On the basis of neuropsychological evidence, it is clear that attention should be given a role in any model of consciousness. What is known about the many instances of dissociation between explicit and implicit knowledge after brain damage suggests that conscious experience might not be linked to a restricted area of the brain. Even if it were true that there is a single brain area devoted to consciousness, the subicular area would seem to be an unlikely possibility.

An active role for conscious processes in the production of behaviour is proposed, involving top level controls in a hierarchy of behavioural control. It is suggested that by inhibiting or sensitizing lower levels in the hierarchy conscious processes can play a role in the organization of ongoing behaviour. Conscious control can be more or less evident, according to prevailing circumstances.

Gray extrapolates from circuit models of psychopathology to propose neural substrates for the contents of consciousness. I raise three concerns: knowledge of synaptic arrangements may be inadequate to fully support his model; latent inhibition deficits in schizophrenia, a focus of this and related models, are complex and deserve replication; and this conjecture omits discussion of the neuropsychological basis for the contents of the unconscious.

Gray unwisely melds together two distinguishable contributions of consciousness: one to epistemology, the other to evolution. He also renders consciousness needlessly invisible behaviorally.

In Gray's conjecture, mismatches in the subicular comparator and matches have equal prominence in consciousness. In rival cognitive views novelty and difficulty especially elicit more conscious modes of cognition and higher levels of self-regulation. The mismatch between Gray's conjecture and these views is discussed.

Gray's comparator model fails to provide an adequate explanation of consciousness for two reasons. First, it is based on a narrow definition of consciousness that excludes basic phenomenology and active functions of consciousness. Second, match/mismatch decisions can be made without producing an experience of consciousness. The model thus violates the sufficiency criterion.

The communicative aspects of the contents of consciousness are analyzed in the framework of a neural network model of animal communication. We discuss some issues raised by Gray, such as the control of the contents of consciousness, the adaptive value of consciousness, conscious and unconscious behaviors, and the nature of a model's consciousness.

In this commentary, I point out some weaknesses in Gray's target article and, in the light of that discussion, I attempt to delineate the kinds of problem a cognitive neuroscience of consciousness faces on its way to a scientific understanding of subjective experience.

Gray, like other recent authors, seeks a scientific approach to consciousness, but fails to provide a biologically convincing description, partly because he implicitly bases his model on a computationalist foundation that embeds the contents of thought in irreducible symbolic representations. When patterns of neural activity instantiating conscious thought are shorn of homuncular observers, it appears most likely that these patterns and the circuitry that compares them with memories and plans should be found distributed over large regions of neocortex.

All recent memory theories of hippocampal function have incorporated the idea that the hippocampus is required to process items only of some qualitatively specifiahle kind, and is not required to process items of some complementary set. In contrast, it is now proposed that the hippocampus is needed to process stimuli of all kinds, but only when there is a need to associate those stimuli with other events that are temporally discontiguous. In order to form or use temporally discontiguous associations, it (...) is essential to maintain some memory of the first component until the second component has occurred. When the temporal gap to he spanned is small, and the number of items to be temporarily retained is low, a limited-capacity, short-term store is sufficient to allow associations to be formed. Such a store is presumed to operate in parallel with the hippocampus in normal animals. Hippocampal damage disrupts a much higher-capacity store that has a slower decay rate, and so leaves animals with only a very limited ability to form temporally discontiguous associations. Hippocampal damage, however, is not held to affect the long-term storage of associations of any kind, if they can be formed. Analyses of both new and existing data are presented to show that by classifying tasks in terms of the need to use a temporary memory store to retain temporally discontiguous information one can cut right across existing classifications as well as achieve a better fit to the data. The hippocampus thus seems best described as a high-capacity, intermediate-term memory store. (shrink)

If sensations were behaviorally conceived, as they should be, as complex functional patterns of interaction between overt behavior and the environment, there would be no point in searching for them as instantaneous psychic elements within the brain or as internal products of the brain.

Gray hypothesizes that the contents of consciousness correspond to the outputs of a subicular (hippocampal/temporal lobe) comparator that compares the current state of the organism's perceptual world with a predicted state. I argue that Gray has identified a key contributing system to conscious awareness, but that his model is inadequate for explaining how conscious contents are generated in the brain. An alternative model is offered.