Monocular and Binocular Depth Cues

In this video we will continue our discussion on perception by learning how we perceive

depth

. This is how we participate in

depth

perception. Now, to perceive depth, we as humans rely on a combination of two different types of

cues

that inform us about depth. of what we are seeing there are

monocular

depth

cues

and

binocular

depth cues let's discuss each of those terms ocular simply means eye mono means one and bi translates to two so

monocular

depth cues mean depth cues They only require one eye to see

binocular

s. depth cues our depth cues that require both eyes.

I'm going to spend the rest of this video talking to you about the various monocular depth cues. There are several and both binocular depth cues, in turn, let's start with monocular depth cues, so the first one. One is relative size; other things being equal, more distant objects tend to appear smaller than objects that are closer to us. Let's look at this scene of a road full of traffic. I get stressed just looking at this. I don't know about you to illustrate here. so take a look at this Lexus here and maybe this car here look how much of our field of vision how much space these two cars take up these cars are very close to us so relatively their size is much larger take a look Some of these cars that are further away in the background take up very little space in our field of vision.

Our brain uses this information to tell which objects those cars should be farther away because they take up less space in our field of vision. Then we have text. The textures of degraded objects become less obvious as they zoom out. The textures of close-up objects are very evident again. Let's take a look at an image to illustrate. Focus your attention first on some of the flowers and grass that are very close to you. Some of these that are here maybe. In this area, this guy here, look how detailed everything is, how much texture the boundaries between objects are very well defined, you can tell a lot about the color of different objects and they don't all blend together, but now focus your attention. later on, to some of these plants and flowers and grass here, look how it all blends together, a lot of textures, a lot of details are lost again, your brain takes this information into account and says, "Okay, the further away I am." I'm looking at the least textures I'll be able to see and use this information to again judge the depth.

Then we have interposition and at this point I want to pause to remind you what we're looking at. These are all monocular depth cues, which means that you. You can do this with just one eye, so if you covered one of your eyes you would still be able to pick up all the cues I'm talking about. Interposition is the idea that if object A blocks our view of object B, this must mean that object A is closer to us than object B. Interposition has another name known as occlusion, which means that you know that objects can include each other and that tells us which object is in front of or behind the other object that you can look at. this very simple scene here of three different objects we have a blue moon we have a green rectangle and a red star and I can ask the simple question and again you can cover your eye and you can probably still get this question right, hopefully which of these three objects is closer to you, I hope you said or at least thought that the red star is right in front, nothing is blocking it, nothing includes it behind, that would be what is behind the red star, probably the green rectangle right on the blue. the moon in the back because the green rectangle is in front of that blue moon, okay, the interposition is pretty simple to do.

Next we have the linear perspective monocular depth cue, this one is a little different, but again you have experienced that parallel lines tend to converge. as distance increases now they don't actually converge parallel lines by definition they never touch converge means they come together eventually they touch well but the key is that they look from our perspective as if they converge over great distances and eventually meet at what we call a disappearance Well let's take a look at this railway track here as a kind of illustration because this is a great example, first of all, railway tracks are parallel lines, that would be very problematic for trains on these railway tracks if they were not parallel lines, but notice they converge as you move away in the distance these lines tend to join, notice: there is a vanishing point very far on the horizon in the distance, it seems that those two lines touch each other and they no longer meet. they see parallels.

You may also notice that the distance between the two parallel lines is very large up close, but very far away, the distance between the two parallel lines is very small, very close, so again your brain observes that it takes that information into account instantly to judge. . The depth you know is based on all of these different factors, plus others like texture, for example, notice that the textures of the objects are very detailed here in front and very little detailed as you go, so your brain looks All this. into account and says okay, all of this needs to be further away, all of this needs to be closer, then we have the height on the plane, this is another simple one that you've probably never thought about before, but again you've come across on a daily basis. distant objects that tend to appear higher in our fields of vision than closer objects, let's illustrate it quickly with this very nice scene too, so look at this post, just this post, this part of this fence and look at this tree, this tree or group of trees, or bush or whatever you want to call it.

This tree is higher in a visual plane than this pole, therefore we know that the tree is further away from us and finally our last monocular indicates the depth of light and shadow. This is simple, the idea that objects cast shadows and those shadows tell us all kinds of things. things about its three-dimensional shape and from that information that those shadows give us we can judge the depth, we can judge all kinds of things, we get a lot of information just by looking at this scene here there is literally light and shadow and almost everything else has been factored there's no color any of that at least not in a useful way and yet we can actually measure the depth of this object well those are your monocular death signals you can do with one eye binocular depth signals require two eyes so If you had than covering one of your eyes, you literally couldn't use the information from these different binocular depth cues to judge depth, so the first one is called binocular disparity because our two eyes are displaced, they've produced two different images and now they don't. you experience two different images because your brain puts those things together into a meaningful experience that is not disjointed, you experience the world as if you were filming with a video camera, but that's not really the case, your brain gets two different images.

In the images we're not cyclops, our eyes are offset, they're not on top of each other, so that's how your brain uses that information in a really clever way. By looking at the disparity between those two images, you can tell how far away the object is. very large disparities between your two eyes between the images that your two eyes are producing should say it means that the object is much closer an object very far away will not produce much disparity at all here is an easy way to illustrate this a demonstration that I recommend to do it , it will only take you a second, take your hand and give a thumbs up, first of all, okay, it's a great confidence booster, but it's also part of the demonstration, so give a thumbs up and now extend your arm as far as possible possible from your face. as much as you can, okay, so you're looking directly at your thumb as far away from your face as you can, now you alternate closing one eye and then the other, so you close your left eye and look through your right and then you switch eyes right is closed now you're looking to your left and it shifts back and forth very quickly to the right you'll see your thumb bounce back and forth a little bit now what I want you to do is take your thumb and put it very close to your face as close as you can to where you can still focus or fixate on your thumb so you can still see it without it being just a big blur, so look at your thumb now very close to your face and again. alternate closing your different eyes you will see your thumb jump a ton again your brain uses that information says okay it is jumping a ton this must be closer to me when it is further away it doesn't jump at all or very little I should say for it to be further away again , you need two eyes to do that.

Last but not least, we have the binocular depth convergence signal. This one is a little different and I think it's really interesting, so you may have noticed it when you took. your thumb and brought it closer to you if you participated in that demonstration great job if you did if you took your thumb and brought it closer to you you probably noticed that you felt a little pressure on your eyes actually what happened when you brought your thumb very close in front of your face is that your eyes started to converge, to fix it on your thumb they have to come together, this is what you are seeing on the right side of the screen, for example if you are focusing on something close you are close to your face your eyes have to converge yes you are looking at something very far away your eyes don't really have to converge now your brain uses that information again and judges the pressure you are physically feeling in your eyes, if you look at something very close, you feel some pressure and your eyes converge and your brain It takes all that information into account to say if I'm converging too much the object is very close to me if I'm not converging at all the object must be very far away now as a final note there are many different signs I hope you find them interesting.

I think it's fascinating that our brains just do this without us asking. It's an automatic thing that we do from a very young age, but what I want to mention is that all of these different depth cues, both monocular and, if you have two eyes, binocular depth cues are also used together at the same time.