here's a question am I walking forward or am I walking backward this may sound like a silly question and one you obviously know the answer to but without your conscious awareness your eyes along with your brain are making dozens of instantaneous calculations to determine where I'm headed this is depth perception the ability to judge how far objects are away from you the ability to see the world in 3D as opposed to a 2d flat surface in this video we're going to talk about all the depth cues we use to make sense of the world around [Music] us now in Psychology death perception is typically divided into two types of cues what we call monocular cues ocular meaning I or vision and mono meaning one so we're able to judge depth and distance only using one eye and also binocular cues ocular once again meaning ey vision and by meaning too so we're able to judge depth and distance using both eyes let's start with monocular cues now the first monocular cue is called linear perspective and this is the idea that when you have two parallel lines like the tracks behind me the further you go in the distance the more these lines tend to converge into a single point this point is often called the vanishing point and you can see linear perspective on sidewalks and in streets and it lets your know that something is getting farther and farther away the next monocular queue is called relative size and this is the basic idea that when you have multiple objects that are relatively the same size like these blue flower pots the ones that cast a smaller image on your eye specifically your retina are going to be perceived as farther away and the ones that cast a larger image on your retina like this one is going to be perceived as closer now you might just assume that the ones behind me are actually getting smaller or shrinking and that's it's not too silly of an idea but because I know the size tends to remain constant I know they're just getting farther and farther away another monocular queue is called texture gradient and I want you to focus on the word texture this is the idea that when you see an object up close you're able to see texture and find details and as you get farther and farther away those details tend to disappear here's a really nice example all the bricks in front of me are extremely detailed right you can see all the lines little leaves little blemishes and colors Within each brick but as I pan out you'll notice that all those little details tend to disappear and eventually it almost becomes one smooth surface telling my brain we're getting farther and farther away one monocular Q artists love to use in their drawings and paintings is light and Shadow and artists use Shadows to help the viewer know where the light source is coming from which in turn helps us know how far an object is away from us and even how big an object is in this example the way that light hits the basketball and the shadow it creates provides some Clues to the brain about its dimensions and depth and in this shot the separation between the basketball and a shadow helps me perceive that the ball is off the ground and in motion Which object is closer to you the tree or the car this might sound like a trick question but it's actually a monocular Quee known as interposition or overlap and this is the idea that when one object blocks another in this case the tree is blocking the car the one that is being blocked is farther away the tree of course is going to be closer looking at these two garbage cans we can actually see two monoc accuse interposition I know the one on the right is closer because it's partially blocking the one in the back and also light and Shadow because the Shadows on the left I know light sources coming from above and to the right just like light and Shadow this queue is also frequently used by artists in their drawings to depict depth this is aerial perspective and rarely using the size of object to see how far summing away is this focuses on color I'm currently at the beach and as you can see the cliffs extend for miles and as your eyes Follow The Cliffs into the water take notice that they become less detailed blurrier and lighter in color almost blending Into the Blue Sky background this is aerial perspective the last monocular queue actually involves motion which is why I'm driving in my car and this is by far one of my favorite ones because we know it we've seen it we just never put a name to it and it's called motion parallax or relative motion and it's the basic idea that things that are far away when you're in motion appear to be moving at a different speed that things that are close up if you fixate on the median dividing the highways it looks like it's going extremely fast right but then when you fixate on the trees in the background it looks like it's going relatively slow this is a phenomenon known as motion parallax so now that we've covered monocular cues judging depth and distance only using one eye let's focus on binocular cues understanding depth perception using both eyes and there's two we're going to focus on the first binocular queue is called convergence and this is the idea that you get closer and closer to an object your eyes begin to converge or get closer together almost getting cross-eyed signaling to your brain this object is really close as you get farther and farther away from an object your eyes begin to spread apart signaling to your brain some is getting farther away you can actually feel convergence notice as they get closer and closer to the stop sign both eyes begin to come together feeling a little strained and as they move away both eyes begin to move apart signals your brain we're getting farther and farther away the last binocular cue is known as retinal disparity retinal for retina that's the back of your eye where light converts into electrial signals and disparity means difference so retinal disparity is the idea that each eye sees a different angle of an object your brain combines those images together to create a clear picture of the world your left eye is most likely seeing this image your right eye is most likely seeing this image and when you combine them together using retinal disparity you get a clear picture of the world to recap our eyes along with our brain have evolved to detect dozens of cues to process depth perception from monocular cues like linear perspective texture grade in relative size to binocular cues which is critical to seeing the world in 3D like convergence and retinal disparity