Human Senses - S1.E2 ∙ Vision
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TVTranscript
00:00I'm here in search of a deadly animal whose vision is just like ours in one extraordinary
00:24way.
00:27It's a cobra.
00:30I have to approach her very carefully.
00:40Her flared hood is a warning.
00:42If provoked, she could unleash a venomous strike which could kill me in minutes.
00:49But I'm betting on a little known fact about snakes' eyes.
00:54If I stay still enough, she shouldn't be able to see me.
00:58The light-sensing cells in her eyes tire if what they're looking at doesn't change.
01:11Because I'm so still, she's totally relaxed.
01:16But if I move too much, she'll spot me.
01:24Like all animals, this snake has evolved to see just what she needs to see to survive
01:29and not much more.
01:33And we're just the same.
01:34The human visual system is superbly good at some things.
01:39But I'm going to show you that just like the cobra, we miss an amazing amount of what's
01:43going on right in front of our eyes.
02:02We're going to reveal the secrets of our super sense of vision.
02:07I'm Nigel Marvin and I've spent my life studying wildlife.
02:11So how do we measure up to the best eyes in the animal world?
02:18I'll be testing the amazing things we do with our eyes.
02:22How we can instantly spot attractive people in a crowded room.
02:27How our eyes guide us around the world with astonishing accuracy.
02:31And even let us see into the future.
02:36And finally, I'm going to show you why being so good at all this means we overlook the
02:40blindingly obvious.
02:43Would you spot this changeover?
02:46Stay with us and you'll discover how we can all miss what's happening right in front of
02:50us.
02:51Sorry, what were you saying?
02:54So set your video recorders now.
02:56When you look back at the tape, you literally won't believe your eyes.
03:04I'm in the skies above Los Angeles, one of the few places where they'll let you play
03:08tag with real planes.
03:11I'm about to put my eyes through a high speed workout.
03:16And you can't get much faster than this.
03:26My job as a co-pilot is to spot the other plane closing in at over 300 miles an hour.
03:32Then I have to get him in our sights and keep track of him as we hurtle around the sky.
03:38But where is that other plane?
03:41I'm looking for the tiniest speck in the distance.
03:44My eyes are scanning the skies all the time.
03:52This takes real concentration.
03:55There he is.
03:56My eyes are drawn to a tiny dot in the sky because it's moving.
04:05He knows we've seen him and he's going to try to lose us.
04:22Even at speed, my eyes stay locked onto him.
04:25As we bank and spin, my visual system has no trouble keeping track of which way he's
04:30moving and how far away he is.
04:34If I can get our laser on target, he'll release a smoke trail.
04:39Yes!
04:40I got him.
04:41You can see the smoke coming from the tail.
04:49This three-dimensional high-speed pursuit shows what we can do with our eyes.
04:54But how does our visual system measure up to the rest of the animal kingdom?
05:04There are plenty of exotic creatures equipped to see in truly fabulous ways.
05:13The mantis shrimp has remarkable eyes on storks which scan the world in twelve different colours.
05:22Chameleons have eyes which can swivel independently, so one eye can be on the lookout for danger
05:29while the other lets them grab their supper.
05:37And some animals have much sharper eyes than us.
05:42From over four miles away, an eagle can spot prey that would be completely invisible to
05:47us.
05:52These animals all have eyes suited to their needs.
05:56So what have owls evolved to be good at?
06:04We are group living animals and our real speciality is looking at the people around us, especially
06:11if we fancy them.
06:14In a busy night spot, we've decided to test exactly what people's eyes get up to with
06:20the help of psychologists Ben Tatler and Cathy Hughes.
06:25And volunteers have agreed to put on a headset that will record every move made by their
06:30eyes.
06:31An eye tracker gives us the opportunity to see where we're actually looking and this
06:35is kind of important to record because the eyes are moving about all the time, they're
06:39darting around three times a second and we're certainly not aware of this so we need some
06:43kind of piece of equipment that's going to show us what's happening.
06:48Our volunteers think they're going to the back of the bar to be tested by the psychologists
06:53but the real test is actually before that.
06:57They're asked to wait next to two women and a man who've been planted there, all attractive
07:02models.
07:03How much will our volunteers ogle them?
07:05And if they do, will they know they're doing it?
07:10Time to play back the tape and our first victim is in for a surprise.
07:14Check this guy's face as he went by.
07:18Did you realise that you were looking at him?
07:19No.
07:20I thought there was someone over there and they were laughing at me, that's all I did.
07:25But not that particular person.
07:32She was very interested in our male model in the sleeveless t-shirt.
07:37And it's not just his face she's checking out.
07:45She takes a look at the bloke's bottoms along the bar and she had no idea she was doing
07:53it.
07:54It's an eye-opener for me, I'm amazed, absolutely, absolutely.
08:02In fact, all our volunteers claim they weren't aware of where they were looking.
08:07In our test, the women actually ogled more than the men.
08:25Our last volunteer thought she was just talking to her friend, but her eyes were all over
08:30the guy in the camel coat.
08:31I'm really embarrassed, I don't even know that there's a guy in the bar with a camel
08:37coat on and yet I must have been sat looking at him, oh my God, from there.
08:42Our brains are so good at people-watching that we do it automatically, without even
08:48realising.
08:49I see you baby, alright, don't touch me.
08:51So I guess the great thing about looking at eye movements and looking at where we look
08:55is that it does give us a window into the way that the brain is working, what the brain
08:58is interested in at some kind of subconscious level, even though it never gets to the point
09:03of us being aware.
09:05Our eyes never settle and there's a good reason why they're constantly darting around.
09:11It's all to do with the basic design of the eyeball.
09:16I went to have a look inside my own eye.
09:19Dr Bill Aylward showed me the layer of cells lining the back of the eyeball that forms
09:25the image.
09:28What you can see here are blood vessels running over the surface of the retina and beneath
09:33them are light-sensitive cells which allow you to see.
09:39Lining the inside of each eyeball there are over 100 million light-sensing cells.
09:47But only the bigger cone cells see in colour.
09:52And amazingly, only in one tiny area of each eye are there enough of these cone cells jam-packed
09:58tightly together for sharp colour vision.
10:04Most of the retina gives you vision which is quite blurry, apart from this very small
10:09area in the middle.
10:10Just that smudge that we can see there.
10:12This little smudge here gives you really fine detailed vision.
10:16And that bright spot is even odder, an area which is completely blind.
10:22That's where all the blood vessels come in and out and where all the optic nerve fibres
10:26go back to the brain.
10:28And there's so much going on there that there aren't actually any light-sensitive cells
10:31in that area.
10:32And that corresponds to your blind spot.
10:35So it is a very odd design.
10:40So if our eyes are designed with a blind spot and a mostly blurred image, how do we see
10:45the world in such intricate detail and such vivid colour?
10:55The patchy image made at the back of the eye is just the beginning of how we see.
11:04As our eyes dart around, we make sure that anything interesting is lined up on our sharp
11:09spot so we get a good look at it.
11:13And you don't know you're doing it because the brain takes these jerky snapshots and
11:17creates a nice smooth movie of the world.
11:25And the brain also compensates for the blind spot.
11:29Because our eyes give us slightly different images, we can combine them to give one complete
11:35picture.
11:43So the raw image made by the eye is really pretty peculiar.
11:47But with the visual information going to both eyes and our big brains to process it, we
11:53can make wonderful sense of the world around us.
12:07Our visual system is constantly keeping track of what's out there and where it's moving.
12:12But it goes way beyond that.
12:15Sometimes we can even see things before they've happened.
12:30Scientists have recently discovered that baseball hitters do something quite extraordinary.
12:38The ball is moving so fast that the hitter can't simply watch the ball as it comes towards
12:43him and then adjust his swing.
12:45So how does his bat end up in the right position?
12:50A novice like me tries to follow the ball through the air and then take aim, which is
12:57disastrous.
12:58It's impossible, I don't even know how you catch it.
13:11But baseball stars like Gabe Kapler don't even try to watch the ball.
13:15I don't think that you actually have time to see the ball out of the pitcher's hand
13:20and then make conscious decisions.
13:21I think it's much more instinctive in that you just have to let your body take over and
13:28allow the physical training that you've done over a long period of time to completely take
13:32over.
13:37After facing thousands of throws, Gabe has learnt to see into the future.
13:43Scientists have discovered that within a few thousandths of a second of the ball leaving
13:46the pitcher's hand, Gabe's brain analyses the speed, spin and angle of the ball and
13:52then he predicts where it's likely to end up.
13:57So he's swinging at the ball before any normal human would know where it's going.
14:02He does it with astonishing accuracy.
14:17Most of us aren't quite that skilled, but every time we cross the road we all use our
14:22eyes to predict where things will move.
14:26With each glance our brains are whirring away, working out where cars will be so we can dodge
14:31the traffic.
14:37We rely on our eyes to guide ourselves around the world.
14:43It's all about coordinating our sense of vision with our bodies.
14:49But we're not even born with the basics.
14:54Babies have to learn where things are and what they have to do to grab them.
15:00And until they get it right, it can be a frustrating process.
15:09By the time we're adults, it all happens automatically.
15:17I just take my coordination for granted.
15:21But what would it be like if you were suddenly back at square one and you had to learn how
15:28to do everything all over again?
15:37In Chicago, psychologist Hubert Dolezal has devised a bizarre way to test how quickly
15:43our brains can adjust.
15:45When everything we've spent years learning is turned on its head, he's built a set of
15:51goggles that flip the world upside down.
16:04Hubert has been wearing his goggles non-stop for two weeks now.
16:07I'm going to join him for just eight hours.
16:10Oh, wow, that is so...
16:14How are you riding a bike?
16:15I mean, if I move...
16:18That is weird.
16:20When I walk, it's as if I'm walking towards myself.
16:23It's stomach-churning, but by the end of the day, I've agreed to try riding Hubert's bike.
16:30I don't think I've got a chance.
16:32Where are you?
16:33I'm right here.
16:34Now, here we go.
16:35Let's shake hands.
16:36Aha.
16:37First, it's back to Hubert's flat.
16:48And to start with, a simple task that any child could do.
16:52It's so weird.
16:53My hand is just, you know, disembodied.
16:57I can't get any signals from where it is in space.
17:02I don't know whether I'm moving it away from my body or towards...
17:04I mean, it must be towards because of the...
17:07Is it?
17:08I tell you what, I'm going to have a new admiration for babies now, when you see them playing
17:20and trying to stack things.
17:22Good for you.
17:23I cannot...
17:24There is a great gaping fridge there, and I can't work out how to get my hand in.
17:36Everything that normally happens automatically is now a real struggle.
17:41You have to think about what you're seeing, work out where things are, and then move your
17:46hands.
17:47It makes you realise how even the simplest movements depend on accurate guidance from
17:52our eyes.
17:53Where is my hand?
17:54Where are you?
18:12That was the hardest thing of all.
18:14I mean, look at it.
18:15In here, there's mirrors, so I'm seeing my reflection upside down.
18:18I don't know where the bowl was.
18:21Hubert, you knew that was going to be difficult.
18:24In this strange upside down world, I have the hand-eye coordination of a toddler.
18:30That's good.
18:32But after a few hours, I'm definitely starting to improve.
18:35There we go.
18:37Would you like some butter?
18:38Yes, please.
18:39I'm nowhere near as good as Hubert, but then he spent weeks wearing the glasses.
18:46That was well done.
18:48And to begin with, he was as hopeless as me.
18:54Oops.
18:55Oops.
18:56I just realised that I'm going to drink with my forehead.
19:04Oh, I'm sorry.
19:05As the days went by, Hubert adapted brilliantly.
19:09His brain started to make sense of this topsy-turvy world, making the right movements automatically
19:16without having to think about it.
19:20Keep going.
19:21Ah.
19:22Ooh.
19:28After eight hours, I'm feeling a bit happier, but will I be up to riding the bike?
19:33I've spent the whole day being trained by Hubert to adapt to this really bizarre upside down world.
19:42And I think I'm ready now to take on Hubert's challenge and ride this bicycle.
20:00Yoo-hoo.
20:04It's a monumental test of concentration not to fall off, but I'm just about hanging on.
20:13Ha, ha, ha.
20:17The human sense of vision is superbly good at some things.
20:21Spotting attractive people in a crowd, guiding us around the world and even predicting where things will end up.
20:31Doing all that takes a lot of brain power.
20:33Almost a third of the brain is taken up with vision.
20:37But there's a limit to how much we can see without overloading the system.
20:43So something has to give, which is why we sometimes miss things happening right in front of us.
20:53A shopping centre in London. I'm going to go up to people and ask for directions.
20:58Excuse me, can you tell us the quickest way to West Street?
21:02Then a door comes through and I swap with someone else.
21:08Sorry, what were you saying?
21:10We don't look that similar, so do you think people will notice the swap?
21:17The experiment's pretty much set up. There's microphones in here.
21:20There's four cameras, one hidden in a bag over there.
21:23There's one hidden in some scarves in a shop over there.
21:26The main camera is up on those steps there.
21:29There's a guy here, he's even got a camera in some glasses.
21:32So let's see if this is going to work.
21:40Amazingly, after a bit of practice, we start getting away with it.
21:45Excuse me, do you live around here?
21:47Yes.
21:55Sorry, what?
21:56West Street.
22:02Sorry.
22:03Come over there.
22:06You were totally different from the other chap.
22:08And you didn't notice that?
22:09No, I didn't.
22:10And I walked away thinking, damn, I can't help that guy.
22:14And he's gone off in the wrong direction, I really don't know where he's going.
22:17Where, where was it?
22:21Sorry, where, where, where was it?
22:25Less than half the people notice the changeover,
22:28which is exactly what happens whenever this experiment is done.
22:33Did you notice anything strange?
22:35Yeah, the fact that I was about to be hit by the door,
22:38and then he swapped places.
22:40Oh, so you were looking at my face and then you noticed?
22:43No, it was someone different.
22:44So when my friend carried on asking you the directions,
22:47you thought you were still talking to me?
22:52Yeah, I did.
22:55Excuse me, sorry to trouble you, do you live around here?
22:57Most people just don't see the change.
22:59There's a lot going on, and they assume they're still talking to the same person.
23:04So that's what they see.
23:08They're looking at our faces,
23:10but their brains are too busy to register what their eyes are telling them.
23:14Excuse me, do you live around here?
23:16Not around here, no.
23:17I'm trying to find a place called West Street.
23:19You're going to have to go out the centre.
23:24Sorry.
23:25I said you're in the centre.
23:28Most of the time, our vision does a wonderful job,
23:32but there's a limit to how much our brains can cope with.
23:36So we just pay attention to one thing at a time,
23:39and we're blind to the rest.
23:42The brain has a huge amount of information being delivered to it by the eyes.
23:46It has to make a decision.
23:48It has to decide where to place its attention,
23:50what information it should scrutinise,
23:52what information it should ignore.
23:54To test just how much we ignore,
23:56we've asked Richard Wiseman and the London Towers basketball team
24:00to try out an experiment designed by scientists at Harvard University.
24:05The idea is simple, but silly.
24:07We film the team practising, and then this happens.
24:15Surely no-one would miss that.
24:18We asked Richard Wiseman and the London Towers basketball team
24:21Surely no-one would miss that.
24:24We get a group of people together,
24:26and Richard briefs them to watch the screen
24:28without letting on what they're being tested for.
24:31So this is an experiment.
24:32It's a battle of the sexes, men against women.
24:34There'll be a difference, but I'm not going to say which way round it's going to be.
24:37And it's just a simple observation test.
24:39All you need to do is, you'll see there are three guys in yellow here,
24:43and they have a basketball.
24:45And it's your job to count the number of times
24:48they throw the basketball to each other.
24:50Now to make things slightly harder,
24:52there's also three guys in blue track suits.
24:55But you ignore them, ignore their basketball,
24:57and just concentrate on this one.
24:59So if we can run the tape.
25:01OK, so that's number one.
25:04Crucially, the volunteers are told to count
25:07how many times the yellow team passes the ball.
25:10But will that be enough to make them miss the gorilla?
25:21So did they see anything?
25:24OK, if we can stop the tape there for the moment.
25:26So how many basketball throws?
25:2820, any more of the others?
25:3021, OK.
25:31OK, be honest here.
25:33Anybody notice anything a little bit unusual?
25:35Be honest.
25:36OK, it's just about four or five of you.
25:38Excellent.
25:39The rest of you, not notice anything strange, honest?
25:42OK.
25:43Right, for you guys, enjoy this moment.
25:46When the first time I saw this, it completely threw me.
25:48Now I want you to watch the tape again,
25:50but this time just watch it as you would a normal piece of television.
25:52No counting the basketball, anything like that.
25:54If we can have the tape.