Warning: this is pure speculation and might not make any sense at all. :-)

So, let's suppose PCT is by and large an accurate model of human behavior. Behavior, then, is a by-product of the difference of the reference signal and the perception signal. What we feel as doing, is generated by first setting some high-level reference signal, which then unfolds as perception signals to control systems at lower levels and so on until it arrives at muscular level.

This whole process takes certain amount of time, especially when the reference signal is modified at a high level of the hierarchy. In contrast, when say the perception signal at the lowest level changes, this re-adjustment at the lowest level is a fast operation, because it only involves the control system at the bottom of the hierarchy. For example, we make unconscious corrections to our balance when we stand straight. The lowest level perception signals change, but they only affect the lowest level control systems.

Then we have the idea from Rodolfo Llinás that "willing" is the process where the brain predicts what will happen and then takes the possession of that prediction. Say for example moving your hand. What happens in such movement is that there is a premotor picture in your head of the hand moving and when the hand actually moves, the brain generates the feeling of you moving the hand.

In the interview he describes an experiment which he did on himself where he stimulated his own premotor [1] cortex so that his left leg moved outwards. When his cortex was stimulated and the leg moved outwards, he told his colleague that he cheated. That is, when they stimulated the cortex, it was actually Rodolfo himself who moved the leg.

[1] I think he says "motor cortex" in the interview, but is my understanding that if you stimulate the motor cortex directly, it generates movements that you feel involuntary. But IANANS. (I Am Not A Neuro Scientist.)

To prove that it was him who moved the leg, he said to the colleague that he will move the leg inwards the next time they stimulate the cortex. So they stimulate the cortex and he moves the leg outwards again. Seems like a good proof that it wasn't Rodolfo who moved the leg but the stimulation? Wrong. Sure, he said that he will move the leg inwards, but he decided to move the leg outwards anyhow.

They do the stimulation for dozen times and sure enough the leg always moves outwards. But the sensation that he feels, each and every time, is that it's he who moves the leg. There is no difference in the sensation generated by the stimulation and him moving the leg by volition.

So when you move your arm, the brain generates a sensation of the self actively doing the movement. Translated back to PCT, the act of moving one's hand is to modify some high level reference signal. What happens after modifying the reference signal is the propagation of the signal to control systems in the hierarchy, which is an automatic process and one that we can't directly interfere with. But this propagation of the reference signal (down to the lowest level to generate muscle tensions) generates the sensation of us (the self) doing whatever happens during the process.

OK, now we're invited by Benjamin Libet to a test. We are asked to move our hand at arbitrary time and report the time we felt doing it. To move our hand, according to PCT, we have to set some high level reference signal.

So if we don't perceive any concrete sensation of setting the reference and if it takes a certain amount of time to propagate the reference signal down the hierarchy and if our brain indeed takes the possession of the actions of the down-propagation and generates the sensation of us doing it, then we have an explanation of why is it so that the brain activity lights up well before we feel like we decided to move the hand. The part of the process that our brain assigns as the sensation of actually moving the hand happens at a later point of this process and thus it is natural that there is brain activity before our feeling of deciding to move the hand.

Unfortunately, I don't know much of the actual details of these systems, so I'm ready to accept that this all complete bollocks. But at least it was fun to think through. ;-)