As to the working memory, researchers described and investigated this mechanism as a psychological construct for temporary assignments of particular memory items to be kept ready by means of rehearsing loops for further processing in the context of personal behaviour control. There is great evidence that the central part of it is located in the dorsolateral pre-frontal cortex. The content of the working memory changes in a serial manner. Only a single entry of the working memory can be processed at a time. This warrants that causality is preserved for ensueing processes in brain circuits which make use of the working memory content. The entry may be a perceptual one (externally activated cortex) and one of "inner senses" like inner speech or imagery (internally activated sensory cortex). The serial processing of the working memory entries leads to a rather low processing power compared to other processing in the brain which is running in parallel. Some experimental results provide some data about processing rates we can expect of working memory operations.
In order to change the content of the working memory as needed for a next step of processing, an assignment process for pertinent long-term memory items has to be made (also called matching of longterm memory against working memory. It is not surprising that this serial process is rather time-consuming. It becomes immediately obvious that there might come up problems, if for instance, as a common experience in the work realm of automotive guidance and control, tasks have to be performed under narrow time constraints which demand for certain more complex deliberations. This is the reason for the automatic mode of unconscious parallel information processing with direct access to stored (learned) time-dependent action patterns which can be matched in only one processing cycle to fulfil a task (automatic behaviour). In the meantime, strongly supported by brain-imaging investigations in the pursuit of revealing the mechanisms of human consciousness, the working memory model has been extended by way of the so-called global workspace hypothesis. The global workspace hypothesis can be considered as a framework for human consciousness. This hypothesis postulates that:
• there are two main computational spaces in the brain, a processing network of distributed, modular subsystems working in parallel as highly specialised processors, and a so-called global workspace consisting of a distributed set of cortical neurons, located in cortex layers 2 and 3 and characterised by their ability to receive from and send back horizontal projections to homologous neurons in other cortical areas with modular processors through long-range excitatory axons,
• the global neural workspace is formed by the higher levels of a hierarchy of connections between brain processors where these levels are assumed to be widely interconnected by strong long-distance interconnections, • there are processors which do not directly interchange information in an automatic mode, but which can nevertheless gain access to each other's content in a co-ordinated, though variable manner, if they become part of the global workspace,
• the global workspace is characterised by the spontaneous activation of a subset of workspace neurons in a sudden, coherent, and exclusive manner with the rest of workspace neurons being inhibited, thereby exhibiting a particular kind of "brain-scale" activity state; there can only be one such activity state at any given time,
• because of its integrative function the global workspace theory accounts for the ability to reach a wide range of specialised processors so that there knowledge sources can be related to each other in an unpredictable manner and in consciousness, therefore the global workspace is the arena of a limited capacity stream of sequential conscious experiences,
• an amplified state of workspace activity, bringing together several peripheral processors in a coherent brain-scale activation pattern can coexist with the automatic activation of multiple local chains of processors outside the workspace,
• the underlying mechanism of selective gating in the global workspace is a top-down attentional amplification of the activity of certain peripheral processors, by which these processes can be temporily mobilised, i.e. being maintained for a limited duration of time and being made available to the global workspace, and eventually to consciousness; this reveals that attention control is intimately involved in what we consider as consciousness; without dynamic mobilisation a process may still contribute to cognitive performance, but only unconsciously,
• the maintained activities of processors attached to the global workspace constitute the working memory, also called the "stage" in the theatre metaphor for consciousness of; only one of the processor activities may enter consciousness at a given time, depending on various types of contexts residing in evaluation processors which are also connected to the gobal workspace,
• the conscious experience is represented by a chunk of explicit meaning (semantic coding); this representation is much richer than any representation which consists of a set of explicit features only. The chunk can represent a set of explicit features, too, though, or a single one, but the meaning of these features is also explicit,
• bidirectional connections must exist between workspace neurons and a peripheral processor which is in an active state, so that a sustained amplification loop can be established,
• at least the following network systems participate in the workspace: perceptual circuits that inform about the present state of the environment, motor circuits that allow the preparation and controlled execution of actions, long-term memory that can reinstate past workspace states, evaluation circuits that attribute them a valence in relation to previous experience, and attentional or top-down circuits that selectively gate the focus of interest.
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