Global Workspace Theory
From Wikipedia, the free encyclopedia
Global Workspace Theory (GWT) is a simple cognitive architecture that has been developed to account qualitatively for a large set of matched pairs of conscious and unconscious processes. It was proposed by Bernard Baars (1988, 1997, 2003). Brain interpretations and computational simulations of GWT are the focus of current research.
GWT resembles the concept of Working Memory, and is proposed to correspond to a "momentarily active, subjectively experienced" event in working memory (WM) –-- the "inner domain in which we can rehearse telephone numbers to ourselves or, more interestingly, in which we carry on the narrative of our lives. It is usually thought to include inner speech and visual imagery."
The easiest way to think about GWT is in terms of a "theater metaphor" --- which is not to say that the brain contains a theater in any concrete way, of course. In the "theater of consciousness" a "spotlight of selective attention" shines a bright spot on stage. The bright spot reveals the contents of consciousness, actors moving in and out, making speeches or interacting with each other. The audience is not lit up --- it is in the dark (i.e., unconscious) watching the play. Behind the scenes, also in the dark, are the director (executive processes), stage hands, script writers, scene designers and the like. They shape the visible activities in the bright spot, but are themselves invisible. (See Figure 1).
GWT involves a fleeting memory with a duration of a few seconds (much shorter than the 10-30 seconds of classical working memory). GWT contents are proposed to correspond to what we are conscious of, and are broadcast to a multitude of unconscious cognitive brain processes, which may be called receiving processes. Other unconscious processes, operating in parallel with limited communication between them, can form coalitions which can act as input processes to the global workspace. Since globally broadcast messages can evoke actions in receiving processes throughout the brain, the global workspace may be used to exercise executive control to perform voluntary actions. Individual as well as allied processes compete for access to the global workspace, striving to disseminate their messages to all other processes in an effort to recruit more cohorts and thereby increase the likelihood of achieving their goals.
Baars (1997) suggests that the global workspace "is closely related to conscious experience, though not identical to it." Conscious events may involve more necessary conditions, such as interacting with a "self" system, and executive interpreter in the brain, such as has been suggested by a number of authors including Michael S. Gazzaniga.
Nevertheless, GWT can successfully model a number of characteristics of consciousness, such as its role in handling novel situations, its limited capacity, its sequential nature, and its ability to trigger a vast range of unconscious brain processes. Moreover, GWT lends itself well to computational modeling. Stan Franklin's IDA model is one such computational implementation of GWT. See also (Dehaene, et al., 2003) and (Shanahan, 2006).
GWT also specifies "behind the scenes" contextual systems, which shape conscious contents without ever becoming conscious, such as the dorsal cortical stream of the visual system. This architectural approach leads to specific neural hypotheses. Sensory events in different modalities may compete with each other for consciousness if their contents are incompatible. For example, the audio and video track of a movie will compete rather than fuse if the two tracks are out of synch by more than 100 ms., approximately. The 100 ms time domain corresponds closely with the known brain physiology of consciousness, including brain rhythms in the alpha-theta-gamma domain, and event-related potentials in the 200-300 ms domain.
Susan Blackmore challenged the concept of stream of consciousness in several papers, by stating that "When I say that consciousness is an illusion I do not mean that consciousness does not exist. I mean that consciousness is not what it appears to be. If it seems to be a continuous stream of rich and detailed experiences, happening one after the other to a conscious person, this is the illusion". Blackmore also quotes William James: "The attempt at introspective analysis in these cases is in fact like seizing a spinning top to catch its motion, or trying to turn up the gas quickly enough to see how the darkness looks."
Baars is in agreement with these points. The continuity of the "stream of consciousness" may in fact by illusory, just as the continuity of a movie is illusory. Nevertheless, the seriality of mutually incompatible conscious events is well supported by objective research over some two centuries of experimental work. A simple illustration would be to try to be conscious of two interpretations of an ambiguous figure or word at the same time. When timing is precisely controlled, as in the case of the audio and video tracks of the same movie, seriality appears to be compulsory for potentially conscious events presented within the same 100 msec. interval.
[edit] References
- Baars, Bernard J. (1988), A Cognitive Theory of Consciousness (Cambridge, MA: Cambridge University Press)
- Baars, Bernard J.(1997), In the Theater of Consciousness (New York, NY: Oxford University Press)
- Baars, Bernard J. (2002) The conscious access hypothesis: Origins and recent evidence. Trends in Cognitive Sciences, 8 (1), 47-52.
- Blackmore, Susan (2002). There is no stream of consciousness. Journal of Consciousness Studies 9. 5-6
- Blackmore, Susan (2004). Why Global Workspace Theory cannot explain consciousness(2004) Presentation.
- Damasio, A.R. (1989). Time-locked multiregional retroactivation: A systems-level proposal for the neural substrates of recall and recognition. Cognition 33. 1-2:25-62.
- Dehaene, S., Sergent, C. and Changeux, J.-P. (2003). A neuronal network model linking subjective reports and objective physiological data during conscious perception. Proc. National Academy of Science (USA) 100. 14: 8520-8525.
- Metzinger, T. (ed) (2000). Neural Correlates of Consciousness: Empirical and Conceptual Questions. MIT Press.
- Shanahan, M.P. (2006). A cognitive architecture that combines internal simulation with a global workspace. Consciousness and Cognition 15: 157-176.
