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Noise is everywhere, but that’s OK. Your brain can still keep track of a conversation in the face of revving motorcycles, noisy cocktail parties or screaming children – in part by predicting what’s coming next and filling in any blanks.

New data suggests that these insertions are processed as if the brain had really heard the parts of the word that are missing.

“The brain has evolved a way to overcome interruptions that happen in the real world,” says at the University of California, San Francisco.

We’ve known since the 1970s that the brain can “fill in” inaudible sections of speech, but understanding how it achieves this phenomenon – termed perceptual restoration – has been difficult. To investigate, Leonard’s team played volunteers words that were partially obscured or inaudible to see how their brains responded.

The experiment involved people who already had hundreds of electrodes implanted into their brain to monitor their epilepsy. These electrodes detect seizures, but can also be used to record other types of brain activity.

Faster/Factor

The team played the volunteers recordings of a word that could either be “faster” or “factor”, with the middle sound replaced by noise. Data from the electrodes showed that their brains responded as if they had actually heard the missing “s” or “c” sound.

This seems to be because one region of the brain, called the inferior frontal cortex, predicts what word someone is likely to hear – and it does this two-tenths of a second before the superior temporal gyrus starts processing the sounds a person has heard.

“They took a well-known phenomenon and showed, undoubtedly, that the brain puts in the acoustics that are missing,” says at New York University.

But although this prediction might seem clever, the team found that it has its limitations. The brain doesn’t seem to use the context of a conversation to improve the accuracy of its guesses. When they primed people to hear a particular word – for example, preceding the obscured word with “I drove my car” – they were just as likely to hear the word “factor” as “faster”.

Journal reference: Nature Communications, DOI:

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