Why Your Brain Thinks This Water Is Spiralling | Science Of Illusions | WIRED

so every once in a while you come across something that just takes you completely by surprise like you think you know how water and gravity work right you turn on the hose and water comes out and then you see something like this I mean what exactly is going on here if you think the camera has something to do with it you're right today we're gonna look at a whole bunch of illusions that mess with your visual perception some rely on camera tricks others require special lighting and some you can even see with nothing but your naked eye but first let's talk about how we wound up building this thing my producer Juno and I had seen something like it online we did some research and found that to make it ourselves we would need a speaker rubber tubing a stand a water source a sump pump for circulating that water and a lot of gaffers tape here's the thing we built this contraption so we know how it works and we'll get to that in a second but we also wanted to know why it works why our brains can be tricked into seeing the water in this very specific way so we called up David Eagleman he's a neuroscientist at Stanford and an expert on visual illusions so have you seen one of these things before oh yeah that is pretty amazing I love that illusion yeah exactly it was it was super fun to build but Juno and I are trying to figure out like sort of why it works like on a neuro mechanistic level is that something you think you could help us out with oh I'd love to yeah and there's a class of illusions that are like that if you just want to come down to my office in Palo Alto we can build some stuff here and I'll show you guys some things yeah that'd be sweet so we took apart our contraption drove down to Palo Alto and put it back together with Eagleman inside his office all right so we pack this thing together see we're going to do this all right now here's the thing you can't actually see this effect with the naked eye so we're watching it through the cameras on our phones here's why we're using a tone generator to run a specific frequency in this case 24 Hertz which is 24 cycles per second through that big speaker when the speaker plays the tone it vibrates at the same rate causing the hose and the water flowing through it to undulate at the same frequency to the naked eye it looks like it's spraying everywhere and it is but it's not spraying randomly if we set our camera to match the rate at which the water is moving then we get this here's what it looks like to the naked eye and here's what happens when we adjust the cameras frame rate and if you manipulate the frequency deliberately you can produce even more effects so right now our tone generator is pumping out 24 Hertz we're gonna offset that by 1 Hertz and so now when I look at this through my phone the corkscrew looks like it's travelling up out of the bucket into the tube what's actually happening with this water we're capturing a view of it that is no longer even and so it looks like it's moving now of course the water isn't actually climbing up into the tube your brain is just telling you that it is and that's because of something neuroscientists call apparent motion when the brain receives a series of adjacent images in rapid succession it interprets them as being in motion it's the same reason old animations and flipbooks work in video - what's happening here is that the cameras frame rate is just barely out of sync with the vibration of the speaker so instead of seeing the spiral in the same position every twenty-fourth of a second we see it in what looks like a slightly higher position and when you string together all those tiny shifts it gives your brain the impression that the water is spiraling slowly upwards or if you adjust the frequency of the tone generator slowly downwards now you don't usually see this kind of effect on camera but there is one place that it pops up all the time and that's when you see a wheel moving on a car for example and that gave David an idea why don't we hop in the car and using the camera film the wheel as we're driving and see if we can reproduce the wagon wheel illusion okay now you may not have heard of the wagon wheel illusion but you have definitely seen it so our producer Juneau is gonna be hanging out the window with a GoPro on a selfie stick okay David in the back has a live view of what's happening oh geez beautiful it's cool right here's what's happening the frame rate on the camera is perfectly matched with the rate of the wheels rotation so every time it captures an image the spokes appear to be in the same position and just like we saw with the spiraling water weird things happen when the frame rate is just slightly out of sync with the motion of the object being filmed but actually keep going so as you're going straight here okay yeah it's beautiful it's going backwards here at this speed it's just going fully backwards right here I'm doing a pretty bad job of driving at a consistent speed which is why the spokes go from looking like they're spinning slowly backwards to standing still to drifting slowly forwards all in the span of a few seconds with the spiraling water illusion we flipped the switch and the water immediately vibrated at the exact frequency we wanted but here the rate at which the wheel is rotating fluctuates based on how slow or fast I Drive which changes with the camera sees at a fixed frame rate oh my god that's wild watch that footage again but this time pay attention to the wheels bolts I mean the really wacky part I have just never noticed this before is there are five bolts and seven spikes and because of the differences in the distances there they are doing different things so the bolts right now look like they are moving backwards and the spokes at this exact moment are not doing anything they're just they're essentially still but the bolts are zipping around like crazy because your brain doesn't know that that's actually spoke number one and then spoke number two and spoke number three in that position it just looks the same to it and the bulbs on the other hand are changing position until your brain picks the shortest direction and says oh okay I think it must be rotating that way as opposed to that way remember a parent motion it applies here too because the bolts in each frame appear to shift ever so slightly counterclockwise your brain interprets them as spinning backwards okay so that was sweet illusion that's requiring the camera to work right we can't see with the naked eye right but there is a way to do that yeah we can do that essentially with a strobe light by illuminating for us where we see the thing and then we see the thing we see every 24 you know 24 times a second we could capture the same thing without a camera right you actually show me you've got like a little yeah so this is the levitating water illusion so this has a pumpkin so even though it looks like that's one drop that's actually catching one drop at that position and then catching the next drop at a position just above that next drop it of Decision just above that so what you see because of the strobing is this going up yeah by switching the rate at which it's dripping we give it get standstill you can make you go the other way in slow motion so essentially you can change the rate at which it's dripping and you can change the rate at which the strobe lights are flickering so the cool thing to me about this illusion is that you don't need a camera to make it work you can actually see it with your naked eye with a little help from the strobe light yeah exactly it's because the strobe light is illuminating though it's turning on the world several times a second just like a camera frame is doing and because of that we can make the drops stand still because we're catching one drop and then the next drop in the next drop in the same position that's when we're turning on the illumination so you can make it run back exactly if you catch this next drop just a little bit higher than your visual system says well I saw that guy and I saw that it must be the same guy it looks like it's climbing up so you know normally in evolutionary time we saw it things under continuous sunlight err with fire light or whatever so this is a very unusual situation for our visual systems to have to deal with where it sees something illuminated and then that goes away and the next time we see illumination it happens to be something in the exact same spot or really close by it yeah there is an illusion that is related to this in which you don't need a strobe light at all you don't need camera at all you can see it under constant sunlight you can see the direction of a moving object reversing it's a very strange thing and we can build that actually if you want we can build that up yeah all right well why don't you have a seat okay so the key is find a spot that you can stare at that's not moving in other words don't track the dots with your eyes here's a view of what I'm seeing if you haven't already full screen this video we're gonna run this shot for a long time so you can try it for yourself fix your eyes on the white dot and keep them steady try not to let them follow the black circles as they whip past now try not to blink and be patient stare long enough and something strange should happen every so often the direction that the dots are spinning will appear to flip it only happens occasionally and while it happens for some people more than others the effect never lasts more than a few seconds here's the difference between what you're seeing here and the spiraling water and wagon-wheel illusions those effects happen at the same time for everyone because the camera is driving the illusion but in this case everyone sees it a little bit differently because it's not the camera that's responsible for the effect it's you did you get it to work if not don't worry we've included an extended version of this shot in the show notes for you to try at home so what's going on you might think this happens because our brains process visual information the way a camera does in discrete frames but david says that's not the case okay so what's to say that the frame rate at which my brain processes it isn't just changing all the time yeah good question so in order to address that when I came up with was a way to test whether your brain is taking the screech snapshots of the visual scene all at once and that was a very inexpensive test that took $5 in a mirror do you want to try that yeah okay I'm gonna ask you to scoot around to that end of the table now what I have here is a big mirror and I'm gonna put this here so that you see two two drums rotating now you should see them about side by sides that would you see yeah the question is do you see both drums reverse direction at the same time when you see reversal or do you see one drum reverse and then a different drum reverse and then the first drum reverse again take a look the rotating dots on the right are in the real world the ones on the left are the reflection just like last time focus on the white dot and keep your eyes steady soften your gaze a little bit and wait the mirror is showing you a perfect visual double of the original device and that is the key to this experiment if our brains did in fact process visual information the way cameras do in discrete frames then you would expect both sets of dots to always switch directions at the same time but that's not what happens you have mechanisms in your brain to detect leftward motion and those are picking up on that and saying oh you clearly have leftward motion in the world but you also have mechanisms for rightward motion and it turns out that those rightward mechanisms can be fooled by a lot of leftward motion like this the right word guys get a little bit activated by leftward motion so what happens is when you stare at this motion for a long time your brain is pretty sure it's going to the left but it has a little bit of a hypothesis that maybe it's moving to the right and so those are in battle with one another and so every once in a while the right story wins just a little bit now this is very similar to other things that we've seen like like with a cube that's drawn just the wireframe of the cube network you the Necker cube soon as you see it coming out one way or you see it going out the other way and they'll switch back and forth but those happen to have the same probability 50/50 chance that it might be one way or the other this has like a 95 versus 5% chance so this is more rare you have to stare at it for a while to see it come out once in a while so you have populations of cells in your brain that are fighting for both stories and it's just a matter of which population dominates the hill at any given moment that's what you perceive yeah and it's all because your brain is locked in silence and darkness it's not seeing any of this directly it's putting together a story of what's going on in the outside world based on the little signals that it sees that's why there's so many different types of illusions and these illusions aren't just for fun they reveal interesting things about the way we're wired and how he experienced the world so in the end if our brains tell us stories that messed with our perception of reality that's not necessarily a bad thing

Channel: WIRED

Views: 2,138,026

Rating: 4.8689556 out of 5

Keywords: animation, illusions, neuroscience, optical illusion, optical illusions, neuroscientist, visual perception, david eagleman, robbie gonzalez, visual illusions, apparent motion, illusion, crazy illusion, optical illusion explanation, illusion explanation, water illusion, optical illusion tire, tire optical illusion, wheel optical illusion, wheel illusion, david eagleman illusion, visual illusion, illusion explained, visual illusions explained, visual illusion explained, wired

Id: 4g2KjWYGEmE

Length: 13min 28sec (808 seconds)

Published: Wed May 29 2019