Bernard J. Baars
The
global brainweb: An update on global workspace
theory
Guest editorial, Science and Consciousness
Review, October 2003
Source (see
also 1997
presentation with an extended bibliography)

The idea that consciousness has an integrative function has a long
history. The late Francisco Varela and colleagues called it the "brainweb"
(2002). Global Workspace theory suggests a fleeting memory capacity that
enables access between brain functions that are otherwise
separate.

This makes sense in a brain that is a brainweb, viewed as a massive
parallel distributed system of highly specialized processors. In such a
system coordination and control may take place by way of a central
information exchange, allowing some specialized processors -- such as
sensory systems in the brain -- to distribute information to the system as
a whole. This solution works in large-scale computer architectures, which
show typical "limited capacity" behavior when information flows by way of
a global workspace. A sizable body of evidence suggests that consciousness
is the primary agent of such a global access function in humans and other
mammals (Baars, 1983, 1988, 1997, 1998).

The "conscious access hypothesis" therefore implies that consciousness
provide a gateway to many capacities of the brain. Table 1 shows the basic
claims made by GW theory.

Table 1: Theoretical claims: Brain capacities enabled by
conscious events.

1.

Conscious perception enables access to widespread brain sources;
unconscious sensory processing is much more limited.

2.

Conscious perception, inner speech, and visual imagery enable
working memory functions;  there is no evidence for unconscious
access to working memory.

3.

Conscious events enable almost  all kinds of learning:
episodic and explicit learning, but also implicit and skill
learning.

4.

Conscious perceptual feedback enables voluntary control over
motor functions, and perhaps over any neuronal population and even
single neurons.

5.

Conscious contents can evoke selective attention.

6.

Consciousness enables access to "self" --
executive interpreters, located in part in the frontal
cortex.

A number of scientists and philosophers now support some version of
global access. Table 2 shows a dozen of such comments from different
sources, suggesting that the same basic idea emerged independently from
different research traditions. The convergence of ideas is
striking.

Table 2: Some "global workspace" themes since 1983.

Baars, 1983. "Conscious contents provide the nervous system with
coherent, global information."

Edelman, 1989. Global mapping in a reentrant selectionist model
of consciousness in the brain. (Edelman, 1989)

Dennett, 2001. "Theorists are converging from quite different
quarters on a version of the global neuronal workspace model of
consciousness … On the eve of the Decade of the Brain, Baars (1988)
had already described a 'gathering consensus' in much the same
terms: consciousness, he said, is accomplished by a "distributed
society of specialists that is equipped with a working memory,
called a global workspace, whose contents can be broadcast to the
system as a whole" (p. 42).

Kanwisher, 2001. "… in agreement with Baars (1988), it seems
reasonable to hypothesize that awareness of a particular element of
perceptual information must entail not just a strong enough neural
representation of  information, but also access to that
information by most of the rest of the mind/brain."

Dehaene & Naccache, 2001. "We propose a theoretical framework
… the hypothesis of a global neuronal workspace. …We postulate that
this global availability of information through the workspace is
what we subjectively experience as the conscious state."

Edelman & Tononi, 2000 p. 148-149: "When we become aware of
something … it is as if,  suddenly, many different parts of our
brain were privy to information that was previously confined to some
specialized subsystem. … the wide distribution of information
is guaranteed mechanistically by thalamocortical and corticocortical
reentry, which facilitates the interactions among distant regions of
the brain. "

Llinas et al, 1998. "… the thalamus represents a hub from which
any site in the cortex can communicate with any other such site or
sites. … temporal coincidence of specific and non-specific thalamic
activity generates the functional states that characterize human
cognition.

John, 2000. "Evidence has been steadily accumulating that
information about a stimulus  complex is distributed to many
neuronal populations dispersed throughout the brain."

Varela et al, 2001. "… the brain … transiently settling into a
globally consistent state.… (is) the basis for the unity of mind
familiar from everyday experience."

Damasio, 1989. "Meaning is reached by time-locked
multiregional retroactivation of widespread fragment records. Only
the latter records can become contents of consciousness."

While global workspace theory is not the only one to postulate
widespread access associated with consciousness, it develops the idea in
great detail, exploring its implications for learning, working memory,
voluntary control, and self.

A theater metaphor and brain hypotheses:

Like other cognitive architectures, GW theory may be thought of as a
theater of mental functioning. The theater metaphor is too simple, but it
offers a useful first approximation. Consciousness in the metaphor
resembles a bright spot on the stage of immediate memory, directed there
by a spotlight of attention, under executive guidance. The rest of the
theater is dark and unconscious.

This approach leads to specific neural hypotheses.  For sensory
consciousness the bright spot on stage is likely to require the
corresponding sensory projection areas of the cortex. Sensory
consciousness in different modalities may be mutually inhibitory, within
approximately 100-ms time cycles. Sensory cortex can be activated
internally as well as externally, resulting in the "internal senses" of
conscious inner speech and imagery.  Once a conscious sensory content
is established, it is distributed widely to a decentralized "audience" of
expert networks sitting in the darkened theater, presumably using
corticocortical and corticothalamic fibers. This is the primary functional
role of consciousness: to allow a theater architecture to operate in the
brain, in order to integrate, provide access, and coordinate the
functioning of very large numbers of specialized networks that otherwise
operate autonomously (Mountcastle, 1978). All the elements of GW theory
have reasonable brain interpretations, allowing us to generate a set of
specific, testable brain hypotheses about consciousness and its many roles
in the brain. Some of these ideas have now received considerable empirical
support (Baars, 2002).

Inner speech, imagery, and Working Memory.  Both auditory
and visual consciousness can be activated from the inside of the brain.
Inner speech is a particularly important source of conscious events, and
visual imagery is especially useful for spatial problem solving. The areas
of the left hemisphere involved in outer speech are now known to be
involved in inner speech as well (Paulesu, Frith & Frackowiak,
1993).  Likewise, mental imagery is known to involve visual cortex.

Likewise, internally generated feelings may reflect emotional and
motivational processes, including pain, pleasure, hope, fear, sadness,
etc. Such internal sensations may communicate to other parts of the brain
via global broadcasting. Prefrontal executive systems may not have direct
access to action control. Rather, they may work by evoking motivational
imagery, broadcast from the visual cortex, to control relevant parts of
motor cortex, thereby generating appropriate actions. Parts of the brain
that play a role in emotion may also be triggered by global broadcasting
of conscious contents from sensory cortices and insular cortex. For
example, it is established that the midbrain amygdalae are needed to
recognize facial expressions of fear and anger from the visual system (Le
Doux, 1996). Ultimately such areas, working together, shape actions
controlled by frontal cortex and subcortical automatic systems like the
basal ganglia.

Thus many cortical areas work together to transform goals and emotions
into actions (Baars, 1988). Since there are many spatial maps throughout
the brain, the trade language of the brain may consist of activated maps,
paced by temporal oscillations in the alpha to gamma spectrum. Such
oscillations may coordinate the activity of multiple sensory, body space,
and external spatial maps.

The attentional spotlight. The sensory "bright spot" of
consciousness involves a selective attention system (the theater
spotlight), under dual control of frontal executive cortex and automatic
interrupt control from areas such as the brain stem, pain systems, and
emotional centers like the amygdala. It is these attentional interrupt
systems that allow significant stimuli to "break through" into
consciousness in a selective listening task, when the name is spoken in
the unconscious channel.

Context vs. content of sensory experience. A conscious sensory
"bright spot' requires the interaction of sensory analyzers and contextual
systems. In vision sensory content seems to be produced by the ventral
visual pathway, while contextual systems in the dorsal pathway define a
spatial domain within which the sensory event is defined. As pointed out
above, parietal cortex is known to include allocentric and egocentric
spatial maps, which are not themselves objects of consciousness, but which
are required to shape every conscious visual event.

There is a major difference between the symptoms of dysfunctional
content systems such as the visual ventral stream, compared to disordered
context systems. In the case of lesioned content, the subject can
generally notice a missing part of normal experience; but for damage to
context, the system of experiential expectations is itself damaged, so
that one no longer knows what to expect, and hence what is missing. This
may be why parietal neglect is so often accompanied by anosognosia, a
massive but very specific loss of knowledge about one's body space.
Patients suffering from parietal anosognosia may reject their own body
limbs, or see themselves with three hands. Such specific loss of
contextual body information is not accompanied by a loss of general
intelligence or knowledge about the world. Damage to such contextual
knowledge systems may be quite specific.

Self-systems. Cortical activation by a seen object may not be
enough to generate subjective consciousness. The activated visual
information may need to be sent to self-systems, which serve to maintain
constancy of an inner framework across different perceptual situations.
When we walk from room to room in a building, we must maintain a complex
and multi-leveled organization that can be viewed in Global Workspace
theory as a higher-level context. Major goals, for example, are not
changed when we walk from room to room, but conscious perceptual
experiences do change. Gazzaniga (1996) has found a number of conditions
under which split-brain patients encounter conflict between right and left
hemisphere executive and perceptual functions. He has proposed the
existence of a "narrative self" in the left frontal cortex, based on
split-brain patients who are clearly using speech in the left hemisphere
to talk to themselves, sometimes try to force the right hemisphere to obey
its commands. When that proves impossible, the left hemisphere will often
rationalize or reinterpret the sequence of events so as to repair its
understanding of the interhemispheric conflict.

Analogous repairs of reality are observed in other forms of brain
damage, such as parietal neglect. They commonly occur whenever humans are
confronted with major, unexpected life changes. The left-hemisphere
narrative interpreter may be considered as a higher-level context system
that maintains expectations and intentions across many specific
situations. While the narrative stream itself is conscious, it is shaped
by unconscious contextual executive influences.

If we consider Gazzaniga's narrative interpreter of the left hemisphere
to be one kind of self-system in the brain, it must receive its own flow
of sensory input. Visual input from one half of the field may be
integrated in one visual hemisphere, as described above, under retinotopic
control from area V1. But once it comes together in visual cortex, it
needs to be conveyed to frontal areas on the left side of the brain, in
order to inform the narrative interpreter of the current state of
perceptual affairs. The left prefrontal self system then applies a host of
criteria to the input, such as "Did I intend this result?" "Is it
consistent with my current and long-term goals?"  "If not, can I
reinterpret the input to make sense in my running account of reality?"

It is possible that the right hemisphere has a parallel system that
does not speak, internally or externally, but that may be more able to
deal with anomalies via irony, jokes, and other emotionally sophisticated
strategies. The evidence appears to be good that the right prefrontal
cortex can understand such figurative uses of language, while the left
does not.

Full consciousness may not exist without the participation of such
prefrontal self systems.

New brain evidence for global distribution of conscious
contents. On the basis of psychological evidence, GW theory predicted
that conscious contents are widely distributed in the brain (Baars, 1988,
1997). Today that case is supported by a sizable body of brain evidence,
at least for sensory consciousness (Baars, 2002). For example, Dehaene and
colleagues showed that backward-masked visual words evoked brain activity
confined to the well-known visual word recognition areas of cortex
(Dehaene et al, 2001). Identical conscious words triggered higher levels
of activity in these areas, but more importantly, they evoked far more
widely distributed activity in parietal and prefrontal cortex. That result
has now been replicated a dozen times, using different brain imaging
techniques, different experimental comparisons between conscious and
unconscious input (e.g. binocular rivalry, inattentional blindness,
neglect, extinction), and different modalities (audition, pain, vision,
and sensorimotor tasks). In all cases conscious sensory input evoked far
wider and more intense brain activity than identical unconscious
input.

These findings support the general claim that conscious stimuli
mobilize large areas of cortex, presumably to distribute information about
the stimuli. This idea is essential to the following discussion. If
consciousness serves to mobilize many unconscious specialized networks,
the active elements of mental life that always need to be conscious --
input, recall, rehearsal, inner speech, visual imagery and report -- may
be widely distributed in order to recruit specific unconscious functions
needed to carry out those tasks.

Evolutionary considerations

A number of neurobiologists suggest that sensory consciousness emerged
with early mammals or transitional reptiles (therapsids), who evolved a
large thalamocortical complex (e.g. Edelman & Tononi, 2000). Working
memory -- what may be called "extended consciousness" beyond the immediate
contents -- involves two endogenous kinds of sensory consciousness, the
phonological loop (for inner speech), and the visual sketchpad (for
voluntary visual imagery). The phonological loop seems to use the classic
speech regions of the left hemisphere, Broca's and Wernicke's areas.
Wernicke's area is located near auditory cortex, and in the case of inner
speech it seems to support internalized auditory speech perception.
Likewise, visual imagery appears to involve visual cortex, especially when
it is vividly conscious.

Working memory involves the purposeful use of such endogenous sensory
consciousness. It is not clear when the purposeful use of visual imagery
and inner speech evolved, but it plausibly did so after the major growth
of prefrontal cortex and speech areas associated with hominid evolution --
that is, in the last few million years. Prefrontal cortex is key to
voluntary goals in humans, and speech is of course the basis of the
phonological loop involved in mental rehearsal.

In contrast, spontaneous imagery may have appeared much earlier -- such
as the visual image of a lion evoked by the sound of a lion's roar.
Such spontaneous imagery may be common among mammalian prey animals, while
predators may have spontaneous visual images of prey that can be smelled
but not seen. Certainly the dream state, characterized by rich conscious
visual imagery, evolved with early mammals.

Thus both external and endogenous sensory capacities may have evolved
millions of years before the hominid capacities needed for human mental
life. These considerations suggest that endogenous sensory consciousness
long precedes specifically human mental capacities, and that the
distinctive hominid development of human thought depends on voluntary
control of these pre-existing functions. This is especially true of
language and its role in voluntary control of inner speech and purposeful
visual imagery.

Summary and Conclusions

Global Workspace theory suggests that consciousness enables multiple
networks to cooperate and compete in solving problems, such as retrieval
of specific items from immediate memory.  The overall function of
consciousness is to provide widespread access, which in turn may serve
functions of coordination and control. Consciousness is the gateway to the
brain, enabling control even of single neurons and whole neuronal
populations (Baars, 1988). None of these control functions become directly
conscious, of course, but conscious feedback seems required to recruit
control by prefrontal networks. In the metaphor of the theater, it is as
if each specialized audience member can decide locally whether or not to
be driven by input from the bright spot on stage. Executive functions --
the director behind the scenes -- are also largely unconscious, often
using the actor in the spotlight on the stage of working memory capacity
to recruit and trigger specific functions.

Footnotes

1. Global workspace theory emerged from the cognitive architecture
tradition pioneered by Alan Newell and Herbert A. Simon. Newell and his
coworkers were the first to show the utility of a global workspace
capacity in a complex system of specialized knowledge sources, which could
cooperatively solve problems no single constituent could solve alone. The
empirical connection with consciousness was not made in this tradition,
however.

Bernard J. Baars

© B.J. Baars, 2003

Related Stories:
Unconscious states
cast light on consciousness
Consciousness lost:
The lightning storm of seizures

References

B. J. Baars (1983) Conscious contents provide the nervous system with
coherent, global information."  In R.J. Davidson, G.E. Schwartz &
D. Shapiro (Eds.),  Consciousness & Self- regulation. p.
41  NY: Plenum Press.

Baars, B. (1988). A cognitive theory of consciousness. New York:
Cambridge University Press.

Baars, B. (1997). In the theater of consciousness: The workspace of
the mind. New York: Oxford University Press.

Baars, B.J. (2002) The conscious access hypothesis: Origins and recent
evidence. Trends in Cognitive Science Vol. 6 (1), p. 47-52.

Stanislas DeHaene & Lionel Naccache (2001) Toward a cognitive
neuroscience of consciousness: basic evidence and a workspace framework.
Cognition, 79, 1-37, p. 1.

Damasio, A.R. (1989) Time-locked multiregional retroactivation: a
systems-level proposal for the neural substrates of recall and
recognition. Cognition, 1989, 33(1-2):25-62. P 25.

Daniel C. Dennett, Chapter 4. (2001) Are we explaining consciousness
yet? Cognition, 79, 221-237, p. 221.

Edelman, G. M. 1989. Neural Darwinism. New York: Basic
Books.

Edelman, G.M. & Tononi, G. (2000). A universe of consciousness.
How matter become imagination. New York: Basic Books.

E.R. John (2000) Consciousness & Cognition, 10 (2).

Kanwisher, N.  (2001), Neural events and perceptual awareness,
Cognition, 79, 89-113, p. 105.

Llinas, R., Ribary, U., Contreras, D., Pedroarena, C., The neuronal
basis for consciousness. Philos Trans R Soc Lond B Biol Sci 1998
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Varela, F., J.-P. Lachaux, E. Rodriguez, J. Martinerie, The brainweb:
Phase synchronization and large-scale integration.  Nature Reviews
- Neuroscience, 2, April 2001, p. 237.

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