[Script Info]
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Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.81,0:00:14.04,Default,,0000,0000,0000,,The average 20-year-old knows between\N27,000 and 52,000 different words.
Dialogue: 0,0:00:14.04,0:00:20.05,Default,,0000,0000,0000,,By age 60, that number averages between\N35,000 and 56,000.
Dialogue: 0,0:00:20.05,0:00:24.33,Default,,0000,0000,0000,,Spoken out loud, most of these words last\Nless than a second.
Dialogue: 0,0:00:24.33,0:00:28.54,Default,,0000,0000,0000,,So with every word, the brain has a quick\Ndecision to make:
Dialogue: 0,0:00:28.54,0:00:32.24,Default,,0000,0000,0000,,which of those thousands of options \Nmatches the signal?
Dialogue: 0,0:00:32.24,0:00:36.34,Default,,0000,0000,0000,,About 98% of the time, the brain chooses\Nthe correct word.
Dialogue: 0,0:00:36.34,0:00:41.12,Default,,0000,0000,0000,,But how? Speech comprehension is different\Nfrom reading comprehension,
Dialogue: 0,0:00:41.12,0:00:44.38,Default,,0000,0000,0000,,but it’s similar to sign language \Ncomprehension—
Dialogue: 0,0:00:44.38,0:00:48.86,Default,,0000,0000,0000,,though spoken word recognition has \Nbeen studied more than sign language.
Dialogue: 0,0:00:48.86,0:00:51.42,Default,,0000,0000,0000,,The key to our ability to understand \Nspeech
Dialogue: 0,0:00:51.42,0:00:54.69,Default,,0000,0000,0000,,is the brain’s role as a \Nparallel processor,
Dialogue: 0,0:00:54.69,0:00:58.69,Default,,0000,0000,0000,,meaning that it can do multiple different \Nthings at the same time.
Dialogue: 0,0:00:58.69,0:01:01.30,Default,,0000,0000,0000,,Most theories assume that each word\Nwe know
Dialogue: 0,0:01:01.30,0:01:05.77,Default,,0000,0000,0000,,is represented by a separate processing \Nunit that has just one job:
Dialogue: 0,0:01:05.77,0:01:10.93,Default,,0000,0000,0000,,to assess the likelihood of incoming \Nspeech matching that particular word.
Dialogue: 0,0:01:10.93,0:01:15.14,Default,,0000,0000,0000,,In the context of the brain, the \Nprocessing unit that represents a word
Dialogue: 0,0:01:15.14,0:01:19.80,Default,,0000,0000,0000,,is likely a pattern of firing activity \Nacross a group of neurons
Dialogue: 0,0:01:19.80,0:01:21.69,Default,,0000,0000,0000,,in the brain’s cortex.
Dialogue: 0,0:01:21.69,0:01:23.51,Default,,0000,0000,0000,,When we hear the beginning of a word,
Dialogue: 0,0:01:23.51,0:01:27.29,Default,,0000,0000,0000,,several thousand such units \Nmay become active,
Dialogue: 0,0:01:27.29,0:01:31.53,Default,,0000,0000,0000,,because with just the beginning of a \Nword, there are many possible matches.
Dialogue: 0,0:01:31.53,0:01:35.54,Default,,0000,0000,0000,,Then, as the word goes on, more and\Nmore units register
Dialogue: 0,0:01:35.54,0:01:40.67,Default,,0000,0000,0000,,that some vital piece of information \Nis missing and lose activity.
Dialogue: 0,0:01:40.67,0:01:43.13,Default,,0000,0000,0000,,Possibly well before the end of the word,
Dialogue: 0,0:01:43.13,0:01:48.09,Default,,0000,0000,0000,,just one firing pattern remains active, \Ncorresponding to one word.
Dialogue: 0,0:01:48.09,0:01:50.83,Default,,0000,0000,0000,,This is called the ‘recognition point.’
Dialogue: 0,0:01:50.83,0:01:53.65,Default,,0000,0000,0000,,In the process of honing in on one word,
Dialogue: 0,0:01:53.65,0:01:56.72,Default,,0000,0000,0000,,the active units suppress \Nthe activity of others,
Dialogue: 0,0:01:56.72,0:01:58.84,Default,,0000,0000,0000,,saving vital milliseconds.
Dialogue: 0,0:01:58.84,0:02:03.64,Default,,0000,0000,0000,,Most people can comprehend up to \Nabout 8 syllables per second.
Dialogue: 0,0:02:03.64,0:02:06.96,Default,,0000,0000,0000,,Yet, the goal is not only \Nto recognize the word,
Dialogue: 0,0:02:06.96,0:02:10.42,Default,,0000,0000,0000,,but also to access its stored meaning.
Dialogue: 0,0:02:10.42,0:02:14.20,Default,,0000,0000,0000,,The brain accesses many possible meanings\Nat the same time,
Dialogue: 0,0:02:14.20,0:02:16.88,Default,,0000,0000,0000,,before the word has been fully identified.
Dialogue: 0,0:02:16.88,0:02:22.02,Default,,0000,0000,0000,,We know this from studies which show \Nthat even upon hearing a word fragment––
Dialogue: 0,0:02:22.02,0:02:23.30,Default,,0000,0000,0000,,like ‘cap’ ––
Dialogue: 0,0:02:23.30,0:02:26.80,Default,,0000,0000,0000,,listeners will start to register multiple \Npossible meanings,
Dialogue: 0,0:02:26.80,0:02:31.97,Default,,0000,0000,0000,,like captain or capital,\Nbefore the full word emerges.
Dialogue: 0,0:02:31.97,0:02:35.12,Default,,0000,0000,0000,,This suggests that every time we hear a \Nword
Dialogue: 0,0:02:35.12,0:02:38.48,Default,,0000,0000,0000,,there’s a brief explosion of meanings in \Nour minds,
Dialogue: 0,0:02:38.48,0:02:43.29,Default,,0000,0000,0000,,and by the recognition point the brain \Nhas settled on one interpretation.
Dialogue: 0,0:02:43.29,0:02:46.22,Default,,0000,0000,0000,,The recognition process moves more \Nrapidly
Dialogue: 0,0:02:46.22,0:02:50.82,Default,,0000,0000,0000,,with a sentence that gives us context \Nthan in a random string of words.
Dialogue: 0,0:02:50.82,0:02:55.01,Default,,0000,0000,0000,,Context also helps guide us towards the\Nintended meaning of words
Dialogue: 0,0:02:55.01,0:02:59.01,Default,,0000,0000,0000,,with multiple interpretations, like ‘bat,’\Nor ‘crane,’
Dialogue: 0,0:02:59.01,0:03:03.01,Default,,0000,0000,0000,,or in cases of homophones\Nlike ‘no’ or ‘know.’
Dialogue: 0,0:03:03.01,0:03:07.39,Default,,0000,0000,0000,,For multilingual people, the language\Nthey are listening to is another cue,
Dialogue: 0,0:03:07.39,0:03:12.71,Default,,0000,0000,0000,,used to eliminate potential words\Nthat don’t match the language context.
Dialogue: 0,0:03:12.71,0:03:16.71,Default,,0000,0000,0000,,So, what about adding completely new \Nwords to this system?
Dialogue: 0,0:03:16.71,0:03:20.71,Default,,0000,0000,0000,,Even as adults, we may come across a \Nnew word every few days.
Dialogue: 0,0:03:20.71,0:03:25.11,Default,,0000,0000,0000,,But if every word is represented as a \Nfine-tuned pattern of activity
Dialogue: 0,0:03:25.11,0:03:27.44,Default,,0000,0000,0000,,distributed over many neurons,
Dialogue: 0,0:03:27.44,0:03:31.99,Default,,0000,0000,0000,,how do we prevent new words from \Noverwriting old ones?
Dialogue: 0,0:03:31.99,0:03:34.32,Default,,0000,0000,0000,,We think that to avoid this problem,
Dialogue: 0,0:03:34.32,0:03:39.08,Default,,0000,0000,0000,,new words are initially stored in a part \Nof the brain called the hippocampus,
Dialogue: 0,0:03:39.08,0:03:42.69,Default,,0000,0000,0000,,well away from the main store of words\Nin the cortex,
Dialogue: 0,0:03:42.69,0:03:46.06,Default,,0000,0000,0000,,so they don’t share neurons\Nwith others words.
Dialogue: 0,0:03:46.06,0:03:49.07,Default,,0000,0000,0000,,Then, over multiple nights of sleep,
Dialogue: 0,0:03:49.07,0:03:54.47,Default,,0000,0000,0000,,the new words gradually transfer over\Nand interweave with old ones.
Dialogue: 0,0:03:54.47,0:03:57.99,Default,,0000,0000,0000,,Researchers think this gradual\Nacquisition process
Dialogue: 0,0:03:57.99,0:04:01.35,Default,,0000,0000,0000,,helps avoid disrupting existing words.
Dialogue: 0,0:04:01.35,0:04:02.77,Default,,0000,0000,0000,,So in the daytime,
Dialogue: 0,0:04:02.77,0:04:07.30,Default,,0000,0000,0000,,unconscious activity generates explosions\Nof meaning as we chat away.
Dialogue: 0,0:04:07.30,0:04:12.30,Default,,0000,0000,0000,,At night, we rest, but our brains are \Nbusy integrating new knowledge
Dialogue: 0,0:04:12.30,0:04:14.12,Default,,0000,0000,0000,,into the word network.
Dialogue: 0,0:04:14.12,0:04:17.66,Default,,0000,0000,0000,,When we wake up, this process ensures \Nthat we’re ready
Dialogue: 0,0:04:17.60,0:04:20.70,Default,,0000,0000,0000,,for the ever-changing world of language.