The Rest Is Science - The Audio Illusion That Proves We Don't Experience Reality

Episode Date: June 28, 2026

Your ears are lying to you right now. In this episode of The Rest Is Science, Professor Hannah Fry and Michael Stevens (Vsauce) dive into the bizarre world of audio illusions where your brain hears sounds that don't exist, fills in frequencies that were never there, and constructs a version of reality that simply isn't real. From the impossible endless ascending tone to the battle between your eyes and ears, explore how auditory illusions reveal the cracks in human perception. Along the way, we uncover how hearing works at a neurological level, why your brain edits sounds before you consciously register them, and what sensory perception research tells us about whether any of us truly experience reality as it is. Could the gap between what's real and what you perceive be wider than you think? The answer might change how you listen to the world. ------------------- For more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit ⁠⁠https://cancerresearchuk.org/restisscience⁠⁠ Cancer Research UK is a registered charity in England and Wales (1089464), Scotland (SC041666), the Isle of Man (1103) and Jersey (247). A company limited by guarantee. Registered company in England and Wales (4325234) and the Isle of Man (5713F). Registered address: 2 Redman Place, London, E20 1JQ. ------------------- Find The Rest Is Science all over the internet by ⁠⁠clicking here.⁠⁠ ------------------- Video Producer: Adam Thornton + Oli Oakley + Jack Meek Animator: Sam Benson Video & Social: Bex Tyrrell Assistant Producer: Lucy Lipscombe Producer: Simona Rata Senior Producer: Lauren Armstrong-Carter Head Of Digital: Samuel Oakley Exec Producer: Neil Fearn Learn more about your ad choices. Visit podcastchoices.com/adchoices

Hello and welcome to the rest is science. I'm Michael Stevens. And I'm Hannah Fry. And Hannah, today, I want to talk about some illusions and how, as I've grown older, I'm starting to feel like maybe they aren't illusions. Oh, go on. Maybe. You know how people will often say, like, everything's an illusion.

I'm starting to wonder if nothing is an illusion. Or is it? Oh. All right, look. I want to start right out with an audience. I was going to say audio illusion, but no, it's just, it's some audio. I want you to listen to this. Okay, I've got a little Hertz generator here that gives me precise audio tones.

These are sawtooth waves. It's called a sawtooth wave because if you graph it out over time, amplitude over time, you get this gradual rise that looks almost like the side of a triangle, and then it suddenly shuts off. And then rises again and shuts off. So it's like a series of right triangles, like the teeth of a saw. I'm going to start it at just one hertz. Okay, I'm going to turn my microphone to my computer so you can hear it really clearly. I hope this works.

Can you hear that? Yeah. Okay. That's one hertz. That's one sawtooth wave every second. I'm going to raise this up to five. So it goes up and decays, up and decays, up and decays. Yeah, it goes up and then it very quickly is cut off.

Right. Unlike a sine wave, which is going to go up and then. down or a square wave, which suddenly is on and suddenly is off. This one comes up and is off. All right. So here it is. This is five hertz. Now we're at a rave. Now we're talking about 300 BPM. That's um, this is reminding me of my youth. It's a little bit stressful. I've never been to a rave. I just have not had certain experiences that I should have had when I was young. I've never been to an illegal rave. I've only been to ticketed well organized. Poser raves. Okay. With sensible health and safety restrictions. That sounds smart. That

sounds smart. Now what I'm going to do is I'm going to turn this beat up to 20 hertz. This episode is brought to you by Cancer Research UK. Scientists have found that cancer risks usually increase with age and size, but some species defy the odds. For example, deep sea greenland sharks. They can grow over six meters long. weigh more than a small car, and yet live for up to 400 years. Now, understanding how Greenland Sharks' cellular repair and immune systems seem to have managed to keep them cancer-free for centuries, that could open up exciting research pathways.

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their research and breakthroughs and how you can support them, visit cancerresearchuk.org slash the rest is science. This episode is brought to you by Activia. You might already be eating yogurt, but not all yogurts are created equal. Activia contains over 1 billion probiotics per serving to survive and reach the gut alive. When it comes to gut health,

Activia is the number one family doctor-recommended probiotic yogurt brand. Choose Activia. Feel good from the inside out. Visitactivia.ca for more details. Now what I'm going to do is I'm going to turn this beat up to 20 hertz. Okay, what are you here now? It's no longer stressful, just irritating. Just irritating. Okay, good.

Now I want you to pull it all the way up to like 80 or 100. Oh, it's actually making my brain go a bit funny. Hang on. Good. Oh, oh. I don't like it. Where are you at now? 100.

Okay, at 100. Now pull it up to like 400. Okay. Okay, now it's less stressful. now. It's more like someone is playing a kazoo. Yeah. A bit too close to my ear. It sounds like a tone. But what you're actually hearing are 400 beats every second. If your ear was better, it wouldn't sound like, it would sound like...

Because it's still the same thing. It sounds continuous, but it's just because it's too fast for my ear to hear. Yes, at a certain point, our brains give up. They actually fail. They just cannot account for every detail in each second. And so they just go, you know what? Make it a pitch. Okay? And so what I'm getting at here is that there is no music. Everything is just percussion. Every oboe, every trumpet, every singing voice is just a combination of drums that are going so fast, we give up and we hear it as a pitch, not a bo-b-b-b-b-b-b-b-b-b-b-b-b-b-b. But there could be animals or aliens who listen to our music and think, man, these people never progressed above percussion. Halt on a second note, is that really true? There's no such thing as a continuous noise. It depends on what we mean by is.

That's the famous Clintonian philosophical doctrine. Do we really know what is is? We know using tools that we can measure that all noises are just motions of air. They're pressure waves that are either coming faster or slower, and they're either louder involving more motion or less. But scientifically, there's nothing that happens magically in the air when we go from 5 hertz to 1,000 hertz where the air changes. And it goes from being just a pressure wave to becoming a beautiful spirit of pitch. No, it's all just waves always has been.

It's all just pressure waves wobbling backwards and forwards. That's right. Before you get all down on hearing for a second here, it took till 400 hertz there before it became a single tone. The ears are way better at this than the eyes. Because we're doing this recording remotely, I'm watching you on something that's probably 24 frames per second and you look like you're moving continuously. I know, right?

Yeah. It totally makes sense, though, because in nature, Where we evolved, there are a lot of percussive sounds that can be pretty quick, even like a buzzing fly. However, there aren't a lot of strobing visuals. There aren't a lot of objects that are somewhere and then magically disappear and then reappear somewhere else. And so, of course, we evolved to just be much more ready to assume that visual staccato is actually smooth movement. But with sound, the same thing happens. And it's biomechanical.

I mean, when sounds hit our ears, we can differentiate individual beats only up to a point. At a certain point, instead of our ears experiencing this succession of waves, a standing wave occurs in our brains, in our ears. And our neurons can only fire so quickly. They can't say, another one happened, another one happened, another one happened, eventually have to just be like, okay, a lot are happening. And it's happening. It's happening.

It's all happening, guys. the really deep, hard problem of consciousness asks, why does it become a pitch? This sounds really wild, but why isn't it that once you cross that threshold of hearing, around 16 or 20 hertz or higher, why doesn't the percussive beat sequence become the smell of peanut butter? If you're just going to have it become an entirely new phenomenon, a whole new experience, why did ooh get chosen and not? gosh, I'm seeing orange. Yeah, that's definitely one way to frame the hard problem of consciousness.

When does the switch happen there? When did you say it happens? It depends on a lot of factors, not just you and your body, but also what kind of wave is being used. We're using a sawtooth wave here. But the threshold for human hearing is down around like 16 hertz, maybe 20, but it goes up very, very high into the thousands. But it's very easy to hear five hertz.

that means five beats a second as individual beats. Tell you what I'm going to do. I just want to hear, okay, so this now is sore tooth wave at 24 hertz. So the same number of beats per second as you get when you're watching footage generally at 24 frames per second. I think that still sounds like distinct moments rather than a single tone. Yeah. So again, it really depends on what it is that's making the sound and how it's physically moving the air. For example, the world record for fastest drumming was set in 2013 by Tom Grosett, and he was able to hit his drum 1,280 times in a minute.

Now, that is more than 20 times a second, but it still sounds like someone hitting a drum really quickly. Hang on, let's do, let's play, can we play 20 hertz? That's essentially how quickly he was playing the drum. Yeah. I mean, that's wild. But if those drummers were able to, you know, drum 10, 20 times faster, we'd start being like, oh, what instrument is that? Is that a bass clarinet? Not really, because of course, the timbre of an instrument depends on a lot of frequencies all working together. But what I'm wondering is, is this an illusion? Because there isn't a pitch there in reality in and of itself. Or maybe there is. I mean, this is all really unknown. We're not going to spend a whole hour just on this one question, but that's what I want everyone to keep in mind. Is pitch just completely constructed in the human

mind? That's right. Are we really just decorating the air with percussion? And then our brains go, no, no, no, no, no. That is Pink Floyd's Dark Side of the Moon. You know, that is beautiful harmonizing tones. I mean, pressure waves can harmonize, physically. we know how to describe that, but the qualia, the experience of the sound, the subjective thing that we hear, the thing that, you know, the famous Mary's room experiment, which asks about a girl named Mary, who lives her whole life inside a little house where there's no color. She's not allowed to see her body. Let's put her in a black and white bodysuit. She has no mirrors. Everything is just black or white. And she's got a lot of books, though. And so she can read about the color red. She can read about

what wavelength is, an electromagnetic radiation, and she can read that roses are red, and she can read about how the retina works, and the different vision parts of the brain. She knows everything there is to know about red. Here's the question. If she's ever allowed to leave that room, and she sees a red rose, has she learned something new about red? It's that redness that I'm getting at, pitchness. Is it an illusion properly? Actually experiencing it is different to understanding what it is and where it comes from. I've always wondered, you know that thing about Mary's room? I've always wondered, A, why does it have to be a girl?

B, why is she called Mary? I've never really understood those two things. But this, of course, is something that has come back around to the sort of forefront of the scientific mind with the advent of artificial intelligence. Because this whole question of experiencing something as opposed to understanding it or even understanding it as opposed to having,

loads of knowledge about it. What does it mean to conceptually grasp something if you can't really experience it? All of these questions are now incredibly prevalent in the scientific literature. Yeah, what's it like to be a bat? What's it like to be an AI model? When you can play a note for AI and it could tell you exactly what note it was or what its frequency was and it could play that frequency back. But maybe it's just its microphone is vibrating at a certain speed. It takes that speed, gives you the answer, and then it plays it back for you by moving its speaker at the same frequency. How do we know inside, in its subjectiveness, wherever that would be if it's there, that they're

experiencing and not just whatever's really there? Let's look at some other audio allusions. Some of these are incredibly famous and have been for a long time, so we don't need to spend forever on them or pretend like, what? Yanni or Laurel. But I didn't know. the stories behind them. So Yanni Laurel, I'm sure many listeners have heard of it before. We'll play it for you. Here it comes. Yeah. Okay. Did you hear Laurel or Yanni there? I can only hear Laurel.

And if I try really hard, Yerry, Yeri, Yeri, Yerie, Yerie, Yerie. I can't hear Yanni at all either. Are we sure it's in there? I'm sure it's in there. I really do believe the people who say they hear it because if you cut out all of the lower frequencies in the sound, it sounds just like Yanni. Listen. Larry. Larry. Okay, that's without like the lower half of the frequencies. Now let's take out the upper half. Listen to this.

Laurel. Clearly Laurel. So they're both in there. Which one you hear depends a lot on how your ears work and also what kind of sense. sounds you've grown up around. In fact, it's been shown that geographically, people in L.A. tend to hear Laurel, but people in the Southern England, apparently, hear Yanni more often. That's why I thought maybe because you're from the same country. Wait, why? Why? Why?

We don't totally know. But the hypothesis is that the types of sounds, like literally the speaking voice registers that you grow up around, train you to focus on certain parts of noises. And so if you're focusing on lower noises, you're going to hear Laurel. But if in your daily life you're experiencing higher-pitched noises, that's what's relevant to your fitness and survival in the world. You're going to hear Yanni. Is that the reason why people in L.A. hear Laurel? Because there's so much around them and people are going,

oh my gosh, hi, that they just learn to tune it out. Look, it could be. It literally could be. And I think it's important to emphasize, we do not understand this illusion well enough that we can just write it up, make a little two-minute YouTube video and say, here's how it works. We can do that for some illusions.

A similar allusion to Yanni Laurel is the famous blue and gold dress, right? This is one where it's also very hard for people to see it one way or the other. There are other illusions where it's very easy to flip, like the Nekker cube. That's the little two-dimensional line drawing of a cube that can either be seen inside out or right-side out

depending on how you look. the brainstorm green needle one. Have you heard that one? No. Hang on. The brainstorm. Can I ask you about the dress, though, while I'm looking this up? Yeah. Which one do you see? I see blue and black. Do you? I always have, but you don't? No, I see green and white. Green? What's so well? Green? Whoa. Okay, there's a third option, folks. I see gold and white. However, that one I can switch. You can switch. With difficulty, but I have seen both. If I really look at it,

especially if you sort of squint at it, then I can switch. But that one in the same way, the sort of research on it demonstrates that people who have grown up around artificial lighting tend to interpret it differently to people who have spent their life outdoors, right? So like farming communities, for example, will see it one way, and people who grew up in cities will see it another. Exactly. It's like very hardwired, but it's like over-easy wired into our brains based on where we live. My wife saw golden yellow. Right. Heck, she saw golden white first.

And I think it has to do with, yeah, the world around you, the kind of lighting you are used to, that affects how you assume the ambient lighting in a photograph is. And that changes how you perceive the colors of the dress. Because the question is, is this a blue and black dress, which is just overexposed in the background? And so it kind of looks a bit washed out. or is it something that is a green, oh my gosh, what is wrong in us? We found a new illusion. We found a new one. It's impossible for us to talk about the dress.

Yeah, or is it a golden white dress that has been overexposed by artificial lighting? If you listeners out there haven't looked at it for a while, go take a look. I mean, it's still a phenomenal illusion. And the teams that I worked with at the University of Chicago when I was a psychology student, They were emailing me about this illusion because it really did lead to new questions and progress in vision research. Oh, yeah. The illusion is so strong and we don't know exactly how it works. Have you seen the Sox and Crocs version of this?

No, no. Tell me about it. Okay, so this is a direct result of the dress and some researchers working on vision perception. But I think in particular it comes back to this idea that it's like your lived experience, ends up changing the way that you interpret the world around you. And what they were trying to do was to recreate the illusion that was there in the dress, but also, I mean, in a different way in Yanni Laurel. And they were looking for things that had ambiguity over their colour

that would allow them to sort of tap into people's lived experiences. And they came up with crocs and socks that they took in sort of ambiguous lighting. Okay. So to me, it looks like... like seafone green socks and like beige brownish crocs. Okay, so to me it looks like I can see that those are actually white socks. I can see they're white socks and the lighting's a bit off. And then there's sort of a pinky tone to the crocs.

So if you assume that there's just like a more electric green light on the scene, you've got white socks and pink crocs. Whereas I'm coming at this thinking, oh, the white is just a white, it's got all the colors in it. themselves are electric, seafoomy green, and those shoes are just kind of like a drab, olive color. Right. But I think that what this managed to do was it really demonstrated this hypothesis that actually

in any situation where there's ambiguity and requires your brain to make a sort of finery interpretation of a scene, right? Is this a particular lighting that is imposing and changing color of this? And should I interpret it in the original way? Or do I take this image as fast? it's really your lived experience and how much you have witnessed those kind of environments of artificial lighting, say, in the past that changes your perception, changes your actual experience of the world. Going back to what you were saying at the beginning about qualia, right,

about the hard problem of consciousness, is your green, my green, is your experience of the world the same as mine? And this is like a tiny little crack in the sort of great wall that we've been unable to break through to answer this question. It's a tiny crack. It doesn't demolish the whole thing because we still know that we're disagreeing, you know. We both know that, wait, you think that it's pink? I know what pink is and that's not pink. Like, the word still means something to both of us. By the way, look at the Crox and Sox picture and look at the caption below.

This image is from Pascal Wallish. That's exactly the guy I worked with at New Chicago. Amazing. This became a huge thing. Yeah, he was one of my teachers. No way. And we talked on Facebook about the illusion. So I don't know.

I'm just trying to, um, Berg. I'm trying to Berg here, bask in reflected glory. I knew that guy. Berg's a good name for it. Berg's a good name for it because it's like, hey, look, you guys, you're seeing the tip of the iceberg, but underneath is me. Yeah, but really Berg, B-I-R-G, basking in reflected glory. It's a thing people do a lot. The opposite is called corphing, cutting off reflected failure. Oh, I was never really for this, or I wasn't really there that long. Mistakes were made. Yeah, yeah. So back to illusions, there are other illusions that are multi-stable. It's very easy for everyone to flip between one perception and the other. So this is the famous brainstorm green needle illusion. What you're about to watch is a toy that says brainstorm. That's the Ben 10 character. It's saying brainstorm. And yet, just like the Stroop color illusion, where it's really hard to say the name of a color when you're reading a

word printed in that color. Here, if text green needle is put on the screen, you hear green needle. That is absolutely wild. I almost don't believe it. I almost sort of want to rewind and it's just, it's like, have I just, by fluke, uh, managed to match, is the actual audio changing? And by fluke, I've sort of been, been concentrating on the correct word at the correct time. But no, it really is. You listen to the, if you rewind and play the precise same piece of audio, but on the other words, you hear something different. Let's set this up so that the listeners can have their own experience. So what you're going to hear is a sound, and it will either sound like Brainstorm or Green Needle.

Just as we loop it, decide which one you're going to hear, you will hear that one. But it was the same sound every single time. So here, again, we've got a kind of small, low-quality speaker producing a sound with a lot of noise in it. However, here, different modalities can get involved to shift the brain to perceive it one way or the other. So if you see Green Needle or Brainstorm written out whenever you hear it, your brain goes, oh, that's what I'm expecting. Even if you watch the video of the original toy and you see that the light blinks three times, that makes you go, oh, there must be three syllables, and you're more likely to hear Green Needle. But Green Needle and Brainstorm sound like such

different words. How could there be ambiguity between those? And yet there is because the stimulus is very complex and the way we take what's out there and turn it into a little show in our brain is dramatic. What is going on there? Is it about attention? Is it about something particular in the way that sound is constructed? Like what is going on? Why is that possible? Can I make my own version? Can I do one that says Michael and Hannah at the same time? You could definitely. It might take some work. You might need to test it on a lot of people.

But yeah, you can always add in noise and change around frequencies and overlay things to the point at which it becomes ambiguous. And maybe only children would hear one word and adults hear the other. And then maybe even like elderly people hear a whole third thing. It's not completely drag and drop because we still don't know all the mechanisms behind it. You can watch every video on these illusions and find audiologists, describing different aspects of the waveform. Though, at the end of the day, it all has to do with either what mindset you're in, what other modalities are there. If you're using your eyes to see the word brainstorm or you're thinking the word green needle, that's what the audio sensation will be perceived as.

However, with Yanni Laurel, that's like a deeper mechanism in the brain at fault, assuming these are illusions, which we'll get to later. where your lived experience is affecting your ability or disability to hear one thing or the other. This is called the brainstorm one is the McCirk effect, right? Yes, exactly. The McGurk effect is another example of how different modalities work together to create a different reality. Tell me if this is the wrong thing because I don't know very much about this, right? But like, when you mouth the word colorful, but the person thinks you're saying, I love you? Yeah.

Let's try that. Let's do a little experiment. Okay. I'm going to say either I love you or colorful. Those of you listening, you'll know the answer, but those of you who are watching the video, hit mute when I say so and then write in the comments below what you think I said. Okay, here we go. And I'll put my hand up when you should turn it back on.

Okay, mute your audio in three, two, one. Colorful. Hey, unmute, come back, come back. If you were only watching me right down below what you thought. So yeah, we don't have like a completely isolated hearing system in our brains. We are taking clues from everywhere and putting them together. And ultimately, that's what we should be doing. It doesn't matter what the truth is.

Here's the truth, okay? Is it Laurel or Yanni? Truthfully, it's Laurel. Because here's the true story behind it. A man named Jay Aubrey Jones recorded the word laurel. That's what you're hearing his voice when you hear that sound. He recorded the word laurel for vocabulary.com. He recorded thousands of words so that people could hear the pronunciations.

Well, then in May of 2018, there was a high school student named Katie Hetzel who either recorded a computer playing back his sound or she downloaded a low quality version of that file. And another classmate of hers was like, that sounds like Yanni. And she's like, no, no, this is a recording of someone saying Laurel. And her classmate put it up on social media and was like, Yanni or Laurel, it's the new dress. The dress, by the way, I want to tell a story about the dress. Because I've never told this story before, and this might be where I finally get some help. So, I almost played a role in the dress. Go on.

Here's what happened. Burgas, Michael. The famous dress illusion started back in 2050. in February of 2015, two people were getting married. Grace and Keir Johnson of Colonse Scotland? Colise. Either or. Either or?

Say it twice. We'll lay them both over each other. We can ask the audience which one they hear correctly. What does the colon say? That's all I can think of. But anyway, that's where they lived and they were getting married. And the brides, so Grace's mother went to, and I got the exact location here, She went to the Cheshire Oaks designer outlet north of Chester.

That's Cheshire, but yeah. Cheshire. Cheshire. Cheshire. Cheshire. Cheddar. You Americans with your Gloucestershire. Anyway, go on.

She went to this outlet and she saw the dress, took the photo, the photo that we now has gone viral. And put it up on Facebook. And all our Facebook friends were like, whoa, is that, you know, gold and white or blue? and black and people were like, what, how can you see it differently than me? But it didn't go viral until the day of the wedding when a friend of the bride and grooms, whose name was Caitlin McNeil, saw it in person being worn by the now mother-in-law, the mother of the bride, and said, holy cow, it really is blue and black. But the photo didn't look that way, and she shared it to her tumbler on the 26th of February, 2015. And then it got really popular.

BuzzFeed wound up covering it. But at four in the afternoon, on the 26th of February 2015, I received an email from a girl named Lizzie Rhodes. I'm giving out her name because I need your help, Lizzie. Who are you? She wrote, Michael, my friends and I were stumped when we began to argue about the color of a certain dress taken by one of us. Some see the colors as white and gold, others see blue and black, I see blue and black. One of my friends posted it, and we were getting all different comments about it. Are we crazy? Is there any way to explain this? What do you see? So, I remember getting this email, a little after midnight, eight minutes after midnight, in fact, if you want to be specific, on that day. And I was like, bleary and sleepy

and about to go to bed. And I'm like, this is one of the craziest fan emails I've ever received, because it's obviously blue and black. But she says people see it as gold and white, I get a lot of emails that are just like, hey, how come my nose is floating? And I'm like, no, you don't need a Vsauce video. You need help. So I just didn't think anything of it.

The next day I went into work and everyone's talking about this thing. And I'm like, what? Oh my gosh. If I had recognized the potential here, it wouldn't have been BuzzFeed that scooped it. It would have been me. It would have me.

But to be fair, you didn't have very long, though, You didn't have very much time. No. So wait, who was the person that emailed you? I was emailed by a person named Lizzie Rhodes. And a few times since then, which this was 11 years ago, I have done a deep dive through Facebook to figure out, is she friends with the Caitlin McNeil who originally posted it or friends with Grace and Kear, the bride and groom?

I've never replied to her email because of my social anxiety and because it feels almost like rude to be like, yo, what up? I thought 11 years was long enough to finally get to this email. Thanks for reaching out. Thanks for watching. But yeah, I just realized this podcast is my chance to say, here's what happened. Lizzie, if you're out there, reply to the thread. I still have it. You emailed me three times, actually. I have all three of them. And I never replied, but I've got them all. Yeah, she emailed me some other visual illusions that might be related. It was really great. And I just, I think at first I didn't believe that there was any illusion in this dress. And then the next day, I felt like I'd missed out.

I think ASAP science made a video about it immediately. And I was just, it was just sour grapes. I just felt like, you know what? I'm not going to talk about it because I missed the boat. So now I have to act like it's not cool. So that's a huge mystery. Wow. What a great story.

But I also think, though, Michael, I mean, I think that that really demonstrates how well-regarded you are, right? I know. Someone would come across something that was a bit strange and unusual and their first thought is to email you about it. There's something really lovely about that. I know. You're right.

That really is the first primary emotion. It's a kind of honor. It's also a kind of responsibility. And I fell short. I was reached out to and I just went to bed. Right. Here's the question. You've mentioned this before.

But like I also get a lot of like, I mean, some of them frankly unhinged in. emails and letters from people. Yeah, I can imagine. Lots of them are really, really lovely. Lots of them are so gorgeous. I've got like a little feel-good folder in my house where I like put everything that's just like really lovely stuff. But some of them, you're right.

You filter the ambiguity through your own experience. And my experience of reading some of these letters is that there's some people who sort claim to have solved, you know, the Riemann hypothesis. And it's like, it's kind of a bit, a bit goofy. And so my expectation, when the. there's ambiguity is that like this is not going to turn out to be anything. And so it does genuinely play on my mind sometimes that I might have missed something really remarkable. Because while this dress story turned out to be like this global sensation that we're still talking about 11 years later,

I can completely imagine in 20, 30, 40 years that people will still occasionally mention this dress has sort of become like a phenomenon that's this kind of evergreen. I wonder about all of the emails in your inbox that just didn't get picked up by BuzzFeed that just didn't get posted to Tumblr, but they are just as valuable and just as interesting. I got to take them all seriously. We'll never know. And taking them seriously is all we can do. We can't take them literally.

I'll talk about what I mean after the break. We're going to come back. I'm going to show you another audio illusion and we're going to talk about perception, reality, and whether anything is an illusion. This episode is brought to you by L'Oreal Group. Beauty is a powerful force that moves us. That's why L'Oreal Group has built a business that is inclusive at its heart with 100% of its brands

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I mentioned that Yanni Laurel perception can be geographically distributed. That, I don't think, has actually been found. I was thinking of what's called the tritone paradox. That's the one where where someone is from correlates with how they hear the sound. So, Hannah, I'm going to play for you two notes. And I want you to tell me if they're going down or up in pitch. All right.

Here we go. Up. No kidding. That's what I expected, because you are British. I hear them going down. To me it sounds like, ba, ba, uh,

really? Yeah. So this was discovered by Dana Deutsch and she calls it the tritone paradox. It involves tritones, which are sounds that are a half octave apart and they're kind of sandwiched together. So you hear two of them

and then one pair goes down and one goes up depending on what frequency you in your lived experience have had to learn to prioritize, you will either hear the ascending notes or the descending notes as being more operative in what's happening. When you answer the question, is this going up or down? I hear that as ba-ba. So hold on. Okay, this is South of England versus Southern California. Southern California. Why? What, why? Like, what possible thing could we be hearing that would be so different?

I think it's the different vocal registers. This is not my guess. This is, from researchers who say that apparently people in Southern California talk with a lower pitch. Oh. So they're all like, yo, you know, wapush, wapish, oh, it was gnarly. I guess even, even like, no matter what gender you are, you're lower in general. But in southern England, they're all like, hey, guvna, oh, give me some brown sauce. Right. The most British thing you could think of, governor and brown sauce.

Oh my gosh. I'm glad that was so bad because I did just do that off the top of my head. No prep. I enjoyed it. And I nailed it. That's so strange. Wait, are those the only two? Have they tried for other countries around the world or are those just the only two? Those are the only two that I've heard of in my limited research on the subject. But it's very cool because Tritones also have a long history of being fascinating to people. They, because of these weird effects, they were even seen as possibly demonic back in the Middle Ages or Middle Ages. medieval period, I believe. I know at some point in history, people were like, don't use them. It's the devil's voice, right? In the comments, can you tell us which way you hear it and where you're from? Yeah, and maybe also tell us your age because I think that as we age, we hear different

frequencies better or worse, usually worse. So yeah, give us that info. Here are the two notes we're talking about. Okay, right down below what you heard. Were they going up in pitch or down in pitch? This is really interesting, though. I mean, it's coming back to a similar thing, right? Which is that like your perception of reality is sort of constructed in your own mind as a basis of your experience.

Yeah, it's not just all of our brains do this one funny trick. No, they all do tricks in their own way based on what environment they have been raised in and learn to navigate. There are a lot of other really good videos online of audio illusions. Veritasium did one a year ago that's really good. I'll tell you what not to do, though. I watched the video last night with no headphones on at one and a half speed. Sorry, Derek. And if you have no headphones on and you've sped it up, instead of being a video of illusions,

it is a video of no illusions. None of them work, right? I just took his word for it. But I also could not figure out what the opposite of an illusion was. What do you call that? So last night, I didn't want to look it up. I just tried to ideate some things. And I came up with, it's not an illusion.

It's in illaborare. Because labourare means labor, which is the opposite of Luder, which is where we get illusion from. Luder means to play. Oh, really? And illusion is in play. Yeah, allusions are playful. And if it's not playful, then it's labor, it's work.

I like that a lot. There was me just thinking you were saying God would go, but actually it was well researched a lifetime of studying words. I did do the research. I don't know Latin off the top of my head, but I wanted to come up with my own antonym of illusion. So like an illusion is cool, but a enlaborare would be, look at this circle. It really is a circle. It's an anti-illusion.

Then I thought maybe unillusion, but that sounded like an illusion that you've undone. Then I thought, well, even though it's etymologically not correct. correct to do this, you could say it's not an illusion, this is a illusion. It's just the way it is, because ill sounds like wrong, ill, sick. However, there is a real word scientists use, psychologists use for something that's just true. Are yours frankly better? No, mine are worse. The word they use is veridical. As in like truthful. As in true. Yeah. Like, veridically, these lines are the same length. But there's an illusion where one appears to be longer than the other. No, I'm going to for illusion, illusion from the rest of time.

There are some places that are called something sound on this? Yeah, like Puget Sound. Yeah. Interestingly, this is completely unrelated, but let's just do it. The Mariana Trench was discovered, like, purely out of luck. It was discovered in 1875 by a research vessel called The Challenger that was just measuring the depth of the ocean in different places. one of the places they tested happened to be what we now know is the

southern end of the Mariana Trench and they just dropped like a weight tied to a rope off the boat. They were like, this isn't stopping. We haven't it's the bottom, what the heck? And it went on and on and on and they were like, dude, this is unbelievable.

And they wrote it down and everyone's like whoa, the ocean is a lot deeper than we thought. So they named it, it became a feature. They knew that it was a trench. But that was in 1875 just by chance, that was one of the spots they checked. We didn't discover the second deepest trench in the ocean until 1952. That's the Tonga Trench.

So the fact that like almost a hundred years prior someone had just checked right at the Mariana trench is like total, total coincidence that we got the deepest one. We just tried that right off the bat. The chances of that have seemed pretty, pretty insignificant. The ocean is a big place. The ocean is a very big place. There was one other really neat thing in Veritasium's video that I'm just going to share. You should go watch the whole video, but he talks about why our ear shapes are so weird.

Why do we need to have this funky thing? Microphones don't look like these. Microphones are just, look at this. It's just like a cylinder or a ball or something. And it has to do with helping us localize the position, the location, the origin of the location, the origin of a sound, when it's not off to the side. Because when a sound is off to the side, we have a lot of clues about where it's coming from because it gets attenuated when it passes through our head, so one ear hears it louder than the other, one ear hears it before the other.

But if a sound is right in front of us along this line, either below or up above me, even behind me, it's symmetric about my ears, they both get the same stimulus. Yeah. But they don't because my ears are so unsymmetrical along that axis. So sounds coming from above me come in like this and they're like going past my earlobe down past the top of my ear and they're going to reverberate and be reflected differently than frequencies that come from below or from right in front of me. Those are going to hit, you know, I don't know how they hit, but they're hitting the ear

different ways and different frequencies are better or worse reflected by the different weird spiral folds of the cartilage of our ear. And over time, from when we're little babies to when we're a bit older, we learn how to connect the perception we get because of what our ear does to the sound to where it is. And researchers have done experiments where they've put little like molds on top of people's outer ears to make them differently spiraled. I could have someone make ears that look like yours, stick them on top of mind, and And now I'm hearing with your outer ear.

By the way, the flap, the thing that we call an ear, like when you say someone, oh, you didn't draw the ears yet, and they draw this outside thing that we can see. This is called the or the Pena. Peta is usually used in zoology, like a penna is a non-human animal ear, outer ear. But for humans, we call this an oracle. Anyway, they put prosthetic oracles on people that were different shapes. And the people suddenly could not tell where a sound was if it was symmetric. situated to their ears. Did the ear look like it could conceivably be another human person's ear?

Yes. So it's just that you hadn't had the training of tuning your, I mean, because you sort of get to verify it, right? Like, you think a sound is coming from over there and you get to verify. You haven't had that training process essentially for your entire life with that particular ear shape. That's right. And it only takes a few days, like a week at most for people to learn how to use their

new ear shapes. And suddenly they're really good at picking out where a sound is that's right above them, right in front of them, right behind them. And then when they remove the prosthetics, people were able to go back to their normal ears very quickly, yeah. Okay, I want to go and grab something that I have downstairs because there are people who study ear shapes to an unbelievable degree. Just hold on a second. Oh. I'm going to get something too. So this idea about people really caring about the shape of the ear.

is, of course, if you design headphones, right? And particularly, if you are designing headphones that are noise canceling, where you want to play a sound into the ear that exactly cancels out any external sounds, then the way that an ear is shaped becomes really, really integral to what you're doing. So anyway, a little while ago, I made this programme. where I got to go and visit Bose in Boston. And literally all over the place. I'm just opening this as I go.

Literally all over. What are you opening? Like some Japanese puzzle box? I know. It's like I've had it framed. So I'm opening the frame. Oh. Okay.

So anyway, in Bose, literally everywhere are these really weird little ears. Oh, cool. Is that your ear? No. They didn't do one of my ear, but they have like genuinely hundreds and hundreds of and hundreds of these, that they are continually testing for how sound changes, for how the different headphones work, for how it reflects sounds, for how it understands, like, I mean, exactly what you were describing about how sound changes depending on the shape of your ear. And they attach them to these

models that have microphones inside them, essentially, and run these, like, insane scientific experiments, like really, really sophisticated in order to make sure that they're making headphones that can actually be used by everybody rather than just a few people. I want to show you it because it's really fun. Okay, while she's opening it, I'm going to show off my new mechanical pencils. And editors, I dare you to leave this in. If you don't, I'll be so disappointed. So look, I hate long pencils. This is an unsharpened taekondroga. So long, I feel embarrassed to use it. But look at this. Look at this winner. This is the Kohinor 5228. Like how much shorter it is. Coenor, as in like a diamond.

It's named after the diamond, the queen's diamond. There you go. Versatile. And they make an even thinner one. That's actually too thin, but it's metal. So this is wood. This feels good. But let me show you something else.

Okay, here's the Coenor 5228. Look at this one. Otoe W-N-O-2. It's a needle. Dinky. Look at that dinkster. Okay, I'm finally in. It's in. Okay, so I won't show off. Okay, here we go. I have one more small one and you guys will have to just subscribe and I'll show it off later.

When we do the club, that's what the club could be. Yeah, ooh, members only. Whatever's hiding behind my hand. Okay, so here, here's the little ear. It's the most. Oh, my goodness. That is. Some people have, some people do have really flippy, floppy ears. Whose ear is that floppy? Children's. Really? I reckon. I mean, they can. I mean, they can. I mean, they do get harder, sort of the cartilage solidifies as you age. But anyway, when you are in Bose, I realize that they had just hundreds and hundreds and hundreds of these lying around all over the place, which are essentially silicon molds of different ear shapes. This one, it's so much fun to play with. It's like, it's really floppy. You know, you can kind of like tickle it and dangle it. Yeah. It's a mold of a human ear, right? So it looks exactly like a human ear. But you realize

when you're in this company, just how much variation there is in human ear shape. Because, I mean, the general structure is kind of the same. You have like the outer part. You have, this is the helix, is it? You've got the dath here. I think this is the conch. Oh, no, hang on. That's the tragus, isn't it?

Sorry. I forget on which bits which. Look how big your daph is. Oh, my gosh. You could get a monster piercing on that if you wanted. Maybe I will. Talk about monster daths. Here's a monster ear.

Look! Hey, look. My ear is not floppy. No, yours is not floppy. But it has a middle and inner ear, so I'm holding up, by the way, a very oversized plastic model for like doctors' offices and medical schools of the ear and the inside parts of the skull, the ossicles, cochlea. But you know what?

You can see the S shape of the ear canal in that, which I always think is really, fascinating, that it's not just this straight tube. I'm a bit obsessed with the ear, you know. I'm going to bring up ears again, but not today. We're not done with ears. No, today we're talking about illusions or unillusions or in la Bararees. Maybe, maybe. So look, we're not going to come to any answers about the true nature of reality today. But, you know, on this show, we bring this up a lot. It usually falls under the hard problem of consciousness. I've said a lot of times that I think illusions show us that being right doesn't really matter. What matters when it comes to existing is survival.

It's fitness. Just because you're right doesn't mean you're alive. It's better to be wrong and alive than right and dead. It's better to make your decisions quickly than wait until you have complete information. It's better to update your guesses based on the evidence that's in front of you and have them as guesses rather than only proceed when you're certain. That's right. That's right. I mean, this has been mathematically shown to be true when constructing little environments.

So, like, of course we don't get everything right. Of course we listen to fast, percussive beats and we perceive a tone. It's more helpful in some way, probably, because natural selection. chose that to happen. And if instead we had the machinery in our brains and we had some kind of special nerve cell that could fire 20,000 times a second so that we could tell where each individual beat was, that would be a waste of resources. So instead, we're wrong. We as a species, or as as life, invented, completely invented a completely made up thing called pitch that we experience in our own heads alone. Because I think it helps us survive. It helps us

make decisions faster and process more efficiently. Well, thank goodness, because it doesn't just help us survive. It's also turns out to be one of the great sources of joy. Yeah, exactly, exactly. It's beautiful as well. And I don't know if it was always beautiful, if we just learned to think it's beautiful. But Donald Hoffman talked about this in the case against reality, which is a fantastic book. He actually gave this a name.

And I forgot about it until I was researching this morning. but he calls it the fitness beats truth theorem. He defines an illusion as a perception that fails to guide adaptive behavior. So he's like, look, let's look at insects that eat feces. Okay? To them, it's amazing. They love it. When they smell it, they go to it and they consume it.

So what's going on there? Are they under some kind of taste illusion where they think it's good? Or maybe it does taste good. And we all have an illusory experience of, ooh, that's gross. Who's right? Which one's the illusion? And he's like, neither. If it's adaptive.

If it helps your species survive, then it just is what it is. And the truth out there will never be accessed. Because there is no ground truth, because it is only via experience. All we have access to is a user interface, basically. What I call my office is actually the user interface my brain makes that I can then navigate without needing to worry about the complexities of all the electromagnetic wavelengths and all of the noisy signals that are coming at me right now. And so he has a name for that as well, and he calls that the interface theory of perception,

where he's like, to ask whether my perception of the moon is veritical. Like, is this an illusion? Does it really appear that large? It looks bigger at the horizon. But he's like, just give it up. Because whether I see the true color, shape, or position of a moon that exists, even when no one looks, is like asking whether the paintbrush icon in my graphics app reveals the true color shape and position of a paintbrush inside my computer. Right. Reality is the computer.

The user interface is on a screen inside here, and we're just perceiving that. And it's very helpful, and it has been built by natural selection to help us live, survive, make decisions as quickly as we should. I like that a lot. I like that a lot. I also just like anything that ends in.

Give up. Just give up. Just embrace it. Yeah. We'll never know what veritical reality is. What we do have access to is even better. It's what's kept us alive. It's what's kept us safe and sound.

And in play. Thank you very much. And in play. Luder, illusion, ludicrous. come from to play. You know, sound, sound meaning healthy, like of sound mind to be safe and sound, that's not redundant. Safe means there's no risk of injury. Sound means there are no current injuries. And that comes from a totally different etymological root. That comes from like old Germanic languages, gazooned, like health. Like gazuntite. Gazunite, right? Sound in the sense

of healthy comes from there, whereas sound that you hear comes from the, the Proto-Indo-European or something, which just meant a sound. It's where we get resonate and sonic. But then there's a third meaning of sound, like Puget sound. Sound can also be a body of water. And that comes also from Germanic.

It comes from Sond, meaning swim. And that is why when we check how deep a body of water is, a Sond, a channel of water, we're sounding the water. We have a sounding line. So sounding can mean making a noise. It can mean being healthy, but it can also mean measuring the depth of a water body. That brings this episode to a resounding end. Yeah, it sure.

A resounding. Oh, it sure does. And I hope you all are safe and sound who are out there listening. We appreciate you listening to our sounds. If you have questions, please send them in to the rest is science at goalhanger. And as ever, leave us comments, like and subscribe. I mean, I feel slightly sick saying that, but it genuinely does make a massive difference. And we will see you next time.

Bye-bye.