22 March 2005

Hearing more complex than believed

Research discovers new sides to human hearing. The results may lead to even better hearing aids in the future.

It has long been conventional wisdom that our way of determining the source and direction of sound is similar to that of the owl, a very highly tuned system.

This has turned out to be true to some extent, but a group of researchers from University College in London has discovered that this only applies to high frequency sounds. At lower frequencies we use a hearing technique more closely associated with smaller mammals with less sensitive hearing, such as gerbils and guinea pigs.

The researchers hope that the more nuanced understanding of human detection of sound direction can help in developing hearing aids that better mimic natural human hearing.

"Knowing how the brain creates a sense of sound space is the first step to recreating spatial hearing in the deaf", explained Dr. David McAlpine of University College, London, to BBC.

Humans as well as animals use the time difference between the sound waves hitting one ear and the other in determining the direction of the sound.

Various brain cells, or neurons, are activated depending on the time lapse between the sound waves reaching one ear and then the other. While the neurons react differently in birds and mammals, the human hearing combines both variations and thus mixes both ways of detecting the direction and source of sounds.

According to the researchers, who studied the way a group of people reacted to sounds in a typical urban setting, the human brain is continuously able to select the most effective way of listening and adapting to the immediate sound conditions.

"For animals and humans, locating the source of a sound can mean the difference between life and death, such as escaping a pursuer or crossing a busy street", said Dr. McAlpine.

Source: www.bbc.co.uk, 04.08.2004

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