Limits of Knowledge

The Limits of Our Knowledge about Our Brain

Blindsight

The term blindsight (Weiskrantz, 1986) is applied to patients with damage to the visual cortex of the occipital lobes – the primary visual cortex – which is where most of the nerve fibers from the retinae terminate. Such patients suffer from “cortical blindness”; they are blind because the part of the cortex that generates visual consciousness is no longer working. Blindness, then, means a lack of visual awareness. Thus, if you were to hold an object before these patients' eyes and ask them what they see, they would respond with the obvious: “I don't see anything; I'm blind.” But when they respond in this way, they are actually mistaken. They are erroneously equating “seeing” with “seeing consciously.” The distinction between vision and conscious vision is demonstrated when you ask these same patients to make a “forced choice” between various options (in other words, you encourage them to guess). The results of such experiments reveal that they guess correctly at a level well above chance, which demonstrates that these patients are seeing – are processing visual information – without realizing it (see Weiskrantz, 1986). They are seeing unconsciously. This occurs because some visual information is projected from the retina onto other parts of the cortex (intact in these patients) that do not generate visual consciousness but are, nevertheless, equipped to process the visual information they receive. In other words, these patients – as far as visual information is concerned – act like the “zombies”. Their brains compute visually, but they do not possess visual consciousness.

Implicit Memory

The same thing occurs with respect to other cognitive faculties. It is not all that rare for neurological patients to lose the ability to lay down new memories. This condition is called amnesia. These patients remember (recall consciously) nothing that happens to them after the onset of their brain disease or injury. If you were to read a list of words to such patients, after a few minutes they would not only forget the words, they would even forget the fact that you read them the list. However, as with cases of cortical blindness, such patients can be encouraged to “guess,” using the forced-choice paradigm. When they do so, they “randomly” select of generate words that were on the original list, at a very much higher rate than chance. So, just as we can see unconsciously, we can also remember unconsciously. The technical term for this unconscious type of remembering is implicit memory (conscious remembering is explicit memory).

What is the self in neurobiological terms? Photo by Elena.

Split-Brain Studies

In so-called split-brain patients, to treat otherwise intractable epilepsy the corpus callosum has been severed, thus separating the left (language-dominant) hemisphere of the brain from the right

By briefly flashing an image on a screen to such patients, it is possible to provide the right hemisphere with information that the left hemisphere cannot access. On this basis, it is possible to influence the patient's behavior without him or her being consciously aware of it. In one of Nobel Prize-winning neuroscientist Roger Sperry's famous cases, pornographic pictures were projected and giggled. When Sperry asked her why she why she was embarrassed, she was unable to account for it. This case (described in Galin, 1974, p.573) demonstrates that an entire cerebral hemisphere can process information “unconsciously.”

The case also reveals something else that is of crucial importance for understanding consciousness. The visual cortex was completely intact in Sperry's patient. This means that the pornographic pictures were perceived by the visual-consciousness generating part of her right hemisphere. Why, then, did she appear not to know what she saw? The answer to this question provides a good illustration of the “functional systems” concept. Although it is true that the primary visual cortex (in either hemisphere) is capable of generation simple visual consciousness, it does not do so in isolation. For someone to reflect consciously on visual experiences, he or she has to recode the visual experiences into words. This capacity is lost when the left (verbal) hemisphere is disconnected from the original visual experience. This shows that a distinction needs to be drawn between two levels or types of consciousness: Simple awareness and reflexive awareness. It also shows that the function of reflexive awareness is intimately connected with the left cerebral hemisphere and therefore with word (or, rather, “inner speech”).

The fact that an entire hemisphere (about half of the forebrain) can, in a sense, function unconsciously raises intriguing questions.

Neuropsychology aims to be entirely objective, and its great power, its advances, com from just this. Illustration by Elena.

The Brain and the Inner World, Introduction to Basic Concepts. Mark Solms, Oliver Turnbull.

Is Mental Life Conscious?

How Much of Mental Life Is Conscious?

There are various ways of addressing the question of how much of mental life is conscious, each of which leads to slightly different answers. What they all reveal, however, is that consciousness is a very limited part of the mind. For example, if the extent of consciousness is equated with the amount of information that we can “hold in mind” at any one point in time, then readers might be surprised to learn that consciousness is restricted to only seven units of information.

It is no accident that most telephone numbers are roughly seven digits long. Digit span (the capacity to repeat a string of random digits) is a standard clinical test of as aspect of working-memory capacity. (“Working-memory: is synonymous with the ability to consciously “hold things in mind:). If a patient cannot retain roughly seven digits, his or her audiverbal working memory (audioverbal consciousness) information (or “location” information) in mind in a similar way, but this aspect of consciousness is even more restricted: most people can hold only some four units of visuo-spatial information in mind at a time. (This capacity is usually tested by tapping a series of blocks scattered before the patient and asking him or her to hold the sequence of taps in mind.) Considering how many thousands of pieces of information we are processing all the time, this way of measuring the capacity of consciousness reveals that it is very limited indeed. The vast bulk of the information we constantly need to process must be processed in the unconscious part of the mind.

Another way of estimating the “size” of consciousness is to measure the extent of its influence on our behavior. What proportion of our actions is consciously determined? In a review of the scientific evidence pertaining to this question (and related masters). Bargh and Chartrand (1999) concluded that 95% of our actions are unconsciously determined. This way of measuring consciousness therefore suggests that it accounts for only 5% of behavior.

So, regardless of how they measure it, mainstream cognitive scientists today agree with Freud on this point: consciousness is attached to only a very small part of our mental life. Where then, is this consciousness generated in the brain? And how does it become attached to mental processes? And why?

The Brain and the Inner World, Introduction to Basic Concepts. Mark Solms, Oliver Turnbull.

What, in neurological terms, might psychotherapists be doing when they treat a disordered “self”?

Materialism and Idealism

Materialism and Idealism

Perhaps the most basic distinction among philosophical approaches to the mind-body problem is the one that divided materialists and idealists. The materialist position is that everything is ultimately reducible to matter. From this standpoint, the thought does not really exist. Its existence is illusory; the mind is really an aspect (or function) of matter.

At the other extreme, the idealist contends that only the mind really exists (for us, at least). For all the apparent substantiality of matter, the “things” we see, touch, and hear are really nothing other than products of our mental processes (i.e., they are actually perceptual images). We can never reach beyond the envelope of conscious awareness and demonstrate the existence of any thing independent of our mind's perceptual images. So, from this standpoint, the concrete thing may not really exist, or at least it, too belongs inside the “thought bubble”.

Although these positions both appear logically tenable, the idealist position has fallen out of favor. This seems to be due to the vagaries of intellectual fashion more than anything else. Within cognitive science today, just about everyone is a materialist. But materialists come in different shapes and sizes.

Monism and Dualism

The dichotomy between monism and dualism is perhaps just as fundamental as the one between materialism and idealism, and is easily confused with it. According to the monist position, we are made of only one kind of “stuff”. In other words, mind and matter (which appear to be two things) are really reducible to one and the same thing. This might seem to be identical to the materialist position just described (and the two arguments do normally go together), but the monist position does not actually state that the singular stuff we are made of is matter. A monist could just as well claim that we really consist only of mind (thereby embracing an idealist position) or even that we are actually made of some other kind of stuff, as yet undefined, which is neither mind nor matter. In the monist position, all that counts is that the apparent distinction between mind and matter dissolves into a common something.

The dualist view – closely associated with the name of René Descartes – simply states the opposite: We are divided in our essence and are made of two kinds of stuff. Matter and mind (or body and soul) are quite irreducible to one another. Like idealism, dualism is very unfashionable nowadays. Most cognitive scientists, therefore, are materialist monists: they believe that mind and brain are ultimately reducible to a single kind of stuff, and that that stuff is physical – specifically, some property of neurons (or an aggregate of subset of neurons).

The mind can be regarded as a higher level of organization of neurons, just as water is a higher level of organization of its constituent atoms. Photo by Elena.

Reductionism, Interactionism, Other Strange Things

Materialist monism defines the relationship between two types of stuff. On this view, one type of stuff (brain tissue) is more fundamental, even more real, than the other (conscious awareness). As Dr. Crick said once “you, your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will are, in fact, no more than the behavior of a vast assembly of nerve cells” - “you” are reduced to nerve cells. The essence of Crick's reductionism resides in these words: “in fact, no more than.” Reductionism reduces one thing to another (in this case, mind to brain) and thereby explains it away. However, not all materialists are reductive.

Dualists are, by definition, nonreductive. The crux of their position is that mind and brain cannot be reduced to one another. What, then, is the nature of the relationship between two? A dualist's answer to this question determines what kind of dualist he or she is. Most dualists describe the relationship between mind and body in interactionist terms; they assert that physical events have mental effects, and vice versa. The interactionist view, then, is simply that body, and mind interact with each other. This seems perfectly plausible and appears easy to demonstrate empirically: plummeting blood sugar causes loss of consciousness (physical event causes mental event); freely deciding to move your hand causes it to move (mental event causes physical event). But when the logical underpinnings of the dualist position are spelled out, it seems less plausible: the interactionist actually claims that bodily stuff and mental stuff interact with each other. This way of putting it immediately reveals the pitfalls of almost any dualist position. How, exactly, does a thought (which has no physical properties whatever) cause the physical stuff of neurons to start firing? This violates all the known laws of physics.

Other varieties of dualism fare no better. One such well-known variety is called psychophysical parallelism. This position avoids some problems of interactionism by claiming that mental and physical events do not have a causal relationship; the two classes of event simply co-occur – they are correlated with one another. Whenever something specific happens in the brain, something equally specific happens in the mind, and vice versa. The two things occur together, in unison. If the basis of this correlation still seems mysterious, that's because it is. The parallelist does not not feel obliged to explain this linkage.

Emergence

We said above that not all materialists are reductionists. Many cognitive scientists today hold the view that the mind is an emergent property of the brain. According to this view, mind and brain are equally real, but they exist at different levels of complexity. Just as water (wet and flowing, at room temperature) emerges from a particular combination of hydrogen and oxygen and has distinctive properties of its own (properties that do not characterize hydrogen or oxygen alone), so, too, mental phenomena emerge when the neurons of the human brain are connected or activated in a particular way.

The Brain and the Inner World, Introduction to Basic Concepts. Mark Solms, Oliver Turnbull.

It is possible to find some merit in all of different philosophical positions. It is also possible, with a little effort, to make all of them look ridiculous. Photograph by Elena.

Tactile Vision

Tactile Vision Experiments

In 1969, “Nature”, Europe's premier science journal, published a short article that had a distinctly sci-fi feel about it. Its lead author, Paul Bach-y-Rita, was both a basic scientist and a rehabilitation physician – a rare combination. The described a device that enabled people who had been blind from birth to see. All had damaged retinas and had been considered completely untreatable.

The “Nature” article was reported in “The New York Times”, “Newsweek”, and “Life”, but perhaps because the claim seemed so implausible, the device and its inventor soon slipped into relative obscurity.

Accompanying the article was a picture of a bizarre-looking machine – a large old dentist's chair with a vibrating back, a tangle of wires, and bulky computers. The whole contraption, made of castaway parts combined with 1960s electronics, weighed four hundred pounds.

A congenitally blind person – someone who had never had any experience of sight – sat in the chaire, behind a large camera the size of those used in television studios at the time. He “scanned” a scene in front of him by turning hand cranks to move the camera, which sent electrical signals of the image to a computer that processed them. Then the electrical signals were conveyed to four hundred vibrating stimulators, arranged in rows on a metal plate attached to the inside of the chair back, so the stimulators rested against the blind subject's skin. The stimulators functioned like pixels vibrating for the dark part of a scene and holding still for the brighter shades.

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This “tactile-vision device,” as it was called, enabled blinded subjects to read, make out faces and shadows, and distinguish which objects were closer and which father away. It allowed them to discover perspective and observe how objects seem to change shape depending upon the angle from which they were viewed. The six subjects of the experiment learned to recognize such objects as a telephone, even when it was partially obscured by a vase. This being the 1960s, they even learned to recognize a picture of the anorexic supermodel Twiggy.

Everyone who used the relatively clunky tactile-vision device had a remarkable perceptual experience, as they wen from having tactile sensations to “seeing” people and objects.

With a little practice, the blind subjects began to experience the space in from of them as three-dimensional, even though the information entered from the two-dimensional array on their backs. If someone threw a ball toward the camera, the subject would automatically jump back to duck it. If the plate of vibrating stimulators was moved from their backs to their abdomens, subjects still accurately perceived the scene as happening in front of the camera. It tickled near the stimulators, they didn't confuse the tickle with a visual stimulus. Their mental perceptual experience took place not on the skin surface but in the world. And their perceptions were complex. With practice, subjects could move the camera around ans say things like “That's Betty; she is wearing her hair down today and does not have her glasses on; her mouth is open, and she is moving her right hand from her left side to the back of her head.”

True, the resolution was often poor, but as Bach-y-Rita would explain, vision doesn't have to be perfect to be vision. “When we walk down a foggy street and see the outline of a buildings,” he would ask, “are we seeing it any less for the lack of resolution? When we see something in black and white, are we not seeing it for lack of color?”

(The Brain that Changes Itself, Stories of Personal Triumph from the Frontiers of Brain Science), by Norman Doidge, M.D.)

“When we walk down a foggy street and see the outline of a buildings, are we seeing it any less for the lack of resolution?". Illustration by Elena.

Epic Myth

Epic Myth

In the dark lush clouds between the stars, new raindrops made of many elements were forming, later generations of stars being born. Nearby, smaller raindrops grew, bodies far too little to ignite the nuclear fire, droplets in the interstellar mist on their way to form the planets. Among them was a small world of stone and iron, the early Earth.

Congealing and warming, it released the ammonia, methane, water and hydrogen gases that had been trapped within, forming the primitive atmosphere and the oceans.

Starlight from the Sun bathed and warmed the primeval Earth, drove storms, generated lightning and thunder. Volcanoes overflowed with lava. These processes disrupted molecules of the atmosphere; the fragments fell back together again into more and more complex forms, which dissolved in the early oceans.

After a time the seas achieved the consistency of a warm, dilute soup. Molecules were organized, and complex chemical reactions driven, on the surface of clays. And one day a molecule arose that was able to make crude copies of itself out of the other molecules in the broth.

As time passed, more elaborate self-replicating molecules arose. Those combinations best suited to further replication were favored by the sieve of natural selection. Those that copied better produced more copies. And the primitive oceanic broth gradually grew thin as it was consumed by and transformed into complex condensations of self-replicating organic molecules. Gradually, imperceptibly, life had begun.

Single-celled plants evolved, and life began to generate its own food. Photosynthesis transformed the atmosphere. Sex was invented. Once free-living forms banded together to make a complex cell with specialized functions. Chemical receptors evolved, and the Cosmos could taste and smell.

One-celled organisms evolved into multicellular colonies, elaborating their various parts into specialized organ systems. Eyes and ears evolved, and now the Cosmos could see and hear. Plants and animals discovered that the land could support life.

Organisms buzzed, crawled, scuttled, lumbered, glided, flapped, shimmied, climbed and soared. Colossal beasts thundered through the steaming jungles. Small creatures emerged, born life instead of in hard-shelled containers, with a fluid like the early oceans coursing through their veins. They survived by swiftness and cunning. And then some small arboreal animals scampered down from the trees. They become upright and taught themselves the use of tools, domesticated other animals, plants and fire, and devised language. The ash of stellar alchemy was now emerging into consciousness. At en ever-accelerating pace, it invented writing, cities, art and science, and sent spaceships to the planets and the stars. These are some of the things that hydrogen atoms do, given fifteen billion years or more of cosmic evolution.

It has the sound of epic myth, and rightly. But it is simply a description of cosmic evolution as revealed by the science of our time. We are difficult to come by and a danger to ourselves. But any account of cosmic evolution makes it clear that all the creatures of the Earth, the latest manufactures of the galactic hydrogen industry, are beings to be cherished. Elsewhere there may be other equally astonishing transmutations of matter, so wistfully we listen for a humming in the sky.

By Carl Sagan.

We have broadened the circle of those we love. Image : © Megan Jorgensen.