-
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
comprehension—
-
though 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 fragment––
-
like ‘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.