The Brain Has Its Own “Autofill” Function for Speech

The world is an unpredictable place. But the brain has evolved a way to cope with the everyday uncertainties it encounters—it doesn’t present us with many of them, but instead resolves them as a realistic model of the world. The body’s central controller predicts every contingency, using its stored database of past experiences, to minimize the element of surprise. Take vision, for example: We rarely see objects in their entirety but our brains fill in the gaps to make a best guess at what we are seeing—and these predictions are usually an accurate reflection of reality.

The same is true of hearing, and neuroscientists have now identified a predictive textlike brain mechanism that helps us to anticipate what is coming next when we hear someone speaking. The findings, published this week in PLoS Biology, advance our understanding of how the brain processes speech. They also provide clues about how language evolved, and could even lead to new ways of diagnosing a variety of neurological conditions more accurately.

The new study builds on earlier findings that monkeys and human infants can implicitly learn to recognize artificial grammar, or the rules by which sounds in a made-up language are related to one another. Neuroscientist Yukiko Kikuchi of Newcastle University in England and her colleagues played sequences of nonsense speech sounds to macaques and humans. Consistent with the earlier findings, Kikuchi and her team found both species quickly learned the rules of the language’s artificial grammar. After this initial learning period the researchers played more sound sequences—some of which violated the fabricated grammatical rules. They used microelectrodes to record responses from hundreds of individual neurons as well as from large populations of neurons that process sound information. In this way they were able to compare the responses with both types of sequences and determine the similarities between the two species’ reactions.

Read more: Scientific American

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