Here is a man called Eliot Fintushel, who neatly exemplifies how people come to talk about the expression of feelings in music. Furthermore, because he is using ‘gestures’ to operate his Theremin he even talks about his feelings being present in his movement and therefore (magically) transferred to the music of the Theremin. So, if you make a ‘nervous’ movement, you get a ‘nervous’ sound.
To my ears, it all sounds like a big circular argument: If you tell people that a certain movement is ‘nervous’ and then that the sound they hear is also ‘nervous’ then what will they see and hear? That’s right, ‘nervousness’. But what if you had not told the audience what to hear or see? They would simply rely on the facial expressions (which are overacted and conventional rather than universally understandable in this case) to know the feelings they should be feeling. Projection will do the rest.
But like I said before, relying on conventions (even if they are shared with only a select few) to achieve some effect is not necessarily a problem. If a concert audience wishes to share a fantasy of going through all sorts of feelings, guided by a performer, then let that fantasy be as real as possible. Some of that feeling may actually be genuine, the rest may serve our emo-thirsty souls just as well.