Psychology 1: How Your Perception (Really) Works | Andre Klapper, PhD | Skillshare

Psychology 1: How Your Perception (Really) Works

Andre Klapper, PhD, Researcher, Neuroscientist, Psychologist

Psychology 1: How Your Perception (Really) Works

Andre Klapper, PhD, Researcher, Neuroscientist, Psychologist

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15 Lessons (1h 4m)
    • 1. Course outline

    • 2. Introduction

    • 3. Quick note: additional material

    • 4. The visual puzzle (Section 1)

    • 5. Parsing: what belongs to what?

    • 6. Color: a game of light and shadows

    • 7. Depth: enter the third dimension (part 1)

    • 8. Depth: enter the third dimension (part 2)

    • 9. Size: a story of giants and dwarfs

    • 10. Form: it's never what it looks like

    • 11. The visual system (Section 2)

    • 12. Conscious and unconscious perception

    • 13. From perception to memory

    • 14. The perception-memory loop

    • 15. The bigger picture

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About This Class

What we see is not the same as what our eyes see.

At every moment, our brain is secretly editing what we see without us noticing it.

This course will uncover how your brain is editing what you see and how you can make this visible. 

Learn how your perception really works and experience directly how your brain is constantly manipulating what you see.

What you will learn in this course

First, you will see how exactly where your brain is fooling you. Specifically, you will learn…

  • How your brain puzzles the pieces that your eyes see together

  • Why the colors we see are not the true colors

  • How our brain makes us think that we see in 3D although we definitely don’t

  • Why our eyes cannot see how big something is and how our brain hides this

  • How our brain edits the form of objects in our eyes

Then you will learn what processes are hidden in our brain…

  • Conscious and unconscious perception

  • How perception and memory work together to construct your reality

Learn exactly what your brain is doing unconsciously and catch the brain in the act of editing what you see again and again during this course.

When I was a psychology student, perception did not seem very interesting to me.

Now it’s one of my absolute favorite topics.

The reason is simply that there is so much going on in our perception that we are not aware of and it is so easy to make those things visible.

Once you know where to look, you can see it everywhere.

And this makes learning about our perception so interesting and enriching: you will never see the world the same way again.

In my experience, especially the people who think that they are not interested in psychology become interested very quickly once they learn about perception.

So enroll now and find out how your perception really works.

Once you enroll you can start with any lecture and see for yourself what it has in store for you.

And you can ask me any question you have about human perception.


Meet Your Teacher

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Andre Klapper, PhD

Researcher, Neuroscientist, Psychologist


Psychology & Neuroscience researcher with more than 10+ years of training and experience.

Learning how our mind and brain work and conducting research on these topics has been incredibly fascinating for me and it definitely enriched my life.

My mission is to share my experience with other people and help them to get the most out of themselves.

I have courses on Psychology, Neuroscience, and research.

Why learn from me?

- 700+ enthusiastic reviews from people all over the world.

- Short and concise lectures - straight to the point without any unnecessary information.

- Simple and easy approach - complex ideas are broken into bite-sized chunks.

- Quality content. PhD, 10+ years of training and experience, scientific publica... See full profile

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1. Course outline: Hi, My name is Andre, and I'm a psychologist and neuroscientist with more than 10 years of experience. And in this course I want to show you how our perception works and how our brain constructs our reality. We walked through the world thinking that what we see is a direct reflection off the world around us. But the truth is that the world we see is constructed by our brain. Our brain is constantly editing with our I C without us being aware of it. And in this course I will show you what our brain is doing there and why it is doing this. First, we will dive into the specific aspects of perception such as the perception off color and depth, which then allows us to catch the brain. Wallet is editing what we see. Then I will show you how the visual system in our brain works and the different strategies it uses to make us perceive. During the whole course, I will shower you with examples and give you lots of opportunity to experience what our brain is doing there. I don't just want to teach you abstract theories. I want to make you experience that it's true. We will also tackle a lot of important questions, such as Can we trust our perception? What is our brain doing outside of our awareness? Why does our brain added what we see? How do optical illusions work? What is unconscious perception? Why do different people see things differently? And if you have other questions during the course, I will be happy to answer those as well. Perception is the best topic to start with if you want to understand the human mind, this course is for everybody who wants to make the first step to really understand the human mind and for everybody wants to learn how our brain constructs are reality. 2. Introduction: Okay, let's start to talk about perception, and we should start with the question. What actually is perception and in the simplest terms, perception is our window into the world. Everything we know about the world, everything we remember about the world initially came in through our senses. It was perceived, and so without perception, our mind would literally be empty. We wouldn't even have a mind if we wouldn't be able to perceive, because perception is where everything starts. Perception is our window into the world. And given that it's so important, we should ask the question. Can we actually trust our perception? And that will be one of the big questions we'll tackle in this course. And it's so important that I want a phrase it a little bit differently. Is perception either something passive that works pretty much like a camera does where it just passively records without their without editing anything? Or is it a more active process where the things we see have been edited? And in this case, what we see is not the same as what our I see, and what people usually initially think is that perception is something passive that works pretty much like camera does. And that's because when they think about perception, they think about our eyes. They have learned in school that's perception is basically when light hits an object and it gets reflected into our eyes. And then it creates an image on the so called retina off our eyes, which is basically the screen of our eyes, and that image is what we see. But that is not true. This description of perception is fundamentally incomplete. It leaves out some of the most important parts of perception, and what we need to do in order to understand perception is asked what is happening after the image was received by our eyes. So after an image was received by our eyes, it gets into the brain, and the brain doesn't just leave the image as it is. Instead, it edits it, and this is where perception turns from something passive into something active. Where the things we see are not the same anymore, is whenever I see and much of this course is there for about what's going on in our brain and why our brain is editing what we see. So before we really get into the specific process that are going on there in the brain. Let's talk a little bit about the question. Why would our brain actually added what we see? And the reason is that there is a problem, because with our I C isn't necessarily the same as what's out there in the world, and what our brain is basically doing is it's trying to play detective and figure out what's really out there, and it corrects for things that are misleading in our eyes. And it feels saying information that is missing in our eyes and it basically tries to tell us what's really out there rather than what are I see? And sometimes that detective gets it right and then we see what's really out there. But in some cases, the detective also gets it wrong, and then we see things that aren't actually there in the world, and I'm going to show you many examples off that later, and I'm also going to show you evidence that what I'm saying is really true, that this is really how our perception works, Okay. But I think you get the basic idea and that means that you're ready to dive into the more specific topics of this course. 3. Quick note: additional material: Okay, just one more thing before you really start with the course. Sometimes during the elections are referred to additional material that you can see out of the lecture. You can find this material in the pdf in the class project that pdf contains a number of links which will take you to more videos that will show you mawr, visual illusions and other stuff that illustrate to you how our brain constructs are reality. So if you hear about additional material out of the lecture, go to the pdf in the class project. Okay, having said that, let's have a look at how our brain construct our reality. 4. The visual puzzle (Section 1): in the first section. I'm going to familiarize you with what our brain is doing beyond what our eyes air doing. And I want to show you with many examples that our perception is not passive but very, very active. Our brain actively decides which things in our eyes belong together. It actively at its the colors that we see so that sometimes we see colors that aren't actually there. Our rain makes things look three dimensional even though they aren't really three dimensional and sometimes are by and makes things look big that aren't really big. And it makes things look small that aren't really small. So they're really a lot of things that our brain is doing in our perception, which were usually not aware off. And in this section, I want to show you what exactly our brain is doing there, and wide is doing this 5. Parsing: what belongs to what?: the first unconscious process. We're gonna look at his visual parsing and to illustrate to you what visual parsing is. Have a look at this picture and have a look specifically at the sun in this picture. When we look at the sun in this picture, we immediately come to the interpretation that the sun is round. It wouldn't even occur to us that it could be otherwise. But if you think about it than strictly speaking, that's not what we see. Instead, what we see is a yellow shape here and the yellow shape there and the yellow shape there and so on and so on. So we see a lot of separate yellow shapes, and yet somehow it is natural to us to think of them as belonging together. And that is visual parsing. Visual parsing is about deciding what belongs to what, and it's something that our brain does automatically and unconsciously, so that we don't even realize that we're making a decision. There to us is just what we see. Let's take another example. Do you think that the grass leaf in this picture here that it ends here, or do you think that it continues and ends here. If you think about it, then you may very well come to the conclusion that it ends here because that's what we see . But without us consciously thinking about it, we automatically think that know the grassy of continues here, and it ends here and again. That's an example of visual parsing. We decide that this part and this part belonged together. So what's happening here is that our brain interprets what we see and makes decisions over what belongs together. And we usually don't realize this, except if we realize that the interpretation is wrong on an example of that is this little illusion. So in this trick, we initially have the impression that there is one thumb. We have the impression that the thumb that starts here ends here. But then all of a sudden, something happens that shows us that our interpretation was wrong. And it's not that we have made the conscious decision that these two parts belong together . Our brain has done that unconsciously for us and only once the brain realizes that the interpretation is wrong and it reinterprets. We realize that there's something going on, and that's one of these rare moments where you can experience visual parson. Visual parsing is also what lies at the heart of many magic tricks, such as the famous saw the Woman in Half Trick. In this trick, you see a box in which seemingly a woman is lying, and then suddenly the magician sauce the box into two pieces, and we're completely shocked because to us it looks as if there's a woman lying flat in that box. However, in reality, what's happening is that there are actually two women in that box, and that hat on one side of the box belongs to a woman one, while the feet on the other side of the box belonged to a woman, too. So there's actually no harm sawing the box in half on. The only reason why this shocks us is because we assume that this hat belongs to these feet and again. That's an example of visual parsing. It's a decision that our brain makes for us unconsciously, and we don't realize it until it turns out that the interpretation is wrong. Here's another example where visual parsing tricks us into seeing something that isn't actually true. In principle. We know that These two has don't belong into these two bodies, but we see them as belonging together anyway. And so what you can see very nicely in this example is that we don't have any control about visual parsing. Visual parsing is something that our brain does unconsciously and automatically, and whatever our brain decides belongs together is what we see as belonging together, even if we know consciously that it doesn't actually belong together. Here's another example where our brain doesn't quite want to align with our conscious thinking. In principle, we know that this is one person's body and this is another person's body, and this is another person's body, and we know that they're just wearing these black and white colors to trick us. But even if you know that, it's very hard not to see these to Alexis belonging together and these two legs as belonging together and these to Alexis belonging together because even if our conscious thinking is not fooled by the colors, our brain is and we can't help. But seeing what our brain decides is the truth. Okay, So far, I've showed you elaborate show tricks in which visual parsing is going wrong. But you can actually also experience that in your everyday life. And a good example is when two people are hugging when two people hug and sometimes can get very difficult to decide which body part belongs to which person such as in this picture for this picture at first sight it looks as if the guy is standing and the girls sitting. But actually it's the other way around, and it takes a moment to figure that out. Here's another example. If you look at the upper part of these people, then everything is fine. But if you go from the back of this guy down to the feet, then suddenly it seems as if the feet of the girl belonged to the guy. And what's happening here is that we think that a part of the trouser of the guy is actually the trials off the girl. So this is the trials of the guy. But it has this white and blue color, and therefore it looks a little bit as if this could be the legs off the woman. So as you can see evidence that we engaging in visual parsing is everywhere. If you just know where to look. Look at people hugging each other. Look at magic tricks. All of these things show you that our brain is engaging in visual parsing. And if you take a moment to look around in the world, if you just look at the ground, for example, you will realize how complex the task is that our brain is doing every day. The world we see is a complex puzzle, and our brain is dealing with that puzzle every day and at all times ends. By the way, have you ever wondered how a newborn sees the world when it first opens his eyes? The world they see when they first opened their eyes is actually incredibly confusing to them because they haven't figured out yet how to solve the visual puzzle that they're facing so newborns can to visual parsing. Yet. And that's one of the reasons why newborns can really focus their eyes on things yet because they haven't figured out yet where one thing ends and the next thing starts. Okay, that was a lot of information, so I want to give you a little summary at the end. One of the main problems are brain faces when we open our eyes is to decide what belongs to what we call that visual parsing. One problem that our brain faces is that things that are separate in our eyes, maybe long together. Another problem that our brain faces is that things that are together in our eyes may not belong together. We've also seen that sometimes our brain gets visual parsing wrong, and then we see illusions. And if you know where to look, you can find these illusions everywhere. Okay, that was the lecture on visual parsing. And in the next lecture, we're gonna look at color. 6. Color: a game of light and shadows: in this lecture, we're going to look at the perception off color and as before, that story will be that we think that we perceive color with our eyes. But in reality, the colors we perceive are to a large extent created by our brain. So how does color perception work if we look at our eyes and the story goes as follows there three different color receptors in our eyes, one for blue color, one for green color and one for red cover, so we can essentially only perceive three colors. But our eyes create all the other colors we can see by combining the three colors that these receptors can receive. So essentially, what's happening here is the same as when you're painting. For example, when you're painting, you can mix blue and yellow color in order to obtain green color. And in the same way, the combination of these three color receptors make it possible to see all the colors that were capable of seeing. But those are not necessarily the colors we end up seeing because our brain and it's what are I see, and to show that to you, I want to give you a little example. Do you think that the color in this tile and the color in this time are the same color? Or do you think that they're different colors? And if you're like most people, you would probably think that this color looks a bit brighter than that one. Well, the truth is that both colors are exactly identical. And if you would see merely through our eyes, they would look identical. But they don't. And that's because our brain added the colors that we perceive. Okay, let me prove to you now that what I'm saying is true and in order to do that I will take a piece of this tile here and a piece of that tile, and then I will move them both here. I will move them next to each other so that he can directly compare the color. Are you ready for it? Here it comes. And as you can see, the colors are exactly identical. I can put them back again, if you like, And now they look different again, and I can put them next to each other again. And now they're exactly identical. And this is something that is done by your brain. People usually accuse me at this point that I've been editing the color somehow that I put in some animation that changes the color. But I really didn't. The changing color that you saw when the two tiles were moving was done by your brain. And to prove to you that what I'm saying is true, I will go out of my presentation now. So all animations are switched off now and now it would just take the tile here and move it around through dragging and dropping. And as you can see, the two colors are exactly identical. You can also take the other tile. And as you can see again, the colors are exactly identical. If that doesn't convince, you can even take both tiles. And I can move them together to create a bridge between the two colors. And now, as you can see, the two colors are exactly identical. Okay, if that doesn't convince you yet, there is also a PowerPoint file in the resource is off this lecture. And if you're still doubting, you can download that PowerPoint file and then he can do the dragging and dropping yourself and you will see that absolutely no animation is necessary to make this work. The only thing that is necessary is your brain editing the color. Okay, so our brain and it's the color that we see. But why does it edit the color? The answer has to do with effect of this tile is in a shadow. Our brain realizes that this tell us in his shadow and therefore looks darker than it actually is. And other brain corrects for that. And that's something our brain is doing all the time. The reason why we see colors as constant, even though the light is changing all the time. It's because our brain is constantly editing what we see and constantly correcting for light and shadows. And if you look around in the world, you will discover once again how complex and essential this task is. Our brain is doing there. If you look at the snow in this picture, then you can get the impression that this no has completely different colors, depending on where you look. If you look here than the snow looks yellow. If you look here than this, no looks dark. If you look here than the snow looks white if you look here than the snow looks blew. The snow literally has completely different colors, depending on how the light falls onto the snow and our brain corrects for that at all times . And the only color we see is the correct color by the brain. But the brain is doing more than just correcting for light and shadows. It also plays with contrasts. And to illustrate that to you have a look at this picture. Most likely, you see a bunch of grey dots popping up in the white intersections right now. Correct. This is an optical illusion that has to do with contrast, and to show to you what I mean. Let's zoom in a little bit and see what's going on here. Our brain always wants to accentuate contrast. So what it is doing here is it notices that there's a color contrast between black and white here, and it makes it more extreme by making us see the white here as more white than it actually is. And the black has more black and it actually yes, and therefore they're part of the white that is adjacent to the black will appear whiter to you than it actually is. And that's the case here. That's the case here. That's the case here. The only place where it isn't the case is here in the middle, because that's the only place where the white isn't adjacent to black. And so what happens is you see a great dot, and this happens, especially when the visual system is a little bit overwhelmed by the task. If you're sure you want intersection, you probably don't see the dogs. But if I show you a whole bunch of intersections, then suddenly you see a bunch of grey dots popping up. And this illusion happens because our brain always wants to make contrast more extreme. But why doesn't want to do this? Part of the reason has to do with what you learned in the last lecture, because if there's no contrast, that makes it very hard to decide where an object starts and weird ants. By increasing the contrast, the brain can see the boundaries between the objects more clearly, and that makes it easier for the brain to engage in visual parsing to figure out what belongs to what and where an object starts and where it ends. Okay, That was the lecture on color perception. And at the end, I want to give you a little summary. First I showed you that our brain corrects for light and shadow. It makes things that are in the shadow look a bit brighter and things that in the light a bit darker to make sure that we see the actual color, another color that we just happened to see because of how the light falls in and again, This is so automatic that we can only see the editors color. Then I told you that our brain also accentuates contrasts, which is the reason for the great dot illusion I showed you. And the reason why our brain does this is because it helps to find the boundaries between objects. Okay, that was a lecture on color perception. In the next lecture, we're gonna look at depth perception, and in that lecture, you're going to see that our brain is constructing an entire dimension that our eyes totally can see 7. Depth: enter the third dimension (part 1): in this lecture, we're gonna look at death, and you will discover that our bonus constantly editing ah whole dimension into our perception that our eyes completely can see. So let's first have a look. At what death? Actually, yes, our world consists of three spatial dimensions. There's one dimension going left and right. There's another dimension going up and down. And finally, there's another dimension moving from far away to close by. But the thing is that our eyes can only see the 1st 2 dimensions. The image that our eyes receive is not three dimensional. It's two dimensional. And so the image that we're seeing with our eyes lacks the information about how far or how close something else. And this is something you can express and is expressed in many wastes. Some people say that the eyes can see the third time engine. Other people just call it depth. They say that our eyes can't see depth, and yet another way to say the same thing is to say that our eyes can see distance. They can see whether something is far or close. All of this refers to the same thing. It's something that are I simply can see. And yet, when we look at something, we do know how far it is away. And when we watch a three D movie, it does look different from a two D movie, and the reason for that is off course again. Our brain, our brain uses a whole arsenal off cues in order for us to make it possible to see depth. And I'm going to introduce you to the main cues that the brain is using in this lecture. First, we're gonna look at what you could call level 13 dimensionality, which, as three dimensionality that arises from static use. Then we're going to go to Level two depth, which is depth that arises from motion cues. And then we're gonna go to Level three death, which is the depth that arises from binocular accuse. And these are actually the accused of three D movies used to create the illusion that there is depth, even though you're just looking at a two dimensional screen. So the first time of cues that our brain is using our static use and essentially static use accused that are not moving cues that you find in pictures, for example, such as this picture in this case here are brain used the information from the shadows below the blocks to come to the conclusion that the blokes are floating above the street, although in reality is just a painting on the street. And this happens because our brain completely constructs an added step. It's something that is completely created by your brain. Another cue that our brain is using our Grady INTs and by Grady. And here I mean the fact that things are gradually getting smaller as they move into the distance. And in this picture here, our brain is using the information from the grating correctly to come to the conclusion that the railways are getting further and further away. But he can also use Grady INTs to fool the brain again, such as in this picture. All you're seeing in this picture is a two dimensional painting on a hand. But because that picture contains a Grady int, we get this illusion that there's a hole in the hand. So these examples off static use shadows and Grady INTs, but our brain doesn't only use that accuse. It also uses motion cues. So these accused that have to do with movement and to illustrate to you how these motion cues work. I created a little animation for you and that animation has to do with this little alien spaceship. And my question for us. How far do you think this alien spaceship is away? Do you think that it is in front of the tree, or do you think that it's between the tree and the mountain? Or do you think that is behind the month? And when you just look at this picture, you probably can't tell any of these possibilities could be true. Now, let's see whether we can change that with one simple trick. I'm going to simulate with you now that you walking to the left while looking at that alien spaceship and he will see that all of a sudden you will know how father alien spaceship is away. Here it comes. And probably you have the impression that the alien spaceship is between the tree and the mountain. Okay, so why do you have this impression? The first part of the puzzle is relatively easy. We seize the spaceship as being in front of the mountain because it includes the Mount But why do we have the impression that the spaceship is behind the tree? The tree and the spaceship aren't even touching each other. And the answer has to do with motion. When things are close to us, they move through our eyes faster than an object that is far away from us. And so all I did here is I made sure that the tree moves faster than the spaceship. I'm gonna show it to you one more time. And if you look at it, you will see that the tree is moving faster than the spaceship. And that creates the impression that the tree is closer to us in the spaceship. Okay, I created another animation for you to make you feel the effect of motion cues even more. And in this animation, all you're going to see our snowflakes falling from the sky. And I created two versions of this animation. In the first version there no motion cues. And in the second version they are motion cues. So let's have a look first. How this looks without motion cues here comes And as you can see, all the snowflakes are falling at the same speed and it looks pretty flat, right? So let's have a look at it again. But this time I add the motion cues. So all that's different here is that the small snowflakes fall slower than the big snowflakes. Okay, here it comes. Andi. It looks more three dimensional, doesn't it? And it's all because of the motion cues that I added to the animation. The death you see is constructed by your brain. 8. Depth: enter the third dimension (part 2): Okay. So far we have seen static use, and we have seen motion cues. But there's one type of Cuba were still missing, which your binocular cues and binocular cues. Other cues that make things seemly pop out of the screen when you're in a three D movie. So how does this work to illustrate how our brain creates the strong impression off depth you can do the following. Hold your hand with your thumb sticking out in front of your face, just like the way it's showing on the picture. Now close one eye and leave the other eye open and then switch from one eye to the other back and forth. And do that several times, and what I want you to look at is how much you thump jumps from left to right as you switch from eye to eye, and you can make this effect a little bit stronger by not looking directly at your thumb but looking past your thumb. So what you should be seeing is that you two I see your thumb at different places in your eyes and one eye it's more to the left and then the other eye. It's more to the right. And now what I want you to do is I want you to try this out while you're holding your thumb very close to your face. And then again while you're holding your from very far away from your face as far away so you can. And what you should see is that your thump is jumping less when you hold your thumb further away. Compared to win, it's close by. So in other words, there is a queue for distance there. By comparing the images in your two eyes to each other and looking how far they are apart from each other, your brain gets a Q. How close something is to you, the closer something as to you, the close of the images will be together, the further away something is from you, the further will the two images be apart. And this is what three D movies air using to create an illusion off depth. So here's how they for your brain. First, they give you the famous three D glasses, and the only purpose of these glasses is that they filter the images you see in the past. This was done with color so that in one eye you can only see red. And in the other eye you can only see blue, and then they show you an overlay of two images where the two images are a little bit apart again. In the past, this was done with color. So if you would be wearing the three D glasses, I just show you right now. One, I could only see the blue part of the image and the other. I could only see the red part of the image. And then what? You're I suddenly see once you wear the glasses that the boys are far apart in your two eyes. The brain then sees that as a cue that the boys are close to you, and all of a sudden it looks two years. If the boys are popping out of the screen and modern three D movies work exactly the same way, they show you an overlay of two images, and then they give you the three D glasses to make sure that one eye sees only one image and the other. I seized the other image, and that creates the illusion that something is closer to you than the screen. So, as you can see, death is another very complicated visual puzzle that our brain is solving for us every day . And because of this, a complex young babies actually can do it yet when they're very young and you put them on a glass table, that doesn't bother them at all. But at some point, as they get older, they suddenly find a glass table really, really scary because suddenly they see an abyss because the brain has now figured out how to construct death. Okay, that was again a lot of material. So let's go through a little summary. Our brain constructs depth from various cues. In the first category of queues I showed you are static. Use examples of static use our shadows and Grady INTs. The second category. I showed you our motion cues, and here are Brain simply uses the fact that distant objects tend to move slower in our eyes than close objects. Then I showed you binocular accuse, which work by comparing the two images in our eyes to each other. Finally, it's worth noting that our Bain doesn't just added depth, it creates it. Our eyes can see death at all, it is completely created by our brain. Okay, that wasn't a lecture on depth perception. In the next lecture, we're gonna look at size perception, and you're going to see that size perception is essentially the other side of the coin to depth perception. 9. Size: a story of giants and dwarfs: in this lecture, we're going to look at the perception off size and, as always, our story starts with something our eyes cannot do. So what is it that our eyes cannot do? Our eyes can not disentangle size from distance. The further something is away, the small it appears in our eyes. The closest something is, the bigger it appears in our eyes. And again, that's a problem, because without the brain helping us, we would not know whether something is big or close. So the problem that our brain faces is that our eyes cannot disentangle distance and size. And so what it does is it uses the depth cues recovered in the last lecture to correct for distance. So size perception works to a large extent through depth perception. And at this point, I could already say End of the lecture, because in the last lecture we already covered the depth cues that our brain is using to correct for distance. But I promise you, at the beginning of this section that I don't just want to explain you how perception works . I want to make you experience it and a great way to experience that our brain is constructing size by correcting for depth cues is to see what happens if you remove depth cues. Because once you remove depth cues, our brain cannot correct for distance anymore, and the results are sigh solutions. This room here is called Aims Room, and the way it works is that this guy's actually much further away than this woman. But the room is constructed in a way that you can see that. Okay, let's have a look how that works. What you can see here is the actual shape of the room. You're seeing the room from here. And as you can see in this picture, the right corner is much closer to you than the left corner. And only you would be able to see that because distant things are smaller in our eyes. So normally would see a size Grady int going from here to there. But at the same time, the room is built so that it gets larger from right to left. And the result is that you can see anymore that this corner, it's further away. And so you get the illusion that the guy who is standing here is actually standing there and that creates the size illusion that the guy on the left side looks super tiny. So that's aims room. But it doesn't even have to be that complicated. It's actually quite easy to create size illusions if you take photos because in photos, most of the depth cues that our brain is using our missing. Normally we have static used. We have motion cues. We have binocular cues, but in photos we only see the static use. And sometimes that Satya cues are just not enough to figure out how far something is away and hands her biggest. Another trick that works very well to create size illusion is to take an object of which we normally know this size and then make it much bigger or much smaller. In this case, we see a chair. Our brain has an idea how big chairs normally are. So it uses that information since it doesn't have any better information based on what it sees. And the result is that we have the impression that that woman is actually super tiny. Here's another example that uses the same trick because the photos flat and deprived of deaf accuse our brain can quite see that the woman on the left side is actually further away than the woman on the right side. And at the same time, our brain uses the knowledge of how big a cheer is and as a result comes to the conclusion that the woman on the left side must be super tiny. Okay, I think by now you get how it works. So I will move forward a little bit quicker. But I want to show you a few more examples of size illusions just to make you experience a little bit more that our brain is constructing size and also to inspire you a little bit where you might observe that in your own life. If you like to travel and you want to play with size illusions, then you might want to go to solar day. You Unit Solider unit is assault leg in Bolivia. Here's another picture, and this salt leg is completely flat and completely white. And as a result, here's another example. This place is very deprived of depth cues, and so pretty much whenever you take a picture, you get a sigh solution. Here's another example. All these pictures are from solid a uni, and it's another great way to experience that our bain is constructing size, okay, and that really gets us to the end of the lecture. So let me give you a little summary. I discussed with you at the beginning that our eyes cannot disentangle distance and size because things that are closer appear bigger. Therefore, our brain corrects for distance, using the depth cues that we discussed in the last lecture. Finally, an easy way to create a size illusion is to take a photo because in pictures, the motion and the binocular deaf accuse are missing, and that can easily result in size allusions. Okay, that was a lecture on size perception. And the next lecture is already gonna be the last lecture of this section in which we're going to look at the perception off for and you will see that although our eyes are in principle able to perceive form, they almost always get it wrong. 10. Form: it's never what it looks like: in this lecture. We're gonna look at the perception off four and I want to start with a little question. Do you think that this shape on this shape are different shapes? Or do you think that they're identical shapes? Most people feel that this shape is a little bit longer here, while this shape is a little bit more like a square, right? Well, the truth is that both shapes are exactly identical. And yet they look different to most people. And to show you that what I'm saying is true, I will strip away the legs of the table here and now I can just move the form onto the other one. And as you can see, they are exactly identical. I can also put the first shape back into the original position, and most likely they will look different to you again. So what is going on here? Why do we see two different shapes even though there aren't really different? And as always, the answer is that our brain is trying to solve a problem here. And the problem is that the shapes we see rarely match the actual shape of the object. Let's take this door as an example. Does the shape we see when we look at the door match the actual shape of the door? When you come to think about it, you will realize that most of the time that's not the case on Lee. When we're right in front of the door, we will see the actual shape of the door, which is a rectangular. But if we had an angle to the door, even at a slight angle, the shape we see won't be rectangular anymore. So the shape we see when we look at the door rarely measures the action shape of the door, and that's a problem. And again, our brain tries to find out what's really out there based on the clues it has. And then it edits what our eyes see before we even become aware of what we're seeing. OK, but how does our brain do that? To understand that, let's analyze the task a little bit. Suppose he would see only this part of the object. Would you be able to tell what it's for, miss? Probably not, Right. OK, but how about this part? This part is a little bit better. This part is a little bit more information what the shape of the object might be, but it's still not great. And now how about this part out of all the parts I just pointed at, this is probably the part that gives you the most information about the shape of the object . So what you can see here is that they're just a few very crucial features in this object that help the brain to figure out what the actual shape of the objectors and because thes features are so crucial, our brain is very, very sensitive to detecting them. And one way to show that is with original Sorge Task Psychologists and neuroscientists have used visual search tasks in order to determine how sensitive we are to detecting certain features. And the way this works is that the feature is hidden between a lot of other distracting shapes, and the participants need to find the feature among the distracters. So in this case is very easy. But you can make it more difficult by adding more distracter shapes. And what researchers found was that for the crucial features, such as the edges in a cube, it almost doesn't matter how many distracter shapes. You put around the features people find the feature of very, very quickly, almost regardless of how many distracters are around it. And this indicates that our brain is very sensitive to detecting these features, as one would expect, given that they're so important for determining form. So whenever we see an object, our brains immediately extracts the relevant features to construct the form of the object. And so even though the form of things changes all the time in our eyes, as we change the angle to the object, we don't get confused by this. We always see one shape. For example, we see a door as a rectangular because of the rain, is always extracting the relevant features and then added into our perception with our brain. Things is the actual form of the object. Okay, that was a lecture on form perception, and I want to give you a quick summary. I showed you that the form our eyes perceived almost never measures the actual form of an object. And because of that, our brain added sour phone perception. It corrects for the fact that the form we see is not only affected by the form of the object, but also by the angle by which we look at the object and our brain does this by extracting the crucial features such as badges that can tell it what the actual form of the object. Okay, that was an extra on form perception. But there's one more thing I would like to show you. As always, I want to make you experience that our brain is constructing form as much as I can. So I added a link to a very cool form illusion out of this lecture. And be sure to check it out because it's a very cool illusion, and it lets you experience very strongly that our brain is really constructing for. 11. The visual system (Section 2): in this section. We're going to zoom out from the details of perception and have a look at the visual system in our brain. And I'm going to tell you about people who thought that they were blind, but unconsciously that could actually still see. And I'm going to tell you about people who can still perceive. But for some reason they can't recognize things any more. They can tell what it is, and I'm going to tell you how perception works together with our memory and uses our knowledge to construct our reality. 12. Conscious and unconscious perception: welcome to the first lecture on the visual system. On in this lecture, we're gonna look at conscious and unconscious processing in the early processing stages in our brain, and I will tell you about a man who thought he is blind. But when he walked through the room, he could actually evade all the obstacles, as if he could still see. But more about that later. So so far, I told you that perception doesn't just happen in our eyes, but to a large extent, it also happens to know our brain. But so far we have looked at the brain as if it's just one thing, while in reality the brain is not just one thing, but it's a combination off different systems working together. And in this lecture, I want to show you the early part of the system and the difference between conscious and unconscious perception in those early parts of the visual system. And to begin with, I would like to tell you a little story from my life, which happened a couple of months ago when I was backpacking in Taiwan by myself. So I was backpacking in Taiwan and I was in the middle of nowhere, and at some point I encountered this sign. This is literally a picture I've taken in Taiwan. And although I didn't understand the symbols, I did understand that there would be snakes somewhere and that I should be very careful about that. So for the rest of the day, I paid a lot of attention when I would encounter any snakes. And as a matter of fact, I did see a lot of snakes, maybe 15 or even 20. But in reality I encountered only two. So what I mean by that is that very often I looked at the ground and I thought I saw a snake. But when I look at it for a little bit longer, I realized that Oh, this is actually just a tree branch or the root of a tree, something that looks like a snake but isn't actually a snake. And what you can see in this example is that perception is not a process that first finishes and then gives you the perfect result. But you get early results and you get late results, and they might be different. And you could say that there is a more early and rough analysis, which is not often accurate. But it is very fast, and what it did in my case is it enabled me to jump away very fast when I thought that I saw a snake and the advantage is that it's very fast, so it makes me jump before a snake can bite me. But there's also the disadvantage that because it's so fast and only very rough, it's also often wrong. But overall is better to jump a little bit too often and not get bitten by a snake rather than not jumping too often and then being too late to jump away when there really is a snake. And that's the reason why our Ben gives us this initial rough analysis to make us respond quickly to potential danger. But the brain doesn't stop there As time goes by, it engages in a more thorough analysis and that analysis that allows me to realize that Oh , I'm just looking at a tree branch or the root of a tree. In any case, not a snake, And that later analysis essentially make sure that I don't run away just because I saw a tree branch. So what you can see here is that our perception is not just one thing, depending on the timing, our brain spit cells, different results to the question. What is out there? And these results maybe conflicting sometimes, but they both help us to respond in an optimal way to our environment. So that's one example where you can see in your everyday life or in this case, my everyday life, that our perception is not just one thing, and we can also see that when we look at the brain, what you see here is a cross section off the brain. So basically what you see is the part of the brain that is between the middle of our eyes. So if you would take a knife vertically and cut between our eyes, then that's what you would see in the brain. And let us have a quick look at how information travels from our eyes through our brain. So, first of all, the main destination of that information is the so called primary visual cortex, and the primary visual cortex is at the back of our brain, and it's a part of the so called cortex, which is this outer layer here, This whole thing, which is the biggest part of the brain and around the primary visual cortex. There is the so called extra stride cortex, and both of these parts help us to perceive. If we look at how information travels for the brain, then we can see that it first travels to the center of the brain. And then from there it goes to the primary visual cortex and from there travels further through the extra stride cortex so we can see that in this pathway, the analysis starts at the primary visual cortex, and then it continues at the excess dried cortex. But that is not the only pathway in the brain. Turns out that there's also a shortcut that goes directly from the middle of the brain to the extra stride cortex. So this part basically bypasses the primary visual cortex and gives us a shortcut to perception. And that maps directly to my example off my trip in Taiwan because it is useful to have shortcuts in our perception, because it should allow us to respond more quickly to the environment. So if we look at the brain, we can again see that our perception is not just one thing the different kind of pathways which together help us to respond to the environment in a relatively optimal way. Okay, so that is the early part of our visual system. But I also promised you at the beginning that we're going to talk about conscious and unconscious perception. So what does that have to do with the things we just talked about? Well, as it turns out, the shortcut is largely unconscious. And one of the reasons we know that is because there are people who have damage to the primary visual cortex so that the long path is impaired. But the shortcut to our perception still works, and now it comes. These people think that they're blind, but if you look more closely attuned so that they can actually still see, But they don't know that because the perception is unconscious and this is called blindside . So blindside happens if the pathway that goes directly to the excess tried cortex is still intact while the pathway through the primary visual cortex is broken. Okay, at this point, you may be wondering, How did people figure out that these people can still see and there's several ways, and I want to show you two of them. In one experiment, the researchers showed the blindsided person an image like this one, and they asked the person, Do you see vertical stripes or do you see horizontal stripes? And of course, the blindsided person thought that he or she is blind, So that person said, I can't see anything. But the researcher insisted and said, Well, if you can't see anything than just guess. And then it turned out that even though the person thought he could not see, he was still guessing it right more often than he should if he was black, so he didn't get it right all the time. But he got it right more often than he should if he was really blind. So basically, what we can see here is that even though these people thought that they were blind unconsciously, that could still see. Okay, let's do one more example, and this is the example I showed you at the beginning. In one really remarkable example, they let a man with blindside walk through a corridor full of obstacles, and as it turned out, this man could just evade all the obstacles, as if he could still see. But consciously, he's blind. He can't see anything, but yet somehow automatically, his body just evades the obstacles, as if he can still see. And again, this shows us that our perception doesn't just consist off the conscious perception that we experience, but that there's also an unconscious pathway in our perception. Okay, if you want to see that, that's possible. After this lecture, I put a link to a video. We can see this man walking through the corridor and evading all the obstacles. It's a very old video, but you can see quite clearly that this man does something that a blind person shouldn't be able to do. So if you want, you can check that out right out of this lecture. But first, let me give you a quick summary off this lecture. So we have seen that our perception has quick and slow parts and that both of these parts help us to respond optimally to our environment. Then we looked at the brain and saw correspondingly that there are also several visual pathways in the brain. In particular, there's a long pathway which goes through the primary visual cortex, and this pathway allows us to see consciously. But there's also a shortcut which bypasses the primary visual cortex and goes directly to the extra stride cortex. And this pathway is unconscious. And one of the reasons why we know that is because if people have a damage in the long pathway that these people think that their blinds, even though that can actually still see unconsciously Okay, that's the end of the lecture. If you want, you can check out the video off the blind side of guy after this lecture, and I also added some additional material, which can help you experience the early stages of our visual processing. And then in the next lecture, we're gonna look at the later parts off the visual system and see what our visual system is trying to achieve at the end. 13. From perception to memory: in this lecture, we're gonna look at what's happening at the end of the visual processing stream when perception transitions into memory. And to begin with, I want to tell you about ignore Asia. Did you know that their patients who are not able to say what something is, even though they can perfectly see it? So a person in this condition would be able to say that this object here has this Iran part and that it's flat here and sharp here and also that there's a wooden handle here. But once that person is asked, So what is this? This person just can't ask. This is a condition called agnosia, and in this election we're going to see more detail what's going on there. But let's start at the beginning. We already covered earlier that in the back of the brain there is the visual cortex, which is responsible for perception. But how does information travel after it has reached the visual cortex? After the visual cortex, the information basically splits up into two streams. There is the want pathway, and there is the wear pathway, and, as the names already say, the what pathway is concerned with determining what something is and the where pathway is concerned with determining where something is. And, for example, form perception would fit more into the what pathway and depth perception fits more into the where pathway. Because that would be more about determining how far something is away. And when we going to do now is, we're gonna zoom into the what pathway and have a look what's going on there. And in order to understand what's going on in the what pathway we need to distinguish between two things. The first thing that is going on in the what pathway is perception and perception is basically about all the things that we covered in Section one. It's about describing what the color off something is or the form. It's basically about figuring out the basic features off the object that is in front of us . The second process is recognition, and recognition is when we can actually say this is what it is. And what's happening there is that we relate what we see to the knowledge in our memory. So, for example, if I'm looking at the ground and I'm determining, am I looking at a snake or a root. I need to know what the snake is and what a rude If if I don't know that, then I can come to the conclusion that this is a snake or this is a tree root. And so that's what recognition is about. It's about finding the relevant piece in your memory that is fitting to what you're seeing right now. So to illustrate that a little bit, if you look at this image here, then you're probably able to say that you're looking at something that is round and something that is yellow, so you are able to perceive it. But I already able to say what it is. Are you able to recognize it? Well, if I add this piece of background, then you probably know immediately Hate. This is the sun and that moment where you can just describe what's in front of you. But he can also say what it is. That's the moment when your brain has access you memory. That's when you have gone from perception to recognition. Okay, so I'm telling you that perception and recognition are two fundamentally different things. But how do we actually know this? And the main piece of evidence comes from patients who have brain damage in the what path. If a patient has a damage in a very specific area off the what path, then it can happen that they become unable to recognize even though they can still perceive . And this condition is called agnosia. So that's what I talked about at the beginning. People with agnosia able to describe something, but they're not able to tell what it ISS. But they're also more specific kinds of ignore Asia, for example. Some people are unable to recognize faces, so they look at an object. They're able to tell what it is. But if they look at a person, they're unable to say who it is. And this condition is called fasig nausea and in serious cases, off basic nausea. It can actually be that this person is not able to recognize his wife or his mother or his Children, and that's because perception and recognition of two different processes Okay, let's go through the content of his lecture very quickly. Again, we have seen that their two main goals off perception, which is determining where something is and determining what something else. Then we zoomed into the what part and found out that at the end of determining what something is, we need to access our memories. We need to find the relevant piece of memory that fits to what we're seeing right now. And if people are unable to do the second thing that's called Ignore Asia. So these people are unable to recognize things, even though they can still perceive them. Okay, so that was the lecture on pretty much the end of the visual processing stream where we go from perception to memory. But we're not quite done with a visual system yet. In the next lecture, we're gonna find out that the visual system is actually not a processing stream by the processing loop. 14. The perception-memory loop: in this lecture, we're going to see that the visual system is actually not a processing stream, but a processing loop. And as always, I'm gonna show you way can experience that. So far, we have treated the visual system as a stream that goes from perception to memory. We basically looked at the visual system as if it first wants to describe something which is the perception part. And then once it has described it well, it wants to access our memories. But in reality, that's not how it works, because information doesn't just travel from perception to memory, but it also travels from memory to perception and together this crazy loop through which our visual system works. Okay, that's very abstract. So let me start with an illustration. There is a report from an anthropologist who went to the Democratic Republic of Congo, and there he met a man who was 22 years old and he had spent all of his life living in the jungle, and he had never, ever seen life outside of the jungle. All he knew was the jungle, and remarkably, this man was able to tell how many insects that there were around him at any time. But then someday the anthropologist took the man outside of the jungle and outside of the jungle. They saw some Buffalos grazing in the distance, and the man who had spent his life in the jungle get confused. And as what kind of insect are we looking at? And then the anthropologists had to explain that that isn't an insect that's actually a buffalo, and Buffalo is actually quite a big animal. But the man didn't believe it because he had never experienced that. A big animal like a buffalo can get so small in his eyes because he had never seen an animal from this far away in the jungle. You always see everything from close by, and his perception was tuned to detecting everything that was closed by, such as the insects around him. But it wasn't well tuned to perception off something that is very far away. And so when he looked at the buffalo is very far away, he thought that they were insects. Then the two men got closer to the buffalo. And then, of course, the man from the jungle had to admit that Oh, gosh, this is really a buffalo until the end. He insisted that Okay, it may be a buffalo, but it's not a real buffalo. Its is just something that is like a buffalo. So till the very end, he was suspicious about what he was seeing. Could not believe that a buffalo can appear this small when it is far away. So what's happening here? And the answer is that our perception always incorporates our knowledge. What we see is influenced by what we know. So if you have never seen that a big animal can get small in our eyes, then we will never come to the conclusion that an animal that is small in our eyes can be a big animal, because that doesn't match our experience. So our perception is influenced by our memory. And actually, we have already seen that before. Such as here. Why does this person appear so tiny? Well, part of the trick is that we have an idea how big chairs normally are in this picture. There aren't really any cues as to how big the chair are, and so what our brain does is it uses the knowledge it has about the normal size of chairs to fill that information in. And because that person is so small relative to the chair, we get the illusion that this person is super tiny and again that's because the knowledge and our memory influences what we see. So at all times, part of what we see is based on the information that is coming from our eyes, and the other part of what we see is based on the information that is coming from our memory. And I want to show you now the process by which these to construct together the image that we see. Our perception is essentially based on the processing loop, where data streams upwards in so called bottom up processing and M bottom of processing. The data streams from our eyes and triggers knowledge in our brain. And that knowledge then sends information downwards in so called top down processing, which then influences the image. What we see. Okay, that's a little bit abstract. So let's do a little example In the Lecture on Form Perception, I gave you the example off the cube where we first extract the relevant features and then based on those features, we come to the conclusion what the shape of the object is, which then in turn tells us that this object is, for example, a cube. However, this is only half of the story because this is only the bottom up processing part. So let's have a look at this example again and see the more complete story of how our visual system works. First, our brain extracts features from our eyes, and that's again the bottom apart off the processing group. But rather than waiting until the bottom of processing part is finished, our memory already kicks in at an early stage and tries to fill in the missing features based on its experience. So it basically just says, Hey, if this feature is there than probably there also these features and then if it can complete this puzzle at an early stage than at this point, it may already come to the conclusion. Hate. This is a cube. And then, while we already think that it is a cube, the bottom up processing continues and extracts more features, which then either confirms or dis conference. What we think the object is in this example here, the visual system got it right immediately, but Sometimes it also gets it wrong. And an example of that was my story from Taiwan, where saw the snakes because it wasn't just that I jumped because I thought that there might be a snake. But I literally thought that I saw a snake sometimes. And that's because in the early stage of the processing, my memory just fills the information in in a way that makes sense. And at an early stage, my bottom apart had just figured out that I'm looking at a long wind. It object, So it made sense for my memory to fill it in as a snake. And that's why, for a brief moment, I actually saw a snake, even though there wasn't it. And by the way, have you ever wondered why people see things differently? Sometimes, for example, when people look at this picture, some people see a rabbit while other people see a duck. And even though all people are capable of seeing both, usually one is easier to some people, while the other is easier to the other people. One of the reasons why people see different things when they look at the same thing is because what we see is constructed by our brain, and our brain uses our experiences to construct what we see. And two people never have exactly the same experiences, which means that inevitably they will see things differently. For example, here they will see either a duck or rabbit. Okay, that gets us to the end of the lecture. So let me give you a quick summary. We saw that the visual system is actually working through a processing loop, and that processing loop consists of bottom up processing, which is driven by data such as features. And it consists of top down processing, which is driven by knowledge in our memory. And that's the end of the lecture and section two. And if you like, you can see a summary of the whole section in the next lecture. 15. The bigger picture: in this lecture, we're gonna have a look at the bigger picture because I know that many of you are not taking this course just to learn about perception, but to learn about the mine in general. And so I want to show you how the things you've learned in this course relate to other topics and psychology. In Section one, I showed you that perception is a very active puzzle whether brain tries to figure out what's going on there based on the ambiguous cues it's getting from our eyes. And in Section two, I showed you that the visual system is actually consisting of several components and that these components are working together to make us perceive. And one connection to other psychological topics that we have already seen in this course is the connection to memory. We have seen that at the end of perception, where we want to say what something is, we need to access our memories. But there are more connections, and I want to show them to you in this election. Another psychological topic that is related to perception is social cognition. Social cognition is a term that refers to thinking about other people, And the thing here is that people are puzzles to just like generally. The information from our eyes is a puzzle to the brain. So suppose, for example, that this guy comes up to you and greets you in a friendly way. At this point, you might be wondering, What is this guy up to? Is this guy really as nice as he seems? Or does he want to sell me something? What does this guy want from me? So again, we're presented with a puzzle. And again, our brain solves this problem to a large extent outside of our awareness, When we look at a person, we usually immediately have a first impression within milliseconds, and this impression can be based on the close of the person is wearing. Or it can just be based on the facial appearance of the person. There's a reason why Jack Nicholson, the guy in this picture here, gets very often casted for movies in which he has to play the bad guy because he has this face that makes us automatically think that must be a bad guy. So what's happening here is that just like we automatically come to a conclusion what the form or the distance of an object is, we automatically come to a conclusion about another person. So social cognition is, to some degree just an extension of what you learned in this course. Okay, let me give you another example how perception relates to other topics in psychology. Let's have a look at depression. Depression often has a lot to do with how our brain chooses to solve the puzzle that is in front of it, because not every interpretation of what's out there is equally healthy. And a good example of that is the famous. The glass is half full versus the glass is half empty. Both are possible interpretations of what you're seeing right now, but one interpretation will make you happy, and the other may make you depressed. So what's open happening in people who are depressed is that their mind very automatically interprets the world in a very negative way. And you have seen in this course how deep this can go. You have seen that our brain is completely constructing our reality. So if our brains suddenly chooses to interpret the world in a negative way, we may see a completely different world. That's to another example. Many people are also struggling with anxiety, and one of the reasons for this is that these people often see constantly threat, even though there isn't any. And if you think back of the things that we have discussed in this course, you may realize that, Hey, this is actually not that strange. For example, when I was backpacking in Taiwan, I constantly saw threat, even though there wasn't any. I saw snakes multiple times, even though it was just looking at tree branches. But there's an important difference between me and a person with an anxiety disorder. In my case, my anxiety. Help me because the really worst next in Taiwan and my anxiety made it less likely that I would get bitten by a snake. However, imagine now that my brain is operating the same way. But now, in an environment where there aren't any snakes, suddenly I would walk through my life and fear, and for what? There wouldn't be anything I need to protect myself from Onley. In that case, one could say that I have an anxiety disorder, and what you can see in this example is that this orders very often don't have to do with our brain going crazy, but with our brain doing something very reasonable in the wrong situation. And that's why, even if you want to understand this orders, it makes sense to first ask. What do we do normally? Because very often, what's happening in the disorder and what's happening in the normal situation is not so different. Okay, let's do one more example, because I really want you to get as much out of this course as possible. Let's talk about Alison nations. Let's talk about seeing something that isn't actually there. Hallucinations are a serious problem where person loses the connection with reality. How can this happen? Well, what you've seen in this course is that hallucinations are actually not that crazy. We see things that aren't actually there all the time. Think about the T. Rex illusion. Think about the distorted face illusion. Actually, Just think about the fact that we can see depth and that our brain is completely editing it into our perception. So seeing something that isn't really there is actually more normal than we tend to think. And so one of the reasons why hallucinations can occur. It's not necessarily that our brain is doing something different, but more that it's doing too much of what it normally does. It over interprets things and thereby makes us see things that aren't actually there much like the snakes that I saw in Taiwan. So if I would summarize the main lesson from this course in one sentence, I would use this sentence to the brain. The world is a puzzle, and that puzzle starts at perception and the things that our mind is doing in our everyday life, such as thinking about things, thinking about people feeling good about something, feeling bad about something. All of these things are basically extensions off perception.