equation But that's what the old Cartesian thought experiment was aiming at, as if my internal states are sufficient for the world. There is very interesting work done now in psychology labs -- for example, work in O'Regan's lab -- on the importance of eye movements and environmental stimulation for capturing attention and directing attention. This is why virtual reality systems are so hard to make really convincing. It's one thing to make a flight simulator -- all you have to do is make a very good replica cockpit and a reactive virtual environment -- But in most video games and in digital technology, there are huge shortcomings in the power of the virtual. In part this has to do with the fact our own perceptual attunement to the environment is so dependent on what the world brings to the table, as it were. Landmarks, markers, signposts that we respond to, all play a role in our experiments. If you take the world out of the equation, I suspect that the brain, with its own internal powers, would be capable of producing only very impoverished experiences. In fact, there is one nice bit of evidence I have to support that. There is a sleep scientist named Stephen Laberge, who has done studies on lucid dreaming. In a series of studies that he did, he would interrogate these lucid dreamers on their experiences. I don't remember all the methodology but the basic conclusion he found was this: in a dream it