Libet's study is terrible -- as with many of these studies it's famous for its controversial conclusion, but its flaws are very obvious. He specifically asked

Libet's study is terrible -- as with many of these studies it's famous for its controversial conclusion, but its flaws are very obvious. He specifically asked his subjects to listen for an urge rather than applying free will ("let the urge [to move] appear on its own at any time without any pre-planning or concentration on when to act”). That the urge is measurable before the decision, then, just means his subjects did what he asked them to -- to wait for a feeling of an urge. And frankly, it's most likely the urge was the tension of having sat there a while, knowing someone's expecting you to feel an urge to move your arm... 1. Ask subjects to wait for an urge to react to (and therefore not apply free will) 2. (Nice-sounding but actually irrelevant measurement set-up with dots, clocks and electrodes) 3. Observe subjects decided after a measurable urge 4. Conclude free will doesn't exist, rather than that your subjects did what you asked them to in step 1.