Signal out of noise

A paper this week out of the University of Washington describes research suggesting that intelligence is positively correlated with the ability to discern what someone is saying in a noisy room.

This was a little distressing to me, because I am terrible at this particular skill.  When I'm in a bar or other loud, chaotic environment, I can often pick out a few words, but understanding entire sentences is tricky.  I also run out of steam really quickly -- I can focus for a while, but suddenly the whole thing descends into a wall of noise.

The evidence, though, seems strong.  "The relationship between cognitive ability and speech-perception performance transcended diagnostic categories," said Bonnie Lau, lead author on the paper.  "That finding was consistent across all three groups studied [an autistic group, a group who had fetal alcohol syndrome, and a neurotypical control group]."

So.  Yeah.  Not a favorable result for yours truly.  I mean, I get why it makes sense; focusing on one conversation when there are others going on is a complex task.  "You have to segregate the streams of speech," Lau explained.  "You have to figure out and selectively attend to the person that you're interested in, and part of that is suppressing the competing noise characteristics.  Then you have to comprehend from a linguistic standpoint, coding each phoneme, discerning syllables and words.  There are semantic and social skills, too -- we're smiling, we're nodding.  All these factors increase the cognitive load of communicating when it is noisy."

While I'm not seriously concerned that about the implications regarding my own intelligence, it does make me wonder about sensory synthesis and interpretation in general.  A related phenomenon I've noticed is that if there is a song playing while there's noise going on -- in a restaurant, 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 clearly.

A while back, some neuroscientists at the University of California - Berkeley elucidated what's happening in the brain that causes this oddity in auditory perception, and it provides an interesting contrast to this week's study.  A paper in Nature: Communications in 2016, by Christopher R. Holdgraf, Wendy de Heer, Brian Pasley, Jochem Rieger, Nathan Crone, Jack J. Lin, Robert T. Knight, and Frédéric E. Theunissen, considered 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."

It makes me wonder about the University of Washington finding, though, if there might be an association between poor auditory discernment and attention-related disorders like ADHD.  My own experience is that I can focus on what's being said in a noisy environment, it's just exhausting.  Perhaps -- like with the song phenomenon, and things like visual priming -- chaotic brains like mine simply can't throw away extraneous information fast enough to retune.  Eventually, it just gives up, and the whole world turns into white noise.

In any case, 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 predator lying in wait.  

Even if it means that I personally would probably have been a lion's afternoon snack.

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Turning the focus knob

I am really distractible.

To say I have "squirrel brain" is a deep injustice to squirrels.  At least squirrels have the focus to accomplish their purpose every day, which is to make sure our bird feeders are constantly empty.  If I was a squirrel, I'd probably clamber my way up the post and past the inaccurately-named "squirrel baffle" and finally get to the feeder, and then just sit there with a puzzled look, thinking, "Why am I up here, again?"

My "Oh, look, something shiny" approach to life has at least a few upsides.  I tend to make weird connections between things really fast, which long-time readers of Skeptophilia probably know all too well.  If someone mentions something -- say, an upcoming visit to England -- in about 3.8 milliseconds my brain goes, England > Cornwall > Tintagel > King Arthur > Monty Python > the "bring out yer dead" scene > the Black Death > mass burials > a weird study I read a while back about how nettle plants need high calcium and phosphorus soils, so they're often found where skeletons have decomposed, and I'll say, cheerfully, "Did you know that nettles are edible?  You can cook 'em like spinach," and it makes complete sense to me even though everyone else in the room is giving me a look like this:

Talking to me is like the conversational equivalent of riding the Tilt-O-Whirl.

Which, now that I come to think of it, is not really an upside after all.

A more significant downside, though, is that my inability to focus makes it really hard in noisy or chaotic environments.  When I'm in a crowded restaurant or bar, I can pay attention for a while to what the people I'm with are saying, but there comes a moment -- and it usually does happen quite suddenly -- when my brain just goes, "Nope.  Done," and the entire thing turns into a wall of white noise in which I'm unable to pick out a single word.  

All of the above perhaps explains why I don't have much of a social life.

However, as a study last week in Nature Human Behavior shows, coordinating all the inputs and outputs the brain has to manage is an exceedingly complex task, and one a lot of us find daunting.  And, most encouragingly, that capacity for focus is not related to intelligence.  "When people talk about the limitations of the mind, they often put it in terms of, 'humans just don't have the mental capacity' or 'humans lack computing power,'" said Harrison Ritz, of Brown University, who led the study, in an interview with Science Daily.  "[Our] findings support a different perspective on why we're not focused all the time.  It's not that our brains are too simple, but instead that our brains are really complicated, and it's the coordination that's hard."

The researchers ran volunteers through a battery of cognitive tests while hooked up to fMRI machines, to observe what parts of their brain were involved in mental coordination and filtering.  In one of them, they had to estimate the percentage of purple dots in a swirling maelstrom of mixed purple and green dots -- a task that makes me anxious just thinking about it.  The researchers found two parts of the brain, the intraparietal sulcus and the anterior cingulate cortex, that seemed to be involved in the task, but each was functioning in different ways.

"You can think about the intraparietal sulcus as having two knobs on a radio dial: one that adjusts focusing and one that adjusts filtering," Ritz said.  "In our study, the anterior cingulate cortex tracks what's going on with the dots.  When the anterior cingulate cortex recognizes that, for instance, motion is making the task more difficult, it directs the intraparietal sulcus to adjust the filtering knob in order to reduce the sensitivity to motion.

"In the scenario where the purple and green dots are almost at 50/50, it might also direct the intraparietal sulcus to adjust the focusing knob in order to increase the sensitivity to color.  Now the relevant brain regions are less sensitive to motion and more sensitive to the appropriate color, so the participant is better able to make the correct selection."

The applications to understanding disorders like ADHD are obvious, although of course identifying the parts of the brain that are responsible is only the beginning.  The question then becomes, "But what do you do about it?", and the truth is that current treatments for ADHD are a crapshoot at best.  Even so, it'd have been nice if this understanding had come sooner -- it might have saved me from being told by my third grade teacher, unkindly if accurately, "You have the attention span of a gnat."

I apparently haven't changed much, because recalling this comment made me go, gnats > a scene in one of Carlos Castaneda's books where the main character was high on mushrooms and hallucinated a giant man-eating gnat > edible mushrooms, which my wife hates > food preferences > licorice, another thing a lot of people hate > a study I read about using licorice extract to treat psoriasis.

Hey, did you know that the word psoriasis comes from the Greek word ψώρα, meaning "itch"?  I bet you didn't know that.

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The voice of nature

Yesterday I wrote about my difficulty with maintaining concentration.  My mind's tendency to wander has been with me all my life, and at after sixty years of fighting with it I'm beginning to think it always will be.  This, coupled with an unfortunate history of not sticking with things long if I don't see quick results, has been why my attempts to make a practice of meditation have, all things considered, been failures.

I've had more than one person recommend meditation and mindfulness training as a means for combatting depression, anxiety, and insomnia, all of which I struggle with.  I even did a six-week mindfulness training course three years ago, thinking that if perhaps I learned some strategies for dealing with my errant brain, I might be more successful.  But even training didn't seem to be able to fix the fact that when I meditate, I nearly always veer off either into an anxiety attack or else fall asleep.  Steering a middle course -- being relaxed and tranquil enough to gain some benefit from it, but not so relaxed and tranquil that I lose consciousness -- just never seemed to be within my grasp.

Part of my problem is that I have a loud internal voice,  I know we all deal with internal chatter, but mine has the volume turned up to eleven.  And it's not even interesting chatter, most of the time.  I sometimes have looped snippets of songs, usually songs I hate.  (Last week, I woke up at two AM with the song "Waterloo" by Abba running through my head.  God alone knows why.  I don't even like that song during the day.)  Sometimes it's just completely random musings, like while I was running yesterday and pondering how weird the word "aliquot" is.  (For you non-science folks, it means "a sample" -- as in, "transfer a 3.5 ml aliquot of the solution to a test tube."  I also found out, because I was still thinking about it later and decided to look it up, that it comes from a Latin word meaning "some.")

So most of the time, my brain is like a horse that's always on the verge of spooking, throwing its rider, and then running off a cliff.

The topic comes up because of a paper that appeared this week in the journal Psychomusicology: Music, Mind, and Brain, which found that the old technique used for combatting distraction during meditation -- to focus on your breath -- simply doesn't work well for some people.  Not only is it an ongoing battle, a lot of people have the same problem I did, which is taking those mindfulness skills and then applying them during the ordinary activities of the day.

In "Exploring Mindfulness Attentional Skills Acquisition, Psychological and Physiological Functioning and Well-being: Using Mindful Breathing or Mindful Listening in a Nonclinical Sample," by Leong-Min Loo, Jon Prince, and Helen Correia, we read about a study of 79 young adults who were trained in mindfulness and meditation techniques -- but for some of them, they were instructed in the traditional "return to your breath if you get distracted" method, and others were told to focus on external sounds like quiet recorded music or sounds of nature.  Interestingly, the ones who were told to focus on external sounds not only reported fewer and shorter episodes of distraction during meditation, they reported greater ease in using those techniques during their ordinary daily activities -- and also reported lower symptoms of depression and anxiety afterward than the group who mediated in silence.

[Image licensed under the Creative Commons anonym, Bronze figure of Kashmiri in Meditation by Malvina Hoffman Wellcome M0005215, CC BY 4.0]

What's funny is I was just thinking about the idea of soothing sounds a couple of days ago, when I participated in one of those silly online quizzes.  One of the questions was, "What are your favorite sounds?" -- and after I rattled off a few, I realized that all but one of them were natural sounds.  Thunder.  Wind in the trees.  The dawn chorus of birds in spring.  A hard rain striking the roof.  Ocean waves.  (The only one on my list that wasn't natural was "distant church bells at night" -- a sound that reminds me of when I was nine and lived with my grandma for a year, and every evening heard the beautiful and melancholy sound of the bells of Sacred Heart Catholic Church in Broussard, Louisiana, rising and falling with the breeze.)

So maybe it's time to try meditation again, but using some recordings of natural sounds to aid my focus.  I know I'll still have to combat my brain's tendency to yell absurd and random stuff at me, and also my unfortunate penchant for giving up on things too easily.  But something external to focus on seems like it might help a bit, at least with the attentional part of it.

And lord help me, if it purges "Waterloo" from my brain, it'll be worthwhile regardless.

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I'm always amazed by the resilience we humans can sometimes show.  Knocked down again and again, in circumstances that "adverse" doesn't even begin to describe, we rise above and move beyond, sometimes accomplishing great things despite catastrophic setbacks.

In Why Fish Don't Exist: A Story of Love, Loss, and the Hidden Order of Life, journalist Lulu Miller looks at the life of David Starr Jordan, a taxonomist whose fascination with aquatic life led him to the discovery of a fifth of the species of fish known in his day.  But to say the man had bad luck is a ridiculous understatement.  He lost his collections, drawings, and notes repeatedly, first to lightning, then to fire, and finally and catastrophically to the 1906 San Francisco Earthquake, which shattered just about every specimen bottle he had.

But Jordan refused to give up.  After the earthquake he set about rebuilding one more time, becoming the founding president of Stanford University and living and working until his death in 1931 at the age of eighty.  Miller's biography of Jordan looks at his scientific achievements and incredible tenacity -- but doesn't shy away from his darker side as an early proponent of eugenics, and the allegations that he might have been complicit in the coverup of a murder.

She paints a picture of a complex, fascinating man, and her vivid writing style brings him and the world he lived in to life.  If you are looking for a wonderful biography, give Why Fish Don't Exist a read.  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!]

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.

Ignoring the unimportant

Before I get into the subject of today's post, I want all of you to watch this two-minute video, entitled "Whodunnit?"

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How many of you were successful?  I know I wasn't.  I've watched it since about a dozen times, usually in the context of my neuroscience class when we were studying perception, and even knowing what was going on I still didn't see it.  (Yes, I'm being deliberately oblique because there are probably some of you who haven't watched the video.  *stern glare*)

This comes up because of some recent research that appeared in Nature Communications about why it is we get tricked so easily, or (which amounts to the same thing) miss something happening right in front of our eyes.  In "Spatial Suppression Promotes Rapid Figure-Ground Segmentation of Moving Objects," a team made up of Duje Tadin, Woon Ju Park, Kevin C. Dieter, and Michael D. Melnick (of the University of Rochester) and Joseph S. Lappin and Randolph Blake (of Vanderbilt University) describe a fascinating experiment they conducted that shows how when we look at something, our brains are actively suppressing parts of it we've (subconsciously) decided are unimportant.

The authors write:

Segregation of objects from their backgrounds is one of vision’s most important tasks.  This essential step in visual processing, termed figure-ground segmentation, has fascinated neuroscientists and psychologists since the early days of Gestalt psychology.  Visual motion is an especially rich source of information for rapid, effective object segregation.  A stealthy animal cloaked by camouflage immediately loses its invisibility once it begins moving, just as does a friend you’re trying to spot, waving her arms amongst a bustling crowd at the arrival terminal of an airport.  While seemingly effortless, visual segregation of moving objects invokes a challenging problem that is ubiquitous across sensory and cognitive domains: balancing competing demands between processes that discriminate and those that integrate and generalize.  Figure-ground segmentation of moving objects, by definition, requires highlighting of local variations in velocity signals.  This, however, is in conflict with integrative processes necessitated by local motion signals that are often noisy and/or ambiguous.  Achieving an appropriate and adaptive balance between these two competing demands is a key requirement for efficient segregation of moving objects.

The most fascinating part of the research was that they found you can get better at doing this -- but only at the expense of getting worse at perceiving other things.  They tested people's ability to detect a small moving object against a moving background, and found most people were lousy at it.  After five weeks of training, though, they got better...

... but not because they'd gotten better at seeing the small moving object.  Tested by itself, that didn't change.  What changed was they got worse at seeing when the background was moving.  Their brains had decided the background's movement was unimportant, so they simply ignored it.

"In some sense, their brain discarded information it was able to process only five weeks ago," lead author Duje Tadin said in an interview in Quanta.  "Before attention gets to do its job, there’s already a lot of pruning of information.  For motion perception, that pruning has to happen automatically because it needs to be done very quickly."

The last thing a wildebeest ever ignores.  [Image licensed under the Creative Commons Nevit Dilmen, Lion Panthera leo in Tanzania 0670 Nevit, CC BY-SA 3.0]

All of this reinforces once again how generally inaccurate our sensory-integrative systems are.  Oh, they work well enough; they had to in order to be selected for evolutionarily.  But a gain of efficiency, and its subsequent gain in selective fitness, means ignoring as much (or more) than you're actually observing.  Which is why we so often find ourselves in situations where we and our friends relate a completely different version of events we both participated in -- and why, in fact, there are probably times we're both right, at least partly.  We're just remembering different pieces of what we saw and heard -- and misremembering other pieces different ways.

So "I know it happened that way, I saw it" is a big overstatement.  Think about that next time you hear about a court case where a defendant's fate depends on eyewitness testimony.  It may be the highest standard in a court of law -- but from a biological perspective, it's on pretty thin ice.

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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!]