Traditionally the dance follows the music; what is the vocabulary when the reverse is true?
What is the meaningful language in a 2D space? Location? Velocity? Acceleration? Proximity? Size?
Simplicity is required for audience to recognize the relationship between gesture and music.
Negative relationships can be equally simple and useful.
Must not be too simplistic for too long; as soon as it's obvious, it begins to lose interest.
But within a musical context, dual (or multiple) simplicities can be interesting.
It all grows exponentially in complexity with each added performer.
Continuous control (of bend, timbre, volume) is often more expressive than mapping motion to pitch.
Can put simple relationship (e.g., notes) into a familiar musical structure (e.g., with table lookup).
Control timbre, or formal structure, of algorithmic or played music.
Introducing delay between gesture and result retains the simplicity of correspondence but offsets it, to potentially interesting effect.
Sampling allows one to explore other relationships, such as gesture-to-text.
One can also explore other relationships, such as gesture-to-object movement (video-controlled animation), gesture-to-image/video (video-controlled video), etc.
More obscure relationships, such as extreme delay, reverse delay, capture and storage of data, etc. can be used to create a formal structure in real time.
New inexpensive wireless cameras present many new possibilities, such as dancers wearing cameras.
Why do interactivity?
Improvisation is the logical conclusion.
Is it interesting to watch interactivity per se? Is audience involvement necessary?
If audience controls the piece, how can you "guarantee" that it will still be artistically compelling?
One solution is reading through a table of possibilities which are an inherently strong sequence but which can be presented in any formal rhythm.
The problem at hand is to create an open form
in which the quality of the music or dance is "guaranteed",
but can be varied within parameters, in a manner that still provides
a compelling experience of interactivity for the audience.