Hi again, this is a mini lecture on sensation and today I will be talking about monocular depth cues and a lot of this information or some of this information certainly is in your readings and uh but I have some examples for you I'll talk about it a little bit okay so as we have a pirate here we can see that He only has one eye and sometimes it's very helpful to have two eyes in terms of depth perception and you're reading talks about that and I would encourage you to read that section for binocular depth cues. But I wanted to talk about the monocular ones. There's several listed here.
Interposition or occlusion. One object blocking another. Relative size. in combination with our understanding of the world of objects and the comparability of objects, convergence or linear perspective, shadows and light, and relative clarity. By the way, I just thought this was interesting.
A friend of mine told me that the reason, I don't know if it's true, but the reason that pirates would keep one eye covered was... So they would save their night vision if they had to go in to invade another ship and go below the deck and attack people. They would be able to see relatively easily because the one eye would have good night vision.
Don't know if it's true, but sounds like a cool story. Okay, so occlusion or interposition. Basically, which shape is in front.
Basically, whatever looks like it's blocking the other one is considered the... the closer one so depth is based on that so hopefully you can all see that next relative size you know and assuming you see the objects recognize the objects are you know essentially equivalent to each other and you understand based on past experience what size is supposed to be and how large they're supposed to look based on your prior experience so here we see cars and all the cars are approximately, you know, the same size. And any, so any vehicle that looks bigger is closer. That's the relative size effect.
And here's how it works. I guess relative retinal projection depends on the size and the distance. So if we have equal sized objects and one object takes up more retinal area, it's closer.
So in the upper picture of the two trees we can see that the tree on the right or takes up much more area on the retina than the tree to the left this is the top row of pictures and you can see the green arrows show how much retinal space is taking up the two arrows in the green and then the back tree to the left is taking up a much smaller area of the retina So if we saw, if we experienced that, we would say that the tree on the right is closer than the tree on the left. Retinal size and knowledge also can influence our understanding of the size of objects in a different scenario. So in this bottom row of information, the bottom image, we have a smaller tree and a bigger tree.
So they happen to be different sizes. And if we're looking at them. and they both use up or take up the same amount of area on the retina, we also know they're not at the same distance.
One is farther away than the other. Otherwise, they wouldn't take up the same retinal space. If they were right beside each other and one was shorter and one was taller, the taller one would take up more retinal area and the smaller one would take up less.
So we know beforehand that... one's a small tree and one's a big tree, and we're looking at them and they take up the same retinal area, we will automatically realize through our visual brain processing system that the big tree is farther away than the little tree. Linear perspectives, another common monocular cue. If two objects are parallel, they cover a smaller and smaller angle in the visual field as they move away.
So we recognize this, so the railway tracks show this here. So, by the way, these two blue lines that are superimposed on this image are actually identical in length. It's the same line, but one looks bigger than the other because of sort of perceptual illusions, because of contextual processing.
Anyway, so lines are supposed to converge. That's what we've learned evolutionarily over time, that if it's just parallel lines, when as they move away from you, converge. and that's what it should look like.
In terms of light and shadow, like an object in front will have the light and an object behind will have a shadow. So I have this mom and a baby and the mom is creating a shadow on the wall and a shadow on the baby. So if you were looking from the back of the mom towards them you would see. or the mums in front of the baby. The images on the right we have balls, spears sitting on top of of a grid and you know the shadow is below each of those balls and we can see so the the ball is on top and the shadows on the bottom and also if you look at the the grid below the bee picture We also get a sense of greater height from the grid floor by the distance between the shadow and the ball.
So both where the shadow falls and how far away the shadow is from the object. Both of those indications, those cues, give us a sense of distance and position and depth. Relative clarity is also another one, or texture. so you can ask yourself which can is closer.
More texture and more details generally means it's closer. So we have two cold cans, one is blurry and one is precise. So it's not super obvious, but if you look, it does feel like, it does seem like, the clear can is a bit closer than the blurry one.
So that's it for the vision. lecture. If you please post any questions you have.