Auditory illusion

Transcription

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.