A Sound You Can't Unhear (And What It Says About Your Brain)
theatlantic.com
theatlantic.com
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
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.
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
fun
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?
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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!
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?
I can't think of one that would reveal information but be near impossible to simulate.
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.
You make a good point--during that time, I suppose it's quite possible that my brain scanned and processed enough of the remaining visible text to spoil the effect.
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
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.
You keep using that word...
Interestingly, I have a horrible auditory memory and have a dreadful time deciphering accents. I would guess that it's not coincidence.
Not a native speaker. if that's important.
There's a skeptoid episode about this phenomenon: 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).
After many tries still no comprehension.
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.
It's still interesting, though.
It gave rise to another thought, is there an audio equivalent of color blindness? Not deaf so much as unable to process certain sounds?
If you played several samples to the audience, they'd start to recognise more words.
Actually, I think she influences the outcome by telling her audience the spoken sentence has been "transformed into gibberish". By doing this she has planted the expectation to not comprehend the sound, since "gibberish" by nature cannot be understood.
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.
Our brain likely does something similar for the same reason.
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.
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.
Apparently this is called 'sine-wave speech' and is an example of 'perceptual set' (http://www.simplypsychology.org/perceptual-set.html)
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.
http://reversespeech.com/reversal/popular-reverse-speech-exa...
http://en.wikipedia.org/wiki/Reverse_speech
http://www.tcprs.com/evps.html (disembodied voice examples.)
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.
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 :)
I'd be interested in how this works for other non-native speakers here as well as "native" bi-lingual speakers.
I'm blue da ba dee da ba die...
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...
As many have already noted, this works best with native speakers. Sounds like (no pun intended) built-in demographic targeting.
Seems odd that that site would let an article through with a repeated spelling error, but it's an easy one to make.
Simply? Really? Don't seem remotely simple to me.