Evidence for perceptual fusion has been cited above to support the possibility of a rather brief 100 millisecond cycle time for the global workspace. One might use biofeedback training to investigate this temporal interaction window. For example, in motor unit training, a discrete and covert neural event (the motor spike) is amplified and fed back through loudspeakers to create a discrete conscious event (the auditory click). It would be easy to delay the click for 50, 100, 200, and 300 milliseconds, to measure the allowable lag time between the two. An approximate 100 millisecond upper limit would be very interesting. If the 100 millisecond cycle time is approximately correct, biofeedback training should not be possible past this conscious exposure time. The same suggestion may be made on the input side. The work of Treisman and her colleagues  suggests that one can easily specify separable features in visual perception. What would happen if one were to delay one feature 50 milliseonds before others became available? If the notion of a minimal cycle time were valid, there should be integration with short temporal disparities, with a rapid loss of integration beyond some "magic number" around 100 milliseconds. Does composition, decomposition, and reorganization of  processors take up limited capacity?  We claimed in that many slips of speech and action show a momentary separation of otherwise integrated action schamata. Does such separation take up limited capacity? And if one re-integrates the fragmented schema, does that require limited capacity? Model 1 would certainly suggest that reintegration between otherwise separate systems makes use of the global workspace. In recent years it has become possible to trigger a variety of predictable slips of speech and action in the laboratory. 

   A related question is whether error detection in performance involves parallel monitoring systems. Notice that monitoring systems are not conscious ordinarily, and that, like other specialized processors, they should be able to operate in parallel unless they are contingent on each other. If monitoring systems operate in parallel, "looking at" a globally displayed event, then the time needed to detect two simultaneous errors in some conscious material should take no longer than detecting only one. The work of Langer and Imber (1979) indicates that error detection becomes quite poor when some skill becomes automatic: the less conscious it is, the more difficult it is to monitor. Of course, automatic skills can "de-automatize" when they encounter difficulties. That is, aspects of these skills can become conscious once again. Any experiment on error-detection in automatic skills must deal with this complication. However, de-automatization presumably takes more time, and the skill should degrade when it becomes more conscious. Thus one could monitor whether some automatic skill continues to be automatic and unconscious during the experiment. Along similar lines, the creation of new specialized modules, perhaps from previously available separate automatic systems, should take up limited capacity and may have testably conscious aspects. 

               A functional explanation for limited capacity.

                  Limited capacity is a prominent and surprising feature of human psychology, but we seldom ask why it exists. Would it not be wonderful to be able to do half a dozen things at the same time? Why has evolution not resulted in nervous systems that can do this? Model 1 suggests an answer. If it is important for information to be available at one time to the system as a whole, global information must necessarily be limited to a single message at a time. There is only one "system as a whole", and if all of its components must be able to receive the same message, then only one message at a time can be broadcast. There are many reasons for making information available to the system as a whole, notably the case where a problem cannot be solved by any single known specialist. The knowledge required to solve the problem may reside somewhere in the system, but in order to reach it, the problem must be made available very widely. Notice that this suggests a purely functional explanation of limited capacity. Of course, global broadcasting is expensive. If some problem can be assigned to a specialized processor, it is efficient to do this and not take up the limited resources of the global workspace. 

               Organization vs. flexibility.

               Other facts about human psychology also fall into place with Model 1. For example, cognitive psychologists over the past few decades have become convinced of the importance of organization in perception and memory. There are numerous powerful demonstrations of the effects of organization. It is easier to remember something if we learn a set of regularities that apply to it; indeed, we cannot remember or even perceive utterly disorganized information. Even "random" noise has specifiable statistical properties.The trouble with this is that organization tends to commit us to a particular way of doing and viewing things. Organization often creates rigidity. Most of the time it is appropriate for adults to analyze language in terms of meaning, but there are times (in proofreading for example) when we must switch from a meaning analysis to a spelling analysis; this switch often leads to problems. The famous "proofreader illusion" shows that we often miss errors of spelling and vocabulary when we focus on meaning. What kind of a system architecture is needed to

reconcile the value of organization with  the need for flexibility? In terms of Model 1, it should be a system in which specialized processors can be decomposed and re-arranged when the demands of the task change. This is very difficult to do with other conceptions of organization in memory. 

                  Some of the best demonstrations of flexibility in the nervous system come from the area of conditioning. Originally conditioning theorists believed that any arbitrary relationship

between stimuli and responses could be connected, and they proved that under surprisingly many circumstances a tone can indeed come to signal a shock, and the like. This is the very opposite of the powerful organizational effects found by cognitive psychologists: there is no natural connection between tones and shocks, or many of the other standard stimuli used routinely in conditioning studies. Indeed, when conditioning occurs between ecologically related stimuli and responses, the effects found are far stronger than when biologically  arbitrary stimuli are used. Nevertheless, it is striking that biologically arbitrary connections can be made at all in a system that is so strongly affected by non-arbitrary, organized, and biologically significant relationships. 

                  Biofeedback training provides an excellent example. When it was first discovered, physiologists and psychologists were surprised that autonomic functions such as heart rate, skin conductivity, blood vessel dilation and contraction and the like were affected by biofeedback (at least in humans). As the word "autonomic" suggests, these activities were thought to be free From conscious control. It now appears that just about any neural system can be responsive to conscious biofeedback control, although autonomic functions seem to resist permanent retraining.

                  To account for this high degree of flexibility we favor something like Model 1, in which routine organization of information and control can be accessed quickly, but which also allows for movement between different levels of organization, for reorganization of modules in different ways,  and for the creation of entirely new, organized coalitions of processors.

               How can people talk about their conscious experiences?

               Finally, how is it that people can talk about the things they experience  consciously? And how can they act upon conscious information? This is after all, our first operational definition of conscious experience, and at some point our model should be able to connect to it. We can already suggest part of the answer. Speech requires a coalition of specialized processors. Since all such processors can receive information from the global workspace, we can explain in general terms how it is that speech processors can describe and act upon conscious contents. Speech systems in the global "audience" can presumably receive the relevant information; but this does not explain how these linguistic system organize a coherent speech act to describe the global information. Nevertheless it is a step in the right direction.  

                  Presumably the same point applies to other voluntarily controlled systems. Instead of asking people to say "There is a banana" when we present a banana, we can ask people to raise their fingers or blink their eyes for bananas, and not for anything else. All of these voluntarily controlled systems must presumably have access to global information provided by the conscious stimulus.                

               We know that surprise triggers all the measures of the Orienting Response, that it loads limited capacity, creates massive neural activity, and tends to cause a loss of current conscious contents. One obvious explanation is that surprise serves to erase the Global Workspace, thereby allowing the new and  surprising information to be distributed for widespread cooperative analysis. This is indeed part of the story that seems to follow from the theory developed so far, though we will have more to say about this  in later chapters.

               Consciousness and executive control.

                We are not claiming, of course, that consciousness is an executive; in the society metaphor, it resembles a broadcasting station rather than a government. However, governments can use broadcasting facilities to exercise control, and presumably executive processors may use consciousness to try to control other processors. In this connection Shallice suggests that consciousness has to do with the selection of a "Dominant Action System", an idea that has obvious similarities with our Models 2 and 3. However, action is not the only thing that is selected in consciousness  --- conscious experience is as selective for perception as it is for action -- and Shallice still leaves unexplained why a Dominant Action System would bother to dominate conscious capacity. What is the pay-off for actions and goals to become conscious.       

               Consciousness and repression. 

               Some readers will no doubt wonder how we can possibly discuss our topic in any depth without dealing with the Freudian unconscious, surely the most influential idea of this kind in this century. The general answer is that Freud's work presupposed a cognitive theory of conscious and unconscious processes, one which we need to work out explicitly. Like most 19th century thinkers, Freud tended to take the existence of conscious experience for granted. He treated it as equivalent to perception, and did not discuss it in much detail. The great surprise at the end of the 19th century was the extraordinary power of unconscious processes, as shown, for example, in post-hypnotic suggestion and the relief of hysterical symptoms after emotional expression of traumatic memories. Freud has nothing to say about unconsciousness that is due to habituation, distraction, or hypnotic dissociation --- those phenomena are all quite obvious to him, and require no explanation. He is really concerned with the dynamic unconscious, the domain in which wishes and fears are purposefully kept unconscious, because their becoming conscious would lead to intolerable anxiety. The dynamic unconscious is a conspiratorial unconscious, one that aims to keep things from us. It is closely associated with primary process thinking,  the magical thinking displayed by young children, in dreams, and in some mental disturbances. But these phenomena presuppose a more general understanding of consciousness and its functions.  

                  Our aim in this work, therefore, is to try to build a solid cognitive foundation from which such phenomena can be understood. We will make some suggestions later for specific ways in which psychodynamic phenomena can be explored empirically, and how they may be modeled in a general cognitive framework. However, there is an interesting relationship between our basic metaphor and the repression concept of psychodynamic theory. The global workspace is a publicity device in the society of processors --- after all, global messages become available to potentially any processor, just as published information becomes available to potentially any reader. Freud originally used the opposite metaphor to explain repression, i.e., motivated unconsciousness: the idea of newspaper censorship.

                 "The political writer who has unpleasant truths to tell to those in power ... stands in fear of the censorship; he therefore moderates and disguises the expression of his opinion. ... The stricter the domination of the censorship, the more thorough becomes the disguise, and, often enough, the more ingenious the means employed to put the reader on the track of the actual meaning." 

                  For Freud, the dynamic unconscious exists because of censorship. Would it follow then that making things conscious is the opposite of censorship, namely publicity? Repression is presumed to be a censoring of anxiety-provoking information, but Freud apparently did not pursue the question, what is the censored information hidden from? We might speculate that it is sometimes desirable to conceal information from global publicity, because some processors in the system might react to it in an unpredictable way, challenging established control mechanisms.

For someone on a diet, it may be useful to exclude from consciousness seductive advertisements for delicious food; conscious contemplation of the food may lead to a loss of control. In the same sense a politician might wish to hide a scandal from publicity, because some political forces might react to this information in an uncontrollable way. In both cases, limiting publicity is a useful device for maintaining control.  

                  There are many ways for information to become unconscious. These mechanisms are not inherently purposeful. Habituation, forgetting, and distraction are not conspiratorial devices to hide a stimulus from conscious experience. However, mechanisms like distraction  may be used by some specialized systems in a purposeful way to help control the system as a whole Experimental psychologists have had great empirical difficulties in assessing the existence repression The points we are making here do not solve these empirical problems. But it is pleasing to find that  this very influential conception of the psychological unconscious may fit our analysis quite readily.   

               Some counterarguments.

               Model 1 is clearly incomplete. Worse than that, it seems to contradict some empirical findings, and certain powerful intuitions about conscious experience. It clearly needs more development. Consider the following four counterarguments.    

               î1. The model does not distinguish between conscious experience and other events that load limited capacity. So far, Model 1 suggests a way of thinking of the limited capacity part of the nervous system, the part that presumably underlies conscious experience. But in fact there are events that load limited capacity which are not consciously experienced. One counterargument to Model 1 is simply that it does not distinguish between conscious experience and other limited capacity-loading events. Later models will correct this deficiency.         

                2. The idea that we are conscious of only a single internally consistent event at any time seems counterintuitive to some people.  

                  In reading this sentence, the reader is presumably conscious of the printed words as well as inner speech. Most experiences, at least in retrospect, seem to combine many separable internal and external events. But of course at any single instance, or in any single 100-millisecond cycle of the global workspace, we may only have one internally consistent object of consciousness; multiple events may involve rapid switching between different conscious contents, just as a visual scene is known to be integrated over many rapid fixations of the eyes. We can call this the bandwidth question: In any single integration period of the global workspace, can more than one internally consistent message gain access?  Again, this is a difficult question to decide with certainty at this point, so we will call this another theoretical choice-point: we will assume for the sake of simplicity that only one global message exists in any psychological instant, and that the sense we have of multiple events is a retrospective view of our conscious contents. Normal conscious experience may be much like watching the countryside flash by while sitting in a train; when we reflect metacognitively on our own experience, we can see parts of the train that have just gone by, as if it has gone around a curve so that we can view it from the outside. Presumably in retrospect we can see much more than we experience at any instant. 

. The 100 millisecond global integration time is much too

short for many integrative processes involving consciousness.         

A single coherent conscious content is presumably at least 100 milliseconds long. Though it may last as long as a second or two, longer than the minimum conscious integration time, even that is not long enough to think through a difficult problem, to integrate information from two domains in memory, or to do many other things that people plainly do consciously. Even if we assume that people  can voluntarily "refresh" a conscious content (by rehearsal, for example), there are surely structures that can gain access to consciousness that last longer than we are likely to voluntarily rehearse a thought. Attitudes, for example, may last an adult lifetime, and attitudes surely must affect one's conscious thoughts, images, and feelings. We need something else to bridge the gap between evanescent conscious contents and long-term knowledge structures. In Chapter 4 we fill this need with a new construct called a "context," defined as a representation that shapes and evokes conscious experiences, but that is not itself conscious.

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