The Brain recreates missing speech sounds

In everyday life we encounter lots of situations that obscure or distort people's voices, yet most of the time we understand effortlessly. This is because our brain pastes in the missing sounds, a phenomenon called phonemic restoration. It is so effective that it is sometimes hard to tell that the missing sounds are not there.

A good demonstration of this effect was published last year by Makio Kashino of NTT Communication Science Laboratories in Atsugi, Japan. He recorded a voice saying "Do you understand what I'm trying to say?" then removed short chunks and replaced them with silence. This made the sentence virtually unintelligible. But when he filled the gaps with loud white noise, the sentence miraculously becomes understandable (Acoustic Science and Technology, vol 27, p 318).

"The sounds we hear are not copies of physical sounds," Kashino says. "The brain fills in the gaps, based on the information in the remaining speech signal." The effect is so powerful that you can even record a sentence, chop it into 50-millisecond slices, reverse every single slice and play it back - and it is perfectly intelligible

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