4 Weird Audio Illusions!

This is what the auditory cortex in your brain
looks like… if it was made out of paper. And had a cute little face. Your auditory cortex seems well-meaning, but
it can be pretty deceptive. Our hearing plays tricks on us all of the time, and it’s not
your ears that are to blame. When you repeat a phrase over and over and
over, it begins to sound like a song. It’s called the Speech to Song Illusion. The repetition
of the words tricks us into hearing a rhythm and thinking it’s musical. And when you
think you’re hearing a song, your brain works even harder to detect musical patterns
and process the pitch. Speaking of pitch, I’m going to play you
some computer generated two-tone patterns and I want you to tell me if they’re ascending
or descending. What did you think? To me it sounds like up,
down, up, down… but you may have heard a completely different pattern. It’s kind
of like “the dress” of sound, no one can quite agree if the tones are moving up or
down. Really… It’s neither. There is no answer…
So maybe that was a misleading question. This illusion is the Tritone Paradox. The tones are half an octave apart – also
called a tritone – and they’re computer generated to be a specific note, say a C and
an F#. But they’re not in a specific octave. What’s weirder is that people are internally
consistent with the direction they hear certain note patterns moving. If you hear, say, C
and F# as ascending, you’ll continue to think that it’s ascending when you hear
it in the future, no matter what octave either of those notes are generated in. The Tritone Paradox was discovered by American
Psychologist Diana Deustch in 1986 and it’s been confusing people ever since. In one study
she found that more participants from California heard a pattern as ascending, and more from
the south of England heard it as descending. Deustch suggests the speech patterns of our
childhood shape the way our brain maps musical notes. If you feel like you’re disagreeing with
everyone about the pattern of the tones, studies show you’re likely to hear the same pattern
as your Mum. Seriously. Send this to her. And then, listen to these words… What do you hear? …Maybe rainbow? …Or
bueno? Or, depending on how you’re feeling… Roganie? …Love me? This Phantom Word Illusion is best experienced
in front of two speakers, it sounds like each speaker is producing a different word. But…
why? Time for a quick musical interlude. So the three bones in your middle ear are
the three smallest in your body. Their job is to translate the energy of sound waves
to the inner ear, which then transmits electrical impulses through the auditory nerve into the
brain. Most of the time, your auditory cortex does
it’s job and we can communicate…. Hey. But remember how it can be deceptive? Your brain is constantly trying to find meaning
in things. The phantom words are individual syllables coming out of different speakers.
But, like with a lot of audio illusions, certain brain waves encode the sound in your brain
as if it’s in one piece. You use those individual sounds to construct lots of different words. Your brain loves to fill in the gaps. [cough] Sorry – your brain loves to fill in the
gaps. Your brain loves to fill in the gaps. Joel we’re so close to finishing! Oh I’m fine. I just digitally added the
cough. And removed a little bit of the one of the words from the last sentence. Your
brain loves to fill in the gaps. Huh. The Phoneme Restoration Effect. Did you
notice? See you next Thursday. But if you haven’t heard enough this week,
follow me over to ACS Reactions for their really cool video on the neuroscience of music.
They use a disembodied voice tell you all about why you love music. And I even join
them to harp on about music. And the brain. It’s pretty ace. And as always, subscribe to BrainCraft for
more brainy videos.


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