Sounding off

Ever have the experience of getting into a car, closing the door, and accidentally shutting the seatbelt in the door?

What's interesting about this is that most of the time, we immediately realize it's happened, reopen the door, and pull the belt out.  It's barely even a conscious thought.  The sound is wrong, and that registers instantly.  We recognize when something "sounds off" about noises we're familiar with -- when latches don't seat properly, when the freezer door hasn't completely closed, even things like the difference between a batter's solid hit and a tip during a baseball game.

Turns out, scientists at New York University have just figured out that there's a brain structure that's devoted to that exact phenomenon.

A research team led by neuroscientist David Schneider trained mice to learn to associate a particular sound with pushing a lever for a treat.  After learning the sound, it became as habituated in their brains as our own expectation of what the car door closing is supposed to sound like.  If after that the tone was varied even a little, or the timing between the lever push and the sound was changed, a part of the mouse's brain began to fire rapidly.

The activated part of the brain is a cluster of neurons in the auditory cortex, but I think of it as the "What The Hell Just Happened?" module.

"We listen to the sounds our movements produce to determine whether or not we made a mistake," Schneider said.  "This is most obvious for a musician or when speaking, but our brains are actually doing this all the time, such as when a golfer listens for the sound of her club making contact with the ball.  Our brains are always registering whether a sound matches or deviates from expectations.  In our study, we discovered that the brain is able to make precise predictions about when a sound is supposed to happen and what it should sound like...  Because these were some of the same neurons that would have been active if the sound had actually been played, it was as if the brain was recalling a memory of the sound that it thought it was going to hear."

As a musician, I find myself wondering if this is why I had such a hard time unlearning my tendency to make a face when I hit a wrong note, when I first started performing on stage.  My bandmates said (rightly) that if it's not a real howler, most mistakes will just zoom right past the audience unnoticed -- unless the musician clues them in by wincing.  (My bandmate Kathy also added that if it is a real howler, just play it that way again the next time that bit of the tune comes around, and the audience will think it's a deliberate "blue note" and be really impressed about how avant-garde we are.) 

My band Crooked Sixpence, with whom I played for an awesome ten years -- l. to r., Kathy Selby (fiddle), me (flute), John Wobus (keyboard)

I found it a hard response to quell, though.  My awareness of having hit a wrong note was so instantaneous that it's almost like my ears are connected directly to my facial wince-muscles, bypassing my brain entirely.  I did eventually get better, both in the sense of making fewer mistakes and also responding less when I did hit a clam, but it definitely took a while for the flinch response to calm down.

It's interesting to speculate on why we have this sense, and evidently share it with other mammals.  The obvious explanation is that a spike of awareness about something sounding off could be a good clue to the presence of danger -- the time-honored trope in horror movies of one character saying something doesn't seem quite right.  (That character, however, is usually the first one to get eaten by the monster, so the response may be of dubious evolutionary utility, at least in horror movies.)

I find it endlessly fascinating how our brains have evolved independent little subunits for dealing with contingencies like this.  Our sensory processing systems are incredibly fine-tuned, and they can alert us to changes in our surroundings so quickly it hardly involves conscious thought.

Think about that the next time your car door doesn't close completely.

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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!]

Giving weight to illusion

The idea that our sensory processing apparatus and our brains are unreliable has been something I've come back to again and again here at Skeptophilia.  "I saw it with my own eyes" is simply not enough evidence by which to make any kind of sound scientific judgment.

Not only are we likely to get things wrong just because the equipment is faulty, our prior ideas can predispose us to get things wrong in a particular way.  Think of it as a sort of built-in confirmation bias; our brains are set up in such a fashion that when we've already decided what's going to happen, it's much more likely that's what we'll perceive.

This latter problem was demonstrated in an elegant, if disturbing, fashion in a paper released last week in Science called "Pavlovian Conditioning–Induced Hallucinations Result From Overweighting of Perceptual Priors," by Albert R. Powers, Christoph Mathys, and Philip R. Corlett, of the Yale School of Medicine, the International School for Advanced Studies (Trieste, Italy), and the University of Zurich, respectively.  Their research springboarded from previous studies wherein individuals who had been trained to associate a tone with an image were more likely to continue "hearing" the tone when shown the image with no accompanying tone than were members of a control group.

[image courtesy of the Wikimedia Commons]

What Corlett's team did was to divide participants into four groups: normal, healthy individuals; self-described psychics; individuals with psychosis who did not report hearing voices; and individuals with schizophrenia who reported hearing voices.  The researchers trained all test subjects to associate a checkerboard image with a one second long, one kilohertz tone.  They not only recorded data on which participants continued to "hear" an illusory tone when shown the checkerboard in silence, they also used a protocol (how hard they pushed the button when they heard the tone, whether real or imagined) to gauge their confidence in what they were experiencing, and they looked at neuronal activity in the brain using an fMRI machine.

The results were intriguing, to say the least.  Both the schizophrenics and the self-described psychics were five times as likely to report hearing a tone when none existed than either the control group of healthy individuals or the psychotic individuals who did not hear voices.  Not only that, the schizophrenics and the psychics were 28% more confident in their perceptions when they did hear a tone that wasn't there than were the other two groups when they made a similar mistake.

Further, the schizophrenics and psychics showed abnormal neuronal activity in two regions of the brain; the parts of the cerebrum involved in creating our internal representation of reality showed strikingly different firing patterns, and the cerebellum -- the part of the brain involved in planning and coordinating our motor responses to stimuli -- showed much lower than normal neuronal activity.

"The findings confirm that, when it comes to how we perceive the world, our ideas and beliefs can easily overpower our senses," said Albert Powers, one of the paper's authors.  Which is about as succinct a cautionary statement about trusting our judgments as I can imagine.

While the researchers specifically tested the likelihood of experiencing auditory hallucinations, I find myself wondering if this study might not have wider applications.  How do our prior perceptions bias us in general?  I know I have frequently been baffled, especially in these fractious times, how two people can see the same event and come to strikingly opposite conclusions about it.  At times, I have found myself asking, "Are we even talking about the same thing, here?"  But if our preconceived notions about the world can bias us strongly enough to hear sounds that aren't there, why should any other perception be immune to the same effect?

This possibility drives me to a disturbing conclusion.  How do you convince people that what they're perceiving is not real, if that conclusion is contrary to what their senses and their brains are telling them?

I think the key, here, is always to keep focused on the statement, "... but I might be wrong."  A lot of our faulty judgments are caused not only by our coming to the wrong conclusion, but our stubborn certainty that we are, in fact, right.  A willingness to revise our beliefs -- failing that, at least to consider the possibility that our beliefs are incorrect -- is absolutely critical.

Otherwise, we're at the mercy of sensory apparatus that are easily fooled, and a brain that bases what it perceives as much on what it already thought to be true as on the actual data it's presented with.

Which seems to me to be awfully shaky ground.

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 just found out what's happening in the brain that causes this oddity in auditory perception.  In a paper in Nature: Communications that came out earlier this week, 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.