WEBVTT 00:00:08.160 --> 00:00:13.559 I'd like now to distinguish two words, which sometimes you'll probably hear me use 00:00:13.559 --> 00:00:21.000 interchangeably, but actually have a subtle difference: sensation and perception. 00:00:22.697 --> 00:00:29.280 In one sense, there's the things that we really hear, and shall we say, the immediate senses. 00:00:29.280 --> 00:00:32.538 This is what in psychology is called sensation. 00:00:32.538 --> 00:00:38.121 So with your eye, the photons actually come into the back of your eye, 00:00:38.121 --> 00:00:44.110 hitting your retina and the nerve cells, noticing those and creating a signal. 00:00:44.110 --> 00:00:50.527 When you hear, little hairs in your ear are getting wiggled by the sound 00:00:50.527 --> 00:00:54.271 and then passing that into your brain. 00:00:54.271 --> 00:00:57.152 So that is the raw sensation. 00:00:57.152 --> 00:01:00.675 That's the absolute raw sense of what's there. 00:01:00.675 --> 00:01:04.949 However, our brains do lots of work with that. 00:01:04.949 --> 00:01:10.141 They process what are those raw sensations 00:01:10.141 --> 00:01:15.953 in order to give that sense of that feeling of actually what's there. 00:01:15.953 --> 00:01:21.368 There's a couple of examples of this you can think of. So, for instance, if you... 00:01:21.368 --> 00:01:25.990 Looking at your room, just glance at the room you're in, you'll have a sense that you can 00:01:25.990 --> 00:01:30.666 see it all, but actually your eyes dance around and builds it up slowly. 00:01:30.666 --> 00:01:35.095 So that raw sensation at any one moment is probably that 00:01:35.095 --> 00:01:38.899 everything in the periphery is fuzzy. 00:01:38.899 --> 00:01:43.070 But you don't see that. What you believe you see is something that's sharp everywhere. 00:01:43.070 --> 00:01:47.103 Because if you ever need to know about a bit of the room your eye will glance to it 00:01:47.103 --> 00:01:50.953 and it will become sharp at that moment. So your 00:01:50.953 --> 00:01:54.557 perception of the room and your visual perception is that it's large, 00:01:54.557 --> 00:01:57.279 it's everywhere, and you can see it all. 00:01:57.279 --> 00:02:03.400 Your actual sensation is much, much tighter than you can see clearly. 00:02:04.293 --> 00:02:10.233 Because these differ and because they are about the meaning of the world... 00:02:10.233 --> 00:02:15.389 We are *meaning-giving creatures*; we're trying to find meaning and sense in this world. 00:02:15.389 --> 00:02:20.900 You can sometimes use this creatively to create effects, but you could also sometimes get, 00:02:20.900 --> 00:02:24.019 shall we say mistaken effects because of this. 00:02:24.019 --> 00:02:29.150 And optical illusions use this very much in order to fool your eyes because your eyes 00:02:29.150 --> 00:02:33.717 are trying to create sense of the world and you can sometimes fool them. 00:02:33.717 --> 00:02:40.840 So here's two optical illusions, both of which are based on linear perspective. 00:02:40.840 --> 00:02:45.367 There's the Ponzo one. So if you look at that picture, it's a ladder with two blocks, 00:02:45.367 --> 00:02:50.196 and it will look as if the block at the top is bigger than the block at the bottom. 00:02:50.310 --> 00:02:54.547 The reason for that is your meaning bit of your brain is saying, 00:02:54.547 --> 00:02:59.360 "It's doing, the ladder's doing this," so it's probably sloping away from you. 00:02:59.360 --> 00:03:04.706 If it's sloping away from you, then something that takes the same amount of visual space 00:03:04.706 --> 00:03:08.354 further away must be bigger. 00:03:08.354 --> 00:03:11.640 On the right is the Müller-Lyer illusion. 00:03:11.640 --> 00:03:16.757 So the Müller-Lyer illusion is two lat[eral] lines and then two arrowheads 00:03:16.757 --> 00:03:20.117 and one has got arrowheads going in and one's got arrowheads going out. 00:03:20.117 --> 00:03:24.975 And if you look at it, you probably will see the one with the arrowheads going out 00:03:24.975 --> 00:03:28.648 as being a longer line than the one at the bottom. 00:03:28.648 --> 00:03:33.099 In fact, they're absolutely the same size and the same length. 00:03:33.099 --> 00:03:38.660 However, your eye sees the one at the top longer because it looks a bit like the back 00:03:38.660 --> 00:03:43.099 edge of a box – so, again, in terms of perspective, if the line's going... 00:03:43.099 --> 00:03:45.778 It's like looking at the back of the box whereas the ones at the front is 00:03:45.778 --> 00:03:48.491 more like if you're seeing the front end of the box. 00:03:48.491 --> 00:03:53.268 And of course, again, your eye is saying that probably means the one on top is further away. 00:03:53.268 --> 00:03:56.900 Although it takes the same amount of distance on the back of your eye, 00:03:56.900 --> 00:03:59.019 that probably means it's actually larger. 00:03:59.019 --> 00:04:02.599 Now all that's happened, when I say "probably", you're not reasoning this out. 00:04:02.599 --> 00:04:07.547 This is all happening tacitly, unconsciously. You've got no idea it's going on. 00:04:07.547 --> 00:04:11.518 And it's very hard, even though you know those two are the same length 00:04:11.518 --> 00:04:14.740 to actually be able to see that. 00:04:14.740 --> 00:04:20.769 Now, it was thought for a long time that a lot of us... and some of these illusions really 00:04:20.769 --> 00:04:26.050 are very basic; they're built into our – shall we say – our most primitive base being, 00:04:26.050 --> 00:04:30.793 the things that we've had for, you know, 10-20 thousand years, 00:04:30.793 --> 00:04:34.035 probably longer as part of the way we see the world. 00:04:34.242 --> 00:04:38.030 And it was thought in particular the Müller-Lyer illusion was one of these. 00:04:38.030 --> 00:04:40.414 Something that's very, very basic. 00:04:40.829 --> 00:04:45.273 I know I found problems with this for many years because linear perspective, 00:04:45.273 --> 00:04:52.215 it's actually hard to think, shall we say, what in the wild corresponds to linear perspective. 00:04:52.555 --> 00:04:57.645 And sure enough actually, what's been realized relatively recently 00:04:57.645 --> 00:05:06.200 is that most subjects of psychological experiments are what's been called WEIRD. 00:05:06.200 --> 00:05:09.680 By "WEIRD", it's White, 00:05:09.680 --> 00:05:15.669 Educated, Industrialized, Rich and Democratic. 00:05:15.788 --> 00:05:23.210 So basically, think of US psychology students as subjects of most psychology experiments 00:05:23.210 --> 00:05:25.827 – or British ones for that matter. 00:05:25.827 --> 00:05:30.771 So you actually end up with a very select set of people 00:05:30.771 --> 00:05:36.889 for which we believe everything is true of. And of course, actually that turns out not to be true. 00:05:36.889 --> 00:05:42.830 Crucially, an awful lot of things which appear to be very fundamental psychological effects 00:05:42.830 --> 00:05:46.395 turn out to be *cultural*. 00:05:46.395 --> 00:05:51.479 And crucially, this thing about the Müller-Lyer illusion is one of the ones that is not the same. 00:05:51.479 --> 00:05:58.218 So if you have a... there is a relatively small number of experiments where this is the case, 00:05:58.218 --> 00:06:01.274 but there are some experiments that have been done with people who have been brought up in 00:06:01.274 --> 00:06:04.431 the middle of forest jungle environments, but 00:06:04.431 --> 00:06:10.051 without built straight lines, concrete and brick structures. 00:06:10.315 --> 00:06:14.430 And when that's the case, the Müller-Lyer illusion doesn't work. 00:06:14.430 --> 00:06:17.206 They see the two lines as the same length. 00:06:17.206 --> 00:06:22.089 This is a learned effect that's happened from childhood, where 00:06:22.089 --> 00:06:27.000 because you live in a built environment, you end up with particular illusions. 00:06:27.000 --> 00:06:32.887 So these are partly about sensory perception, but perception is based partly on 00:06:32.887 --> 00:06:36.080 – shall we say – built-in parts of your brain. 00:06:36.080 --> 00:06:41.630 But also the culture in which you live changes the relationship between 00:06:41.630 --> 00:06:45.760 raw sensation and perception. 00:06:46.410 --> 00:06:49.479 So, you know, optical illusions can fool you. 00:06:49.479 --> 00:06:52.740 However, actually, if you think about it... 00:06:52.740 --> 00:06:56.440 So there's the kind of optical illusion like Müller-Lyer, but also you've probably seen 00:06:56.440 --> 00:07:00.182 those trick photographs where you think something's bigger than it is 00:07:00.182 --> 00:07:03.749 or you see something and it says, what's this? And you've got no idea. 00:07:03.749 --> 00:07:08.629 And then there's some small tweak and it's zoomed out and "aha, of course". 00:07:08.629 --> 00:07:15.209 Now the interesting things about those is partly it's a perception thing that your eye can get fooled. 00:07:15.209 --> 00:07:19.477 But they're often deliberately chosen at a very unusual eye position. 00:07:19.477 --> 00:07:23.962 So you may take a photograph of something so that certain things line up, 00:07:23.962 --> 00:07:27.783 that then make it confusingly look like something else. 00:07:27.783 --> 00:07:30.130 And you only have to perhaps move your head a little bit. 00:07:30.130 --> 00:07:33.508 You know, if it was a real thing that you were looking at, you would move it, 00:07:33.508 --> 00:07:37.760 you would move your head. And suddenly it would all make sense. 00:07:37.760 --> 00:07:41.530 Our perception systems are designed for the real world. 00:07:41.530 --> 00:07:44.740 They're not designed for static images on screens. 00:07:44.740 --> 00:07:48.123 We've learned to deal with them – I said culture comes in here. 00:07:48.123 --> 00:07:51.558 So our brain is trying to make sense of this all the time. 00:07:51.558 --> 00:07:56.470 And that can sometimes mean you can get these optical illusions that can be confusing. 00:07:56.470 --> 00:08:00.987 But also that can work to our advantage because we're trying to make sense. 00:08:00.987 --> 00:08:04.674 So this is something you can think about in design, both things that can go wrong, 00:08:04.674 --> 00:08:07.710 but also things that can go right.