“The Cocktail Party Effect” noise filter is revealed at last.

BBC unveils how exactly our brains are able to turn the garbled sounds of a crowded room into understandable speech:

A team measured people’s brain activity as the words of a previously unintelligible sentence suddenly became clear when a subject was told the meaning of the “garbled speech”.

The findings are published in the journal Nature Communications.

Lead researcher Christopher Holdgraf from the University of California, Berkeley, and his colleagues were able to work with epilepsy patients, who had had a portion of their skull removed and electrodes placed on the brain surface to track their seizures.

Seven of these subjects took part in the scientists’ auditory test.

First, the researchers played a very distorted, garbled sentence to each subject, which almost no-one was able to understand. They then played a normal, easy to understand version of the same sentence and immediately repeated the garbled version.

“After hearing the intact sentence” the researchers explained in their paper, all the subjects understood the subsequent “noisy version”.

The brain actually changes the way it focuses on different parts of the sound,” explained the researchers. “When patients heard the clear sentences first, the auditory cortex (the part of the brain associated with processing sound) enhanced the speech signal.”

Mr Holdgraf said: “We’re starting to look for more subtle or complex relationships between the brain activity and the sound.

“Rather than just looking at ‘up or down’, it’s looking at the details of how the brain activity changes across time, and how that activity relates to features in the sound.

This, he added, gets closer to the mechanisms behind perception.

“By understanding the ways in which our brains filter out noise in the world, the researcher concluded, “we hope to be able to create devices that help people with speech and hearing impediments accomplish the same thing.”