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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Signal out of noise

I think I share with a lot of people a difficulty in deciphering what someone is saying when holding a conversation in a noisy room.  I can often pick out a few words, but understanding entire sentences is tricky.  A related phenomenon I've noticed is that if there is a song playing while there's noise going on -- in a bar, or on earphones at the gym -- I often have no idea what the song is, can't understand a single word or pick up the beat or figure out the music, until something clues me in to what the song is.  Then, all of a sudden, I find I'm able to hear it more clearly.

Some neuroscientists at the University of California - Berkeley have found out what's happening in the brain that causes this oddity in auditory perception.  In a paper in Nature: Communications, authors Christopher R. Holdgraf, Wendy de Heer, Brian Pasley, Jochem Rieger, Nathan Crone, Jack J. Lin, Robert T. Knight, and Frédéric E. Theunissen studied how the perception of garbled speech changes when subjects are told what's being said -- and found through a technique called spectrotemporal receptive field mapping that the brain is able to retune itself in less than a second.

The authors write:

Experience shapes our perception of the world on a moment-to-moment basis.  This robust perceptual effect of experience parallels a change in the neural representation of stimulus features, though the nature of this representation and its plasticity are not well-understood. Spectrotemporal receptive field (STRF) mapping describes the neural response to acoustic features, and has been used to study contextual effects on auditory receptive fields in animal models.  We performed a STRF plasticity analysis on electrophysiological data from recordings obtained directly from the human auditory cortex. Here, we report rapid, automatic plasticity of the spectrotemporal response of recorded neural ensembles, driven by previous experience with acoustic and linguistic information, and with a neurophysiological effect in the sub-second range.  This plasticity reflects increased sensitivity to spectrotemporal features, enhancing the extraction of more speech-like features from a degraded stimulus and providing the physiological basis for the observed ‘perceptual enhancement’ in understanding speech.

What astonishes me about this is how quickly the brain is able to accomplish this -- although that is certainly matched by my own experience of suddenly being able to hear lyrics of a song once I recognize what's playing.  As James Anderson put it, writing about the research in ReliaWire, "The findings... confirm hypotheses that neurons in the auditory cortex that pick out aspects of sound associated with language, the components of pitch, amplitude and timing that distinguish words or smaller sound bits called phonemes, continually tune themselves to pull meaning out of a noisy environment."

A related phenomenon is visual priming, which occurs when people are presented with a seemingly meaningless pattern of dots and blotches, such as the following:

Once you're told that the image is a cow, it's easy enough to find -- and after that, impossible to unsee.

"Something is changing in the auditory cortex to emphasize anything that might be speech-like, and increasing the gain for those features, so that I actually hear that sound in the noise," said study co-author Frédéric Theunissen.  "It’s not like I am generating those words in my head.  I really have the feeling of hearing the words in the noise with this pop-out phenomenon.  It is such a mystery."

Apparently, once the set of possibilities of what you're hearing (or seeing) is narrowed, your brain is much better at extracting meaning from noise.  "Your brain tries to get around the problem of too much information by making assumptions about the world," co-author Christopher Holdgraf said.  "It says, ‘I am going to restrict the many possible things I could pull out from an auditory stimulus so that I don’t have to do a lot of processing.’  By doing that, it is faster and expends less energy."

So there's another fascinating, and mind-boggling, piece of how our brains make sense of the world.  It's wonderful that evolution could shape such an amazingly adaptive device, although the survival advantage is obvious.  The faster you are at pulling a signal out of the noise, the more likely you are to make the right decisions about what it is that you're perceiving -- whether it's you talking to a friend in a crowded bar or a proto-hominid on the African savanna trying to figure out if that odd shape in the grass is a crouching lion.

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Not long ago I was discussing with a friend of mine the unfortunate tendency of North Americans and Western Europeans to judge everything based upon their own culture -- and to assume everyone else in the world sees things the same way.  (An attitude that, in my opinion, is far worse here in the United States than anywhere else, but since the majority of us here are the descendants of white Europeans, that attitude didn't come out of nowhere.)  

What that means is that people like me, who live somewhere WEIRD -- white, educated, industrialized, rich, and democratic -- automatically have blinders on.  And these blinders affect everything, up to and including things like supposedly variable-controlled psychological studies, which are usually conducted by WEIRDs on WEIRDs, and so interpret results as universal when they might well be culturally-dependent.

This is the topic of a wonderful new book by anthropologist Joseph Henrich called The WEIRDest People in the World: How the West Became Psychologically Peculiar and Particularly Prosperous.  It's a fascinating lens into a culture that has become so dominant on the world stage that many people within it staunchly believe it's quantifiably the best one -- and some act as if it's the only one.  It's an eye-opener, and will make you reconsider a lot of your baseline assumptions about what humans are and the ways we see the world -- of which science historian James Burke rightly said, "there are as many different versions of that as there are people."

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

Tuning in and tuning out

Mexican free-tailed bats (Tadarida brasiliensis) are remarkable animals.  They live in staggeringly huge colonies.  The largest known, in Bracken Cave in Comal County north of San Antonio, Texas, has twenty million bats.  I got to see a smaller (but still impressive) colony, in Carlsbad Caverns National Park, New Mexico, when I was a kid, and I'll never forget the sight of the thousands and thousands of bats streaming out of the cave mouth at dusk.

Free-tailed bats echolocate, which you probably already knew; they navigate in the dark by vocalizing and then listening for the echoes, creating a "sonic landscape" of their surroundings accurate enough to snag an insect out of the air in pitch darkness.  But this engenders two problems, which I honestly never though of until they were brought up by the professor of my Vertebrate Zoology course when I was in graduate school:

1. If these bats live in groups of millions of individuals, how do they tune in to the echoes of their own voices, distinguishing them from the cacophony of their friends and family all vocalizing at the same time?
2. In order to echolocate, they must have exquisitely sensitive hearing.  They're picking up the faint echoes of their own calls with an accuracy that allows them to detect the contours and motion (if any) of the object they're sensing.  To create an audible echo, they have to vocalize really loudly.  So how does the original vocalization not deafen those sensitive ears?

The answer to the first was discovered by some research at the University of Tübingen back in 2009.  Using recordings, scientists found that bats are sensitive not only to the echoes themselves, but can pick out from those echoes enough information about the sonic waveform that they can recognize their own voices.  Each bat's voice has a distinct, if not unique, sonic "fingerprint" -- much like human voices.

The answer to the second is, if anything, even more astonishing.  Just as humans do, bats have three tiny sound-conducting bones in their middle ear -- the malleus, incus, and stapes (commonly known as the hammer, anvil, and stirrup) -- that transmit sound from the eardrum into the cochlea (the organ of hearing).  Bats have a tiny muscle attached to the malleus, and when they open their mouths to vocalize, the muscle contracts, pulling the malleus away from the incus.  Result: dramatically decreased sound transmission.  But even more amazing, as soon as they stop vocalizing, the muscle relaxes -- fast enough to bring the malleus back in contact with the incus in time to pick up the echo.

Bats, it turns out, aren't the only animals to experience these sorts of problems.  The reason this whole topic comes up is because of some research that was published last week in The Journal of Neuroscience.  In a paper called "Signal Diversification is Associated with Corollary Discharge Evolution in Weakly Electric Fish," by Matasaburo Fukutomi and Bruce Carlson of Washington University, we learn about a group of fish called mormyrids (elephant fish) that have, in effect, the opposite problem from bats; they have to find a way to tune out their own communication so they can sense that of their neighbors.

Long-nosed elephant fish (Gnathonemus petersii)  [Image licensed under the Creative Commons spinola, Elefantenrüsselfisch, CC BY-SA 3.0]

Mormyrids communicate by electrical signals; the long "trunk" is actually an exquisitely-sensitive electrical sensor.  They not only use it to pick up electrical signals given off the nerves and muscles of the insect larva prey they feed on, they use it to pick up those sent by other members of their own species.  In effect, they talk using voltage.

Here, though, they have to be able to ignore the voltage shifts in the water around them given off by their own bodies.  It's as if you were in a conversation with a friend, and instead of doing what most civilized friends do -- taking turns talking -- you both babble continuously, and your brain simply stops paying attention to your own voice.

They do this using a corollary discharge, an inhibitory signal that blocks the higher parts of the brain from responding to the signal.  The researchers found that corollary discharges only occurred in response to voltage changes from the individual itself, and not to those from other individuals.

In other words, just like the bats, mormyrid fish can recognize their own communications.  "Despite the complexity of sensory and motor systems working together to deal with the problem of separating self-generated from external signals, it seems like the principle is very simple," said study co-author Bruce Carlson, in an interview with Science Daily.  "The systems talk to each other.  Somehow, they adjust to even widespread, dramatic changes in signals over short periods of evolutionary time."

So there you have it.  Another natural phenomenon to be impressed by.  It reminds me of the wonderful TED talk by David Eagleman called, "Can We Develop New Senses for Humans?" that talks about an animal's umwelt -- in essence, how it perceives the world.  What must the world seem like to a fish that gathers most of its information from electrical signals?

Staggers the imagination, doesn't it?

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Fan of true crime stories?  This week's Skeptophilia book recommendation of the week is for you.

In The Poisoner's Handbook:Murder and the Birth of Forensic Medicine in Jazz Age New York, by Deborah Blum, you'll find out about how forensic science got off the ground -- through the efforts of two scientists, Charles Norris and Alexander Gettler, who took on the corruption-ridden law enforcement offices of Tammany Hall in order to stop people from literally getting away with murder.

In a book that reads more like a crime thriller than it does history, Blum takes us along with Norris and Gettler as they turned crime detection into a true science, resulting in hundreds of people being brought to justice for what would otherwise have been unsolved murders.  In Blum's hands, it's a fast, brilliant read -- if you're a fan of CSI, Forensics Files, and Bones, get a copy of The Poisoner's Handbook, you won't be able to put it down.

[Note: if you purchase this book using 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!]

Noise alert

The week after I retired I made the mistake of saying to my wife, "I don't know what I'm going to do with all of my free time!"

Two days later we found out we had to have major foundation work done on our house.  I do mean major; erosion and settling on one corner was causing the slab to twist, and if we didn't do something, we were going to have our slab -- and almost certainly our walls -- crack catastrophically.

So yeah.  Me and my big mouth.  It's times like this I have a hard time maintaining my status as Non-Superstitious Guy.

The foundation work required that we more or less gut our formerly-finished basement.  We were already planning on redoing it, just not this completely or this precipitously.  It could be a nice space -- it's got a walk-out (we're built on a hill, which is part of what caused the problem in the first place) and with some messing about it could be a den or even a rental apartment, now that we're empty nesters and it's just me and Carol in this big house.

Me and my son working on demolition.  You can probably see the amazing family resemblance between us.

In any case, this all comes up because of a paper that appeared last week in Nature Communications  about why we perceive some sounds as unpleasant (such as shop vacs, reciprocating saws, dehumidifiers, and air filters -- all of which we had going at once down there).  And it turns out that it's not just the volume (amplitude) of the sound waves.

In "The Rough Sound of Salience Enhances Aversion Through Neural Synchronisation," by Luc H. Arnal, Andreas Kleinschmidt, Laurent Spinelli, Anne-Lise Giraud, and Pierre Mégevand of the University of Geneva, we find that the degree of perceived unpleasantness of a sound has to do with repeated peaks in "fast repetitive modulations" in the sound.  Put simply, there are two kinds of frequency most sounds have: the fundamental frequency of the tone, which we perceive as its pitch; and the rise and fall of overall loudness.  And what the researchers discovered is when that second frequency is between 30 and 150 hertz, we find it really unpleasant.  (One hertz is one vibration per second; so even 30 hertz is fast enough that we're not consciously aware of it as a repetitive noise.)

Apparently sounds in that range cause our neurons to synchronize at that frequency, heightening awareness and making them difficult to ignore.  The researchers suspect that it may be an evolved response because those sorts of noises may signal danger, but that's speculation at this point.

The authors write:

Fast repetitive modulations produce “temporally salient” flickering percepts (e.g. strobe lights, vibrators, and alarm sounds), which efficiently capture attention, generally induce rough and unpleasant sensations, and elicit avoidance.  Despite the high ecological relevance of such flickering stimuli, there is to our knowledge no existing operational definition of temporal salience and only limited experimental work accounting for the intriguing aversive sensation such auditory textures produce and the reactions they trigger.  Here, we introduce and explore the notion of temporal salience and investigate its behavioural and neural underpinnings.  Of note, although salience may not systematically result in aversive percept, we argue that in this specific context, temporal salience—owing to the imperative effect of exogenously saturating perceptual systems in time—constitutes a valid proxy of aversion.  Therefore, we hypothesise that providing fast, but still discretisable and perceptible, temporally salient acoustic cues should enhance neural processing and ensuing aversive sensation.

This discovery led to some surprising connections.  "These sounds solicit the amygdala, hippocampus and insula in particular, all areas related to salience, aversion and pain.  This explains why participants experienced them as being unbearable," said Luc Arnal, who was the paper's lead author.   "This is the first time that sounds between 40 and 80 hertz have been shown to mobilise these neural networks, although the frequencies have been used for a long time in alarm systems...  We now understand at last why the brain can't ignore these sounds.  Something particular happens at these frequencies, and there are also many illnesses that show atypical brain responses to sounds at 40 Hz.  These include Alzheimer's, autism and schizophrenia."

Which is unexpected and startling.  What is happening in the brain at those frequencies -- and how does it connect with overall mental functioning?  Does schizophrenia (for example) involve some sort of "brain noise" that is at a frequency that the sufferer can't ignore?

In any case, it's a fascinating piece of research, and on a more banal level explains why I find that shop vac so damned annoying.  At least we've got the demolition done, so I won't have any more huge messes to clean up.

Unless the universe is listening and causes some catastrophic upheaval in another part of our house.  You never know.  Just because I'm not superstitious doesn't mean I can't jinx myself.

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This week's Skeptophilia book recommendation is by the team of Mark Carwardine and the brilliant author of The Hitchhiker's Guide to the Galaxy, the late Douglas Adams.  Called Last Chance to See, it's about a round-the-world trip the two took to see the last populations of some of the world's most severely endangered animals, including the Rodrigues Fruit Bat, the Mountain Gorilla, the Aye-Aye, and the Komodo Dragon.  It's fascinating, entertaining, and sad, as Adams and Carwardine take an unflinching look at the devastation being wrought on the world's ecosystems by humans.

But it should be required reading for anyone interested in ecology, the environment, and the animal kingdom. Lucid, often funny, always eye-opening, Last Chance to See will give you a lens into the plight of some of the world's rarest species -- before they're gone forever.

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