Stuff You Should Know - How Optical Illusions Work

Episode Date: March 2, 2017

Now you see it, now you don't — optical illusions can fool us into seeing what's not actually there. But what causes that disconnect between perception and reality? Learn all about this visual trickery in today's episode. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

Hey everybody, when you're staying at an Airbnb, you might be like me wondering, could my place be an Airbnb? And if it could, what could it earn? So I was pretty surprised to hear about Lauren in Nova Scotia who realized she could Airbnb her cozy backyard treehouse and the extra income helps cover her bills and pays for her travel. So yeah, you might not realize it, but you might have an Airbnb too. Find out what your place could be earning at airbnb.ca. On the podcast, HeyDude the 90s called, David Lasher and Christine Taylor, stars of the

cult classic show, HeyDude, bring you back to the days of slip dresses and choker necklaces. We're going to use HeyDude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it, and now we're calling on all of our friends to come back and relive it. Listen to HeyDude the 90s called on the iHeart radio app, Apple Podcasts, or wherever you get your podcasts. Hey, March is tripod month, my friend. And you know what that means?

Yes. That means it's time to let people know about your favorite podcasts just to share the sheer joy of podcast listening. That's right. It's T-R-Y pod, still a nascent industry. A lot of people don't know what podcasts are and helps everybody out. If you would go out and just say, Hey, family member who I see it Thanksgiving once a year. You should try out this thing called a podcast.

Here's what they are. Here's a cool show you should try. And here's how to get it. Yeah, and it doesn't have to be our show. Just any podcast you like in general that you think someone else would like. Just share it. Yeah. Yeah.

So get on board the tripod train. Welcome to Stuff You Should Know from HowStuffWorks.com. Hey, and welcome to the podcast. I'm Josh Clark and there's Charles W. Chuck Bryant and there is, well, Jerry just disappeared Chuck. Did she? She did. Oh, there she's back.

David Copperfield's in here with us as well today. He made the Statue of Liberty disappear and now Jerry. Jerry is drawn by MC Escher. Oh, that's nice. So how do you feel about optical illusions? I feel happy about optical illusions. No, no, no. I'm not asking Josh from the third grade.

But I feel sad about articles on optical illusions in general. It's a really difficult thing to write about. As we're about to demonstrate, it's an even more difficult thing to talk about. But it's just, I think the idea that every article has to inherently describe an optical illusion and then basically follows that description up with and scientists don't really know what's going on. Here's a couple of guesses that will be fully discredited in 20 years. It's just dissatisfying.

Yeah. I mean, because we're the kind of dudes who like concrete answers. Or at least like really solid hypotheses. Some of these are flimsy to me. Yeah. So we would encourage folks if you are listening at home or work, because you can blow off work, let's be honest, look up some of these. We'll describe them as best we can.

And most of them you've probably seen before because as you will learn, many, many illusions, optical illusions were drawn and conceived many years ago and have just been sort of played upon over the years in different ways. Right. Yeah. The 19th century was like the... The classics. The foundation of optical illusions, which not coincidentally coincided with the foundation

of psychology and brain research. And optical illusions were created to kind of test this stuff or explore this stuff, right? Yeah. And they are just variations on these themes. Yeah. So like I was saying, if you're able to just kind of just Google this junk as we say them and you'll go, oh, that thing.

And Chuck, actually, there's a website called MichaelBach.de. Okay. .de. Yeah. Which is Deutschland or Germany in the English. But it's m-i-c-h-a-e-l-b-a-c-h.de. And this guy just listed. He's got links to every optical illusion you could possibly imagine.

So that'd be a good place to go. Just sit there and click on his site while we're talking about these things. Yeah. And what I found is that I get a bit of optical illusion fatigue when I look at too many of these things in a row. Well, that should be studied. Well, I think that's... I mean, we know so little about optical illusions that that is, I mean, that's kind of groundbreaking.

Well, I don't mean fatigue is in scientifically, I just mean I'm tired of looking at this junk. Oh, I see what you mean, yeah. Yeah. It just bores me after a bit. Plus, a lot of them require ugly color combinations or unpleasant color combinations. So I think that probably contributes to it too. Yeah. And it does for me.

We should do a... We don't talk a lot about Escher in this one, but he deserves his own show. Sure. Escher and Geiger. Maybe we'll do a combo show with those two. Oh, H.R. Geiger? Yeah. Oh, yeah.

Man, that guy's brain is beautiful. Yeah, there's a lot of cultural icon biographies that are floating out there. Mr. Rogers and Dr. Seuss, I know we've talked about those, so maybe we'll go on a kick. Okay. I'm ready for some kicking. All right, so let's go back a little bit to the history of thinking about or studying optical illusions, right? Okay.

One of the most things in the West, the basis of optical illusions or the first mention of optical illusions in the literature comes from the Greeks, an Aristotle in particular. Yeah. He probably munched on some weird root and stared at a waterfall for a little while. Sure. And he said, hey, dudes, if you stare at that waterfall long enough, man, and then you quickly look at that rock, it looks like the rock is moving. Right.

And they said... And the rock's like, I'm not moving, Aristotle. But that actually has a name, correct? Yeah, it's called the waterfall illusion, appropriately. Or what's the other word for it? The motion after effect. Yeah, that's what I was looking for. This is like, if this is true, the explanation for it, then I'm just disappointed with our

brains. The explanation is that when we're staring at the waterfall, our neurons tracking the movement of the water become tired out, exhausted, overwhelmed. So when we stop looking at it and they take a break, all the other ones that weren't at work are suddenly working overtime and making things move that aren't actually moving. Right. That's a stupid explanation. I don't know, I buy that.

I mean, it makes sense, but I think it's stupid, it's boring. Yeah, just worn out neurons. Yeah, I'm tired. I need to sit down over here. Yeah, and then if we go forward a bit, in the 19th century, like you were talking about, that was when people got really interested in studying these things and what was going on in the brain because it coincided with studying perception and how our eyes worked in relation to our brain.

And then I guess some of the earliest optical illusions kind of proved, though, was this longstanding idea that our perception of vision, our visual experience, was based in how the eyes interpreted objects. And what these early optical illusions started to prove was, no, it's actually the brain that's getting messed up here. And now we're starting to get into here at this point, like some theories that make sense to me that I think are cool. But what this early study started to reveal was that the brain is extremely lazy and it

likes to take shortcuts. Right? Yeah. I thought this was actually pretty interesting. Are you talking about the lag time? The lag time, but also, yeah, there's plenty of other stuff. The lag time seems to me to be like one specific slice of the general tricks of the trade that the brain uses to cut corners.

Yeah. And the lag time is basically when everything seems to happen instantaneous. When you look at something, your eyeballs pick it up, the neurons start firing, and the brain tells you that's a coffee cup. But there's just the slightest little lag in the time it takes for that to happen. And one of the theories with optical illusions is the brain is trying to predict, and that slight, slight, slight, you know, I'm not good with small units of time, is nanosecond short?

Yeah, nanosecond is definitely short, but I think we're talking tenth of a second. Okay. So the brain basically tries to predict what should come next based on what we're used to seeing in real life. Right. Is that a good way to say it? Yeah. And the reason it would do this is because a tenth of a second, something can change,

like a tiger can suddenly appear. So the brain's constantly looking for clues in the environment to predict what a tenth of a second in the future is going to be like, right? Yeah. I think things move slow enough for us humans that it usually works pretty well. But what this researcher, Mark Cengizzi, says is an optical illusion, some of the optical illusions are actually reliable ways to trick the brain into making the wrong decision about what the future is going to hold.

One of the ones that classically falls into this example is, what's the one that he talks about where it's the one with the, so that you've got two parallel lines running horizontally, just separated by a little amount of space. And then in the background, there's radial lines all going toward the vanishing point on the horizon. Right? Yes. I can't remember the name of this one.

But the point that Cengizzi makes is that the radial lines, lines that radiate from a center point, our brains use as a shortcut indicator of motion. The herring illusion. Thank you. H-E-R-I-N-G. So these radial lines that we see tell our brain, oh, we're moving and we're moving toward this vanishing point in the distance. So these horizontal lines that are in the foreground are actually appear to be bent

in the center, bent outward from one another. Oh yeah, very much so. So what Cengizzi is saying is that the brain is predicting, since it thinks we're moving forward toward this point and then toward these lines, that as we get closer, they have to bend to basically allow us to enter in another way. But the thing is, they're not moving because it's a static image, but it's the brain being tricked into thinking we're moving forward and changing our perspective unnecessarily. Yeah, because the brain is used to the way we move forward in real life, IRL, for you

kids out there. And so a lot of this seemed like the brain almost kind of negotiating with itself. Yeah. You know? Yes. But part of it, so that lag time one makes sense, right? Sure. Another one that makes sense to me as far as why the brain makes shortcuts is that when

like the physical world is in at least three dimensions that we interact with it in, right? Yeah. But our eyes are giving us two dimensional representations that the brain then has to reconstruct into three dimensions. And it's learned to take all sorts of neat little clues to put together a pretty good prediction of what it's looking at. Yeah. And you can also flip-flop between two different views like the, is it the Necker cube?

Mm-hmm. I love that thing. N-E-C-K-E-R. And it's sort of that classic cube that you learn to draw, the one that's slightly more advanced than the basic cube that you first learned to draw. Right. It's the second cube that you learn to draw. Right.

On your, what was those things that you put on your books in high school? Oh, just like, yeah, homemade book covers. Right, exactly. Yeah. Basically, a brown grocery sack is what I used. Yeah, same here. That's because we were poor. Well, the pluses, those things held up.

Oh, sure. Yeah. So, you look at the Necker cube, and the fun thing about the Necker cube is you look at it and your brain is able to flip back and forth between the cube, basically having two different positions. Is that the best way to say it? I keep saying that. But, you know, again, these things are kind of hard to describe.

Well, yeah, it's kind of like the cube is transparent, and you can see all corners of it. Yeah. So, your brain is saying, okay, is that corner close to be or furthest away from me? And it can be both. It changes perspective. Yeah. And so, thanks to the Wonder Machine, we can put people in these things and see the neurons

responsible for the different perspectives flipping back and forth, depending on how we're looking at it. Yeah. Exactly. Which is pretty helpful at this point, because you had the 19th century where they started to suss out the ideas that the brain was responsible for this. It was the brain messing up. And then not a lot happened in between then and the 2000s when FMRI came into widespread

use. Yeah. So, yeah, a lot of these early theories are actually correct, because we can see the neurons responsible for them. All right. Well, let's take a little break here, and then we're going to come back and talk about the Hermann illusion and what the MRI said about that one. Hey, friends, when you're staying at an Airbnb, you might be like me wondering, could my place

be an Airbnb? And if it could, what could it earn? So I was pretty surprised to hear about Lisa in Manitoba, who got the idea to Airbnb the backyard guest house over childhood home. Now the extra income helps pay her mortgage. So yeah, you might not realize it, but you might have an Airbnb too. Find out what your place could be earning at airbnb.ca-host. On the podcast, Hey Dude, the 90s called David Lasher and Christine Taylor, stars of the

cult classic show Hey Dude, bring you back to the days of slip dresses and choker necklaces. We're going to use Hey Dude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it, and now we're calling on all of our friends to come back and relive it. It's a podcast packed with interviews, co-stars, friends, and non-stop references to the best decade ever. Do you remember going to Blockbuster? Do you remember Nintendo 64?

Do you remember getting frosted tips? Was that a cereal? No, it was hair. Do you remember AOL Instant Messenger and the dial-up sound like poltergeist? So leave a code on your best friend's beeper, because you'll want to be there when the nostalgia starts flowing. Each episode will rival the feeling of taking out the cartridge from your Game Boy, blowing on it and popping it back in as we take you back to the 90s.

Listen to Hey Dude, the 90s, called on the iHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Okay, so the Hermon Airmon, I'm not sure how to pronounce that, H-E-R-M-A-N-N, the Hermon Grid, conceived by Ludemur Hermon in 1870. And you nailed his first name. Oh yeah. Well, it's one of those classic illusions that we've all seen, and it's really simple. It's just a black and white grid of squares, and that's the one where, if you're just

looking at it, it looks like there's these little gray circles, little gray dots in between where these things intersect. And there's really nothing there, though, of course, when you focus on that, it goes away. Right. And I showed that when you're looking at an illusion like this, and others like this, the neurons are competing with one another to see the light and the dark. And basically, one set of neurons wins out over the other and then influences the message

to the other for what you end up perceiving. Right. Fairly interesting, I think. It is. It is. And this one kind of stands on its own, or in its own class, in that it's not really the brain that's being duped. It's because of the physiology of the eyes and the light receptors in the eyes, right?

So they're arranged so that they sense distinction, like contrast between light and dark, right? And if they're sensing both, they create this blob, their spillover, where some receptors in a single cell are getting dark and some are getting light, and they can create these blobs in the intersection. But then when you focus your attention on the white part, the intersection between the black squares, you're using your foveal receptors, which have far less inhibition or spillover so that the gray blob disappears in what you see is white. It's actually really, I read probably like four different explanations of it before it

started to sink in. It's straightforward, but it's tough to explain, I think, another word. Yeah, I totally agree. And one of the reasons we know that these neurons are sort of individually picking things up is because in 1981, these two dudes, David Hubel and Torsten Fiesel, great name. Great name. I knew you were going to say that. In 1981, they won the Nobel Prize in Physiology or Medicine because they found out that there's

actually a process in how the brain picks the stuff up and what the eye sees, and they found that each neuron is actually responsible for one little part, one little detail of that pattern in the retinal image, and so that explains why these neurons can duke it out basically on what it's seeing. Yeah, and it's not just like neurons competing, seeing light and dark. From what I understand, the understanding of our brain and vision is that an individual neuron is responsible for, say, a circle. It sees circles and it's transmitting any circular information to the brain.

Another neuron is responsible for seeing dark, another is responsible for seeing light, another is responsible for seeing red, another is responsible for seeing texture, and all of this sensory information, this visual information is coming to the brain all at once, and these various brain regions responsible for vision are putting it together the best way it can and you see a red ball, and there's a lot of cues that the brain uses that just fascinate me for basically what's called monocular vision, right? So when you are using both of your eyes, especially when something's up close, you're getting two separate pictures of the same thing, and the differences between these pictures

the brain can use to easily translate it into three dimensions, right, to handle things like perspective and stuff like that. But when something's further away, the brain has to use other little tricks of the trade, right? So you've got things like inner position, that's a pretty straight up one, where if one object's in front of another object, your brain says, well, the object that's behind is further away. Yeah, is that what explains like force perspective?

Yes. In art? Yes. Right? I do like force perspective stuff. I do too. It's kind of cool. It's neat stuff.

It's probably part of the op art movement, right? Yeah. When was that like 60s and 70s? Yeah. It seems like it. Yeah. And then, you know, kind of coincided with drugs, not surprisingly. And then there's another one that I hadn't heard of called atmospheric perspective.

Had you heard of that one? I had not. So atmospheric perspective is it's basically the dust particles and the water vapor in the air. The further something is away, the more of an effect those things have on the detail you see. The brain says, well, that's a little blurry, that's a far away object. And then there's plenty of other ones, but the gold standard is object size, right?

That's where you know roughly the size of an object and you can use it to compare to see whether it's far away or close, depending on whether it's small or large. Or if you don't know the size of an object, but you know two objects are identical and one is smaller than the other, well, then you know the smaller one is further away. So the brain's like constantly using all of these little cues and tricks to put together a conception of what it's seeing at any given point in time. And then what optical illusions are are, again, these things you can produce to reliably trick the brain into making these wrong decisions that shows its hand.

It reveals how the brain functions to take these shortcuts and the tricks it uses. Right, like a brain, you think you're so smart, you're really dumb. Look at this. Yeah. And the brain says, oh, stop looking at those things, look at normal things. I kind of like the apparent motion ones, although I can't look at a lot of them. Those are the ones where something is drawn in such a way that it looks like it's moving when it's not.

Right. I think the very famous snake illusion is a great example and you know this is another one of those theories that to me is a little weak, but one of the theories is that they're these almost like unnoticeable rapid eye movements that we make, how do you pronounce that? R-E-M. No. S-A-C-C-A-D-E-S.

Yeah, saccades, saccades, I think you could probably get away with either one. All right. Well, that's what they're called. It's like Pruitt-Taylor-Vint syndrome. Do you remember him? Yeah, he's a great actor. Yeah, he is. So those little movements, you usually get smoothed out by the brain, so we get like

a static picture, but what it's causing in this case is perceiving motion where there is no motion. And then the other theory on this one for apparent motion illusions is there's just so much information going on that there's just confusion. Right. I saw one that actually combined the two that's basically said that the saccades are creating the illusion of motion. But what they're really doing is because the brain is being hit with all this visual

information that just totally doesn't make sense, it would never happen in nature except maybe in motion, that these saccades actually each time your eye makes this tiny movement, it refreshes this overwhelming overload of information onto the brain, which creates the sensation of movement. Oh. Yeah, pretty cool. Well, one of the cool aspects of all of this to me is the fact that once you've seen the illusion and the trick to it, you can't undo that.

So the brain is like, aha, I got this one, the famous one, the old lady or the young woman, the black and white, it's a classic illusion. And once you can stare at it and be like, I just see the young lady or I just see the old lady. Once you've seen both, then your brain has, like I said, it says, aha, and it files that away as prior knowledge and a little folder in the brain, and you can't undo that. So once you've seen it and you've seen the trick, you can always look at it and kind of make that flip in your mind.

Right, exactly. And it's the same thing too with contourless figures where is it a wine goblet or is it two people's faces facing one another kind of thing, right? Oh, yeah, yeah, yeah. You know, the negative space? Yeah. And apparently the trick to those is you focus on the black or the white and you see whichever one appears to be in the foreground because what your brain is doing is saying, I need

a foreground and I need a background and then I've got something to work with. And depending on which one it's looking at, it decides this is the foreground or this is the background. So it's either a wine goblet in the foreground or it's two people's faces in the foreground. You know, I wonder if this stuff, if they know anything about, because I didn't see anything in the research, but if they know anything that this is like a brain exercise and helps you out, like, you know, playing Sudoku or doing word puzzles or if the brain is like, stop looking at these, you know, I don't like this.

I can't take any more, you know, or, you know, like literally maybe or if it causes stress on the brain by, by taxing it in a way that it is not accustomed to or doesn't say doesn't like, obviously the brain doesn't have a, you know, it's not a little person, right? But you know what I'm saying, yeah, no, I know what you mean, yeah. But the brain, even if it's not a little person, it could still not like things, right? So let's take another break and then I want to tell everybody what my favorite optical illusion of all time is. Hey, everybody, when you're staying at an Airbnb, you might be like me wondering, could

my place be an Airbnb? And if it could, what could it earn? So I was pretty surprised to hear about Lauren and Nova Scotia who realized she could Airbnb her cozy backyard treehouse and the extra income helps cover her bills and pays for her travel. So yeah, you might not realize it, but you might have an Airbnb too. Find out what your place could be earning at airbnb.ca slash host. On the podcast, Hey Dude, the 90s called David Lasher and Christine Taylor, stars of the cult classic show, Hey Dude, bring you back to the days of slip dresses and choker necklaces.

We're going to use Hey Dude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it and now we're calling on all of our friends to come back and relive it. It's a podcast packed with interviews, co-stars, friends and non-stop references to the best decade ever. Do you remember going to Blockbuster? Do you remember Nintendo 64? Do you remember getting frosted tips?

Was that a cereal? No, it was hair. Do you remember AOL instant messenger and the dial-up sound like poltergeist? So leave a code on your best friend's beeper, because you'll want to be there when the nostalgia starts flowing. Each episode will rival the feeling of taking out the cartridge from your Game Boy, blowing on it and popping it back in as we take you back to the 90s. Listen to Hey Dude, the 90s called on the iHeart radio app, Apple Podcasts or wherever

you get your podcasts. All right, Chuck. Yeah, I'm ready. Well, there's two. One I like slightly less than the other. Okay. So start with the second place one. Okay.

I knew you were going to say that. Yeah. I think that's a great way to do it too. So you've got, I don't know the name of it. I'm sure there is a name, but actually I think it's the contourless figure as well. You take three circles and you cut a pie slice out of all of them like a Pac-Man. And you orient those pie slices so that each one forms what appears to be the corner of a coherent square.

And you look at it and you're like, well, there's a square right there with some that's overlaying four circles. But if you stop and think about it, there's no line whatsoever that that makes that square. It's your brain exclusively filling in some suggestible information to say, well, there's a square over a field of four circles. It's pretty neat to me. I like that one. So what's what's number one?

Oh boy. Yeah. It's called the Adelson Checkerboard. Okay. Surely you've seen this one, right? I'm looking it up as we speak. It's from the 90s. There was a MIT vision researcher named Edward Adelson.

And he created this checkerboard where on the checkerboard, there's dark and light squares like a normal checkerboard. And then there's like, I think a cylinder on the checkerboard and it's casting a shadow. And so he says, look at this white square and then look at this black square, which is lighter, which is darker. And you say, well, that's easy. The darker square, figure B, say, is obviously darker than figure A. Yeah.

And he says, that's wrong. That's absolutely wrong. Figure A and figure B are exactly the same color and shade. Yeah. I'm looking at it. I've seen that one for sure. The whole thing really, really works because it takes advantage of two different tricks that you can play on the brain.

Or it takes advantage of two different shortcuts the brain makes. One is that cylinder is casting a shadow that appears to be putting figure A into a shadow. So your brain automatically makes assumptions that if something is in a shadow, it would normally be lighter, which is in this case an incorrect assumption. It's actually the same shade as the other one. And then the other assumption it's making is that because that square is surrounded by squares of a darker color, and it's in a shadow, it seems to contrast it. Where the other figure, figure B, is a dark square surrounded by light.

It seems to be darker because of the context of the squares that it's surrounded by. So your brain is using two different things, the presence of a shadow and then the context where if something is surrounded by lighter stuff, it seems darker. If something's surrounded by darker stuff, it seems lighter. And that's just not always the case, obviously, because Edward Adelson proved it's not so. You want to know my favorite? Yeah. The classic Ebbinghaus illusion.

Oh, that's a good one. E-B-B-I-N-G-H-A-U-S. This one is sort of similar, but it's not so much about color, but it uses adjacent objects. And a lot of these do, too, they use other things surrounding something to trick your brain. Right. And in this case, it's the classic one. Go look it up.

It's the, you have two orange dots. One on the left, let's say, is surrounded by six larger gray dots, and the other one on the right is surrounded by eight smaller dots. It's very simple. That's why I love it. And the orange dots are the same size, but they look completely different sizes. And it's just, it's so simple. And I think this is one of the ones that, and two, they have this contest every year,

I think for like, I don't know, it's been going on for at least 10 or 12 years, right? For new illusions. And like we said earlier, you know, a lot of these new illusions are still just sort of riffs on the classics. But the one that won a couple of years ago in 2014 was a new version of the Ebbinghaus illusion, where it's actually a video that you have to play. So it moves the outer dots, they, it looks like it pulsates and, well, it is pulsating. They get bigger and smaller.

And the orange dot stays the same, but it looks like it's shrinking and expanding. Right. So it's kind of cool. It's just a, just a play on the Ebbinghaus illusion. Right. But that's, that's what we were saying earlier too, is like, it's almost like they invented all of them in the 19th century, and then now we're just able to perfect them a little more.

Yeah. Pretty cool. Another thing I thought was really neat was that there is this biological basis that is the same for everyone on planet Earth, obviously, but they did find there's some across different cultures that they didn't take the same visual cues necessarily. Right. So it's a classic Mula-Laya illusion that everyone has seen, and that's just the really simple one of two straight lines, horizontal lines, and they have arrows on the ends.

On one of them, the arrows are pointing out. On the other, the arrows are pointing in, and those two horizontal lines appear to be different lengths. Right. And so they did a study in South Africa, and they found that most of the European South Africans thought, yeah, like, look at them, they're different lengths. And they showed it to the Bushmen of South Africa, and they were like, no, dummies. Right.

They're the same length. Can't you see that? And the researchers are like, what? Yeah. And they really, I mean, they have some theories about it that kind of makes sense that Western societies may be a little more used to these things that are built in straight lines and a little more geometrical where the other culture might be just more attuned to nature where there aren't so many straight lines.

Right. And because the explanation for the, what was it, the Meyer? The Mueller Liar? The Mueller Liar effect, or optical illusion, is that depending on which way the arrow is pointing, whether at the end of the line or away from the line, the brain is used to seeing corners, right? Two walls coming together at a ceiling make that same kind of arrow. And one that's pointing away means the point of it is further away.

So it would make the line look longer, whereas one that's pointing inward would make it look like the corner is closest to us, right? So it would seem like the line is shorter, but the explanation was that, well, Bushman have never seen two walls come together at the ceiling, so that's why it didn't happen to them. But the thing that disproved that is that they trained a computer to look at this stuff, and they didn't train it on three-dimensional objects. So it wasn't familiar with walls coming together with the ceiling, and it was fooled by it

as well. So they were like, well, we have no idea what's going on then. Bushman or magic is what they said. I wonder why so many of these illusion enthusiasts seem to be like German and Austrian. I think I had to do, that was largely where psychology took off. Yeah. I guess that makes sense. I think it was Dutch.

Was he? Yeah, I think it was Dutch, but it seems like a lot of these are like German and Austrian. Yeah. I think it has to do with that was where the hot seat of psychology and brain research was at the time. Interesting. Yeah. You got anything else?

Yeah. Actually, I do have one more. There was a guy named Herman von Helm Holtz. Oh, he wasn't German. Right. No. Nice Irish guy. He was from Indiana.

Herman Helm Holtz came up with these squares that are not actually, they don't have confining lines or defining lines. They're just equal lines of squares or lines equally apart that form to the brain a square. But ones that are horizontal seem smaller and shorter than ones that are vertical. Which is weird because if you are wearing like a horizontally striped shirt, everybody's like, you look fat in that shirt. Well, Von Helm Holtz, you don't. You should actually look slimmer, which surprised me.

So I started wearing horizontal stripes as a result. You got your Charlie Brown shirt out? Yeah. Because that was sort of the old, I don't know if it's true or not, but they said that the New York Yankees designed their pinstripes to make Babe Ruth look thinner. I could totally buy that. But I don't know if that's true. I thought they had pinstripes before then.

And Babe Ruth was eating a steak while they were fitting them for and he said, thanks for thinking of me. But he wasn't even using silver or he was eating it with his hand. Yeah. And he also blended a steak into a milkshake and drank that along with his regular steak. Right. And he didn't take his cigar out while he drank it. He just put that in the corner of his mouth.

Yeah, sure. And it's after dinner at Kanyak. That's why we love Babe Ruth. You know what we didn't get into at all and I don't know if they even count as illusions or if there's something else or those. And they were a boy. And all the rage in the early 90s, I feel like, were those... Magic eye.

Yeah. Where you stare at the thing and all of a sudden a ship pops out at you. If you're lucky enough to be able to see it, I know a lot of people that would just endlessly not be able to see you and it would frustrate them to no end. I think if I remember correctly, they advised that you stare into the middle ground. Yeah. And sort of like unfocus your eyes. Yeah.

I was looking those up. There's a mental floss article on it that was pretty brief and it made sense. I think they were machine vision learning researchers who were like, hey, let's make some money on the side. Right. But they start with like a depth map of something and put it in grayscale. And I think they make two of them so your eyes are getting the two different versions of it, but one smaller than the other.

So it really makes it pop as far as depth goes. Right. And somehow the random repeating pattern that overlays it transmits that information to your brain unconsciously. Oh, well, so you did look it up then. I did. I don't know if I got it fully right because it's actually kind of complex, but I thought they did a pretty good job of describing it.

Could you see those? Yeah. Sometimes, sometimes. Yeah. I always could see them. And that's another one of those where once you see it, you can just immediately like draw it out. And of course, there's the one Ethan Supley in Mall Rats.

Sort of the one joke through that movie was he just stares at this thing like through the whole movie. Oh, and he couldn't see it? Couldn't see it. Poor guy. What a great joke. You know, speaking of that, something that's always bothered me, Stephen King said in one of his books or something like that, he was talking about how you can't unsee something.

I thought he was going to say he was talking about Mall Rats. And he used the man and the moon as an example. He's like, it's like the man and the moon, once you see it, you can't unsee it, right? I don't get that. Like I've seen the man and the moon before and I totally can't find them again. So you can unsee it. Stephen King is wrong. What is the man and the moon?

What are you talking about? You've never seen the man and the moon? No. So I guess probably look it up. I think it would help to see somebody else pointing it out. And then when you see the, when you look at the full moon, you should be able to see it. But there's a man looking down. It's Jackie Gleason.

I don't think, are you looking it up right now? Yeah, I'd never do that was a thing. That's weird. And then the Japanese think it's a rabbit and that the rabbit is up there making mochi. Really? I don't know what other cultures think. Those are the two I'm familiar with. Huh.

Yeah. So mochi. All right. If you want to know more about optical illusions, type those words into the search bar at how stuff works. Better yet, go to michaelbach.de and just have some fun. And since I said DE, it's time for listener mail. I'm going to call this Aussie slang.

We love our, and I said Aussie, I meant Aussie. We love our Australian listeners. We've got a lot of them. They've long supported the show, so we'd like to shout them out. Yeah. Australia. He said, get out fellas. That's pretty good.

I'm not going to read the whole thing like that, but I will read. It's just nailed Canberra. I'm a devoted listener from down under and I'm doing my best to get through your podcast. I love the show and finish every show with a smile and some new fact to tell my mates about. Anyway, I got a quick story for you to have a laugh at and possibly be very confused by the other night. My mate and I were going on a mochus run, M-A-C-C-A-S. I think we've talked about that before,

right? No. Isn't that beer? I don't know. What about Foster's was Australian for beer? And he goes, Oi mate. After we've been to Macus, we can drop by the servo, grab a pack of dearies, and then the bottle-o, grab a slab of E-B-Stubbys, and head back to yours and get pissed.

Okay, so let me, let me see if I can translate this. Oi mate. Uh, hello friend. After we've been to Macus, uh, after, I don't know what that was, is next. When we drop by the servo, we can go hang out with Tom's servo. I bet you anything a servo is like a gas station. Okay. Uh, grab a pack of dearies, uh, get some milk, and then the bottle-o, uh, get a bottle,

grab a slab of V-B-Stubbys, get some ribs, I think, I think that's Australian for ribs. It is, uh, and head back to yours and get pissed, uh, and then go to sleep. Okay. I think you're right on the money. Yeah. Uh, I know you guys don't often do requests, but you'd be rad if you guys did a podcast on Aussie Slangs history and meanings, mostly because I would love to hear Chuck's Aussie accent.

Oh well. Yeah. Granted. He didn't, wait, he didn't translate it himself? No. So we'll never know whether I was completely right. Someone, someone will. Okay.

Uh, and I'd love to hear both of you pronounce as much Aussie slang as possible, but also because I'd like to have facts about why I speak the way I do. Stay rad. And that is from Liam. And he said, PS, we swear a lot down here, uh, and if that's why you can't do an Aussie slang podcast, I don't blame you. Well, I swear a lot, I-R-L, Liam, but we just keep it clean for the show. That's right.

Nice. Yeah. Well, thanks, Liam. I'm not going to do an Australian accent because it would hurt everyone's ears. Uh, if you want to get in touch with us like Liam did, you can tweet to us. I'm at Josh, um, Clark, and at S-Y-S-K podcast, Chuck's on facebook.com slash stuff you should know, and Charles W. Chuck Bryant. And you can send us an email to stuffpodcast.howstuffworks.com, and as always, hang out with us at our

home on the web, stuffyoushouldknow.com. For more on this and thousands of other topics, visit howstuffworks.com. On the podcast, Hey Dude, the 90s called David Lasher and Christine Taylor, stars of the cult classic show, Hey Dude, bring you back to the days of slip dresses and choker necklaces. We're going to use Hey Dude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it. And now we're calling on all of our friends to come back and relive it.

Listen to Hey Dude, the 90s called on the I heart radio app, Apple podcasts or wherever you get your podcasts. Hey, I'm Lance Bass, host of the new I heart podcast frosted tips with Lance Bass. Do you ever think to yourself, what advice would Lance Bass and my favorite boy bands give me in this situation? If you do, you've come to the right place because I'm here to help and a different hot sexy teen crush boy bander each week to guide you through life. Tell everybody, yeah, everybody about my new podcast and make sure to listen.

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