Online research in philosophy

Our heads are full of representations, according to cognitive science. It might seem inevitable that conscious states are a type of brain-based representation, but in this paper I argue that representation and consciousness each form conceptually distinct domains. Representational content depends on context, usually causal, as shown by familiar cases in which context varies while brain states do not -- twin earth cases and brains-in-vats, for example. But these same cases show that conscious content does not depend on context. The vatted brain, for example, enjoys the same experiences as its in vivo counterpart. The structure of experience -- its parts and their distinctive characters -- is the dynamic structure of the brain, viewed "from within." I call this position methodological phenomenalism (MP), and consider its prospects as a foundation for a science of consciousness. I close with a consideration of MP on the subjective "character" of conscious states. Turning away from representation dissolves the perplexity of subjectivity, leaving hopeful prospects for the scientific study of consciousness.

The neurophilosophy of consciousness brings neuroscience to bear on philosophical issues concerning phenomenal consciousness, especially issues concerning what makes mental states conscious, what it is that we are conscious of, and the nature of the phenomenal character of conscious states. Here attention is given largely to phenomenal consciousness as it arises in vision. The relevant neuroscience concerns not only neurophysiological and neuroanatomical data, but also computational models of neural networks. The neurophilosophical theories that bring such data to bear on the core philosophical issues of phenomenal conscious construe consciousness largely in terms of representations in neural networks associated with certain processes of attention and memory.

In the past decade, the notion of a neural correlate of consciousness (or NCC) has become a focal point for scientific research on consciousness (Metzinger, 2000a). A growing number of investigators believe that the first step toward a science of consciousness is to discover the neural correlates of consciousness. Indeed, Francis Crick has gone so far as to proclaim that ‘we … need to discover the neural correlates of consciousness.… For this task the primate visual system seems especially attractive.… No longer need one spend time attempting … to endure the tedium of philosophers perpetually disagreeing with each other. Con- sciousness is now largely a scientific problem’ (Crick, 1996, p. 486).2 Yet the question of what it means to be a neural correlate of consciousness is actually far from straightforward, for it involves fundamental empirical, methodological, and _philosophical _issues about the nature of consciousness and its relationship to the brain. Even if one assumes, as we do, that states of consciousness causally depend on states of the brain, one can nevertheless wonder in what sense there is, or could be, such a thing as a neural correlate of consciousness.

For a theory of phenomenal consciousness, the real issue is not that between vehicle and process, but between naturalistic and deconstructive theories. Most current naturalistic theories combine a hypothesis about the neural correlate of consciousness with a subsequent naturalistic proposal about how to close the explanatory gap. Deconstructive theories use theses about the neural correlate of consciousness only to motivate and support their claim that the “hard problem” of consciousness is a pseudo-problem which is not to be solved, but rather dissolved on non-naturalistic grounds. O'Brien & Opie present a hypothesis concerning the neural correlate of consciousness, but no genuine strategy to close the explanatory gap. Their theory can, however, contribute to the success of a deconstructive theory of PC.

The prima facie heterogeneity between psychical and physical phenomena seems to be a serious objection to psychoneural identity thesis, according to many authors, from Leibniz to Popper. It is argued that this objection can be superseded by a different conception of consciousness. Consciousness, while being conscious of something, is always unconscious of itself . Consciousness of being conscious is not immediate, it involves another, second-order, conscious state. The appearance of mental states to second-order consciousness does not reveal their true nature. Psychoneural identity can thus be considered a valid hypothesis. Related views of Kant, Freud, Shaffer, Bunge and others are considered. “Naive psychical realism” is criticised. Consciousness of mental events is considered as the result of the action of a cerebral system that observes the neural events hypothetically identical to mental events. The theory combines a materialist view with a due consideration of subjective experience.

Neural Darwinism (ND) is a large scale selectionist theory of brain development and function that has been hypothesized to relate to consciousness. According to ND, consciousness is entailed by reentrant interactions among neuronal populations in the thalamocortical system (the ‘dynamic core’). These interactions, which permit high-order discriminations among possible core states, confer selective advantages on organisms possessing them by linking current perceptual events to a past history of value-dependent learning. Here, we assess the consistency of ND with 16 widely recognized properties of consciousness, both physiological (for example, consciousness is associated with widespread, relatively fast, low amplitude interactions in the thalamocortical system), and phenomenal (for example, consciousness involves the existence of a private flow of events available only to the experiencing subject). While no theory accounts fully for all of these properties at present, we find that ND and its recent extensions fare well.

Though we fully agree that unconscious processing produces explicit representations that form the conscious phenomenal experience of the subject, identifying phenomenal experience with stable patterns of activation in a PDP network seriously limits O'Brien & Opie's thesis. They fail to recognize the constructive role of consciousness during the learning episode itself, reducing consciousness to a resulting outcome of the learning episode. We illustrate how consciousness can guide and shape the formation of increasingly structured representations of the world by presenting a brief outline of a model for speech segmentation.

O'Brien & Opie make unnecessary distinctions between vehicle and process theories and neglect empirically based distinctions between conscious and unconscious processing. We argue that phenomenal experience emerges, not just as a byproduct of input-driven parallel distributed processing, but as a result of constructive processing in recurrent neural networks. Stable network states may be necessary, but are not sufficient, for consciousness.

O'Brien & Opie's connectionist vehicle theory of consciousness is heavily dependent on their notion of explicitness as (1) structural and (2) necessary and sufficient for consciousness. These assumptions unnecessarily constrain their position: the authors are forced to find an intrinsic property of patterns that accounts for the distinction between conscious and unconscious states. Their candidate property, stability, does not capture this distinction. Yet, I show that we can drop assumptions (1) and (2) and still develop a vehicle theory of consciousness. This alternative is better served by models that incorporate both connectionist and symbolic representations.

Biological foundations of the psychoneural identity hypothesis are explicated and their implications discussed. "Consciousness per se" and phenomenal contents of consciousness per se are seen to be identical with events in the (unobserved) brain in accordance with Leibniz's Law, but only informationally equivalent to neural events as observed. Phenomenal content potentially is recoverable by empirical means from observed neural events, but the converse is not possible. Consciousness per se is identical with events which do not represent anything distal to sensory receptor-transducer systems. Thus, on the psychoneural identity hypothesis, consciousness per se comprises directly physical events-in-themselves rather than being a Euclidean representation of physical events as is the case for phenomenal content. After comparing consciousness per se to "onta," a paradox is suggested: rather than being irreducible to physical reality, consciousness per se is the only experience congruent with the ultimate nature of physical reality as conceived by contemporary physics.