How the Mind Works

by: Steven Pinker

In this extraordinary book, Steven Pinker, one of the world’s leading cognitive scientists, does for the rest of the mind just what he did for language in his 1994 best-seller, The Language Instinct.

This time, he explains what the mind is, how it evolved, and how it allows us to see, think, feel, laugh, interact, enjoy the arts, and ponder the vast mysteries of life.

And, he does it all with the wit, clarity, and verve that earned The Language Instinct its world-wide critical acclaim and awards from the major scientific societies that it did.

Pinker explains the mind by “reverse-engineering” it----figuring out what natural selection designed it to accomplish in the environment in which we evolved. The mind, he writes, is as system of “organs of computat-ion” that allowed our ancestors to understand and thus outsmart objects, animals, plants, and especially each other.

How the Mind Works explains many of the imponderables of our every day life. Why does a face appear more natural with makeup? Just how do “Magic-Eye” 3-D stereograms manage to work? And just why do we feel that a run of heads makes the coin more likely to land tails the next time? And, why is the thought of eating worms so disgusting? Why do men challenge each other to duels and murder their ex-wives so often? Why are children (ours and others) so damn bratty? And, also, why do fools fall in love? Why are we soothed by paintings and music? And why do puzzles like the self, free will, and consciousness leave us so dizzy?

Believe me, the arguments in the book are bold as its title. Pinker rehabilitates unfashionable ideas, such as that the mind is a computer and that human nature was shaped by natural selection. And, furthermore, he challenges fashionable ones, such as the passionate emotions are irrational, that parents socialize their children, that creativity springs from the unconscious, that nature is good and modern society corrupting, and that art and religion are expressions of our higher spiritual yearnings.

How the Mind Works presents a big pictutre, but it is not a personal musing; it is a grand synthesis of the most satisfying explanations of our mental life that have been proposed in cognitive science and evolution-ary biology, with insights from disciplines ranging from neuroscience to economics and social psychology. It is also very fascinating, provocative and thoroughly entertaining. ( all 650 pages, that is)

Steven Pinker is professor of psychology and director of the Center for Cognitive Neuroscience at the Massachusetts Institute of Technology, (MIT). He was educated at McGill and Harvard, and taught at Harvard and Stanford before moving on to MIT. He has won numerous awards for his research, teaching and books on visual cognition and language. And has written fir Time, The New Republic, and the New York Times.


Quote: Pinker explains the mind by “reverse-engineering” it --------------figuring out what natural selection designed it to accomplished in the environment in which we evolved.

What is Reverse-Engineering as regards the Psyche?

The complex structure of the mind is the subject of this book. (Pg. 21) Its key idea can be captured in a sentence; the mind is a system of organs of computation, designed by natural selection to solve the kinds of problems our ancestors faced in their foraging way of life, in particular, understanding and out maneuvering objects, animals, and other people.

The summary can be unpacked in several claims. The mind is what the body does, specifically, the brain processes information, and thinking is a kind of computation. The mind is organized into modules or mental organs, each with a specialized design that make it an expert in one arena of interaction with the world. The modules’ basic logic is specified by our genetic program. Their operation was shaped by natural selection to solve the problems of the hunting and gathering life lead by our ancestors in most of our evolutionary history. The various problems for our ancestors were subtasks of one big problem for their genes, maximizing the number of copies that made it into the next generation.

On this view, psychology is engineering in reverse.

In forward-engineering , one designs a machine to do something; in reverse-engineering one figures out what a machine was designed to do. Reverse-engineering is what the boffins at Sony do when a new product is announced by Panasonic, or vice-versa. They buy one, bring it back to their lab, take a screwdriver to it, and try to figure out what all the parts are for and how they combine to make the device work.

(Now, fast forward to page 43)

Reverse-engineering is possible only when one has a hint of what the device was designed to accomplish. We do not understand the olive-pitter until we catch on that it was designed as a machine for pitting olives rather than as a paperweight or wrist-exerciser. The goals of the designer must be sought for every part of a complex device and for the device as a whole. Automobiles have a component, the carburetor, that is designed to mix air and gasoline, and mixing air and gasoline is a subgoal of the ultimate goal, carting people around.

Though the process of natural selection itself has no goal, it evolved entities that (like the automobile) are highly organized to bring about certain goals and subgoals. To reverse-engineer the mind, we must sort them out and identify the ultimate goal in its design. Was the human mind ultimately designed to create beauty? To discover truth? To love and to work? To harmonize with other human beings and with nature?

(Now, fast forward to pg. 165.)

One claim is that reverse-engineering, the attempt to discover functions of organs (which I am arguing should be done to the human mind), is a symptom of a disease called “adaptationism.” Apparently, if you believe that any aspect of an organism has a function, you absolutely must believe that every aspect has a function, that monkeys are brown to hide amongst the coconuts. The geneticist Richard Lewontin, for example, has defined adaptationism as “that approach to evolutionary studies which assume with out any further proof that all aspects of the morphology, physiology and behavior of organisms are adaptive optimal solutions to problems.” Needless to say, there is no such madman.

(Now, fast forward to pg .(187.)

There are grains of truth in these accounts, but they lack the leverage of good reverse-engineering. Natural selection for success in solving a particular problem tends to fashion an idiot savant like the dead-reckoning ants and stargazing birds. We need to know what the more general kinds of intelligence found in our species are good for. That requires a good description of the improbable feats the human mind accomplishes, not just one-word compliments like “flexibility” or the other “intelligence.” That description must come from the study of the modern mind, cognitive science.

(For the last time.-----fast forward to pg. 213)

Perception is the only branch of psychology that has been consistently adaptative-minded, seeing its task as reverse-engineering. The visual system is not there to entertain us with pretty patterns and colors; it is contrived to deliver a sense of the true forms and materials in the world. The selective advantage is obvious; animals that know where the food, the predators, and the cliffs are can put the food in their stomachs, keep themselves out of the stomachs of others, and stay on the right side of the cliff top.

The grandest vision has come from the late, great artificial intelligence researcher David Marr. Marr was the first to...............

The Mind’s Eye. pg. 237- 241.

Stereo vision does not come free with the two eyes; the circuitry has to be wired into the brain. We know this because about 2 percent of the population can see perfectly well out of each eyeball but not with the cyclopean eye; random-dot stereograms remain flat. Still, another 4 percent can see stereo only poorly. An even larger minority has more selective deficits. Some can’t see stereo depths behind the point of fixation; others can’t see it in front.

Whitman Richards, who discovered these forms of stereoblindness, hypothesized that the brain has three pools of neurons that detect differences in the position of a spot in the two eyes. One pool is for pairs of spots that coincide exactly or almost exactly, for fine-grained depth perception at the point of focus. Another is for pairs of spots flanking the nose, for further objects. Still, a third is for pairs of spots approaching the temples, for nearer objects.

Neurons with all these properties have since been found in the brains of monkeys and cats. The different kinds of stereoblindness appears to be genetically determined, suggesting that each pool of neurons is installed by a different combination of genes.

Stereo vision is not present at birth, and it can be permanently damaged in children or young animals if one of the eyes is temporarily deprived of input by a cataract or a patch. So far, this sounds like the tiresome lesson that stereo vision, like everything else, is a mixture of nature and nurture. But, a better way of thinking about it is that the brain has to be assembled, and the assembly requires project scheduling over an extended timetable. The timetable does not care about when the organism is extruded from the womb; the installation sequence can carry on after birth. The process also requires, at very critical junctions, the intake of information that the genes cannot predict.

Stereo vision appears abruptly in infants. When newborns are brought into a lab at regular intervals, for week after week they are unimpressed by stereograms, and then suddenly they are captivated. Close to that epochal week, usually around three or four months of age the babies converge their eyes properly for the first time (for example, they smoothly track a toy brought up to their nose), and they find rivalrous displays-----a different pattern in each eye-------annoying, whereas before they had found them very interesting.

It is not the case that babies “learn to see in stereo,” whatever that would mean. The psychologist, Richard Held has a simpler explanation. When infants are born, every neuron in the receiving layer of the visual cortex adds up the inputs from corresponding locations in the two eyes rather than keeping them separate. The brain cannot tell which eye a given bit of pattern came from, and simply melts one eye’s view on top of the other’s in a 2-D overlay.

Without information about which eye a squiggle came from, stereo vision, convergence, and rivalry are logically impossible. Around the three-month mark each neuron settles on a favorite eye to respond to. The neuron lying one connection downstream can now know when a mark falls on one spot in one eye and on the same spot, or a slightly shifted-over spot, in the other eye-----the grist of stereo vision.

In cats and monkeys, whose brains have been studied directly, this is indeed what happens. As soon as the animal’s cortex can tell the eyes apart, the animal sees stereograms in depth. That suggests that when the inputs are first tagged “left eye” or “right eye.” the circuitry for stereo computation one layer downstream is already installed and functioning.

In monkeys it’s all over in two months; by then each neuron has a favorite eye and the baby monkey sees in depth. Compared with other primates, humans are “altricial”: babies are born early and helpless, and complete their development outside the womb. Because human infants are born earlier than monkeys in proportion to the length of their childhood, the installation of their binocular circuitry appears at a later age as measured from the date of birth. More generally, when biologists compare the milestones of the maturation of the visual systems of different animals, some born early and helpless, others born late and seeing, they find that the sequence is pretty much the same whether the later steps take place in the womb or in the world.

The emergence of the crucial left-eye and right-eye neurons can be disrupted by experience. When the famous neurobiologists David Hubel and Torsten Wiesel raised kittens and baby monkeys with one eye covered, . The input neurons of the cortex all tuned themselves to the other eye, making the subject animal functionally blind in the eye that was covered. The damage was permanent, even with only brief privation, if the eye was covered in a critical period in the animal’s development. In monkeys, the visual system is especially vulnerable during the first two weeks of life, and the vulnerability tapers off during the first year. Covering the eye of an adult monkey, even for four years, does no harm.

At first, this looked like a case of “use it or lose it.” But, a surprise was in store. When Hubel and Wiesel covered both eyes, the amazing brain did not show twice the damage; half the cells showed no damage at all. The havoc in the single-eyepatch experiment came about not because a neuron destined for the covered eye was starved of input but because the input signals for the uncovered eye elbowed the covered eye’s inputs out of the way. The eyes compete for real estate inn the input layer of the cortex. Each neuron begins with a slight bias for one eye or the other, and the input from that eye exaggerates the bias until the neuron responds to it alone. The inputs do not even have to originate in the world; waves of activation from intermediate way-stations, a kind of internally generated test patterns, can do the trick. The developmental saga, though it is sensitive to changes in the animal’s experience, is not exactly “learning,” in the sense of registering information from the world. Like an architect who hands a rough sketch to a low-level draftsman to straighten out the lines, the genes build eye-specific neurons crudely and then kick off a process that is guaranteed to sharpen them unless a neurobiologists meddles.

Once the brain has segregated the left eye’s image from the right eye’s, subsequent layers of neurons can compare them for the minute disparities that signal depth. These circuits, too, can be modified by the animal’s experience, though again in surprising ways. If an experimenter makes an animal coss-eyed or wall-eyed by cutting one of the eye muscles, the eyes point in different directions and never see the same thing on two retinas at the same time.

Of course, the eyes don’t point 180 degrees apart , so, in theory, the brain could learn to match the out-of-whack segments that do overlap. But apparently it is not equipped for matches that stretch more than a few degrees across the two eyes; the animal grows up stereoblind, a condition called “amblyopia. (Amblyopia is sometimes called “lazy eye,” but that is misleading. It is the brain, not the eye, that is insensitive, and the insensitivity is caused by the brain actively suppressing one eye’s input in a kind of permanent rivalry, not by the brain lazily ignoring it.)

The same thing can happen in children, and does. If one of the eyes is more far-sighted than the other, the child habitually strains to focus nearby objects, and the reflex that couples focusing and convergence draws that eye inwards. The two eyes point in different directions ( a condition called strabismus). And their views don’t align closely enough for the brain to use the disparity information in them. Therefore, the child will grow up amblyopic and stereoblind unless early surgery on the eye muscles line the eyeballs up.

Until Hubel and Wiesel discovered these effects in monkeys and then Held found similar ones in children, surgery for strabismus was considered cosmetic and done only on school-aged children. But, there is a critical period for the proper alignment of two-eye neurons, a bit longer than the one-eye neurons but probably fading out near the age of one or two. Surgery after that point is often too late. (nearly always)

Why is there a critical period, as opposed to rigid hard-wiring or life-long openness to experience? In kittens, monkeys, and human babies, the face keeps growing after birth, and the eyes get pushed farther apart.

Their relative vantage; points change, and the neurons must keep up by re-tuning the range of inter-eye disparities they detect. Genes cannot anticipate the degree of spreading of the vantage ;points, because it depends on other genes, nutrition, and various accidents. So the neurons track the drifting eyes during the window of growth. When the eyes arrive at their grownup separation in the skull, the need disappears, and that is when the critical period ends.

Some animals, like rabbits, have precocious babies whose eyes are set in adult positions within faces that grow very little. (These tend to be prey animals, which don’t have the luxury of a long, helpless childhood) The neurons that receive inputs from the two eyes don’t need to re-tune themselves, and I fact these animals are wired at birth and do without a critical period of sensitivity to the input.

The discoveries about the tune-ability of binocular vision in different specie offers a new way of thinking about learning in general. Learning is often described as the indispensable shaper of amorphous brain tissue. Instead, it might be an innate adaption to the project-scheduling demands of a self-assembling animal. The genome builds as much of the animal as it can, and for the parts of the animal that cannot be specified in advance (such as the proper wiring for two eyes that are moving apart at an unpredictable rate), the genome turns on an information-gathering mechanism at the time of development at which it is most needed. In The Language Instinct I develop a similar explanation for the critical period for language in childhood.

Good Ideas. pgs.316.-321.

We live in a material world, and one of the first things in life we must figure out is how objects bump into each other and fall down elevator shafts. Until just recently, everyone thought that the infant’s world was a kaleidoscope of sensations, a “blooming, buzzing confusion,” in William James’ memorable words.

Piaget claimed that infants were sensorimotor creatures, unaware that objects cohere and persist and that the world works by external laws rather than the infants’ actions. Infants would be like the man in the famous limerick about Berkeley’s idealist philosophy;

There once was a man who said, “God
Must think it exceeding odd
If he finds that this tree
Continues to be
When there’s no one about in the Quad.

Philosophers are fond of pointing out that the belief that the world is a hallucination or that objects do not exist when you aren’t looking at them is not refutable by any observation. A baby could experience the blooming and buzzing all its life unless it was equipped with a mental mechanism that interpreted the blooms and buzzes as the outward signs of persisting objects that follow mechanical laws. We should expect infants to show some appreciation of physics from the very start.

Only careful laboratory studies can tell us what it is like—rather, what it was like—to be a baby. Unfortunately, infants are difficult experimental subjects, worse than rats and sophomores. They can’t easily be conditioned, and they don’t talk. But, a very ingenious technique, refined by the famous psychologists Elizabeth Spelke and Renee Baillargeon, capitalized on one feat that infants are very good at: getting bored.

When infants see the same old thing again and again, they signal their boredom by looking away. If a new thing happens to appear, they perk up and stare. Now, “old thing” and “new thing” are in the mind of the beholder. So, by seeing what revives babies’ interest and what prolongs their ennui, we can guess at what things they see as the same and what things they see as different----that is, how they categorize experience. It’s especially informative when a screen first blocks part of the infant’s view and then falls away, for we can tell what the babies were thinking about the invisible part of their world. If the babies eyes are only momentarily attracted and then wander off, we can infer that the scene was in the baby’s mind’s eye all along. But, if the baby stare longer, we can then infer that the scene came as a surprise.

Three-to-four-month-old infants are usually the youngest tested in this manner, because they are better behaved than younger babies and because their stereo vision, motion perception, visual attention, and the acuity have just matured. The tests cannot, by themselves, establish what is and what is not innate. Three-month-olds were not born yesterday, so anything they know they could, in theory, have learned. And three-month-olds still have a lot of maturing to do, so anything they come to know later could emerge without learning, just as teeth and pubic hair do. But by telling us what babies know at what age, the findings narrow the options.

Spelke and Philip Kelman wanted to see what infants treated as an object. Remember, from Chapter 4, that it is not easy, even for an adult, to say what an “object” is. An object can be defined as a stretch of the visual field with a smooth silhouette, a stretch with a homogeneous color and texture, or a collection of patches with a common motion. Often these definitions pick out the same pieces, but when they don’t. It is common motion that wins the day. When pieces move together, we see them as a single object; when pieces go their separate ways, we se them as separate objects. The concept of an object is useful because bits of matter that are attached to one another usually move together. Bicycles and grapevines and snails may be jagged agglomerations of different materials, but if you pick up one end, the other end, comes along for the ride.

Kelman And Spelke bored babies with two sticks poking out from behind the top and bottom edges of a wide screen. The question was whether the babies would see the sticks as part of a single object. When the screen was removed, the babies saw either one long stick or two short ones with a gap between them. If the babies had visualized a single object , then seeing a single object would be a bore, and two would come as no surprise. If they had thought of each piece as its own object then seeing a single object would come as a surprise, and two a bore. Control experiments measured how long infants looked at one verus two objects without having seen anything beforehand; these baseline times were then subtracted out.

Infants might have been expected to see the two pieces as two pieces, or, if they had mentally united them at all, to have used all the correlations among the features of an object as criteria: smooth silhouettes, common colors, common textures, and common motions. But apparently infants have an idea of objecthood early in life, and it is the core of the adult concept: parts moving together. When two sticks peeking out from behind the screen moved back and forth in tandem, babies saw them as a single object and were surprised if the raised screen revealed two. But, when they didn’t move, babies did not expect them to be a single object, even thought the visible pieces had the same color and texture. When a stick peeked out from behind the top edge and a red jagged polygon peeked from behind the bottom edge, and they moved back and forth in tandem, babies expected them to be connected, even though they had nothing in common but motion.

The child is parent to the adult in other principles of intuitive physics. One is that an object cannot pass through another object like a ghost. Renee Baillargeon has shown that four-month-old infants are surprised when a panel just in front of a cube somehow manages to fall back flat to the ground, right through the space that the cube should be occupying. Spelke and company have shown that infants don’t expect an object to pass through a barrier or through a gap that is narrower than the object is.

A second principle is that objects move along continuos trajectories; they cannot disappear from one place and materialize in another, as in the transporter room of the Enterprise. When an infant sees an object pass behind the left edge of a left screen and then seem to reappear from behind the right edge of a right screen without moving through the gap between the screens, she assumes she is seeing two objects. When she sees an object pass behind the left screen, reappear at the other edge of the screen, cross the gap, and then pass behind the right screen, and then out, she assumes she is seeing only one object.

A third principle is that objects are cohesive. Infants are surprised when a hand picks up what looks like an object but part of the object stays behind.

A fourth principle is that objects move each other by contact only-----no action at a distance After repeatedly seeing an object pass behind a screen and another object pop out, babies expect to see one launching the other like billiard balls. They are surprised when the screen reveals one ball stopping short and the second just up and leaving.

So three-to-four-month-old infants see objects, remember them, and expect therm to obey the laws of continuity, cohesion, and contact as they move. Babies are not as stoned as James, Piaget, Freud, and others thought. As the psychologist David Geary has said, James’ “blooming, buzzing confusion” is a very good description of the parents life, not the infants. The discovery also overturns the suggestion that babies stop their world from spinning by manipulating objects, walking around them, talking about them, or hearing them talked about. Three-month-olds can barely orient, see, touch, and reach, let alone manipulate, walk, talk and understand. They could not have learned anything by the standard techniques of interaction, feedback, and language. Nonetheless, they are sagely understanding a stable and lawful world.

Proud parents should not call MIT admissions just yet. Small babies have an uncertain grasp, at best, of gravity. They are surprised when a hand pushes a box off the table and it remains hovering in midair, but the slightest contact with the edge of the table or a fingertip is enough for them to act as if nothing were amiss. And they are not fazed when a screen rises to reveal a falling object that has defied gravity by coming to rest in midair. Nor are they nonplused when a ball rolls right over a large hole in a table without falling through. Infants don’t quite have inertia down, either. For example, they don’t care when a ball rolls towards one corner of a covered box and then is shown to have ended up in the other corner.

But then, adults’ grasp of gravity and inertia is not so firm, either. The psychologist Miahael McCloskey, Alfonso Caramazza, and Bert Green asked college students what would happen when a ball shot out of a curved tube or when a whirling tetherball was cut loose. A depressingly large minority, including many who had taken physics, guessed that it would continue in a curving path. (Newton’s first law states; that an object in motion tends to remain in motion in a straight line unless acted upon by an outside force) The students explained that the object acquires a “force” or “momentum” (some students, remembering the lingo but not the concept, called it “angular momentum”), which propels it along the curve until the momentum gets used up and the path straighten out. Their beliefs come right out of the medieval theory in which an object is impressed with an “impetus” that maintains the object’s motion and gradually dissipates.

These howlers come from conscious theorizing; they are not what people are prepared to see. When people view their paper-and-pencil answers as a computer animation, they burst out laughing as if watching Wile E. Coyote chasing the Road Runner over a cliff and stopping in midair before plunging straight down. But the cognitive misconceptions do run deep. I toss a ball straight up. After it leaves my hand, which forces act on it on the way up, at the apogee, and on the way down? It’s almost impossible not to think that momentum carries the ball up against gravity, the forces equal out, and then gravity is stronger and pushes it back down. The correct answer is that gravity is the only force and that it applies the whole time. The linguist Leonard Talmy points out that the impetus theory infuses our language. When we say The ball kept rolling because the wind blew on it, we are constructing the ball as having an inherent tendency towards rest. When we say The ridge kept the pencil on the table, we are imbuing the pencil with a tendency towards motion, not to mention flouting Newton’s third law ( to every action there is an equal and opposite reaction) by imputing a greater force to the ridge. Talmy, like most cognitive scientists, believes that the conception drive the language, not the other way around.

When it comes to more complicated motions, even perception fails us. The psychologist Dennis Proffitt and David Gildan have asked people simple questions about spinning tops, wheels rolling down ramps, colliding balls, and Archimedes-in-the-bathtub displacements. Even physics professors guess the wrong outcome if they are not allowed to fiddle with equations on paper. (If they are, they spend a quarter of an hour working it out and then announce that the problem is “trivial.” When it comes to these motions, video animations of impossible events look quite natural. Indeed, possible events look unnatural: a spinning top, which leans without falling, is an object of wonder to all of us, even physicists.

It is not surprising that the mind is non-Newtonian. The idealized motions of classical mechanics are visible only in perfectly elastic point masses moving in vacuums on frictionless planes. In the real world, Newton’s laws are masked by friction from the air, the ground, and the objects’ own molecules. With friction slowing everything that moves and keeping stationary objects in place, it’s natural to conceive of objects as having an inherent tendency towards rest. As historians of science have noted, it would be hard to convince a medieval European struggling to free an oxcart from the mud that an object in motion continues at a constant speed along a straight line unless acted upon by some external force.

Complicated motions like spinning tops and rolling wheels have a double disadvantage. They depend on revolutionarily unprecedented machines with negligible friction, and their motions are governed by complex equations that relate many variables at once; our perceptual system can handle only one at a time even in the best of circumstances.

Even the brainiest baby has a lot to learn. Children grow up in a world of sand. Velco, glue, Nerf balls, rubber balloons, dandelion seeds, boomerangs, television remote controls, objects suspended by near-invisible fishing line, and countless other objects whose idiosyncratic properties overwhelm the generic predictions of Newton’s laws. The precociousness that infants show in the lab does not absolve them of learning about objects, it makes the learning possible. If children did not carve the world into objects, or if they were prepared to believe that objects could magically disappear and reappear anywhere, they would have no pegs on which to hang their discoveries of stickness, fluffiness, squishiness, and so on.

Nor could they develop the intuitions captured in Aristotle’s theory, the impetus theory, Newton’s theory, or Wile E. Coyote’s theory. An intuitive physics relevant to our middle-sized world has to refer to enduring matter and its lawful motions , and infants see the world in those terms from the beginning.

Return to the books..

D.U.O Project
Church of the Science of God
La Jolla, California 92038-3131

© Church of the Science of GOD, 1993
Web Designed by WebDiva