There is one kind of functional equivalent to the Global Workspace system, in which the Mind's Senses are global workspaces, wired so that only one can work at a time. As we have noted, the Mind's Senses can be treated as workspaces of a kind. Inner speech has of course long been associated with Short Term Memory or "working memory". Note however that we have some voluntary control over visual imagery, and especially over inner speech. Voluntary control is something which a theory of conscious experience should tell us about. Certainly we cannot take voluntary control for granted, or presuppose it in a theory of mental imagery. Further, current models of mental imagery have little to say about consciousness as such. They typically do not account for habituation and automatization. What is the global code? . Such a common code seems plausible to make a GW system work, though it may not be absolutely necessary, since one could broadcast local codes through a global workspace.  One possibility is that input into the GW may be perceptual or quasi-perceptual, and that processors in the "audience" respond only to the most general aspects of these global message, namely their spatio-temporal properties. Thus a motor control program may be able to recognize at least the spatio-temporal aspects of a rich perceptual scene, enough  to know that "something of interest is happening at 12 o'clock high at this very moment". The motor program could then cause other receptors to orient to the stimulus, thereby helping to make better information available to all relevant parts of the system. The idea that the lingua franca may be a spatio-temporal code is consistent with the fact that many brain structures are sensitive to spatio-temporal information. 

We know that biofeedback training, which can be done with any specialized system,  always involves temporal near-simultaneity between the biofeedback event and the conscious feedback signal. This is consistent with the notion of global temporal coding.  Ideas related to the GW system have been discussed for some time. More recently, Lindsay and Norman have pointed to the global workspace architecture as a psychological model, as have others. Recent work on formal models of distributed systems also has explored a global workspace architecture. Others refer to the "spotlight of consciousness" .
A GW is a natural domain for interaction between otherwise separate capacities. There are fewer sources for the somewhat surprising notion that conscious experiences may be broadcast everywhere in the nervous system.  E.R. John's "statistical model of learning" seems to be closely related to this, and Gazzaniga suggests a specific connection between conscious experience an a publicity device. Neurophysiologists have long known about diffuse and non-specific anatomical areas, and some neuroanatomists have explicitly related the brain stem reticular formation to Aristotle's common sense. Gazzaniga has recently proposed that consciousness serves as a publicity organ in the brain. Curiously enough, he also suggests that its primary function is post-hoc rationalization of past events. This seems an unduly limited view of the functions of consciousness.   Conscious processes are computationally inefficient, but unconscious processors are highly efficient in their specialized tasks. Try to calculate (9 x 325)/4, doing each mental operation completely consciously. Or try to "diagram a sentence" consciously --- assigning syntactic clause boundaries, word categories like noun, verb, adjective, etc., and deciding on the subject and object of the sentence. Probably no one can do even one of these symbolic operations completely consciously. Even linguists who have studied syntax for many years cannot parse a sentence consciously. The rare individuals who are extremely good at mental arithmetic have probably learned through long practice to do most computational steps automatically, with minimal conscious involvement.

                  Compared to similar unconscious processes, tasks performed consciously are slow, vulnerable to interference from other conscious or effortful mental processes, and hence prone toerror. Consider each of these characteristics in turn:  The speed of conscious events is relatively slow. Simple reaction time (the time needed to give a single known response to a single known stimulus) is at best about 100 milliseconds. This is also the time region in which we experience perceptual fusion between physically different stimuli, and Blumenthal gives seven arguments in favor of the idea that the minimum "conscious moment" is ranges around 100 milliseconds. In contrast, unconscious processes may take place at the speed  of neural firing, ranging from 40 to 1000 times per second. In speech, when we say "bah", the vocal cords begin to vibrate before the lips open; when we say "pah" the order is reversed. The difference in this voice-onset time between "pah" and "bah" is about 20 milliseconds, much faster than conscious reaction time, and faster than the minimal integration time discussed by Blumenthal. But of course we do not consciously control the details of the /pa/-/ba/ difference.
                  Conscious events are vulnerable to interference. Below we will make much of the remarkable fact that any conscious event can interfere with any other. Perceptual experiences in any sense modality interfere with those in any other. Any percept we experience will interfere with any mental image. Any mental image interferes with any simultaneous emotional or bodily feeling. Any of these experiences interfere with any voluntary, effortful action. And anything said in  inner speech interferes with percepts, feelings, images, or mentally effortful actions.This fact is fundamental.       Unconscious processes, on the other hand, interfere with each less predictably. We have previously shown the lack of interference between automatic and voluntarily controlled skills. Finally, conscious events are prone to error. Even simple mental arithmetic is hard to do without error, much less conscious syntactic analysis, visual scene analysis, etc. This vulnerability to error is of great practical importance, since most airplane crashes, road accidents, and industrial disasters have a significant component of human error. Not all human errors are due to the limitations of consciousness --- many are due to the rather different limitations of unconscious events. But conscious processing limitations are surely part of the problem.  

                  By contrast to conscious limits, of course, unconscious processing of highly practiced, specialized functions is much more efficient. Given this catalogue of woe about conscious processes, we may be tempted to ask, what good does it do? Should we give up consciousness if we had a choice? Or does it give the nervous system some selective advantage not provided by unconscious processes? The answer, fortunately, is yes. Consider the following points.   

               Conscious processes have a great range of possible contents, but the range of any single unconscious processor is limited. We can be conscious of an essentially endless range of possible contents: sensory and perceptual aspects of the world around us, internally generated images, dreams,  inner speech, emotional feelings, pleasures and pains. If we include conscious aspects of beliefs, concepts, and intentions, the range of possible contents becomes even greater. There is good evidence that we can gain a degree of conscious control over virtually any population of neurons, provided that we receive immediate conscious feedback from the neural activity. Put all these things together, and it becomes clear that conscious contents can be involved in essentially any aspect of neural functioning. The range of conscious contents and involvements is simply enormous. 

                  How do we know that unconscious processors tend to have limited range? One consideration is that specialization in general seems to lead to limitation. If there is an unconscious syntax processor, it is unlikely to be much good analyzing visual scenes can easily avoid these errors by remaining conscious of what we are doing. Langer and Imber have been able to induce mindless behavior by over-practicing people on a simple task, and found that once the task has been practiced to the point of being automatic and unconscious, the subjects can no longer accurately estimate the number of steps in the task. Further, subjects are much more willing than before to accept the false inference that they have performed poorly on the task, even when they have performed quite well! Obviously automaticity has its drawbacks. 

                  These examples are revealing because they seem to show the functioning of  conscious components (specialized processors) without the intervention of conscious control. In each case, this functioning seems exceptionally "blind" because it seems to proceed in ignorance of apparently obvious changes in task and context. The overall pattern supports our basic contention that "unconscious processors have relatively limited range". 

                  The whole pattern makes sense if we consider the advantages and disadvantages of specialization. Clearly the main advantage of specialization is that one knows exactly what to do in a particular, routine situation. In computer language, one has a well worked-out algorithm for solving a particular problem. This off-the-shelf algorithm is unexcelled for its particular purpose, but it is likely to be useless for any other. The main drawback of specialization for routine tasks is a loss of flexibility in dealing with new situations. 

                  Thus it seems that unconscious processors are excellent tools for dealing with whatever is known. Conscious capacity is called upon to deal with any degree of novelty. This leads directly to the next point. But consciousness has more than this kind of relational capacity; it also facilitates context-sensitivity. Context-sensitivity" is defined here as the way in which conscious events are shaped by unconscious factors. There are numerous examples of this. Perhaps the most obvious ones come from everyday examples of carrying out a routine action. When driving a car, we may take the same route every day, so that the predictable actions needed to drive become less conscious over time. If we something new happens on the route from home to work, previously unconscious elements must become more conscious to adapt to the new situation. If we resolve one day to drive to the grocery store on the way home, we may suddenly find ourselves already home without having gone to the store, because we failed be conscious of our goal at a critical intersection. Similarly, even if we know ahead of time that the road is blocked along our familiar route, that knowledge must become conscious in time to make the appropriate decisions to drive another way. In general, changes in context are not encoded automatically; they require consciousness. But once‹ contextual information is encoded, it may control our routine actions and experiences without again becoming conscious.   

                  Perception textbooks are filled with examples in which our conscious experiences are profoundly shaped by numerous unexpected unconscious factors. For example, we live in a "carpentered" world, a world of rectangular surfaces and square corners. But we usually look at the surfaces in this world aslant, so that our eyes receive trapezoidal projections, not rectangular ones. Each of these trapezoidal projections can result from an infinite set of rectangles or trapezoids, placed at different angles to the eye. What would happen if we were to look into a space that was made up of trapezoids, positioned in such a way as to cast the same retinal projections as a normal carpentered room?  

                  Adelbert Ames first tried this experiment some fifty years ago, and found that people see the distorted space as a normal, rectangular room. The walls in a trapezoidal room are not of constant height, even though they seem to be constant, and it seems likely that the height of other objects is scaled relative to the nearest wall. What would happen if we observed someone walk back and forth in the Ames distorted room? The person is not changing height, while the walls, which seem of constant height, do change. Hence there is a perceptual conflict between the fact that human height does not change quickly, and the fact that walls are assumed not to change at all. The upshot is quite remarkable: people appear to grow and shrink dramatically as they walk to and from the observer.              

               As they walk toward the short end of the trapezoidal wall, their size in comparison to the perceived height of room may double, and as they walk toward the tall end of the trapezoid, they shrink in comparison. But why do we not see the room's actual proportions, and keep the perceived height of the people constant? For some reason the visual systems seems "committed" to seeing the room as constant in height, and as a result, its only option is to interpret the person's height as changing. Clearly our conscious experience of the person in the Ames room is shaped by unconscious assumptions about the space in which he or she appears.  There are numerous other examples of this sensitivity of conscious contents to unconscious content. Our ability to comprehend a sentence in a conversation depends in great part on whether the new information in the sentence fits into what we take to be given in the conversation . But when we hear the new information, the givens are already unconscious: again, the unconscious context helps to shape the novel, conscious information.  Our ability to learn any  new information is critically dependent on prior, largely unconscious knowledge.

                  Scholars who study changes or differences in knowledge  are often acutely aware of the effects of unconscious presupposed context.  An anthropologist studying a new culture is often forced to confront his or her own unconscious presuppositions, which may become become conscious only in the encounter with a social world that violates them. And historians are well aware that each new age reinterprets the "same" past in accordance with its own presumptions, most of which are quite unconscious at the time they have this effect. 

                  All these examples indicate that unconscious expectations guide our conscious appreciation of the world. This is quite different from the "relational capacity" defined above, which involves relating two conscious events to each other. Context- sensitivity, as we use the term in this book, implies that all conscious experiences are constrained by unconscious context. The contrasting claim about comparable unconscious events is that "unconscious processors are relatively isolated and autonomous." It is the unconscious processors that are presumably responsible for the very smooth and efficient actions cited in the action errors above, which are carried out perfectly well, except for the fact that they are wildly inappropriate to the circumstances. These errors are often amusing because of the inappropriateness of the isolated action, which may be carried out perfectly even though its relevance and purpose are utterly lost.  

                  Action errors all seem to involve either a failure to adjust to a change in the physical situation, or a loss of the current task context. Getting up on a holiday and dressing for work is an error that involves a failure to access a new context. It seems that routine activities run off automatically, and adjusting to a new situation demands some conscious thought. Taking a can opener instead of scissors to cut some flowers seems to involve a loss of the current task context ---  we have "forgotten what we are doing".   

               Conscious experiences have internal consistency, but unconscious processors may be mutually contradictory. We have already pointed out that selective attention always involves a densely coherent stream of events. We never mix up two streams of speech with different contents, or even with different vocal quality. It is generally true that conscious experiences are internally consistent. We never see a mix of the two conscious interpretations. For instance, we never see corner (a) in a different depth plane than corner (b), because to do so would violate the consistency constraints of a rigid, square cube. These phenomena are well known in perception, but they are not limited to perception. The same things are true at the conceptual level. Social psychologists for some decades have investigated cognitive consistency in value judgments and in person perception. Here, too, internal consistency is maintained. We cannot think of two alternative ideas at the very same instant, though we can consider two contradictory ideas one after the other. This becomes very clear when we consider ambiguous words: most words have at least two different abstract, conceptual interpretations. It seems impossible for people to entertain two meanings of words like  "turn," "look," or "book," at the same instant.  

                  By contrast to conscious consistency, unconscious processors working at the same time may be mutually inconsistent. There is a great deal of evidence, for example, that the unconscious meaning of an ambiguous word is represented in the nervous system at the same time as the conscious meaning. Conscious processes are serial, but unconscious processors can operate in parallel. There is much evidence for the seriality of conscious contents, but it is difficult to prove that the seriality is absolute. Conscious experience is one thing after another, a "stream of consciousness" as William James called it. Psychological theories that are largely confined to conscious processes, such as Newell and Simon's theory of human problem solving, postulate largely serial mechanisms.  

                  Automaticity shows the close relationship between consciousness and seriality. As a skill becomes more and more practiced, it becomes less and less conscious; it can then also begin to operate independently from other processes, just as parallel processors does. Conversely, when we interfere with an automatic skill so that  it becomes "de-automatized," it will be more conscious, and it will be slower and more serial as well. However, at very fine time resolution, say the level of milliseconds, the seriality of conscious processes is not so clear. Just as a serial digital computer can simulate a parallel system simply by switching rapidly back and forth between different processes, so it is possible that some apparently parallel events are really controlled by a serial system. For these reasons it is difficult to be absolutely sure about the seriality of consciousness. But it is clear that over a period of seconds and longer, conscious events appear to be serial, while unconscious ones seem to work in parallel.  

                  The claim here is that unconscious processors îcanï operate in parallel, not that they must always do so. Indeed, if unconscious processors are required for a contingent series of decisions, it is hard to conceive how they could work in parallel: if A leads to B which leads to C, then A,B, and C must become available in that order. Thus the linguistic hierarchy discussed in a previous section may operate serially when there is no "top-down" information, even though the hierarchy is largely unconscious. Further evidence for parallel unconscious processing comes From neurophysiology. As Thompson (1967) remarks, organization and functioning of the brain "is suggestive of parallel processing". Many areas of the brain are active at the same time. Within the past few years, mathematical models of parallel processing have become available that cast light on the ways in which many of these neural systems could work, and several systems have been modeled in some detail.   

               Conscious processes have limited capacity, but unconscious processors, taken together, have very great capacity. We have previously discussed limited capacity in terms of three phenomena: (1) selective attention, in which one is conscious of only one of two demanding streams of information to the exclusion of the other (1.xx). (2) Dual-task paradigms, in which two conscious or voluntary tasks degrade each other; and (3) immediate memory studies, in which only a very limited amount of novel or unorganized information can be retained. All three of these phenomena are associated with consciousness, though they are  not identical to it. 

                  There is one interesting counter-argument to the notion of conscious limited capacity, and that is the case of a very rich perceptual scene. In looking at a football game with a stadium full of cheering sports fans, we seem to have an extremely complex visual experience, apparently full of detail, but apparently completely conscious. The key here is the internal organization of the football scene, the fact that each part of it helps to predict the rest. If instead we present people with an arbitrary number of small unrelated visual objects, and ask them to estimate the number in a single glance, visual perceptual capacity drops down again to about four to six items. In addition, we scan even a coherent scene with serial eye-movements, picking up a relatively small information with each fixation. Thus the complex scene is not necessarily in perceptual consciousness at any one time: we accumulate it over many serial fixations. 

                  Thus conscious capacity does appear to be quite limited, as shown both by the selective attention experiments and by the limitations of short-term memory. What about the idea that unconscious processors "taken together have very great capacity"? This is obvious just from considering the size of the central nervous system. The cerebral cortex alone, taking up about half the volume of the cranium, contains on the order of 55 billion neurons, according to recent estimates (Mountcastle, 1983). Each neuron may have as many as 10,000 connections to other neurons. The interconnections between neurons are extremely dense --- one can reach any neuron from any other neuron by passing through no more than  six or seven intervening neurons. Each neuron fires on the average forty impulses per second, up to 1,000 when activated, and this activity continues in all parts of the brain, including those that are not currently conscious. This is by any standards a very large system. Viewed as an information processor, it is orders of magnitude larger than anything built so far by human beings. And clearly, most of its activities at any one moment are unconscious. Further, Long Term Memory, which has enormous capacity, is unconscious. The information processing capacity of all the automatic skills learned over a lifetime is similarly great. And neurophysiologically, it is clear that the great bulk of brain activity at any single time is unconscious.  

                  Why does this awesome system have such remarkable limitations of conscious capacity? There is something very paradoxical about these differences between conscious limitations and the huge unconscious processing capacity. Is this paradox a functional property of the nervous system, or is it somehow a mistake made by evolution? Later in this book we will suggest that humans have gained something valuable in return for our apparently limited conscious capacity. 

                Before we begin to interpret the contrasts discussed so far, we will take a glance backwards. If one is willing to accept the vocabulary of information-processing we apply here, speaking of conscious and unconscious "representations" and "processes", some facts can be established very clearly.  Conscious processes are computationally inefficient; they are relatively slow, awkward, and prone to error. But they involve an unlimited range of possible contents; any two conscious contents can be related to each other; and conscious contents are also profoundly shaped by unconscious contextual factors. Conscious experiences appear to be internally consistent; different ones appear serially; and there are rather narrow limits on our capacity to perform tasks that have conscious components. On the other hand, unconscious processors seem to be highly efficient in their special tasks. Each unconscious processor seems to have a limited range, and it behaves relatively autonomously from the others. Unconscious processors are highly diverse and capable of mutual contradiction; can operate in parallel; and together have very great processing capacity. 

                  In the following section we will suggest a theoretical metaphor to explain these observations. This metaphor greatly simplifies the diverse facts described above, combining them into only a few basic theoretical properties. Further, it suggests a functional interpretation for these facts, a selective advantage for having this kind of nervous system.

                The basic model: A global workspace (blackboard) in a

               distributed system of intelligent information processors.

               In recent years computer scientists, psychologists and some neuroscientists have become increasingly interested in distributed information processing systems --- systems that are really collections of intelligent, specialized processors.  They have been used to model the visual system, human memory, control of action, and speech perception and production. In a distributed system, numerous intelligent specialists can cooperate or compete in an effort to solve some common problem. Together, several specialists may perform better than any single processor can. This is especially true if the problem faced by the distributed system has no precedent, so that it must be handled in a novel way. 

                  In a true distributed system there is no central executive --- no single system assigns problems to the proper specialists, or commands them to carry out some task. For different jobs, different processors may behave as executives, sometimes handing off executive control to each other in a very flexible way. Control is essentially decentralized. The intelligent processors themselves retain the processing initiative --- they decide what to take on and what to ignore. (In a later chapter we will argue that  the nervous system does have components that act as executives.
                  But even without a true executive, a distributed collection of processors still needs some central facility through which the specialists can communicate with each other. This kind of central information exchange has been called a "global workspace",  "blackboard", or "bulletin board". A "workspace" is just a memory in which different systems can perform operations, and the word "global" implies that symbols in this memory are distributed across a variety of processors. Each processor could have local variables and operations, but it can also be responsive to global symbols. Analogies will be used throughout this book to make things a bit more comprehensible. For instance we may speak of the global workspace as a television station, broadcasting information to a whole country. There is one especially apt analogy: a large committee of experts, enough to fill an auditorium. Suppose this assembly were called upon to solve a series of problems which could not be handled by any one expert alone. Various experts could agree or disagree on different parts of the problem, but there would be a problem of communication: each expert can best understand and express what he or she means to say, by using a technical jargon that may not be fully understood by all the other experts. One helpful step to solve this communication problem is to make public a global message on a large blackboard in front of the auditorium, so that in principle anyone can read the message and react. In fact, it would only be read by experts who could understand it or parts of it, but one cannot know ahead of time who those experts are, so that it is necessary to make it potentially available to anyone in the audience. 

                  At any time a number of experts may be trying to broadcast global messages, but the blackboard cannot accomodate all of the messages at the same time --- different messages will often be mutually contradictory. So some of the experts may compete for access to the blackboard, and some of them may be cooperating in an effort to broadcast a global message.(Indeed, one effect of a global message may be to elicit cooperation from experts who would not otherwise know about it. Coalitions of experts can be established through the use of the blackboard.              

                  The subsequent history of the Hearsay project is rather interesting. In working with the various expert knowledge sources used by Hearsay, the researchers discovered a way to improve the acoustic processor so that it could do predictive tracking of acoustical formants, the regions of the highest acoustical energy in the frequency spectrum. In other words, they discovered a Successful algorithm which made it possible for the acoustical processor to solve problems which previously required cooperation From other processors, like syntax and semantics. Once the became clear, the Hearsay team was able to dispense with the distributed architecture of Hearsay, since cooperative computation was less necessary. They developed a new system called Harpy based on the improved acoustical processor, which could do the same job in a more specialized way (ref). But from our point of view, Hearsay is actually more interesting as a psychological model than the specialized Harpy. Hearsay did not fail; rather, it succeeded as a development system, a stepping stone to a specialized algorithm for translating sounds into phonetic code.  

                  There is a nice analogy between this history and the development of new human skills. When people start learning some new task, doing it takes a great deal of conscious processing. Apparently many functionally separate processors need to cooperate in new ways in order to perform the task. Over time, however, simpler means are found for reaching the same goal, and control over the task is relegated more and more to a single specialized processor (which may take components from existing processors). Thus the distributed "committee system" should be surpassed in the normal course of events by the development of a new expert system. This is certainly what we would expect to happen as a new skill becomes automatic and unconscious.                 

                  What about the "internal consistency" of conscious contents? This fits well also, because blackboard messages require at least tacit cooperation from the audience of experts. If some global message immediately ran into powerful competition, it could not stay on the blackboard. And what about the contrastive point that "... unconscious processors are highly diverse"? Further claims that "conscious processes are serial". This follows directly from the requirement that they be internally consistent --- different messages, those which cannot be unified into a single message, can only be shown one after the other. Thus we cannot see two objects occupying the same location in space at the same time, as we would have to, to interpret the Necker Cube in two different ways simultaneously. The blackboard portion of the system is therefore forced into seriality. But "... unconscious processors can operate in parallel". This, too, is already inherent in our model.   

                  Finally, "conscious processes have limited capacity..." . This feature also flows from the "internal consistency" requirement. If any global message must be internally consistent, one must exclude irrelevant or contradictory messages that may come up at the same time. Such irrelevant or contradictory messages are likely to exist somewhere in some of the distributed processors, and are therefore a part of the system. But they cannot gain access to the blackboard unless they can drive off the current message, or unless it leaves the blackboard of its own accord. Hence, "... unconscious processors, taken together, have very great capacity", and can be doing many things locally at the same time, provided these local processes do not require access to the global workspace. Like consciousness itself, this system works best when routine tasks are directly delegated to the best expert that is ready to solve it, and the use of the blackboard is reserved for just those problems that cannot be solved by any expert acting alone. When the cooperating processors discover a single algorithm able to solve the problem, that algorithm can again be handled by a single expert, freeing up limited global capacity for other unsolved problems.            

               When is a Global Workspace System useful?

               The main use of a GW system is to solve problems which any single expert cannot solve by itself ---  problems whose solutions are underdetermined. Human beings encounter such problems in any domain that is novel, degraded, or ambiguous. This is obvious for novelty: if we are just learning to ride a bicycle, or to understand a new language, we have inadequate information by definition. Further, if the information we normally use to solve a known problem becomes degraded, deteriminate solutions again become indeterminate. So much is clear.  What may not be so obvious is that there are problems that are inherently ambiguous, in which all the local pieces of information can be interpreted in more than one way, so that we need to unify different interpretations to arrive at a single, coherent understanding of the information. 

                  This kind of inherent ambiguity is often found in language processing and even in visual perception. We discuss the prevalence of local ambiguity in the world of perception, action, language, and thought in Chapter 4. Briefly, the argument is that any restricted amount of information tends to have more than a single interpretation. Since we often must deal with a restricted information, ambiguities must be resolved by reference to new and unpredictable information. The Global Workspace architecture is designed precisely to allow resolution of ambiguity by unpredictable knowledge sources.

                               A further use of a global workspace is to update many specialized processors at the same time. Updating is necessary not merely to remember where one's car is parked, but also to track changes in social relations, perceptual conditions, and the like. There is good evidence that social perception can be changed by a single conscious experience, and similarly, phoneme perception is known to be changed by recent experiences.    

---

Be first to comment this article

Only registered users can write comments.
Please login or register.

Powered by AkoComment Tweaked Special Edition v.1.4.6
AkoComment © Copyright 2004 by Arthur Konze - www.mamboportal.com
All right reserved