but I think that this cross modal experience is always present, it is just overlooked most of the time. You would just be "tuning" your space. when you speak of figure ground within sound, maybe the actual figure (the occupant) would be creating the aural figure. The question is, what is the aural ground? If it is silence, then you would have effectively isolated a sound (which is a response to an action). I think that this is much like the doors of the Brion cemetery that I spoke about in my presentation. One doesn't notice a door unless it is pointed to / pointed out. Sound could then become your means of pointing. On the other hand, if your aural ground is a sort of white noise something different could happen.

I'm just thinking about the scenario of being in a music hall with an orchestra. Here sound is obviously very important. Think of the drone created by the hundreds of quietly talking people with the orchestra warming up as compared to the moment after the entire audience becomes quiet. A figure appears... Also, I'm pretty sure that even when people are talking before the concert begins, the sound of the violin to the violinist always remains a figure, because he/she is the one creating the sound. Here figure creates figure.