Two ears are better than one

Introduction

Fancy yourself as a musical maestro…so you think you know your music??…did you know?….music has been changed with the evolution of mankind , for example tribal drumming progressed into melodic tunes with vocals.

Whether you like Rihanna or Elton John, music is of personal choice and ‘taste’. Music choice can also depend on personal experiences for instance if one is to experience feelings of love they will listen to love songs as they can relate to the meaning of the lyrics it has been proven that music can alter moods. It has been proven listening to music activates different parts of the brain, in which both serotonin and dopamine are released. These hormones are responsible for causing pleasurable feelings similar to those of eating chocolates or even having orgasms. Although the reminiscence of a song can have a have a positive influence on emotions, it can also have the opposite effect and make you feel sad.

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Have you ever wondered why listening to a specific song can bring back memories that associated with that song??…this is because music has that ability to take you back in time, which makes it useful for studying and learning. For those of you having difficulty learning a new language, try listening to a song in that language to improve your vocabulary…and who said learning isn’t be fun!!! .

Also it has been found music stimulates brainwaves to synchronize with the beat – a faster beat encourages alertness and concentration while a slower beat calms, relaxes and creates a meditative state. So depending on your needs, music can enhance every activity and balance every mood.

There are many different aspects of music; pitch, rhythm, melody and stereo sound, they all play individual roles in how music is perceived in the human brain. Modern technology has allowed for further research in to these areas. Most people have probably heard of the first three aspects but what is stereo sound…stereo sound is what gives music it sense of ‘realness’ it creates the illusion of sound heard from different directions, as one would hear in natural hearing. For instance if listening to an advert on the radio one will be able to sense if the voice is nearer or further away.

Did you know?????… The first radio broadcast using stereo was done by the BBC in 1925. However stereo sound was established much earlier by Clement Ader in 1881 when he placed two microphones on a stage. Surprisingly it was Walk Disney’s film called Fantasia, a cartoon released in 1940, which was the first commercial film which used stereophonics. Nowadays stereophonics is essential in any film. The use of stereophonic grew and record labels began to tape in stereo, which made the first stereophonic discs available to people in 1958.

So as mentioned above Stereo sound is used in broadcasting, so let’s talk about the radio…..what’s the difference between FM and AM radio???….stereophonics use a complex system which has certain requirements. Given that the AM receivers are very restricted in number AM radios can almost never use stereophonics. On the other hand FM radio is able to use stereophonic sound. With time AM radio stations are adapting and have been looking into digital radio which would then be able to implement stereophonics

It is also used in Television various modulation schemes are used in different parts of the world to broadcast more than one sound channel. These are sometimes used to provide two mono sound channels that are in different languages, rather than stereo. Multichannel television sound is used mainly America

So how is this 3D style sound possible??Now concentrate because here’s the clever part …..To achieve stereo sound two microphones have to be placed in separate places and both record at the same time. Because of where the microphones are placed even thought they both recorded the same sound, the time that the sound arrives will be different. These small differences are picked up in the brain which helps the person to establish where a sound is coming from. This phenomenon can only be achieved when two speakers are used.

Have you ever wondered when listening to music why it feels as though the sound is in your head???…when you use earphones you cannot determine certain cues due to the pinna. Therefore a device known as Head-Related Transfer Function (HRFT) is used to make the music sound external. The HRFT changes the sound before it arrives at the eardrum, this allows for the person to establish where a sound is coming from.

Pump up the jam!!!….more like pump down the jam. It is easy to forget using headphones at a sufficiently high volume level can cause temporary problems or permanent deafness due to the “masking” effect. This occurs went the volume of music is so high that it competes with your surroundings, for example in train stations. The ears become indifferent to the detrimental effects of listening to music at a high volume.

Having two ears does not mean our hearing is limited to two directions,they can locate sounds in three dimensions – in range (distance), in direction above and below, in front and back, as well as to either side. The brain, inner ear and the external ears (pinna) help locate sound this is called spatial hearing

All the above information might be confusing to get your head ‘around’ at once, so in simpler terms stereo sound is based entirely upon the principles spatial hearing get it?….and for those of you who have forgotten what spatial hearing is….spatial hearing is what makes us hear in 3D.

So why do we need spatial hearing?…..well most importantly we need it assess danger for instance hearing somebody creeping up behind you……also if you were at a party, spatial information effectively allows people to “zoom in” on a particular signal of interest. This has been demonstrated in a multitude of studies.

Kidd et al presented a target speech signal from one of three loudspeakers placed horizontally in front of their subjects. From the other two loudspeakers, very similar competing speech signals were presented. Under these challenging conditions, knowing the spatial location of the target signal strongly aided the subjects’ ability to recall it.

Another study by Cameron et al on children with auditory processing disorders concluded “… of those children with auditory processing disorder APD, there may be a high proportion who have deficits in the binaural processing mechanisms that normally use the spatial distribution of sources to suppress unwanted signals.”In simpler term, they argued that normally perceived spatial cues help suppress secondary signals, such as background noise.

This research has shown spatial information and spatial hearing are highly important, not only for the purpose of sound localization, but for speech recognition in challenging acoustic environments with multiple competing signals.

Where in the brain does all this happen then??…..an fmri study by Colline Poirier et al found that V5 which is found in the visual cortex is activated by auditory motion processing

Studies by a young scientist called Sam Irving have maybe helped us identify where in the brain spatial hearing may occur,

The oxford study in which participants were placed in “ring of sound” where a sound is played from one of 12 speakers placed in a circle around the subject their response is monitored to see if they can detect which speaker the sound is coming from. People with normal hearing are very good at this and have excellent spatial hearing. The participants where then given an ear plug to wear on one side in which they were tested to see how well their hearing would cope in such conditions. At first the participants found it difficult to identify where the noise was coming from, but after a couple of days, the participants began to regain their ability to hear, and got the same results as they did without earplugs. This experiment was also done on ferrets, and the results were the same as humans.

It has been thought by Irving that OCB, the Olivocochlear Bundle, which is a part of the brain that we know, is a centre of feedback information being transmitted from the brain back to the ear, maybe responsible for spatial hearing.

As discussed earlier, music has an effect on the brain although many are unknown. Research suggests that music relaxes people’s moods, long after the actual music stops. It’s as if a memory of the relaxation is imprinted on the brain. Music has also been shown to help people prepare for surgery and heal faster. When patients listen to relaxing music, their breathing deepens, more oxygen is transported throughout the body, and there is a secretion of serotonin in the brain which stabilizes moods.

As previously mentioned music is known to be a form of stress relief. Due to technological advances, it has now become easier to incorporate music into our daily lives, using devices such as car radios/CD players, iPods and mobile phones etc. However these devices are not as effective as stereophonic sound as they use monophonic (single) speakers, so the sound is not as realistic thus not having the same stress relieving affects

Stereophonic although it is taken for granted, and not generally thought about by most individuals. Stereophonic sound has proven to be very beneficial, as it is used in our everyday lives, whether it’s listening to hip hop/pop or reggae music in the car, or watching easterners in the evening, these tasks would not be possible without stereo sound.

References

Behrens T. Spatial hearing in complex sound environments: clinical data. Hearing Review.2008; 15(3):94?102.

Cameron S, Dillon H, Newall P. The listening in spatialized noise test: an auditory processing disorder study. J Am Acad Audiol. 2006;17:306?320.

Blauert J. Spatial Hearing—The Psychophysics of Human Sound Localization. Cambridge, Mass:The MIT Press; 1983.

Bronkhorst AW. The cocktail party phenomenon: a review of research on speech intelligibility in multiple?talker conditions. Acta Acust Acust. 2000;86:117?128.

Laske R.D., et al., 2009. Subjective and Objective results after bilateral cochlear implantation

in adults. Otol Neurotol. Vol. 30. pp.313-316

Kidd G Jr, Arbogast TL, Mason CR, Gallun FJ. The advantage of knowing where to listen. J Acoust Soc Am. 2005;118:3804?3815.

Schneider BA, Li L, Daneman M. How competing speech interferes with speech comprehension in everyday listening situations. J Am Acad Audiol. 2007;18:559?572.

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