
How Brain Waves Surf Sound Waves to Process Speech - dnetesn
http://nautil.us/blog/how-brain-waves-surf-sound-waves-to-process-speech
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beautifulfreak
I'm baffled by the video of a sound that can be heard as either "green needle"
or "brainstorm," depending on which word one imagines while listening to it.
They don't even have the same number of syllables. I'd like to know what's
going on in the brain to create this auditory illusion.
[https://www.youtube.com/watch?v=5pRY3wlKwm8](https://www.youtube.com/watch?v=5pRY3wlKwm8)

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codetrotter
First I heard brainstorm, then green needle and then brain needle, ha ha! Yeah
that was weird!

Found a related video that talks a bit about this sort of thing:
[https://www.youtube.com/watch?v=yDiXQl7grPQ](https://www.youtube.com/watch?v=yDiXQl7grPQ)

Also related is this one that I remember seeing on HN or Reddit a while back:
[https://soundcloud.com/whyy-the-pulse/an-audio-
illusion](https://soundcloud.com/whyy-the-pulse/an-audio-illusion). There is
an article about that one as well at [https://gizmodo.com/this-audio-illusion-
will-make-you-never-...](https://gizmodo.com/this-audio-illusion-will-make-
you-never-trust-your-ears-1593113324) but I never bothered to read the article
because I think the audio recording is sufficiently interesting in its own
right.

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tasp
I wonder if the results would be different if the study subjects were people
who often listen to podcasts or audiobooks in faster speed settings.

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innocentoldguy
That's an interesting hypothesis. I listen to audiobooks at 2 or 3 times
speed, depending on the clarity of the readers voice. When I first heard the
"green needle" vs. "brainstorm" audio, I heard "brainstorm" once but then the
pitch of the audio seem to shift up and I could only hear "green needle" after
that. The change in audio quality was similar to what I've experienced when
listening to a book at 1X speed and then shifting it up to 2X or 3X. I haven't
been able to reproduce this though. Now the recording always sounds like
"green needle" to me.

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obelix_
Interesting. I'd like to hear more about this "entrainment" concept mentioned.
How does the brain know what the "envelope" is? Sounds like magic.

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a-dub
It's the peaks in the spectral domain. The cochlea is lined with little hairs
that are tuned to different frequency bands. When they're stimulated by sound
waves, the nerves they're attached to create tiny electrical impulses which
propagate into the larger networks of neurons that make up the auditory
cortex.

When a neurophysiologist uses the term "entrainment" it usually means that
they either observe neuronal firing rates or spectral content of energy over
populations that is somehow directly influenced by properties of the auditory
or visual stimulus. In cases like this, it's like "we played an x hertz tone
and shortly after stimulus onset we saw energy at x hz appear in a population
of neurons"

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jc763
Perfect explanation, thank you.

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dinojames
Interesting enough :P

