Okay, so, we've talked about some of the processing that's happening in the eye, before a visual signal even leaves the eyeball. from that point of course the visual signal goes back to the occipital lobe, goes back to the primary visual cortex. Now, primary visual cortex is in some way doing the same kind of thing as the retina. It's almost like mapping the retinal image onto the brain tissue back there. And so, it's encoding things like you know, patterns of like, where in the visual world they're associated with. Of course, we've had edges accentuated, color differences accentuated. but to some extent, the primary visual cortex is really just kind of another one of these screens, as it were. Another one, another place in which the world is projected. And the next problem that the visual system has, and in fact, you know, this is echoed across all our century systems, of course, is figuring out what it is that's out there. And that's what we're going to talk about in the next couple of lectures. So, Week 3: Lecture 3, Perceiving What. What do you see when you look down here by the way? this is what's called an ambiguous figure. When you look at it, you maybe see a face, you maybe see a guy playing saxophone. if you look at it long enough, you can probably see both, okay? The important point of this is that sensation and perception are different, that what we perceive can change even when the sensory input stays the same. Let me give you a couple of more examples. these are sort of famous what are sometimes called ambiguous figures. I'll do this one really quickly. This is called the, the young lady old hag, ambigious image sometimes. Depending on how you look at this image you should be able to see one of two things. Let's do the young lady first. The young lady we're kind of seeing from behind, from over her left shoulder. so this would be her left shoulder and let me just do it this way. This is her hair, here's her forehead, her eye socket. We don't really see much of her eye. Her nose coming out here and then this like her cheek area, her chin and her jaw line coming back to her hair. This is like a necklace of some sort and this is just her neck. you know, going into her dress. So hopefully you could see that. Now, let me see if I can let you see the old hag. For the old hag the, the big thing is this is her eye. This is a great big honking nose. So I want you to see that great big honking nose. I don't know what this is. Some sort of wart on her nose. But a great big honking nose and this is actually her mouth. So a thin mouth with her cheek here, and a, and a few more wrinkles etcetera. And her chin kind of tucked right in to this clothing. [LAUGH] This dress, I guess. so, hopefully you can see both of those things. And again, kind of notice how you can see one for a little bit and then you kind of see the other one for a little bit. And sometimes you can sort of feel like you can see both, but this ones even more dramatic. Now it's going to be really hard for me to guide you through this one. What you really gotta do is stare at it, stare right around here. in fact if, if you look at these three corners here. These ones tend to contain the most information. or at least this is where the most dramatic things happen. so this corner for example at sometimes will seem very close to you, while those ones will seem relatively further away. But when it flips the opposite will happen. So really, what I suggest you do is just stare around here and blink every now and then. And what you might see at some point is that the whole three dimensional image your looking at seems to change before your eyes. It almost seems to flip around this way. Flip around this way. This is something called the necker cube. you could find other examples of it online. and you know, again I can't guide you through it so well, but keep looking at it. Keep trying it and it'll flip. Really cool. Alright, so it's, so the point to gain here is there's the sensory input, but then there's what we perceive. And there's something interesting that happens between those two. What is that? Well, a lot of psychologists have been trying to get to the, get to the bottom of that. It's a, it's a very complex problem, how we're able to perceive objects in the world. Here's are some of the big issues people have talked about. The first one is. You know, really the first part of this problem is figuring out along with visual input where do the objects begin and end. And this is sometimes called separating figure from ground, where figure is like the object and ground is like the background. how do we know what are the objects? That's sort of the first problem. Once we know, you know, where, that's an object, that's an object, that's an object, then we can start to ask, okay what is that object? What is that object? But first we have to know, which clumps of light are the objects. And so one notion is well, edges are very important. in fact, that's why we think the bipolar cells are accentuating those edges, and accentuating color distinctions. If you, if you, you know, have a color distinction, that seems to produce an edge, of a sort, that defines an object relative to a ground. If that edge is accentuated, as it was in this bottom one, then even more so we get the impression that this is an object against a background. So there, it seems like right at the retina already, some of this is going on. And the purpose of accentuating those edges is probably to help us detect the objects. Okay, now this can be well, really difficult, but what I want to make a point here is it's not all about the eyeball. It's also about memory and previous experience. So hopefully some of you are looking at this and just seeing a whole bunch of black and white, and not seeing any object at all. You're in a state of ignorance and I, and I use that term nicely. a state of ignorance that I'm going to take away from you. And, and once I take it away from you you won't have it back. So enjoy for a little bit. If you're looking around and just seeing black and white enjoy that, because I'm about to rob you of it. which is kind of the point. I am going to show you the object in this image, and once you see it, I want you to kind of feel what changes in your mind. You know, feel like, wow, okay, it's emerged. Alright. So let me just do it. What we have here is a dalmatian. And I'm going to generally outline the dalmatian, it's over here. Sniffing the ground and I assume it's kind of a leafy forest or something like that. So the dalmatian, obviously is black and white spotted. And then let me, let me try to really help you out here. This is his head, his snout and he's down sniffing the ground. So his nose is somewhere around here. This is like his jaw and his nose, this is like his ear dangling down. Think of this as a collar if, if helps you out. It's probably more like a shadow on a shoulder blade, but you can think of it as a collar. So, once you see the head, then you probably see the, the foreleg here, his left foreleg, then you can kind of see the stomach and chest. Things get really kind of ambiguous back here. The back end is harder to, to see. maybe a tail up here, but it, once you get over here, now you get the back and the shoulder coming down the neck and back to the head. 'Kay, so, if you look at that a bit, you should be able to detect that. Now, this is the cool thing. I'm going to show it to you in a little while again. And you will just see it. Like if you can see it here, you know, fight with it here until you can see it. and then once you do see it, you will always be able to see it, forever and ever. which is kind of an interesting point but it's showing the role that memory is playing in terms of helping interpret the raw sensory experience, ultimately producing a perception. Okay. So figure ground, one thing. Now, another this is well, okay figure ground's perfectly fine, but if you, if you look at somebody, like you know, even if you look at me you see that there are edges. There are distinctions happening here, but this is all a part of the same thing. So there's, you know, the world is never easy on us, it really isn't. And so the visual system has to figure out, okay what goes with what? and that's a problem that's called grouping sometimes. How do I figure out what parts of that visual scene go with what other parts of that visual scene. and that whole area is an area of called gestalt psychology, at least gestalt psychology really pushed this grouping thing. Again this was kind of a post Freud reaction, a kind of running back to perception because perception felt like something that we were getting at very scientifically. So a lot of researchers said, let's go back there. that's a really kind of good, scientific place to start, and so they were really worried about this grouping issue. And they, and they found all these things they called laws. Laws, gestalt laws of grouping. Some of them are pretty simple but still important. So, for example, proximity. The idea here is this is really 16 circles, but we will tend to see this as four vertical groupings of four circles each. that is, each of these four feel like they group together. Why? Because they're closer to each other than they are to their next neighbor on the horizontal dimension. So, they just group because they're close. Things that are close together tend to group. It's this is a different example. In this case we tend to see more horizontal bars. Why? Because these things are more similar to each other. So they're grouping together because they're similar looking. Okay, similarity can group things. Continuity. Well, let's call these four, four lines. But if I said these are four lines, but I said you can group two together and group another two together. Most of us would say, well, this goes with this, and this goes with this. But it needn't, right. We could think of this as like an arrow head pointing down to the right and another arrow head pointing up to the left. that would be a perfectly reasonably interpretation of it, but we don't want to see it that way. Usually our system likes things to continue on something we call good continuation. And so that makes us want to see this as being part of this and this as being part of this. Okay, these are pretty basic things, but this is what underlies a lot of our basic perceptual abilities. closure as well, we call this closure, but I like the notion of simplicity too. Simplicity kind of gets into this. So how do we see this? Well, we could literally see it as three Pac-Men, because they are kind of like Pac-Man-like figures. You know, little circles with mouths, facing each other in just the right way. That's what's out there. But we tend to see this as 3 complete circles with a triangle sitting on top of them. Now, that triangle's not there. those lines that you might feel like you see here, are what we call illusory contours. There, there is no triangle there. but her perceptual system likes a really simple interpretation of things. And by simple, we mean sometimes similar to things we've experienced before. and so we've experienced a lot of circles, there's a lot of circles in the world. there's not a lot of Pac-Man in the world, unless you play Pac-Man every day. and so for three circles with a triangle is simple. If anything's bounded by something else, we tend to see that bounded thing as all being part of the same thing, nothing profou, no, nothing profound. Wow. Um, [LAUGH] yeah, profound. Sure. I thought I'd say profane, but I didn't. I said profound. yeah, yeah. We'll, we'll leave it. symmetry. Let's do the symmetry one. This is another case where we could view this as a rectangle with a little bite out of it. And this also being a rectangle with a little bite out of it. So two of these rectangles with bites out of it, touching up against each other. but again we don't, we like simple things. In this case two overlapping squares and we seem to like symmetry. That's the other reason we don't seem to like this. We, our visual system seems to prefer things be relatively symmetrical. and that's the interpretation that we'll draw, given the chance. So all of these things can, can come together to produce, you know, these kind of things. Where we have good continuation suggesting that these lines are continuing, but are just being occuluded by this rectangle I'm sorry, square, that doesn't even exist. So we can get these fancy illusions because of the way our system wants to group this. It wants to see four black circles, a square in the back and a white square on top. That's a nice straightforward simple way of, of seeing this that fits with the kinds of things we see in the world. Let me show you one other gestalt principle, because I think this one's critical and, and I think it really makes the point in the way some of the others don't. I mentioned that my shirt has these different colors. why don't you see these as, as designating separate parts of different objects? Well, in the real world things aren't static. Things tend to move. And movement provides a very important cue. So, so let me go back to, I don't know if you had this same fascination as I did when I was a kid, but I was always fascinated by nature kind of movies. And so you'd have something like this. So, you see here What we have is a frog hidden in the leaves. And the frog is so carefully camouflaged that you cannot see the frog in the leaves. It all blends together. But, wait, the frog will move in just a sec and as soon as it moves, you see it. Okay. So, what do we have going here? Well, these four circles are said to be suffering, suffering's a strange word. But, a common fate, they are moving together through time. and when that happens, that seems to suggest, or it certainly suggests to our visual system that, that all goes together somehow. That's all part of a single object that's moving, okay. And that's largely why we can have one-color pants and a different shirt, and all kinds of crazy colors on us, but as soon as we move down the hallway, we're perceived as a single human being. All these various you know, mixed matched features of us get glued together into a single object. So common fate's a very powerful one in the real world. for anything that moves, you know? Think of cars, think of people, think of bikes and motorcycles and etcetera. we very quickly perceive those as, as single objects. In fact, if you think of a motorcycle with a rider on it, we kind of see that as a single object even though it is a rider and a motorcycle. But because they're moving together, they become almost a single object. Okay. So, again, that's a critical first step, figuring out the object. I want to highlight the role that memory is playing in this early step and, and the way it can play a general role. We're going to really focus on memory when we start talking about recognizing what objects are, but even in this very general, early perceptual stage Memory plays a role. So for example context, the context in which an item occurs. And we're going to really focus on this middle item. This is the exact same slide duplicated. All I've done is put these little boxes either over the A and C here, or over the 12 and 14 here. But otherwise, these are the exact same. And the point is, if this is all you saw, then this middle object would look a lot like a 13. And if this is all you saw, then this middle object would look a lot like a B, even though it's the exact same sensory stimulus. So, the point here is that every time we come into any context, so if we're in a hospital, we expect hospital kinds of sights, hospital kinds of sounds. If we're in a university, we expect university sights, university sounds. If we're in a park, we expect park sights, park sounds. So our system walks into these situations primed. It's ready to experience certain things that are high probability in that environment. and so those concepts in memory are, are heightened a little bit. And if we get a little bit of stimuli from the world that suggests that that's there, a squirrel in a park, for example, that's a real important part of how we perceive this ambiguous kind of information. Okay. We're really going to ratchet up the memory influence in the next lecture, I just wanted to bring it in here and, you know, actually hit you over the head again with it here. Here, here's our friend, the dalmation again, and I expect he just popped out for you now, and will forevermore, by the way. I could show you this five years from now and you would still see the dalmation. Creepy but true, alright. So here's just a few other things for you to follow. Here's a video on sensation and perception, just to make a lot of that. stuff I've been talking about a little clearer for you, This is kind of a funny, short youtube video of these two kind of puppets that talk in funny, German voices. German accents I should shall but talking about gestalt principles. So I found it humorous and and informative so I thought it was pretty good. This is a deeper know a deeper video about perception and what, how we interpret the world around us. so this, this one's kind of cool a little bit longer, little bit more ominous but cool. and then just a couple things for you to check out, how gestalt principles are used in design. and just another website that kind of walks you through some of the gestalt principles so you get a sense of those okay. So I'm going to leave it there for now, but we're going to take right over. We've now figured out sort of where an object begins and where it ends. And so the next problem that we're going to face is, well, how do you know what that object is. Talk about that next. I hope you have a great day.
