How can this study be reconciled with the idea of free choice, if at all?

Why does this contradict the notion of free will? There is also a mirage, where a person is sure that he really sees something, and that is not true. It is an illusion. So does it follow from this that our entire sense of sight is an illusion? And the same goes for all the visual deceptions that we all know—there are many such cases. It is also possible, by artificial means such as electrical stimulation, to cause a person to imagine that he sees his grandmother standing in front of him. So from now on, every time he sees his grandmother, is that an illusion? The fact that an illusion can be created is a known fact, but that does not mean that everything is an illusion.