Constraint propagation: A completely new take on souls

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by Jeremy Sherman, Ph.D.

Constraint propagation: A completely new take on souls

Constraint propagation: A completely new take on souls

Published on November 4, 2009

This post is a response to Broken Symmetry: Nobel physicist explains why you miss old places, friends by Jeremy Sherman, Ph.D.

It's not true about the 21 grams. That was an error in measurement back in 1907 when Duncan McDougall claimed to have weighed a soul. There's no weight loss with death, which is fine with most people because we've long assumed the soul was a weightless, sizeless, timeless substance anyway. Still, weightless, size-less, timeless substances are scientific dead ends. If there's no way to detect a thing, then there's no way for science to get a grip on it. That's fine with most fans of the soul. Science should keep its hands off souls. But it's not OK with scientists. The dead end forces them to look for another explanation for why living bodies act so differently from dead ones.They have a new explanation, but it's not a thing. It is, in fact weightless and sizeless, but not timeless or a substance. I don't mean to be mysterious. I'm talking science so let me be concrete.Picture a small pile of metal. A machinist shapes it up and voila you've got, let's say, a lock and key. It's great. It's got function. It serves your purposes. Much more so than a small pile of metal. So what did you add that made it functional? Oxford professor Michael Polanyi says nothing was added. What makes it functional is not an addition but a subtraction. A pile of metal can take all sorts of forms. You can pile it this way; you can pile it that way. Locks and keys are highly constrained. Machinists make the parts with what they call "low tolerances" meaning a lot of constraint and specificity on their shapes and sizes so that the parts interact with each other just so. As a result, the lock and key do fewer things, not more than the pile did. When the lock and key get old and worn out, they lose function, but, Polanyi points out, they do so by gaining more possibilities, more configurations of the parts or technically, more "degrees of freedom." In other words the parts get looser than they were. Now the old clunker can jam or the key flops around. A broken machine does more things, not less. We prefer our machines highly constrained. An unreliable computer has more behaviors, more states it can be in. A reliable one has less, only the behaviors we want. The weightless, sizeless non-substance that makes things functional is constraint. You can't talk about the weight of the states the lock and key can't be in. You can't talk about the size of the states they can't be in. The states they can't be in aren't some added substance. But you can talk about time because constraint is a difference that occurs over time: Before, a loose pile of metal; after, a constrained lock and key, after, again a loose lock and key. I used to have an unreliable computer. I'm not saying whose operating system it ran, but I'll tell you it was way too versatile for me. I was amazed by the sheer variety of ways it would act. It seemed to invent new creative ways of bombing every day. For example, at the drop of a hat it would do blue screens which I'll grant was clever but not what I wanted when writing under a deadline. I wanted it to behave itself, to show some self-constraint. One day I got out of my blue-lighted chair and dropped down to the competitor's store. I had heard that their computers were less versatile. They did fewer things like blue screening. That was fine with me. I didn't need versatility; I needed functional constraint. I bought one and it's been a good three years for me and my much more limited computer. As a result, I've become more constrained too. I love my replacement computer by which I mean to say I'm constrained by it. I'd even say loyal, addicted and domesticated to it. Before, if you asked me what kind of computer I wanted, I'd have been more flexible. Now, I'm less flexible. I want only the kind I have. It is, what in business we call a proprietary good, one you shop for by brand. You accept no substitutes. In other words, you're constrained by it. My computer's makers likes it that way. They wants me to be as loyal, addicted and domesticated as I am. And now that the likes of me are buying their products, their employees go to work and rather than working on just anything all day, they're highly constrained too. They're constrained to working on how to make things that are constrained the way people like me want them to be. That way we customers will become that much more loyal, addicted and domesticated to their products. In other words more constrained. And then also if a friend asks me what kind of computer to buy, I won't say "Oh, I don't know," or name any of a dozen other brands. I'll be constrained to saying this brand. And in that way the constraint spreads or propagates. And what has this got to do with souls? Constraint and constraint propagation apply all the way up and down, with differences along the way that mark the shift from physics to chemistry, to biology to psychology sociology. At the bottom, if you read my article about Broken Symmetry, you'll find constraint even there. Remember, as the balanced broomstick tips over, the more it tips the more it tips? Before it tips, it is balanced symmetrically. It could tip in any direction. After it tips, its tip-able direction is highly and increasingly constrained. Your body is not a machine made by a man or, I'll argue, a creator. At least for scientists to fulfill their (constrained) obligation, they can't settle for saying the soul is a weightless, size-less, time-less substance that is made by a bigger fancier weightless, size-less, time-less substance. We can't therefore treat a living soulful being as the equivalent of lock and key made by the machinist. Still, in its functionality, your body and even your mind are like the lock and key if only in that they do consist of parts that are highly constrained to and by each other, and to their context. As the great philosopher Emannuel Kant said, "The definition of an organic body is that it is a body, every part of which is there for the sake of the other (reciprocally as end, and at the same time, means)” In later articles I'll talk more about how Kant's "means and ends" business relates to constraint, constraint propagation, causality, the origin of life, and souls, and also to missing the sweet souls that come and go in our lives. In the mean time, if this article constrains your thinking even a little, let it be by encouraging you to tip less toward explaining all behaviors as caused by new things and more toward explanations based on constraint. The leading researcher in this area, Terrence Deacon says, the whole is not more than the sum of its parts, its less. In other words, when parts start interacting with each other as wholes, they constrain each other. The whole lock does less things than the pile of metal pieces can do. And I know I know, this material is likely to give a reader a headache. That's the way it is with novel constraints sometimes, like the ones imposed by new counter-intuitive ideas. I'll do my best to keep these reflections grounded. And after all, it might be worth the effort. Researchers like Deacon are coming at old mysteries from new angles that might finally split them open, explaining lots.

Broken Symmetry: Nobel physicist explains why you miss old places, friends

Broken Symmetry: Nobel Physicists explain why you miss old places, friends.

Published on November 1, 2009

This post is a response to Emergence research: Just how did matter become mattering? by Jeremy Sherman, Ph.D.

The bittersweet sad intense pain of missing a place, a person, a crew, a time.

What's with that? How does that happen? Here's a take on it you probably haven't heard before.

I'll start way back with the big bang. If everything was all concentrated and homogeneous at the origin, how did our universe ever get so lumpy, with separate things like stars and planets, you and me? The 2008 Nobel Prize in physics was awarded to scientists who identified the source as broken symmetry. A first pass explanation of their idea is simple.

You know how you can easily balance a broomstick on the palm of your hand? If it's centered, symmetrically upright, it tends to stay there. But if it tips asymmetrically toward one direction, then it becomes increasingly difficult to balance. The symmetry was broken. The tipped get tippier.

The butterfly effect is the most familiar version of this. Remember it? Conceivably a butterfly's wings flapping could lead to major shifts in weather patterns. People latched onto that idea as evidence of uncertainty and the potential for miracles. We like ideas that suggest that life has chutes-and-ladder-like qualities, so it's not just stepwise plodding. It gives us hope of rag-to-riches leverage but also allows that if we don't end up fulfilling our ambitions we have an explanation that makes it not our fault: "I tried, but life has surprising shoots and I fell down one."

Shoots and ladders aside, the butterfly effect is really about broken symmetry, how a little thing can start a big thing. How just as a slight tip can cause the broomstick to fall or how a shout can cause an avalanche. Think of it also as the way a meteorite passing the earth could fall under our gravitational influence, being taken off course. The closer it gets to the earth, the stronger the earth's gravitational pull. That's broken symmetry too.

With the big bang everything flew apart. It would have flown apart evenly but the tiniest little micro-variation got things tipping. Not falling over as like the broomstick but comparable. The universe got lumpy by the same basic process that made our moon. The moon formed when a meteor hit the earth kicking up an enormous dust cloud. Imagine that the dust started out almost evenly distributed, but little variations caused the gravitational pull in some regions to be greater than in others. The dense grew denser. And now most of that dust is concentrated in that great lump of green cheese. A little difference in distribution causes a big difference in concentrations. Broken symmetry explains seperateness and difference.

There's broken symmetry in thought and culture too. You meet someone, fall under their gravitational influence, start hanging out, fall further. For good or ill--it could be the love of your life or a heroin dealer. Either way a little tipping becomes a lot. And these days we're rarely tipped in just one direction. In ancient tribal days, you could be born into a tribe that tipped you strongly into its ways there, in the tribe you would stay for all your days. Now, we're under diverse influences. You move a thousand miles to be with your new partner, but miss your old town and people. You design your whole life around a job you love and then they lay you off and you have to find a new place to orbit.

Broken symmetry implies something really fundamental about the universe but also about your life. If the universe is lumpy, then this notion that we are all one and that everything is connected needs to be refined. We are all one but some of us are more one than others of us. Everything is connected but not equally. There are plenty of people who have negligible influence on you. They are off in their own lumpy region under their own influences. They're not part of your tribe and therefore are different from you. But then you happen to meet. You've been on independent pages a long time so you start out on different pages. But vive la difference, you like each other. Being with each other you start to influence each other. But lumpy life that it is, you're not just under their influence. You've got other influences operating on you from before and they still tug. So you miss what you had even while your drawn into what you're having. We are all planets under changing influences falling in with some and tearing away from others. Something like that.

There's more to this story of course. In particular I'll want to say more about influence. How does influence happen? For that we get into another one of these new scientific concepts: Constraint propagation.

Jan 13, 2010 03:00 PM in Energy & Sustainability | Post a comment

Paleontologist Peter Ward's "Medea hypothesis": Life is out to get you

By John Matson

What if the only thing life has to fear is life itself?

At a lecture Monday evening at the American Museum of Natural History in New York City, paleontologist Peter D. Ward laid out the argument that life as we know it serves to make Earth less habitable—a downward spiral that might spell the eventual end of life on the planet. Ward, a professor at the University of Washington, calls this the Medea hypothesis, named for the murderous mother of Greek mythology. It is a direct challenge to scientist and futurist James Lovelock's Gaia hypothesis, which asserts that life constantly tweaks the dials on Earth's control systems to keep the planet in a nice, habitable homeostasis.

Ward has a recent book on the subject, The Medea Hypothesis: Is Life on Earth Ultimately Self-Destructive? (Princeton University Press, 2009). To illustrate the difference between his theory and Lovelock's, the traveling Ward, in town to make the media rounds for his book, used a hotel analogy for Earth. Gaians, Ward says, think that hotel guests are likely to repaint their rooms and leave fresh flowers before checking out, whereas Medeans think that guests are liable to throw furniture out the window, trashing the room like Keith Moon in his prime.

At the lecture, moderator Neil deGrasse Tyson, an astronomer and the director of the museum's Hayden Planetarium, struggled to define the work of the polymath Ward, finally settling on "paleobiogeoastronomer."

And indeed, Ward's dour claim rests on analyses of carbon isotopes, paleofossils, asteroid impact rates and geologic formations. Most of the mass extinctions in history, Ward says, were caused by microorganisms, not by asteroid or comet impacts. Here is how: When Earth warms to the point that it no longer has cold poles and warm tropics, as the result of geologically released greenhouse gases, the oceans stop mixing. Without mixing, only the uppermost layer of the ocean remains oxygenated, and anaerobic bacteria that produce poisonous hydrogen sulfide gas thrive. Before long, the level of hydrogen sulfide in the atmosphere becomes lethal, simultaneously poisoning living creatures and shredding the ozone layer. "This is life killing itself off," Ward says.

As with today's climate crisis, carbon dioxide is the culprit in the ultimately catastrophic warming. Of course, the ultimate source of Earth's massive die-offs wasn't anthropogenic or even the fault of life—Ward points to volcanic floods that churned out enough CO₂ to shut down ocean mixing driven by temperature differentials. But thanks to the actions of humankind, the delicate balance that keeps Earth habitable is once again in danger. "All you need is enough [warming] to reduce the temperature difference between the poles and the equator, and the whole system goes down," Ward says.

Thankfully, perhaps, such dire predictions for climate change—not displacement, war or even famine but a nearly wholesale elimination of life of Earth—rest on equally dire forecasts for CO₂ levels. Whereas many experts set 350 parts per million as the maximum acceptable level for atmospheric CO₂ (today's atmosphere is at about 390 ppm), Ward says that these warming-driven catastrophes arise at about 1,000 ppm. That's not to say that things won't get ugly along the way, with arable land disappearing and rising seas rewriting maps of the world, but there may at least be some air to breathe for another two centuries or so.

As for fixes, Ward did not have any ready answers other than hoping that currently iffy technologies can take off. Practicable nuclear fusion would help a lot, as would advances in bioengineering. "We can convince microbes to do some very interesting things," he says, pointing specifically to their promise in systems to produce food and fuel. Ward is aware that betting on currently untenable technologies as the way out may seem like pie-in-the sky dreaming. "Look, if you don't have hope, you don't do anything," he says. "You go out and get a drink."

Cover image: Princeton University Press

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scientific american

From the January 2010 Scientific American Magazine | 12 comments

The Nuclear Doomsday Clock Still Ticks

As long as opportunities and excuscientific americanses for nuclear aggression persist, the world will never be safe from annihilation

By Lawrence M. Krauss

Early last October the Nobel Prize committee announced that it was awarding Barack Obama the Peace Prize for his “vision of and work for a world without nuclear weapons.” At the same time, in counterpoint to that news, it was reported that the director of India’s 1998 nuclear testing program had called for new tests. That move provoked fears of escalation, in case it motivated Pakistan and China to recommence testing and made it even harder for the U.S. to ratify the Comprehensive Nuclear Test Ban Treaty (CTBT). Although some 150 countries have ratified the treaty, neither the U.S., China nor India has yet done so.

The chair of India’s Atomic Energy Commission has stated that his nation does not need to carry out any more tests; one can only hope that India’s policy makers agree and that by the time this essay appears, the world will not yet have taken one more step toward the brink.

Such news underscores that nuclear weapons and nuclear proliferation won’t be going away soon. On January 13 and 14 the Bulletin of the Atomic Scientists is hosting in New York City its first annual Doomsday Clock Symposium, where a decision regarding the setting of the minute hand on its famous Doomsday Clock will be made. The clock has served for nearly 65 years as an international symbol of the level of risk that the world faces from nuclear weapons and, more recently, from all potentially globally destructive technologies.

In the interests of full disclosure, I should mention that I am co-chair, along with physicist Leon Lederman, of the board of sponsors of the Bulletin, a group formed by Albert Einstein in 1946, with J. Robert Oppenheimer as its chair. But my purpose here is not to promote the Bulletin itself but rather what it stands for.

No issue carries more importance to the long-term health and security of humanity than the effort to reduce and, perhaps one day, rid the world of nuclear weapons. The U.S. can and should take a leading role in this effort, but until recently, President Obama’s verbiage aside, our actions have done far too little to encourage this goal, and quite frankly we have too often discouraged it.

We live in a dangerous world, and actions by countries such as Iran and North Korea need to be monitored carefully, but the response should be commensurate with the threat.

President Obama was correct to end the planned installation of a missile defense system in Poland, not merely because Iran does not possess ICBMs capable of carrying nuclear warheads but because the proposed missile defense system, a mirror of the flawed one currently installed in the U.S., does not work and never has. Commissioning an unworkable defense against a nonexistent threat, especially when such a system in Eastern Europe clearly increased other international tensions with Russia, made no strategic sense. The mobile short-range missile defense system proposed as an alternative is more likely to function against any actual threat from Iran.

Still, President Obama’s hopes for a nuclear-free world cannot be met if we continue to act as if the U.S. should have an unfettered monopoly on such weapons. How can we expect other countries to show restraint when we have not yet ratified the CTBT, even though we can verify compliance effectively and our own nuclear arsenal does not need testing? How can we hope for a safer world when the U.S. and Russia have between them more than 10,000 nuclear weapons, with perhaps 1,000 still on trigger alert, despite the absence of any credible, justifying threat?

We have lived in a world where nuclear weapons have not been used against a civilian population in more than 60 years. I am not optimistic that this nuclear truce will last another 60. But until we honestly recognize the threat and minimize the opportunity and motivation for governments or terrorist organizations to carry out such an act, we continue to increase the odds that it will one day happen. As Einstein said 65 years ago, after the explosion of the first nuclear weapon, “Everything has changed, save the way we think.” We need to take his words to heart now more than ever.

ABOUT THE AUTHOR(S)
Lawrence M. Krauss, a theoretical physicist, commentator and book author, is Foundation Professor

Bulletin of the Atomic Scientists

http://www.thebulletin.org/

Hands of the "Doomsday Clock" to be moved in New York City and seen live on web for first time ever

… News Advisory for January 14, 2010 …

Factors In Change to Include Nuclear Proliferation, Weapon Stockpile Shifts, and Climate Change; Bulletin of Atomic Scientists Will Open Event to World With Real-Time Streaming Web Broadcast.

NEW YORK CITY///NEWS ADVISORY///January 14, 2010///The Bulletin of the Atomic Scientists (BAS) will move the minute hand of its famous "Doomsday Clock" at 10 a.m. EST/1500 GMT on January 14, 2010 in New York City. For the first time ever, the event will be opened up to the general public via a live Web feed at http://www.TurnBackTheClock.org.

The last time the Doomsday Clock minute hand moved was in January 2007, when the Clock's minute hand was pushed forward by two minutes from seven to five minutes before midnight.

The precise time to be shown on the updated Doomsday Clock will not be announced until the live news conference in New York City takes place on January 14, 2010. Factors influencing the latest Doomsday Clock change include international negotiations on nuclear disarmament and nonproliferation, expansion of civilian nuclear power, the possibilities of nuclear terrorism, and climate change.

News event speakers will include:

• Lawrence Krauss, co-chair, BAS Board of Sponsors, foundation professor, School of Earth and Space Exploration and Physics departments, associate director, Beyond Center, co-director, Cosmology Initiative, and director, New Origins Initiative, Arizona State University.


• Stephen Schneider, member, BAS Science and Security Board, professor of environmental biology and global change, Stanford University, a co-director, Center for Environment Science and Policy of the Freeman Spogli Institute for International Studies, and senior fellow, Stanford Woods Institute for the Environment.


• Jayantha Dhanapala, member, BAS Board of Sponsors, president, Pugwash Conferences on Science and World Affairs, and chair, 1995 UN Nuclear Nonproliferation Treaty Conference;


• Pervez Hoodbhoy, member, BAS Board of Sponsors, professor of high energy physics, and head, Physics Department, Quaid-e-Azam University, Islamabad, Pakistan; and


• Kennette Benedict, executive director, Bulletin of the Atomic Scientists.

Founded in 1945 by University of Chicago scientists who had helped develop the first atomic weapons in the Manhattan Project, The Bulletin of Atomic Scientists subsequently created the Doomsday Clock in 1947 as way to convey both the imagery of apocalypse (midnight) and the contemporary idiom of nuclear explosion (countdown to zero). The decision to move the minute hand of the Doomsday Clock is made by the Bulletin's Board of Directors in consultation with its Board of Sponsors, which includes 19 Nobel Laureates. The Clock has become a universally recognized indicator of the world's vulnerability to catastrophe from nuclear weapons, climate change, and emerging technologies in the life sciences.

TO PARTICIPATE IN PERSON: Attend the live news event on January 14, 2010 at 10 a.m. EST, at the New York Academy of Sciences Building, at 7 World Trade Center, 250 Greenwich St, 40th floor, New York City. The event will be limited to credentialed members of the news media. For security reasons, all attendees must RSVP in advance by contacting Patrick Mitchell, (703) 276-3266, or pmitchell@hastingsgroup.com.

CAN'T PARTICIPATE IN PERSON?: Reporters outside of New York City who are unable to attend the live news event in person can watch and listen to the news conference via a live Webcast by registering by 945 a.m. EST on January 14, 2010 at http://www.TurnBackTheClock.org/media. A streaming audio replay of the news event will be available on the Web at http://www.thebulletin.org as of 6 p.m. EST/2300 GMT on January 14, 2010.

CONTACT: Patrick Mitchell, (703) 276-3266 or pmitchell@hastingsgroup.com.

Brain scanners can tell what you're thinking about

• 28 October 2009 by Ewen Callaway, Chicago

WHAT are you thinking about? Which memory are you reliving right now? You may think that only you can answer, but by combining brain scans with pattern-detection software, neuroscientists are prying open a window into the human mind.

In the last few years, patterns in brain activity have been used to successfully predict what pictures people are looking at, their location in a virtual environment or a decision they are poised to make. The most recent results show that researchers can now recreate moving images that volunteers are viewing - and even make educated guesses at which event they are remembering.

Last week at the Society for Neuroscience meeting in Chicago, Jack Gallant, a leading "neural decoder" at the University of California, Berkeley, presented one of the field's most impressive results yet. He and colleague Shinji Nishimoto showed that they could create a crude reproduction of a movie clip that someone was watching just by viewing their brain activity. Others at the same meeting claimed that such neural decoding could be used to read memories and future plans - and even to diagnose eating disorders.

Understandably, such developments are raising concerns about "mind reading" technologies, which might be exploited by advertisers or oppressive governments (see "The risks of open-mindedness"). Yet despite - or perhaps because of - the recent progress in the field, most researchers are wary of calling their work mind-reading. Emphasising its limitations, they call it neural decoding.

The development of 'mind-reading' technologies is raising concerns about who might exploit them

They are quick to add that it may lead to powerful benefits, however. These include gaining a better understanding of the brain and improved communication with people who can't speak or write, such as stroke victims or people with neurodegenerative diseases. There is also excitement over the possibility of being able to visualise something highly graphical that someone healthy, perhaps an artist, is thinking.

So how does neural decoding work? Gallant's team drew international attention last year by showing that brain imaging could predict which of a group of pictures someone was looking at, based on activity in their visual cortex. But simply decoding still images alone won't do, says Nishimoto. "Our natural visual experience is more like movies."

Nishimoto and Gallant started their most recent experiment by showing two lab members 2 hours of video clips culled from DVD trailers, while scanning their brains. A computer program then mapped different patterns of activity in the visual cortex to different visual aspects of the movies such as shape, colour and movement. The program was then fed over 200 days' worth of YouTube clips, and used the mappings it had gathered from the DVD trailers to predict the brain activity that each YouTube clip would produce in the viewers.

Finally, the same two lab members watched a third, fresh set of clips which were never seen by the computer program, while their brains were scanned. The computer program compared these newly captured brain scans with the patterns of predicted brain activity it had produced from the YouTube clips. For each second of brain scan, it chose the 100 YouTube clips it considered would produce the most similar brain activity - and then merged them. The result was continuous, very blurry footage, corresponding to a crude "brain read-out" of the clip that the person was watching.

In some cases, this was more successful than others. When one lab member was watching a clip of the actor Steve Martin in a white shirt, the computer program produced a clip that looked like a moving, human-shaped smudge, with a white "torso", but the blob bears little resemblance to Martin, with nothing corresponding to the moustache he was sporting.

Another clip revealed a quirk of Gallant and Nishimoto's approach: a reconstruction of an aircraft flying directly towards the camera - and so barely seeming to move - with a city skyline in the background omitted the plane but produced something akin to a skyline. That's because the algorithm is more adept at reading off brain patterns evoked by watching movement than those produced by watching apparently stationary objects.

"It's going to get a lot better," says Gallant. The pair plan to improve the reconstruction of movies by providing the program with additional information about the content of the videos.

Team member Thomas Naselaris demonstrated the power of this approach on still images at the conference. For every pixel in a set of images shown to a viewer and used to train the program, researchers indicated whether it was part of a human, an animal, an artificial object or a natural one. The software could then predict where in a new set of images these classes of objects were located, based on brain scans of the picture viewers.

Movies and pictures aren't the only things that can be discerned from brain activity, however. A team led by Eleanor Maguire and Martin Chadwick at University College London presented results at the Chicago meeting showing that our memory isn't beyond the reach of brain scanners.

Movies and pictures aren't the only things that can be discerned from brain activity

A brain structure called the hippocampus is critical for forming memories, so Maguire's team focused its scanner on this area while 10 volunteers recalled videos they had watched of different women performing three banal tasks, such as throwing away a cup of coffee or posting a letter. When Maguire's team got the volunteers to recall one of these three memories, the researchers could tell which the volunteer was recalling with an accuracy of about 50 per cent.

That's well above chance, says Maguire, but it is not mind reading because the program can't decode memories that it hasn't already been trained on. "You can't stick somebody in a scanner and know what they're thinking." Rather, she sees neural decoding as a way to understand how the hippocampus and other brain regions form and recall a memory.

Maguire could tackle this by varying key aspects of the clips - the location or the identity of the protagonist, for instance - and see how those changes affect their ability to decode the memory. She is also keen to determine how memory encoding changes over the weeks, months or years after memories are first formed.

Meanwhile, decoding how people plan for the future is the hot topic for John-Dylan Haynes at the Bernstein Center for Computational Neuroscience in Berlin, Germany. In work presented at the conference, he and colleague Ida Momennejad found they could use brain scans to predict intentions in subjects planning and performing simple tasks. What's more, by showing people, including some with eating disorders, images of food, Haynes's team could determine which suffered from anorexia or bulimia via brain activity in one of the brain's "reward centres".

Another focus of neural decoding is language. Marcel Just at Carnegie Melon University in Pittsburgh, Pennsylvania, and his colleague Tom Mitchell reported last year that they could predict which of two nouns - such as "celery" and "airplane" - a subject is thinking of, at rates well above chance. They are now working on two-word phrases.

Their ultimate goal of turning brain scans into short sentences is distant, perhaps impossible. But as with the other decoding work, it's an idea that's as tantalising as it is creepy.

The risks of open-mindedness

The feats of decoding brain scans to predict someone's thoughts are undoubtedly dazzling (see main story), but "neural decoding" techniques are also limited in how they can be applied. Right now, they only work if someone's brain has already been scanned multiple times, and in very specific circumstances. So can we really call this mind reading? And should we worry about potentially creepy uses for such technology?

To some extent it's a question of semantics, but many researchers, including neuroscientist Russell Poldrack at the University of Texas at Austin, say it's clear that the work done to date is a far cry from what most people think of as mind reading, such as predicting whether a terrorist has plans to detonate a bomb on an aircraft.

Yet even if such applications are a very distant possibility, we should start thinking about the ethical issues now, says John-Dylan Haynes at the Bernstein Center for Computational Neuroscience in Berlin, Germany.

Some companies already claim that brain scans can help to pick out liars and determine whether an advert works or not, and there may be some truth in such claims. Haynes says standards are needed to spell out what neural decoding can and cannot reliably do, so as not to erode public trust in the field.

Neuroscientist Jack Gallant at the University of California, Berkeley, agrees. He says that neural decoding could be a double-edged sword. If his hopes for the technology ever come to fruition, he says, the same machine that reads the thoughts of patients with a neurodegenerative disease may well find more nefarious applications at some point.