By PETER COATES

Reviewed:
On Growth and Form by D’Arcy Wentworth Thompson
Cambridge University Press, 345 pp., $31.00

Completed in 1915 and first published in 1917, On Growth and Form had already been in print for 50 years when I found it, but it was revelatory: like opening the curtains and finding not the backyard but the Himalayas. Fourteen is an impressionable age, but any number of more mature readers have reacted in the same way, for Thompson’s book is not just about a theory of biology — it presents a way of seeing the natural world through ideas rendered as literature.

Too often, we’re introduced to the natural sciences by a route that seems designed to repel anyone with a degree of sensitivity to beauty: hacking away at brain-dead frogs, calculating the trajectory of imaginary cannon balls, and coaxing minuscule electric currents from vegetables. The scientific content of On Growth and Form has the opposite effect; it is about how a few simple mathematical principles dictate the structure of living things. Animals and plants are presented as the living embodiment of equations of scale across domains of linear measure, mass, temperature, speed; each plant and animal as a cloud of mathematical, almost Platonic, truths. Scientific principles are also revealed in the context of their connection to philosophy, history, and the elegant use of language and learning; a profound revelation of both the spaciousness and the interconnectedness of ideas. It is difficult to convey the impact this combination of ideas and writing delivers to a young mind at the right moment.

Peter Medawar famously called On Growth and Form “beyond comparison the finest work of literature in all the annals of science that have been recorded in the English tongue,” but it is not merely a literary expression of established knowledge; it’s one of the most peculiar and original works of modern science, advancing an idiosyncratic view of how organisms develop, a view that was deeply at odds with the intellectual climate of Thompson’s time. An elegant expression of an original idea that is still, possibly even increasingly, influential in biology, it’s a work of literature that can be read for pleasure by scientists and nonscientists, and a textbook on how to think in any field.

Stylistically, it has profoundly influenced generations of scientist-authors: Benoit Mandelbrot’s seminal The Fractal Geometry of Nature (1982) emulates both Thompson’s literary approach and his audacity in presenting a mathematical view of nature contrary to the prevailing view. Mandelbrot’s somewhat imperious style excites more admiration than affection. Oliver Sacks’ Migraine, which for many years was the most comprehensive overview of the field, though mostly nonmathematical, has more of Thompson’s grace and modesty. In this, Sacks may be Thompson’s truest heir. One of the lasting pleasures of On Growth and Form is in finding echoes of it in so many places, from the essays of Isaac Asimov, to Douglas Hofstadter’s Gödel , Escher, Bach, to Edward Tufte’s influential (and gorgeous) The Visual Display of Quantitative Information. One work contemporary with Thompson’s is also worth mentioning. The Curves of Life (1914) by Theodore Andrea Cook covers some of the same mathematical territory, particularly as related to natural spirals, but with a heavy emphasis on their occurrence in architecture and art.

*****

Chapter two, my favorite, deals with simple mathematical principles that dictate how the form of an animal must change with size: why elephants cannot be shaped like deer; the nonintuitive relationship between leg size and walking speed (if mice moved at speeds proportional to their size, you wouldn’t need cats — you could just pick them up like box turtles); why birds can be only so large, and mammals only so small; why eyes vary in size so much less than animals do. Although Thompson died before computers were invented, this chapter made the analysis of algorithms — the study of how computational processes behave as problems increase in size — seem completely natural to me when I began to study computer science almost 70 years after the chapter was written.

While it’s not easy reading by any means, there are few ideas in the book that require mathematics beyond the level of advanced high school or the first year of college. (I was an undistinguished scholar in high school, to say the least, and got through it.) Given high school algebra and geometry, most of the concepts are developed from scratch, and are not difficult. If some of the technicalities do not get through, the strength of the writing usually bridges the gap, and getting every detail is not critical — they build to a fascinating and subtle argument that depends less on mastering the formulas themselves than understanding the general importance of their very existence.

There are 17 chapters, covering an enormous range of issues, and not all have worn equally well scientifically, nor will all be of equal interest to the casual reader. But you can hardly crack the book without finding something fascinating: how the geometry that controls soap bubbles also determines a wide range of living forms; the geometrical order underlying the growth of shells, leaves, and horns; the engineering principles of skeletons. The most famous chapter is probably the last, which contains the best-known of the many illustrations in the book. The subject is the underlying unity of animal design — how a few basic designs can be systematically distorted to represent almost any animal by a process that we would now call morphing. The process is described by Thompson as simple manipulations of the grid on which they are drawn (in mathematical terms, replacing the regular X and Y coordinate values on the grid with smooth mathematical functions of these values). Less abstractly, it’s as if images that cannot be erased from or added to are drawn on a rubber sheet that can be stretched and compressed, but not cut. In this way, he warps a human infant’s skull into that of an ape, and turns one canonical fish into a multiplicity of species, showing how these simple warping functions unify huge families of species.

Read on

By MARIANNE FREIBERGER  l  +Plus  April 19, 2012

There’s an old Indian story about six blind men who go to visit an elephant. One touches its leg and decides that elephants must be like trees. A second examines its trunk and declares they are like snakes. A third feels its side and concludes they are like walls. You can imagine the rest. Everyone is right yet they are all wrong and it all ends in an argument. Only a major leap of the imagination, inspired by a lot more careful feeling around, could reveal the true nature of the animal that combines so many different characteristics.

In physics such leaps do sometimes occur. And when they do — when seemingly different things are unified under one idea — this represents a great advance in our understanding of how the world works. One of the first examples of such a leap was Newton’s realisation, in the 17th century, that the motion of the planets around the Sun and an apple falling to the ground are due to the same thing: the force of gravity. Almost 200 years later James Clerk Maxwell unified electricity and magnetism in his theory of electromagnetism. The drive for unification continued and today we know that there are just three fundamental forces (gravity, the electroweak force and the strong nuclear force) and that there are only twelve basic building blocks of matter (see this Plus article for more information).

But there is a problem. Gravity is described by Einstein’s general theory of relativity, which applies to the world at the scale of planets, stars and galaxies. The other two forces are negligible on such large scales. They come into play at the level of atoms and even smaller components of matter. This tiny world, in which gravity usually plays no part, is described by the other great theory to come out of the twentieth century: quantum mechanics.

Both theories do exceptionally well when they are tested against reality. But they are in conflict about the nature of space, or, as Einstein would have it, spacetime. When you combine the two theories you get mathematical results that make no physical sense: they imply that spacetime should tear itself apart (see this Plus article for more information). So the biggest challenge for twenty-first century physics is to come up with a unified theory of quantum gravity, which describes the world at all scales and retains the aspects of general relativity and quantum mechanics that work so well.

Currently the strongest contender for such a unifying theory is something called M-theory. The name was invented by the originators of the theory, but nobody seems to know what the M stands for — it could be “mother”, “mystery” or even “magic”, though it’s probably the slightly less enticing “membrane”. The Isaac Newton Institute, a mathematical research institute in Cambridge, is currently holding a six-month-long programme, bringing together the leading lights in the field. We went along to meet two of them, David Berman of Queen Mary, University of London, who organises the programme, and Andrew Strominger of Harvard, to find out more about this supposed mother of all theories.

From points to strings

The origin of M-theory lies in a clever trick designed to overcome the quantum gravity conundrum. Rather than thinking of the fundamental particles that make up matter — for example electrons — as being like points, think of them as tiny little strings. Like the strings on a guitar, these fundamental strings can vibrate, and it’s these vibrations we observe as fundamental particles and forces. That’s the basic idea behind the pre-runner of M-theory, string theory, and it gets around the mathematical and conceptual problems that arise from combining relativity and quantum mechanics.

“It is a natural idea in music,” says Berman. “We don’t think that every single sound in a piece of music is produced by a different instrument; we know that a rich and varied set of sounds can be produced by even just a single violin. String theory is based on the same idea. The different particles and forces are just the fundamental strings vibrating in a multitude of different ways.”

But to produce all the physics we observe, the fundamental strings need more wriggle room, more directions to vibrate in, than is provided by the ordinary three-dimensional space we can perceive. In order to work, the theory requires ten dimensions. Three of these are the familiar up-down, right-left, and forward-backward directions of space and one of them is time. The reason we can’t detect the other six dimensions, so the theory goes, is that they are rolled up so tightly that our coarse-grained perception just doesn’t pick them up. Thankfully mathematics provides the tools to deal with any number of dimensions, so the extra ones aren’t a problem when it comes to formulating string theory. (You can find out more about string theory in the Plus articles From Newton to Einstein and beyond and Tying it all up.)

String theory has not been verified directly in experiments because the hypothetical strings are far too small, a predicted 10^-34m, to be detected by any methods available in the foreseeable future. But during the 1970s and 1980s string theory emerged as a prime contender for a unified theory of quantum gravity: it was free from contradictions, its predictions about reality made sense and its mathematics was seductively elegant.

The only problem was that the theory started to multiply. “What was remarkable was that people developed five possible types of string theory,” says Berman. “That’s not very satisfactory because what you want is a unified theory. Why would you have this choice of five different possible string theories? What M-theory did, when it happened in 1995, was to unify the five different types of string theory.”

From strings to membranes

The leap that created string theory was to move from points to strings: from zero-dimensional to one-dimensional objects. M-theory goes a step further. The theory itself requires 11 dimensions to work in and its fundamental objects are not strings, but two-dimensional vibrating membranes. The idea is that these membranes are wrapped up so tightly that they appear one-dimensional, just as a tightly rolled up sheet of paper viewed from far away appears like a line. The five different types of string theory correspond to different aspects of M-theory, only that in the string theories the tightly wrapped-up membranes are treated simply as strings.

The fundamental particles and forces we observe in nature come from specific vibrational modes of the membranes in M-theory. But within its 11 dimensions there is room for a lot more. Objects of higher dimensions, simply called branes, also play an important role in M-theory (in fact, they had already emerged as important objects in string theory). Their physical interpretation is a little trickier, but there are some intriguing possibilities. “It has been proposed that we could actually be living on a three-dimensional brane,” says Berman. “The idea is that we’re trapped in this 3-brane and confined to it. It’s like in Superman III, where the baddies are trapped in a two-dimensional plane.” This is just one possible answer to the question of how we fit into the multi-dimensional world of M-theory. “It’s a very complicated question, but this is one possibility.”

Black holes made from strings

In terms of unification M-theory has been a double success: it has unified the five string theories which themselves unify Einstein’s theory of relativity and quantum mechanics. But why should anyone believe in such a theoretical construct which cannot be directly tested in the lab?

One reason comes from those gravitational monsters we call black holes. Black holes are formed when a large amount of mass becomes concentrated at a point in space, for example during the collapse of a massive star. The resulting gravitational pull is so strong that nothing, not even light, can escape from the vicinity of the point: hence the name black hole.

You can’t ignore gravity when you’re thinking about black holes, but the small scale also means that effects described by quantum mechanics come into play. So black holes can make or break a candidate theory of quantum gravity: the theory needs to give a coherent description of them, otherwise it has failed.

“The biggest question about black holes is what’s inside them,” says Strominger. “One of the legacies of twentieth century physics is that we’ve been given two radically contradictory pictures of what’s inside a black hole. One of them, which came from Einstein and the physicist Karl Schwarzschild is that there is nothing inside. In fact, there’s less than nothing. It’s not that there is empty space inside a black hole: it’s the end of space and there isn’t an inside.”

The other picture was provided by Jacob Bekenstein and Stephen Hawking in the 1970s. When you’re looking at a region of space you can ask yourself how much information you need to describe what’s going on in it. The amount of information is measured by a number called the entropy. For example, to describe a messy room you need lots of bits of information: you need to give the exact location of every single sock and empty tea mug. So a messy room has a high entropy. Describing a tidy room requires less information, so it’s got a lower entropy.

Based on some pretty elementary musings, Bekenstein proposed that, despite not being ordinary regions of space, black holes too have an entropy. And he suggested that the entropy of a black hole is always larger than the entropy of an ordinary region of space of the same size. So a black hole contains more information than any other region of space. Work by Stephen Hawking confirmed and refined Bekenstein’s results. “According to Bekenstein and Hawking, a black hole behaves not as if it were empty, but as if it were full of stuff,” says Strominger. Bekenstein and Hawking’s result cannot be tested for black holes of cosmological sizes, but their reasoning was so elementary that it is universally believed to be true.

But how can we make sense of a black hole, which is after all just a gravitational entity, containing information? To explain where this information resides we need to understand the stuff that makes up gravity at the smallest scales. We are in the position of a 19th century scientist who knows the laws that govern how a gas behaves without knowing that gases are made up of atoms. One of the major achievements of M-theory has been to give a description of the microscopic structure of gravity in terms of strings. This explains the entropy puzzle: the information is in the strings.

The fact that M-theory has been able to explain the black hole information question has given the theory a major boost. And black holes weren’t the first challenge the theory has overcome. “By the time it came to describing black holes the theory had already jumped through many hoops,” says Strominger. There was no more room to fiddle with it: you couldn’t just tweak an equation here or add a term there to make things work. The ability to simultaneously satisfy many demands counts as theoretical evidence that M-theory might be the solution to the quantum gravity conundrum. “We know there has to be a solution because we’re here. For a time it looked like there might be unrelated solutions in theory [the five different versions of string theory], which was very weird, but now there’s only one.”

To the test

But what about hard experimental evidence for M-theory? We will not be able to see the fundamental membranes in experiments any time soon. There is some hope that the Large Hadron Collider (LHC) at CERN will provide evidence for a concept that’s closely related to M-theory, called supersymmetry. It implies that fundamental particles should have siblings, called their superpartners, whose existence the LHC may be able to detect. But while supersymmetry is a necessary consequence of M-theory, the converse doesn’t apply: there may be supersymmetry in the world even if M-theory is false. So discovering supersymmetry at the LHC would only count as indirect evidence for M-theory.

But Strominger does not think that the lack of experimental evidence should deter us. “I don’t think that research on this most fundamental of all questions should come to a screeching halt because we don’t have a proposal for an experiment that would [confirm the theory]. There is some chance that we will see supersymmetry. It’s not the same thing as M-theory, but [discovering it] would certainly put us in a good mood. The kind of reasoning that got us to supersymmetry is like the kind of reasoning that got us to M-theory. So [seeing supersymmetry] would be evidence for the power of pure reasoning, the power of the human mind.”

Last year results from the LHC at CERN made a splash, providing strong evidence for the notorious Higgs boson (you can read more on this on Plus). This counts as a triumph for the power of the human mind: it was purely theoretical considerations that led the physicist Peter Higgs to predict the particle’s existence nearly 50 years ago. Now it has, to all intents in purposes, been found. Perhaps in another 50 years we will have similarly strong evidence for M-theory and it will enter the ranks of established physical theories, along with Newton’s laws of motion and Einstein’s theory of relativity.

youmightfindyourself:

Where did we come from? I find the explanation that we were made in stars to be deep, elegant, and beautiful. This explanation says that every atom in each of our bodies was built up out of smaller particles produced in the furnaces of long-gone stars. We are the byproducts of nuclear fusion. The intense pressures and temperatures of these giant stoves thickened collapsing clouds of tiny elemental bits into heavier bits, which once fused, were blown out into space as the furnace died. The heaviest atoms in our bones may have required more than one cycle in the star furnaces to fatten up. Uncountable numbers of built-up atoms congealed into a planet, and a strange disequilibrium called life swept up a subset of those atoms into our mortal shells. We are all collected stardust. And by a most elegant and remarkable transformation, our starstuff is capable of looking into the night sky to perceive other stars shining. They seem remote and distant, but we are really very close to them no matter how many lightyears away. All that we see of each other was born in a star. How beautiful is that?

By KATIE DRUMMOND  l  Wired Jan.4, 2012

Soldiers could one day conduct covert operations in complete secrecy, now that Pentagon-backed physicists have figured out how to mask entire events by distorting light.

A team at Cornell University, with support from Darpa, the Pentagon’s out-there research arm, managed to hide an event for 40 picoseconds (those are trillionths of seconds, if you’re counting). They’ve published their groundbreaking research in this week’s edition of the journal Nature.

A recent research has uncovered a remarkable ability to manipulate and control electromagnetic fields to produce effects such as perfect imaging and spatial cloaking. To achieve spatial cloaking, the index of refraction is manipulated to flow light from a probe around an object in such a way that a ‘hole’ in space is created, and the object remains hidden. Alternatively, it may be desirable to cloak the occurrence of an event over a finite time period, and the idea of temporal cloaking has been proposed in which the dispersion of the material is manipulated in time, producing a ‘time hole’ in the probe beam to hide the occurrence of the event from the observer. This approach is based on accelerating the front part of a probe light beam and slowing down its rear part to create a well controlled temporal gap—inside which an event occurs—such that the probe beam is not modified in any way by the event. The probe beam is then restored to its original form by the reverse manipulation of the dispersion. Here we present an experimental demonstration of temporal cloaking in an optical fibre-based system by applying concepts from the space–time duality between diffraction and dispersive broadening. We characterize the performance of our temporal cloak by detecting the spectral modification of a probe beam due to an optical interaction and show that the amplitude of the event (at the picosecond timescale) is reduced by more than an order of magnitude when the cloak is turned on.

This is the first time that scientists have succeeded in masking an event, though research teams have in recent years made remarkable strides in cloaking objects. Researchers at the University of Texas, Dallas, last year harnessed the mirage effect to make objects vanish. And in 2010, physicists at the University of St. Andrews made leaps towards using metamaterials to trick human eyes into not seeing what was right in front of them.

Masking an object entails bending light around that object. If the light doesn’t actually hit an object, then that object won’t be visible to the human eye.

Where events are concerned, concealment relies on changing the speed of light. Light that’s emitted from actions, as they happen, is what allows us to see those actions happen. Usually, that light comes in a constant flow. What Cornell researchers did, in simple terms, is tweak that ongoing flow of light — just for a mere iota of time — so that an event could transpire without being observable.

The entire experiment occurred inside a fiber optics cable. Researchers passed a beam of green light down the cable, and had it move through a lens that split the light into two frequencies, one moving slowly and the other faster. As that was happening, they shot a red laser through the beams. Since the laser “shooting” occurred during a teeny, tiny time gap, it was imperceptible.

Sure, the team’s got a ways to go before they’re able to mask 30 seconds of action, let alone several minutes. But the research certainly opens up new possibilities. For one, masking super-quick events, like those that occur with data transmission, could help conceal covert computer operations.

In the words of Nature editors, the research marks “a significant step towards full spatio-temporal cloaking.” But it could be decades before military personnel will basically be able to zap history, as it happens: According to Cornell scientists, it’d take a machine 18,600 miles long to produce a time mask that lasts a single second.

By COURTNEY HUMPHRIES  l  The Boston Globe Dec. 11, 2011

Yes, your ears can change what you taste. What discoveries about cross-sensory perception are revealing about the brain.

The senses have always been our portals into the outer world. We have the classic five that Aristotle talked about — sight, hearing, smell, taste, and touch — plus more recently recognized senses of balance, temperature, pain, and body position and movement. Each evolved to collect some distinct type of information about our environment, and to tell us our status within it.

That’s largely how we tend to think about the senses, anyway: separately, each one its own distinct way to understand the world around us.

But in recent years, various findings have emerged to challenge that assumption — strange illusions in which one sense seemed to change the perceptions of another. One study published in 2000 particularly grabbed people’s attention: When researchers at Caltech showed test subjects a brief flash of light accompanied by two quick tones, many people saw two flashes instead of one. The same effect occurred when the researchers tapped their subjects’ skin twice as the light flashed. Vision — considered our most reliable and dominant sense — could be altered by sound or touch.

And that wasn’t all. Other studies showed that what people saw affected what they heard; that certain types of music or background noise affected how food tasted; and that smells could influence how a texture felt to the touch.

What the researchers were uncovering, in other words, is that our senses are not so separate after all. Scientists have realized that interaction between the senses “is the rule rather than the exception,” says Ladan Shams, one of the researchers who conducted the light-flashing study and now a sensory scientist at the University of California at Los Angeles. From the earliest stages of perception, it appears, the senses are enhancing, competing with, and even altering one another in surprising ways.

Since then, a new field has emerged to study cross-sensory perception, with laboratories throughout the world devoted to understanding how the senses merge. Scientists are developing a new way of thinking about how our brains are organized and how we perceive the world. And what began as basic scientific research to understand the brain’s organization is spreading into other fields, such as marketing: Companies are starting to engineer foods that taste better by appealing to the eyes and ears, for instance. The work may even have implications for medicine — helping to explain, say, how the brain can compensate for a missing sense — and for education.

It might seem unsettling that the perceptual tools we rely on to navigate the world are so fluid — not just capable of being fooled, but capable of fooling one another. But the constant interaction and interference between our senses, in fact, is central to one of the brain’s most astonishing feats: its ability to take a sea of complex, conflicting sensory input and assemble it into a fairly reliable picture of the world.

Philosophers have long debated the primacy of the senses in knowing truth, but they have rarely questioned their separateness. The Epicurean poet and philosopher Lucretius, for example, argued that the senses couldn’t influence one another, “for each has powers discrete and apart, its separate force.” Because of these separate powers, he reasoned, “it must be, then, that one sense cannot prove another wrong.”

Yet we’ve always understood intuitively that senses do affect one another in certain ways. As anyone who’s ever eaten dinner while nursing a bad cold knows, nearly all of food’s flavor comes from our sense of smell, not taste. Since the dawn of the talkies, moviegoers have experienced this kind of sensory interaction, too. Their ears might hear sounds from a speaker behind them, but their eyes persuade them that the voices are coming from actors projected on the screen.

Now, science is showing that such connections among the senses are more widespread and deeply rooted than we ever imagined. What happens in the movie theater isn’t just an isolated illusion — the blending of sensory information is critical for the brain to create a seamless interpretation of its outside world.

Research into perception is following suit. Over the past decade, previously disparate studies of the senses have begun to merge. There is now a yearly conference devoted to multisensory research, and the topic is finding its way into neuroscience meetings. Some scientists focus specifically on the integration of senses, while others have expanded their previously single-sense research to include others. Shams, at UCLA, says that while some people initially doubted whether isolated illusions had bearing on the everyday function of the senses, most now accept there are countless ways they are intertwined.

One researcher who has spearheaded this change is psychologist Charles Spence, head of the Crossmodal Research Laboratory at Oxford University. While neuroscientists have been piecing together how senses connect in the brain, his work has revealed how the crossing of sensory information affects perception and behavior. His recent work on the psychology of flavor perception, for instance, has shown that the flavor of your food is influenced by touch, vision, and even sound. A study from his lab a few years ago showed that people rate potato chips as crisper and better-tasting when a louder crunch is played back over headphones as they eat. A study published this year showed that people thought a strawberry mousse tasted sweeter, more intense, and better when they ate it off a white plate rather than a black plate. Other researchers have conducted similar studies showing that our impressions of experiences, and our emotional responses to them, derive from a blending of different kinds of sensory input — a process that is usually completely unconscious.

These findings are leading to a fuller picture of how we really perceive the world around us. Barry Stein, a multisensory scientist at Wake Forest University, says that what’s been surprising is how early in the process of perception the senses begin to overlap. Even before the brain makes higher-level judgments about the sensory information it is receiving, Stein says, special “multisensory neurons” that respond to more than one sense begin to synthesize it.

This process allows the brain to quickly blend different channels of information into one impression. In some cases, senses enhance one another: A distant image paired with a weak sound can appear more noticeable than each alone. In some cases they compete with each other and one wins out (as your eyes win over your ears in the movies). In others, the information merges into something new; when people watch a video of a person saying “ga” while the audio is dubbed with a voice saying “ba,” they hear an intermediate “da.” Though the senses can fool us in certain cases, being able to integrate them helps us make a quick judgment and move on, rather than puzzling over conflicting information.

The ability to coordinate among the different senses seems to be something the brain learns; we’re not born being able to do it. “You’d think that the brain comes with all this hardware built into it,” says Stein. “But that’s not the case.” Instead, research shows that after we’re born, the brain quickly learns to put information from the senses together. This early wiring of the brain to coordinate sensory input helps explain why people born without a sense who then regain it — such as deaf people who receive cochlear implants later in life — have a difficult time learning to integrate the new sensory information.

This research sheds light on other fascinating phenomena that neuroscientists have observed in those with impaired sensory functions, too — and it may ultimately suggest possible therapies. In blind people, for example, research has shown that the sense of touch activates the visual cortex; in other words, areas of the brain normally designated for processing one sense can adjust to make use of information from another. Then there are people, like those with autism or other conditions, who have impaired abilities of sensory integration. Therapists influenced by the science of multisensory integration have worked with people with autism to create “sensory diets,” interventions that focus on using senses together.

And the new work may ultimately affect how the rest of us learn, as well. Shams’s group at UCLA has found that people learn a visual task better when it’s accompanied by sound, for instance — even when they are later tested using only vision.

In broader commercial applications, meanwhile, the science is already providing a new basis for what marketers have long surmised: They are selling customers more than just the core sensory experience. Restaurant owners, for instance, know that choosing decor, lighting, music, and table settings that complement their food can boost their bottom line, and companies have long market-tested food products for texture and packaging as well as taste. But we are now beginning to understand that these elements don’t just create atmosphere and associations — they can actually make food taste different. For example, several studies have found that adding red coloring can make drinks taste sweeter, allowing a company to reduce sugar content while turning color up a notch.

Scott King, part of a UK company called Condiment Junkie that creates sounds to enhance products and events, says that recruiting multiple senses works best when “one sense is choreographed with another in a way that has an effect greater than the sum of its parts.” The company has worked with Fat Duck restaurant in Bray, England, run by celebrity chef Heston Blumenthal, to develop soundtracks to bring out specific flavors in the food, based on their finding that hearing certain sounds (high tones, tinkling pianos) make people perceive a bittersweet toffee as more sweet, while hearing low-pitched tones and trombones make the toffee taste more bitter.

Beyond the practical consequences of this new model of how we perceive the world, however, lie the philosophical implications. What does it mean that Lucretius was wrong — that our perceptions of the world are not just a product of five pure separate senses, but of a dynamic interaction between them?

Barry Smith, a philosopher at the University of London, says that philosophers have long puzzled over the relationship between the senses and the truth: Descartes, for instance, felt that we could never trust our senses as representing an outer reality. But Descartes felt we could at least rely on our own minds. By showing how much our minds are the sites of intersecting, conflicting sensory input, Smith says, neuroscience shakes up this trust. “Descartes seems to have not been going far enough,” Smith says. If senses can change one another, “we’re not so reliable about even our own experiences.”

On the other hand, seeing the senses as interdependent can be a boon to more than just marketers, educators, or those trying to overcome disabilities: In everyday life, the reminder to consider all our senses may change our experience. Smith says he hopes the research will encourage people to value senses they often overlook, like smell, and to look for ways to make our senses work better together to enhance our experiences, whether we’re cooking a holiday meal, decorating our houses, or creating art. Though it might seem strange or even superfluous to think about the color of the plates we will eat from, it stands to alter our experience. After all, no sight or sound exists in a vacuum; at the deepest neurological level, when we sit down to that meal, all our senses will be working together.

We know that our species is unique, but it can be surprisingly hard to pinpoint what exactly makes us so. The fact that we have DNA is not much of a mark of distinction. Several million other species have it too. Hair sets us apart from plants and mushrooms and reptiles, but several thousand other mammals are hairy, too. Walking upright is certainly unusual, but it doesn’t sever us from the animal kingdom. Birds can walk on two legs, after all, and their dinosaur ancestors were walking bipedally 200 million years ago. Our own bipedalism–like much of the rest of our biology–has deep roots. Chimpanzees, whose ancestors diverged from our own some seven million years ago, can walk upright, at least for short distances.

If looking for human uniqueness on the outside is difficult, is it any easier to look on the inside–in particular, at our mental lives? There’s no doubt that our minds allow us to do things that even our great ape relatives cannot. For one thing, we can represent the world symbolically in our heads, and we can use words to communicate that symbolic thought to one another. Yet we can sometimes find surprising links between our own mental lives and those of other animals. We’re very good at making and using tools, but that doesn’t mean other animals can’t do so as well. Thinking about the future may seem like a quintessentially human activity, but there’s some evidence that some bird species can travel forward in time, too.

Yet even as scientists find more links between our own faculties and those of other animals, some continue to stand out. And their rugged distinctiveness makes them all the more interesting. One of the most distinctive of all is, to me at least, the most surprising: teaching.

If you’re a college student reading this during a lecture because your professor is boring you out of your mind, you may not consider teaching a very big deal. But when you consider everything that goes into one person teaching another, it’s a remarkable behavior. Consider what it takes for you to teach a child how to tie her laces, or write her name in cursive, or skip a stone. She has to watch you do the action and store a representation of that action in her brain. She also needs to listen to you, to understand why a twist of the fingers or the flick of a wrist is important to the procedure. You, the teacher, have to watch her try it, recognize when she gets it wrong, and explain how to do it right. Just as importantly, you have to help the child understand why learning a particular action matters–so that she won’t cut her foot, so that she could throw a stone across the pond, and so on.

Another reason that teaching may not seem very remarkable is that it seems easy. After all, even older kids will spontaneously teach younger ones how to play a game. It’s certainly true that teaching comes naturally to us humans. There’s no culture on Earth without teachers. But just because something’s easy doesn’t mean it’s not special. And in the animal kingdom, teaching is exceedingly rare. In fact, it’s not clear whether any other animal can teach.

I know this may come as a surprise, but it does so because we tend to mix up teaching and learning. A young chimpanzee can learn how to smash nuts on a rock by watching an older chimpanzee in action. And when she grows up, her own children can learn by watching her. But in these situations, the students are on their own. They have to watch an action and try to tease apart the underlying rules. A few years ago, I got to see the striking difference between chimpanzees learning and human teaching when my own four-year-old daughter participated in a psychology experiment. As a human, she was so primed to imitate a teacher that she would easily make obvious blunders–blunders no chimpanzee would make. (Here’s an essay I wrote about the experience for the New York Times.)

In the current issue of the journal Animal Behavior, Richard Byrne of the University of St Andrews and Lisa Rapaport of Clemson University, have published a fascinating review of what we know about the evolution of teaching. When scientists got interested in this question in the 1970s, they discovered just how hard it was to find a good example of an animal teacher. Chimpanzees rarely, if ever, intervene to correct a young chimp’s nut-cracking technique. If chimpanzees could teach each other, it would make a huge difference to their species. It can take an adolescent chimpanzee four years of untutored practice to become a skilled nutcracker.

As scientists looked for animal teachers, they realized just how tricky it can be to know whether you’ve found one or not. It’s not as if you can figure out the intention of a killer whale while it’s hunting for seals with younger whales. One way around this quandary is to just stick to what you can see, with a so-called operational definition of teaching. A knowledgable individual alters its behavior only around a rookie. Its behavior doesn’t bring itself any benefit, and might even come at a cost (wasting time showing how to peel a termite probe rather than eating termites yourself, for example). The knowledgeable animal encourages some actions and punishes others, with the result that the rookie learns faster than it would have on its own.

This operational definition has guided the study of animal teaching for two decades, and it’s opened the way to some amazing discoveries. According to this definition, for example, meerkats can teach their pups how to hunt. Adult meerkats can kill and eat scorpions, but it’s a difficult skill to learn without getting badly hurt. Researchers have found that wild meerkats will bring dead or wounded scorpions to their pups to practice with. As the pups get better, the adults bring less badly hurt scorpions, allowing the pups to improve their skill. Ants even meet the operational definition of teaching. If an ant finds food, it will go back to its nest and teach another ant the way there, communicating information as they run and correcting the student ant’s speed and course.

As intriguing as these studies have been, though, they are few and far between. In fact, Byrne and Rapaport argue, the operational definition of teaching has run its course and now actually hinders a better understanding of teaching. It’s hard to tell if an interaction between two individuals meet all the criteria, for example. South American monkeys known as golden lion tamarins will call to their offspring when they find insects and let the young tamarins capture the prey. During this time in the lives of young golden lion tamarins, they get much better at foraging, but it’s impossible to tell whether they’re improving because they’re being taught, or thanks to their own trial-and-error learning. Even with humans, obvious examples of teaching may fail to meet the operational definition. Say a father shows his son how to make a bow. It might take the father a bit longer to make the bow as a teacher than if he were doing so on his own. But it’s hard to say that an extra minute or two would represent much of a cost.

Last year, two British researchers, Alex Thornton and Nichola J. Raihani, offered what they argue is a better way to identify animal teachers. Scientists should run experiments in which they deprive some naive animals of whatever behavior they suspect is actually teaching. Then they can compare the skills of the tutored animals and the unschooled ones to see if the behavior made any difference. But Byrne and Rapaport suspect that even this kind of approach could miss some of the most important examples of teaching.

To see why, imagine a teacher showing children how to write in cursive, as in the photograph above. Once she’s gotten across the basics, she lets them practice on their own, looking over their shoulders as they work. She stops to help one student who is having a hard time of it, while the others display good penmanship. The struggling student ends up with average handwriting, but at least it’s better than it was before. By Thornton and Raihani’s argument, however, this special tutoring is not teaching. The struggling student ends up no better than his classmates, despite the interaction with the adult.

Byrne and Rapaport argue that we may be missing examples of animal teaching in which adults are targeting young animals that would otherwise fall behind. They point to one remarkable example from female elephants. When a female elephant becomes fertile for the first time (goes into oestrus, in other words), she will typically accept the approaches of the biggest bull in the group. Sometimes a female will flee the bull, however. That’s a mistake, because he can protect her from being molested by a lot of young bulls.

In these situations, an older female relative will sometimes go into a false oestrus. Even if she’s pregnant or nursing, she will behave as if she’s fertile and approach the big bull. The young female learns the error of her ways, and accepts the big bull’s approaches. She is no better off than other females who figured out this important life lesson their own, however.

To document this kind of teaching, scientists have to go to the place they’ve avoided before: into the heads of animals. They have to observe animals observing each other, and tailoring their behavior to help not just any young student, but the ones who need the most help. That won’t be easy. But we can’t understand the origin of human teaching by treating it as something so automatic that even an ant can do it. Human teaching is an empathetic art. Only when we look for versions of that kind of teaching in other animals will we be able to understand how our own ancestors became teachers, and how teaching helped make us uniquely human.

By CHRIS BERDIK  l  Boston Globe Nov. 20, 2011

He who laughs last usually has to have the joke explained. But then why bother? After all, nothing kills humor faster than analysis. That sentiment has long dogged humor studies, a field often disparaged as an affront, even an existential threat, to its subject matter. It’s just a joke: Don’t overthink it.

But what if humor (or mirth, in research speak) is intimately linked to thinking? What if we’d have trouble thinking without it? That’s the argument of “Inside Jokes: Using Humor to Reverse-Engineer the Mind” (MIT Press, 2011).

Coauthored by three scholars, the book had an unusual genesis: It began in 2004 as an undergraduate term paper. First author Matthew Hurley, a native of Reading, Mass., had enrolled at Tufts University after a few years of travel and work as a computer programmer. As part of a self-designed major in cognitive science, Hurley took a course on humor taught by the psychologist Reginald Adams Jr. It struck Hurley that most humor theories focused on why we find certain things funny. But, he wondered, why do humans find anything funny? Why do we have a sense of humor in the first place?

Hurley, now a doctoral student in cognitive science at Indiana University, offered his own theory, first in a final paper and then as a thesis guided by the prolific philosopher of mind Daniel Dennett. Encouraged to revise and publish his theory, Hurley solicited Dennett and Adams as coauthors on what became this book.

Hurley and his coauthors begin from the idea that our brains make sense of our daily lives via a never ending series of assumptions, based on sparse, incomplete information. All these best guesses simplify our world, give us critical insights into the minds of others, and streamline our decisions. But mistakes are inevitable, and even a small faulty assumption can open the door to bigger and costlier mistakes.

Enter mirth, a little pulse of reward the brain gives itself for seeking out and correcting our mistaken assumptions. A sense of humor is the lure that keeps our brains alert for the gaps between our quick-fire assumptions and reality. As “Inside Jokes” argues, much of what we consider comedy takes advantage of this cognitive reflex, much as McDonald’s taps our evolved taste for high-energy food.

To learn more, we crossed the road, walked into a bar, and tapped Hurley for a serious talk about funniness. Hurley spoke to Ideas by phone from his home.

Ideas: What’s so funny about how we think?

Hurley: As Dan Dennett puts it, our brains are Chevy engines running Maserati software. We’re a species that thinks prodigiously. In every situation, the human brain needs to constantly anticipate the future by making assumptions about the world that unfold at breakneck speed.

We do a quick and dirty assessment and make a lot of best guesses. But this fills our mental spaces with junk, small mistakes that could trigger a cascade of errors if they go undetected, leading us to waste a lot of energy and resources and, in the worst case, inviting disaster.

Finding and disabling these errors is a critical task. But it’s a resource-hungry job that has to compete with everything else our brains are doing. We think the pleasure of humor, the emotion of mirth, is the brain’s reward for discovering its mistaken inferences. Basically, the brain has to bribe itself to do this important work.

Ideas: Can you give an example?

Hurley: Sure. The basic, most simple humor is first-person humor. It’s when you catch yourself in an error, like looking for the glasses that happen to be on the top of your head. You’ve made an assumption about the state of the world, and you’re behaving based on that assumption, but that assumption doesn’t hold at all, and you get a little chuckle.

But we’ve become complex social creatures, and as we grow, humor takes on all the aspects of our complex social life. For instance, here’s a joke we tell in our book: A man and a woman who have never met before find themselves sharing a sleeping car on an overnight train. After some initial embarrassment, they both go to sleep in their bunks . . . .But in the middle of the night, the woman leans over and says to the man: “I’m sorry, but I’m a little cold. Could I trouble you to get me another blanket?”

“I’ve got a better idea,” the man replies with a glint in his eye. “Just for tonight, let’s pretend we’re married.”

“OK, why not,” giggles the woman.

“Great,” the man says. “Get your own damn blanket!”

The woman and the audience both make the same mistake by assuming something about what the man said. Punch lines make us aware of these automatic covert inferences. Humor rewards the discovery of our mistakes.

Ideas: But joking aside, couldn’t discovering these mistakes also be shameful, discouraging, or even terrifying?

Hurley: Well, anytime you find yourself making an error, it’s a downer initially. The initial emotional response to any discovery of error in your understanding of the world has got to be “uh oh.” But in humor, the brain doesn’t just discover a false inference, it almost simultaneously recovers and corrects itself. It gets the joke. The pleasure of the punch line is enhanced by that split second of negativity just before the resolution.

Ideas: Would we be doomed without humor?

Hurley: We claim in the book that humor is a requirement for thinking beings like us. But that’s probably too severe a claim. The ability to detect humor certainly improves your chances at getting by in this world. It reduces the mistakes we make and act upon.

But it is probably an overstatement to say, as we do in the book, that the world would not forgive the humorless person. The more proper claim would be just that somebody with a sense of humor would be a lot more fit as a thinker.

Ideas: If a sense of humor is part of our basic, human thinking machinery, then why can’t we agree about what’s funny?

Hurley: What’s universal about humor is the process, not the content. Everybody faces every situation with different beliefs, knowledge, and understandings about the world. And different understandings lead to different assumptions and therefore different false assumptions.

Mirth is agnostic of the content, because it’s just the reward for the discovery of a false assumption, and that process doesn’t require particular content. It can happen with any content in the world, which is why we have so many jokes out there. When different minds bring different content to bear, they find different kinds of mirth. So, in that way, humor is both universal and uniquely personal.

Ideas: Your book isn’t comedy, but it is well-stocked with jokes. Did you feel pressure to be funny?

Hurley: Yeah, to some extent, because people might think that if you write a book on humor and it’s not funny, then the question is: Do you even know the subject matter?

But if we try too hard to be funny, then there’s a chance that we wouldn’t be taken seriously, which is a problem in humor studies generally. Some people believe that humor’s not a topic of science, and that it’s a subjective feeling and there’s nothing more to it. So, we tried to bring a light tone to this book as much as we could without undermining ourselves.

Whether we’re falling or flying, dancing or driving, moving in our dreams feels very real to us at the time. And our brains, it seems, agree. By imaging the brains of sleeping subjects, researchers have found that when we move in our dreams, our brains fire in the same pattern as when we move in the real world.

Because we tend to forget our dreams as soon as we wake up, researchers know little about how our minds create them. Neuroscientists Martin Dresler and Michael Czisch, both of the Max Planck Institute of Psychiatry in Munich, Germany, and their colleagues wanted to find a way to use brain-imaging techniques to watch what people were doing in their dreams. To interpret these images of the dreaming brain, however, they would first have to know how the brain looks when it is performing a certain task in the dream—a difficult challenge because most dreamers can’t control what they’re doing.

Very rarely, however, dreamers experience a phenomenon known as lucid dreaming, in which a sleeper is aware that he or she is dreaming and has some level of control over actions in the dream. “About half of people have had a lucid dream, Dresler says, but “very few have them on a regular basis.” Certain people can learn to dream lucidly more often. The training involves techniques such as writing down dreams and committing to remember that you’re dreaming when you see a certain theme, such as a flying cow, says neuroscientist Daniel Erlacher of the University of Bern, who was not involved in the current research.

Dresler and Czisch recruited six people who had been trained in lucid dreaming, instructed them to dream that they were clenching either their left or their right hand, and then let them fall asleep in a brain scanner. Once the sleepers were dreaming and lucid, they let the researchers know by moving their eyes from left to right twice. The researchers checked the volunteers’ brain activity patterns to make sure they really were in the dream phase of sleep known as rapid eye movement. The team then recorded brain activity using either functional magnetic resonance imaging (fMRI), which shows high-resolution images of brain activity throughout the brain, or near-infrared spectroscopy (NIRS), which shows activity on the surface of the brain.

Only two of the subjects were able to have lucid dreams in the noisy scanners. But in each of them, one in fMRI and one in NIRS, the researchers saw the area of the motor cortex that controls the left hand light up in the same way as in someone who was awake. The subjects were able to perform the task in two different dreams each, the researchers report online today in Current Biology. That suggests that “dreams are not just represented as a visual scene” like watching a movie, Dresler says, but involve the whole body.

“It’s a clever use of that patient population,” says neurologist Allen Braun of the National Institute on Deafness and Other Communication Disorders in Bethesda, Maryland. He says it’s interesting that although the motor cortex, which controls movement itself, was active, the midline area of the brain, which is known to be activated when people are making a decision whether to move a limb, was not active in the lucid dreamer whose brain was imaged with fMRI. “They must know they’re not really moving,” he says. Although the researchers imaged only two subjects, Braun says that they have done “more than enough” to show that these two brain-imaging techniques can read lucid dreamers’ dreams.

“It’s a very impressive work,” Erlacher says, particularly given the difficulty of getting someone to dream lucidly in a noisy scanner. To strengthen their findings, the authors plan to recruit more lucid dreamers to determine whether the brain responds similarly in everyone. And they hope to find out what happens when their dreamers perform more complex tasks such as walking, speaking, or even flying, which would help researchers interpret dreams and understand how and why the mind creates them.