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The conscious access hypothesis: origins and recent evidence

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Abstract

Consciousness might help to mobilize and integrate brain functions that are otherwise separate and independent. Evidence for this ‘conscious access hypothesis’ was described almost two decades ago, in a framework called global workspace theory. The theory had little impact at first, for three reasons: because consciousness was controversial; the evidence, though extensive, was indirect; and integrative theory was unfashionable. Recent neuroimaging evidence appears broadly to support the hypothesis, which has implications for perception, learning, working memory, voluntary control, attention and self systems in the brain.

Section snippets

The rediscovery of consciousness

The idea that consciousness has an integrative function has a long history. Global workspace theory suggests a fleeting memory capacity in which only one consistent content can be dominant at any given moment 1, 2, 3, 4, 5, 6. Dominant information is widely distributed in the brain. This makes sense in a nervous system viewed as a massive distributed set of specialized networks. In such a system, coordination, control, and problem solving could take place by way of a central information

Philosophical questions

Scientific efforts to understand consciousness evoked vigorous philosophical objections. These were essentially the classic mind–body problems: how does private experience relate to the physical world? How do subjective goals result in physical action? Philosophers typically focus on logical arguments and the apparent evidence of private experience. From this basis, conceptual puzzles abound.

Difficult conceptual questions are routine when the sciences turn to new topics. The traditional

Scientific questions about evidence

What constituted relevant evidence for conscious functions was not obvious to many scientists. The apparent answer has emerged slowly over the past few decades. Today, conscious functions are studied experimentally by comparison with closely matched unconscious processes, an approach I have called ‘contrastive analysis’ 1, 2, 3, 4. Research traditions on subliminal priming, automaticity, and implicit cognition have made it clear unconscious comparison conditions for conscious processes are

General criticisms of the theory

The conscious access hypothesis has only recently achieved a degree of consensus. Before brain imaging, it was necessarily dependent on indirect evidence. Integrative theories were often viewed as untestable. Certain assumptions – such as seeing the brain as a set of unconscious specialized networks – were controversial until the past decade. Global workspace theory was mistakenly thought to be a ‘Cartesian theater,’ though not by the author of that critique [12]. And of course, scientific

Seven predictions

Each of the following predictions was controversial twenty years ago, but evidence has accumulated for all of them, as noted below.

(1) Conscious perception involves more than sensory analysis; it enables access to widespread brain sources, whereas unconscious input processing is limited to sensory regions.

To many scientists the term ‘conscious perception’ seemed redundant, and ‘unconscious perception’ a self-contradiction. Yet in the last twenty years many sources of evidence have emerged for

Possible mechanisms of global access

The brain mechanisms of widespread conscious access are unclear at present. Dehaene and Changeux have focused on frontal cortex [9], Edelman and Tononi on complexity in re-entrant thalamocortical dynamics 46, 47, Singer and colleagues on gamma synchrony [48], Flohr on NMDA synapses [49], Llinas on a thalamic hub [50], Newman and Baars on thalamocortical distribution from sensory cortex 1, 51, and so on. Several of these mechanisms could work together.

Conclusions

Consciousness might be a gateway to brain integration, enabling access between otherwise separate neuronal functions. Although this case can be made with cognitive evidence, direct testing of the hypothesis is now possible by brain monitoring. More studies are needed to explore the hypothesis.

Acknowledgements

The author gratefully acknowledges the support of The Neurosciences Institute, San Diego, and its Director Gerald M. Edelman, in preparing this paper.

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