On this week's edition of the Naked Scientists radio show and podcast, Bob Carlyon from the MRC Cognition and Brain Sciences Unit, Ian Russell from Sussex University and Trevor Cox from the University of Salford will be trying to tune us in to the science of sound, as Sabina Michnowicz explains...

This week on the Naked Scientists we bring you naked sound - cutting edge research will be making its way from the frontlines of science via the radio straight to your ear. Professor Ian Russell will discuss his research with the greater moustached bat, Professor Trevor Cox will explain the importance of architectural sound and Dr Bob Carlyon will tell us about cochlear implants. There are three acoustic experts in the mix and their combined sound will educate, enlighten and entertain!

Ian Russell is a fellow of the Royal Society and each year swaps his lab at the University of Sussex for a spell of research in a hot cave in Cuba, (over 40 degrees C and 100% humidity). Why does he choose this summer destination? Because that's where the Greater Moustached Bat 'hangs' out! But this is no ordinary bat - it has the most finely tuned hearing system of any animal in the world (check out its mug shot in figure 1). Ian has been observing these animals in order to find out how they've evolved to navigate perfectly through pitch black forests at speeds of up to 40mph. By understanding how these bats use sound for navigation, ideas can be explored which may lead to greater knowledge of how humans and other mammals process speech.

Understanding the biological basis of hearing and deafness involves getting to grips with how the inner ear (or "cochlea") works. The cochlea is a tube of bone spiralling round the auditory nerve and is notoriously inaccessible. Ian's work combines mathematical modelling, biophysics, physiology, cell biology and genetics to show how the cochlear cells respond to noise, and this response is translated into electrical signals which the brain processes as sound. As the Greater Moustached Bat is so specialised at hearing, it serves as the perfect model for learning about how the brains of mammals process the sounds they hear, especially how the cochlea amplifies sound by more than a thousand fold.

The cochlea translates sound waves into electrical signals which are interpreted as sound by the brain, but it is also important in providing humans with a sense of balance. Environmental and genetic factors (as well as ageing) can all lead to cochlea damage and result in an irreparable loss of hearing. Genetic disorders are responsible for deafness in 1 in every 1,000 births, whereas over 25% of the population above the age of 75 has significant hearing loss. Research which allows scientists to understand how the cochlea functions are useful to society because they may eventually help to cure deafness and are helpful in improving the quality of hearing aids.

Regarding hearing aids; Bob Carlyon works with cochlear implants and explains hearing and deafness using the House of Commons as a metaphor. Here in his own words is Bob's description of how we filter sound to hear what we need -

"Imagine you are Tony Blair, during Prime Minister's Questions. The Leader of the Opposition is asking a question, but all around you are loud cheers from the Tory benches, and even louder jeers from your parliamentary colleagues. Somehow, your ears and your brain must, together, extract David Cameron's voice from the competing babble. Some of these competing voices will be quite similar to his, some will be louder than his, and the sound will be bouncing around the Chamber and reaching your ears from all directions. Even with one ear, or when listening to the programme on a mono radio, normal-hearing listeners can perform this task remarkably well. To do this, the auditory system exploits physical regularities in sound - such as the fact that, at any given time, different talkers are producing sounds that differ in pitch.

Now, imagine you are deaf. Some deaf people are suitable for a device known as a cochlear implant. Sound is picked up by a microphone worn behind the ear, and transmitted across the skin to a receiver inside the head. The receiver then stimulates the auditory nerve using an array of electrodes, which bypass the damaged receptor cells in the inner ear. Now you can hear again, and many implant users converse very confidently in a one-on-one situation, and even use the telephone. However, you will have great difficulty in noisy situations, such as the one Tony finds himself in on Wednesday lunchtimes."

Bob's research group in Cambridge looks at ways of improving the way that implants encode sound. This will hopefully improve the hearing of implant users in a wide range of situations, including places with lots of background or competing noise, which brings me on to the work of our final expert.

Trevor Cox works with indoor acoustics and his latest research could make hearing easier. For the first time a technique has been developed which accurately measures exactly how sound behaves in "real world" situations, which could help to improve acoustics in all sorts of buildings from concert halls to railway stations. The impact of this technique was first explained at the British Association Festival of Science in Norwich last month (regular fans will know the Naked Scientists were there also - as ever, treading carefully along science's cutting edge to bring you the latest developments). The technique is designed to pinpoint precisely how indoor environments respond to music and speech while those environments are in everyday use. This opens up the prospect of basing acoustic design on more realistic information about the way sound behaves than has previously been possible. It may also contribute to the development of hearing aids that adapt the way they process sound according to the acoustic environment they are in, thus providing a much better listening experience for hearing aid users. This will be very valuable to the hard of hearing as it's not just the House of Commons that gets very noisy. Up until now the way of measuring acoustics has been to make a short blast of noise (e.g. a gunshot), record it and analyse how it dies away. The noise has to be very loud so that the environment's effect on it can be assessed across the full range of sound, from very loud to very quiet - only in this way can comprehensive information on an environment's acoustic performance be obtained. However, gunshot noise poses a risk to hearing and is unpleasant to listen to. This means that measurements taken in unoccupied areas are the norm even though these do not accurately indicate 'real' acoustic performance when people are present, moving and talking etc. Now, with EPSRC (Engineering and Physical Sciences Research Council) funding, Trevor is leading a team of engineers at the University of Salford in a project to explore whether the loud, short blast of noise could be replaced by music played at an average level of audibility, or even the conversation of people in the indoor environment being tested.The team are developing groundbreaking computer programmes capable of isolating snippets or phrases from normal music or speech, analysing their decay and extrapolating this data so it provides an accurate indication of an environment's effect on sound. Since loud test sounds are not required, this approach avoids the need to vacate the environment when testing takes place, enabling more realistic acoustic data to be gathered. Last week Trevor also delivered 'Beautiful Music, Horrible Sounds' to an audience of 7-14 year olds by exploring what sound is, why different sounds provoke positive and negative reactions, and how technology can be used to make sounds nicer - or nastier. It also explained why humans have two ears. Volunteers sat on a specially made 2 metre-diameter whoopee cushions - the largest in the world (Figure 2) - to demonstrate exactly how wind instruments work. The physics involved when whoopee cushions make a noise is the same as blowing through the mouthpiece of a saxophone, for instance (although the sound produced is quite different!)

So, to hear more about the naked sound of science turn on and tune in!