Deric Bownds

Chapter 1

Thinking About Thinking

This is a book about the biology of mind, and it is very tempting just to get on with the evolutionary story outlined in the first section of the book. However, before we can do this, it is necessary both to discuss some definitions of mind and consciousness and to ask how we might approach a scientific understanding of them. Before we can study whether or how the operations going on in our brain might explain consciousness, we have to begin to attempt a description of what it is that we are trying to explain. We must do some "thinking about thinking."

How Do We Define Mind and Consciousness?

One of the problems we face is that sometimes there seem to be as many definitions of words such as "mind" and "consciousness" as there are people using them. Each of these words refers not to a single entity, but rather to an array of phenomena. Webster's dictionary gives more than five definitions of the word "mind." These definitions are offered mainly with reference to humans. We need to consider also that other animal species besides ourselves have their own distinctive versions of mind.

Let's begin by thinking about experiences that we all share. You probably can remember moments of daydreaming or being lost in thought while driving a car and then noting with a start that you have been completely unaware of traveling the past several blocks. During all of this time, your brain was still processing all the relevant information, directing steering, watching the road. An unexpected occurrence, like a child running into the road, would have immediately snapped your attention back to your driving. As another example, you can probably recall an occasion when you have focused on the verbal content of a discussion with someone and have realized only after some time that you have become annoyed, an emotional reaction that grew out of your awareness as your body reacted to signals sent by the other person's posture and tone of voice. Such simple experiences tell us that much more is usually going on than we choose to be aware of.



Our consciousness can include much more than we are aware of at a given moment.



What we are aware of does not necessarily depend on its importance to us. We can be aware of trivial things and unaware of very important things. Reading these words might be most important to you right now, but you might also be partially aware of many things not relevant to this task---perhaps the sound of machinery in the next room, or your leg rubbing against the side of your chair. By the same token, you might be able to remember an occasion when you were walking down the street taking in random sights and smells and were unaware, until after the fact, of something very important: that you quickly dodged to the side after a shadow suddenly appeared in your path that might have been caused by a falling object.

In such cases we can, if we choose, switch the focus of our attention to what we have not been aware of. Underlying what we can be aware of, however, are many unconscious or implicit operations that may not be accessible to our introspection. These can occur, for example, in the fraction of a second just after we encounter new sensory stimuli. Current inputs are matched with past experiences of similar events to generate our perceptions. These unconscious processes can sometimes make mistakes that fool us. This happens in a well-known experiment in which subjects are shown a brief view of an impossible playing card such as a red ace of spades. Many report seeing what their experience leads them to expect, either a black ace of spades or a red ace of hearts. The brain has edited the actual stimulus and reported something else. You may also have experienced another kind of biasing when, on meeting someone, you immediately liked or disliked that person, for no obvious reason. Perhaps the individual resembled someone from your past, who was loved or feared? Emotional memories can act as filters to give a slight positive or negative "spin" to encounters in the present.



We can be oblivious to unconscious or implicit mechanisms that bias our conscious awareness.


Thus our current focus of awareness is just a part of our consciousness, which in turn is a small fraction of the vast number of implicit or unconscious operations going on in our brains. Our minds are something larger than our consciousness, and they involve operations that extend beyond our brains. These brains are constantly involved in an array of interactions with other parts of our nervous systems: the spinal cord and autonomic nervous system, as well as muscular, endocrine, and immune systems. This whole ensemble is what carries out actions upon and within the physical and social environment to which we humans have adapted. We can change this environment, and this environment can change our minds. The fact that our minds exist in the context of such complex interactions makes it difficult to offer a precise definition of their boundaries. 1 Probing these relationships is one of the goals of this book.



The nature and the bounds of our minds are quite fuzzy. A neat boundary between the thinker and the thinker's world doesn't exist.


Think of your stream of conscious awareness from moment to moment. Does it always feel the same? Although our awareness seems smooth and continuous, you will probably agree that it can be of several different kinds, and also built in stages of increasing complexity. To start at the more simple ends of things, you probably have experienced some quiet moments during which your mind felt quite empty, or blank. The simplest notion of awareness is one that is devoid of the content of specific sensing and acting---the state of "just being" that is described by mystical traditions and meditators. At a next level, we all are familiar with various phenomenal states of awareness, such as what it is like to taste an orange or what it is like to feel pain when your forearm is pinched. This is what we mean by having sensations: a simple, direct, and unreflective experience. Behavior experiments raise the possibility that animals and human babies might have such phenomenally conscious states without any concept of a self.

Introspection and Reflection

A next stage is being "conscious of" our feelings and thoughts, having introspective or reflective access to them. At this point we become selves, the "I" observing ourselves, and can do things like think about how it feels to taste an orange. A further twist is that our conscious awareness can be intentional: related to an object, action, or goal in the outside world. These latter forms of consciousness are clearly observed in higher primates as well as humans. However, talking to ourselves in our heads and talking to others---the narrative self consciousness based on grammatical language---seems to be unique to our human species.

The stages listed here are crudely drawn, and professional philosophers and psychologists would wish to make further functional distinctions. Their efforts to define the functional correlates of these and other phenomenal states of consciousness are very important, because we can't hope to address effectively the nerve activities in the brain that correlate with consciousness unless we have described what they are supposed to be doing.

How Does Consciousness Emerge from a Brain/Body

How do we set about explaining our conscious experience? How do we connect our two different worlds, the inner one of our subjective experience---how we feel, our emotions, what it is like to be somebody---and the objective world "out there" of objects that obey lawful relationships? The book you are holding is "out there"; your experience of it is "what is happening to me." Any complete description of mind or consciousness has to unify these into one whole and describe how they depend on one another. We don't yet know how to relate our subjective experiences to what our brains and bodies are doing, even though most practicing neuroscientists take it as an article of faith that we someday will. This current lack of understanding is generally called the explanatory gap, and it is the subject of intense debate and speculation among philosophers and scientists.



The issue of an explanatory gap can be posed with a simple exercise: Take a moment to pinch your forearm gently. Take time to notice how it feels. Now increase the pressure until you just begin to feel pain. At a distinct time and place, you have just had a subjective feeling of mild pain that goes with a particular emotional tone. Now suppose that during this experiment, some super-neuroscientist with access to the interior of your head had measured and accounted for all the nerve messages that occurred during your experience. How much would this explain?


Defining the Problem

Some in the field of consciousness studies insist on making a distinction between the "easy" problem and the "hard" problem of consciousness. The easy problem is said to be explaining the neural basis of things like attention, memory, and sensory motor coordination. These people say that no matter how much neuroscientists discover about these things, it won't crack the hard problem: They still won't be able to tell us why we experience the color and smell of a rose as we do. Third-person science will never get us to first-person experiences. There has to be something else, some really radical solution beyond the province of conventional psychology and neuroscience.

One response to this position, however, is to argue that the objective and the subjective refer to different ways of knowing rather than different bodies of knowledge. Why should translating between them be required for theories of consciousness? If we are materialists who take mind to be based on matter, any theories of consciousness must blend with neurobiological and psychological theories and descriptions. 2 The hard problem, then, is being addressed by current experiments that are revealing neural correlates of conscious subjective experiences such as vision, attention, and memory. The really hard problem is to find a unified or integrated description of all of these. (Approaches to this problem are the subject of Chapter 12.) Once we have assembled enough of the pieces, the supposedly hard problem of consciousness may evaporate, just as the concept of phlogiston disappeared when the true nature of fire was illuminated, the mystery of light yielded to the discovery of electromagnetic waves, and the mystery of life (how each organism replicates itself) was clarified by the discovery of DNA.



The debate over the "easy" versus the "hard" problems of consciousness remains to be resolved.


This argument takes the view that there are no questions concerning the physical basis of consciousness that differ in principle from other ordinary problems about the physical and functional basis of genes, inheritance, or solidity and liquidity. However, it is also possible that at this point, we could be in the position of a person ignorant of relativity theory who is informed that matter is a form of energy but does not understand the physical concepts that link quantum phenomena to matter and energy alike. Future theory might provide the scientific concepts we need to close the explanatory gap.

Problems with Words

Note: this section was not included in published book

As we get into the thicket of thinking about minds, consciousness, and brains, we bump into some major quandaries in dealing with our language. I frequently find myself thinking: "I know what I mean, or feel, but I just can't put it into words." As an example, the French translation of the title of an article "What is it like to be a bat." must be rendered as "What effect (or impression) does it make to be a bat." 3 French speakers surely have the concept of "what it is like to be...." but no clear, concise expression for it. Different cultures develop different systems of description. An opposite problem occurs when a word or phrase seems to represent something but in fact does not. A well known example is " phlogiston", coined in the eighteenth century to refer to the hypothetical material with negative mass that was supposed to be released from burning bodies. Other examples are "elan vital", "animal magnetism" and "telepathy". So, there can be a double jeopardy, words playing hard to get or easy to get and meaning nothing. Language also is made ambiguous by the existence of multiple belief systems that use the same words in different ways, so that language and thought have to be studied the same way that ecologists study multi-species communities. 4

Imposing words are used in talking about mind: concept, attribution, intention, affect, representation, strategy, consciousness, cognition, phenomenology. The traditions of ethology, psychology, philosophy and cognitive science differ over how to use these mental terms. I am going to proceed as simply as possible, adopting an evolutionary and ecological perspective, noting what animals and humans do in their natural habitats, and then asking what sorts of underlying mental operations might account for this behavior. One mental operation that can bias our insights, frequently outside our awareness, is the use of metaphors (words for one object or idea being used for another to suggest a similarity between them, but without an explicit comparison). In our common sense, or folk, psychology we often describe our mental states and processes using metaphors. Someone saying to you "I don't want to put ideas in your head" is taking mind to be a container. If you say "Part of me doesn't want to do that" you are using the metaphor of mind parts as persons. "John saw that Jim could not be trusted" is making believing like seeing. This sort of process is pervasive in our lives. As another example, consider how the fundamental physical verticality schema of up and down - relevant to any animal moving against gravity - is usually metaphorically projected to a whole array of oppositions: happy is up, sad is down; health is up, sickness is down, rational is up, emotional is down. 5

Assembling an Explanation

How, then, do we set about assembling an explanation for anything as complicated as our consciousness? We might start with some design principles that we know something about. We know that our bodies are hierarchical systems built up from smaller subunits and components, as shown in Figure 1-1. The ultimate particles of atomic physics make up our atoms and molecules. Our molecules then organize themselves into cells. Systems of nerve cells form our nervous systems and brains. The entities at each level are building blocks of those at the next level. The description can be expanded beyond our individual selves, as our minds become components of the larger entities of societies and cultures. Each level of this hierarchy has its own laws and theories, which armies of academic specialists study. 6

Figure 1-1
A hierarchy diagram depicting how complicated structures are built up from simpler ones.

This book takes the tack of sidestepping, or bypassing, the issue of relating our brain operations to our subjective feelings (bridging the explanatory gap mentioned above), and suggests instead, as indicated by the solid arrows to the left of the dashed ones in Figure 1-1, that mind is what brain/body does---in the same sense that digesting our food is what the gut does. We can trace up through the lower levels in the hierarchy to observe that in practice, each level of organization, built up of simpler ones, has its own laws and that its members in turn serve as the building blocks for the next level of organization. We then ask what rules are working at this next level, what new operating environment we are in.

We tend to visualize the assembly of our component molecules into cells, of our cells into tissues, and so on as being like working with building blocks or a simple erector set where things come together in an intuitive, linear fashion. 7 This can be a misleading vision, for in fact, all complex entities, whether organisms or thunderstorms, are nonlinear systems. They emerge from their simpler components in a way that cannot be predicted by merely summing their components. Examples of nonlinear processes include schools of fish and flocks of birds, whose grouping is aided by attractive energies arising because the surrounding fluid moves with them, and groups of lipid molecules that organize themselves into a biological membrane by minimizing the repulsive forces between lipid chains and water molecules. 8

We might view consciousness as a higher-level or emergent property of the brain in the simple sense that solidity is an emergent property of water molecules when they are in a lattice at low temperatures. In this view, consciousness might be taken as a physical property of the processes of the brain in the same sense in which solidity is a property of the molecules in an oak table or an icicle. The perspective that brain processes cause consciousness, but also that consciousness is a feature of the brain, avoids both the extreme of making mind separate from body and the excessively reductive materialistic view that mind is "nothing but" a group of molecules organized into nerve cells. In our present state of knowledge we can observe, in the brain, neuronal activity that correlates with, but does not explain, consciousness. We eventually hope to have a causal theory that explains why consciousness and neuronal activities are correlated, just as we now have causal theories that explain why the solidity of a substance correlates with its molecular structure, or why thunder and lighting are correlated during a storm.



We can think of our "mindstuff" as different from our "nervestuff" without edging back toward a dualism that separates body and mind, because we are talking about the same kind of distinction we make when we say that DNA is different from the elementary particles of atomic physics of which it is ultimately composed.


It is important to avoid some potential confusion about explanations. We appreciate that more complex entities can be explained in terms of simpler components. Knowing what we do about nerve cells, we can see how the laws governing a nerve signal follow from the laws of chemistry and electricity, and in this sense we can "reduce" it to them. But this is a very peculiar relationship. Under other conditions, the same laws of chemistry and physics explain liquid crystal displays of wrist watches, clouds forming over the ocean, thunder and lightning, and sugar dissolving in our coffee. Those laws of chemistry and physics in turn follow from the laws of quantum mechanics, which the physicists call fundamental, but only under the conditions where we normally find matter. Quantum mechanics has very different consequences in particle accelerators ("atom smashers") and at the edges of black holes than it does in your kitchen. To propose a genuine explanation, we must be armed with knowledge of both the lower-level laws and the conditions under which they act. Those conditions are so variable that we could never hope to have the higher-level laws just "fall out" (as the physicists say) of the quantum equations. If we were to restart the universe, would everything happen in just the same way? Perhaps there would eventually be clouds and quartz crystals, but what about mushrooms and animals with nerve cells and action potentials---and, in particular, us, puzzling over consciousness? These are not all entities whose appearance anyone could have predicted just from the equations of quantum mechanics: There are simply too many different ways in which things could have been fit together by evolution.

Figure 1-1 shows arrows pointing in both the upward and downward directions. The up arrows indicate simpler things coming together to make more complicated things, such as lipid molecules making cell membranes or the organ systems of our bodies constructing a skin or epidermis that encloses us. The downward arrows show that emergent entities can constrain and direct the components that built them up. A cell membrane is a physical compartment, or bag, that contains and exerts some control over all of its smaller components, just as on a larger scale our skins establish the context for what our muscles and other tissues can do. By the same token, if a whole organism constrains and regulates its component tissues, it should not surprise us that an emergent property like our subjective consciousness can organize, monitor, or direct the nerve assemblies of which it is constructed. And as we will see in later chapters, there is good evidence that this really happens. There doesn't have to be anything mystical about it. Our self conscious behavior can affect and shape the nerve and muscle physiology in our bodies. 9 Finally, the consciousness or mind that each of us experiences is not the final step in the causal chain, for it is strongly influenced and organized by the particular human culture in which we grew up.

Organism and Environment

The hierarchy drawing in the previous section looks tidy, but it can give the false impression that complicated things build themselves in isolation. The building is instead a historical process that depends strongly on the environment in which it occurs. In the hubris that accompanied the early days of molecular biology, one could hear scientists say, in effect, "Give me the structure of human DNA and I will compute you a human." Today this is recognized as nonsense, and few now take that extreme sort of reductionism very seriously. DNA is expressed only in a complex environment, first in the egg and then in different tissues as they form. As the fertilized eggs that generated you and me started dividing to generate the trillions of cells in our bodies, they were partners in an exquisite series of interactions with other cells. Each of these cells contained all of our genes, yet only particular subsets of their progeny turned on the genes that were needed to specify a liver cell, kidney cell, or nerve cell. Their fate was instructed by their particular surroundings in the embryo, surroundings that contained a rich broth of growth factor molecules. If taken away from this broth and placed in a minimal solution of nutrients just sufficient to sustain life, these cells might live, but they would probably return to an undifferentiated state. Not only do cells within a developing embryo regulate each other, but the hormones in the embryo's intrauterine environment influence its sexual development and behavior. Embryos exposed to higher levels of testosterone, for example, emerge as more aggressive individuals.

The wiring connections in our brains---the specific circuits formed during development---depend on features of the sensory and motor environment in which we grow up after birth. If those environments are absent or abnormal, the brain develops differently. Just as the differentiated state of every cell in our body is maintained by constant flux and interaction with its environment (including other cells), so the differentiated state of our brains is maintained by unique details of our own environment. The brain we grow, the self we generate, the language we speak---all are functions of our unique history and culture. Language, thought, and ways of experiencing the world can be culturally relative and very different for those living in Western industrial cultures and those belonging to isolated Stone Age tribes in Borneo. None of us can claim to have a "God's eye" view of an objective external reality.



Our development is shaped by the very environment we try to describe scientifically. Thus there is an inevitable circularity to our knowing.


This can lead us to an uncomfortable confrontation with our common-sense belief that the way things seem to us is the way things really are. Of course, we all know that we make mistakes, and sometimes we are fooled by tricks and illusions, but the problem goes deeper than that. Each of us develops in a tight interaction with a particular part of the external world, in a particular human culture and language, and all our beliefs and ways of describing things are shaped by that interaction. We are one part of an interacting whole trying to understand other parts. The distinction between subjects and objects is not so simple as we commonly think. It is with a slightly dizzy sensation that we realize we are using our instrument of analysis (the brain) to analyze that very instrument of analysis (the brain), like asking an eye to see itself or a mirror to reflect its own image. 10 Figure 1-2, a reproduction of the famous illustration by the Dutch artist M.C. Escher showing two hands shaping each other, illustrates the quandary. 11 Which is the "real" hand? It sometimes can be useful for us to put aside our tendency to stamp a seal of certainty on our experience, as though it perfectly reflected the world. The experience of anything "out there" is validated by the human structure, which makes possible "the thing" that arises in the description. This is not to deny that there is an objective world but only to say that our ability to describe it is shaped by our history of interactions with it. (We will consider the issue of the relativity of our knowledge a bit further in Chapter 7.)

Figure 1-2
Which is the real hand? Both. We shape our environment, and our environment shapes us.

Where Is the "I"?

We still haven't faced head-on the question of where the "I" is in the space between our ears. Who is watching inside when you recall how the Mona Lisa looks? What is this consciousness or mindstuff? Perhaps you can imagine the "I" in your head as shown in Figure 1-3, corresponding to an array of purposeful little agents scrambling around inside, some watching the movie screen of what is going on in the outside world, others operating the levers on the control panels that direct our movements. But this just takes the problem back another step, like opening the Russian wooden doll toy that has another doll nested inside. Opening that doll, you find the next. The hunt for purposeful agents somewhere down in there becomes fruitless. As we look further inside the brain, we become increasingly convinced that there doesn't appear to be anyone at home. We don't find a specific place where there is a thinker or a feeler or an actor. Rather, there are billions and billions of nerve cells wired together in complex arrays. We search in vain among all the specialized areas of our brain to find one that is the president. Is it in the frontal lobes? (We will take up this question in more detail in Chapter 12.)

Figure 1-3
Where is the I? It can't reside in other little humans inside our heads, as suggested here, even though such a picture perhaps corresponds most closely to our subjective experience.

It might be helpful at this point to peek at the sort of answer that is outlined in subsequent chapters. The best idea seems to be that the brain isn't like a classical top-down corporation or a computer run by a master central processor. Our consciousness is mechanically implemented by a process more analogous to an economy or an ecosystem---a distributed system without any central authority. There is no central place from which a puppeteer pulls all the strings. Our brains are a collection of semi-independent subsystems designed to perform specific jobs. They are not general-purpose problem solvers that invoke the same distributed, common processes for all tasks. They are more like a Swiss Army knife that has special gadgets for different tasks. Large computational problems (such as vision, audition, movement, and language generation) are split into a collection of parts processed by specific brain regions. These parts can be revealed when they are damaged by brain lesions or genetic mutations. And they can sometimes be directly visualized in living brains via imaging techniques or electrical recordings. The specialized modules are not isolated but interact extensively with each other. In Chapter 8 we consider one of the best-known examples of this, the different areas of the brain that process different aspects of a visual image, such as form, motion, distance, and color.

We seem to be a society of mind, built up of a hierarchy of agents 12 referred to by different authors as simpletons, 13 stable subassemblies, 14 multiple drafts, 15 component selves, and so on (the words vary more than the ideas). The modules are not what an engineer starting from scratch would have designed (supposing there were an engineer who could design a brain) but rather a hodgepodge of evolutionary adaptations and accidents piled one on top of the other, with some components possibly duplicated and adopted for uses and tricks quite different from their original "purpose." 16 Consciousness, at least in part, was natural selection's way of endowing us with thoughts that helped us survive in the world of our ancestors, not necessarily thoughts that are consistent or true. 17 These last points bring us to the subject of the first main section of this book, how biological evolution has shaped the minds we use today.



Just as we are stuck with the QWERTY keyboard---an awkward design that slows typing speed, devised in 1872 to avoid jamming of type bars that vanished long ago---so the modern brain makes do with modules designed to solve ancient problems.



This chapter has spelled out a number of positions and attitudes adopted by most of those who study the scientific basis of mind. A working assumption is that mind has its origin in physical stuff, just like the rest of the universe that we know about. Mind is what our brain/body does. Consciousness arises from the activity of neurons. What it is for---its function---needs to be described, as well as the hardware that carries out its activities. For the purposes of this book, mind is very broadly defined as the sum of the vast number of operations that proceed as our nervous system interacts with other body systems and with the world to generate cognitions, only a fraction of which are accessible to our awareness. The book takes take the optimistic view that we are not blocked, in principle, from understanding how our conscious awareness works. The "hard problem" of explaining what it is like to be someone may be resolved as we learn more from descriptions of what humans do and from experiments in cognitive psychology and neuroscience.

We can use what we already know about how our complex bodies are built up hierarchically, from simpler components, as a model for thinking about how consciousness might arise from groups of nerve cells. We have to admit that our processes of knowing are somewhat circular, because they are shaped and formed by the very environments they are trying to describe. But we are certain that the "I" of our subjective awareness is not like a little human, the 16th century's homunculus, residing somewhere inside our heads as a master puppeteer pulling all the strings. Rather, our consciousness is a distributed process that involves many semi-independent assemblies and agents whose activities are coordinated. One of the goals of this book is to sketch out the many components of our perceiving, acting, emotional, and linguistic minds that make us a society of mind. It is the origins of these components that we now want to consider by going back to the beginning and starting to tell the story of how our minds evolved over millions of years.

Questions for Thought

1. Several levels of conscious awareness were discussed at the beginning of this chapter, levels that culminate in the internal narrative made possible by human language. Some psychologists have argued that without language there can be no conscious awareness. Do you agree or disagree with this? Why?

2. Given what you have read here about definitions of consciousness, awareness, and mind, how would you respond if someone asked you, "How do you define mind?"

3. Rene Descartes's famous formulation, "I think, therefore I am" posited a clear dividing line between the mind and the brain, assigning the former to a nonphysical or spiritual realm and the latter to the physical world. Perhaps the central point of this chapter is the contrary assertion that mind has a physical basis, just like the rest of the world we know about. What is your opinion on this question? (This is an issue we discuss further in Chapter 12.)

Suggestions for Further General Reading

Churchland, P.M. 1995. The Engine of Reason, the Seat of the Soul: A Philosophical Journey into the Brain. Cambridge, MA: M.I.T. Press. A discussion of computational models of the brain based on modern findings in neuroscience and psychology.

Dennett, D.C. 1991. Consciousness Explained. Boston: Little, Brown. A controversial and engaging introduction to philosophical and technical issues involved in explaining consciousness.

Scott, A. 1995. Stairway to the Mind. New York: Springer-Verlag. A discussion of how mind might emerge from assemblies of simpler components.

Clark, A. 1997. Being There. Cambridge, MA: M.I.T. Press. This book emphasizes how mind and body are defined by their participation in an extended physical and social environment.

Reading on More Advanced or Specialized Topics

Flanagan, O. 1992. Consciousness Reconsidered. Cambridge, MA: M.I.T. Press. A more advanced discussion of issues in the philosophy of mind, including naturalistic explanations of consciousness.

Hardcastle, V.G. 1996. Ways of knowing. Consciousness and Cognition 5:359--367. A discussion of how mind and consciousness are defined that suggests how the "explanatory gap" might be closed.

1. Clark, 1997, Ch. 11.

2. Hardcastle, 1996. Kurthen et al., 1998, provide a useful reivew of questions surrounding the possibility of a neuroscientific view of consciousness, defining a number of philosophical terms and positions. Churchland, 1997, provides a caustic view of the "hard" problem of consciousness.

3. This problem with the title of a well known essay by Nagel is pointed out by Humphrey, 1992, Ch. 2, who discusses these points in more detail.

4. See Wilson, 1995, for more on this point.

5. The book by Johnson, 1987, describes how many linguistic operations derive from physical operations of the human body.

6. One approach has been to suggest skipping levels in the hierarchy to bridge the explanatory gap. The quantum phenomena that describe subatomic processes are taken to underlie consciousness, sometimes along with suggesting that novel laws of physics will have to be discovered to provide a complete explanation (see Penrose, 1989 and Zohar, 1990.) One idea behind this seems to be that there is much that is indeterminate or mysterious at the level of quantum physics, just as there is much that is indeterminate or mysterious at the level of human consciousness and brain function. Therefore, there must be a deep link between the two! I find it hard to credit that the unique features of quantum phenomena are relevant to understanding how the mind works. There is no viable research program to establish whether this is the case, and no plausible model of how quantum phenomena might play out in the nitty gritty world of real neurons. In striking contrast, numerous elegant experiments are now correlating our subjective experience with the electrical activity of neurons in our brains.

7. Saying that the relationship between two quantities is linear simply means that when you graph one against the other, you get a straight line. Physicists and mathematicians say that a system is linear if the rates at which its variables change has a linear relation to those variables; in principle, at least, linear systems are easy to solve, and don't do anything very interesting. Any other sort of system is non-linear, and it might be impossible to solve and do very interesting things. The canonical example of a linear system is a spring, where the force produced is proportional to how far it is stretched (stretch the spring out twice as far, and it pulls back twice as hard.) A very simple non-linear system is air drag, where the frictional force goes up as the square of the velocity of a moving body (so that doubling the speed increases the resistance fourfold). Two very good books on linear and non-linear systems for non-mathematicians are Stewart, 1989, and Abraham and Shaw, 1992.

8. Scott, 1995, gives an elegant description of the construction of non-linear systems.

9. Sperry, 1977, pg. 120

10. Maturana and Varela, 1992, pg. 24

11. M.C.Escher's "Drawing Hands" copyright 1997, Cordon Art, Baarn Holland, all rights reserved.

12. Minsky, 1986.

13. Ornstein, 1991.

14. Simon, 1969

15. Dennett, 1991

16. See the essay by Clark, 1995, "I am John's Brain" for a clever summary of our current scientific picture of what the brain is doing.

17. This quote from a book review by S. Pinker, 1995, is relevant: "Thoughts and the world can sometimes fall out of sync because selection adapts organisms only to their typical world, not to all worlds. Color vision, taste, and sexuality don't work as designed in a world with sodium lamps, saccharin, and contraception, and cognition doesn't work as designed in the worlds thought up by philosophers."

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