The neural correlates of consciousness: New experimental approaches needed?

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Abstract

It appears that consciousness science is progressing soundly, in particular in its search for the neural correlates of consciousness. There are two main approaches to this search, one is content-based (focusing on the contrast between conscious perception of, e.g., faces vs. houses), the other is state-based (focusing on overall conscious states, e.g., the contrast between dreamless sleep vs. the awake state). Methodological and conceptual considerations of a number of concrete studies show that both approaches are problematic: the content-based approach seems to set aside crucial aspects of consciousness; and the state-based approach seems over-inclusive in a way that is hard to rectify without losing sight of the crucial conscious–unconscious contrast. Consequently, the search for the neural correlates of consciousness is in need of new experimental paradigms.

Introduction

Finding the neural correlates of consciousness (the NCC) is a major focus of cognitive neuroscience. There are two dominant methodological approaches to finding the NCC (set out early by Baars, 1988). One approach is directed at finding the neural correlates of conscious content (such as the conscious perception of a face rather than a house). Another approach is directed at finding the neural correlates of a creature’s overall state of consciousness (such as being awake rather than in dreamless sleep or a vegetative state). It is shown here that, from the point of view of philosophy of science, these approaches are problematic both conceptually and methodologically. In Section 3, I support and develop the view that the first, content-based approach is methodologically compromised because it is unable to target a crucial aspect of consciousness, and I show that reflection on this problem casts doubt on whether the content-based approach is truly directed at a property of being conscious at all. In Section 4, I show how the second, state-based approach has oddly contradictory findings, it risks being over-inclusive, and attempts to evade these problems seem to make the contrast between conscious and unconscious states slip away or make the approach collapse to the problematic content-based approach. I conclude that the field is in need of new experimental approaches.

Section snippets

The two approaches to the neural correlates of consciousness

A discussion by John Searle is useful to introduce the two different approaches and the initial problem for the content-based approach (notice that Searle uses the term “unified conscious field” as a cognate term for state of consciousness; later in this introductory Section I elaborate on some of the terminology common in the debate).

Searle is arguing against the approach taken by for example Christof Koch, who favours the content-based approach to the NCC. In a review of Koch’s influential

The content-based approach to the NCC

The notion of minimal sufficiency is a pragmatic one. It concerns what, in certain background conditions, makes a particular difference in some target phenomenon (cf. Lipton, 2004). What we decide to leave in or out of the minimally sufficient conditions therefore depends on what the particular difference and target phenomena are, as well as on what the background conditions are taken to be. The particular difference will often be a contrast such as “did the target phenomenon occur rather than

The state-based approach to the NCC

It could be thought that if, as Searle suggests and I have just elaborated and developed at length, the content-based NCC approach is not directed at what it is for a content to be conscious, then researchers should discard the content-based approach and adopt the state-based NCC approach on which the crucial contrast is between creatures in overall conscious and in unconscious states. But, contra Searle, this is not what I shall advocate here. It turns out that the state-based approach faces a

Discussion

The argument has been that the content-based approach to identifying the NCC presupposes consciousness in a methodologically compromised manner, and that it may in fact fail to be a methodology uniquely suited to reveal the content NCC, at least when the focus is on what it takes for contents to be conscious rather than for contents to be selected for consciousness. And it has been argued that the state-based approach risks being over-inclusive in a way that is difficult to resolve without

Acknowledgments

Thanks to audiences at ANU, Melbourne University’s Brain and Mind Club, AAP08, and ASSC12. Special thanks to Tim Bayne. This research was supported by Australian Research Council grant DP0984572.

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