We discuss the role of short-term auditory verbal storage within a working memory system. Data from single case studies of patients with left parietal lesions and selective impairment of memory span are discussed in order to address the question of the functions of short-term memory in language processing. The backup resource of auditory verbal short-term memory is required for those tasks that necessitate backtracking in order to integrate a verbal message within a developing central cognitive representation.

Caplan & Waters's arguments for separate working memory subsystems for “interpretive” and “post-interpretive” comprehension processes do not have a solid empirical basis. The likely involvement of a separate phonological loop makes their memory-load data irrelevant to theory evaluation, and the lack of statistical power from nonoptimal experimental designs and analyses unfairly reduces the chances of detecting the relevant interactions.

Caplan & Waters propose a dedicated linguistic working memory to handle “interpretive” language comprehension, but there are data suggesting that more general working memory capacity can predict syntactic comprehension difficulty, and their claims depend on the existence of a principled distinction between “interpretive” and “post-interpretive” processes, which seems unlikely. Other conceptions of the source of individual differences also deserve consideration, as more flexible explanations of the phenomena.

The target article differentiates a new, syntactic component in verbal working memory. We suggest that several more components could be differentiated to make a model of working memory complete. Next, syntax is not always separable from the subject's verbal memory capacity as measured by standard working memory tasks. Finally, interference between different processes cannot be taken as evidence for the processes sharing the same resources. Interference might be a result of active mutual inhibition.

Working memory span forms an important cornerstone of current accounts of cognition, and cognitive development. We describe data that challenge the conventional interpretation of span as a measure of working memory capacity. We argue that the implications of these data undermine the analysis provided by Caplan & Waters concerning the role of working memory in sentence comprehension.

Caplan & Waters's model differentiating levels of processing and the role of working memory is important and likely right. However, their claim rests on a lack of correlation between working memory and structural complexity. We examine sources of variability in these measures that remain unaccounted for (by anyone), variability that muddies a straightforward claim that the lack of correlation is cleanly established.

The target article argues for the modularity of language interpretive processes without the usual criterion that a module be informationally encapsulated. It is the encapsulation criterion, however, that gives modularity most of its testability. Without the criterion of encapsulation, testing whether relatively automatic comprehension processes use their own unique resource is a very tricky matter.

Caplan & Waters argue that the processing resources used for sentence comprehension are not drawn from an undifferentiated verbal working memory resource. This commentary cites data from normal aging to support this position. Still lacking in theory development is a specification of the transient memory representations necessary for interpretive and post-interpretive operations.

Commentaries on our target article raise further questions about the validity of an undifferentiated central executive that supplies resources to all verbal tasks. Working memory tasks are more likely to measure divided attention capacities and the efficiency of performing tasks within specific domains than a shared resource pool. In our response to the commentaries, we review and further expand upon empirical findings that relate performance on working memory tasks to sentence processing, concluding that our view that the two are not strongly related remains viable in light of the material presented in the commentaries. We suggest that a productive research enterprise would be to develop the concept of working memory as a pool of resources in relation to specific tasks.

When cognitive scientists apply computational theory to the problem of phenomenal consciousness, as many have been doing recently, there are two fundamentally distinct approaches available. Consciousness is to be explained either in terms of the nature of the representational vehicles the brain deploys or in terms of the computational processes defined over these vehicles. We call versions of these two approaches vehicle and process theories of consciousness, respectively. However, although there may be space for vehicle theories of consciousness in cognitive science, they are relatively rare. This is because of the influence exerted, on the one hand, by a large body of research that purports to show that the explicit representation of information in the brain and conscious experience are dissociable, and on the other, by the classical computational theory of mind – the theory that takes human cognition to be a species of symbol manipulation. Two recent developments in cognitive science combine to suggest that a reappraisal of this situation is in order. First, a number of theorists have recently been highly critical of the experimental methodologies used in the dissociation studies – so critical, in fact, that it is no longer reasonable to assume that the dissociability of conscious experience and explicit representation has been adequately demonstrated. Second, classicism, as a theory of human cognition, is no longer as dominant in cognitive science as it once was. It now has a lively competitor in the form of connectionism; and connectionism, unlike classicism, does have the computational resources to support a robust vehicle theory of consciousness. In this target article we develop and defend this connectionist vehicle theory of consciousness. It takes the form of the following simple empirical hypothesis: phenomenal experience consists of the explicit representation of information in neurally realized parallel distributed processing (PDP) networks. This hypothesis leads us to reassess some common wisdom about consciousness, but, we argue, in fruitful and ultimately plausible ways.

The target article offers an intriguing hypothesis relating the content of phenomenal experience to a qualitative characteristic of information processing. This hypothesis, however, offers only an explanation of the “what” of consciousness, not the “who” – the experiencing agent remains mysterious. Their hypothesis about the unity of consciousness can be linked to an informational account of the agency or subjectivity of consciousness.

The notion of an explicit representation plays a crucial role in O'Brien & Opie's arguments. Clarifying what explicit representation involves proves difficult, however, as various explications of this key notion fail to make sense of the overall argument. In particular, neither the notion of encoding in discrete objects nor the notion of active versus potentially active representation seems to help in specifying what is distinctive of conscious representation.

O'Brien & Opie's theory of consciousness relies heavily on a distinction between explicit activation vectors and inexplicit weight vectors. But determining which representations are explicit vehicles requires appeal to process, and so their vehicle theory is in fact a process theory.

Stability of activation, while it may be necessary for information to become available to consciousness, is not sufficient to produce phenomenal experience. We suggest that consciousness involves access to information and that access makes information symbolic. From this perspective, implicit representations exist, and are best thought of as subsymbolic. Crucially, such representations can be causally efficacious in the absence of consciousness.

O'Brien & Opie believe that some mental representations are evoked by stimuli to which a person is attending, and other mental representations are evoked by stimuli to which attention was not paid. I argue that this is the classical view of consciousness; yet this is the view which they wish to challenge.

A pure vehicle theory of the contents of consciousness is not possible. While it is true that hard-wired tacit representations are insufficient as content vehicles, not all tacit representations are hardwired. O'Brien & Opie's definition of stability for patterns of neural activation is not well-motivated and too simplistic. We disagree in particular with the assumption that stability in a network is purely intrinsic to that network. Many complex forms of stability in a network are apparent only when interpreted by something external to that network. The requirement for interpretation introduces a necessary functional element into the theory of the contents of consciousness, suggesting that a pure vehicle theory of those contents will not succeed.

Connectionism can provide useful theories in which consciousness is the exclusive vehicle of explicit representation. The theories may not, however, handle some phenomena adequately: sense of agency, modes and contents of awareness, propositional and deliberative thought, metacognitive awareness and consciousness of self. They should, however, be useful in describing automatic, activational relations among nonpropositional conscious contents.

According to “imaginability arguments,” given any explanation of the physiological correlates of consciousness, it remains imaginable that all elements of that explanation could occur without consciousness, which thus remains unexplained. The O'Brien & Opie connectionist approach effectively shows that perspicuous explanations can bridge this explanatory gap, but bringing in other issues – for example, involving biology and emotion – would facilitate going much further in this direction. A major problem is the ambiguity of the term “representation.” Bridging the gap requires perspicuously explaining not just how we form “representations” in the sense of outputs isomorphic to what is represented, but also what makes representations conscious; I sketch briefly what this would entail.

A connectionist vehicle theory of consciousness needs to disambiguate its criteria for identifying the relevant vehicles. Moreover, a vehicle theory may appear entirely arbitrary in sorting between what are typically thought of as conscious and unconscious processes.

Discrimination of forms defined solely by color and discrimination of hue are dissociated in cerebral achromatopsia. Both must be based on potentially explicit information derived from differentially color-sensitive photoreceptors, yet only one gives rise to phenomenal experience of color. By analogy, visual information may be used to form explicit representations for action without giving rise to any phenomenal experience other than that of making the action.