In the blink of an eye

One of the things I love about science is how it provides answers to questions that are so ordinary that few of us appreciate how strange they are.

I remember how surprised I was when I first heard a question about our vision that had honestly never occurred to me.  You know how images jump around when you're filming with a hand-held videocamera?  Even steady-handed people make videos that are seriously nausea-inducing, and when the idea is to make it look like it's filmed by amateurs -- such as in the movie The Blair Witch Project -- the result looks like it was produced by strapping a camera to the head of a kangaroo on crack.

What's a little puzzling is why the world doesn't appear to jump around like that all the time.  I mean, think about it; if you walk down the hall holding a videocamera on your shoulder, and watch the video and compare it to the way the hall looked while you were walking, you'll see the image bouncing all over the place on the video, but won't have experienced that with your eyes.  Why is that?

The answer certainly isn't obvious.  One guess scientists have is that we stabilize the images we see, and compensate for small movements of our head, by using microsaccades -- tiny, involuntary, constant jitters of the eyes.  The thought is that those little back-and-forth movements allow your brain to smooth out the image, keeping us from seeing the world as jumping around every time we move.

Another question about visual perception that I had never thought about was the subject of some research out of New York University and the University Medical Center of Göttingen that was published in the journal Current Biology.  Why don't you have the perception of the world going dark for a moment when you blink?  After all, most of us blink about once every five seconds, and we don't have the sense of a strobe effect.  In fact, most of us are unaware of any change in perception whatsoever.

[Image licensed under the Creative Commons Mcorrens, Iris of the Human Eye, CC BY-SA 3.0]

By studying patients who had lesions in the cerebrum, and comparing them to patients with intact brains, the scientists were not only able to answer this question, but to pinpoint exactly where this phenomenon happens -- the dorsomedial prefrontal cortex, a part of the brain immediately behind the forehead.  What they found was that individuals with an intact dmPFC store a perceptual memory of what they've just seen, and use that to form the perception they're currently seeing, so the time during which there's no light falling on the retina -- when you blink -- doesn't even register.  On the other hand, a patient with a lesion in the dmPFC lost that ability, and didn't store immediate perceptual memories.  The result?  Every time she blinked, it was like a shutter closed on the world.

"We were able to show that the prefrontal cortex plays an important role in perception and in context-dependent behavior," said neuroscientist Caspar Schwiedrzik, who was lead author of the study.  "Our research shows that the medial prefrontal cortex calibrates current visual information with previously obtained information and thus enables us to perceive the world with more stability, even when we briefly close our eyes to blink...  This is not only true for blinking but also for higher cognitive functions.  Even when we see a facial expression, this information influences the perception of the expression on the next face that we look at."

All of which highlights that all of our perceptual and integrative processes are way more sophisticated than they seem at first.  It also indicates something that's a little scary; that what we're perceiving is partly what's really out there, and partly what our brain is telling us it thinks is out there.  Which is right more often than not, of course.  If that weren't true, natural selection would have finished us off a long time ago.  But that fraction of the times that it's wrong, it can create some seriously weird sensations -- or make us question things that we'd always taken for granted.

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The visual time machine

I don't know if you've ever considered what I'm about to describe; I know I had to have it pointed out to me.

Let's say you're walking down a long hallway, where there are other people, doorways, windows, pieces of art on the wall -- lots of stuff to look at.  As you walk, you move your head and your eyes to check out the surroundings, and also so you don't run into anyone.  Now, let's say that at the same time, you have a miniature videocamera attached to your forehead, so that it's recording the scene using the exact same perspective and movements as you.

Now, consider the difference between what you saw while walking, and what you'd see if you looked at the video of the same walk down the hall.

The recorded video would have incorporated every jolt from your feet striking the ground, every jerky movement of your head.  The visual field would bounce all over the place.  You know that show, Finding Bigfoot?  The one that's been going on for ten years, wherein despite the name, they have found exactly zero Bigfoots?  They're always showing video footage taken with hand-held video recorders, as the crew of the show run about in the woods excitedly not finding any Bigfoots, and those videos look like someone strapped the camera to a kangaroo on speed.  The movie The Blair Witch Project was filmed to look like it had been taken with a hand-held recorder, and they succeeded -- to the point that some people find it unwatchable, and end up feeling queasy or headachy from the scene being jostled around continuously.

The question is, why don't we see exactly the same thing?  Unless we're rattled way harder than usual -- like riding too fast in a car over a rutted and potholed road -- we have no visual sense of the fact that just like the video recorder, the scene we're looking at is jittering around continuously.

One possible explanation that has been given is microsaccades -- continuous minuscule back-and-forth jerks of the eyes that everyone has (but are so fast that you need a slowed-down video recording to see them).  It's possible that the brain uses these quick-but-tiny shifts in the visual field to smooth out the input and erase the sense that what you're seeing is bouncing around.

As an aside, there's another curious feature of microsaccades; they can be used to detect when someone's not paying attention.  I read about funny bit of research a few years ago, but unfortunately I can't find a link referencing it -- if anyone knows the source, please post a link in the comments.  The gist was that they took volunteers and attached head-mounted cameras to them, but the cameras weren't looking at the surroundings -- the lens was pointed backwards at the volunteers' eyes.  The instructions were that the volunteers were supposed to chat with the bartender, and not look around at anything or anyone else.  

Then, during the middle of the experiment, an attractive person of the volunteer's preferred gender walked in and sat down a few barstools over.  

The volunteers all did what they were told -- none of them turned and looked toward the eye candy parked only a few feet away.  But their microsaccades reacted big time.  The little jitters in the eye suddenly all were aimed in the same direction -- toward the hot-looking person near them.  It's like the brain is saying, "No, I can't look, I told the researchers I wouldn't," while the microsaccades are saying "LOOK AT THAT SEXY PERSON!  LOOK!  I KNOW YOU WANT TO!"

[Image licensed under the Creative Commons Laurinemily at English Wikipedia, Hazel-green eye 2, CC BY-SA 2.5]

In any case, some research came out last week, by Mauro Manassi (University of Aberdeen) and David Whitney (University of California - Berkeley), that suggests that there's another smoothing effect at work in addition to microsaccades.  What the researchers found was that there is a feature of our brain that does the same thing in time that the microsaccades do in space; they blur out little jolts by averaging the input.  In this case, your brain coalesces the images we've received during the last fifteen seconds, so any small vibrations get blended into a sense of a smooth, continuous visual field.

What the researchers did was to show volunteers a thirty-second video clip of a face that was slowly morphing in such a way that it appeared to change age.  The volunteers were then asked what age the individual was at the end of the clip.  Across the board, they underestimated the age of the face. On the other hand, given a still shot of the face as it was at the end resulted in fairly accurate assessment of the person's age.  But when watching the video, the answer they gave was consistently the apparent age of the individual not at the end, but the average over the previous fifteen seconds of the video.

The authors write:

In other words, the brain is like a time machine which keeps sending us back in time.  It’s like an app that consolidates our visual input every 15 seconds into one impression so that we can handle everyday life.  If our brains were always updating in real time, the world would feel like a chaotic place with constant fluctuations in light, shadow and movement.  We would feel like we were hallucinating all the time...  This idea... of mechanisms within the brain that continuously bias our visual perception towards our past visual experience is known as continuity fields.  Our visual system sometimes sacrifices accuracy for the sake of a smooth visual experience of the world around us.  This can explain why, for example, when watching a film we don’t notice subtle changes that occur over time, such as the difference between actors and their stunt doubles.

So once again, our sensory-perceptive systems (1) are way more complex than we thought, and (2) are recording the perceptions we have in such a way that they're not necessarily completely accurate, but the most useful.  "I saw it with my own eyes!" really doesn't mean very much.  As my neuroscience professor told us many years ago, "Your senses don't have to reflect reality; they just have to work well enough that you can find food, avoid being killed, and find a mate."

And if that means losing some visual accuracy in favor of the world not looking like hand-held video footage from Finding Bigfoot, I'm okay with that.

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It's obvious to regular readers of Skeptophilia that I'm fascinated with geology and paleontology.  That's why this week's book-of-the-week is brand new: Thomas Halliday's Otherlands: A Journey Through Extinct Worlds.

Halliday takes us to sixteen different bygone worlds -- each one represented by a fossil site, from our ancestral australopithecenes in what is now Tanzania to the Precambrian Ediacaran seas, filled with animals that are nothing short of bizarre.  (One, in fact, is so weird-looking it was christened Hallucigenia.)  Halliday doesn't just tell us about the fossils, though; he recreates in words what the place would have looked like back when those animals and plants were alive, giving a rich perspective on just how much the Earth has changed over its history -- and how fragile the web of life is.

It's a beautiful and eye-opening book -- if you love thinking about prehistory, you need a copy of Otherlands.

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

Color my world

Our ability to perceive color is, when you think about it, a peculiar thing.

First, there's the rather hackneyed question of whether we all see color the same way (exclusive, of course, of people who are colorblind).  The way the question is usually phrased goes something like, "How could we tell if when you look at something red, what you see what I call green, but you still call it red because that's what you've learned?"  In other words, if I were to take a look through your eyes and brain, would the colors of objects be the same as what I see?

The answer is: we can't know for sure.  Thus far there's no way for one person to perceive the world through another person's sensory organs and brain.  But the great likelihood is that we all see colors pretty similarly.  All of our visual receptors are put together the same way, as are the visual cortices in our brains.  To assume that even with this structural and functional similarity, each person is still perceiving colors differently, runs counter to Ockham's Razor -- so without any evidence, it seems like a pretty untenable position.

More interesting is the comparison between how we see the world and how other animals do.  Once again, we run up against the issue that we can't see through another's eyes, but at least here we're on more solid ground because we can see that different animals have differently structured eyes.  Dogs, for example, have retinas with a much higher density of rods (the structures that operate in dim light, but only see in shades of gray) and a much lower density of cones (the structures that operate in bright light, and are able to differentiate by wavelength -- i.e., see colors).  Dogs aren't completely colorblind -- their two types of cones peak in sensitivity in the blue and yellow regions of the spectrum -- but they're relatively insensitive to colors outside that.  (This explains why my dog, Guinness, routinely loses his bright orange tennis ball in the bright green lawn -- to me, it stands out from fifty meters away, but he'll walk right past it without seeing it.) 

Then, there are bees and butterflies, which have eyes sensitive not only in the ordinary visible light spectrum but in the infrared and ultraviolet regions, respectively.  There are flowers that look white to our eyes, but to a butterfly they're covered with streaks and spots -- ultraviolet-reflecting markings that advertising nectar to those who can see it. 

A flower of the plant Potentilla reptans, photographed in ultraviolet light.  To the human eye, the flower looks solid yellow -- this is what it might look like to a butterfly.  [Image licensed under the Creative Commons Wiedehopf20, Flower in UV light Potentilla reptans, CC BY-SA 4.0]

But the winner of the wildly complex vision contest is the mantis shrimp, which has sixteen different color receptors (contrasted with our paltry three), rendering them sensitive to gradations of color we aren't, as well as detecting ultraviolet and infrared light, and discerning the polarization angle of polarized light.  How the world looks to them is a matter of conjecture -- but it certainly must be a far brighter and more varied place than what we see.

The reason all this colorful stuff comes up is because of a paper that appeared last week in Proceedings of the National Academy of Sciences, called "What We Talk About When We Talk About Colors," by Colin Twomey, Gareth Roberts, David Brainard, and Joshua Plotkin of the University of Pennsylvania.  The researchers looked at how words describing different colors vary from language to language.  "The color-word problem is a classical one," Plotkin said, in an interview with Science Daily.  "How do you map the infinitude of colors to a discrete number of words?"

And, more central to this research: does everyone do it the same way?  If you showed me a series of gradations from pure blue to pure green, at what point to I switch from saying "this is blue" to saying "this is green" -- or do I call the intermediate shades by a third, discrete name?

What the researchers found was that across 130 different languages, humans tend to group and name colors the same way.  Further, if you give people tiles with varying shades of red and asked them to pick out "the reddest red," the results show remarkable consistency.

Another interesting result of the research was that the sensitivity of our eyes to color variation isn't the same from color to color; we are much better at picking out subtle variations in red, orange, and yellow than we are at seeing differences in (for example) different shades of brown.  The researchers believe this is due to a difference in what they call communicative need; since reds, oranges, and yellows are the colors of ripe fruit, we've evolved eyes that are most sensitive to variations in those colors.  "Fruits are a way for a plant to spread its seeds, hitching a ride with the animals that eat them," Twomey said.  "Fruit-producing plants likely evolved to stand out to these animals.  The relationship with the colors of ripe fruit tells us that communicative needs are likely related to the colors that stand out to us the most...  No one really cares about brownish greens, and pastels aren't super well represented in communicative needs."

So it seems like the great likelihood is that we all see the world pretty much the same way.  Well, all humans, at least.  What the world looks like to a dog, with their better dim-light vision and better motion detection, but far poorer color discrimination, can only be guessed at; and what colors a mantis shrimp sees is beyond the ability of most of us to imagine.

Study lead author Colin Twomey wonders whether the same techniques could be used to study other facets of sensory perception.  "This is something that could be carried to other systems where there is a need to divide up some cognitive space," he said, "whether it's sound, weight, temperature, or something else."

One I wonder about is the sense of taste.  We know that taste differs a great deal between different individuals, not only because everyone likes (and dislikes) particular flavors, and those preferences differ greatly; but there are some people called "supertasters" who are sensitive to minor variations in flavor that the rest of us don't even notice.  (I am most definitely not a supertaster; the joke in my family is that I have two taste buds, "thumbs up" and "thumbs down.")  The daughter of a friend of mine, for example, has amazingly sensitive taste buds, to the point that she can discern whether the coffee was brewed with filtered water or ordinary tap water.

Me, as long as it's brewed with water and not turpentine, I'm fine with it.

But that's all potential future research.  For now, we have a better idea of how each of us colors our world.  And despite our individual differences, the answer appears to be that what you're seeing and what I'm seeing look very much alike.  

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As someone who is both a scientist and a musician, I've been fascinated for many years with how our brains make sense of sounds.

Neuroscientist David Eagleman makes the point that our ears (and other sense organs) are like peripherals, with the brain as the central processing unit; all our brain has access to are the changes in voltage distribution in the neurons that plug into it, and those changes happen because of stimulating some sensory organ.  If that voltage change is blocked, or amplified, or goes to the wrong place, then that is what we experience.  In a very real way, your brain creates your world.

This week's Skeptophilia book-of-the-week looks specifically at how we generate a sonic landscape, from vibrations passing through the sound collecting devices in the ear that stimulate the hair cells in the cochlea, which then produce electrical impulses that are sent to the brain.  From that, we make sense of our acoustic world -- whether it's a symphony orchestra, a distant thunderstorm, a cat meowing, an explosion, or an airplane flying overhead.

In Of Sound Mind: How Our Brain Constructs a Meaningful Sonic World, neuroscientist Nina Kraus considers how this system works, how it produces the soundscape we live in... and what happens when it malfunctions.  This is a must-read for anyone who is a musician or who has a fascination with how our own bodies work -- or both.  Put it on your to-read list; you won't be disappointed.

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

The mental starburst

Eminent astrophysicist Neil de Grasse Tyson was talking about the unreliability of the human sensory-perceptive system -- how, despite our confidence in what we see and hear, so often it is inaccurate or incomplete -- and said, "You know those trick drawings... optical illusions?  Well, 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 on a sheet of paper, and your brain can't handle it."

I've been interested in optical illusions -- or brain failures, if you prefer -- for a long time.  I think the feature of this phenomenon that intrigues me the most is the fact that even once you know what's going on, you still can't see it for what it is.  Here's one of the best examples of that I've ever seen:

Japanese artist Kokichi Sugihara created this, and others like it, that defy our expectation of how the world works.  Note that when the whole apparatus is rotated, and you see how it's done, it doesn't help.  You'd think your knowledge that gravity does indeed pull things toward the Earth, plus your knowledge of how exactly your eye was tricked, would be enough for the brain to go, "Oh, okay!  I get it now!  Duh!"

But no.  He rotates the apparatus back to its original configuration, and presto!  Upside-down gravity again.

The reason the topic comes up is because of a paper in the journal Perception this week about a fascinating illusion called the "scintillating starburst."  Here's what it looks like:

What do you see here?  If you're like me (and apparently most people), besides the obvious dark interlocking polygons, you see a pattern of light-colored lines radiating out from the center.

You've undoubtedly already guessed what the problem is; those lines don't exist.  Your brain, in effect, created those lines.  But how?  And why?

The authors write:

[The scintillating starburst illusion is] a unique kind of stimulus that evokes ghostly or ephemeral illusory rays that appear to shimmer or scintillate... We ascertained that the [effect] experienced by observers when viewing this stimulus type is modulated by all stimulus dimensions we suspected to be relevant when piloting the study, namely the number of vertices of the polygons, contrast, the line width of the wreaths, the number of wreaths, and whether the polygons are bisecting or not. The strongest effect was yielded by the number of wreaths, followed by whether the strands are bisecting, stimulus contrast, line width of the braids, and the number of vertices of the polygons, in that order...  [N]o stimulus dimension by itself produces a strong effect, only the optimal confluence of many stimulus parameters does so.  We believe that these results are consistent with probabilistic inference—for instance, the percept of illusory lines from an occluder is more likely if there are more intersection points where the vertices bisect, and if this happens at higher contrast.  This is not implausible, as deciding on a coherent interpretation of ambiguous visual information is a fundamental challenge faced by the visual system.  Of course, probability by itself is not sufficient—the specific stimulus situation matters—for instance, a row of street lights does not evoke the impression of a bright band that connects them.  But in the case of street lights, the bright beacons are broken up by the darkness of the night.  This darkness is unambiguously present.  However, in the case of Starbursts, the bright beacons are separated by background of the same color, yielding the percept of an occluder of that color on top of the stimulus.

What I find puzzling about this explanation is the last bit -- that we don't see a bright band connecting streetlights at night, because there is the unambiguous presence of darkness between the lights -- doesn't really account for seeing bright lines where none exist.  After all, the entire background is the same color; our brains generate an illusion that the vertices of the polygons are connected by radial lines even though the entire area is unambiguously the same shade of gray.

What I'd like to see is how the brain is actually responding -- perhaps fMRIs of people looking at the polygons with no braiding and concentric patterns, then a pattern of actual radial lines, then the illusion itself.  My guess is that the last two would activate the same parts of the brain and the first would not.  It might not explain why it happens, but at least we'd see what module is being tricked.

So here we have once again an example of how our brains, when confronted with quite ordinary stimuli, proceed to make shit up.  

Think about that next time you're tempted to say, "Of course it happened that way.  I saw it with my own eyes."

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One of the most devastating psychological diagnoses is schizophrenia.  United by the common characteristic of "loss of touch with reality," this phrase belies how horrible the various kinds of schizophrenia are, both for the sufferers and their families.  Immersed in a pseudo-reality where the voices, hallucinations, and perceptions created by their minds seem as vivid as the actual reality around them, schizophrenics live in a terrifying world where they literally can't tell their own imaginings from what they're really seeing and hearing.

The origins of schizophrenia are still poorly understood, and largely because of a lack of knowledge of its causes, treatment and prognosis are iffy at best.  But much of what we know about this horrible disorder comes from families where it seems to be common -- where, apparently, there is a genetic predisposition for the psychosis that is schizophrenia's most frightening characteristic.

One of the first studies of this kind was of the Galvin family of Colorado, who had ten children born between 1945 and 1965 of whom six eventually were diagnosed as schizophrenic.  This tragic situation is the subject of the riveting book Hidden Valley Road: Inside the Mind of an American Family, by Robert Kolker.  Kolker looks at the study done by the National Institute of Health of the Galvin family, which provided the first insight into the genetic basis of schizophrenia, but along the way gives us a touching and compassionate view of a family devastated by this mysterious disease.  It's brilliant reading, and leaves you with a greater understanding of the impact of psychiatric illness -- and hope for a future where this diagnosis has better options for treatment.

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

 

Jumbo shrimp

After yesterday's rather humbling post about how easy it is to fool the human senses, today we get knocked down another peg or two with some new research showing our visual perception is beat hands down...

... by a species of shrimp.

You've probably heard the term refresh rate used in regards to computer monitors, but it also applies to our eyes.  The photoreceptors in your retina have to reset after firing, and during that time -- the refractory period -- the receptor cell is insensitive to further stimuli.  I recall finding out about this in my animal physiology class at the University of Washington thirty years ago, and finding out that human photoreceptors reset in about 1/60th of a second.  This is why the flicker in a fluorescent light is barely detectable to the human eye; it's driven by the oscillations of alternating current at a frequency of sixty hertz; and the fact that we have millions of photoreceptors, all out of phase with each other, smooths out the signal and makes it look like one continuous, evenly-bright light.

To a fly, however, which has a refresh rate double ours -- about 120 times per second -- a fluorescent light would look like a strobe, brightening and dimming every sixtieth of a second.

Must be really freakin' annoying.  Yet another reason I'm glad I'm not a fly.

But even they are not the fastest.  A paper in Biology Letters this week describes research into the visual systems of a species of snapping shrimp (Alpheus heterochaelis), which already is badass enough -- it snaps its claws together with such force that it creates a shock wave in the water, stunning its prey.  And this little marine crustacean has a refresh rate of 160 times per second.

So what looks like a blur of motion to other animals is visible as clear, discrete images moving across its field of vision.

Not only that, they have one of the widest ranges of sensitivity to light level known, functioning well with only 1 lux of incident light (the light intensity of late twilight) all the way up to 100,000 lux (direct, intense sunlight).

[Image licensed under the Creative Commons Rickard Zerpe, Snapping shrimp (Synalpheus sp.) (23806570264), CC BY-SA 2.0]

The snapping shrimp isn't the only amazing crustacean out there.  Its cousins, the mantis shrimps (Order Stomatopoda) don't just snap their claws and stun their prey, they actually punch the shit out of them.  They can accelerate their claws at the astonishing rate of 102,000 m/s^2, delivering a force of 1,500 Newtons (equivalent to the Earth's gravitational pull on a 150 kilogram mass).  Not only that, but they move their claws so quickly they overcome the cohesion of the water molecules as they pass through, creating vapor-filled bubbles (a process called cavitation) in their wake.  These bubbles then collapse with astounding force, delivering a second deadly shock wave to the unfortunate recipient.

No wonder the folks in the Caribbean have nicknamed the native species of mantis shrimp "the thumb-splitter."

But wild as that is, it's not why I brought up mantis shrimp.  They have the most sensitive color vision of any animal known.  Humans are (mostly) trichromats, having three functioning types of color receptor in our eyes.  Dogs are dichromats -- they have only two, which is why their color acuity is worse than ours.  A few lucky humans, and a great many bird species, are tetrachromats, having four kinds of color receptors.

Mantis shrimp have sixteen.  They can not only see in the ultraviolet region of the spectrum -- a range of light completely invisible to the human eye -- they can detect polarization angle, and even have sensors for detecting circular polarization, something that is thought to be unique in the animal kingdom.

Why they need this many different kinds of light receptors is unknown, although it probably has to do with predator-prey interactions -- finding lunch and avoiding being made into lunch.  With so many different strategies used by shallow tropical marine species to confound the eye -- shimmering scales, transparency, cryptic coloration, countershading -- having eyes that beat everyone else in sensitivity and range would be a pretty neat adaptation.

So that's yet another excursion into the weird world of sensory perception.  It never fails to fascinate me to think about what a different kind of animal's experience of the world must be like.  As philosopher Thomas Nagel pointed out, the only way to know what it's like to be a bat is to be a bat; all of our ideas of echolocation and flight and being nocturnal only gives us the answer to what it's like for a human to think about being a bat.

But even so, and all pondering about the mind/body problem aside, I can't help but wonder what the world looks like to a shrimp.

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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!]

Along came a spider...

Sometimes there's a discovery that's just so cool that I need to tell y'all about it.  It's not apropos of much except that you never know what science is going to uncover next.

Have you ever wondered why some animals' eyes glow in the dark, and others don't?  I've seen raccoons, cats, and (given where I live, lots of) deer get caught in my car headlights at night, and been fascinated by the eerie reflections from their eyes.

But not all animals do this.  You can shine a bright light into a squirrel's eyes all you want, and you'll never see anything but a pissed-off squirrel.

The reason is a fascinating structure you only find in nocturnal animals called the tapetum lucidum.  This is basically a mirror behind the retina.  When light enters the eye and focuses on the retina, some of it passes through that tissue-thin layer of cells without activating one of the light-sensing structures -- i.e., it gets absorbed without contributing to vision.  If you're a diurnal animal (like us) this is no big deal; most of the time we have light to spare, and in fact a more common problem is too much light, which is why we have a sensitive iris that acts like the shutter on an old-fashioned camera, reducing the aperture so the inside of the eye doesn't get fried.

But nocturnal animals need every photon they can get, so many of them have evolved a tapetum.  Some of the light hitting the retina passes through and gets "wasted" -- but then it hits the tapetum and reflects back through the retina, providing a second opportunity to detect it.  This gives animals with this structure much better dim-light vision -- and makes their eyes glow in headlights.

I got to see another, more surprising, animal with a tapetum when I was on a night hike in Belize some years ago looking for nocturnal birds (many of which also have tapeta, for what it's worth).  We were all wearing headlamps, and the guide pointed out that on the trail there were what looked like hundreds of tiny rubies, emeralds, and sapphires, glittering as the beam of the lamps passed across.

"What do you think those are?" she asked, and her eyes were also glittering -- with mischief.

"No idea," I said.

"Get closer," she said.

I knelt down and peered at the little jewel-like sparkles, and very quickly discovered they were...

... spiders.

"Each species glows a different color," she said.  "We're not really sure why."

Fortunately, I'm not an arachnophobe, but I did stand up rather quickly.

So that brings us to the discovery, which appeared last week in the Journal of Systematic Paleontology.  Spider fossils aren't very common, given that they are small and don't have bones or teeth (the most commonly preserved parts), and most spider fossils known have come from amber.  So it was quite a surprise to find a beautifully-preserved fossilized spider in Korea in a formation of chert.  Chert is a sedimentary rock (obviously, since that's pretty much where you find fossils) made up of tiny crystals of quartz.  Most of it comes from the layers of the evocatively-named siliceous ooze that coats the deep ocean floor and is made mostly of the silica skeletons of diatoms, microscopic algae that build shells out of glass.  But some chert forms when water passes through cracks in silica-rich rocks, dissolving bits of it that are then deposited in layers somewhere else.  (This is, essentially, the process that forms petrified wood.)

Here, it preserved this little spider so well that after 110 million years, you can still see its tapetum -- meaning it was a nocturnal hunter, rather like a modern wolf spider.

Without further ado, here he is:

... and the tapeta still reflect light.

"This is an extinct family of spiders that were clearly very common in the Cretaceous and were occupying niches now occupied by jumping spiders that didn’t evolve until later," said Paul Selden of the University of Kansas, who co-authored the paper, in a press release.  "But these spiders were doing things differently.  Their eye structure is different from jumping spiders.  It’s nice to have exceptionally well-preserved features of internal anatomy like eye structure.  It’s really not often you get something like that preserved in a fossil."

So pretty amazing stuff, and my apologies to the arachnophobes in the studio audience.  Hopefully the title of the post was enough to forewarn you.  Me, I think they're cool, although I wasn't as sanguine as my guide in Belize was about getting nose-to- ... um... nose-to-chelicerae with them.  But this illustrates something I've mentioned many times before; science never loses its capacity to astonish us with the complexity and beauty of the natural world.

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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!]

Finding the right search parameters

I was making dinner last week, and the recipe called for soy sauce.  I knew we had a bottle of it -- and I was pretty sure it was somewhere in the door shelves of the fridge, amongst the various salad dressings, jellies, jams, sauces, and marinades we'd collected.  But I could not find the damn thing, and was becoming increasingly frustrated.

So instead of a quick scan -- usually sufficient to find what I'm looking for -- I decided on a one-at-a-time, bottle-by-bottle search, and as you've probably already guessed, I found the soy sauce in under thirty seconds.  I realized immediately what the problem was; in my mind I pictured it as having a red cap, and our bottle had a green cap.

You'd think that wouldn't make a difference, given that everything else about it was exactly like what I was picturing, up to and including being full of soy sauce and having a big label on the front that said, "SOY SAUCE."  But one piece of the search parameter was off, and that made me scan right past it, not once but several times.

[Image licensed under the Creative Commons GanMed64, Soy Sauce selection (6362318717), CC BY 2.0]

This is far from the first time this sort of thing has happened to me, and it amazes me how subtle the error can be and still derail my efforts.  It doesn't have to be anything nearly as egregious as in the hilarious anecdote Dave Barry writes about when his mother, groceries in a cart and two small children in tow, spent an hour trying to find her car in the store parking lot.  She looked so pathetic that several kind shoppers pitched in to try to help her.  "It's a black Chevrolet," she said, over and over.  It was only after the search had gone on for a ridiculous length of time, up and down the parking lot lanes, that she remembered that the previous week they'd traded in their old car for a new one, and told the helpers, "Wait!  I just realized, it's not a black Chevrolet, it's a yellow Ford!"

The helpers apparently were not amused, and his mom spent the rest of her life trying to live down the embarrassment.

So we can be confounded by our brain's preconceived notions of what we're looking for, from the subtle to the (should be) obvious.  And some researchers at Johns Hopkins University have found that finding the right search parameters even extends to characteristics we can't see.

This puzzling result came out of a series of experiments that were the subject of a paper this week in the Journal of Experimental Psychology.  The team, led by cognitive neuroscientist Li Guo, timed how long it took test subjects to isolate a target object from clutter, and they found that knowing characteristics of the object that aren't apparent to the eye -- like hardness or fragility -- significantly improved the speed with which subjects could find the object in question.  The authors write:

Our interactions with the world are guided by our understanding of objects’ physical properties.  When packing groceries, we place fragile items on top of more durable ones and position sharp corners so they will not puncture the bags.  However, physical properties are not always readily observable, and we often must rely on our knowledge of attributes such as weight, hardness, and slipperiness to guide our actions on familiar objects.  Here, we asked whether our knowledge of physical properties not only shapes our actions but also guides our attention to the visual world.  In a series of four visual search experiments, participants viewed arrays of everyday objects and were tasked with locating a specified object.  The target was sometimes differentiated from the distractors based on its hardness, while a host of other visual and semantic attributes were controlled.  We found that observers implicitly used the hardness distinction to locate the target more quickly, even though none reported being aware that hardness was relevant.  This benefit arose from fixating fewer distractors overall and spending less time interrogating each distractor when the target was distinguished by hardness.  Progressively more stringent stimulus controls showed that surface properties and curvature cues to hardness were not necessary for the benefit.  Our findings show that observers implicitly recruit their knowledge of objects’ physical properties to guide how they attend to and engage with visual scenes.

What I find most curious about the results of this experiment is if the characteristic you're given can't be seen, how does it help your brain to locate the object you're searching for?  "What makes the finding particularly striking from a vision science standpoint is that simply knowing the latent physical properties of objects is enough to help guide your attention to them," said study senior author Jason Fischer.  "It's surprising because nearly all prior research in this area has focused on a host of visual properties that can facilitate search, but we find that what you know about objects can be as important as what you actually see...  To me what this says is that in the back of our minds, we are always evaluating the physical content of a scene to decide what to do next.  Our mental intuitive physics engines are constantly at work to guide not only how we interact with things in our environment, but how we distribute our attention among them as well."

So it may be that we're approaching our search from a set theory perspective; searching through "the set of all things in my living room" is more efficient if I can eliminate "the subset of things in my living room that are rigid, heavy, stand upright," etc., so eventually my brain can whittle it down to "the couch throw-pillow my dog dragged behind the recliner."

It's still puzzling to me how our brains actually accomplish this, because it means some kind of interaction is occurring between our visual interpretive systems and our non-visual memories (of such things as texture, durability, and so on).  It'd be interesting to have people perform this task while in a fMRI machine -- and see how their brain firing pattern differs while performing this task as compared to performing a task that simply requires memory retrieval.

So that's our latest look at the fascinating world of cognitive neuroscience.  It doesn't explain, however, the weird phenomenon that happens to me while I'm doing home repair projects, wherein I spend 5% of the time doing actual home repair and 95% stomping around swearing and looking for the tool that was just in my damn hand five seconds ago.  That one's a mystery.

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This week's Skeptophilia book-of-the-week is one that should be a must-read for everyone -- not only for the New Yorkers suggested by the title.  Unusual, though, in that this one isn't our usual non-fiction selection.  New York 2140, by Kim Stanley Robinson, is novel that takes a chilling look at what New York City might look like 120 years from now if climate change is left unchecked.

Its predictions are not alarmism.  Robinson made them using the latest climate models, which (if anything) have proven to be conservative.  She then fits into that setting -- a city where the streets are Venice-like canals, where the subways are underground rivers, where low-lying areas have disappeared completely under the rising tides of the Atlantic Ocean -- a society that is trying its best to cope.

New York 2140 isn't just a gripping read, it's a frighteningly clear-eyed vision of where we're heading.  Read it, and find out why The Guardian called it "a towering novel about a genuinely grave threat to civilisation."

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

The attentional window

One of the critical functions of our brain, and one that we don't often think about, is its ability to determine quickly what stimuli are important to pay attention to, and which can safely be ignored.

Which is not to say that it always gets things right.  There have been a number of fascinating experiments run on inattentional blindness, our complete lack of awareness of something we saw, presumably because the brain thought other stuff it was witnessing was more important.  You've probably heard about the most famous inattentional blindness experiment -- the video clip with a half-dozen people tossing around balls, where the instructions were (for example) to count the number of times a person in a black shirt caught a red ball -- and test subjects literally did not see the person in the gorilla suit who walked out into the middle of the scene, pounded his chest a few times, then walked off.

Even more curious is a less-known experiment where a table was set up in a hotel lobby, with one of the researchers sitting behind it (and a tablecloth over the table and down the front, obscuring what was happening underneath).  The researcher asked passersby if they'd mind taking a survey, and when he got a "yes" he handed them a clipboard, then "accidentally" dropped the pencil.  He ducked down to pick up the pencil -- then slipped under the table, and a completely different person came back up with the pencil.  No facial similarities at all.

Not only did virtually no one hesitate at all when the pencil was handed to them -- no reaction whatsoever -- when questioned afterward, a number of the test subjects claimed the researchers were lying about the switcheroo, even after seeing that there were two researchers behind the table who looked nothing alike.

By far my favorite, though, is the short video called "Whodunnit?" that was put together to increase public awareness of how inattentive and distractible we are (in the context of driving safely).  I won't clue you in about what's going on, but if you haven't seen it, take a look.  If you're anything like me, you'll spend the second half of the video with your mouth hanging open in astonishment.

So our brains aren't perceiving everything around us.  Far from it.  There's a filter applied to everything we sense, and the brain is the ultimate arbiter of what it deems important enough to notice and/or remember.  This is at least partly responsible for the experience I suspect we've all had, of having yourself and a friend describe an event and finding out that you and (s)he recall completely different parts of it.

This all comes up because of some research done at the National Eye Institute, published this week in the Journal of Neuroscience, that shows -- at least if human sensory/perceptive systems work like those of mice -- that there's a tenth of a second window during which your brain has to decide something's important, and if that window is missed, the stimulus is simply ignored.

A team made up of Lupeng Wang, Kerry McAlonan, Sheridan Goldstein, Charles R. Gerfen, and Richard J. Krauzlis took mice that had been genetically engineered to have cells that were switchable using a laser, and turned off some neurons in a region of the brain called the superior colliculus that is known to have a role in mammalian visual processing.  The switching mechanism was extremely fast and precise, allowing researchers to time the activity of the cells with astonishing accuracy.  They found that if the cells in the superior colliculus were turned off for a tenth of a second following a visual stimulus, the mouse acted as if it hadn't seen the stimulus at all.

So it looks like (again, if we can generalize a mouse model to a human brain) we may have an explanation for the invisible gorilla and the survey-switcheroo; our brains have a vanishingly short window in which to say "hey, this is important, pay attention!"  If that window passes, we're likely not to notice what's right in front of us.  Obviously, the mechanism works well enough.  It enabled our ancestors to notice their environment sufficiently well to avoid danger and respond quickly to threats.  But what it means is that once again, we're left with the rather unsettling conclusion that what we experience (and remember) is incomplete and inaccurate no matter how much we try to pay attention.  Even if you're concentrating, there are going to be some stimuli about which your superior colliculus says, "Meh, that's not important," and you just have to hope that most of the time, it makes the right call.

Me, I'm still wondering how I missed all that stuff in Lord Smythe's living room.  I guess my superior colliculus was really out to lunch on that one.

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This week's Skeptophilia book recommendation of the week is brand new -- only published three weeks ago.  Neil Shubin, who became famous for his wonderful book on human evolution Your Inner Fish, has a fantastic new book out -- Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA.

Shubin's lucid prose makes for fascinating reading, as he takes you down the four-billion-year path from the first simple cells to the biodiversity of the modern Earth, wrapping in not only what we've discovered from the fossil record but the most recent innovations in DNA analysis that demonstrate our common ancestry with every other life form on the planet.  It's a wonderful survey of our current state of knowledge of evolutionary science, and will engage both scientist and layperson alike.  Get Shubin's latest -- and fasten your seatbelts for a wild ride through time.