Any signal, that's the point. The cerebellum learns the patterns of signals involved in motor control.
This is why you train your skills by doing the correct movement over and over again. Once the cerebellum has adjusted to the correct motor signal patterns the correct movement will become effortless.
You'd have to apply an adverse stimulus in under a ~5ms threshold to actions that were 'wrong'. It would depend on the exact task you're trying to do though. That would then cause other areas to potentiate that specific movement/firing as incorrect.
Its a active area of research in sports and DoD. As you'd theoretically be able to train marksmen and athletes at a much faster and better rate. However, even really really fast computers aren't quite fast enough to apply the adverse stimulus to 'wrong' movements/firing.
Also, your computer better be really accurate and never mess up, or that person is going to have a hell of a time retraining their brain. Also, their brain may view that the clouds/temperature/itchy grass/breakfast are the reasons for the adverse stimulus, as this is all happening at in subconscious time frame. So, good luck there.
Any signal, that's the point. The cerebellum learns the patterns of signals involved in motor control.
This is why you train your skills by doing the correct movement over and over again. Once the cerebellum has adjusted to the correct motor signal patterns the correct movement will become effortless.