Imagine, a science fiction story in which a mad scientist has captured a brain and put it in a bat. Imagine, further that the mad scientist has devilishly contrived to keep the brain alive and healthy by supplying it with nutrients and oxygen. Imagine finally that he fiendishly tickles the cut-off nerve endings of the brain so as to imitate the simulation of nerves that would occur if the brain was in active, aware human being. What would the brain know? The brain would have no choice but to believe that it was still in a person, living the life of a person. In fact, each of us has no way of knowing that we are not in such a brain in a vat. Everything we see around us, every sound we hear could simply be the result of the mad scientist simulating our nerves. When we look, he stimulates our vision nerves so that we see; when we listen, he stimulates our hearing nerves so that we hear. We command with our hands or feet to move, he stimulates the nerves cut off from our muscles so that we think we move. In our science fiction story, the whole world of our experience could be caused by the activities of the mad scientist.

- 'Psychology' by James D.Laird and Nicholas S.Thompson