
A Sound You Can't Unhear (And What It Says About Your Brain) - givan
http://www.theatlantic.com/technology/archive/2014/06/sounds-you-cant-unhear/373036/
======
shmageggy
Since this is a technically inclined audience, here's a tiny bit of
mathematical background.

When Ms. Das says that our brains constantly use prior information, she
(probably) means prior in a certain specific, technical sense. Modern
cognitive scientists often think about perception and cognition in
probabilistic terms, so you might characterize the brain's task in
interpreting that utterance as finding the most probable sentence ( _S_ )
given the acoustic input ( _X_ ), or P( _S_ | _X_ ). Bayes' rule says you can
write this expression as P( _X_ | _S_ )P( _S_ )/ _Z_ , where _Z_ is a
normalizing constant (don't worry about it for now).

Because these expressions are so common, we've come up with names for
referring to their parts. The first part, P( _X_ | _S_ ), is called the
likelihood, which tells us how probable the input we experienced would be
given a particular interpretation. For instance, if the sentence actually read
"competition center" rather than "Constitution center", the sound in the
recording would be less likely (although maybe still possible, aka non-zero
probability, due to noise, speaker variance, etc). The second part, P( _S_ ),
represents the prior probability of the sentence. Given our knowledge of
English, some sentences are simply more likely than others. For instance, the
sentence "colorless green ideas sleep furiously" is grammatically well-formed
but tremendously unlikely.

So, to conclude, when the presenter says we use prior information, she
(probably, no pun intended) means that upon hearing what the correct
interpretation should be, we increase the value of P( _S_ ), thereby allowing
us to compute the proper perception.

Here's a nice and fairly readable overview paper (with a whole section on
prior knowledge) if you think this stuff is as cool as I do --
www.indiana.edu/~kruschke/articles/JacobsK2010.pdf

*edits for clarity and formatting

~~~
troymc
The Bayes Model is certainly a nice way to combine old and new information in
an optimal sort of way.

But is it _really_ a good model of what goes on inside the brain? Where? How?
It seems too clean, too pat, too optimal. Biology is messy.

The paper says, "Bayesian models are not intended to provide mechanistic or
process accounts of cognition." We deserve better.

~~~
shmageggy
This is a great point and one that cognitive scientists have a successful and
productive way to think about. What you are after, and rightfully so, is an
_algorithmic_ account of the mind. You'd like to know what steps our minds are
actually taking to compute whatever it is computing. However, with something
as mysterious and complex as the mind, even knowing what it is we're computing
is far from trivial.

That's where the account I sketched above comes in, usually referred to as a
_computational_ level explanation. It defines what the actual problem is that
the mind is solving and gives mathematical constraints (and predictions) about
behavior. The distinction between the two levels is subtle -- even published
papers conflate or ignore it. However it's extremely important. Reverse-
engineering the algorithm we use to perform that listnening/interpretation
task is already extremely difficult, but it would be _even harder_ without
having any of the above formalization. The computational account sets up the
goalposts, so to speak.

Now, there's actually a third level as well. Even once you've written down
your algorithmic-level account, that says nothing about how the brain
implements that algorithm. That further explanation is referred to as the
_physical_ level, the level of implementation by neurons.

If you want to read more, this paradigm is known as Marr's levels of analysis.
[https://www.google.com/search?q=marr's+levels](https://www.google.com/search?q=marr's+levels)

------
reporter
This is really interesting to me. I can't hear it and I am a native english
speaker. I was just in a room of people and played it and everyone clicked
into the meaning right away. I played it about seven more times and I guess I
kind of hear it now, but still, not really.

I did horrible in elementary school and high school until I realized I was
what I labelled myself a "visual learner". I excelled in college and am just
about to finish my PhD in evolutionary biology, largely because I stopped
attending lectures and decided to learn everything on my own. After listening
to this illusion I decided to search for auditory dyslexia and sure enough
there are disorders like this and I definitely fit the definition, especially
central auditory processing disorder. Does anyone know if this test is
correlated with audio disorders or where I can get more information on this?

~~~
dbbolton
I wonder if I have something similar. Often times when someone spells a word
or recites a number, it's as if I'm completely "spaced out" and don't get any
of the information (while actively paying attention) _unless_ I make a
conscious effort to visualize the letters/digits as they are being spoken. I
also frequently experience visual disturbance type dyslexia when reading and I
always assumed the two phenomena were somehow related.

------
atesti
I'm not a native speaker and I feel a similar effect to have happened to me
very often with song lyrics: Parts I could not understand clearly are like
text that makes no sense, I hear other words than the real ones. Once I read
through the lyrics, I always hear the right words, the real text.

~~~
weinzierl
I'm not a native speaker too and I often experienced what you described.
Interestingly the "The Constitution Center is at the next stop." sample didn't
work for me at all. Sounds like gibberish no matter how often I hear it.

~~~
weinzierl
I see my previous post twice, as regular comment and as dead comment. Does
that mean I'm shadow banned?

~~~
eridius
It means you double-posted and the second post was killed.

~~~
weinzierl
Ok, thanks. I have no idea how I managed to double post but that is the most
likely explanation.

~~~
jacquesm
Typical causes:

HN timing out on a submission of a comment, but it got saved anyway. Then you
click 'back' or 'refresh' and it posts it again.

The second possibility is double clicking on the submission form (most
browsers will not allow a second submission to be sent in that case).

In either situation one of the two comments will be dead, the other will
survive because HN checks for exact duplicate comments and marks duplicates as
dead.

------
suprgeek
The first time I encountered this effect was when I was listening to this TED
Talk "Michael Shermer: Why people believe weird things"
[https://www.youtube.com/watch?feature=player_detailpage&v=8T...](https://www.youtube.com/watch?feature=player_detailpage&v=8T_jwq9ph8k#t=566)

The whole thing is worth a listen ..but in the relevant clip he talks about
audio illusions and gives a great example.

This just reinforces the lesson, it is the Brain that is Hearing!

~~~
noir_lord
Excellent link and now I'm a fan of Katie Melua (not her music just her for
having the humour to redo her song).

------
brainless
This article brings me back to a thought I have been having for some time now
- could we use illusions (audio, visual) to distinguish between humans and
bots?

If CAPTCHAs are becoming increasingly easier to break, could illusions give
stronger guarantees because they use more inherent "human" features of our
brain - things that bots will not easily decipher in the foreseeable future?

~~~
srean
Not all illusions are universal, but what a fantastic idea, very clever.

------
Riseed
[SPOILER ALERT!]

The first time through, I heard "[jibberish jibberish jibberish] is at the
next stop." (Perhaps I've spent too much time on public transport.) What does
that say about my brain?

But yes, once I heard the whole sentence, I couldn't _not_ hear it.

~~~
interpol_p
Had you read the sentence prior to listening? I found that just reading the
sentence once in the article caused me to understand the distorted version
without having listened to the plain version.

~~~
michaelsbradley
Having read the sentence before listening to the jibberish version, I clearly
understood each word. It wasn't more or less clear to me after hearing the
non-jibberish version.

~~~
Springtime
I had read the text beforehand, and could make out parts of the words but I
was surprised how much clearer the distorted recording became once I heard the
original.

------
the_cat_kittles
this might be a good lesson in why its so hard to have insights sometimes. in
this case, you need to exert energy to _not_ hear the words after you know
what the phrase is. in the context of problem solving, maybe this phenomenon
can cause you to stick at a local maximum- your brain is forcing the
information to conform to your best mental model, and that makes your search
for a more optimal solution even harder. those visually ambiguous pictures
that have two or more "sticking points" are another example. in any case, that
audio example is an absolutely amazing example!

------
srean
It is really interesting and amusing how persistent certain 'illusions' can be
even when one is exposed to it just once and for a short time.

Fun story, this was a long time ago: I was interning at Google at that time.
One day I tell my then cube neighbor about an interesting experiment on visual
perception that I had read about. A professor at MIT had carried out
experiments on his class. Students were asked to wear prismatic goggles that
shifted their vision and then try to catch objects. Hilarity ensued, but soon
enough the brain adapted to the shift. Same with inverting glasses, soon the
students would not even realize that their vision was inverted. The fun part
was when they took their glasses off, their motor reflexes would still
compensate assuming that they were wearing those glasses. Much hilarity again.
I was telling all this to my cube neighbor Michael Riley, not knowing who he
was, he says with a twinkle in his eye "Yeah, that was us".

The most remarkable thing about these experiments that I learned from him was
that the professor would provoke an illusion on the students on the first day
of class. I dont remember exactly what the illusion was, but it was some
visual artifact, seeing patterns that werent visible a moment ago, much like
the OP. At the end of the semester the professor would demonstrate that the
entire class could still see that illusion, although they have not been
exposed to it in the intervening 4 months !

I tried hard to find an articles on these experiments and phenomena, but my
google fu is not working today. I distinctly remember wikipedia articles on
it, but am not able to retrieve them. Either my keyword memory has gone down
or Google's search quality/relevance.

Navigating Google was such a nerd minefield, but in the best possible way. The
excited student that I was, I ended up lecturing about longest common
subsequence to Thomas Szymanski not knowing his association with the history
of diff on unix. Same thing happened with SVM's, I was explaining its merits
and demerits to Corinna Cortes, my other cube neighbor, not knowing she was
the first author of the paper on SVMs. Not only would they not take offence
they would all keep indulging. Then one day I step out for a break, a senior
person whom I knew had a cube on the row behind me, approaches me, apologizing
profusely and ad infinitum that he had got locked out, could I please let him
in. No big deal, but he just would not stop apologizing and thanking me. A few
days later a co-intern asks me if I know that guy. I said sure, I let him in
once. He says no, do you know who he is. He asked me to checkout the name tag
on his cube. I saunter off, "Brian Kernighan" !

An important takeaway of this internship was to experience the humility of all
these people, and the sense that you are surrounded by such iconic stalwarts
in CS and you wouldn't even know it because they are so... normal.

Coming back to illusions, another visual/auditory one that does not stop
working even when you know exactly what is going on is the McGurk effect
[https://www.youtube.com/watch?v=G-lN8vWm3m0](https://www.youtube.com/watch?v=G-lN8vWm3m0)

EDIT Ummm so many downvotes ? I did not see that coming, would greatly
appreciate what you found downvote worthy. It is always insightful to know how
ones comment may rub someone the wrong way. Feel free to reply, I promise no
offence will be taken and I will learn something along the way.

@tbirdz thanks for the perspective, I did not realize that it could come off
as bragging. IMO you can brag only about things that you have achieved using
your own efforts. For me it was a mix of foot in the mouth and an important
learning experience, especially in humility.

~~~
tbirdz
I would assume the downvote is for the extended discussion, bordering on
bragging about your internship at google. The first comment was relevant to
the story, but the part about how you got to work with famous people in
computer science was not. I don't really have a problem with that myself, but
I could see how that could cause someone to downvote.

------
jtchang
For some reason I can't seem to hear it. I just hear the general tempo and
beat but not the words.

~~~
Lost_BiomedE
Same here. My brain can translate it due to the tempo and inflection, but I do
not hear it in the way that I see a ghost image in the common optical
illusion.

~~~
B-Con
I got nothing. After looping the video twice, the third time I still had no
association between the sound and the sentence. As I write this, I can't even
remember what the sentence was.

Interestingly, I have a horrible auditory memory and have a dreadful time
deciphering accents. I would guess that it's not coincidence.

------
ajuc
I've read the description before listening to the sample and I've heard it the
first time.

Not a native speaker. if that's important.

~~~
zapu
Same here. It felt like I ruined this whole experiment for myself ;-)

------
Luyt
Not really an illusion, but a case of pareidolia. Our brain is wired to
recognize patterns in chaos, even the more so when _prompted in advance_.
Another example is 'seeing faces' in everything that vaguely resembles a face.

There's a skeptoid episode about this phenomenon:
[http://skeptoid.com/episodes/4105](http://skeptoid.com/episodes/4105), 'When
People Talk Backwards'. Is has more audio examples, from the same researchers.
They were using _" three-tone sinusoidal replica", or a complicated sine wave
sound. They found that people were able to perceive speech, when in fact there
were no traditional speech sounds present in the signal._ (from the skeptoid
podcast transcription).

~~~
pcrh
It is also similar to the well-known phenomenon of Mondegreens. My favorite
being the Beatles phrase "the girl with colitis goes by" in Lucy in The Sky
with Diamonds

[https://en.wikipedia.org/wiki/Mondegreen](https://en.wikipedia.org/wiki/Mondegreen)

------
baby
Doesn't really work on me, maybe because I'm not a native speaker?

~~~
BoppreH
Same here. It sounds like someone playing with a weird instrument and is not
even close to a human voice. It reminds me of the beeps from R2D2 in Star
Wars, but with less abrupt transitions.

After many tries still no comprehension.

~~~
hysan
I'm a native speaker who used to commute to work by train every day but have
been living in Japan for 3 years (rural area, no other English speakers in my
town). I was a bit curious because after hearing the phrase, I could only hear
the resemblance and not the full phrase. So I did an experiment.

I replayed it a second time to try and remember the sounds. Then I went and
did some work for 2+ hours before coming back to HN. I played the clip and the
sounds became gibberish again until I reheard the phrase.

I'm going to try this again tomorrow (if I remember), but my guess is that the
ability to hear & unhear the sound is dependent on how much natural English is
used around you. The less it is used around you, the less your brain is
actively trying to match sounds to an English pattern. In my case, my brain is
most likely trying to map sounds to Japanese rather than English because that
is all I hear around me.

~~~
hysan
Did it again a day later and same result. Though I noticed that the more I
replayed the clip, the easier it got for me to "hear" the phrase within the
distorted clip.

------
ChuckMcM
I think it is fascinating that I can hear it and my wife can't. The only
difference I can imagine is that I play music and she doesn't so perhaps I've
trained myself a bit to pick out structure. Conversely she can see those 3D
images when you hold up the picture to your face and I can't.

It gave rise to another thought, is there an audio equivalent of color
blindness? Not deaf so much as unable to process certain sounds?

~~~
Asparagirl
Yup, Central Auditory Processing Disorder (CAPD). It tends to run in families,
too.

------
arikrak
Once you understood the distortion, could you understand new words too? It
would be cool to play around with recordings and distortions to try it out...

------
alan_cx
Slightly bemused by the reaction. From what I can make out, this is is the
same as when someone speaks in a thick accent and you can't understand them
until something else prompts you as to what they are saying, then suddenly
more of what they say becomes clear. Maybe here in the UK, accents are much
wider apart than they are in the US.

~~~
bane
It depends where in the U.S. For big swaths of the country you really only
have to deal with 1 or 2 accents: the local and the mid-west neutral (used on
the National News).

But on the coasts it's about (but not quite) as complex as London might be.
New York may be the king of all accent centers in the U.S. (followed maybe by
D.C. or L.A.) You get all the various New York accents (not unlike London's
various native accents), various native ethnic accents (like AAVE, which even
has accents within), regional accents, the various north East Coast accents
(every city from Boston to D.C. all have different native accents) as well as
rural accents, you also get all the various local accents from the U.S. and
Canada since everybody ends up in NYC, then you get all the foreign accents
(at various levels of English attainment) from immigrants and tourists and
finally you also get all the various native-English accents, including many
(but not all) of the ones from the UK.

To be fair, the distance between native accents in the U.S. is generally not
quite as far as between native accents in the U.K. I've been in the U.K. and
Ireland a few times and there really were places I ended up where the local
accent was not intelligible to me, and I struggled at times in London. I also
notice generally wider distance between the various accents in London that I
assumed were native London accents than I've experienced anywhere in a single
place in the U.S.

------
thinkersilver
I'm a native speaker of English, and I speak a few other European languages.
I'd like to add my experience. I listened to the recording and in both cases
it sounded like gibberish. Hearing the translation did not help and I listened
to it 8-9 times trying to get the effect. This result did not surprise me
since, I tend to be quite pedantic on pronunciation when hear language being
spoken, even languages which are my second or third. I've been known to
correct native speakers of lanaguage I am learning. After reading this article
I think that I am not very good at using prior knowledge to understanding
phrases spoken in any language. If I were, I would not hold onto pronunciation
as crutch for comprehension, hence my need for everyone to speak clearly and
well for me to follow. It's just a thought.

------
wcoenen
A Kalman Filter[1] keeps an internal model of the thing it is measuring to
maximize the information it can extract from noisy sensory input.

Our brain likely does something similar for the same reason.

[1]
[http://en.wikipedia.org/wiki/Kalman_filter](http://en.wikipedia.org/wiki/Kalman_filter)

------
fela
This and the linked "you can't unsee article" are great example of how our
perception is very far from a direct representation of the world, and instead
is the end result of a complex processing happening inside our brain.

Another example of the same effect (although here actually there _is_ no real
message) can be heard in songs when listened to in reverse (for example see
[1]). One lesson to learn might be: be wary of our brain recognizing patters,
it tends to err on the side of seeing patterns when there are none. I would
argue that religion and superstition are examples of this.

[1]
[https://www.youtube.com/watch?v=mlvFkws9PYY](https://www.youtube.com/watch?v=mlvFkws9PYY)

------
dully
You know when you learn a new word, and then you suddenly start seeing it
everywhere? You've probably been seeing the word your entire life but you
haven't noticed it because you didn't know what it meant. This is pretty
similar.

------
tobr
Great effect.

I would love to hear _another_ sentence distorted the same way, though,
because I wonder if I just learned to recognize this particular sentence, or
if I learned to separate the signal from the noise in this type of distortion.

~~~
gwern
Here's some more:
[http://www.lifesci.sussex.ac.uk/home/Chris_Darwin/SWS/](http://www.lifesci.sussex.ac.uk/home/Chris_Darwin/SWS/)

Apparently this is called 'sine-wave speech' and is an example of 'perceptual
set' ([http://www.simplypsychology.org/perceptual-
set.html](http://www.simplypsychology.org/perceptual-set.html))

------
oakwhiz
The processing that produced the masked audio sample is very similar to the
processing behind low-bitrate lossy voice codecs. I wonder what sort of
program they used to produce it.

Perhaps one method of doing this would be to compute the lapped discrete
cosine transform of the input signal, and then turn that into power spectrum
density over time. For each time interval, take the N most intense frequency
bins, and then create N sine waves at those frequencies.

It's kind of like having a set of beeping noises that follow the pitch of the
loudest component of the sound.

------
emgeee
This reminds me of when people talk about hearing demonic messages in popular
songs when played backwards. I think Stairway to Heaven is one of the more
famous examples

~~~
__david__
It reminded me of the Ghost Hunters show, where they are constantly playing
spooky audio that they recorded and finding words and sentences in it. It's
almost _always_ the same format as in this article: play some spooky sound,
then say what they think it says and then play it again (with subtitles). You
can almost _always_ hear the words after they are suggested. But then they
treat this like _actual_ evidence of ghosts :-/.

Also, this phenomena is occurring to me frequently as my 2 year old nephew is
learning to talk. He tries to communicate with me, saying a word over and over
and it doesn't click until he points at the object he's talking about or my
sister tells me what he's saying and then his mangled speech suddenly makes
complete sense.

Our brains are so cool.

------
byuu
If you like Game of Thrones, do _not_ watch the South Park - Black Friday
trilogy. There's a .... _rendition_ of the opening song, where they add in
some lyrics to the song. It becomes almost impossible to listen to the
original song again without your brain humming in the South Park lyrics, which
really detract from the mood of the song, to say the least.

------
HappyDuck
When I was a kid I used to love listening to black and death metal. In these
genres of music the vocalists do not... sing but more like growl or yell which
makes deciphering the lyrics very difficult.

But after reading the lyrics first then you can make sense what they 're
saying without a problem.

If you 're looking for such "audio illusions" try it yourself :)

------
byteface
I noticed if i imagined hearing. "they can't if you should sell her, is that
the next step" instead, and told myself it was that. I went through similar
mental processing. This probably fits into the memory/prediction model
explained by Jeff Hawkins. the mind is a layer of interpretation over the
world but also fills bits in.

------
bane
My wife is not a native English speaker and couldn't hear the sentence in the
distorted version even after listening to the whole thing a few times. I
suspect that this is tied in deeply with our native language faculties.

I'd be interested in how this works for other non-native speakers here as well
as "native" bi-lingual speakers.

------
Nevermark
Listen to Eiffel 65's Blue (Da Ba De) song and when you here this:

    
    
      I'm blue da ba dee da ba die...
    

Think this for one pass through the song:

    
    
      I'm blue,
    
      I bleed, I will die, I be-lieve I will die
    
      I bleed, I will die, I be-lieve I will die...
    

Now rewind and try NOT to hear that.

------
teekert
This is the basis of a popular radio segment in the Netherlands (Mama
Appelsap). Someone calls in claiming to hear a specific dutch sentence in an
English song. They tell you what to hear, they play it and you can't un-hear
it. It's always funny. If you're dutch, Google "Mama Appelsap".

------
miralabs
I remember this talk by Michael Shermer: Why people believe weird things. It
has exactly what the article is saying.
[http://www.youtube.com/watch?v=8T_jwq9ph8k#t=572](http://www.youtube.com/watch?v=8T_jwq9ph8k#t=572)

------
bostik
Okay - any bets on which company or advertising agency will be the first to
apply this research to generate an irresistible earworm?

As many have already noted, this works best with native speakers. Sounds like
(no pun intended) built-in demographic targeting.

------
tomsun
[http://www.youtube.com/watch?v=mlvFkws9PYY](http://www.youtube.com/watch?v=mlvFkws9PYY)
It's just like this.

------
mrottenkolber
But the rythm pattern is identical, of course your breain will regognize that,
and to prove that point to you, overlay your recording and the gibberish.

------
opendais
Did anyone else find the only part of the jibberish they heard was "...next
stop" and they heard it on the first pass?

~~~
rm445
FYI the normal spelling of that word is 'gibberish'.

Seems odd that that site would let an article through with a repeated spelling
error, but it's an easy one to make.

------
ryanmim
This is interesting, but I don't see how it is news. Our brains can take
gibberish and impart meaning to it if we are looking for it (as our brains are
primed to in the example in this article). Maybe I'm missing the new insight,
but this seems like a very old and already known thing. This is basically why
you can see faces in clouds and things as weird as moldy bread--because your
brain is looking for faces.

------
dav-
Wow, that's so cool - are there any other examples of these audio illusions?

~~~
shutupalready
Yes, thousands of them in the context of listening to songs:

[http://en.wikipedia.org/wiki/Mondegreen](http://en.wikipedia.org/wiki/Mondegreen)

------
nomnombunty
nooooo i cannot unhear it! #foreverstuck

------
dickdales
I really don't like the philosophers anecdote about cognition and perception.
Why is it so shocking that perception is simply a chemical reaction to sensory
input and cognition is an identified repetition of such?

~~~
ars
> simply a chemical reaction

Simply? Really? Don't seem remotely simple to me.

