Part 3 - Visual Perception: Sensation and Perception

hi everyone this video will cover part three of sensation and perception more specifically it will cover the visual perception so in this slide it's a just a simple review of how light travels through the eye to the visual cortex but we're going to focus on what's happening in the visual cortex and how that information is being processed if you can see on the next slide this is also review this is taking it into the eye the sensation part where that light information is being picked up and taken in you can see how the image in the environment is refracted upside down onto the back of the eye and then this information will be understood in the brain and will be processed as right side up we also know that what is seen in the right visual field is taken in through both eyes and is processed in the left occipital lobe and we know that what's seen in the left visual field is taken in through both eyes but is processed in the right occipital lobe so we'll take our information that we already know just a little bit further so here is a person who is looking at a single cube in the distance so you can see the cube in the distance has three sides that can be seen so there's an a on top a c on the left side and a b on the right side notice that the right eye is taking in a slightly different image than the left eye and the reason that is is because of the space between both eyes that's called retinal disparity there is a gap between both eyes so the difference between both eyes and the difference between the images that are seen by both eyes is called the retinal disparity and because we have retinal disparity you will notice that we get an image that is processed in the back of these two left and right sides put together and so we actually get a better more full image because the right eye sees slightly to the right and the left eye or i should say the the right visual field is coming in just slightly to the right and the left visual field is slightly to the left of that object and so we're getting a more full picture this is called a binocular cue a binocular cue is where you use two eyes binocular so that's two eyes to pick up cues about depth so if we were just to use one eye suppose we were just using the right eye you would really only get an image kind of like this so you really wouldn't get a full picture of that block but because we've put in the left eye we can have a better more full picture of this particular block and it helps us understand dimensions so much better so binocular cues are depth perception u cues that we use both eyes which is two slightly offset images to see a more full picture of an object and it allows us to understand depth and dimension much better those are binocular cues the next slide is a slide you can use to see your own retinal disparity so you can do what this image is doing you can take your thumb you can put your thumb if you close let's say let's close your left eye you can put your thumb over an object in the distance if you're closing your left eye now switch eyes and close your right eye and open your left and you'll notice your thumb has jumped about an inch to two inches and what you're noticing is the difference between the images your eyes are getting you're seeing your retinal disparity you can also do this with another demonstration called the floating finger sausage i'll move my my picture here if you want to pause it and you want to try this it's another way for you to see your retinal disparity let's talk about another way to understand depth another way to understand depth is called monocular cue so you can use monocular cues meaning you can still if you only had one eye and you weren't using both eyes you can still tell depth you can still tell how far away an object is from you even if you are not using both of your eyes if you're using monocular or one eye so some of these monocular cues are below and i'll go over those just briefly here one monocular cue is called relative height meaning something in your visual field if it is higher up in your visual field it is farther away if it is lower down in your visual field it is closer to you relative size helps us understand depth as well if something is larger then it is closer to you if something is smaller it is farther away so notice this stuck here we know that ducks we know what size they are but if you notice this duck in my visual field here is much much much larger than this house in the distance so that tells me that this duck is closer to me and the house in the distance is farther away not necessarily that the duck is actually larger than the house but that the duck is closer to me light and shadows are hard to perceive in this particular animation but in real life if you were to stand in some landscape some nice scene things that are farther away tend to have dimmer colors than things that are close up to you they tend to be more vibrant the closer they are than they are farther away they tend to be dimmer and less vibrant in the distance linear perspective is best seen on the next slide and i'll show that in a second interposition is another way to understand depth it's more simply put as overlapping so if something is overlapping we can tell if it is closer to us or farther away so you might notice that this tree right here is overlapping the trees behind it so that tells me that this tree is closer to me there are other things overlapping you notice these trees are overlapping the hill in the distance so it tells me that this tree is closer than the hill in the distance so that is called interposition the next depth perception monocular cue is called linear perspective linear perspective is when two parallel lines appear to converge in the distance it's telling me that off those lines out here in the distance are farther away than the lines closer to me and so linear perspective perspective is just another monocular cue where parallel lines appear to converge in the distance another aspect of depth perception is the testing of depth perception when do we or when do we develop death perception or are we born with it so there's a test that can be done on young children to see at what point they understand depth perception so this is called the visual cliff it is an experimental table that a child is put on so you can see this is a child who can crawl but cannot walk the child is put on this plexiglass top so the plexiglas top goes and stretches across the whole table but it has the appearance of a drop off so this child can actually crawl across safely and not fall but there's an appearance that there's a drop off so if the child does have depth perception abilities and can pick up on those cues the child will be hesitant and will not want to crawl across that that space that appears to be a cliff if the child does not have depth perception abilities and can't pick up on those cues the child is going to crawl all the way across to the mother and what is found is that infants who are at crawling abilities will not want to crawl across they will be hesitant the mother can coax them across because they are trusting of their mother but typically they will not and they will be very hesitant and so that tells us that infants do have depth perception abilities some other aspects of perception are motion motion perceptual abilities so we'll start on the left the motion parallax is a perception of motion that helps us understand distance or depth when we're moving so you can tell in this mario game mario is moving across the screen and notice that the hills and the farthest uh part of that screen tend to be moving slower than the hills that are closer and you can even tell by that let's even look at just the ground that's moving those are moving so much more quickly the ground the bricks is moving so much more quickly than the hills in the distance and that is a depth perception cue that helps us understand how far away something is when we're in motion the phi phenomenon is another um just illusion of motion so if you have uh something that is flashing dots or lights that are flashing in succession what appears to occur is motion in like a fluid motion um we see the phi phenomenon occur uh in marquee signs if you've ever seen a marquee sign that has words that are scrolling across the screen um it's actually just flashing lights and the occurrence of the flashing lights make this this illusion of motion the stroboscopic effect is where and i don't have it on the screen because it can trigger if someone has a tendency to have epilepsy this could trigger that so you've probably seen it before though a stroboscopic movement is where you flash still shots one after another and it has the appearance of movement or motion the gestalt principles are principles where if you have many objects you perceive them as one whole so here are some examples of many objects perceived as a whole and these are specifically called grouping and i'll give you some examples so if you see i'm sorry my my lights went off in my classroom but i'll keep on going so if you see objects close together we tend to perceive them in groups so this is called proximity you can see here there are eight lines but we tend to perceive them as four because there are pairs of two that are closer together here we have nine objects but we tend to perceive them as three columns because there are similarities in the columns we don't typically see them as three rows figure ground is another grouping type of principle where we have the tendency to see one object and then the rest just kind of becomes the background so in figure ground illusions you will have a tendency to have one thing stick out so here you might either see two faces or you might have this like base standing out and then it's sometimes hard to see the other because it's become the background continuity is another grouping principle where you tend to see continuous lines that are fluid in motion and not jagged so you can if you're looking at this you probably see a straight line and a curving line we typically don't see it as like uh hills and then valleys like two separate lines of hill hill hill and valley valley valley because that's not very continuous closure is another grouping principle where we have the tendency to see things that aren't necessarily together but we close the lines and so a lot of times students will see three boxes as opposed to six separate lines here we have connectedness this is where you have many objects and if there is is something touching we tend to perceive it as one group as opposed to separate objects next we have perceptual constancies perceptual constancies are because we've seen something before we tend to understand it as the same even if our visual input is not the same so here's an example of shape which we our shape is changing because the door is opening so we have a rectangle and then we have this shape that i'm not great with geometry but probably some kind of parallelogram here and then it is even changing shape again and we don't have these right angles anymore but we still perceive it as a rectangle because we understand that it has remained the same even if our visual input has changed the same thing happens with size uh for example like if someone was throwing a basketball at you from across the court the basketball across the court is in your visual input probably about this big but as it's coming closer to you it's growing the visual input it appears that it's growing but we perceive it as constant because we've seen a basketball before and we know it's not actually growing here's another example if you look at square a and square b they probably appear to be different colors but in fact they are the same color you can actually put your finger over the space between a and b and you can or a piece of paper and you will notice that a and b are actually the same color but because we our brain understands shadows and our brain understands lightness we understand that something in a shadow is usually darker so our brain is perceiving them as different colors when in actuality they are not okay our last little bit is perceptual adaptation perceptual adaptation is a really interesting ability that we have if we are uh here here is here is the example we've got a child here who is wearing goggles and the goggles have changed her visual input and so what they've done is is these goggles have flipped her visual input upside down so when she's looking through these goggles she's actually seeing everything upside down it's actually really hard at first when you get this visual input that is upside down but you will eventually adapt and your brain will adapt and you will be able to operate completely functionally after you give your brain some time to adapt um you there are um perception goggles that uh change your vision by 40 degrees so what you are seeing in your eyes is actually a picture of 40 degrees to the left and it's kind of hard to walk it's kind of hard to give people high fives because you're actually getting what you see over here rather than what's directly in front of you so if you try to give them a high five you'll completely miss if you try to walk you'll hit the door but what will happen is your brain will understand eventually and will adapt and you will eventually be able to function and walk and high five just in in a a very functional way because your brain will adapt to an inverted um visual input okay we are at the end of our slides that was a lot of information and my lights even turned off on me but you stuck with it uh from this set of slideshows these slides you should be able to just briefly explain how the brain is processing images and understanding them and interpreting them and the input that's coming in i hope this was helpful please reach out if you have questions

Channel: Joelie McCrary

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Id: 9G-i2l3IYz0

Length: 14min 41sec (881 seconds)

Published: Mon Nov 09 2020