WEBVTT 00:00:04.000 --> 00:00:09.360 I'd like now to distinguish two words, which sometimes you'll probably hear me use 00:00:09.360 --> 00:00:16.840 interchangeably, but actually have a subtle difference: sensation and perception. 00:00:18.360 --> 00:00:24.960 In one sense, there's the things that we really hear, and shall we say, the immediate senses. 00:00:24.960 --> 00:00:28.200 This is what in psychology is called sensation. 00:00:28.200 --> 00:00:33.800 So with your eye, the photons actually come into the back of your eye, 00:00:33.800 --> 00:00:39.760 hitting your retina and the nerve cells, noticing those and creating a signal. 00:00:39.760 --> 00:00:46.200 When you hear, little hairs in your ear are getting wiggled by the sound 00:00:46.200 --> 00:00:49.920 and then passing that into your brain. 00:00:49.920 --> 00:00:52.800 So that is the raw sensation. 00:00:52.800 --> 00:00:56.320 That's the absolute raw sense of what's there. 00:00:56.320 --> 00:01:00.600 However, our brains do lots of work with that. 00:01:00.600 --> 00:01:05.800 They process what are those raw sensations 00:01:05.800 --> 00:01:11.600 in order to give that sense of that feeling of actually what's there. 00:01:11.600 --> 00:01:17.040 There's a couple of examples of this you can think of. So, for instance, if you... 00:01:17.040 --> 00:01:21.640 Looking at your room, just glance at the room you're in, you'll have a sense that you can 00:01:21.640 --> 00:01:26.320 see it all, but actually your eyes dance around and builds it up slowly. 00:01:26.320 --> 00:01:30.760 So that raw sensation at any one moment is probably that 00:01:30.760 --> 00:01:34.560 everything in the periphery is fuzzy. 00:01:34.560 --> 00:01:38.720 But you don't see that. What you believe you see is something that's sharp everywhere. 00:01:38.720 --> 00:01:42.760 Because if you ever need to know about a bit of the room your eye will glance to it 00:01:42.760 --> 00:01:46.600 and it will become sharp at that moment. So your 00:01:46.600 --> 00:01:50.200 perception of the room and your visual perception is that it's large, 00:01:50.200 --> 00:01:52.920 it's everywhere, and you can see it all. 00:01:52.920 --> 00:01:59.080 Your actual sensation is much, much tighter than you can see clearly. 00:01:59.960 --> 00:02:05.880 Because these differ and because they are about the meaning of the world... 00:02:05.880 --> 00:02:11.040 We are *meaning-giving creatures*; we're trying to find meaning and sense in this world. 00:02:11.040 --> 00:02:16.560 You can sometimes use this creatively to create effects, but you could also sometimes get, 00:02:16.560 --> 00:02:19.680 shall we say mistaken effects because of this. 00:02:19.680 --> 00:02:24.800 And optical illusions use this very much in order to fool your eyes because your eyes 00:02:24.800 --> 00:02:29.360 are trying to create sense of the world and you can sometimes fool them. 00:02:29.360 --> 00:02:36.520 So here's two optical illusions, both of which are based on linear perspective. 00:02:36.520 --> 00:02:41.040 There's the Ponzo one. So if you look at that picture, it's a ladder with two blocks, 00:02:41.040 --> 00:02:45.840 and it will look as if the block at the top is bigger than the block at the bottom. 00:02:45.960 --> 00:02:50.200 The reason for that is your meaning bit of your brain is saying, 00:02:50.200 --> 00:02:55.040 "It's doing, the ladder's doing this," so it's probably sloping away from you. 00:02:55.040 --> 00:03:00.360 If it's sloping away from you, then something that takes the same amount of visual space 00:03:00.360 --> 00:03:04.000 further away must be bigger. 00:03:04.000 --> 00:03:07.320 On the right is the Müller-Lyer illusion. 00:03:07.320 --> 00:03:12.400 So the Müller-Lyer illusion is two lat[eral] lines and then two arrowheads 00:03:12.400 --> 00:03:15.760 and one has got arrowheads going in and one's got arrowheads going out. 00:03:15.760 --> 00:03:20.640 And if you look at it, you probably will see the one with the arrowheads going out 00:03:20.640 --> 00:03:24.320 as being a longer line than the one at the bottom. 00:03:24.320 --> 00:03:28.760 In fact, they're absolutely the same size and the same length. 00:03:28.760 --> 00:03:34.320 However, your eye sees the one at the top longer because it looks a bit like the back 00:03:34.320 --> 00:03:38.760 edge of a box – so, again, in terms of perspective, if the line's going... 00:03:38.760 --> 00:03:41.440 It's like looking at the back of the box whereas the ones at the front is 00:03:41.440 --> 00:03:44.160 more like if you're seeing the front end of the box. 00:03:44.160 --> 00:03:48.920 And of course, again, your eye is saying that probably means the one on top is further away. 00:03:48.920 --> 00:03:52.560 Although it takes the same amount of distance on the back of your eye, 00:03:52.560 --> 00:03:54.680 that probably means it's actually larger. 00:03:54.680 --> 00:03:58.240 Now all that's happened, when I say "probably", you're not reasoning this out. 00:03:58.240 --> 00:04:03.200 This is all happening tacitly, unconsciously. You've got no idea it's going on. 00:04:03.200 --> 00:04:07.160 And it's very hard, even though you know those two are the same length 00:04:07.160 --> 00:04:09.280 to actually be able to see that. 00:04:09.440 --> 00:04:12.320 Perception is based partly on 00:04:12.320 --> 00:04:15.520 – shall we say – built-in parts of your brain. 00:04:15.520 --> 00:04:21.040 But also the culture in which you live changes the relationship between 00:04:21.040 --> 00:04:25.200 raw sensation and perception. 00:04:25.840 --> 00:04:28.880 So, you know, optical illusions can fool you. 00:04:28.880 --> 00:04:32.160 However, actually, if you think about it... 00:04:32.160 --> 00:04:35.880 So there's the kind of optical illusion like Müller-Lyer, but also you've probably seen 00:04:35.880 --> 00:04:39.600 those trick photographs where you think something's bigger than it is 00:04:39.600 --> 00:04:43.160 or you see something and it says, what's this? And you've got no idea. 00:04:43.160 --> 00:04:48.040 And then there's some small tweak and it's zoomed out and "aha, of course". 00:04:48.040 --> 00:04:54.640 Now the interesting things about those is partly it's a perception thing that your eye can get fooled. 00:04:54.640 --> 00:04:58.880 But they're often deliberately chosen at a very unusual eye position. 00:04:58.880 --> 00:05:03.400 So you may take a photograph of something so that certain things line up, 00:05:03.400 --> 00:05:07.200 that then make it confusingly look like something else. 00:05:07.200 --> 00:05:09.560 And you only have to perhaps move your head a little bit. 00:05:09.560 --> 00:05:12.920 You know, if it was a real thing that you were looking at, you would move it, 00:05:12.920 --> 00:05:17.200 you would move your head. And suddenly it would all make sense. 00:05:17.200 --> 00:05:20.960 Our perception systems are designed for the real world. 00:05:20.960 --> 00:05:24.160 They're not designed for static images on screens. 00:05:24.160 --> 00:05:27.560 We've learned to deal with them – I said culture comes in here. 00:05:27.560 --> 00:05:30.960 So our brain is trying to make sense of this all the time. 00:05:30.960 --> 00:05:35.880 And that can sometimes mean you can get these optical illusions that can be confusing. 00:05:35.880 --> 00:05:40.400 But also that can work to our advantage because we're trying to make sense. 00:05:40.400 --> 00:05:44.080 So this is something you can think about in design, both things that can go wrong, 00:05:44.080 --> 00:05:47.120 but also things that can go right.