This week we explore the science of sound including the mathematics of music and the geometry of jazz with mathematicians Tim Gowers, from Cambridge University, and Robin Wilson from the Open University. We also get to the bottom of why helium makes your voice go all squeaky, we nail a crook by using the sound of his voice in an audio line up, and Kirsty MacDougall explains where accents come from.
In this episode
An Eye For an Eye
For the first time researchers have successfully repaired the damaged retina. The technique restored vision in mice that had been genetically programmed to mimic various forms of human vision loss. Writing in this week's edition of the journal Nature, UCL's Rachel Pearson, Jane Sowden and colleagues collected cells from the developing retina of a donor animal and injected them into an adult recipient. By labelling the donor cells with a glowing green protein borrowed from a jellyfish the researchers were able to chart the progress of the injected cells. After three weeks they had migrated to a region of the retina called the outer nuclear layer and turned into photoreceptors, the rods which convert light into electrical signals that the brain can understand. Shining a light into the eye caused the pupil to constrict, proving that the new cells had correctly wired themselves up. The other eye, which had been left unrepaired as a control, didn't respond to light, proving that the injected cells must be responsible for the effect. Other researchers have previously tried to achieve this feat using stem cells, but without success; the critical breakthrough in this study was the time at which the donor cells were harvested, which was just as the rods were beginning to form. These cells seem to intuitively know how to integrate themselves into the retina in the correct location. "This study proves, for the first time, that repair of the mammalian retina is possible. Now we just need to find a way to produce the cells needed to do it", says study author Jane Sowden.
Brain Packaging Makes Memories
The human brain is an incredible thing, enabling us to recall past events in great detail. But sometimes people only remember parts of an experience, while they can perfectly recall all the details of a different event. Now researchers at the University of California may have found a clue as to why this is. The team have been using a technique called functional MRI scanning to look at how different regions of the brain are used during certain tasks, such as remembering things. This type of brain scans allows scientists to spot regions of activity in the brain, in real time. The scientists tested 23 people by giving them a list of words while they were in the scanning machine. The words were in different colours, and appeared in different area on a computer screen. Then later on, the people were shown the words again, mixed with new words, and asked which ones they remembered, and if they could recall what colour and where the words were. The team found that if people remembered what colour the words were, then the part of their brain associated with colour recognition had been active when they first saw the words. A similar thing happened with the location of the word on the screen - people could remember it if the spatial awareness bit of their brain was active when they were learning the word. But the team found that if people remembered the word, the colour and the location, then an extra bit of their brain had been active when they were learning. This region is known as the intra-parietal sulcus, and it looks like it's responsible for linking together all the aspects of the memory. The results suggest that in order to remember all the details about something, this extra brain region has to be active to bind all the memories together. In fact, people who have brain damage in this region find it hard to remember different aspects of things. The lead researcher, Michael Rugg, says the results mean that you can't get out of memory what you don't put into it. Basically, this means it's not possible to recall things later on if you don't remember them in the right way at the time. But unfortunately the team don't have any good suggestions as to how to improve your memory.
Why Humans Are Like Sea Urchins
You might not feel much like a Californian purple sea urchin, but you're more like one than you might think, according to the latest results from Baylor College of Medicine in Houston. Researchers there have decoded all 814 million letter of DNA in the urchin's genome, revealing more than 23,000 genes. So why are the urchins so interesting? Well they're thought to share a common ancestor with humans. Now I don't mean your granny, but a sea creature that lived around 540 million years ago. This ancestor lead to a group of animals called Deuterostomes - which include humans and all other vertebrates (that's creatures with backbones). The researchers found that sea urchins shared most of the gene families found in humans, although we have more genes in each family. Most intriguingly, sea urchins have genes for sensory proteins that are important for vision and hearing in humans. But the urchins have no eyes or ears, but instead has its sensors in a tube-like appendage. One of the project leaders, Erica Sodergren, says that the sea urchin reminds us of the underlying unity of all life on earth. It's a similar set of genes and proteins being used in different ways by different creatures to create the huge diversity of living forms on our planet.
Analysing Voices And Accents
with Kirsty McDougall, Cambridge University
Chris - What is your voice and how does it work?
Kirsty - The voice is a bit like an instrument when we produce a vowel sound where we have the mouth and throat (the vocal tract) acting as a resonator. We have air coming from the lungs making the vocal chords vibrate very rapidly and the vocal tract will emphasise some frequencies a bit like the te body of a flute or clarinet.
Chris - You have a bit of a twang that says... down under. You sound a bit different to me, why is that?
Kirsty - Different language communities have agreed different targets for what the sounds of language should be and how they are going to realise them. Comparing a british and Austrailian accent the vowels sounds are different, eg the a sound in park is differnt. I produce it with my mouth and toung a bit higher and with a bit more nasalisation.
Chris - It is all learned isn't it?
Kirsty - Yes, it is agreed by the community and you learn your accent as a child.
Chris - I can begin to do an austrailian accent... G'day mate... but Rory Bremner does this brilliantly and sounds like tony blair etc. So when I try to sound like you what am I having to do? Is it like changing you accent?
Kirsty - Within a language community, it isn't really adopting an accent it is copying more individual habits, if you are trying to change your accent you are trying to change your linguistic targets to those of eg. Austrailians.
Chris - Kat has brought in some instruments. You are going tou use these to illustrate the difference between a man and a woman's voice.
Kirsty - We are going to show the difference between the resonances in a shorter female vocal tract and a male.
Kat - I have a B flat clarinet which sounds like this...
Kat - And a bass clarinet which sounds like this ... much deeper
Kat - So it is the same timbre of sound but the bigger one is much deeper.
Chris - so it this like the difference between a male and female voice?
Kat - It is in the sense that the female vocal tract is shorter than the male one, but the different vowel sounds involve changing the shape of the resonantor using the tongue and lips rather than changing its length.
Chris - Does this mean that really good singers have exactly the right head anatomy to sound really nicest resonances?
Kat It is to do with the head anantomy and also the control that such people have developed over the years.
Chris - How would you analyze a voice?
Kirsty - This is where a witness has heard a voice at a crime scene and thinks that they could recognise it again. So a bit like an identification line up.
Chris - Can we do this by computer, as the stress of a situation could distort someone's memory?
Kirsty - This type of evidence is only used in a very limited set of conditions, the witness would have had a resonable amount of exposure to the voice in question.
Chris - How can you use a computer to help an identification?
Kat - In forensic situations when you have a recording of a voice you can use a computer to do an analysis of a recording, this is normally a different situation as you rarely have a tape recorder running when you are attacked.
Kat - What are the most identifyable parts of the voice?
Kirsty This is a big problem for us, and actually we spend more time pointing out the problems with voice identifications than making them. There is no 100% reliable technique for identifying people from a recording of their voice. We just put together a whole series of indicators.
Scales and the Maths of Music
with Tim Gowers, Cambridge University
Kat - We want to find out about the maths and music. Can you tell us a little about the basics of music? What is a scale, what are notes, and how do they fit together?
Tim - A scale is any sequence of notes that goes up in smallish steps. You can get major scales, or a minor scale.
Kat - What is different about the minor scale?
Tim - For some reason that I can't really explain, major scales seem to make you feel happy but minor don't.
Kat - Does a major scale sound happy and minors sad in all cultures or is it just us here in Cambridge?
Tim - That would be an interesting experiment that should be done and possibly has but I don't know.
Kat - In Western classical music, we have a very defined idea a major or a minor scale, is this true in other cultures?
Tim - Even in Western music, jazz uses scales which are not major or minor.
Kat - These are modal aren't they?
Tim - Some of them are modal and some are more complex. In jazz this is the diminished scale. Some classical musicians call it the octatonic scale. You make it by going up alternating by a semi-tone then a tone. It sounds strange as it has a lot of chords in it called diminished fifths which sound strange. There is a mathematical reason for this. None of the ratios between the two frequencies are close to a whole number ratio of one another.
Chris - So we like notes that are a whole number ratio of one another's frequency?
Tim - Yes. For example, two notes that are an octave apart sound nice together and one is exactly twice the frequency of the other. In fact the ratio of 2:1 seems to make us perceive it as the same.
Kat - If you play two notes a semitone apart, it sounds to my ears horrible. Has what is considered as horrible changed over time?
Tim - It has changed a lot. A long time ago people even found things based on major thirds as dissonant, and everything was based on fifths and octaves.
Chris - You are the Rouse Ball Professor of Mathematics at Cambridge University. Is it a hobby or part of your research?
Tim - It definitely isn't part of my research, as I think the maths involved in music isn't very complex. So I would say that the fact I am a mathematician means that I have a certain way of looking at music.
Kat - It has been said that mathematical people are better at music or vice versa.
Tim - I like to say both mathematics and music are dealing with abstract ideas; so it's like saying does being good at football and cricket go together? In some ways yes, as if you are good at one you are probably reasonably coordinated, but it doesn't necessarily follow.
How Maths and Music go Hand in Hand
with Robin Wilson, The Open University
Chris - Tell us a bit about your work, and why maths and music go hand in hand.
Robin - I am a professional mathematician and I am interested in the history of maths, but ever since I was a child I have been interested in music. I am a recorder player and a singer. In recent years, I got more and more interested in the mathematical basis of music; in scales, chords and the structure of music. Quite a lot of music has mathematical structure in how composers build a piece of music from ideas.
Kat - Our music and our scales have twelve notes in them. How are they constructed?
Robin - Our scale is constructed from semitones. You go up twelve of them every time you go up an octave and the frequency doubles. There are other cultures that use different numbers of notes. A Balanese gamalan orchestra is based on a scale with seven notes in it; some Chinese scales have 53 notes in the octave; and one interesting scale has 31. The reason you have so many notes in the octave is that you can then get very accurate thirds, fourths and fifths.
Kat - Here is a piece of music called Organum based on this 31 note scale [MUSIC]. How long has Western music been based on a twelve note system?
Robin - The twelve notes have been around a long time. The Ancient Greeks were very interested in finding ratios. If you have an octave, the ratio is 2:1, and a perfect fifth 3:2 etc.. Up until about the 1300s or so much of the music used octaves, fourths and fifths, and then other intervals such a thirds and sixths. It turned out that in one key it worked but in other keys it sounded wrong. That is when the equal temper scale was brought in, so you could play in any key you like.
Kat - I remember hearing about Bach's Well-Tempered Klavier, when they learn how to tune pianos.
Robin - It was certainly around that time that there were lots of different tunings going on, and it is not certain which one Bach wrote things in. But the idea of the Well-Tempered Klavier was to allow you to play music in all 24 keys; major and minor.
- Solar Flares and Global Temperature Change
Solar Flares and Global Temperature Change
with Chelsea Wald and Bob Hirshon
Jan - We found periods of about 2.5 million years and another period of about 1 million years, these are the same frequencies which describe variations in the orbit and tilt of the earth which made us think that there may be a connection.
Chelsea - Van Dam says that these variations in the earth's orbit and tilt may have created periods of global cooling which in turn would have caused some mammals to perish whilst other flourished.
Bob - Scientists have discovered that powerful solar flares could cause some GPS receivers to fail, including the type used by planes to navigate Cornell engineer Paul Kinler says it is lucky they found the problem now when the sun is at the lowest point of its activity in it's 11 year cycle.
Paul - GPS is primarily entering our technical infrastructure at a period of solar minimum. the next maximum will be around 2011 and is predicted to be more powerful than the previous maximum. The reason for publishing these results is so that people know that although they have become used to GPS being unaffected by solar weather in several years it will be affected.
Bob - Kinler explains that the radio waves that accompany strong solar flares happen to be at the same frequency as GPS work on. Kinler says that now aviation authorities know about this they are developing backup plans to deal with the problem. It is possible that passengers will have to deal with space as well as normal weather delays. What worries Kinler is that other organisations may not have the backups to fall back on.
Paul - GPS is wedded into our power grid in ways that many people are not aware of. For example the US power grid is synchonised using GPS signals along with many parts of the internet, some secure financial transactions use GPS receivers to make sure that the transaction is valid.
Bob - He says that GPS is just one example of how new technologies should be acceped with caution in case unexpected difficulties arise.
- Why does your hair turn grey as you get older?
Why does your hair turn grey as you get older?
A hair is made of keratin which is the same protein that makes up finger nails which is white. On your head you have a group of cells specialised for making keratin, and near them you other cells called melanocytes which make the dark browney black pigment called melanin (its job is to absorb ultra violet light and protect the skin) a lot of these keratin making cells are squashed flat and painted with pigment, squirted through a nozzle called a folicle and form a hair. Sometimes for reasons that are not well understood, these melanocytes seem to burn out leaving the hair its natural white colour. Grey hair is actually a mixture between normal dark hairs and white hairs, which if you are standing a way away look grey.
- What is a mosquito eating when it isn't eating me?
What is a mosquito eating when it isn't eating me?
It is only the female mosquito that drinks your blood, they need the protein to make all their eggs. Male mosquitoes and females the rest of the time just eat nectar. It is very hard to eradicate mosquitoes, because they are not very fussy about what kind of animal they drink from. However the Poison Arrow frog can fight back. It is extremely poisonous, and when the mosquitoes drink its blood, they rapidly die.
Why is it that bubbles are always round?
You may have heard of surface tension this is due to water molecules pulling together and trying to minimise the number of them on the surface and not surrounded by other water molecules, it can hold up pond skaters and float pins etc. Now the water in the soap film is trying to minimise it's area too, and as there is a fixed amount of air trapped within the bubble and the shape with the least surface area for its volume is a sphere, bubbles are spherical.