We are now ready to discuss the strongest source of evidence for the informativeness of conscious experience: the Redundancy Effects. If we ask the average student of psychology whether practice helps people to deal with new material, the student would no doubt reply, "Yes, of course, repeating something helps you to perceive and remember it." Rehearsing a telephone number helps us to recall it, doesn't it? And if you do not understand a sentence, reading it over again will surely give you more time to think about it? There is however a fundamental class of cases in which repetition harms rather than helps conscious access. When we already know an event, repeating it further tends to harm our ability to consciously perceive, understand, recall, and  monitor it. To say it slightly differently: whether repetition helps conscious access or not depends upon the information value of the event in question. As long as information increases with each repetition, conscious availability will improve; but once the stimulus is known, repeating it only creates more redundancy, resulting in a loss of conscious access.               

                   Redundancy, the lack of information, is defined formally as the presence of a signal after the uncertainty at the receiver is already zero. Redundancy implies a perfect match of input with expectation. The context of alternatives described in the section above collapses to only a single representation, with one degree of freedom, and maximum certainty. In the Piagetian dimension of assimilation and accomodation, redundancy corresponds to the extreme pole of assimilation. Of course, most of the time when we pay attention to something we do not wait for complete adaptation to occur. We are satisfied to understand some idea or clarify some perceptual event up to a point, and then go on to another. Redundancy Effects present the extreme case of absolute adaptation, but most of the time we are satisfied with relative adaptation. Once the conscious information is understood to some criterion, we go on.  Redundancy Effects for the different senses are quite clear in hearing, olfaction, taste, and touch; in all these senses a repeated or lasting stimulus fades rapidly from consciousness.

In the case of hearing, Miller was able to show a rapid decrement in the experienced intensity of even a single tone after several hundred milliseconds. In olfaction, we can observe every day that we lose track of a smell that may have been quite noticeable when we first encountered it. Most people are quite unaware of stable, surrounding odors, though these may be quite obvious to a newcomer. The act of sniffing, which changes the concentration of odor chemicals over the smell and taste receptors, may serve to change the stimulus, to dishabituate previously adapted receptors. Similarly, it is a common experience that even the most delicious food becomes less noticeable after the first mouthful. Gourmet cooking often consists of selecting deliberate taste contrasts, to re-awaken appreciation of otherwise habituated flavors. And the reader can probably verify at this moment that a previously felt object --- such as one's clothing --- has now faded from consciousness.

               One might object that vision seems different. Consciousness of visual stimuli does not seem to fade with repetitive stimulation, even when we stare fixedly at an object. But this neglects the existence of eye-movements.  Our eyes are in continual jumpy motion, both voluntary and involuntary, in addition to head and body motion. As long as the eye keeps scanning a differentiated visual field, new information will enter the retina. Therefore there may always be some element of uncertainty at the level of retinal receptors, as long as the eyes keep moving. It is difficult to completely stop even large eye-movements, and there is a continual tiny eye tremor (physiological nystagmus) that cannot be stopped voluntarily at all. Thus light under normal conditions, light patterns coming into the eye are never wholly constant and predictable. However, one can artificially defeat physiological nystagmus, and then interesting things happen. For instance, Pritchard, Heron, & Hebb mounted a tiny projector on a contact lens that was firmly attached to the eye, so that the projected image moved along with all eyecmovements. Under these conditions the visual image fades in a few seconds. The method of "stabilized retinal images" shows that even vision is subject to rapid habituation when it is not protected by constant eye movements. Similarly, when people look at a bright but featureless field (the Ganzfeld), they experience "blank-outs" --- periods when visual perception seems to fade altogether . It seems therefore that conscious experience of highly predictable stimulation fades rapidly, in all sensory modalities, without exception. In nature, all the senses continually change their relationship to the input: the nose sniffs the air, changing the concentration of odors;  the tongue tastes in an exploratory way, with the same effect; the hands and body explore by moving and touching (haptic touch); in most mammals the ears can be pricked up and oriented, and even humans tend to "cock" one ear to the source of sound when listening carefully; and of course our eyes are ceaselessly searching for significant information.  Thus the same physical event can enter a sensory system in many different ways, so that habituation can be avoided. But in the laboratory we can show that truly constant input fades rapidly from consciousness.  Note again that conscious fading does not mean that the event has disappeared from the nervous system. The Sokolov argument  shows that fading does not involve a fatiguing of receptors, or anything else that is dysfunctional. Rather, the fact that some stimulus fades from consciousness after repetition is highly functional; it is a sign that learning has occurred.

              Habituation is not limited to perception: it may occur at all levels of analysis. Fading of conscious access to abstract concepts is shown by "semantic satiation." A word repeated over and over again will soon seem different, somehow meaningless, estranged from its previous familiarity, as if it were being pronounced by some particularly impersonal robot. Semantic satiation is similar to stimulus habituation, but it seems to operate on the level of abstract meaning rather than sensation. It suggests, therefore, that the informativeness criterion does not just apply to perception and imagery, but to conceptual thought as well.  

       There has been some controversy about the empirical validity of semantic satiation , but the evidence for conceptual redundancy is actually quite pervasive. It is most common for experts in any discipline, who do not need to communicate their expertise to novices, to find it difficult to retrieve their knowledge explicitly. This is likely to happen even though the inaccessible knowledge continues to inform their actions and experiences.                       

                               Research on Adaptation Level theory  indicates that conceptual events are evaluated in a context of alternatives that is shaped by previous experience with the same events. Thus, one's judged happiness is strongly affected by previous judgments of happiness. In general, when one achieves a new level of desired functioning --- in getting a higher level of income, a desired job, or a desired mate --- people report high levels of happiness for some time. However, the new situation rapidly becomes adapted to, so that now one evaluates events with respect to the new Adaptation Level (AL). The reported level of happiness declines relative to one's expectations. In addition, people frequently raise their sights again, so that they become unhappy relative to their new desired state. Naturally, the Adaptation Level at any particular time --- the level of one's predictions about the world --- is not immediately consciously available, though it is established by conscious experiences, and it will become conscious again upon violation. In general, it may be said that those aspects of the world that we have learned most completely tend to be the least conscious.

 Redundant goals also fade from consciousness, even though  

      they continue to operate as goals.

                    We can now make a direct connection between goals, information, and consciousness, because redundant goals are lost From consciousness as well . A graduate student may be ve much aware in the beginning of graduate education of his or her goal of obtaining an advanced degree. But this goal tends to fade into the background as long as it remains highly predictable. Everyday concerns have more to do with subgoals needed to carry out the goal of gaining an advanced degree, than with this topTlevel goal. When the  student goes to find a book in the library, it is not necessary to be reminded that this is done in pursuit of the ultimate goal.  A subgoal can even fail without bringing to mind the highclevel goal: one may fail to find the right book in the library, or one may even fail to pass an examination.  However, if all subgoals fail without alternatives, the top goal also comes into question and must become conscious again. If money for school runs out, if the student has a disabling accident, etc., the topclevel goal of gaining an advanced degree comes into consciousness, as alternatives to it  need to be examined. But as long as goals are predictable, they are as unconscious as any other potentially conscious content.              

                               In actual fact, the goal of gaining a graduate degree may be a poor example, because it is a socially agreedcupon goal, one that can be communicated to others for whom it is not redundant but informative. Thus the goal of gaining a graduate degree is fairly easy to access, even when it becomes routine, because it often needs to be communicated. In the same way, teachers may be able to access information that practitioners with the same knowledge allow to become unconscious, because teachers must always be ready to communicate the presupposed information to students who do not share the presuppositions. From this point of view, it seems likely that constant private goals may be much more difficult to make conscious. Thus the goal of gaining the respect and affection of  others may become presupposed and unconscious, even while we pursue its subgoals. Or the goal of advancing one's social control, or to outshine competitors, may become unconscious and still be pursued. From this point of view, adaptation to goals may behave much like repression  that is to say, people will spontaneously disavow having such goals, even though the unconscious routine goals will continue to guide their actions.        

   Conscious experience is not the only thing that habituates. Selective habituation to repeated input seems to be a universal property of neural tissue. Even a single neuron will respond to electrical stimulation at a given frequency only for a while; after that, it will cease responding to the original frequency, but continue to respond to other frequencies. Thus a pulse train of 300 Hz. will cause the neuron to fire, until it habituates. After that point, it will no longer fire to a 300 Hz stimulus, though it will continue to respond to stimuli less than 280 Hz or more than 320 Hz (for example) . Neuronal habituation is selective, just as habituation of the Orienting Response is selective. Further, Sokolov's arguments also seem to apply at this level: fatigue canot be explain selective habituation, because the neuron continues to be respond to nonchabituated frequencies.  This kind of selective habituation can be observed at many different levels of organization in the nervous system: in single cells, in small assemblies of neurons, in larger nuclei and pathways, in complete sensory and motor systems, and in the nervous system as a whole. This point is very important in our theoretical development because it suggests that all specialized processors attempt to adapt to (match) input, and become quiescent when they have done so.  But what then is the difference between local neural habituation, and loss of conscious access to some experience? Below, we will propose that loss of conscious access is a global result of many cases of local habituation by specialized processors.
 

           Adapted systems can provide new context for later     

                        conscious experiences.                                        

                    What happens after some conscious event is matched exactly? We have just stated that the input does not disappear; what does it do instead?  We can now extend this point to the creation of new contexts. One interesting possibility is that systems that adapt to conscious input create new contexts, which then begin to shape future conscious events. Going back to the epigraph for this chapter, we can now begin to explain James' observation that "what we hear when thunder crashes is not thunder pure, but thunder- breaking-upon-silence-and-contrasting-with-it." Those systems that have adapted to the silence, and that therefore predict continuing silence, must make major changes as a result of the thunder clap. Further, they have become contextual with respect to the experience of thunder: They notify us not only that thunder has occurred, but that it was very different from the foregoing level of sound.   

                    But why, when the act of driving becomes automatic, do we become conscious of the road? Presumably the road is much more informative within our purposes than driving has become. Dodging another car, turning a blind corner, braking for a pedestrian --- these are much less predictable than the handling of the steering wheel. These are now the differences that make a difference. But once the road itself becomes routine and predictable, it too can become context for other events, and so on indefinitely.          

                    Notice that goals provide some of the constraints for the conscious domain. Indeed, goals involve one kind of context of alternatives. Paying attention to choices at street crossings determines whether we shall get to our destination (our immediate goal), and driving safely determines whether we shall survive (an enduring goal). Like other contexts, these goals are not usually conscious when they shape action and experience. In the act of dodging another car, we do not consciously remind ourselves that we want to survive. We can interpret purposeful actions as having a kind of informativeness, making a difference within a goal context of alternatives. Goal contexts specify a set of alternatives that our actions serve to select, so that our purposeful actions are also informative at various levels of significance. Not running over that pedestrian selects our goal of not harming people, of avoiding trouble with the law, and of getting where we are going with minimum effort. These are all significant goals --- some are more significant than others, and some are sub-goals for deeper goals. In all these cases we can think of conscious events and voluntary actions as being informative, in the sense of selecting alternatives within the contextual goal hierarchy.        

                    A contextual system does not have to remain unconscious for a lifetime. It can be decontextualized to become once again a domain of conscious experience. Suppose we are accustomed to driving a car with power-steering, and one day the power-steering fails. Suddenly the steering wheel becomes harder to turn, especially at slow driving speeds. Our contextualized predictions about the force needed to turn the wheel are violated; our strategy for driving the car must change. Now the act of moving the steering wheel becomes conscious again. Previously predictable events decompose into several different alternatives, as previously contextual processes become the objects of conscious experience. We notice that we must keep the car moving, in order to turn the wheel with less effort. This was not a consideration before, but it has now become relevant. Presumably a global display of the newly conscious information helps to bring such new considerations to bear upon our overall goal of steering the car. This phenomenon of decontextualization of previously unconscious tools and effectors is very general. When we break an arm, this normally presupposed part of the bodily context becomes an object of experience, one that now involves conscious choices; the arm, too, has become decontextualized. This view gives a new perspective on context  In a sense, context consists of those things to which the nervous system has already adapted; it is the ground against which new information is defined. The same point can be made at the conceptual level, as we see next.

                    The case of conceptual presuppositions: conscious contents 

        can turn into new contexts.                       

                    The development of conceptual presuppositions provides another example of context-creation by adaptation. We have previously made the case that all consciously accessible concepts exist in a framework of prior unconscious presuppositions.  Without such presuppositions, the concepts themselves are different. We now suggest that this presupposed knowledge is simply the result of previously conscious concepts. When we first encounter someone from a different culture, we become conscious of many things that are normlly presupposed:  the person may speak from an uncomfortably close distance, he or she will have different conceptual presuppositions, etc. If we live in the foreign culture, all these prominent features disappear, and now we are shocked when we discover our old culture again. Previously presupposed ideas and actions now become conscious. As usual, it is contrasts and transitions that bring out these points. Experts have much less conscious access to such material than novices.  

                    We can usefully refer to these phenomena in terms of contextualization and decontextualization. When we encounter some new assumptions about reality, we often need to make them explicit. That does not mean that we must define them verbally; it may be good enough to contrast two different points of view, a politically rightist vs. leftist viewpoint, for example. Once we become familiar with the contrasts, they can become automatic and contextualized, so that they will shape subsequent thought without becoming conscious. If the new context is then violated, however, it must become decontextualized; some contrast between right-wing and left-wing politics, which was previously unconscious becomes conscious again. (Decontextualization is really the same as objectification, mentioned above.)        

                    Take the process of constructing scientific reality, as in the discovery of the atom. In modern times, the first serious proposals for the existence of atoms go back to George Dalton  who discovered that an electrical current will decompose water into two parts hydrogen and one part oxygen. Dalton proposed that tiny indivisible (atomic) particles of hydrogen and oxygen must combine in a twoctocone ratio to form water. But this hypothesis did not establish the reality of atoms and molecules; it merely began a debate that continued for the rest of the 19th century, with many facts pro and con being offered by both sides. Some scientists refused to believe in atoms, or only treated them as useful fictions, facons the parler, without any reality. They had many arguments in their favor. Not all substances fell apart into elements with simple ratios. The relationships between the supposed elements were confusing, and could not be organized coherently until quite late in the century. The reality of atoms was not universally recognized until the various alternatives were shown to reduce to essentially one interpretation.  This reduction in alternatives culminated with Einstein's work early in this century. At that point, the reality of atoms became the conceptual framework of a new world-view; no longer were atoms considered to be merely convenient fictions. They were "real" objects.  In general, it appears that scientific constructs are not considered "real" until other ways to interpret the evidence are lost from sight. At that point the community stops arguing about them, and begins to take the new construct for granted . Indeed, the newly "real" objects can become the fulcrum of novel explorations that now presuppose the existence of the construct. Thus atoms have become part of the unquestioned context within which modern physicists are exploring subnuclear particles. For scientific constructs like atoms, it is not so much that they disappear from consciousness of the scientists who accept their reality. Rather, the construct is accepted when alternatives are forgotten.
                    Thus in particle physics today no one challenges the reality of atoms; to do that would undermine the task of exploring subatomic and subnuclear particles. It would force researchers to challenge the context within which protons and quarks are defined. Challenging context is not impossible, of course. Einstein's relativity theory decontextualized Newtonian presuppositions about space and  time, and quantum mechanics decontextualized Einstein's assumptions about determinism . In both cases, physicists became conscious once more of the alternatives to their presupposed reality. But it is very difficult to decontextualize one's assumptions and also at the same time engage topics within that set of assumptions. In driving the car, one cannot be absorbed in moving  the steering wheel and successfully engage the road at the same time. In general, a context must remain stable, presupposed, and largely unconscious, in order for us to engage the objects that are defined within it.  These parallels between a perceptual-motor task like driving a car and the pursuit of scientific reality are quite intriguing. They suggest that consciousness of the perceptual world and consciousness of a conceptual reality like science may follow similar laws. Notions like predictability and uncertainty, informativeness and redundancy, context of alternatives, and decontextualization may have very wide application.  The thrust of this section has been that human beings adapt to information at all levels: perceptually, in imagination, skills, concepts, and goals. As they adapt, they lose conscious access. The next section argues that people also seek informative input, so that there are actually two countervailing tendencies.
        

Human beings also seek information at many levels.

                                   So far we have discussed ways in which the nervous system adapts to some conscious event, thereby reducing conscious access to it. But the opposite process occurs as well: there is extensive evidence that people seek out novel and informative conscious contents. We do not wait for the perceptual world to fade. We always go on to seek new and interesting things. In sum, there seem to be two tendencies: a tendency to reduce conscious access by adaptation, and a countervailing tendency to increase conscious access by searching for informative stimulation. These two tendencies may alternate, so that we seek conscious information, adapt to it, seek a new source of information, adapt to that, etc.. The process may approach a self- regulating homeostasis that tends toward optimal information flow. In this section we explore the search for information at different levels of conscious access: in perception, in conceptual processes, and in the domain of goals, where the search for information helps to define the significance of conscious input.  

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