0:00:02 > 0:00:06Touch...sight...smell...
0:00:06 > 0:00:09hearing...and taste.
0:00:11 > 0:00:15The rich sounds of a symphony orchestra.
0:00:15 > 0:00:19The visual splendour of the natural world.
0:00:19 > 0:00:22The subtle notes of a fine wine.
0:00:23 > 0:00:27Our senses help define what it means to be human.
0:00:27 > 0:00:29Ugh!
0:00:31 > 0:00:32In the animal kingdom,
0:00:32 > 0:00:36we're alone in seeking out pure sensory pleasure.
0:00:36 > 0:00:39Lovely day, innit? Beautiful.
0:00:39 > 0:00:43But they give us far more than just an appreciation of beauty.
0:00:45 > 0:00:47METRONOME TICKS
0:00:47 > 0:00:49Every second our senses gather
0:00:49 > 0:00:52millions of details about the world around us,
0:00:52 > 0:00:55feeding our brains a constant stream of information.
0:00:55 > 0:00:57RINGING, EXPLOSION
0:00:57 > 0:01:01By interpreting those signals, we can feel the lightest touch,
0:01:01 > 0:01:03hear the quietest sound.
0:01:03 > 0:01:07They're our only link with the outside world.
0:01:07 > 0:01:13Every experience we have is entirely shaped by our senses.
0:01:14 > 0:01:17For over 40 years, Horizon and the BBC
0:01:17 > 0:01:22have followed science's bid to learn how our senses decipher the world...
0:01:24 > 0:01:28Bar. Bar. Bar.
0:01:28 > 0:01:31I've seen stimuli thousands and thousands of times
0:01:31 > 0:01:34'but the effect still works on me. I can't help it.'
0:01:34 > 0:01:35Bar. Bar.
0:01:35 > 0:01:38..discovering how they equip us for survival...
0:01:38 > 0:01:41The eyes are moving about all the time.
0:01:41 > 0:01:44They're darting around three times a second.
0:01:44 > 0:01:47..and charting the advance of pioneering technology
0:01:47 > 0:01:50that could step in if our senses fail.
0:01:50 > 0:01:53BUZZER SOUNDS
0:01:53 > 0:01:55- Good boy.- Well done.
0:01:55 > 0:01:59Now we're going back into the archives...
0:01:59 > 0:02:01This is BBC Two.
0:02:01 > 0:02:05..to reveal how our understanding of the senses has changed...
0:02:05 > 0:02:06As you look at me now,
0:02:06 > 0:02:10what I really look like is this on the back of your retina.
0:02:10 > 0:02:13..so we can begin to answer the disarmingly simple question -
0:02:13 > 0:02:17how DO we sense the world around us?
0:02:29 > 0:02:31Have you ever wondered how you'd cope
0:02:31 > 0:02:35without the steady flow of information coming from your senses?
0:02:40 > 0:02:45In 2008, a bold experiment investigated sensory deprivation.
0:02:48 > 0:02:51Six volunteers were taken deep inside a nuclear bunker...
0:02:51 > 0:02:55Oh, wow. That's bleak.
0:02:55 > 0:03:00..and kept in dark rooms for 48 hours with nothing to see or hear.
0:03:03 > 0:03:05OK, Mickey, so, going to turn the light off now.
0:03:05 > 0:03:08- We'll see you a bit later on.- OK, thanks. See you later.- Take care.
0:03:10 > 0:03:14The lack of sensory information had a dramatic effect.
0:03:16 > 0:03:18Oh, it's getting tough now.
0:03:19 > 0:03:22This is harder than I thought. I don't know if I can do this.
0:03:22 > 0:03:23HE LAUGHS
0:03:23 > 0:03:26HE MUTTERS TO HIMSELF
0:03:28 > 0:03:31After 30 hours with no external stimuli,
0:03:31 > 0:03:33they began to invent their own.
0:03:35 > 0:03:38Oh, God, I'm losing it now. Tim, I'm hallucinating.
0:03:48 > 0:03:51By the end of the two-day experiment,
0:03:51 > 0:03:54the volunteers had become anxious.
0:03:55 > 0:03:58I think I'm hitting a wall now in my mind.
0:04:00 > 0:04:03And tests showed that their reasoning skills
0:04:03 > 0:04:07and short-term memory were temporarily impaired.
0:04:07 > 0:04:12Sensory deprivation had robbed them of their ability to make sense of the world.
0:04:12 > 0:04:14- Hello.- Oooh!
0:04:14 > 0:04:19In fact, it can have such a severe effect that it has been used as a form of torture.
0:04:19 > 0:04:23God, I never thought a nuclear bunker would look so beautiful.
0:04:29 > 0:04:34We're obviously not alone in being so reliant on our senses.
0:04:36 > 0:04:40All animals share the ability to sense the world outside
0:04:40 > 0:04:45but how they do that and the information that they gather varies wildly between species.
0:04:45 > 0:04:47Butterflies have special cells in their feet
0:04:47 > 0:04:50that allow them to taste everything that they land on,
0:04:50 > 0:04:55while bees are attracted to the ultraviolet patterns of light that they see on flowers,
0:04:55 > 0:05:00and birds can navigate by detecting the magnetic field of the Earth.
0:05:00 > 0:05:03But all of those senses share a common purpose.
0:05:03 > 0:05:06And that's survival.
0:05:10 > 0:05:14Over millions of years, the senses of every animal have evolved
0:05:14 > 0:05:17to solve life's most vital problems -
0:05:17 > 0:05:21how to reproduce and avoid danger.
0:05:25 > 0:05:28For many animals, their primary survival weapon
0:05:28 > 0:05:30is their powerful sense of smell.
0:05:43 > 0:05:46One of the hamster's babies is taken out of the nest
0:05:46 > 0:05:47and as soon as she realises
0:05:47 > 0:05:50he is missing, she hurries out to bring him home.
0:05:57 > 0:06:00On the other hand, if a baby mouse is taken from its home
0:06:00 > 0:06:02and you put it near the hamster's nest,
0:06:02 > 0:06:04her reaction is quite different.
0:06:10 > 0:06:13To her, it's food.
0:06:17 > 0:06:19While mother hamster is away,
0:06:19 > 0:06:22a tiny mouse is put into the nest along with her own offspring.
0:06:22 > 0:06:26The purpose is to dress the baby mouse in hamster clothing, or,
0:06:26 > 0:06:28in this case, hamster smell.
0:06:31 > 0:06:34If, after only a quarter of an hour in the nest
0:06:34 > 0:06:36along with the hamster babies,
0:06:36 > 0:06:38the mouse is taken away and stranded like the other was
0:06:38 > 0:06:39on the far side of the cage,
0:06:39 > 0:06:44what will happen when mother hamster is returned to the scene?
0:06:51 > 0:06:56Her reaction is blindly automatic. It looks nothing like her babies.
0:06:56 > 0:06:59It is pink and naked. But now it has the right smell.
0:07:02 > 0:07:05This time, the baby mouse is safe
0:07:05 > 0:07:08because smell signals are so critical to the hamster
0:07:08 > 0:07:12they override all other signs that the mouse doesn't belong.
0:07:18 > 0:07:22Smell is a key communication tool
0:07:22 > 0:07:25and many animals emit chemical smell messages called pheromones
0:07:25 > 0:07:29to signal that they're ready to mate.
0:07:33 > 0:07:34He's a big heavy animal
0:07:34 > 0:07:38and successful mating is no light task for his lady friend.
0:07:38 > 0:07:41She'll only stand in the arched posture that will support him
0:07:41 > 0:07:44if she's both in a receptive state and receiving the pheromone.
0:07:47 > 0:07:51If you remove the boar's scent gland, she won't stand.
0:07:51 > 0:07:54It seems to be an automatic response on her part to his chemical message.
0:08:01 > 0:08:02On a farm where there are no boars
0:08:02 > 0:08:04and they use artificial insemination,
0:08:04 > 0:08:08a pig man can broadcast fake messages.
0:08:15 > 0:08:18A squirt of factory-made canned boar taint.
0:08:18 > 0:08:20Now she's getting both signals -
0:08:20 > 0:08:22the weight on her back and the chemical.
0:08:22 > 0:08:26She does stand so it means everything is exactly right to inseminate her.
0:08:34 > 0:08:36Sexual signals...
0:08:39 > 0:08:41..finding your way by following a smell trail...
0:08:44 > 0:08:48..alarms, the recognition of friends or enemies...
0:08:50 > 0:08:54..all these are functions that smell messages perform.
0:08:55 > 0:08:58Smell and taste are closely linked.
0:08:58 > 0:09:00Together they act as a warning system
0:09:00 > 0:09:06and can help an animal decide what's safe to eat and what isn't.
0:09:10 > 0:09:15This footage of wolves eating a dead sheep was filmed in the 1980s
0:09:15 > 0:09:17by a team of American scientists
0:09:17 > 0:09:20trying to prevent wolf attacks on sheep.
0:09:22 > 0:09:24The scientists put a pill
0:09:24 > 0:09:27containing a mild poison into a piece of mutton wrapped in sheep hide.
0:09:29 > 0:09:33Within half an hour of eating the bait, the wolves started to vomit.
0:09:36 > 0:09:41Several days later, a live sheep was put into the pen with the wolves.
0:09:43 > 0:09:46You'd expect it to be pulled apart.
0:09:48 > 0:09:51But after just one nip, the wolves backed off,
0:09:51 > 0:09:56having learnt that the smell and taste of sheep now represented danger.
0:10:07 > 0:10:09Ugh.
0:10:09 > 0:10:13Humans are less reliant on their sense of smell than most animals.
0:10:13 > 0:10:18But we still use it instinctively to recognise potential danger.
0:10:18 > 0:10:21By the time it smells off,
0:10:21 > 0:10:24rotting meat contains such high levels of bacteria
0:10:24 > 0:10:26that eating it could be fatal.
0:10:26 > 0:10:28HE GAGS
0:10:28 > 0:10:30So we find the smell disgusting
0:10:30 > 0:10:34to stop us putting rotting flesh anywhere near our mouths.
0:10:34 > 0:10:37Ugh.
0:10:37 > 0:10:39Oh. Hideous.
0:10:42 > 0:10:47Smell became less important to us once we evolved to stand upright.
0:10:47 > 0:10:51The best noses stay close to the ground.
0:10:51 > 0:10:52Nothing at all.
0:10:52 > 0:10:55- You can't smell them?- Not at all, no.
0:10:57 > 0:11:01So if not smell, which of our senses do we depend upon the most?
0:11:01 > 0:11:03BABY CRIES
0:11:03 > 0:11:07At birth, many of our senses are still fuzzy.
0:11:07 > 0:11:10Our eyes can't focus properly
0:11:10 > 0:11:13and our ears just hear a roar of meaningless sounds.
0:11:16 > 0:11:19So the sense we rely upon when we enter the world
0:11:19 > 0:11:22is the one that offers the most direct link to it.
0:11:22 > 0:11:24Touch.
0:11:24 > 0:11:27BABY CRIES
0:11:27 > 0:11:30At this stage, our capacity to feel
0:11:30 > 0:11:34seems far more advanced than our capacity to use our other senses.
0:11:39 > 0:11:45It provides the basis for our first understanding of someone else outside ourselves.
0:11:57 > 0:12:00Without touch cells in our lips, moreover,
0:12:00 > 0:12:02we would be denied the very source of life.
0:12:10 > 0:12:14As we grow, touch remains an essential part of our development.
0:12:16 > 0:12:21To understand its importance, scientists in the '60s and '70s
0:12:21 > 0:12:26examined the effect of depriving other young primates of physical contact.
0:12:28 > 0:12:32Individuals who do not have a reasonable background,
0:12:32 > 0:12:35in terms of tactile stimulation,
0:12:35 > 0:12:38often fail to form meaningful relationships.
0:12:38 > 0:12:41The interactions tend to be unco-ordinated
0:12:41 > 0:12:43and by and large they tend to be exceedingly aggressive.
0:12:46 > 0:12:49They discovered that a lack of touch in the early years
0:12:49 > 0:12:53could have a heavy impact on their emotional development.
0:12:55 > 0:12:58For us, even as adults,
0:12:58 > 0:13:02the briefest touch can have a surprisingly powerful effect.
0:13:04 > 0:13:07At this library at Purdue University, Indiana,
0:13:07 > 0:13:11a most curious experiment is being conducted.
0:13:14 > 0:13:18When a book is checked out, the clerical procedure is boring,
0:13:18 > 0:13:21mechanical and quite unremarkable.
0:13:21 > 0:13:26The library clerk in this case is instructed to conduct this operation identically with everybody.
0:13:26 > 0:13:32Her posture, gaze, vocabulary, voice tone and so on must be held constant.
0:13:33 > 0:13:36The next encounter has just one difference.
0:13:36 > 0:13:40The clerk touches the other person when handing back the identity card,
0:13:40 > 0:13:44and the touch must be as fleeting and insignificant as possible.
0:13:48 > 0:13:50- There you go.- Thanks.
0:13:52 > 0:13:54Every reader is approached after the check-out
0:13:54 > 0:13:58and asked to fill in a questionnaire about the library in general.
0:13:58 > 0:14:01A brief interview then follows.
0:14:01 > 0:14:02- Have you finished?- Yes.
0:14:02 > 0:14:03Thank you.
0:14:03 > 0:14:06We're particularly interested in how the clerk behaved.
0:14:06 > 0:14:10- Did you notice whether the clerk smiled at you?- Yes, she did.
0:14:10 > 0:14:14Did you notice whether she touched you?
0:14:14 > 0:14:17I don't think she touched me.
0:14:17 > 0:14:18OK.
0:14:18 > 0:14:22Well, the librarian didn't smile, but she did touch.
0:14:22 > 0:14:25The questionnaire was about the reader's feelings that day
0:14:25 > 0:14:27about the library, librarians and other readers.
0:14:27 > 0:14:30Typically, these are perceived as unremarkable
0:14:30 > 0:14:32unless the person was touched.
0:14:32 > 0:14:35Then perceptions become enthusiastic and quite vivid.
0:14:35 > 0:14:36Professor Dick Heslin.
0:14:36 > 0:14:41That kind of a touch has such potency as to actually change a person's mood
0:14:41 > 0:14:45and even change their feeling towards something like a library, where it occurred.
0:14:49 > 0:14:53The addition of one fleeting touch transformed this encounter.
0:14:53 > 0:14:55- There you go.- Thanks.
0:15:00 > 0:15:05So how might an experience be affected by removing sense?
0:15:09 > 0:15:12In a fast ball game like squash,
0:15:12 > 0:15:15you'd think the main thing was to keep your eye on the ball.
0:15:18 > 0:15:21But a surprising amount of information comes through the ear,
0:15:21 > 0:15:24as Suzanne is about to find out.
0:15:26 > 0:15:30Suzanne Burgess is ranked 10th in the country for women's squash,
0:15:30 > 0:15:33but even she will find it difficult playing under these conditions.
0:15:36 > 0:15:39MUSIC PLAYS
0:15:48 > 0:15:52The music conflicts with the sounds Suzanne would normally hear in the squash court
0:15:52 > 0:15:55so she keeps missing the ball.
0:15:55 > 0:15:58It was much more difficult because you couldn't tell how hard you were hitting the ball
0:15:58 > 0:16:02and it slowed down your reaction time because you take a lot of signals from your hearing
0:16:02 > 0:16:05that you don't really realise until you haven't got them there.
0:16:08 > 0:16:11That experiment shows how our senses work together,
0:16:11 > 0:16:16even when we're unaware of it, to give us a full picture of the world.
0:16:21 > 0:16:23But of all the senses,
0:16:23 > 0:16:26the one we've evolved to rely upon the most is vision.
0:16:26 > 0:16:30The visual system is incredibly sophisticated.
0:16:30 > 0:16:34With the briefest glance, it can extract the finest detail from a scene
0:16:34 > 0:16:37and then process that information in a split second.
0:16:37 > 0:16:42It's capable of distinguishing between millions of different colour hues,
0:16:42 > 0:16:44assessing depth and distance,
0:16:44 > 0:16:49of recognising faces and tracking moving objects.
0:16:54 > 0:16:57Man is primarily a visual animal.
0:16:57 > 0:17:02The eyes alone account for 70% of the total information reaching our brains.
0:17:05 > 0:17:10Your brain seems to take visual information much more seriously
0:17:10 > 0:17:12than information from your muscles and balancing mechanisms.
0:17:12 > 0:17:15Here, the floor isn't moving at all,
0:17:15 > 0:17:18only the walls are moved just a little.
0:17:20 > 0:17:23That's quite enough to make the toddler fall down.
0:17:32 > 0:17:37We use our eyes for more than just the obvious task of navigating the world.
0:17:42 > 0:17:46Eye tracking software has shown how well our eyes scout out
0:17:46 > 0:17:50potential mates without us even realising.
0:17:51 > 0:17:53In this nightclub,
0:17:53 > 0:17:58scientists have set up an experiment to see what people's eyes get up to.
0:17:58 > 0:18:04These volunteers have agreed to wear a headset that will record every move their eyes make.
0:18:04 > 0:18:06An eye tracker gives us the opportunity
0:18:06 > 0:18:08to see where we're actually looking
0:18:08 > 0:18:11and this is kind of important to record
0:18:11 > 0:18:14because eyes are moving all the time. They're darting around three times a second
0:18:14 > 0:18:16and we're certainly not aware of this
0:18:16 > 0:18:19so we need some piece of equipment that will show us what's happening.
0:18:19 > 0:18:23The volunteers think they're waiting to be tested by the psychologists,
0:18:23 > 0:18:26but the real test is happening now.
0:18:28 > 0:18:31The software will track their eye movements as they wait
0:18:31 > 0:18:35next to a table of attractive models who have been planted there.
0:18:39 > 0:18:42Afterwards, they're shown the results.
0:18:42 > 0:18:44Here we are,
0:18:44 > 0:18:47you check this guy's face as you walk by.
0:18:47 > 0:18:48Did you realise you were looking at him?
0:18:48 > 0:18:53No, I noticed someone over there laughing at me. That's all I did.
0:18:53 > 0:18:56But not that particular person.
0:18:56 > 0:18:59The volunteers thought they were just chatting with their friends
0:18:59 > 0:19:02but the software reveals where their eyes were actually looking.
0:19:02 > 0:19:05I'm really embarrassed!
0:19:05 > 0:19:08I don't even know there was a guy in the bar with a camel coat on,
0:19:08 > 0:19:11and yet I must have been sat looking at him.
0:19:11 > 0:19:12Oh, my God! Oh, no!
0:19:21 > 0:19:26So what's really happening as our eyes are checking out the world?
0:19:27 > 0:19:31How are photons of light collected, then turned into moving pictures?
0:19:36 > 0:19:38To understand its secrets,
0:19:38 > 0:19:42scientists first probed the eye's physical properties.
0:19:42 > 0:19:44How does an eye work?
0:19:44 > 0:19:46Well, here's a model of an eye.
0:19:46 > 0:19:48Supposing I turn this round,
0:19:48 > 0:19:51you'd be able to see what the eye is like inside.
0:19:51 > 0:19:54So light comes through this transparent skin,
0:19:54 > 0:19:57through the hole in the iris, through the lens,
0:19:57 > 0:20:00and right across the eye to the far side there,
0:20:00 > 0:20:02which is called the retina -
0:20:02 > 0:20:06a whole area of light-sensitive cells.
0:20:09 > 0:20:13Studying the retina revealed that it's made up of millions of specialist cells
0:20:13 > 0:20:17that respond to light and individual colours.
0:20:18 > 0:20:23Keep staring at the screen at the dot in the centre of the flag.
0:20:23 > 0:20:26In about 20 seconds, we'll take the pattern away
0:20:26 > 0:20:28and the screen will go white.
0:20:28 > 0:20:30But you should still see an image.
0:20:33 > 0:20:36At this moment, we're not transmitting any image to you
0:20:36 > 0:20:39but you should be seeing the Union Jack in its proper colours.
0:20:42 > 0:20:45What's happening is that as you stare at the green area,
0:20:45 > 0:20:51your green and blue cones get tired out and respond less than normally to the white screen,
0:20:51 > 0:20:56but the red cones fire normally giving a red after-image,
0:20:56 > 0:21:01and the yellow areas tire out the red and green cones, leaving blue.
0:21:11 > 0:21:12As we learned more,
0:21:12 > 0:21:15we became increasingly aware that the eye alone
0:21:15 > 0:21:19couldn't explain the remarkable abilities of our visual system.
0:21:25 > 0:21:27Being able to receive an image through the eye
0:21:27 > 0:21:29is only the very beginning of the process.
0:21:30 > 0:21:34For a long time, people thought simply that light came into the eye,
0:21:34 > 0:21:36you've got the picture at the back of the eye,
0:21:36 > 0:21:40and somehow the mind accepts that picture.
0:21:40 > 0:21:41Almost like Brighton Rock.
0:21:41 > 0:21:44You have a picture at one end, a picture at the other, that's all there is to it.
0:21:44 > 0:21:47In fact, this is entirely wrong.
0:21:47 > 0:21:51The difference is that you have to read the picture in the eye,
0:21:51 > 0:21:53rather like reading the words in a book.
0:21:55 > 0:21:59Steve, a player in an amateur basketball team.
0:22:02 > 0:22:05Steve's noticed the ball and recognised it as a ball,
0:22:05 > 0:22:10and now, like us, he's following the action with his eyes.
0:22:10 > 0:22:13At the back of the eye, on the retina,
0:22:13 > 0:22:15it's upside down, but that's the least of the problems.
0:22:15 > 0:22:20Light levels vary wildly and it's also ambiguous.
0:22:20 > 0:22:23There seems to be nothing there to tell you if the ball is enormous and far away
0:22:23 > 0:22:26or small and close, or whether it's you, your eye,
0:22:26 > 0:22:28or something in the scene which is moving.
0:22:34 > 0:22:38When you look around the world, usually it looks nothing like this.
0:22:38 > 0:22:40It looks so real.
0:22:40 > 0:22:44It's hard to realise that what you see is not a picture at all,
0:22:44 > 0:22:47but a description of the world in brain language.
0:22:52 > 0:22:55Investigating the role of the brain
0:22:55 > 0:22:59and how it processed the eye's signals was the next big challenge.
0:23:05 > 0:23:09In the 1980s, the BBC replicated a classic experiment
0:23:09 > 0:23:11that turned the world upside down
0:23:11 > 0:23:16to see if the brain could still make sense of the images it received.
0:23:18 > 0:23:21Susannah Fiennes is trained to look and to see.
0:23:21 > 0:23:24What happens if the image in the eye is turned upright?
0:23:27 > 0:23:31A pair of spectacles were made for her by an optician.
0:23:31 > 0:23:34She was to wear them for a whole week, whenever her eyes were open.
0:23:34 > 0:23:37They're obviously going to feel very strange at first,
0:23:37 > 0:23:39that's only to be expected.
0:23:41 > 0:23:45I can't quite see your face so it must... Oh, perhaps...
0:23:45 > 0:23:47If I come down to your level, that might be easier.
0:23:47 > 0:23:50How does that feel? OK?
0:23:56 > 0:24:00Heavens, it's really peculiar! Now, just let me...
0:24:00 > 0:24:04The image entering her eyes has been inverted.
0:24:04 > 0:24:08I've just got to see if I can walk around a bit.
0:24:09 > 0:24:11I'm being rational about this.
0:24:11 > 0:24:15All right? Oh, no!
0:24:15 > 0:24:16Erm...where is it?
0:24:20 > 0:24:24Because I'm sure I'm holding the cup up. Oh, God.
0:24:24 > 0:24:29Now I'm going to try and write my name normally
0:24:29 > 0:24:31while I'm looking at it.
0:24:31 > 0:24:34I can't think how I do it
0:24:34 > 0:24:37because I don't really even know where to begin.
0:24:41 > 0:24:45By the end of the experiment, Susannah's brain had adapted to the glasses
0:24:45 > 0:24:48and she could once again see the world the right way up.
0:24:53 > 0:24:57She'd learnt to re-interpret the world and the alien information
0:24:57 > 0:25:00she was getting through her eyes in just one week,
0:25:00 > 0:25:05and that shows you how hard the brain works to process visual messages.
0:25:05 > 0:25:08Information from your eyes finds its way to the back of the brain
0:25:08 > 0:25:13here, to the visual cortex, and it's at this location
0:25:13 > 0:25:17that we form an image of the world to give us a picture that makes sense.
0:25:21 > 0:25:26Scientists still didn't understand exactly how that image forms.
0:25:27 > 0:25:35So they began to investigate the way individual sections of the cortex respond in monkeys.
0:25:36 > 0:25:38It used to be thought
0:25:38 > 0:25:41that the brain uses a building-block strategy to analyse vision,
0:25:41 > 0:25:45that, as information passed through different areas of the brain,
0:25:45 > 0:25:48it was analysed in greater and greater complexity,
0:25:48 > 0:25:54but the building-block model was challenged by studies of single cells in monkey brains.
0:25:54 > 0:25:59In this area, called V5, cells responded only to moving objects.
0:26:03 > 0:26:09In this area, V3, cells were mainly responsive to the form and depth of an object.
0:26:11 > 0:26:14And V4, the colour-coded cells,
0:26:14 > 0:26:18making decisions about colour on the basis of everything in the scene.
0:26:20 > 0:26:26So a new theory emerged which suggests that different areas of the brain perform specialised tasks.
0:26:29 > 0:26:32The discovery that different parts of the brain had evolved
0:26:32 > 0:26:37to respond to specific parts of an image was a major breakthrough.
0:26:39 > 0:26:43And scientists were keen to devise more experiments.
0:26:43 > 0:26:48They soon found that even when an image is pared down to just one element such as movement,
0:26:48 > 0:26:51the brain can still work out what it's seeing.
0:26:54 > 0:26:58The points of light mean very little...
0:26:58 > 0:26:59until they move.
0:27:01 > 0:27:05These are fixed to the joints of people's limbs.
0:27:05 > 0:27:09Using rules about relative motion derived from prospective geometry,
0:27:09 > 0:27:15you can recognise absolute form in spite of changes in size or shape in the image.
0:27:15 > 0:27:19That allows you to find out an enormous amount about things in the world
0:27:19 > 0:27:22from minimal information about just how they're moving.
0:27:25 > 0:27:30We've learned a lot more about where in the brain signals from the eye were being processed,
0:27:30 > 0:27:34but we were still grappling with how it made sense of that information.
0:27:34 > 0:27:38New insight would come from an unexpected source.
0:27:38 > 0:27:44It was the 1980s and the computer revolution was making itself felt in every branch of science,
0:27:44 > 0:27:49and it would inspire a radical new theory of vision.
0:27:51 > 0:27:53The theory was developed by David Marr.
0:27:53 > 0:27:55He combined computer science
0:27:55 > 0:27:58with existing knowledge of the eye and brain.
0:27:58 > 0:28:04The principle behind his theory is that vision extracts the essential features from images.
0:28:04 > 0:28:08Seeing is rather like weather forecasting.
0:28:13 > 0:28:16The weather data are collected in several forms -
0:28:16 > 0:28:19temperature, pressure, wind speed and wind direction.
0:28:22 > 0:28:26Similarly, the eye responds to light, colour and motion.
0:28:29 > 0:28:34Just as there is no real wind, pressure or temperature in the collected weather data,
0:28:34 > 0:28:38so there is no colour, light or motion in the brain.
0:28:38 > 0:28:41Instead there is a code representing the incoming information.
0:28:42 > 0:28:44'Sule Skerry,
0:28:44 > 0:28:49'south southeast 3, 11 miles, 981...'
0:28:49 > 0:28:52This is a symbol for the weather.
0:28:52 > 0:28:56There are symbols which represent objects in the brain.
0:29:00 > 0:29:03But in what form are the brain's equivalent of isobars?
0:29:05 > 0:29:10How might an object such as a deer be encoded and symbolised?
0:29:11 > 0:29:13The problem is considerable
0:29:13 > 0:29:17because as a deer turns its shape changes totally,
0:29:17 > 0:29:19yet it is still seen as a deer.
0:29:22 > 0:29:24Before David Marr began his work,
0:29:24 > 0:29:28a popular theory was that the brain analysed and refined the signals
0:29:28 > 0:29:31until finally a single deer cell responded.
0:29:32 > 0:29:34Whitman Richards.
0:29:34 > 0:29:37You're going to run out of cells very quickly.
0:29:37 > 0:29:41I mean, think of all the objects, possible objects,
0:29:41 > 0:29:45and size and shape and orientations that you could encounter.
0:29:45 > 0:29:49Even just take one of them, like the deer.
0:29:49 > 0:29:54You can put that in many different orientations and positions and distances,
0:29:54 > 0:30:00and each of those, the single cell would have to respond to - deer.
0:30:00 > 0:30:02And you're just going to run out of cells.
0:30:02 > 0:30:07There are an infinite number, unlimited number of possible combinations.
0:30:07 > 0:30:10So David Marr discarded the single cell idea
0:30:10 > 0:30:14and instead asked what was the simplest recognisable symbol of an animal.
0:30:14 > 0:30:19The stick figure is simple to store in non-picture form in the brain's computer
0:30:19 > 0:30:23as the length, angle and junctions of the lines.
0:30:26 > 0:30:30It can also be used to represent any angle at which the deer is seen.
0:30:30 > 0:30:34The various elements are brought together with colour, texture
0:30:34 > 0:30:37and movement to see the animal in all its detail.
0:30:41 > 0:30:45This work revolutionised the field of visual theory.
0:30:45 > 0:30:49Marr showed that the human brain works rather like a computer,
0:30:49 > 0:30:53storing visual information in code form and paring it down
0:30:53 > 0:30:57to its most basic elements to be rapidly processed and understood.
0:31:00 > 0:31:06In fact, we read information from the eye so fast that we can even predict the future.
0:31:09 > 0:31:11Scientists have recently discovered
0:31:11 > 0:31:16that baseball hitters do something quite extraordinary.
0:31:18 > 0:31:22The ball is moving so fast that the hitter can't simply watch the ball
0:31:22 > 0:31:25as it comes towards him and then adjust his swing,
0:31:25 > 0:31:29so how does his bat end up in the right position?
0:31:31 > 0:31:36Top baseball stars like Gabe Kapler don't even try to watch the ball.
0:31:36 > 0:31:39I don't think that you actually have time to see the ball
0:31:39 > 0:31:42out of the pitcher's hand and then make conscious decisions.
0:31:42 > 0:31:45I think it's much more instinctive
0:31:45 > 0:31:48in that you just have to let your body take over
0:31:48 > 0:31:53and allow the physical training that you've done over a long period of time to completely take over.
0:31:57 > 0:31:59After facing thousands of throws,
0:31:59 > 0:32:02Gabe has learned to see into the future.
0:32:02 > 0:32:06Scientists have discovered that within a few thousandths of a second
0:32:06 > 0:32:08of the ball leaving the pitcher's hand,
0:32:08 > 0:32:12Gabe's brain analyses the speed, spin and angle of the ball
0:32:12 > 0:32:16and then he predicts where it's likely to end up.
0:32:17 > 0:32:19So he's swinging at the ball
0:32:19 > 0:32:22before any normal human would know where it's going.
0:32:22 > 0:32:25And he does it with astonishing accuracy.
0:32:42 > 0:32:45Our brains process information incredibly quickly
0:32:45 > 0:32:49but they still have to decide what's important and what isn't.
0:32:49 > 0:32:51Right now I'm focusing on this camera,
0:32:51 > 0:32:54even though I'm bombarded by sensory inputs.
0:32:54 > 0:32:58I have to filter out the sound of voices in the corridor,
0:32:58 > 0:33:00the feel of these clothes on my skin,
0:33:00 > 0:33:04even the sight of this microphone just hovering here above my head.
0:33:04 > 0:33:08And there's a very famous experiment that shows just how much
0:33:08 > 0:33:12our brains can miss if they get distracted by too much information.
0:33:12 > 0:33:14Watch carefully.
0:33:21 > 0:33:24This is an experiment, a battle of the sexes, men against women.
0:33:24 > 0:33:27There'll be a difference but I won't say which way round.
0:33:27 > 0:33:29It's just a simple observation test.
0:33:29 > 0:33:33All you need to do, you'll see there are three guys in yellow here.
0:33:33 > 0:33:36They have a basketball and it's your job to count
0:33:36 > 0:33:39the number of times they throw the basketball to each other.
0:33:39 > 0:33:41To make things slightly harder,
0:33:41 > 0:33:45there's also three guys in blue tracksuits.
0:33:45 > 0:33:49Ignore them, ignore their basketball, and just concentrate on this one.
0:33:49 > 0:33:50So, if we can run the tape?
0:33:50 > 0:33:53OK, so that's number one.
0:34:09 > 0:34:14OK, if we can stop the tape there for the moment. OK, be honest here.
0:34:14 > 0:34:17Anybody notice anything unusual? Be honest.
0:34:17 > 0:34:20OK, about four or five of you. Excellent.
0:34:20 > 0:34:24The rest of you didn't notice anything strange? OK.
0:34:24 > 0:34:27Right, for you guys, enjoy this moment.
0:34:27 > 0:34:29The first time I saw this, it completely threw me.
0:34:29 > 0:34:34I want you to watch the tape again but this time as you would a normal piece of television,
0:34:34 > 0:34:37no counting the basketball. If we can have the tape?
0:34:37 > 0:34:39He's going to make his entrance this time.
0:34:39 > 0:34:41Here he comes.
0:34:41 > 0:34:43LAUGHTER
0:34:43 > 0:34:48No way! That didn't happen. That did not happen!
0:34:48 > 0:34:51It totally did. It did.
0:34:51 > 0:34:52I'm absolutely shocked.
0:34:52 > 0:34:56I thought I'd spot a monkey walking across the screen.
0:34:57 > 0:35:02If you were fooled, it's because your brain was distracted by counting
0:35:02 > 0:35:05and your eyes weren't expecting the gorilla.
0:35:07 > 0:35:11But can you be tricked even if you know the truth?
0:35:12 > 0:35:18This is simply a face, actually two faces.
0:35:18 > 0:35:22This face on the left is an ordinary face.
0:35:22 > 0:35:24Plaster of Paris, but it's a face.
0:35:24 > 0:35:26This one however is not.
0:35:26 > 0:35:29It is actually hollow but look what happens when you move it.
0:35:29 > 0:35:32They're fixed together rigidly
0:35:32 > 0:35:34in this box.
0:35:34 > 0:35:37You'll see them moving in opposite directions.
0:35:37 > 0:35:41That's because you assume that this nose is sticking out
0:35:41 > 0:35:44when it's really in, so all the motions get reversed.
0:35:44 > 0:35:48This is even more dramatic if we make them nod.
0:35:48 > 0:35:51If we make them nod, it really looks weird.
0:35:51 > 0:35:56If I make it nod a great deal, you'll see it really is hollow.
0:35:56 > 0:35:59The face simply disappears inside the box.
0:35:59 > 0:36:02Now you'll see it popping out again.
0:36:03 > 0:36:08As soon as the features become visible, these outlines,
0:36:08 > 0:36:11all your knowledge of faces comes back into your brain.
0:36:11 > 0:36:14It has to be a face because it's got these features.
0:36:14 > 0:36:17You see it incorrectly, even when you know the answer.
0:36:17 > 0:36:20The probability is so low that that's hollow,
0:36:20 > 0:36:22you just don't see it as hollow.
0:36:24 > 0:36:28The brain has an uncanny ability to make things up,
0:36:28 > 0:36:31filling in the gaps to complete patterns and recognise objects
0:36:31 > 0:36:34with very few visual cues.
0:36:35 > 0:36:39It's a skill that scientists think may have developed
0:36:39 > 0:36:42as part of our survival strategy,
0:36:42 > 0:36:46allowing us to see predators and prey even when they're well hidden.
0:36:47 > 0:36:53In the course of evolution, the ability to discover prey despite camouflage
0:36:53 > 0:36:58has certainly played an important role for survival.
0:36:59 > 0:37:02So there may be an evolutionary advantage
0:37:02 > 0:37:05behind our eyes' tendency to be fooled.
0:37:08 > 0:37:11But what's the explanation for our ears being tricked?
0:37:14 > 0:37:17Bar. Bar. Bar.
0:37:17 > 0:37:20Have a look at this. What do you hear?
0:37:22 > 0:37:24Bar. Bar. Bar.
0:37:25 > 0:37:28Bar. Bar. Bar.
0:37:28 > 0:37:32But look what happens when we change the picture.
0:37:32 > 0:37:36SOUNDS LIKE: Far. Far. Far.
0:37:36 > 0:37:39Far. Far. Far.
0:37:39 > 0:37:44- Far... - And yet the sound hasn't changed.
0:37:44 > 0:37:49In every clip, you are only ever hearing "bar" with a B.
0:37:49 > 0:37:51Bar. Bar.
0:37:51 > 0:37:53Bar.
0:37:53 > 0:37:59It's an illusion known as the McGurk Effect. Take another look.
0:37:59 > 0:38:00Bar...
0:38:00 > 0:38:03Concentrate first on the right of the screen.
0:38:03 > 0:38:05Now to the left of the screen.
0:38:05 > 0:38:07..bar...
0:38:07 > 0:38:11The illusion occurs because what you are seeing
0:38:11 > 0:38:13clashes with what you are hearing.
0:38:13 > 0:38:18In the illusion, what we see overrides what we hear
0:38:18 > 0:38:22so the mouth movements we see as we look at a face
0:38:22 > 0:38:24can actually influence what we believe we're hearing.
0:38:24 > 0:38:28If we close our eyes, we actually hear the sound as it is.
0:38:28 > 0:38:31If we open our eyes, we actually see how the mouth movements
0:38:31 > 0:38:32can influence what we're hearing.
0:38:32 > 0:38:36Bar. Bar. Bar.
0:38:36 > 0:38:38It's a bizarre effect.
0:38:38 > 0:38:42Remember, the only sound you're hearing is "bar" with a B.
0:38:42 > 0:38:44SOUNDS LIKE: Far. Far..
0:38:44 > 0:38:47Bar. Bar. Bar.
0:38:47 > 0:38:49What's remarkable about this illusion
0:38:49 > 0:38:53is even knowing how it's done doesn't seem to make a difference.
0:38:53 > 0:38:55Far.
0:38:55 > 0:38:58The effect works no matter how much you know about the effect.
0:38:58 > 0:39:00I've been studying the McGurk Effect for 25 years now
0:39:00 > 0:39:03and I've been the face in the stimuli,
0:39:03 > 0:39:06I've seen stimuli thousands and thousands of times,
0:39:06 > 0:39:08but the effect still works on me. I can't help it.
0:39:08 > 0:39:12Bar. Bar. Bar.
0:39:12 > 0:39:14Bar. Bar. Bar.
0:39:14 > 0:39:18The McGurk experiment shows us that even when our senses are working normally,
0:39:18 > 0:39:22we can still make mistakes in interpreting their signals.
0:39:24 > 0:39:26But in some people, the senses merge.
0:39:29 > 0:39:31Sight and sound intermingle.
0:39:34 > 0:39:37Touch and taste run together.
0:39:39 > 0:39:42It's called synaesthesia.
0:39:43 > 0:39:47The oboe for me makes a rich, creamy-yellow sound.
0:39:47 > 0:39:50It's not a disease or a psychological problem...
0:39:52 > 0:39:55..more a difference in perception.
0:39:56 > 0:40:00Denny Simon has a complicated form of synaesthesia
0:40:00 > 0:40:03where music will cause her to see shapes.
0:40:03 > 0:40:06I'm listening to Pat Metheny now. It's a really wonderful piece.
0:40:06 > 0:40:08It makes me feel really good.
0:40:08 > 0:40:10I'm seeing it on a screen in front of my face.
0:40:10 > 0:40:12It's about this big and wide.
0:40:12 > 0:40:16It's a very horizontal piece on the screen
0:40:16 > 0:40:18and it's got points of light and colour.
0:40:18 > 0:40:20It's golden, just golden.
0:40:20 > 0:40:23When I listen to it, I feel kind of like
0:40:23 > 0:40:25there's warm water inside of my body.
0:40:25 > 0:40:29It's a very relaxing piece, which is why I like to listen to it when I'm skating.
0:40:29 > 0:40:32These bands are seen, not imagined.
0:40:32 > 0:40:34In the same way we see the blue sea,
0:40:34 > 0:40:38the red towel on the lifeguard station, Denny sees golden bands.
0:40:40 > 0:40:45Unlike Denny, most synaesthetes see words and numbers as colours and shapes.
0:40:49 > 0:40:52But there are some relatively rare variations.
0:40:54 > 0:40:59Running this pub can get very confusing for James Wannerton.
0:40:59 > 0:41:02He has an unusual form of a condition
0:41:02 > 0:41:07which means that he doesn't just hear words, he also tastes them.
0:41:07 > 0:41:11The problems I have are, somebody will come in and then order,
0:41:11 > 0:41:13say, a pint of that.
0:41:13 > 0:41:16I get the bacon rind taste.
0:41:16 > 0:41:18They then pay with a fiver,
0:41:18 > 0:41:23from which I get a taste of strawberry jam sandwiches, very, very specific.
0:41:23 > 0:41:26I then have to give them their change.
0:41:26 > 0:41:30Change invariably tastes of... processed cheese, a cheesy taste.
0:41:32 > 0:41:35John Fullwood sees colours
0:41:35 > 0:41:39when he hears certain words, even though he's blind.
0:41:39 > 0:41:43It's a nice thing to have because it enables you to be able
0:41:43 > 0:41:47to distinguish things, one from another.
0:41:47 > 0:41:51You can distinguish Saturday from Sunday because they've got different colours.
0:41:52 > 0:41:55Researchers were so intrigued by John's case,
0:41:55 > 0:41:58they invited him for an MRI scan.
0:42:00 > 0:42:03Megan Steven of Oxford University is conducting an experiment
0:42:03 > 0:42:07to discover what is happening inside John's brain
0:42:07 > 0:42:10when he sees his synaesthetic colours.
0:42:10 > 0:42:15First, she studies his brain activity when he listens to words that don't give him colours.
0:42:15 > 0:42:17Master.
0:42:17 > 0:42:19Like.
0:42:20 > 0:42:22Exquisite.
0:42:24 > 0:42:28As expected, John's brain scan shows activity
0:42:28 > 0:42:33in his sound processing areas when he listens to these ordinary words.
0:42:34 > 0:42:35OK, here we go.
0:42:35 > 0:42:40Megan Steven then reads John a list of words that do trigger his colours.
0:42:40 > 0:42:41February.
0:42:42 > 0:42:43April.
0:42:45 > 0:42:48When John hears words like Monday or January,
0:42:48 > 0:42:51he sees a specific colour and you can see here
0:42:51 > 0:42:55the area of his brain that lights up when he sees that colour,
0:42:55 > 0:42:57an area of the brain we call V4.
0:42:57 > 0:43:01It's a visual area, an area that processes information about colour.
0:43:02 > 0:43:08Brain scans reveal that synaesthesia is caused by the creation of special connections
0:43:08 > 0:43:11between areas of the brain that are normally quite separate.
0:43:14 > 0:43:17But rather than finding it to be a curse,
0:43:17 > 0:43:21those who have it often consider it more of a blessing.
0:43:21 > 0:43:27When I kiss my husband, I see...purple frosting!
0:43:27 > 0:43:29- Purple frosting?- Purple frosting.
0:43:33 > 0:43:36Synaesthesia is the result of faulty wiring in the brain.
0:43:39 > 0:43:44Some sensory conditions can be caused by damage to the brain.
0:43:47 > 0:43:50Horizon followed the case of John Alderson,
0:43:50 > 0:43:53a man whose eyes work perfectly
0:43:53 > 0:43:57but who finds it difficult to make sense of what he sees.
0:43:59 > 0:44:04Um, I think that I'm not doing too well.
0:44:04 > 0:44:06'John, I understand that five years ago you had a stroke'
0:44:06 > 0:44:10and you've been having some trouble with your vision since.
0:44:10 > 0:44:12Yes, that's true.
0:44:12 > 0:44:16They've told me it's called visual agnosia
0:44:16 > 0:44:20which I, being a good, well-brought-up Greek scholar know
0:44:20 > 0:44:22means I don't know what I'm looking at.
0:44:22 > 0:44:24Um, I don't know who's with me
0:44:24 > 0:44:30but somebody I hope is not too upset...
0:44:32 > 0:44:37They're being terribly approachable. Oh, wait a minute.
0:44:37 > 0:44:39Yes, I recognise my wife.
0:44:41 > 0:44:44Because I know what shoes she's wearing.
0:44:44 > 0:44:47When he's identifying objects,
0:44:47 > 0:44:50he only seems to pick up bits at a time.
0:44:50 > 0:44:54You can see when he tries to identify things,
0:44:54 > 0:44:57he goes around picking out the very noticeable parts of objects.
0:44:57 > 0:45:01He knows it's a pig because it's got a curly tail.
0:45:01 > 0:45:05So what it looks like from this is that he's only getting fragments of the world.
0:45:05 > 0:45:07In a way, he sees the bits
0:45:07 > 0:45:12but he's unable to pick up a whole picture of what the world should look like.
0:45:14 > 0:45:17So when John looks at what is for us an obvious scene,
0:45:17 > 0:45:21he has to try to determine what it is from individual details.
0:45:21 > 0:45:24- What's that building?- The tall one?
0:45:24 > 0:45:28- Yes.- As it's got very large windows
0:45:28 > 0:45:31and very extended corner pieces
0:45:31 > 0:45:37and something right at the very top that looks like a flagpole or something equivalent...
0:45:37 > 0:45:41I'm not awfully sure but it's not a domestic building.
0:45:41 > 0:45:45I think it's more likely to be some sort of storehouse or storage building.
0:45:45 > 0:45:50I don't think the owners of the building would be very flattered by your description.
0:45:50 > 0:45:55Although John's failure to recognise the Houses of Parliament is bizarre,
0:45:55 > 0:45:59it gives us an insight into how we must structure detail
0:45:59 > 0:46:03in order to recognise this object as a tower at all.
0:46:05 > 0:46:10Through John, we glimpse how, from a collection of lines,
0:46:10 > 0:46:12we create order.
0:46:14 > 0:46:19Studying agnosia helps scientists understand how the brain interprets visual signals,
0:46:19 > 0:46:25but they still don't know enough to help sufferers like John.
0:46:25 > 0:46:28- A church, it must be. - I'm sorry, dear, you're wrong.
0:46:28 > 0:46:30It's the Houses of Parliament. That's Big Ben.
0:46:32 > 0:46:34Good girl.
0:46:37 > 0:46:39Where's the house?
0:46:39 > 0:46:43It's often said that people who lose one sense altogether...
0:46:43 > 0:46:45HIGH-PITCHED WHINING
0:46:47 > 0:46:51..can compensate because their other senses become extra keen.
0:46:51 > 0:46:53Yes, I see.
0:46:53 > 0:46:59However, in the 1970s, this was cast into doubt.
0:46:59 > 0:47:03Part of the evidence for this belief stems from a series of experiments
0:47:03 > 0:47:09in which children, sighted and blind,
0:47:09 > 0:47:12were required for example to identify where a sound came from.
0:47:15 > 0:47:19The sighted child is blindfolded and told to swivel her chair
0:47:19 > 0:47:22so as to face directly the person calling her name.
0:47:25 > 0:47:26Justine.
0:47:29 > 0:47:31Justine.
0:47:31 > 0:47:35Although blindfolded, she does well, as do other sighted children.
0:47:36 > 0:47:41Blind children are also blindfolded to exclude any residual vision.
0:47:41 > 0:47:42Ian.
0:47:45 > 0:47:46Ian.
0:47:46 > 0:47:48This blind boy, for example,
0:47:48 > 0:47:52consistently faces about 30 degrees away from the source of the sound.
0:47:52 > 0:47:56And the implication is that sight has been acting
0:47:56 > 0:47:58as a kind of integrating sense,
0:47:58 > 0:48:04allowing one to develop the non-visual senses more rapidly and more finely.
0:48:04 > 0:48:07Far from compensating, by refining their other senses,
0:48:07 > 0:48:10visually handicapped children may be hampered in doing so.
0:48:10 > 0:48:13All along the line, their development is a struggle.
0:48:13 > 0:48:14Ian.
0:48:18 > 0:48:22To lose a sense is to lose a vital link with the world
0:48:22 > 0:48:26but can science step in where biology fails?
0:48:26 > 0:48:30Over the years, the BBC has documented some of the groundbreaking ways
0:48:30 > 0:48:37that technology has enhanced, altered and even replaced the human senses.
0:48:41 > 0:48:43That's fine.
0:48:45 > 0:48:48In the 1970s and '80s, millions of pounds
0:48:48 > 0:48:53were poured into research aimed at helping to restore sight.
0:48:55 > 0:49:00Some scientists turned to the animal kingdom for inspiration.
0:49:00 > 0:49:05This 1977 invention tried to create a human version
0:49:05 > 0:49:09of the echo locators used by bats.
0:49:09 > 0:49:12It looks like a pair of glasses but it's not.
0:49:12 > 0:49:15The important bit is here.
0:49:15 > 0:49:18This central spot has a tiny transmitter.
0:49:18 > 0:49:20It sends out a very high-pitched sound.
0:49:20 > 0:49:24When the sound hits an object, it bounces back, an echo.
0:49:24 > 0:49:27These two little receivers hear that echo.
0:49:28 > 0:49:32Then the sound is carried to your ears through these little earpieces.
0:49:32 > 0:49:35THROBBING HUM
0:49:35 > 0:49:37HIGH-PITCHED THROBBING
0:49:37 > 0:49:39There's a lamppost.
0:49:39 > 0:49:43Notice how the pitch goes from high to low as I get nearer.
0:49:43 > 0:49:46THROBBING FADES AND LOWERS IN PITCH
0:49:49 > 0:49:52REGULAR THROBBING
0:49:52 > 0:49:54THROBBING BECOMES MORE HIGH-PITCHED
0:49:54 > 0:49:58That, I think, is a car. It's parked by the side of the road.
0:49:58 > 0:50:03And there's a bush. Yes.
0:50:03 > 0:50:06REGULAR THROBBING
0:50:06 > 0:50:07WHINEY THROBBING
0:50:07 > 0:50:10This is a sound I rather like.
0:50:10 > 0:50:12It reminds me very much of church bells
0:50:12 > 0:50:17and it does in fact mean a basket-weave fence.
0:50:17 > 0:50:19THROBBING FADES
0:50:19 > 0:50:23So, with their other senses, the help of good ideas
0:50:23 > 0:50:26and modern technology, people with no sense of sight
0:50:26 > 0:50:28can get about almost as easily as the rest of us.
0:50:32 > 0:50:34Despite this optimism,
0:50:34 > 0:50:38the echo-locating glasses never quite took off.
0:50:38 > 0:50:41But the idea of using one sense to replace another did.
0:50:41 > 0:50:44Thank you very much. That's quite enough of that.
0:50:46 > 0:50:51One 1970s device substituted touch for vision.
0:50:51 > 0:50:54It allowed blind people to see things
0:50:54 > 0:50:56that were beyond reach, for the first time.
0:51:00 > 0:51:04The visual display represents approximately the image
0:51:04 > 0:51:06Bill is receiving via his camera.
0:51:06 > 0:51:08By controlling the camera,
0:51:08 > 0:51:11he's picking up a two-inch model 15 feet away.
0:51:14 > 0:51:17The image in the camera is transferred to the back of the chair
0:51:17 > 0:51:20and then split up electronically.
0:51:22 > 0:51:25Each part of the image is then represented
0:51:25 > 0:51:28by a tiny, vibrating, blunted needle.
0:51:29 > 0:51:32It's these vibrations on the skin of his back
0:51:32 > 0:51:34which Bill has learned to interpret visually.
0:51:36 > 0:51:40The information's presented as touch, but Bill is actually perceiving it
0:51:40 > 0:51:43as if it were vision, although he's totally blind.
0:51:45 > 0:51:48OK. It's a telephone.
0:51:50 > 0:51:54And the receiver is to the right.
0:51:54 > 0:51:59The tactile chair offered its users a whole new outlook on the world.
0:52:00 > 0:52:03All of a sudden I had acquired a new sense
0:52:03 > 0:52:06because before I had always been restricted to feeling things.
0:52:06 > 0:52:09Now I could perceive objects that were far away.
0:52:10 > 0:52:13The most interesting thing about first seeing a candle
0:52:13 > 0:52:16was that I realised the flame had a definite shape
0:52:16 > 0:52:20and that it would change shape if someone moved it or blew on it.
0:52:20 > 0:52:24Of course I had never been able to experience a flame directly
0:52:24 > 0:52:28because when you touch a flame you only experience heat.
0:52:29 > 0:52:33So I think that was the most interesting piece of it.
0:52:33 > 0:52:34Very surprising, actually.
0:52:34 > 0:52:37It never occurred to me that a flame would have a shape.
0:52:38 > 0:52:43This innovative device opened the door to a new wave of research
0:52:43 > 0:52:47and led to the development of ever smaller and more portable versions.
0:52:47 > 0:52:51- I'm guessing this is going on my tongue.- That's right.
0:52:52 > 0:52:55What do you think the object is?
0:52:55 > 0:52:57A spoon.
0:52:57 > 0:53:01But it still couldn't come close to replacing
0:53:01 > 0:53:03the complexity of the human eye.
0:53:03 > 0:53:10Since the 1970s, scientists have tried a range of radical ideas
0:53:10 > 0:53:12in an attempt to restore sight.
0:53:14 > 0:53:16OK, that's fine. Put your head up.
0:53:16 > 0:53:19From plugging directly into the brain's visual cortex...
0:53:19 > 0:53:21Let's go. First word?
0:53:23 > 0:53:25Eye?
0:53:26 > 0:53:29..to retinal implants.
0:53:29 > 0:53:30But advances take time.
0:53:31 > 0:53:34There are no distinct edges.
0:53:34 > 0:53:39It's just a subtle difference in the illumination.
0:53:45 > 0:53:49Scientists working on another sense would have more success.
0:53:51 > 0:53:53Now, you should feel that on the finger.
0:53:53 > 0:53:55SHE SPEAKS INDISTINCTLY
0:53:55 > 0:53:59In the 1970s, a range of devices were developed
0:53:59 > 0:54:01to help deaf people communicate.
0:54:01 > 0:54:03PHONE RINGS
0:54:03 > 0:54:07Mrs Grant sees the phone ring and switches on.
0:54:12 > 0:54:15She reads the message as it's written on her television.
0:54:23 > 0:54:28Without even having to speak, Mrs Grant can now reply.
0:54:31 > 0:54:33In the days before instant messaging,
0:54:33 > 0:54:37this simple idea had an immediate impact.
0:54:38 > 0:54:41But the greatest breakthrough in restoring hearing
0:54:41 > 0:54:44came from the world of medical innovation.
0:54:44 > 0:54:47Deep breath!
0:54:47 > 0:54:51Four-year-old Nicholas was one of the first children in the country
0:54:51 > 0:54:53to receive a cochlear implant,
0:54:53 > 0:54:57a groundbreaking device placed directly into the ear.
0:54:57 > 0:55:02It's this inner ear, or cochlea, that was damaged before Nicholas was born.
0:55:02 > 0:55:05A cochlear implant will take its place,
0:55:05 > 0:55:07processing sound electronically
0:55:07 > 0:55:10and sending it directly to the hearing nerve
0:55:10 > 0:55:12through 22 minute electrodes.
0:55:15 > 0:55:18The electrodes are placed deep inside Nicholas's ear.
0:55:20 > 0:55:23We're going to make a very small hole in the inner ear
0:55:23 > 0:55:27and insert all those 22 electrodes, or wires,
0:55:27 > 0:55:30right in the spiral of the inner ear itself.
0:55:31 > 0:55:35Then his surgeon can test whether the implant is working.
0:55:37 > 0:55:41In the middle ear we have a little muscle which is used to dampen sound.
0:55:41 > 0:55:43If our implant system is working,
0:55:43 > 0:55:46when we stimulate it to an uncomfortable level,
0:55:46 > 0:55:50that muscle should contract rather dramatically. Let's go.
0:55:52 > 0:55:55That's a massive response. You saw that?
0:55:59 > 0:56:02For Nicholas, the crucial day has arrived.
0:56:02 > 0:56:06During surgery at Nottingham, only half of the device was implanted,
0:56:06 > 0:56:08the radio receiver.
0:56:08 > 0:56:11Now Nicholas is due to be fitted with the rest of the system,
0:56:11 > 0:56:13which he'll wear on the outside.
0:56:15 > 0:56:19It's time for his implant to be switched on.
0:56:19 > 0:56:24But will he hear and if he does, how will he react?
0:56:25 > 0:56:26HARSH BUZZING
0:56:27 > 0:56:31- Good boy!- Well done.
0:56:31 > 0:56:33That was a bit of a shock.
0:56:36 > 0:56:38Can you hear the noise of the water?
0:56:38 > 0:56:40SHE HISSES
0:56:40 > 0:56:42Good boy.
0:56:42 > 0:56:44Listen, Nicholas.
0:56:45 > 0:56:47Good boy! Did you hear that?
0:56:47 > 0:56:50Moo!
0:56:51 > 0:56:53Good boy.
0:56:53 > 0:56:56Cochlear implants are now commonplace
0:56:56 > 0:57:01and have revolutionised life for hundreds of thousands of deaf people worldwide.
0:57:01 > 0:57:04- Say goodbye. Bye-bye.- Bye-bye.
0:57:04 > 0:57:08- Bye-bye.- Bye-bye. Bye-bye!
0:57:16 > 0:57:19Through our senses, we experience the world.
0:57:19 > 0:57:22CHILDREN SHRIEK
0:57:22 > 0:57:24And their loss is keenly felt.
0:57:24 > 0:57:27I've never yet discovered anybody that's been able
0:57:27 > 0:57:32to convey in words the aesthetic beauty of vision.
0:57:33 > 0:57:37To understand how and why our senses operate,
0:57:37 > 0:57:41scientists have explored the inner workings of the human body...
0:57:42 > 0:57:45These cells react to light.
0:57:47 > 0:57:49..and looked deep inside the brain.
0:57:50 > 0:57:55They've put our sensory abilities through their paces...
0:57:55 > 0:57:58I thought I'd spot a monkey walking across the screen!
0:57:59 > 0:58:04..and developed pioneering new techniques to help when they fail.
0:58:10 > 0:58:15Our senses have evolved over millions of years to give us the best chance of survival
0:58:15 > 0:58:19and that's something they do remarkably well.
0:58:19 > 0:58:21But they are so much more than that.
0:58:21 > 0:58:27Those complex systems come together to create everything that we know about the world.
0:58:27 > 0:58:29Everything we see, everything we feel,
0:58:29 > 0:58:34everything we love is a product of our senses.
0:58:36 > 0:58:40# And I've got one, two, three, four, five
0:58:40 > 0:58:43# Senses working overtime
0:58:43 > 0:58:47# Trying to take this all in
0:58:47 > 0:58:51# I've got one, two, three, four, five
0:58:51 > 0:58:54# Senses working overtime... #
0:58:57 > 0:58:59Subtitles by Red Bee Media Ltd