The phantom touch illusion

It seems like every time researchers look further into our sensory-perceptive systems, we have another hole punched in our certainty that what we think we're perceiving is actually real.

We've looked at optical illusions -- and the fact that dogs fall for 'em, too.  We've considered two kinds of auditory illusions, the postdictive effect and the McGurk effect.  Sometimes we see patterns of motion in still objects -- and illusory "impossible" motion that our brains just can't figure out.  A rather simple protocol convinced test subjects their hands had turned to stone.  Stimulating a particular clump of neurons in the brain made patients see the doctor's face as melting.  We can even be tricked into feeling like we're controlling a second body, that just happens to be invisible.

As eminent astrophysicist Neil deGrasse Tyson put it, "The human brain is rife with ways of getting it wrong."  Honestly, at this point it's a wonder we trust anything we perceive -- and yet you still hear people say "I saw it with my own eyes" as if that somehow carried any weight at all.  Add to that all the problems with the reliability of memory, and you have to ask why eyewitness accounts are still considered the gold standard of evidence.

If you needed more proof of this, take a look at some research that came out last week from Ruhr-Universität Bochum into what happens when a person watches a virtual-reality avatar of their own body.  Participants were suited up in VR gear, and after a period of acclimation -- during which they got used to their avatar's arms and hands moving as their own did -- they were instructed to use a virtual representation of a stick to touch their avatar's hand.  Nearly all of the subjects reported feeling a sensation of touch, or at least a tingling, at the spot the virtual stick appeared to touch.

[Image licensed under the Creative Commons Samuel Zeller samuelzeller, VR (Unsplash VK284NKoAVU), CC0 1.0]

The researchers decided to check and see if the sensation occurred simply by drawing awareness to the hand, so they did the same thing only using a virtual laser pointer -- and no feeling of touch occurred.

Apparently all it took was convincing the subjects they were being touched to stimulate the sensation itself.

"The phantom touch illusion also occurs when the subjects touched parts of their bodies that were not visible in virtual reality," said study co-author Marita Metzler.  "This suggests that human perception and body sensation are not only based on vision, but on a complex combination of many sensory perceptions and the internal representation of our body."

The whole thing brings to mind a conversation I had with an acquaintance, a Ph.D. in philosophy, some years ago about the impossibility of proving materialism.  I'd always considered myself a hard-nosed materialist, but her stance was that no one could prove the external world was real.  I shot back with a snarky, "Well, that works until someone throws a rock at your head.  Hard to deny the rock isn't real after that."  She patiently responded, "No.  What is real are the sensations you experience -- the shock, the pain, the adrenaline rush.  Possibly a period of loss of consciousness.  You're still locked inside your own skull, and the only thing you have access to are your own thoughts and feelings.  Those are all you can be certain are real experiences -- and even those might well be false or misleading."

Well, it was a fair knockout (pun intended), and I still haven't really come up with a rejoinder.  Not that this is surprising; philosophers have been discussing the whole materialism vs. idealism thing for centuries, and haven't really settled it to anyone's satisfaction.  And since the time of that argument, I've found more and more evidence that we experience through our sensory-perceptive apparatus only the barest fraction of what's out there -- what neuroscientist David Eagleman calls our umwelt -- and even that part, we see inaccurately.

Kind of humbling, isn't it?  Think about that next time someone starts acting so all-fired certain about their own perceptions, memories, experiences, and opinions.  The more you know, they more you should realize that none of us should be sure of anything.

But after all, doubt isn't a bad place to start.  I'll end as I did yesterday, with a quote from the brilliant physicist Richard Feynman: "The first principle is that you must not fool yourself; and you are the easiest person to fool."

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Mimes in the brain

Maybe there's a reason why so many people despise mimes.

Okay, I know that seems like a non sequitur even for me, but the topic comes up because of a study by Patrick Little and Chaz Firestone (of Johns Hopkins University) called "Physically Implied Surfaces," which appeared this week in the journal Psychological Science.  And from this study, we find that the problem with watching a mime is that you can't help "seeing" the invisible wall or rope or cage or whatnot that (s)he is interacting with.

Apparently you can't ignore a mime even if you want to.

[Image licensed under the Creative Commons Stalinjeet, Stalinjeet & Rohit Bansal performing Mime, CC BY-SA 4.0]

The authors write:

In addition to seeing objects that are directly in view, we also represent objects that are merely implied (e.g., by occlusion, motion, and other cues).  What can imply the presence of an object? Here, we explored (in three preregistered experiments; N = 360 adults) the role of physical interaction in creating impressions of objects that are not actually present.  After seeing an actor collide with an invisible wall or step onto an invisible box, participants gave facilitated responses to actual, visible surfaces that appeared where the implied wall or box had been—a Stroop-like pattern of facilitation and interference that suggested automatic inferences about the relevant implied surfaces.  Follow-up experiments ruled out confounding geometric cues and anticipatory responses.  We suggest that physical interactions can trigger representations of the participating surfaces such that we automatically infer the presence of objects implied only by their physical consequences.

The "Stroop-like pattern" the authors mention refers to the Stroop effect, wherein a test subject is given an image where there are the names of various colors represented in different colors of ink, but they don't match -- e.g. the word "green" is written in red ink.  The subject is then asked to state, as quickly as possible, the colors of each word, ignoring the word that's actually written and focusing only on the ink color.

It's quite difficult to do.  You are attempting to force your brain to ignore the textual information (the words themselves) and focus only on the colors, but the two interfere with each other so much -- and we're so geared to getting information by reading text -- that to do it accurately, most people have to concentrate and slow down, and still they make mistakes.

Here, the implied surfaces the mime is creating generate such a strong illusion that if they don't correspond with a visual indicator of where the surfaces are, we tend to believe the mime rather than the indicator.  For example, in one test, volunteers were asked to state whether a line superimposed on a video clip of a mime was horizontal or vertical.  In some of the clips the line was oriented the same way, and in the same position, as the "surface" the mime was creating; in other cases, they didn't agree.  In the latter case, test subjects were routinely tripped up -- they tended to answer based on the (invisible) surface the mime's actions indicated rather than the (visible) marker they were supposed to be focusing on.

"Very quickly people realize that the mime is misleading them, and that there is no actual connection between what the person does and the type of line that appears," said study co-author Patrick Little, in an interview with Science Daily.  "They think, 'I should ignore this thing because it's getting in my way', but they can't.  That's the key.  It seems like our minds can't help but represent the surface that the mime is interacting with -- even when we don't want to."

It also reminds me a bit of the McGurk effect, a rather baffling interference between sound and sight that occurs when we hear a person say one syllable ("ba," for example) and watch their mouths move as if they were saying a different one (such as "va").  You'd think that since we're talking about making sense of an auditory input, the brain would rely much more on what's coming in through the ears than what's coming in through the eyes, but that's not what happens; if you see someone's lips moving as if they're saying "va" but you hear them say "ba," what you think you're hearing is "va."  It's absolutely convincing, and works even if you know what's going on.

So yet another example of how easy it is to befuddle our brains with contradictory input.  It also explains why, in Berke Breathed's brilliant comic strip Bloom County, Opus the Penguin got arrested for assaulting a street mime, but the charge was eventually ruled by the judge to be "justifiable."

It's one thing to do street performances, but creating invisible surfaces in our brain just crosses a line, even though we probably won't be able to determine if the line is vertical or horizontal.

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This week's Skeptophilia book-of-the-week is a bit of a departure from the usual science fare: podcaster and author Rose Eveleth's amazing Flash Forward: An Illustrated Guide to the Possibly (and Not-So-Possible) Tomorrows.

Eveleth looks at what might happen if twelve things that are currently in the realm of science fiction became real -- a pill becoming available that obviates the need for sleep, for example, or the development of a robot that can make art.  She then extrapolates from those, to look at how they might change our world, to consider ramifications (good and bad) from our suddenly having access to science or technology we currently only dream about.

Eveleth's book is highly entertaining not only from its content, but because it's in graphic novel format -- a number of extremely talented artists, including Matt Lubchansky, Sophie Goldstein, Ben Passmore, and Julia Gförer, illustrate her twelve new worlds, literally drawing what we might be facing in the future.  Her conclusions, and their illustrations of them, are brilliant, funny, shocking, and most of all, memorable.

I love her visions even if I'm not sure I'd want to live in some of them.  The book certainly brings home the old adage of "Be careful what you wish for, you may get it."  But as long as they're in the realm of speculative fiction, they're great fun... especially in the hands of Eveleth and her wonderful illustrators.

[Note: if you purchase this book from the image/link below, part of the proceeds goes to support Skeptophilia!]

Canine illusions

I've always had a fascination for optical illusions.

The enjoyment of bizarre trompe-l'oeil is connected to a persistent theme in my fiction; how do we know what's real?  If something occurs that challenges our notions of how things are, by what criteria could we know if we're seeing reality -- or if it's a malfunction in our frequently errant sensory-perceptual systems?

My favorite optical illusions are ones where even once you know what's going on, your mind just won't accept it.  Our brains, apparently, are very prone to hanging on to a solution to a perceptual anomaly even once it's been conclusively demonstrated that they've got it wrong.  The best example of this I know of is the checker shadow illusion:

In the above image, which square is darker, A or B?

If you know anything about optical illusions, you've probably guessed that they're the same darkness, and you'd be right if you did.  But I'd bet cold hard cash that even once you know the two squares are the same darkness, you can't actually see it that way.  (In fact, if you doubt they are of equal darkness, use some scraps of paper to cover up everything but a vertical strip of the image, to eliminate the green cylinder and most of the checkerboard.  The fact that they're the same will be obvious.  Then remove the paper, and voilà -- you'll be back to seeing A as darker than B.)

Another fine example of this phenomenon is the hollow-face illusion, which seems to occur because our brains have a finely-developed ability to see nuances of other human faces, but the concept of an inside-out face is so far out of anything we typically experience that we just can't process it.  Check it out:

A lot of optical illusions have to do with the fact that we often interpret what we see based upon comparisons, and those comparisons persist even once we know they're inaccurate.  (That's the key to the checker shadow illusion; because we think square B is in shadow, it must be intrinsically lighter in color than square A.)  It's also what made the infamous blue dress/white dress illusion so maddening; apparently it works because we judge something's color not only by the intrinsic frequencies of the light striking our eye, but by comparison to the color(s) surrounding it.  So someone who focuses on one part of an image and judges the rest of the image based upon that will come to a different conclusion than someone who does the same thing but starting with a different part of the image.

A lot of size-based illusions work in a similar fashion, such as the Ebbinghaus-Titchener illusion, in which the question is to determine which of the two orange circles is larger:

You've undoubtedly already guessed that they're the same size, but it's a remarkably persistent illusion even when you know that.  The right-hand circle looks larger because we're judging its size by comparison to the small dots surrounding it; and the opposite holds for the left-hand circle.

The topic of optical illusions comes up because of a cool study out of La Trobe University (Australia), led by psychologist Sarah Byosiere.  Byosiere became interested in optical illusions a few years ago, and wondered whether humans' advanced brains made us fall for them more easily -- we're always calculating, comparing, weighing options, which brings with it some pitfalls -- and whether other animal species might not be fooled.

So she decided to test dogs.  Using copious amounts of dog cookies, she trained some dogs to interact with a touch screen, rewarding the dogs if they touched their noses to the larger of two circular shapes shown.  Once they got good at it, she threw the Ebbinghaus-Titchener illusion at them.

And they fell for it.  Apparently dogs think the right-hand circle is larger, too.

What's even more fascinating is that dogs didn't fall for the Delboeuf illusion...

 ...which you'd think would work precisely the same way.  Getting tricked by the Delboeuf illusion is apparently pretty ubiquitous in humans, which is why restaurants have discovered that a medium-sized entrée looks like a more generous serving in a small plate than in a larger one.  But dogs presented with two plates of food, which differ in the plate size but not in the quantity of food, showed no preference whatsoever for the smaller plate.

As a side note, however, I do wonder if the apparent failure of dogs to get taken in by the Delboeuf illusion isn't because of faulty experimental design.  I know my own dogs don't seem to respond to portion size in their (equal-sized) food bowls.  I can fill one to overflowing and put only a handful of kibble in the other, and my dogs will generally go for whichever bowl is closer.  "Oh, well, I can always go for the other bowl once I'm done with this one," seems to be their general attitude, along with "Any food is a good thing."

Byosiere and her colleagues have expanded their research into other illusions, and I encourage you to go to the link I posted and check out what she and others have done.  She's also started a citizen-science effort called “What the Fluff!?” to study how animals respond to an illusion you probably have seen on YouTube -- where a pet owner holds a sheet up in front of them, and drops the sheet while simultaneously ducking out of sight, and seeing how the pets respond to their owners' apparent vanishing act.  "We’re asking owners to do this at home with their dogs," Byosiere said.  "We’ll be analyzing the footage and seeing if we can make any conclusions about object permanence and violation of expectation in that kind of magic trick."

So if you're inclined, try playing some mind games with your pets, and send her your results.  I may try it with my dogs and see what happens.  My guess is Guinness might fall for it and try to figure out what happened, but our hound Lena, who shows the level of energy and intelligence usually associated with a plush toy, would probably not notice if I mysteriously vanished.  Or if she did notice, she'd kind of shrug and go, "Oh, well, I'm sure he'll be back at some point" and resume the very important nap she'd been taking before I started bothering her.

Either way, it might be interesting to see how they respond.  If you try it, let me know in the comments section what your results were.  And now, I'm off to play a round of Confuse-a-Dog.

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What are you afraid of?

It's a question that resonates with a lot of us.  I suffer from chronic anxiety, so what I am afraid of gets magnified a hundredfold in my errant brain -- such as my paralyzing fear of dentists, an unfortunate remnant of a brutal dentist in my childhood, the memories of whom can still make me feel physically ill if I dwell on them.  (Luckily, I have good teeth and rarely need serious dental care.)  We all have fears, reasonable and unreasonable, and some are bad enough to impact our lives in a major way, enough that psychologists and neuroscientists have put considerable time and effort into learning how to quell (or eradicate) the worst of them.

In her wonderful book Nerve: Adventures in the Science of Fear, journalist Eva Holland looks at the psychology of this most basic of emotions -- what we're afraid of, what is happening in our brains when we feel afraid, and the most recently-developed methods to blunt the edge of incapacitating fears.  It's a fascinating look at a part of our own psyches that many of us are reluctant to confront -- but a must-read for anyone who takes the words of the Greek philosopher Pausanias seriously: γνῶθι σεαυτόν (know yourself).

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

The stone hand illusion

One of the reasons I trust science is that I have so little trust in my own brain's ability to assess correctly the nature of reality.

Those may sound like contradictions, but they really aren't.  Science is a method that allows us to evaluate hard data -- measurements by devices that are designed to have no particular biases.  By relying on measurements from machines, we are bypassing our faulty sensory equipment, which can lead us astray in all sorts of ways.  In astronomer Neil deGrasse Tyson's words, "[Our brains] are poor data-taking devices... that's why we have machines that don't care what side of the bed they woke up on that morning, that don't care what they said to their spouse that day, that don't care whether they had their morning caffeine.  They'll get the data right regardless."

We still believe that we're seeing what's real, don't we?  "I saw it with my own eyes" is still considered the sine qua non for establishing what reality is.  Eyewitness testimony is still the strongest evidence in courts of law.  Because how could it be otherwise?  Maybe we miss minor things, but how could we get it so far wrong?

But as I wrote about two weeks ago, even our perception of something as simple as color is flawed, and is mostly a construct of the brain, not a function of what's really out there.  We are ignoring as much as we perceive, making stuff up to bridge gaps, and in general, creating a montage of what's actually there, what your brain decides is important enough to pay attention to, and inferences to fill in the spaces in between.

If that's not bad enough, a scientist in Italy has knocked another gaping hole in our confidence that our brain can correctly interpret the sensory information it's given -- this time with an actual hammer.

Some of you may have heard of the "rubber hand illusion" that was created in an experiment back in 1998 by Matthew Botvinick and Jonathan Cohen.  In this experiment, the two scientists placed a rubber hand in view of a person whose actual hand is shielded from view by a curtain.  The rubber hand is stroked with a feather at the same time as the person's real (but out-of-sight) hand receives a similar stroke -- and within minutes, the person becomes strangely convinced that the rubber hand is his hand.

The Italian experiment, which I found out about in an article in Discover Online, substitutes an auditory stimulus for the visual one -- with an even more startling result.

Irene Senna, professor of psychology at Milono-Bicocca University in Milan, rigged up a similar scenario to Botvinick and Cohen's.  A subject sits with one hand through a screen.  On the back of the subject's hand is a small piece of foil which connects an electrical lead to a computer.  The subject sees a hammer swinging toward her hand -- but the hammer stops just short of smashing her hand, and only touches the foil gently (but, of course, she can't see this).  The touch of the hammer sends a signal to the computer -- which then produces a hammer-on-marble clink sound.

After repeating this only a few times, the subject feels absolutely convinced that her hand has turned to stone.

[Image is in the Public Domain]

What is impressive about this illusion is that the feeling persists even after the experiment ends, and the screen is removed -- and even though the test subjects knew what was going on.  Subjects felt afterwards as if their hands were cold, stiff, heavier, less sensitive.  They reported difficulty bending their wrists.

To me, the coolest (and freakiest) thing about this is that our knowledge centers, the logical and rational prefrontal cortex and associated areas, are completely overcome by the sensory-processing centers when presented with this scenario.  We can know something isn't real, and simultaneously cannot shake the brain's decision that it is real.  None of the test subjects was crazy; they all knew that their hands weren't made of stone.  But presented with sensory information that contradicted that knowledge, they couldn't help but come to the wrong conclusion.

And this once again illustrates why I trust science, and am suspicious of eyewitness reports of UFOs, Bigfoot, ghosts, and the like.  Our brains are simply too easy to fool, especially when emotions (particularly fear) run high.  We can be convinced that what we're seeing or hearing is the real deal, to the point that we are unwilling to admit the possibility of a different explanation.

But as Senna's elegant little experiment shows, we can't rely on what our senses tell us.  Data from scientific measuring devices will always be better than pure sensory information.  To quote Tyson again: "We think that the eyewitness testimony of an authority -- someone wearing a badge, or a pilot, or whatever -- is somehow better than the testimony of an average person.  But no.  I'm sorry... but it's all bad."

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I know I sometimes wax rhapsodic about books that really are the province only of true science geeks like myself, and fling around phrases like "a must-read" perhaps a little more liberally than I should.  But this week's Skeptophilia book recommendation of the week is really a must-read.

No, I mean it this time.

Kathryn Schulz's book Being Wrong: Adventures in the Margin of Error is something that everyone should read, because it points out the remarkable frailty of the human mind.  As wonderful as it is, we all (as Schulz puts it) "walk around in a comfortable little bubble of feeling like we're absolutely right about everything."  We accept that we're fallible, in a theoretical sense; yeah, we all make mistakes, blah blah blah.  But right now, right here, try to think of one think you might conceivably be wrong about.

Not as easy as it sounds.

She shocks the reader pretty much from the first chapter.  "What does it feel like to be wrong?" she asks.  Most of us would answer that it can be humiliating, horrifying, frightening, funny, revelatory, infuriating.  But she points out that these are actually answers to a different question: "what does it feel like to find out you're wrong?"

Actually, she tells us, being wrong doesn't feel like anything.  It feels exactly like being right.

Reading Schulz's book makes the reader profoundly aware of our own fallibility -- but it is far from a pessimistic book.  Error, Schulz says, is the window to discovery and the source of creativity.  It is only when we deny our capacity for error that the trouble starts -- when someone in power decides that (s)he is infallible.

Then we have big, big problems.

So right now, get this book.  I promise I won't say the same thing next week about some arcane tome describing the feeding habits of sea slugs.  You need to read Being Wrong.

Everyone does.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

The stone hand illusion

One of the reasons I trust science is that I have so little trust in my own brain's ability to assess correctly the nature of reality.

Those may sound like contradictions, but they really aren't.  Science is a method that allows us to evaluate hard data -- measurements by devices that are designed to have no particular biases.  By relying on measurements from machines, we are bypassing our faulty sensory equipment, which can lead us astray in all sorts of ways.  In Neil deGrasse Tyson's words, "[Our brains] are poor data-taking devices... that's why we have machines that don't care what side of the bed they woke up on that morning, that don't care what they said to their spouse that day, that don't care whether they had their morning caffeine.  They'll get the data right regardless."

But we still believe that we're seeing what's real, don't we?  "I saw it with my own eyes" is still considered the sine qua non for establishing what reality is.  Eyewitness testimony is still the strongest evidence in courts of law.  Because how could it be otherwise?  Maybe we miss minor things, but how could we get it so far wrong?

A scientist in Italy has knocked another gaping hole in our confidence that our brain can correctly interpret the sensory information it's given -- this time with an actual hammer.

Some of you may have heard of the "rubber hand illusion" that was created in a study back in 1998 by Matthew Botvinick and Jonathan Cohen.  In this experiment, the two scientists placed a rubber hand in view of a person whose actual hand is shielded from view by a curtain.  The rubber hand is stroked with a feather at the same time as the person's real (but out-of-sight) hand receives a similar stroke -- and within minutes, the person becomes strangely convinced that the rubber hand is his hand.

The Italian experiment, which I found out about from an article in Discover Online, substitutes an auditory stimulus for the visual one -- with an even more startling result.

Irene Senna, professor of psychology at Milono-Bicocca University in Milan, rigged up a similar scenario to Botvinick and Cohen's.  A subject sits with one hand through a screen.  On the back of the subject's hand is a small piece of foil which connects an electrical lead to a computer.  The subject sees a hammer swinging toward her hand -- but the hammer stops just short of smashing her hand, and only touches the foil gently (but, of course, she can't see this).  The touch of the hammer sends a signal to the computer -- which then produces a hammer-on-marble chink sound.

And within minutes, the subject feels like her hand has turned to stone.

[Image licensed under the Creative Commons Tony Hisgett from Birmingham, UK, Hand Sculpture 1 (22797821268), CC BY 2.0]

What is impressive about this illusion is that the feeling persists even after the experiment ends, and the screen is removed -- and even though the test subjects knew what was going on.  Subjects felt afterwards as if their hands were cold, stiff, heavier, less sensitive.  They reported difficulty bending their wrists.

To me, the coolest thing about this is that our knowledge centers, the logical and rational prefrontal cortex and associated areas, are completely overcome by the sensory-processing centers when presented with this scenario.  We can know something isn't real, and simultaneously cannot shake the brain's decision that it is real.  None of the test subjects was crazy; they all knew that their hands weren't made of stone.  But presented with sensory information that contradicted that knowledge, they couldn't help but come to the wrong conclusion.

And this once again illustrates why I trust science, and am suspicious of eyewitness reports of UFOs, Bigfoot, ghosts, and the like.  Our brains are simply too easy to fool, especially when emotions (particularly fear) run high.  We can be convinced that what we're seeing or hearing is the real deal, to the point that we are unwilling to admit the possibility of a different explanation.

But as Senna's elegant little experiment shows, we just can't rely on what our senses tell us.  Data from scientific measuring devices will always be better than pure sensory information.  To quote Tyson again: "We think that the eyewitness testimony of an authority -- someone wearing a badge, or a pilot, or whatever -- is somehow better than the testimony of an average person.  But no.  I'm sorry... it's all bad."

***********************************

Back in 1989, the United States dodged a serious bullet.

One hundred wild monkeys were imported for experimental purposes, and housed in a laboratory facility in Reston, Virginia, outside of Washington DC.  Soon afterwards, the monkeys started showing some odd and frightening symptoms.  They'd spike a fever, become listless and glassy-eyed, and at the end would "bleed out" -- capillaries would start rupturing all over their body, and they'd bleed from every orifice including the pores of the skin.

Precautions were taken, but at first the researchers weren't overly concerned.  Most viruses have a feature called host specificity, which means that they tend to be infectious only in one species of host.  (This is why you don't need to worry about catching canine distemper, and your dog doesn't need to worry about catching your cold.)

It wasn't until someone realized the parallels with a (then) obscure viral outbreak in 1976 in Zaire (now the Republic of Congo) that the researchers realized things might be much more serious.  To see why, let me just say that the 1976 epidemic, which completely wiped out three villages, occurred on...

... the Ebola River.

Of course, you know that the feared introduction of this deadly virus into the United States didn't happen.  But to find out why -- and to find out just how lucky we were -- you should read Richard Preston's book The Hot Zone.  It's a brilliantly-written book detailing the closest we've come in recent years to a pandemic, and that from a virus that carries with it a 95% mortality rate.  (One comment: the first two chapters of this book require a bit of a strong stomach.  While Preston doesn't go out of his way to be graphic, the horrifying nature of this disease makes some nauseating descriptions inevitable.)

[Note:  If you purchase this book through the image/link below, part of the proceeds will go to supporting Skeptophilia!]

The second self

It's a source of some amusement to me how certain we are of what comes in through our sense organs.

"I saw it with my own eyes" is treated as if it were as good as proof, even though we know our brains are easy to fool.  Consider optical illusions (here's a website that has a great sampler of illusions, along with explanations of what's going wrong with the sensory-integrative system when you look at them).  I tend to agree with Neil DeGrasse Tyson that "optical illusion" isn't what we should be calling them.  "We should call 'em brain failures," Tyson said.  "Because that's what they are.  You look at a funny, clever line drawing, and your brain can't handle it."

There was another blow to our confidence in what we're experiencing from a study that was just published two days ago in Nature.  The paper, titled "Illusory Body Ownership of an Invisible Body Interpolated Between Virtual Hands and Feet Via Visual-Motor Synchronicity," by Ryota Kondo, Maki Sugimoto, Kouta Minamizawa, Takayuki Hoshi, Masahiko Inami and Michiteru Kitazaki of the Toyohashi University of Technology in Toyohashi, Japan, describes an experiment wherein test subjects shown a very simple optical illusion ended up feeling as if they were controlling a mostly-invisible whole-body second self.

If you're thinking "These people must be really suggestible to fall for something like that," think again.  The illusion was remarkably consistent across test subjects of different ages, genders, and intellectual abilities.  The authors write:

Body ownership can be modulated through illusory visual-tactile integration or visual-motor synchronicity/contingency.  Recently, it has been reported that illusory ownership of an invisible body can be induced by illusory visual-tactile integration from a first-person view.  We aimed to test whether a similar illusory ownership of the invisible body could be induced by the active method of visual-motor synchronicity and if the illusory invisible body could be experienced in front of and facing away from the observer.  Participants observed left and right white gloves and socks in front of them, at a distance of 2 m, in a virtual room through a head-mounted display.  The white gloves and socks were synchronized with the observers’ actions.  In the experiments, we tested the effect of synchronization, and compared this to a whole-body avatar, measuring self-localization drift.  We observed that visual hands and feet were sufficient to induce illusory body ownership, and this effect was as strong as using a whole-body avatar.

So as weird as it sounds, people had a convincing sense of operating another body simply if they watched gloves and socks mimicking their movements -- and even if they knew ahead of time that this was all that was going on.

It's astonishing to what extent the illusory body can replace our actual body as a source of input stimuli to the brain:

An entire invisible body ownership is induced when participants observe a paintbrush moving in an empty space and by defining the contours of an invisible body through an HMD [head-mounted display] from a first-person perspective while receiving simultaneous touches on the corresponding parts of their real body.  The illusory ownership of an entire invisible body reduces autonomic and subjective social anxiety responses caused by standing in front of an audience.  In contrast, an illusion of missing body parts through illusory ownership of an amputated virtual body can be induced by eliminating a virtual (visual) body part and not applying physical touches to the body part corresponding to the missing part.  This illusory experience of amputation decreases corticospinal excitability of the illusory amputated body part.

So not only can we be convinced that we have a mostly-invisible second body, we can be convinced that our mostly-invisible second body has had its arm amputated.

The whole thing is profoundly humbling, and a little scary.  It has to make you wonder what part of our ordinary perception of the world is illusory -- how much of it is inaccurate, incorrect, misperceived, or just plain made-up.  Your brain does this on a minor scale all the time -- take the visual blind spot that we all have, located approximately twenty degrees on the outside of straight ahead in each eye's visual field.

If you've never experienced this phenomenon, it's easy to demonstrate.  You can do it with either eye -- I'll give you instructions for doing it with your left eye, but if you want to do it with your right eye instead, simply reverse all the directions right-to-left.

1. Draw a dark dot and a plus sign on a piece of paper, about ten centimeters apart (you don't have to measure).  The plus sign should be on the right, the dot on the left.
2. Close your right eye, and place the plus sign right in front of your left eye.  Gradually move the piece of paper away from your face, keeping your left eye on the plus sign.
3. At some point -- usually about thirty centimeters or so away from your face -- the dot will seem to vanish.  At that point, the light from the dot is falling on the spot where your optic nerve strikes your retina, a point where you have no visual receptors!

With both eyes open, it's easy to understand why we aren't aware of them; your left eye covers for your right eye's blind spot, and vice versa.  But why don't you experience a hole in your visual field with one eye open?  After all, even with one eye open, none of us feel like there's a floating blank spot out there in our peripheral vision.

The answer is that our brain basically makes stuff up, and fills in the hole.  It makes some assumptions about what we're seeing -- and that's what we perceive.  Never mind that there's really no light actually being sensed from that area; your brain just says, "Oh, well, I'll bet that's what's out there."

So "I saw it with my own eyes" is really a pretty crappy benchmark for accuracy.  I'll end with another quote from Tyson, this one taken from a talk he did on UFOs, and which seems a fitting way to conclude:

There's a fascinating frailty of the human mind...  We know, not only from research in psychology but from simple empirical evidence... that the lowest form of evidence that exists in this world is eyewitness testimony.  Which is scary, because that's the highest form of evidence the court of law...  So now, it wouldn't matter if you saw a flying saucer.  In science, even if you have something less controversial than a flying saucer, and you come into my lab and say, "You've got to believe me, I saw it," and you're one of my fellow scientists, I'm going to say, "Go home!  Come back when you have some other kind of evidence than 'you saw it.'"  Because the human perception system is rife with all kinds of ways of getting it wrong.  But we don't like thinking of it that way.  We have high opinions of our human biology -- when in fact, we should not.

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This week's recommended book is an obscure little tome that I first ran into in college.  It's about a scientific hoax -- some chemists who claimed to have discovered what they called "polywater," a polymerized form of water that was highly viscous and stayed liquid from -70 F to 500 F or above.  The book is a fascinating, and often funny, account of an incident that combines confirmation bias with wishful thinking with willful misrepresentation of the evidence.  Anyone who's interested in the history of science or simply in how easy it is to fool the overeager -- you should put Polywater by Felix Franks on your reading list.