Face Control for Electric Guitar: I mapped the output of a real-time face-tracker onto the parameters of an audio effects processor. The result: an effects processor that uses face-position as its primary mode of control - the ultimate headbanger-guitar-player's interface.
D. Merrill. Head-Tracking for Gestural and Continuous Control of Parameterized Audio Effects. Demo and short paper at the 2003 Conference on New Instruments for Musical Expression (NIME'03). Montreal, Canada. 2003 [PDF].