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

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

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

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

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which of those thousands of options 
matches the signal?

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

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But how? Speech comprehension is different
from reading comprehension,

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but it’s similar to sign language 
comprehension—

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

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The key to our ability to understand 
speech

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is the brain’s role as a 
parallel processor,

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

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Most theories assume that each word
we know is represented

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by a separate processing unit that has 
just one job:

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

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

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is likely a pattern of firing activity 
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 
may become active,

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

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Then, as the word goes on, more and
more units register

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that some vital piece of information 
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, 
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 
the activity of others,

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saving vital milliseconds.

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

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Yet, the goal is not only 
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
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 
that even upon hearing a word fragment––

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like ‘cap’ ––

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listeners will start to register multiple 
possible meanings,

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like captain or capital,
before the full word emerges.

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This suggests that every time we hear a 
word

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

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

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The recognition process moves more 
rapidly with a sentence

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

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Context also helps guide us towards the
intended meaning of words

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with multiple interpretations, like ‘bat,’
or ‘crane,’

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or in cases of homophones
like ‘no’ or ‘know.’

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

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

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

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

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

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distributed over many neurons,

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how do we prevent new words from 
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 
of the brain called the hippocampus,

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well away from the main store of words
in the cortex,

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so they don’t share neurons
with others words.

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Then, over multiple nights of sleep,

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

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Researchers think this gradual acquisition
process

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helps avoid disrupting existing words.