Hook a guy up to some device that monitors his brain activity, set him in front of a screen with images on it, and tell him to pick any one of the images and tell him to announce the moment he makes the decision. Turns out, you can tell better than chance which he will pick before he decides.
The interpretation of the results is that there is no “free will”. The experiment might very clearly disprove the existence of some meaning of free will, the question is, was it ever reasonable to believe in the sort of free will that is disproved in the experiment?
For St. Thomas, free will is presupposed in the instructions of the experiment: “choose one”. Note right away that the freedom is not implied in the word “choose”- this would be to beg the question- it’s implied in the word “one”. Of the objects on the screen, which one does “one” apply to? The question is absurd: it’s like asking, “Which dog is “dog”: Lassie or Fido?” “One” is indeterminate, and so there is a necessary indetermination in “choose one”.
That said, this sort of indetermination is utterly compatible with some ability to foresee the results someone’s action, especially when all one must do is foresee it in a way more accurate than sheer chance. My wife and my mother could probably foresee my choices before I make my decision more accurately than sheer chance. Even if they couldn’t, this would just show that brain scans could give more reliable information than familiarity.
Besides which, when someone tells yu to pick something more or less at random, don’t you go into a mode where you clearly feel more “moved” than “mover”? Don’t you actually try to surrender your faculty of choice? When someone says “pick something random” isn’t the experience something like this: you try to suppress any criteria and just “go with the flow” of your mental processes? Is it any shock that the brain forms some determination before we decide? Weren’t we trying to make it do this?