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.

O'Brien & Opie's vehicle hypothesis is an attractive framework for the study of consciousness. To fully embrace the hypothesis, however, two of the authors' claims should be extended: first, since phenomenal content is entirely dependent on occurrent brain events and only contingently correlated with external events, it is no longer necessary to regard states of consciousness as representations. Second, the authors' insistence that only stable states of a neural network are conscious seems ad hoc.

O'Brien & Opie's connectionist interpretation of “vehicle,” “process,” and “explicit representation” depends heavily on the notions of “information” and “information processing” that underlie the classic account. When the “cognitivist” assumptions, shared by both accounts, are removed, the connectionist versus classic contrast appears to be between behavioral and linguistic accounts.

O'Brien & Opie's (O&O's) theory demands a view of unconscious processing that is incompatible with virtually all current PDP models of neural activity. Relative to the alternatives, the theory is closer to an AI than a parallel distributed processing (PDP) perspective, and its treatment of phenomenology is ad hoc. It raises at least one important question: Could features of network relaxation be the “switch” that turns an unconscious into a conscious network?

O'Brien & Opie's theory fails to address the issue of consciousness and introspection. They take for granted that once something is experienced, it can be commented on. But introspection requires neural structures that, according to their theory, have nothing to do with experience as such. That makes the tight coupling between the two in humans a mystery.

O'Brien & Opie do not address the question of the psychotherapeutic role of unconscious representational states such as beliefs. A dilemma is proposed: if they accept the legitimacy of such states then they should modify what they say about dissociation, and if they do not, they owe us an account of why.

O'Brien & Opie hold that phenomenal experience should be identified with “stable patterns of activation” across the brain's neural networks, and that this proposal has the potential for closing the ‘explanatory gap' between mental states and brain processes. I argue that they have too much respect for the conceivability argument and that their proposal already does much to close the explanatory gap, but that a “perspicuous nexus” can in principle never be achieved.

O'Brien & Opie's admirably sharp hypothesis gains some of its force by ignoring distinctions in murky areas. I attempt to agitate the waters by suggesting that process and vehicle theories are not so different, that classicism can support a vehicle theory, and that several of the key concepts underlying their theory are less clear than depicted. The connection to information I find especially tenuous. Finally, I address the implications of their theory for unconscious thought.

The theory of consciousness proposed by O'Brien & Opie is open to the Sorites paradox, for it defines a consciousness system internally in terms of computationally relevant units which add up to consciousness only if sufficient in number. The Sorites effect applies on the assumed level of features.

O'Brien & Opie's position is consistent with the existence of implicit learning and subliminal perception below a subjective threshold but it is inconsistent with various other findings in the literature. The main problem with the theory is that it attributes consciousness to too many things. Incorporating the higher order thought theory renders their position more plausible.

O'Brien & Opie present an attractive alternative to the popular but flawed computational process approach to conscious awareness. Their “vehicle” theory, however, is itself seriously flawed by overstrict allegiance to the notion that explicit representation and stability are defining hallmarks of consciously experienced neural activity patterns. Including reentrant interactions among time-varying patterns in different brain areas can begin to repair their theory.

To assess O'Brien & Opie's connectionist vehicle theory of consciousness, (1) it is not enough to point to the methodological weakness of certain experiments (dichotic listening, etc.). Successful cognitive theories postulating explicit unconscious representations have to be taken into account as well. (2) The distinction between vehicle and process theories cannot be drawn in the way envisaged by the authors because a representation's explicitness depends not only on its structural but also on its processing properties. (3) The stability of an activation vector is not very suitable for implementing the explicitness of a representation.

Neither of the explanations O'Brien & Opie offer to account for “subject unity” succeeds. Subject unity cannot arise from constructed personal narratives, because such narratives presuppose a prior unity of experience. Subject unity also cannot arise from projection of experiences to the same position in space, as reflection on pregnant women and the spatially deluded reveals.

The basic postulate that consciousness arises from stable states of recurrent activity is shown to need considerable modification from our current knowledge of the neural networks of the brain. Some of these modifications are outlined.

We address two points in this commentary. First, we question the extent to which O'Brien & Opie have established that the classical approach is unable to support a viable vehicle theory of consciousness. Second, assuming that connectionism does have the resources to support a vehicle theory, we explore how the activity of the units of a PDP network might sum together to form phenomenal experience (PE).

O'Brien & Opie run into conceptual problems trying to equate stable patterns of neural activation with phenomenal experiences. They also seem to make a logical mistake in thinking that the brute association between stable neural patterns and phenomenal experiences implies that they are identical. In general, the authors do not provide us with a story as to why stable neural patterns constitute phenomenal experience.

O'Brien & Opie unfairly restrict the classicist's range of options for explaining phenomenal consciousness. Alternative approaches that rely upon differences among representation types offer better prospects of success. The authors rely upon two distinctions: one between symbol processing and connectionist models, the other between process and vehicle models. In this context, neither distinction may be as clear as they assume.

O'Brien & Opie defend a “vehicle” rather than a “process” theory of consciousness largely on the grounds that only conscious information is “explicit.” I argue that preconscious and unconscious representations can be functionally explicit (semantically well-formed and causally active). I also suggest that their analysis of how neural activation space mirrors the information structure of phenomenal experience fits more naturally into a dual-aspect theory of information than into their reductive physicalism.

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.