This paper on ‘Biology of Consciousness’ embodies a remarkable alliance: authored by Gerald Edelman, Joseph Gally, and Bernard Baars, it brings together Edelman’s Neural Darwinism and Baars’ Global Workspace into a single united framework. In this field we’re used to the idea that for every two authors there are three theories, so when a union occurs between two highly-respected theories there must be something interesting going on.
As the title suggests, the paper aims to take a biologically-based view, and one that deals with primary consciousness. In human beings the presence of language among other factors adds further layers of complexity to consciousness; here we’re dealing with the more basic form which, it is implied, other vertebrates can reasonably be assumed to share at least in some degree. Research suggests that consciousness of this kind is present when certain kinds of connection between thalamus and cortex are active: other parts of the brain can be excised without eradicating consciousness. In fact, we can take slices out of the cortex and thalamus without banishing the phenomenon either: the really crucial part of the brain appears to be the thalamic intralaminar nuclei. Why them in particular? Their axons radiate out to all areas of the cortex, so it seems highly likely that the crucial element is indeed the connections between thalamus and cortex.
The proposal in a nutshell is that dynamically variable groups of neurons in cortex and thalamus, dispersed but re-entrantly connected constitute a flexible Global Workspace where different inputs can be brought together, and that this is the physical basis of consciousness. Given the extreme diversity and variation of the inputs, the process cannot be effectively ring-mastered by a central control; instead the contents and interactions are determined by a selective process – Edelman’s neural Darwinism (or neural group selection): developmental selection (‘fire together, wire together’), experiential selection, and co-ordination through re-entry.
This all seems to stack up very well (it seems almost too sensible to be the explanation for anything as strange as consciousness). The authors note that this theory helps explain the unity of consciousness. It might seem that it would be useful for a vertebrate to be able to pay attention to several different inputs at once, thinking separately about different potential sources of food, for example: but it doesn’t seem to work that way – in practice there seems to be only one subject of attention at once; perhaps that’s because there is only one ‘Dynamic Core’. This constraint must have compensating advantages, and the authors suggest that these may lie in the ability of a single piece of data to be reflected quickly across a whole raft of different sub-systems. I don’t know whether that is the explanation, but I suspect a good reason for unity has to do with outputs rather than inputs. It might seem useful to deal with more than one input at a time, but having more than one plan of action in response has obvious negative survival value. It seems plausible that part of the value of a Global Workspace would come from its role in filtering down multiple stimuli towards a single coherent set of actions. And indeed, the authors reckon that linked changes in the core could give rise to a coherent flow of discriminations which could account for the ‘stream of consciousness’. I’m not altogether sure about that – without saying it’s impossible a selective process without central control can give rise to the kind of intelligible flow we experience in our mental processes, I don’t quite see how the trick is done. Darwin’s original brand of evolution, after all, gave rise to speciation, not coherence of development. But no doubt much more could be said about this.
Thus far, we seem on pretty solid ground. The authors note that they haven’t accounted for certain key features of consciousness, in particular subjective experience and the sense of self: they also mention intentionality, or meaningfulness. These are, as they say, non-trivial matters and I think honour would have been satisfied if the paper concluded there: instead however, the authors gird their loins and give us a quick view of how these problems might in their view be vanquished.
They start out by emphasising the importance of embodiment and the context of the ‘behavioural trinity’ of brain, body, and world. By integrating sensory and motor signal with stored memories, the ‘Dynamic Core’ can, they suggest, generate conceptual content and provide the basis for intentionality. This might be on the right track, but it doesn’t really tell us what concepts are or how intentionality works: it’s really only an indication of the kind of theory of intentionality which, in a full account, might occupy this space.
On subjective experience, or qualia, the authors point out that neural and bodily responses are by their nature private, and that no third-person description is powerful enough to convey the actual experience. They go on to deny that consciousness is causal: it is, they say, the underlying neural events that have causal power. This seems like a clear endorsement of epiphenomenalism, but I’m not clear how radical they mean to be. One interpretation is that they’re saying consciousness is like the billows: what makes the billows smooth and bright? Well, billows may be things we want to talk about when looking at the surface of the sea, but really if we want to understand them there’s no theory of billows independent of the underlying hydrodynamics. Billows in themselves have no particular explanatory power. On the other hand, we might be talking about the Hepplewhiteness of a table. This particular table may be Hepplewhite, or it may be fake. Its Hepplewhiteness does not affect its ability to hold up cups; all that kind of thing is down to its physical properties. But at a higher level of interpretation Hepplewhiteness may be the thing that caused you to buy it for a decent sum of money. I’m not clear where on this spectrum the authors are placing consciousness – they seem to be leaning towards the ‘nothing but’ end, but personally I think it’s to hard to reconcile our intuitive sense of agency without Hepplewhite or better.
On the self, the authors suggest that neural signals about one’s own responses and proprioception generate a sense of oneself as a separate entity: but they do not address the question of whether and in what sense we can be said to possess real agency: the tenor of the discussion seems sceptical, but doesn’t really go into great depth. This is a little surprising, because the Global Workspace offers a natural locus in which to repose the self. It would be easy, for example, to develop a compatibilist theory of free will in which free acts were defined as those which stem from processes in the workspace but that option is not explored.
The paper concludes with a call to arms: if all this is right, then the best way to vindicate it might be to develop a conscious artefact: a machine built on this model which displays signs of consciousness – a benchmark might be clear signs of the ability to rotate an image or hold a simulation. The authors acknowledge that there might be technical constraints, but I think they an afford to be optimistic. I believe Henry Markram, of the Blue Brain project, is now pressing for the construction of a supercomputer able to simulate an entire brain in full detail, so the construction of a mere Global Dynamic Core Workspace ought to be within the bounds of possibility – if there are any takers..?