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The average 20-year-old knows between[br]27,000 and 52,000 different words.

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By age 60, that number averages between[br]35,000 and 56,000.

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Spoken out loud, most of these words last[br]less than a second.

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So with every word, the brain has a quick[br]decision to make:

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which of those thousands of options [br]matches the signal?

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About 98% of the time, the brain chooses[br]the correct word.

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But how? Speech comprehension is different[br]from reading comprehension,

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but it’s similar to sign language [br]comprehension—

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though spoken word recognition has [br]been studied more than sign language.

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The key to our ability to understand [br]speech

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is the brain’s role as a [br]parallel processor,

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meaning that it can do multiple different [br]things at the same time.

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Most theories assume that each word[br]we know is represented

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by a separate processing unit that has [br]just one job:

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to assess the likelihood of incoming [br]speech matching that particular word.

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In the context of the brain, the [br]processing unit that represents a word

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is likely a pattern of firing activity [br]across a group of neurons

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in the brain’s cortex.

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When we hear the beginning of a word,

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several thousand such units [br]may become active,

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because with just the beginning of a [br]word, there are many possible matches.

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Then, as the word goes on, more and[br]more units register

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that some vital piece of information [br]is missing and lose activity.

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Possibly well before the end of the word,

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just one firing pattern remains active, [br]corresponding to one word.

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This is called the ‘recognition point.’

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In the process of honing in on one word,

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the active units suppress [br]the activity of others,

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saving vital milliseconds.

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Most people can comprehend up to [br]about 8 syllables per second.

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Yet, the goal is not only [br]to recognize the word,

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but also to access its stored meaning.

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The brain accesses many possible meanings[br]at the same time,

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before the word has been fully identified.

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We know this from studies which show [br]that even upon hearing a word fragment––

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like ‘cap’ ––

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listeners will start to register multiple [br]possible meanings,

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like captain or capital,[br]before the full word emerges.

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This suggests that every time we hear a [br]word

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there’s a brief explosion of meanings in [br]our minds,

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and by the recognition point the brain [br]has settled on one interpretation.

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The recognition process moves more [br]rapidly with a sentence

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that gives us context than in a random [br]string of words.

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Context also helps guide us towards the[br]intended meaning of words

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with multiple interpretations, like ‘bat,’[br]or ‘crane,’

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or in cases of homophones[br]like ‘no’ or ‘know.’

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For multilingual people, the language[br]they are listening to is another cue,

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used to eliminate potential words[br]that don’t match the language context.

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So, what about adding completely new [br]words to this system?

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Even as adults, we may come across a [br]new word every few days.

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But if every word is represented as a [br]fine-tuned pattern of activity

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distributed over many neurons,

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how do we prevent new words from [br]overwriting old ones?

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We think that to avoid this problem,

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new words are initially stored in a part [br]of the brain called the hippocampus,

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well away from the main store of words[br]in the cortex,

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so they don’t share neurons[br]with others words.

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Then, over multiple nights of sleep,

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the new words gradually transfer over[br]and interweave with old ones.

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Researchers think this gradual acquisition[br]process

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helps avoid disrupting existing words.