[cronjobber]

I find it easy to replicate this for myself. I cannot stop me from sort-of imagining the movement before the "decision".

After a few repetitions, it became apparent why this may be so. It's the instructions. I'm to move the finger "immediately". My brain prepares the movement because it wants to do it "immediately" after "deciding".

Here's a more relaxed setup. Alternate between looking at two fingers at a relaxed pace. At any moment, decide to move the finger you're currently looking at after silently counting to five.

Introspectively, I find no imagined movement before the decision with this task.