Descartes' own solution invoked the mystery of an immaterial soul, who indeed views the picture in the brain sent up from the eyes, like a man viewing a television monitor of a remote scene. But the soul supposedly does not see the picture on the monitor; instead, it sees the world itself directly, out where it lies, seeing transparently backwards through the optic nerve, retina, and lens as if they didn't exist! This explanation is an unhappy compromise between the irrefutable neurophysiological facts and our personal experience of vision. For we do indeed seem to experience the world out where it lies, not as a picture inside our head. Many modern theorists have equally confused views on this issue.
But the problem with direct perception becomes perfectly clear as soon as we set out to replicate that principle in a robot intelligence. How on earth do you get a robot to "see" beyond its sensory surface and to experience the world itself directly, out where it lies? The whole concept becomes incoherent when you try to implement it in insensate physical matter. Like Descartes, these people still cling to some magical mystical concept of Mind which can never be replaced by mere machines. They are the modern equivalents of vitalism, the theory that there is some vital essence inherent in living conscious beings, which can never be reduced to plain physical terms.
But as soon as we acknowledge that mind is nothing other than the electrochemical functioning of the physical brain, then conscious experience reduces to an information theoretic problem. Visual experience has an information content, and information cannot exist without some kind of carrier to carry that information. Experience cannot exist in the abstract, it must be encoded in some information processing system, and our experience is encoded as a physical state of the physical brain. No aspect of the external world can possibly appear in our experience except by being represented explicitly in the brain.
MLU: How do you believe that experience is represented in the brain, then?
SL: Well, this has been the great stumbling block that has led to the current impasse. Everything we know about neurophysiology seems to suggest that experience is encoded in the brain as electrical activity in networks of neurons. What is prominently absent from our neurophysiological understanding of the brain is the question: Where are the moving colored pictures in the brain, that we know from our experience to be in there?
The consensus in modern neuroscience seems to be that there are no pictures in the brain, because we have not found them, and modern philosophy has attempted to conform to this neurophysiologcal reality by claiming that there are no pictures in our experience either, so don't even bother looking for them in the brain! But our experience is clearly spatially structured, and not just our perceptual experience, but also our experience of dreams and hallucinations, which are obviously constructs of our brain. So my first point is that however they might be encoded in the brain, there are in fact explicit moving colored pictures in the brain that correspond to our experience of the world, and if modern neuroscience cannot find them, that is a problem for modern neuroscience, not for the notion of pictures in the brain.