From: Reuters
Published March 4, 2008 08:05 PM

Pitch is key to cocktail party conversation: study

By Michael Kahn

LONDON (Reuters) - Cutting through the chatter to understand a conversation during a crowded cocktail party is a gift researchers said on Wednesday stems from how the brain distinguishes the pitch of different voices.

Scientists call this ability to listen to someone speaking while many others are talking loudly at the same time the cocktail-party-phenomenon and thought for a long time the direction where the sounds came from was key to doing this.

"What was believed was that the sounds come from different locations in space and the brain distinguishes from those directions to determine the source of the sound," said Holger Schulze, who led the study. "We think what the brain is also doing is picking up fluctuations in sound waves."

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People with hearing aids often struggle distinguishing these sounds in crowds so the finding published in the journal PLoS One may lead to better devices for them, said Schulze, a neurobiologist at the Leibniz Institute in Germany.

"You could maybe change the acoustic signal to filter out noise the way the brain does," Schulze said. "If we could implement this in hearing aids to do the job you would not have to do it with your own brain."

The study of gerbils -- which have auditory systems similar to humans - showed that differences in the pitches produced by sound waves are the cues the brain uses to sort out auditory information, Schulze said in a telephone interview.

Each voice carries these different sound waves containing so-called temporal structures, which determine pitch. A deep male voice produces slow sound waves while a high-pitched female voice would generate much quicker ones, Schulze said.

In the study, the researchers attached electrodes to the brains of the gerbils to measure activity in the brain when the animals heard a series of artificial sounds.

These sounds mimicked the different temporal structure of voices and showed the researchers how the brain suppressed sounds. In humans, the researchers believe the brain is able to decide which conversation is the one to key in on, Schulze said.

"There is a mechanism in the brain that separates these voices, inhibits the ones you don't want and keeps the other ones active," he said.

The paper is available at: http://www.plosone.org/doi/pone.0001735.

(Reporting by Michael Kahn; Editing by Julie Steenhuysen)

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