Everything we know about the physical world, including what we know about our own bodies, comes through our brain. In the first part of this book I have shown that our brain does not simply transmit knowledge to us like a passive TV set. Our brain actively creates pictures of the world. We know how creative the brain is because sometimes these pictures of the world can be completely false. This discovery is shocking because it makes us wonder how we can ever know whether what our brain tells us about the world is true. The surprise is that our brain ever gets things right. The brain creates its pictures of the world from the very limited and imperfect signals provided by our senses. For example, the visual image on our retina is in two dimensions only and yet our brain creates for us a vivid experience of a world of objects arranged in three-dimensional space. Thankfully, 99 times out of 100 the pictures our brain creates about the world are correct.
What I have been arguing in these posts is that Frith's book presents data to us which is designed to support these astonishing statements and conclusions, but that what is surprising and apparently in need of explanation comes rather from tacit and unwarranted philosophical commitments built into the theoretical structures used to interpret them.
The principle conceptual confusion inscribed in the heart of Frith's work is what, following Anthony Kenny, I have called the homunculus fallacy. This fallacy occurs when, in trying to explain the neurophysiological structures causally necessary for a person to be able to see, one supposes that these structures mediate the act of perception, such that the real perceptual act occurs after the neurological structures have done their work. On this conception real perception - visual presence itself - becomes a kind of inner act: the brain carefully prepares, cooks and then serves up inner representations of the outer world, and the person who is now a kind of detached inner witness of these inner representations is now restricted to only having direct contact with inner pictures.
Now if I really thought this was true, I suspect I would kill myself. Never to be able to actually make contact with my friends, to touch them, to see the world around me, to directly act on and count myself as part of the world: what an intolerably miserable life that would be. Rather than actively making love, for example, I am to understand myself as merely on the receiving end of a variety of sensory impressions dished up by my cortex. Further, Frith is surely right about the following. If he is right about the general form of the relation between mind and brain, then we really would start to 'wonder how we can ever know whether what our brain tells us about the world is true'.
In fact things are surely worse than this. On his picture there seems to be no way of even understanding how we could even conceive of the 'outer world' at all. If all we see are inner 'pictures', then how would we ever come up with the idea of a world beyond these pictures? Why would we think they represented anything? How would the idea of representation come about? How would I know that there was anyone other than myself in this world? In fact, how would I ever be able to conceive of the very idea of other people, or of the idea of a genus of people of which I am an instance? Rampant scepticism seems completely in order, and, even worse, the very intelligibility of our everyday conceptual scheme about physical objects and other people seems completely in doubt.
Frith's homuncularism is of course very evident in the passage cited above. 'Everything we know ... comes through our brain'. But, well, this isn't true. We don't stand on the receiving end of our brain. Rather, our brain is a part of the human being which we are. The neurological processes in question are the mechanisms of perception itself, not mechanisms which provide for an image which then needs to be further seen (but this time with an 'inner eye' or with 'consciousness'). Our capacity to see is instantiated in these neurophysiological mechanisms which support it; the mechanisms are not anterior to the true act of consciousness, and our perception accordingly does not come through the brain.
'Our brain actively creates pictures of the world.' Well - what would be the point of that? Who is there to look at these pictures? Human beings create pictures of the world - occasionally. They hang on walls or moulder in cupboards. Brains, as far as I know, have never spontaneously created any images. And if my brain were to produce a picture, I can imagine that someone else might be able to see it - perhaps if my head was cut open; I myself, however, have yet to witness anything which has occurred in my own skull.
Frith's textbook conceptual confusion is best portrayed in the final two sentences. It is supposed that 3D vision is made possible because the brain processes the 2D image on the retina and adds in the requisite depth. But this is deeply confused. It is not as if perception would instead be 2D if not for this processing, since we are never looking at images on the retinae, but rather at 3D objects in the world. It is only if we theoretically presuppose that we are somehow on the receiving end of processed inputs from the visual system that we would ever come to suppose that the brain needs to do work in order to preserve the depth of the world which is not visually present on the retinal image. Our brain does not 'create for us' our experiences, since our experiences are typically not created. My experience is my contact with the object. It is not that this contact occurs externally to myself, and I am restricted to contact with images that have been created for us. My experience is rather made possible by, grounded in, causally realised in, the various optical and neurophysiological structures occuring in me and extending between me and the object.