The Neutrality Thesis, Neural Correlates and the Encroachment of Science on Metaphysics
Ask a philosopher of mind about the relation between the metaphysics and science of consciousness and they will usually respond in the following way: ‘‘of course, we metaphysicians of mind all agree that our theories of consciousness ought to be consistent with what the empirical sciences are saying about the neural basis of consciousness - and our ontological theories are so consistent - but really, the evidential data can’t settle the ontological questions we’re interested in, so we’re justified in ignoring the details of this research and continuing with a priori argumentation’’. Call views of this kind the Neutrality Thesis. Put in less colloquial terms, this can be stated as follows:
The Neutrality Thesis: the current evidential data - in this instance, from the science of consciousness - is neutral with regard to, or rather underdetermines, ontological theory choice in the metaphysics of consciousness.
There are many examples in the literature where some variation of this thesis is explicitly stated or relied upon. I’ll just quote one of my favourites here, which comes from the research statement of the New Directions in the Study of Mind project at the University of Cambridge (2015-17) (a project which recently funded the development and elaboration of alternative naturalistic non-physicalist research frameworks). In the description of the project’s main research aims, PI Tim Crane writes:
''The current project rejects this assumption[that the empirical study of consciousness demands the truth of physicalism]. It will maintain that the scientific investigation of the mind—by psychology and neuroscience—does not require that physicalism is true. One of the distinctive features of this project, then, is the combination of a skeptical attitude to physicalism with a fully scientific approach to the mind’’.
On one view of the relationship between philosophy and science more broadly, acceptance of this neutrality thesis is to be expected. If one endorses the view that philosophy and science can be distinguished, for example, both on the basis of the subject matter studied and the methodology used to study it (perhaps you might think that metaphysics is best understood as an entirely a priori enterprise concerned exclusively with answering questions on modality and essence) then it would hardly make sense to question the claim that the science of consciousness is philosophically unilluminating. However, a brief look at past developments in the philosophy of mind over the last 50 years suggests that this characterisation of metaphysics and science - at least when applied to the metaphysics of consciousness - is incorrect. Examination of the ongoing debate over consciousness’ ontological status reveals not only that scientific developments have potential to impact ontological theorising about the nature of consciousness, but that they have in fact had a huge influence on what philosophers now take to be credible theories of consciousness.
The primary example which can be used to demonstrate this is the scientific case for, and subsequent philosophical acceptance of, the causal closure principle (roughly, the claim that every physical effect has a sufficient physical cause). Motivated by inductive arguments based on empirical premises (from fundamental physics and contemporary neuroscience respectively) the causal closure principle figures as a crucial premise in the central argument in favour of physicalism - the now dominant and widely accepted metaphysical world view and ontological theory of consciousness. Even those who reject the physicalists’ metaphysical thesis, tend to do so only if the resultant non-physicalist theory can be reconciled with the acceptance of causal closure - for example by either by adopting an epiphenomenalist position, or endorsing a variation of Russellian Monism. This predicament will be familiar to contemporary philosophers of mind (note the diagnosis of the rise of physicalism in the context of the ‘causal closure argument’ is due to David Papineau - see here and here) however it’s methodological implications are rarely considered. In other words, scientific developments have played a direct role in determining the parameters of acceptable metaphysical theories of consciousness.
Once this is recognised, it makes the uncritical or blanket acceptance of the neutrality thesis in contemporary philosophy of mind all the more striking. We can’t support the neutrality claim by appealing to the robust topical and methodological independence of science and philosophy, because to do so would contradict or go against the standard explanation for acceptance of causal closure and subsequent rise of physicalism. Unless we want to celebrate the return of the interactionist dualism that the closure arguments supposedly repudiated, we need an alternative argument for the neutrality thesis, specific to the (neuro)science of consciousness, which gives us positive reason to think that the rich amount of empirical data emerging from this field is ontologically uninformative (and thus compatible with radically different metaphysical theories).
One - and, as far as I can tell, the only - such argument has been proposed by David Chalmers in his book ‘The Character of Consciousness’, which has recently been developed further by Uriah Kriegel. According to these authors, the justification for the neutrality thesis lies not in the robust independence of philosophical and empirical methods of inquiry into consciousness, but rather follows as a natural consequence of the correlational nature of the facts that the neuroscientific research programme aims to establish. As mentioned in my first post, the cornerstone of the empirical science of consciousness since its conception has been the Neural Correlates of Consciousness (NCCs) Research programme (you can read a review of this framework here) which aims at identifying the minimal conditions sufficient for a given conscious representational content or global state. According to Chalmers and Kriegel, the NCC programme allows for straightforward argument in favour of the neutrality thesis, which can be put as follows:
1. Neuroscience as it pertains to the study of consciousness discovers correlational facts.
2. Correlational facts are metaphysically neutral with respect to competing metaphysical theories of mind.
3. Therefore the neuroscience of consciousness is neutral with respect to the metaphysics of mind.
(1.) At first glance appears to be obvious, and follows as a natural analysis of the NCC programme taken at face value. In his discussion, Chalmers’ argues this correlational facts claim follows from what he takes to be the ultimate aim (end game) of of the science of consciousness - the production of of a number of law-like fundamental principles connecting phenomenal and neural data:
‘‘For many purposes, the science of consciousness can remain neutral with respect to these philosophical questions. One can simply regard them as principles of correlation, while staying neutral on their underlying causal and ontological status’’ (2010:47).
Defence of (2.) is similarly straightforward. It is uncontroversial that correlational claims or principles, no matter how systematic, underdetermine a number of broader explanatory relations which hold between the two correlated relata. From the perspective of the metaphysics of mind, the correlational claims produced by NCC paradigms are explanatorily empty, leaving open which precise metaphysical dependency relation - causation, constitution, nomological or metaphysical supervenience and so on - obtains in these cases. When it comes to the neural correlates of consciousness, the main ontological theories of consciousness (barring, of course, interactionist dualism) produce the same empirical predictions and thus, are evidently equivalent.
Case closed, or is it not so simple?
In the first chapter of my thesis I put forward two objections to this argument which I’ll briefly summarise. Sideling my thoughts about the elucidation of second claim, my objections to the argument - which aim to cast doubt on the truth of the first premise of this argument- centre around the following questions:
Is the NCC programme best analysed in terms of the search for correlational facts?
And even so, is the NCC programme exhaustive of the relevant empirical research in the science of consciousness?
I think that the answer to both questions is likely no. Taking this second question first. It should be obvious to those familiar with the field that the NCC paradigms which took centre stage in the 1990s, while central to the contemporary research programme, are no longer constitutive of it. NCC research has since been superseded by discussion and construction - not of law like fundamental relational principles - but of various competing theories and theoretical frameworks which seek to integrate the masses of data produced from the NCC programme - think Global Workspace Theories, Integrated Information Theory and Predictive Coding Frameworks (for review which situates these in the broader scientific context see here). In light of the foregoing argument, what are we to make of these theories? Can we view them as also producing ontologically inoffensive correlational claims, or do they have further explanatory (and ontologically loaded) commitments? While some of these, it might be argued, fail to adequately address the phenomenal aspect of consciousness that philosophers are interested in (GWT I’m looking at you), others - such as IIT - appear to commit us to quite specific ontological theses (claims which, it should be stressed, are not only the uncritical metaphysical meanderings on behalf of its proponents, but result from careful examination of it’s commitments on behalf of philosophers). If there is such research within the contemporary scientific research programme (and I think that there’s a good case to be made that there is) the first claim of the argument - and by extension, the neutrality thesis - is in trouble.
Moving on to the second claim. It’s called the neural correlates of consciousness research programme, how could it possibly be controversial that NCC produces correlational claims? A growing number of philosophers and neuroscientists have begun to challenge the claim that the NCCs are best understood as the search for the neural correlates of consciousness. The central claim here is that assessment of the question - what does the NCC programme aim at? - cannot be ascertained from the purview of philosophy and metaphysics of mind, but is rather a question for the philosophy of science. That is, we need to ask What is cognitive neuroscience in the business of doing? How does it go about explaining phenomena (and by extension, consciousness)? An account of how cognitive neuroscience proceeds, and of its aims, norms and explanatory practices has been a central topic in contemporary philosophy of science. According to the dominant view proposed by the new mechanists, neuroscientific explanation works by uniformly accounting for higher level cognitive phenomena, diverse behaviours such as memory, language and action, via the identification and detailed description of the neural mechanism which brings it about and, in doing so, situating such cognitive phenomena within the causal structure of the world. In other words, the deductive-nomological model of scientific explanation, implicitly relied upon in Chalmers’ discussion of the science of consciousness, is no longer accepted. The claim then, is this extensive explanatory framework places interpretational demands on a philosophical analysis of NCCs which, accordingly, ought to be characterised as the search for the neural mechanisms responsible for consciousness. In the context of the neutrality thesis, such a conclusion is problematic: a recent and growing body of literature on the metaphysics of mechanistic explanation suggests that mechanistic explanation in cognitive neuroscience is not free from ontological commitments.
What are these commitments, and can we not claim that these are just correlative? At the very least, can we not continue with standard philosophical argumentation in tandem until we have a better idea of what the science is telling us? I’ll address these questions in my next few posts, but to pre-empt: we’re currently living through a period in which science is rapidly encroaching on a traditional area of philosophical and metaphysical interest. In my view, this should not provide philosophers with cause for concern, but rather - much like when the causal closure principle became accepted in philosophical circles - with a cause for philosophical optimism and excitement. The potential that research produced as part of the contemporary science of consciousness has to constrain the space of possible theories on the metaphysical nature and constitution of consciousness is not a vice - which we should resist by sticking to our guns with claims about viewing neuroscience as offering explanatorily empty correlational data - but rather a virtue, safeguarding metaphysical enquiry from the objections raised to other areas of contemporary analytic metaphysics which float free from scientific lines of inquiry. I’ll elaborate on this claim in my next post, where I set out one potential methodological framework for navigating this period of philosophical and scientific uncertainty.