Tom Clark recently drew my attention to Thomas Metzinger's chapter in Conscious Experience in support of his counter-intuitive conclusions on the hard problem debate. I would endorse Tom's view that it is an excellent book -- in fact I would encourage all readers of this forum to buy it (of course this has nothing to do with the fact that we publish it!) However I found Metzinger's chapter (1995) unconvincing for a number of reasons.
He begins with an outline of our "folk psychological" experience, which certainly seems to be centred around a phenomenal I, the experiencer. But if you look inside the brain you can't find any little green men and this has given rise to a fear of homunculi, agents and Cartesian theatres which I will refer to as homuphobia. All this has resulted in various attemps to build a bottom-up theory, at any cost.
Metzinger draws on the research of von der Malsburg, Engel, Gray, Singer, Llinas, Crick, Koch and others to construct what he calls a truly natural-science, bottom-up theory to resolve the binding problem. Perceptual binding is held to result from phase-locked oscillations in the feature-detection neurons involved in the perception of a particular object. This binding is both spatial in nature (across distributed areas in the brain) and also temporal, as illustrated by Llinas (1996). Metzinger cites Valerie Gray Hardcastle's (1994) article Psychology's binding problem and possible neurobiological solutions, pointing out that she proposes a bottom-up associative Humean answer to a Kantian problem. (However he fails to mention that Hardcastle is highly critical of the "premature" significance given to these 40 hz. oscillations, and it is hard to see what support for his thesis he can hope to gain from this particular source. In fact she explicity rejects the 40 hz. model, saying "this too is a 'Kantian' solution: the brain actively binds together separately processed features") The consequence of this process of perceptual binding is that the brain constructs models of objects, scenes and the world. According to Metzinger the phenomenal self is just another model that we forget is a model and take to be ontologically real.
Hardcastle is quick to point out that the evidence for the 40hz. model as a solution to the binding problem doesn't really add up and it's interesting to note that much of the enthusiasm for this model has evaporated recently. The obvious question that one would ask is whether the oscillations are the cause or the consequence of perceptual binding. Is it just a spurious correlation? Put more directly:
how does the brain "know" that the output of certain feature-detecting neurons is part of any particular object without a prior (top-down) model of that object?
Or as Hardcastle puts it "They must somehow work out how to indicate that this neuron over here with this particular receptive field is signalling a bit of the same feature as that neuron over there with that particular receptive field" (p. 77). There is no way that this could be accounted for by synchronous oscillations alone as this would require some prior relational knowledge by the system. If there are other cues (neighbourhood, similarity, continuity of motion, common retinal location etc.) then synchronous oscillations are the effect, not the cause of perceptual binding. And it is even less clear how a purely bottom-up approach could account for Necker cubes, Rubin vases, Wittgenstinian duck-rabbits and other perceptual gestalts.
If this is in fact the case then the argument for binding through synchronous oscillations is at best trivial and at worst circular. And if we have to introduce top-down models to explain feature binding and object recognition, then the attempt to describe the phenomenal self in exclusively bottom-up terms is doomed from the outset.
It seems to me that the contributions of philosophers to cognitive science are of two forms. First of all, we have the "so what" approach, which is intended to keep brain researchers on their toes and to point out when they are guilty of conceptual confusion or conflation. A good recent example here is Block (1996), in which he targeted Crick and Koch's recent Nature article where they conclude that striate cortex is not part of the neural correlate of consciousness. Block argued that C&K are guilty of a confusion between "phenomenal" and "access" consciousness. This sort of philosophical critique is an invaluable constraint on theory building in the brain sciences.
The other approach though is when philosophers trawl through the neuroscientific data in order to give their own (thinly concealed) metaphysical theories a spurious empirical quality. There is a widespread belief within the cognitive sciences that the phenomenal self is a constructed illusion. This is partly due to a robust homuphobia but in some cases also seems to result from a misunderstanding of certain teachings of the Buddha. For example, Claxton (1996) makes a remarkably similar case to Metzinger, but acknowledges explicity his inspiration -- Abhidhamma Buddhism. I have no way of knowing whether Metzinger draws on similar sources, but authors in general could be more explicit as to how their own philosophical and religious convictions affect their theory building.
I don't actually have any a priori objection to incorporating religious insights to help unravel the problem of consciousness. As John Searle pointed out at Tucson, now that we live in a de-mystified world there is no principled problem in including such insights within a testable natural-science approach. But, I would maintain, in the field of human consciousness it is better to start with our own experience rather than dogma. One's own experience, which is perhaps the only starting point, seems to be centred around a phenomenal experiencer. But if you look inside the brain you can't find any little green men and this has given rise to a fear of homunculi, agents and Cartesian theatres. All this has resulted in some desperate and flawed attemps to build a bottom-up theory.
Metzinger devotes just half a sentence (and tucked away in a footnote at that!) to the possibility that top-down effects may exist "in some cases" and then, panicking that the ghost of agency has not been truly exorcised adds: "However, one must [my emph] not conceive of such downward-processes as if there was a homunculus in the system, a little man pointing a beam of its already given awareness at inner states and thereby turning them into intentional objects: the phenomenal self, the centre of our inner experiential space, must [my emph] itself be thought of as a naturally emerged representational object, a transient computational model, which the system uses in organizing its behaviour". (p. 435, f.)
Sorry Thomas, the cat's out of the bag -- the magician has pulled the rabbit out of his hat. Just like the behaviourists with their "fractional antedating goal responses" (article Rosch, 1994), the agent has crept back into the system just like he always will.
Metzinger also chooses to ignore the entire literature on the psychology of perception! The only reason I can imagine for this is that it fails to accord with his "bottom-up" approach. For anyone working in perception research it is self-evident that some kind of top-down object hypothesis is essential -- whether it takes the form of Treisman's attentional "master map" or Prinzmetal's "object templates". And many neurologists (Turner, 1996) are drawing our attention to the data from fMRI that area V1 is subject to modulation from higher cortical areas, due to generous re-entrant pathways. The evidence reported by Turner contradicts the widespread view that "primary sensory areas and lower level integrative areas merely contain passive maps or representations of external conditions accessible to the senses".
However Metzinger does quote approvingly von der Malsberg (1986):
It is an ineradicable misconception that the unity of perception has to be established in a separate center, which in addition is often imagined as being of structureless unity itself. This mental archetype leads to infinite regress and to absurdity. Instead, the unity of mind has to be seen as an organic equilibrium among a great multitude of elements.
According to this approach there is no alternative to the reductive method. Well, I've no problem with this in principle, but the argument from the evidence fails to convince. I would argue that, given our own experience and the current state of the neurosciences that a more plausible and Occam-compatible solution is the radical conclusion of Erwin Schroedinger (1993), outlined so nicely in Andrew Robinson's lead article in the THES Tucson supplement.
How can "I" observe "I"? What are we really seeing when we stare into the depths of our own eyes in a mirror? Another great physicist, Erwin Schroedinger, one of the founders of quantum theory, pondered on the problem in the tantalising epilogue of his classic What Is Life?
Consciousness is never experienced in the plural, only in the singular. Even in the pathological cases of split consciousness or double personality the two persons alternate, they are never manifest simultaneously. In a dream we do perform several characters at the same time, but not indiscriminately: we are one of them; in him we act and speak directly, while we often eagerly await the answer or response of another person, unaware of the fact that it is we who control his movements and his speech just as much as our own.
Schroedinger encapsulated the problem of consciousness in the form of two premises:
- My body functions as a pure mechanism according to the laws of nature.
- Yet I know, by incontrovertible direct experience, that I am directing its motions, of which I foresee the effects, that may be fateful and all-important, in which case I feel and take full responsibility for them.
To avoid a contradiction here, he said, "The only possible inference from these two facts is, I think, that I -- I in the widest meaning of the word, that is to say, every conscious mind that has ever said or felt 'I' -- am the person, if any, who controls the 'motion of the atoms' according to the laws of nature." And this would lead you to say, Schroedinger provocatively suggested: "Hence I am God Almighty".
Though even today to many western ears such a statement sounds both "blasphemous and lunatic" -- and in 1943 it caused the rejection of What is Life? by its original (Catholic) publisher -- the idea is hardly new. As its author noted, this "grandest of all thoughts" was recorded in the Upanishads more than 2,500 years ago, and has long been considered the deepest insight in Indian philosophy. Surely, said Schroedinger, the singularity of consciousness is more intuitively convincing than the western idea of a plurality of consciousnesses, which leads inevitably to the invention of souls -- as many as there are bodies -- and to unhelpful questions such as whether the soul survives death and whether animals (and bacteria) have souls? Towards the end of his life Schroedinger stated: "The world is a construct of our sensations, perceptions and memories. It is convenient to regard it as existing objectively on its own, But it certainly does not become manifest by its mere existence."
Schroedinger would have been quite happy with Metzinger's constructivist theory of experience and the world (and fell out with Einstein over this, and other issues). But he would have concluded that the notion that the self was a construct was as incoherent as the idea of a sentence without a subject.
But if Schroedinger's account is too radical for your taste there are other natural-science top-down approaches such as Harth (1993). It is interesting that Metzinger devotes no space to a critique of such theories, simply tarring them with his homuphobic brush with all the finesse and discrimination of an Old Salem witchhunt.
However, I would maintain that a science of consciousness which embraces a truly radical empiricism would have no problem with Schroedinger's bold conclusion. Perhaps in a way analogous to the emergence of large cardinals in set theory the final outcome of the positive reductive method in the brain sciences will prove to be yet another equally embarassing infinity.
Block, N. (1996), "Is V1 conscious and in what sense?", Toward a Science of Consciousness 1996, Tucson conference proceedings.
Claxton, G. (1996), "Structure, strategy and the self in the fabrication of conscious experience", JCS 3 (2), pp. 98-111.
Hardcastle, V.G. (1994), "Psychology's binding problem and possible neurobiological solutions", JCS, 1 (1), pp. 66-90.
Harth, E. (1993), The Creative Loop: How the Brain Makes a Mind (London: Addison-Wesley).
Llinas, R. (1996), "Content and context in the thalamocortical system: The basis for congnition", Toward a Science of Consciousness 1996, Tucson conference proceedings.
Metzinger, T. (1995), "Faster than thought: holism, homogeneity and temporal coding" in Conscious Experience, ed. T. Metzinger (Exeter: Imprint Academic).
Rosch, E. (1994), "Is causality circular", JCS, 1 (1), p. 59.
Schrodinger, E. (1993), What is Life? (Cambridge: CUP), originally published 1994.
Turner, R. (1996), "Evidence from functional MRI studies for modulation of neural activity in are v1 by higher cortical activity", Toward a Science of Consciousness 1996, Tucson conference proceedings.
von de Malsberg, C. (1981), "The correlation theory of brain functioning", internal report 81-2 (Gottingen: Max-Planck-Institut fur Biophysikalische Chemie).