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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Trompe l'oeil

I have a fascination for optical illusions.

Not only are they cool, they often point out some profound information about how we process sensory input.  Take the famous two-and-a-half pronged fork:

The problem here is that we're trying to interpret a two-dimensional drawing as if it were a three-dimensional object, and the two parts of the drawing aren't compatible under that interpretation.  Worse, when you try to force your brain to make sense of it -- following the drawing from the bottom left to the top right, and trying to figure out when the object goes from three prongs to two -- you fail utterly.

Neil deGrasse Tyson used optical illusions as an example of why we should be slow to accept eyewitness testimony.  "We all love optical illusions," he said. "But that's not what they should call them.  They should call them 'brain failures.'  Because that's what they are.  A clever drawing, and your brain can't handle it."

(If you have some time, check out this cool compendium of optical illusions collected by Michael Bach, which is even more awesome because he took the time to explain why each one happens, at least where an explanation is known.)

It's even more disorienting when an illusion occurs because of two senses conflicting.  Which was the subject of a paper out of Caltech, "What You Saw Is What You Will Hear: Two New Illusions With Audiovisual Postdictive Effects," by Noelle R. B. Stiles, Monica Li, Carmel A. Levitan, Yukiyasu Kamitani, and Shinsuke Shimojo.  What they did is an elegant experiment to show two things -- how sound can interfere with visual processing, and how a stimulus can influence our perception of an event, even if the stimulus occurs after the event did!

Sounds like the future affecting the past, doesn't it?  It turns out the answer is both simpler and more humbling; it's another example of a brain failure.

Here's how they did the experiment.

In the first trial, they played a beep three times, 58 milliseconds apart.  The first and third beeps were accompanied by a flash of light.  Most people thought there were three flashes -- a middle one coincident with the second beep.

The second setup was, in a way, opposite to the first.  They showed three flashes of light, on the right, middle, and left of the computer screen.  Only the first and third were accompanied by a beep.  Almost everyone didn't see -- or, more accurately, didn't register -- the middle flash, and thought there were only two lights.

Sorry, I had to.

"The significance of this study is twofold," said study co-author Shinsuke Shimojo.  "First, it generalizes postdiction as a key process in perceptual processing for both a single sense and multiple senses.  Postdiction may sound mysterious, but it is not—one must consider how long it takes the brain to process earlier visual stimuli, during which time subsequent stimuli from a different sense can affect or modulate the first.  The second significance is that these illusions are among the very rare cases where sound affects vision, not vice versa, indicating dynamic aspects of neural processing that occur across space and time.  These new illusions will enable researchers to identify optimal parameters for multisensory integration, which is necessary for both the design of ideal sensory aids and optimal training for low-vision individuals."

All cool stuff, and more information about how the mysterious organ in our skull works.  Of course, this makes me wonder what we imagine we see because our brain anticipates that it will there, or perhaps miss because it anticipates that something out of of place shouldn't be there.  To end with another quote from Tyson: "Our brains are unreliable as signal-processing devices.  We're confident about what we see, hear, and remember, when in fact we should not be."

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It's a bird, it's a plane... no, it's both

One topic I've come back to over and over again here at Skeptophilia is how flawed our sensory/perceptive apparatus is.  Oh, it works well enough; most of the time, we perceive the external world with sufficient clarity not to walk into walls or get run over by oncoming trains.  But our impression that we experience the world as it is -- that our overall ambient sense of everything around us, what the brilliant neurophysiologist David Eagleman calls our umwelt, is a crystal-clear reflection of the real universe -- simply is false.

All it takes is messing about with optical illusions to convince yourself how easy our brains and sensory organs are to fool.  For example, in the following drawing, which is darker; square A or square B?

They're exactly the same.  Don't believe me?  Here's the same drawing, with a pair of gray lines superimposed on it:

Because your brain decided that B was in the shadow and A wasn't, then it concluded that A had to be intrinsically darker.  What baffles me still about this illusion is that even once you know how the trick works, it's impossible to see it any other way.

As astronomer Neil deGrasse Tyson put it, "Our brains are rife with ways of getting it wrong.  You know optical illusions?  That's not what they should call them.  They should call them brain failures.  Because that's what they are.  A few cleverly drawn lines, and your brain can't handle it."

Well, we just got another neat hole shot in our confidence that what we're experiencing is irrefutable concrete reality with a study that appeared in the journal Psychological Science this week.  What the researchers did was attempt to confound the senses of sight and hearing by showing test subjects a photograph of one object morphing into another -- say, a bird into an airplane.  During the time they studied the photograph, they were exposed to a selection from a list of sounds, two of which were relevant (birdsong and the noise of a jet engine) and a number of which were irrelevant distractors (like a hammer striking a nail).

They were then told to use a sliding scale to estimate where in the transformation of bird-into-airplane the image was (e.g. seventy percent bird, thirty percent airplane).  What the researchers found was that people were strongly biased by what they were hearing; birdsong biased the test subjects to overestimate the birdiness of the photograph, and reverse happened with the sound of a jet engine.  The irrelevant noises didn't effect choice (and thus, when exposed to the irrelevant noises, their visual perceptions of the image were more accurate).

"When sounds are related to pertinent visual features, those visual features are prioritized and processed more quickly compared to when sounds are unrelated to the visual features," said Jamal Williams, of the University of California - San Diego, who led the study, in an interview with Science Daily.  "So, if you heard the sound of a birdsong, anything bird-like is given prioritized access to visual perception.  We found that this prioritization is not purely facilitatory and that your perception of the visual object is actually more bird-like than if you had heard the sound of an airplane flying overhead."

I guess it could be worse; at least hearing birdsong didn't make you see a bird that wasn't there.  But it does once again make me wonder how eyewitness testimony is still considered to carry the most weight in a court of law when experiment after experiment has demonstrated not only how incomplete and easily biased our perceptions are, but how flawed our memories are.

Something to keep in mind next time you are tempted to say "I know it happened that way, I saw it with my own eyes."

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Effect-before-cause

Astrophysicist Neil deGrasse Tyson said (apropos of UFO sightings), "The human brain and perceptual systems are rife with ways of getting it wrong."

It might be humbling, but it's nothing short of the plain truth, and doesn't just apply to seeing alien spaceships.  Especially in perfectly ordinary situations, we like to think that what we're hearing and seeing is an accurate reflection of what's actually out there, but the fact is we not only miss entirely a significant fraction of what we're experiencing, we misinterpret a good chunk of the rest.

Think you're immune?  Watch the following two-minute video, and see if you can figure out who killed Lord Smythe.

I don't know about you, but I didn't do so well.

It turns out that we don't just miss things that are there, we sometimes see things that aren't there.  Take, for example, the research that appeared last week in the journal Psychological Science, that suggests we make guesses about what we're going to see, and if those guesses don't line up with what actually happens, we "see" what we thought we were going to see rather than reality.

The experiment was simple enough.  It uses a short video of three squares (call them A, B, and C, from left to right).  Square A starts to move quickly to the right, and "collides" with B, which starts to move.  As you track it across the screen, it looks like B is going to collide with C, and repeat what happened in the previous collision.

The problem is, square C starts to move not only before B hits it, but before B itself starts moving.  In other words, there is no way a collision with B could have been what triggered C to start moving.  But when test subjects were asked what order the squares started moving, just about everyone said A, then B, then C.  Our expectation of cause-and-effect are so strong that even on multiple viewings, test subjects still didn't see C begin to move before B.

"We have a strong assumption that we know, through direct perception, the order in which events happen around us," said study co-author Christos Bechlivanidis, of University College London.  "The order of events in the world is the order of our perceptions.  The visual signal of the glass shattering follows the signal of the glass hitting the ground, and that is taken as irrefutable evidence that this is indeed how the events occurred.  Our research points to the opposite direction, namely, that it is causal perceptions or expectations that tell us in what order things happen.  If I believe that the impact is necessary for the glass to break, I perceive the shattering after the impact, even if due to some crazy coincidence, the events followed a different order.  In other words, it appears that, especially in short timescales, it is causation that tells us the time."

As I and many others have pointed out about previous research into what is now known as "inattentional blindness," this is yet another nail in the coffin of eyewitness testimony as the gold standard of evidence in the court of law.  We still rely on "I saw it with my own eyes!" as the touchstone for the truth, even though experiment after experiment has shown how unreliable our sensory-perceptive systems are.  Add to that how plastic our memories are, and it's a travesty that people's fates are decided by juries based upon eyewitness accounts of what happened, sometimes in the distant past.

[Image licensed under the Creative Commons Eric Chan from Palo Alto, United States, Mock trial closing, CC BY 2.0]

To end with another quote by NdGT -- "There's no such thing as good eyewitness testimony and bad eyewitness testimony.  It's all bad."

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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!]

Color my world

Perception is such a mystery.

Neuroscientist David Eagleman, in his brilliant TED talk "Can We Create New Senses For Humans?", touches on this with a concept he calls the umwelt -- the slice of the objective reality we're aware of.  That differs from animal to animal -- as he points out, for dogs, the umwelt is all about smell; it's sound-related for echolocating bats; it consists of electrical field fluctuations for the black ghost knife-fish; and so on.  Eagleman says:

What this means is that our experience of reality is constrained by our biology.  And that goes against the common-sense notion that our eyes and our ears and our fingertips are just picking up the objective reality that's out there.  Instead, our brains are sampling just a little bit of the world...  Now, presumably, every animal assumes that its umwelt is the entire objective reality out there, because why would you ever stop to imagine that there's something beyond what we can sense?  Instead, what we all do is that we accept reality as it's presented to us. 

What never ceases to amaze me is that even the parts of the human umwelt most of us are pretty good at picking up on are still made largely of faulty and incomplete information.  Our brains have evolved to fill in the gaps in what we see and hear -- so your perception of the world is built of what you're actually sensing of the real world, and what your brain assumes is there and fills in for you.  (That it sometimes does this incorrectly is the basis of a lot of optical illusions.)

If you need further evidence that you're seeing some bits of reality but otherwise just kind of making shit up, consider a paper published this week in Proceedings of the National Academy of Sciences, by Michael Cohen (of Amherst College) and Thomas Botch and Caroline Robertson (of Dartmouth University).  In "The Limits of Color Awareness During Active, Real-World Vision," Cohen, Botch, and Robertson tested something that's been known for years -- that the acuity of our color vision in the periphery of our visual field is fairly poor -- and challenged the prevailing explanation, which is that cones (our color-sensitive retinal cells) are dense in the fovea (center of the retina) and sparse in the edges.

[Image is in the Public Domain]

For one thing, "sparse" is comparative, and not even especially accurate.  In a normal retina, the periphery still has four thousand cones per square millimeter.  Plus, even the statement that peripheral color vision is bad turns out to be a misstatement; we can detect the color of a small, brightly-colored object almost as well in the periphery as we can in the dead center of the visual field.

However, Cohen, Botch, and Robertson did an experiment that turns the whole question upside down.  They gave test subjects head-mounted visual displays that were equipped with devices for tracking eye movements.  They then showed the test subjects images of outdoor scenes, and without alerting them, began to decrease the color saturation in the edges of the image.  The test subjects failed to notice the fact that the image was gradually turning to black-and-white from the edges inward until the colored bit spanned an angle of only 37.5 degrees, something that "does not correspond to known limitations imposed by retinal or neuroanatomy."

It appears that what's going on is that the edges of our visual field are reasonably good at recognizing color, but our brain simply ignores the input.  Motion, on the other hand, is quickly detected even in the peripheral vision; makes some sense evolutionarily, where seeing the lion coming up from behind you is way more critical than determining what color his fur is.

It was a fairly shocking result even for the researchers.  "We were amazed by how oblivious participants were when color was removed from up to 95 percent of their visual world," said study senior author Caroline Robertson, in an interview with EurekAlert.  "Our results show that our intuitive sense of a rich, colorful visual world is largely incorrect.  Our brain is likely filling in much of our perceptual experience."

How and why the brain does this, however, is still a mystery.  The authors write:

If color perception in the real world is indeed as sparse as our findings suggest, the final question to consider is how this can be.  Why does it intuitively feel like we see so much color when our data suggest we see so little?  While we cannot offer a definitive answer, several possibilities can be explored in future research.  One possibility is that as observers spend time in an environment, their brains are able to eventually “fill-in” the color of many items in the periphery.  Of course, providing direct evidence for this explanation is challenging since it is extremely difficult to differentiate between scenarios where a subject knows the color of an object (i.e., “I know the tree behind me is green even though I currently cannot see the color green”) from instances where the subject is experiencing the color of that object online (i.e., “I can see the color green at this very moment”).

So our umwelt is apparently an even smaller slice of reality than we'd thought.  A little humbling, and something to think about next time you're in an argument with someone and you are tempted to say, "I know it happened that way, I saw it with my own eyes."

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This week's Skeptophilia book-of-the-week is for people who are fascinated with the latest research on our universe, but are a little daunted by the technical aspects: Space at the Speed of Light: The History of 14 Billion Years for People Short on Time by Oxford University astrophysicist Becky Smethurst.

A whirlwind tour of the most recent discoveries from the depths of space -- and I do mean recent, because it was only released a couple of weeks ago -- Smethurst's book is a delightful voyage into the workings of some of the strangest objects we know of -- quasars, black holes, neutron stars, pulsars, blazars, gamma-ray bursters, and many others.  Presented in a way that's scientifically accurate but still accessible to the layperson, it will give you an understanding of what we know about the events of the last 13.8 billion years, and the ultimate fate of the universe in the next few billions.  If you have a fascination for what's up there in the night sky, this book is for you!

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

Walls in our minds

One of the biggest unsolved mysteries of science is how the brain encodes what we know, think about, and experience.

For many types of information, we know where in the brain they are stored.  But in what form, and how we retrieve it, is still not known.  As I tell my neuroscience students: think of something simple, like your middle name, the name of your first pet, the name of the first president of the United States.  Now: where in your mind was that information before I asked you to remember it?

Pretty bizarre to consider, isn't it?

Interpretation of sensory input is as mysterious as memory.  When I look around my office, where I'm currently writing this, I can recognize all sorts of objects -- my CD collection, books, the masks hanging on the wall, a wine glass hand-made by my son, an antique typewriter my wife got me for my last birthday.  But... how?  What's being projected onto my retina is just a bunch of splotches of light, shadow, and color, and my brain has to take that chaos and somehow make sense of it.  How can we tell where the edge of an object is?  How do we recognize things -- and know them to be the same objects if seen from a different angle, meaning the pattern of colors thrown onto your retina is completely changed?

Interestingly, there are some people who can't do this.  In apperceptive visual agnosia, usually caused by damage to the visual cortex of the brain, people are cognitively normal in every respect except that they can't recognize anything they see.  It all looks like a random moving kaleidoscope of colors.  Because in other respects they're normal, they can remember what they're told and respond appropriately -- if someone said, "Hey, you see that blob of blue and tan and brown over there?  That's a person, and he's named Gordon," a sufferer from apperceptive visual agnosia would be able to say, "Oh, hi, Gordon," and have a normal conversation with me.  But if I stood up (changing the shape of the blob of color) or changed my shirt, or made any other sort of alteration to what he's seeing, he'd no longer recognize me, not only as a particular human, but as human at all.  Because they're perfectly intelligent, he might be able to reason that since Gordon was over there a few seconds ago, and there's a different blob of blue and tan and brown nearby, that's probably Gordon, too, but it wouldn't be because he actually recognized me.  It would be a logical inference, not visual interpretation.

An interesting piece was added to the puzzle last week with a paper in Neuron that came from some research at Columbia University led by neuroscientist Nikolaus Kriegeskorte.  He and his team were investigating how we perceive walls -- how we know where the edges and barriers are in our environment, a pretty critical skill for spatial navigation.  By showing participants images with walls and other barriers and allowing them to navigate the space virtually, and using fMRI and magnetoencephalography (MEG) neuroimaging, they were able to narrow down where we do edge and obstacle processing to the "occipital place area" (OPA), one of the visual processing centers.

[Image licensed under the Creative Commons Pawel Wozniak, Brick wall close-up view, CC BY-SA 3.0]

"Vision gives us an almost instant sense where we are in space, and in particular of the geometry of the surfaces -- the ground, the walls -- which constrain our movement," Kriegeskorte said.  "It feels effortless, but it requires the coordinated activity of multiple brain regions.  How neurons work together to give us this sense of our surroundings has remained mysterious.  With this study, we are a step closer to solving that puzzle...  Previous studies had shown that OPA neurons encode scenes, rather than isolated objects.  But we did not yet understand what aspect of the scenes this region's millions of neurons encoded...  We would like to put these [data] together and build computer vision systems that are more like our own brains, systems that have specialized machinery like what we observe here in the human brain for rapidly sensing the geometry of the environment."

Once again, we have an idea of where our perception of barriers is housed, but not so much information about how it's stored or accessed.  How, when we see a wall -- especially, as in this experiment, a two-dimensional representation of a wall -- do we recognize it as such, and not just as a smear of colors, lines, and angles?  As Kriegeskorte said, we're a step closer, which is fantastic -- but still a long way away from solving the puzzle of perception.

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When the brilliant British neurologist and author Oliver Sacks died in August of 2015, he was working on a collection of essays that delved into some of the deepest issues scientists consider: evolution, creativity, memory, time, and experience.  A year and a half ago, that collection was published under the title The River of Consciousness, and in it he explores those weighty topics with his characteristic humor, insight, and self-deprecating humility.

Those of us who were captivated by earlier works such as The Man Who Mistook His Wife for a Hat, Musicophilia, Awakenings, and Everything in its Place will be thrilled by this book -- the last thoughts of one of the best thinkers of our time.

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