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  • "Language alone protects us from the scariness of things with no names." - Toni Morrison, The Nobel Lecture in Literature, 1993

  • The average 20 year old knows between 27,000 and 52,000 different words.

  • By age 60, that number averages between 35,000 and 56,000.

  • Spoken out loud, most of these words last less than a second.

  • So with every word, the brain has a quick decision to make: which of those thousands of options matches the signal?

  • About 98% of the time, the brain chooses the correct word.

  • But how?

  • Speech comprehension is different from reading comprehension, but it's similar to sign language comprehensionthough spoken word recognition has been studied more than sign language.

  • The key to our ability to understand speech is the brain's role as a parallel processor, meaning that it can do multiple different things at the same time.

  • Most theories assume that each word we know is represented by a separate processing unit that has just one job: to assess the likelihood of incoming speech matching that particular word.

  • In the context of the brain, the processing unit that represents a word is likely a pattern of firing activity across a group of neurons in the brain's cortex.

  • When we hear the beginning of a word, several thousand such units may become active, because with just the beginning of a word, there are many possible matches.

  • Then, as the word goes on, more and more units register that some vital piece of information is missing and lose activity.

  • Possibly well before the end of the word, just one firing pattern remains active, corresponding to one word.

  • This is called the "recognition point."

  • In the process of honing in on one word, the active units suppress the activity of others, saving vital milliseconds.

  • Most people can comprehend up to about 8 syllables per second.

  • Yet, the goal is not only to recognize the word, but also to access its stored meaning.

  • The brain accesses many possible meanings at the same time, before the word has been fully identified.

  • We know this from studies which show that even upon hearing a word fragmentlike "cap"— listeners will start to register multiple possible meanings, like captain or capital, before the full word emerges.

  • This suggests that every time we hear a word, there's a brief explosion of meanings in our minds, and by the recognition point the brain has settled on one interpretation.

  • The recognition process moves more rapidly with a sentence that gives us context than in a random string of words.

  • Context also helps guide us towards the intended meaning of words with multiple interpretations, like "bat," or "crane," or in cases of homophones like "no" or "know."

  • For multilingual people, the language they are listening to is another cue, used to eliminate potential words that don't match the language context.

  • So, what about adding completely new words to this system?

  • Even as adults, we may come across a new word every few days.

  • But if every word is represented as a fine-tuned pattern of activity distributed over many neurons, how do we prevent new words from overwriting old ones?

  • We think that to avoid this problem, new words are initially stored in a part of the brain called the hippocampus, well away from the main store of words in the cortex, so they don't share neurons with others words.

  • Then, over multiple nights of sleep, the new words gradually transfer over and interweave with old ones.

  • Researchers think this gradual acquisition process helps avoid disrupting existing words.

  • So in the daytime, unconscious activity generates explosions of meaning as we chat away.

  • At night, we rest, but our brains are busy integrating new knowledge into the word network.

  • When we wake up, this process ensures that we're ready for the ever-changing world of language.

  • At TED, we're passionate about the human capacity to share ideas.

  • That's why the TED-Ed team created a program to help you mine your life experience for ideas and stories worth sharing, and then craft those experiences into compelling talks.

  • It's called TED Master Class, and you can learn more and download the app at ted.com/masterclass.

"Language alone protects us from the scariness of things with no names." - Toni Morrison, The Nobel Lecture in Literature, 1993

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B1 US TED-Ed brain recognition language activity context

How do our brains process speech? - Gareth Gaskell

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    Celine Chien posted on 2020/10/11
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