Professionals showed fundamental differences in the way they made information-carrying gestures vs. non-information carrying gestures (students less so). A third feature I discovered in the EMG data is that the signals generated by the action of turning pages are inherently different in character from the signals generated by actions that are intended to convey musical information. That is, it seems as if page turns are done in such a way as to purposefully not attract attention or convey musical information. An example page turn from subject P1 is shown below in Figure 27:
A corollary to this is that the professionals tended to generate far less muscular force for noninformative events than the students do. For example, P3 typically used almost no force when turning a page. In Figure 28, below, the EMG0 (left forearm) and EMG1 (left biceps) signals show the relative difference between an information-bearing and non-information-bearing gesture. The first feature is an emphasis cue in the left arm; the following feature (samples 40-44,000) is the page turn. In the page turn gesture, the arm moved to perform the action, but without force or emphasis. This lack of muscle tension during the gesture is significant; perhaps this is because musicians are sensitive on a subconscious level to muscle-tension cues and therefore are trained to ignore gestures that do not have tension in them. This may suggest an advantage of EMG sensing over motion or accelerational sensing.
An alternate explanation for the relative size and envelope differences between information- and non-information bearing EMG signals might also be that beats require more accelerational, jagged gestures, whereas page turns require more smooth motions. Since smooth actions of the limbs involve more communication and feedback between different muscle groups, their signal profiles tend to appear more irregular, whereas forceful gestures don’t require as many adjustments and therefore their signals have a more defined envelope.