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All right, so this week we are
going to talk about language,

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language being one of
the really cool things

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that humans do that we haven't
gotten to talk about yet

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language is different
from everything else

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you've been talking
about because it's

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pretty much uniquely
human lots of animals

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communicate in one
way or another.

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But they are not using language
per se as a linguist would

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define it so let's start
out by talking about

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some ways in which-- thank you.

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OK.

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Language is different from--

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I'll snag Helen's, too.

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Language is different
from animal communication.

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Can anyone think of any ways
in which humans and animals

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communicate in this, really
fundamentally differently?

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Think about it.

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I don't know how much
you guys might know

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about animal communication.

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You've got everything
from vervet monkeys who

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have specialized warning
calls for different predators,

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versus humpback whales and
their unique identifying songs,

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versus honey bees
and dances and stuff.

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Some of the ways in
which human language

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is different from other
kinds of communication--

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one is that human language
can talk about things

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that aren't here right now.

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00:02:08,970 --> 00:02:11,620
You told me that Jen is in
Harvard, trying to catch

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00:02:11,620 --> 00:02:14,086
the bus to get over here.

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00:02:14,086 --> 00:02:16,020
[INAUDIBLE]

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00:02:16,020 --> 00:02:18,790
Hynes, trying to catch
the bus to get over here.

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00:02:18,790 --> 00:02:21,107
Not here, talking about
a place that isn't here.

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00:02:21,107 --> 00:02:22,690
So we're not just
talking about things

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00:02:22,690 --> 00:02:24,730
that we can actively
perceive right now--

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00:02:24,730 --> 00:02:28,540
we're talking about stuff
that's abstract or distant

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or temporally
separated-- in time.

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00:02:39,789 --> 00:02:43,700
[INAUDIBLE] talk about it.

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00:02:43,700 --> 00:02:45,500
Good.

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00:02:45,500 --> 00:02:47,040
We're going to have six things--

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00:02:47,040 --> 00:02:49,050
six, five, some number--

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00:02:49,050 --> 00:02:50,794
of things that
languages are, and there

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aren't any forms of
animal communication

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that meet all of these things.

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00:02:53,690 --> 00:02:55,850
But you're right-- honeybees
are talking about directions

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00:02:55,850 --> 00:02:57,808
to a place that's not
where they are right now.

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00:02:57,808 --> 00:03:00,780
That's a really good point.

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00:03:00,780 --> 00:03:08,660
Another thing about language
is that language is arbitrary.

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What that means is
that in English, you

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have a specific sound
to represent something--

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we've got a sound for chair,
and a set of sounds for window,

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and a set of sounds for ceiling.

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And the nature of these sounds
doesn't have any connection

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to the objects themselves--

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they're just an
arbitrary phoneme string

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that we've assigned
a meaning to.

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Hey, Natasha.

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Hi.

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How are you?

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Feeling like it's Monday?

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We are talking about
languages, and things

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that languages are that other
forms of communication are not.

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What makes language
different from other kinds

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of communications.

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Languages are arbitrary--
symbols and languages aren't

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necessarily related to the
things they're representing.

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And again, there are
some counterexamples

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to this-- every language has
its share of onomatopoeia words.

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00:04:03,550 --> 00:04:05,830
Words-- for example, the
noises animals make--

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00:04:05,830 --> 00:04:10,550
which are related to what
they're representing.

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But for the most part, the
symbols involved in languages

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are arbitrary.

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This is always someone's
cue to say, but what

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about sign language?

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Sign language from people who
aren't really familiar with it

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tend to assume that
it's just gestures.

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It's not-- I mean, often
if you're looking at a sign

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you can figure out kind of
a gestural basis for it.

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For example, the
ASL for give is--

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00:04:37,750 --> 00:04:42,490
like this, kind of like you're
holding a hand out to somebody.

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00:04:42,490 --> 00:04:46,140
On the other hand, the
ASL for water looks like--

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looks like that,
which is a lot less

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00:04:50,710 --> 00:04:53,470
directly derivative from
some kind of gesture.

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00:04:56,350 --> 00:04:58,241
A lot of ASL has
little mnemonics,

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00:04:58,241 --> 00:04:59,740
where you can think
about what might

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00:04:59,740 --> 00:05:02,980
be a gestural basis for
it, but it's a stretch--

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00:05:02,980 --> 00:05:05,020
so languages are arbitrary.

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00:05:05,020 --> 00:05:12,220
Languages are
generative-- people

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00:05:12,220 --> 00:05:15,670
come up with new pieces
for them, and add them in.

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00:05:15,670 --> 00:05:17,717
I bet everybody in
this room can think

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00:05:17,717 --> 00:05:20,050
of at least one word that
wasn't in the English language

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00:05:20,050 --> 00:05:20,841
when you were born.

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00:05:20,841 --> 00:05:21,706
Google.

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00:05:21,706 --> 00:05:23,698
One.

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00:05:23,698 --> 00:05:25,690
[INAUDIBLE] What?

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00:05:25,690 --> 00:05:29,216
Google wasn't not in
the language in 1990?

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00:05:29,216 --> 00:05:32,120
It wasn't the word for
[INAUDIBLE] some number?

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00:05:32,120 --> 00:05:35,920
It was, but not
spelled like that.

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00:05:35,920 --> 00:05:37,670
Googol the number's
spelled differently.

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00:05:37,670 --> 00:05:39,657
No, I mean, Google the
search engine is from--

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00:05:39,657 --> 00:05:40,240
It's a number?

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00:05:40,240 --> 00:05:41,680
Googol-- G-O-O-G-O-L.

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00:05:41,680 --> 00:05:43,120
10 to the 100.

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00:05:43,120 --> 00:05:46,608
Yes-- the search engine
is named after the number.

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00:05:46,608 --> 00:05:47,471
Yay!

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00:05:47,471 --> 00:05:47,970
Six!

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00:05:47,970 --> 00:05:49,576
We're getting there.

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00:05:49,576 --> 00:05:51,568
[INAUDIBLE]

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00:05:51,568 --> 00:05:55,054
[SIDE CONVERSATION]

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00:06:03,022 --> 00:06:06,053
The company is named after the
number, and the searche engine

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00:06:06,053 --> 00:06:06,552
[INAUDIBLE]

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00:06:06,552 --> 00:06:07,910
[INAUDIBLE]

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00:06:07,910 --> 00:06:08,880
Yeah.

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00:06:08,880 --> 00:06:12,084
Well, more or less--

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00:06:12,084 --> 00:06:13,500
the company is the
search engine--

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00:06:13,500 --> 00:06:15,880
the company, when it started,
was the search engine.

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00:06:15,880 --> 00:06:18,046
All of the other things
Google does are more recent.

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00:06:19,399 --> 00:06:21,940
What's a word that wasn't in
the language when you were born,

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00:06:21,940 --> 00:06:22,850
Zachariah?

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00:06:25,670 --> 00:06:28,960
[INAUDIBLE]

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00:06:28,960 --> 00:06:31,230
Sure, or as a noun
for that matter.

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00:06:33,810 --> 00:06:36,660
Hybrid, in the sense of car,
for example-- probably wasn't.

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00:06:36,660 --> 00:06:37,260
Wikipedia.

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00:06:37,260 --> 00:06:38,430
Facebook.

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00:06:38,430 --> 00:06:40,124
Facebook.

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00:06:40,124 --> 00:06:44,697
[INAUDIBLE] part of the
language, though [INAUDIBLE]

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00:06:44,697 --> 00:06:46,530
I think once you start
using them as a verb,

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00:06:46,530 --> 00:06:49,470
they're definitely
being expanded

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00:06:49,470 --> 00:06:51,770
beyond just their name use.

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00:06:51,770 --> 00:06:54,810
Like, you can definitely say, "I
Facebook so and so," can't you?

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00:06:54,810 --> 00:06:56,310
[INTERPOSING VOICES]

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00:06:56,310 --> 00:06:56,880
Can you?

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00:06:56,880 --> 00:06:59,730
I don't know-- I may not be
hip and young enough to make

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00:06:59,730 --> 00:07:01,140
these kinds of distinctions.

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00:07:04,112 --> 00:07:06,450
[INAUDIBLE]

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00:07:06,450 --> 00:07:09,280
Languages are generative--
they produce new words,

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00:07:09,280 --> 00:07:12,620
they produce new uses
of words-- so you'll

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00:07:12,620 --> 00:07:15,370
see words that change their
meaning, change their use.

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00:07:15,370 --> 00:07:17,620
You'll see people who believe
that language should not

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00:07:17,620 --> 00:07:23,670
change get very unhappy
about this from time to time.

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00:07:23,670 --> 00:07:26,524
Who here has ever said, oh well,
hopefully it won't rain-- we

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00:07:26,524 --> 00:07:28,690
want to go to the Red Sox
game tonight, or something

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00:07:28,690 --> 00:07:30,430
along those lines.

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00:07:30,430 --> 00:07:32,020
Hopefully in the
sense of "I hope

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00:07:32,020 --> 00:07:36,350
that this will not happen,"
or "that this will happen."

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00:07:36,350 --> 00:07:36,920
Right.

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00:07:36,920 --> 00:07:39,880
So some people will say,
that's not what that means!

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00:07:39,880 --> 00:07:44,110
Hopefully originally meant
"in a hopeful manner,"

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like he looked at the sky
hopefully or something.

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00:07:50,050 --> 00:07:52,090
It has been established
in this other sense

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that everybody uses it
in for a very long time--

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languages change,
languages are generative,

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languages add new pieces.

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00:07:58,740 --> 00:08:01,400
This is one way in which
languages and honeybee

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00:08:01,400 --> 00:08:05,140
dances are different, is that
honeybee dances seem to be set,

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they don't seem to
shift over time,

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00:08:06,880 --> 00:08:08,463
change over time in
the way that you'd

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00:08:08,463 --> 00:08:09,901
see a human language doing.

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00:08:09,901 --> 00:08:10,400
Yeah.

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00:08:10,400 --> 00:08:12,820
Would the establishment
of grammar

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00:08:12,820 --> 00:08:16,208
predict changes in [INAUDIBLE].

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00:08:16,208 --> 00:08:20,564
Because people will be corrected
on what they think and say,

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00:08:20,564 --> 00:08:22,990
[INAUDIBLE]

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I don't know.

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00:08:23,680 --> 00:08:24,850
Listen to your
peer group, listen

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00:08:24,850 --> 00:08:27,225
to your parents' peer groups--
do you guys talk the same?

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00:08:30,534 --> 00:08:33,350
Because English isn't
my first language.

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00:08:33,350 --> 00:08:36,080
All right, so
there's one reason.

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So to some extent, yes.

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00:08:37,520 --> 00:08:43,980
I can try to answer that
question [INAUDIBLE]

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00:08:44,480 --> 00:08:46,220
Some things will
slow it down a bit.

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00:08:46,220 --> 00:08:49,390
One thing that's really happened
is that spelling changes slowed

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00:08:49,390 --> 00:08:51,220
down when English
started having fixed

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00:08:51,220 --> 00:08:54,084
spelling about 200 years ago,
when people started really

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00:08:54,084 --> 00:08:56,500
compiling dictionaries and
having this idea that there was

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00:08:56,500 --> 00:08:58,720
a right and a wrong
way to spell things,

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00:08:58,720 --> 00:09:00,361
and I think from
the 1700s earlier,

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00:09:00,361 --> 00:09:02,110
you'll see a whole
assortment of spellings

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00:09:02,110 --> 00:09:04,485
first off-- it's just whatever
seemed good to that author

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00:09:04,485 --> 00:09:06,700
at that time.

187
00:09:06,700 --> 00:09:10,990
For grammatical structure, seems
to change slowly and steadily

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00:09:10,990 --> 00:09:13,160
no matter what anybody
does about it--

189
00:09:13,160 --> 00:09:17,440
but vocabulary definitely
changes really fast.

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00:09:17,440 --> 00:09:18,745
We all see this--

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00:09:18,745 --> 00:09:20,870
words that weren't in the
language when I was born,

192
00:09:20,870 --> 00:09:21,610
for example.

193
00:09:21,610 --> 00:09:25,640
Cell phone was not in the
language when I was born.

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00:09:25,640 --> 00:09:29,275
Might be for you guys,
early '90s I don't know.

195
00:09:29,275 --> 00:09:32,170
[INAUDIBLE] Those big bricks.

196
00:09:32,170 --> 00:09:32,670
The big--

197
00:09:33,640 --> 00:09:36,065
Cell phones were [INAUDIBLE]

198
00:09:36,065 --> 00:09:37,035
Cell?

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00:09:37,035 --> 00:09:38,475
[INAUDIBLE]

200
00:09:38,475 --> 00:09:38,975
Yup.

201
00:09:43,437 --> 00:09:45,770
All right, so we've got--
language can talk about things

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00:09:45,770 --> 00:09:47,900
that are not immediately
present, languages are

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00:09:47,900 --> 00:09:51,780
arbitrary, languages
are generative,

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00:09:51,780 --> 00:09:56,880
languages are
culturally transmitted.

205
00:10:04,260 --> 00:10:07,710
Language is not-- or
a particular language

206
00:10:07,710 --> 00:10:09,894
is not something that you
are genetically born with.

207
00:10:09,894 --> 00:10:11,310
It's something
you've got to learn

208
00:10:11,310 --> 00:10:15,000
from being exposed to
language, to other people who

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00:10:15,000 --> 00:10:17,319
are speaking a language.

210
00:10:17,319 --> 00:10:19,110
You learn it, you learn
it from your peers,

211
00:10:19,110 --> 00:10:21,150
you learn it from your
family, you learn it

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00:10:21,150 --> 00:10:22,691
from all of the
language that you are

213
00:10:22,691 --> 00:10:24,000
exposed to as a smallish kid.

214
00:10:26,860 --> 00:10:29,460
There's a more or less--

215
00:10:29,460 --> 00:10:31,800
like with many things,
there's a critical period

216
00:10:31,800 --> 00:10:34,260
for being exposed to language.

217
00:10:34,260 --> 00:10:35,760
I don't know if any
of you guys have

218
00:10:35,760 --> 00:10:42,000
heard of the case of Genie
who was a girl in the '70s who

219
00:10:42,000 --> 00:10:46,320
was found at the age of
11, and had basically

220
00:10:46,320 --> 00:10:49,500
lived her entire life
locked in a closet.

221
00:10:49,500 --> 00:10:52,080
Her parents didn't interact
with her, didn't talk to her,

222
00:10:52,080 --> 00:10:55,390
locked her in a closet, gave
her food and water periodically,

223
00:10:55,390 --> 00:10:55,890
and was--

224
00:10:55,890 --> 00:10:57,000
Why?

225
00:10:57,000 --> 00:10:58,770
Because they were
nuts-- like, completely

226
00:10:58,770 --> 00:11:01,317
batshit insane crazy.

227
00:11:01,317 --> 00:11:03,900
It's pretty much the only answer
I have come up with for that.

228
00:11:03,900 --> 00:11:05,760
So as you might
imagine, social services

229
00:11:05,760 --> 00:11:08,130
eventually found out
about this situation,

230
00:11:08,130 --> 00:11:13,310
took the kid away, moved
the kid into foster care.

231
00:11:13,310 --> 00:11:16,650
And what they found with
Genie is that she eventually

232
00:11:16,650 --> 00:11:18,060
developed some
vocabulary-- like,

233
00:11:18,060 --> 00:11:21,146
about 150 word vocabulary.

234
00:11:21,146 --> 00:11:22,770
To put that in
perspective, most adults

235
00:11:22,770 --> 00:11:30,067
have something like a
40,000 word vocabulary.

236
00:11:30,067 --> 00:11:32,150
The other thing is that
she developed vocabulary--

237
00:11:32,150 --> 00:11:33,691
she didn't really
develop the ability

238
00:11:33,691 --> 00:11:37,861
to use sentence structure
in any kind of useful way.

239
00:11:37,861 --> 00:11:39,360
Sentence structure
lets us build all

240
00:11:39,360 --> 00:11:44,010
of these complicated, elaborate
strings that we can all

241
00:11:44,010 --> 00:11:47,040
parse just fine, you know.

242
00:11:47,040 --> 00:11:49,380
This is the red chair in
the corner of the classroom

243
00:11:49,380 --> 00:11:51,570
that we have Junction in,
that I am in four days

244
00:11:51,570 --> 00:11:54,300
a week, as are most of you.

245
00:11:54,300 --> 00:11:56,190
One, perhaps not
terribly well crafted,

246
00:11:56,190 --> 00:11:58,220
sentence-- but it's
got a lot of subpieces

247
00:11:58,220 --> 00:12:00,300
that you could pick out
and parse just fine.

248
00:12:00,300 --> 00:12:02,094
Genie can't do that.

249
00:12:02,094 --> 00:12:04,260
There's a critical period
for language development--

250
00:12:04,260 --> 00:12:05,634
this is why little
kids can learn

251
00:12:05,634 --> 00:12:08,070
second, third, fourth
languages just fine,

252
00:12:08,070 --> 00:12:11,220
and grownups have a
really hard time with it.

253
00:12:11,220 --> 00:12:13,917
The things that is often
frustrating to people

254
00:12:13,917 --> 00:12:15,750
who study language is
that most schools will

255
00:12:15,750 --> 00:12:18,697
start a second language
in middle school, right?

256
00:12:18,697 --> 00:12:20,280
Usually it's where
you'll start taking

257
00:12:20,280 --> 00:12:22,985
French or Spanish or
Latin, or what have you--

258
00:12:22,985 --> 00:12:25,110
right about when this
critical language development

259
00:12:25,110 --> 00:12:28,500
period is closing, and it
starts being really hard for you

260
00:12:28,500 --> 00:12:29,911
to learn new languages.

261
00:12:32,105 --> 00:12:34,230
Languages are culturally
transmitted-- you get them

262
00:12:34,230 --> 00:12:35,354
from the people around you.

263
00:12:37,790 --> 00:12:40,800
All right, slightly more
complicated-- languages

264
00:12:40,800 --> 00:12:45,408
are what's called
dual patterned.

265
00:12:48,540 --> 00:12:53,070
What this means
is that you get--

266
00:12:53,070 --> 00:12:55,110
the English language
has a fixed number

267
00:12:55,110 --> 00:13:00,000
of sound units that
make it up, of phonemes.

268
00:13:00,000 --> 00:13:02,640
If we talk about the
word chair, for example,

269
00:13:02,640 --> 00:13:07,640
it's spelled C-H-A-I-R, but
that's not terribly useful.

270
00:13:07,640 --> 00:13:09,690
There's three major sound
units that go into it--

271
00:13:09,690 --> 00:13:12,270
there's the "ch"
at the beginning,

272
00:13:12,270 --> 00:13:15,960
and in "a" the middle
and the "r" at the end--

273
00:13:15,960 --> 00:13:16,460
chair.

274
00:13:19,170 --> 00:13:22,410
Each of those individual
phonemes, those sound units,

275
00:13:22,410 --> 00:13:24,770
is not meaningful--

276
00:13:24,770 --> 00:13:29,940
the sound unit alone is not
a unit that has meaning.

277
00:13:29,940 --> 00:13:32,800
There are a few single phoneme
words in English, like "oh"

278
00:13:32,800 --> 00:13:35,580
and "eye" and "a,"
but there aren't many.

279
00:13:35,580 --> 00:13:37,500
How about "ow?"

280
00:13:37,500 --> 00:13:38,790
Ow.

281
00:13:38,790 --> 00:13:40,675
Wouldn't those
technically be made up

282
00:13:40,675 --> 00:13:44,300
of multiple phonemes
[INAUDIBLE] diphthongs?

283
00:13:44,300 --> 00:13:47,130
The one in the middle of "chair"
is kind of a diphthong, yeah.

284
00:13:47,130 --> 00:13:51,240
Well, "oh" isn't-- "oh" is a
straight up tense, fronted,

285
00:13:51,240 --> 00:13:52,320
rounded vowel--

286
00:13:52,320 --> 00:13:53,895
no, backrounded vowel, "oh."

287
00:13:57,220 --> 00:14:02,910
"Ow" is, but a lot
of these aren't.

288
00:14:02,910 --> 00:14:06,420
Single phonemes can be
morphemes, units with meaning--

289
00:14:06,420 --> 00:14:09,840
often, but usually aren't.

290
00:14:09,840 --> 00:14:12,390
Languages are dual patterned--
so the units that have meaning

291
00:14:12,390 --> 00:14:15,000
are made up of smaller units
that don't have meaning, that

292
00:14:15,000 --> 00:14:17,670
can then be jiggled together and
broken around in different ways

293
00:14:17,670 --> 00:14:19,440
to form these morphemes.

294
00:14:19,440 --> 00:14:23,150
A morpheme is the smallest
unit that carries meanings.

295
00:14:23,150 --> 00:14:27,660
Any word is a morpheme--
any base root word--

296
00:14:27,660 --> 00:14:32,370
but also "d" you might add to
something if you're saying,

297
00:14:32,370 --> 00:14:34,110
OK, I wanted.

298
00:14:34,110 --> 00:14:36,760
You've got two morphemes there--
the "want" part and the "ed"

299
00:14:36,760 --> 00:14:37,540
part.

300
00:14:37,540 --> 00:14:39,050
How do you spell morpheme?

301
00:14:39,050 --> 00:14:42,710
M-O-R-P-H-E-M-E.

302
00:14:42,710 --> 00:14:43,410
E-N-E?

303
00:14:43,410 --> 00:14:45,100
E-M-E-- morpheme.

304
00:14:45,100 --> 00:14:48,558
[INAUDIBLE] I thought
you said morphine.

305
00:14:48,558 --> 00:14:51,030
[INTERPOSING VOICES]

306
00:14:51,030 --> 00:14:52,680
Morpheme.

307
00:14:52,680 --> 00:14:54,130
Phoneme and morpheme.

308
00:14:54,130 --> 00:14:56,730
These are different
units that linguists

309
00:14:56,730 --> 00:14:58,770
use to talk about what
makes up a language.

310
00:15:05,310 --> 00:15:07,100
All right, six
things languages are

311
00:15:07,100 --> 00:15:08,516
that other forms
of communications

312
00:15:08,516 --> 00:15:13,090
aren't is that
languages are recursive.

313
00:15:16,802 --> 00:15:18,630
Wait, what's the other -neme?

314
00:15:18,630 --> 00:15:19,130
[INAUDIBLE]

315
00:15:19,130 --> 00:15:20,260
Phoneme.

316
00:15:20,260 --> 00:15:32,150
P-H-O-N-E-M-E.
Languages are recursive.

317
00:15:32,150 --> 00:15:39,880
You can take a sentence,
"The chair is red,"

318
00:15:39,880 --> 00:15:43,290
and you put it inside
another sentence,

319
00:15:43,290 --> 00:15:46,240
"The girl couldn't tell
that the chair is red,"

320
00:15:46,240 --> 00:15:48,580
and you can put that
inside another sentence

321
00:15:48,580 --> 00:15:52,210
and say, "The girl that I
met last week in the park

322
00:15:52,210 --> 00:15:54,220
couldn't tell that
the chair is red."

323
00:15:54,220 --> 00:15:57,310
And at least in theory, you
can just keep doing this,

324
00:15:57,310 --> 00:16:00,400
and still be building perfectly
valid English sentences.

325
00:16:00,400 --> 00:16:03,520
This recursive ability
lets you take one piece

326
00:16:03,520 --> 00:16:07,420
and nest it inside
of another piece.

327
00:16:07,420 --> 00:16:09,850
It means you use the same
pattern over and over again.

328
00:16:13,460 --> 00:16:17,030
Questions about languages, about
other kinds of communication,

329
00:16:17,030 --> 00:16:20,625
about critters who communicate?

330
00:16:20,625 --> 00:16:25,960
So that last one is, the
meaning can be used [INAUDIBLE]

331
00:16:25,960 --> 00:16:27,415
Hm?

332
00:16:27,415 --> 00:16:29,840
The last [INAUDIBLE]

333
00:16:29,840 --> 00:16:32,990
It means that you can take
sentences and nest them inside

334
00:16:32,990 --> 00:16:34,940
of other sentences,
more or less.

335
00:16:38,850 --> 00:16:41,889
In practice, if you're
actually speaking sentences

336
00:16:41,889 --> 00:16:43,680
you want other people
to be able to follow,

337
00:16:43,680 --> 00:16:46,327
if you nest more than about
four deep, it starts--

338
00:16:46,327 --> 00:16:47,910
your listeners won't
be able to do it.

339
00:16:47,910 --> 00:16:50,430
This is where normal
human ability to keep

340
00:16:50,430 --> 00:16:53,610
track starts breaking off.

341
00:16:53,610 --> 00:16:56,430
But in theory, it would
still be a perfectly good

342
00:16:56,430 --> 00:16:59,910
English sentence-- it would just
be a pain in the butt to read.

343
00:16:59,910 --> 00:17:02,940
Or hear, or make sense out of.

344
00:17:02,940 --> 00:17:05,339
All right.

345
00:17:05,339 --> 00:17:08,490
These are things
that languages are

346
00:17:08,490 --> 00:17:11,114
that other forms of
communication are not.

347
00:17:15,670 --> 00:17:17,859
Switching gears now--
let's talk a little bit

348
00:17:17,859 --> 00:17:20,480
about-- we're going to talk
about auditory perception.

349
00:17:20,480 --> 00:17:23,710
We're going to start
out, move into thinking

350
00:17:23,710 --> 00:17:27,030
about language by talking about
how your hearing system works.

351
00:17:27,030 --> 00:17:29,400
We talked about vision
a couple of weeks ago.

352
00:17:29,400 --> 00:17:30,490
I'm in S&P, kids.

353
00:17:30,490 --> 00:17:32,448
You're going to have to
sit through this again.

354
00:17:34,810 --> 00:17:38,560
Basic organs for seeing
things with are your eyes,

355
00:17:38,560 --> 00:17:40,630
basic organs for hearing
things with are your--

356
00:17:40,630 --> 00:17:41,680
Ears.

357
00:17:41,680 --> 00:17:42,940
Ears, good.

358
00:17:42,940 --> 00:17:43,690
All right.

359
00:17:43,690 --> 00:17:44,730
So ears.

360
00:17:44,730 --> 00:17:47,580
Here's an ear.

361
00:17:47,580 --> 00:17:51,550
There's an ear canal,
kind of a big one.

362
00:17:51,550 --> 00:17:55,680
Ears have all kinds of
funky little wobbly bits--

363
00:17:55,680 --> 00:18:00,012
take a look around, look at
the years of your classmates.

364
00:18:00,012 --> 00:18:01,470
They probably all
look more or less

365
00:18:01,470 --> 00:18:02,845
the same-- they
probably all have

366
00:18:02,845 --> 00:18:07,040
pretty much the same pattern of
ridges and swirls and swooshes.

367
00:18:07,040 --> 00:18:12,930
This outer ear part
is called the pinna.

368
00:18:12,930 --> 00:18:15,630
There you go-- it's from
the Latin word for "wing."

369
00:18:15,630 --> 00:18:19,410
This pinna structure
is pretty much uniquely

370
00:18:19,410 --> 00:18:23,178
mammalian-- other animals don't
seem to have these pinnas.

371
00:18:23,178 --> 00:18:27,840
Humans can't really move our
pinnas very much-- some of us

372
00:18:27,840 --> 00:18:29,160
can wiggle them a little bit.

373
00:18:29,160 --> 00:18:31,320
Anyone here who can
wiggle their ears?

374
00:18:31,320 --> 00:18:32,660
I can't.

375
00:18:32,660 --> 00:18:34,230
I know-- I always
wish I could do it.

376
00:18:34,230 --> 00:18:34,980
I'm not that cool.

377
00:18:34,980 --> 00:18:37,660
[INAUDIBLE] there a
point to [INAUDIBLE]

378
00:18:37,660 --> 00:18:40,279
It makes little
kids laugh at you.

379
00:18:40,279 --> 00:18:41,820
Which may or may
not be a good thing,

380
00:18:41,820 --> 00:18:43,320
depending on your life goals.

381
00:18:47,670 --> 00:18:53,860
The point of having a
pinna, having this fancy ear

382
00:18:53,860 --> 00:18:55,770
structure that sticks
out of your head,

383
00:18:55,770 --> 00:19:01,617
is that it collects sound
waves and it funnels them

384
00:19:01,617 --> 00:19:04,200
into the ear canal, so there's
a little bit of amplifying-- it

385
00:19:04,200 --> 00:19:06,930
also shapes the sound waves,
so certain frequencies

386
00:19:06,930 --> 00:19:11,610
get amplified and certain
frequencies get diminished.

387
00:19:11,610 --> 00:19:15,450
The pinna collects sound
waves, and the sound waves

388
00:19:15,450 --> 00:19:23,360
run down an auditory canal,
like the ear canal, right?

389
00:19:26,150 --> 00:19:33,830
Sound waves go down here,
and they hit the ear drum,

390
00:19:33,830 --> 00:19:34,800
which has a fancy name.

391
00:19:34,800 --> 00:19:38,450
Some people who study sound
call it the tympanic membrane.

392
00:19:46,930 --> 00:19:48,280
Now we're into the middle ear.

393
00:19:48,280 --> 00:19:59,050
So here's-- outer, middle.

394
00:19:59,050 --> 00:20:01,250
There's a little
opening in here.

395
00:20:01,250 --> 00:20:02,940
Here's our eardrum.

396
00:20:02,940 --> 00:20:08,180
So sound waves come through
the air, are collected

397
00:20:08,180 --> 00:20:12,530
by the outer ear, transmitted
down the auditory canal there,

398
00:20:12,530 --> 00:20:14,990
and they cause your
eardrum to vibrate.

399
00:20:18,590 --> 00:20:19,100
Then what?

400
00:20:19,100 --> 00:20:22,316
Anyone know where the smallest
bones in your body are?

401
00:20:22,316 --> 00:20:23,180
In the ear?

402
00:20:23,180 --> 00:20:24,140
In your ear, right.

403
00:20:24,140 --> 00:20:25,880
There's three little
bones in here.

404
00:20:25,880 --> 00:20:28,430
[INAUDIBLE]

405
00:20:28,430 --> 00:20:30,110
Three little bones in your ear--

406
00:20:30,110 --> 00:20:32,240
there's one that looks
kind of like this, that's

407
00:20:32,240 --> 00:20:34,800
called the hammer,
and the other one

408
00:20:34,800 --> 00:20:36,600
that looks kind of like this--

409
00:20:36,600 --> 00:20:38,120
it's called the anvil.

410
00:20:38,120 --> 00:20:41,450
And then one that has a
very distinctive shape,

411
00:20:41,450 --> 00:20:44,080
and it's called the stirrup.

412
00:20:44,080 --> 00:20:46,100
So hammer, anvil, and stirrup--

413
00:20:46,100 --> 00:20:53,480
they have fancypants Latin names
that some people use as well.

414
00:20:53,480 --> 00:20:57,770
What happens is, as sound
vibrates the ear drum--

415
00:20:57,770 --> 00:21:00,140
vibrates the tympanic
membrane here--

416
00:21:00,140 --> 00:21:03,320
then that motion
gets transferred

417
00:21:03,320 --> 00:21:04,400
to this chain of bones.

418
00:21:04,400 --> 00:21:06,340
The bones are rigid--

419
00:21:06,340 --> 00:21:08,330
all of this is, of
course, tucked right

420
00:21:08,330 --> 00:21:09,320
inside your skull--

421
00:21:09,320 --> 00:21:12,860
right in here.

422
00:21:12,860 --> 00:21:15,290
The bone that actually
surrounds this whole setup

423
00:21:15,290 --> 00:21:17,630
is the densest bone in your
body-- the temporal bone

424
00:21:17,630 --> 00:21:20,030
there, on the
sides of your head.

425
00:21:20,030 --> 00:21:22,550
One reason is to isolate
all of the vibration that's

426
00:21:22,550 --> 00:21:26,480
happening inside here from
getting jostled around

427
00:21:26,480 --> 00:21:31,430
by whatever else might be
going on at the same time.

428
00:21:31,430 --> 00:21:36,590
The vibrations get transferred
to these little bones,

429
00:21:36,590 --> 00:21:45,880
and these little bones bonk into
an organ called the cochlea.

430
00:21:48,460 --> 00:21:52,270
In particular, the
stirrup here pushes up

431
00:21:52,270 --> 00:21:55,120
against the oval
window of the cochlea.

432
00:21:59,250 --> 00:22:02,494
The cochlea here-- we're
getting into the inner ear.

433
00:22:02,494 --> 00:22:05,700
How do you spell that?

434
00:22:05,700 --> 00:22:11,177
C-O-C-H-L-E-A. Like that.

435
00:22:11,177 --> 00:22:13,010
All right, so we started
out with vibrations

436
00:22:13,010 --> 00:22:14,926
that were traveling
through the air around us.

437
00:22:14,926 --> 00:22:17,350
They get funneled into
the auditory canal

438
00:22:17,350 --> 00:22:20,060
by the pinna-- they
vibrate the eardrum,

439
00:22:20,060 --> 00:22:23,450
that tympanic membrane,
which in turn vibrates

440
00:22:23,450 --> 00:22:29,630
this chain of little bones,
which in turn pushes on

441
00:22:29,630 --> 00:22:34,070
the membrane here, on the
oval window of the cochlea.

442
00:22:34,070 --> 00:22:38,285
The cochlea-- up to this point,
we've been going through air.

443
00:22:38,285 --> 00:22:40,160
Now, we've been moving
through different kind

444
00:22:40,160 --> 00:22:43,430
of bits, solid pieces.

445
00:22:43,430 --> 00:22:45,185
The cochlea's actually
filled with fluid.

446
00:22:48,170 --> 00:22:52,520
When the oval window membrane
gets pushed on by these bones,

447
00:22:52,520 --> 00:22:54,050
then the fluid
inside the cochlea

448
00:22:54,050 --> 00:22:55,730
sloshes back and
forth a little bit.

449
00:23:02,800 --> 00:23:06,340
One of the other interesting
things the middle ear can do

450
00:23:06,340 --> 00:23:09,670
is that these bones that
are transferring vibration

451
00:23:09,670 --> 00:23:16,030
from the eardrum to
the cochlea are--

452
00:23:16,030 --> 00:23:17,830
there's a couple of
little muscles in there

453
00:23:17,830 --> 00:23:20,540
that can control them.

454
00:23:20,540 --> 00:23:26,339
When these muscles are
relaxed, then the joints

455
00:23:26,339 --> 00:23:27,880
between these bones
are really loose,

456
00:23:27,880 --> 00:23:30,520
and the vibrations
from the eardrum

457
00:23:30,520 --> 00:23:32,800
can make big vibrations
on the cochlea.

458
00:23:32,800 --> 00:23:34,670
They can go back and
forth between them,

459
00:23:34,670 --> 00:23:38,270
and it all moves a lot.

460
00:23:38,270 --> 00:23:41,800
If, for example, you hear
something really loud, then

461
00:23:41,800 --> 00:23:44,530
very quickly, it is triggered
for a muscle in here

462
00:23:44,530 --> 00:23:50,110
to tighten up so that this
whole construction is a lot less

463
00:23:50,110 --> 00:23:55,150
flexible, and so that the
amplitude of the waves

464
00:23:55,150 --> 00:23:59,350
in the cochlea end up being
smaller so that it can kind

465
00:23:59,350 --> 00:24:02,970
of dampen the
strength of the input

466
00:24:02,970 --> 00:24:06,220
to your perceptual system.

467
00:24:06,220 --> 00:24:10,390
This can protect your inner
ear from really loud noises.

468
00:24:10,390 --> 00:24:14,230
It also, like when you
talk or cough or sneeze,

469
00:24:14,230 --> 00:24:18,070
anytime you're kind of
making a noise of your own,

470
00:24:18,070 --> 00:24:19,290
this would be really--

471
00:24:19,290 --> 00:24:21,170
this should be
really, really loud.

472
00:24:21,170 --> 00:24:22,660
It's coming from
right here, right?

473
00:24:22,660 --> 00:24:25,060
Very close, and it's being
transferred through bone.

474
00:24:25,060 --> 00:24:28,010
It should all be very loud
relative to everything else,

475
00:24:28,010 --> 00:24:29,920
but we don't hear it
that way, and that's

476
00:24:29,920 --> 00:24:35,410
partly because when you talk or
cough or anything, then again,

477
00:24:35,410 --> 00:24:37,630
the muscles around
these bones tighten

478
00:24:37,630 --> 00:24:42,190
up so that the whole assembly is
stiffer, not so much vibration

479
00:24:42,190 --> 00:24:45,730
is transmitted, or smaller
vibrations are transmitted--

480
00:24:45,730 --> 00:24:47,080
not such big vibrations.

481
00:25:01,200 --> 00:25:03,325
The interesting part of
what we want to talk about,

482
00:25:03,325 --> 00:25:06,500
the cochlea, happens inside
all of this coiled up part.

483
00:25:06,500 --> 00:25:09,940
So let's uncoil it,
and uncoiled, it

484
00:25:09,940 --> 00:25:15,680
looks something like this.

485
00:25:15,680 --> 00:25:19,210
It's wider on one end
than on the other end,

486
00:25:19,210 --> 00:25:21,500
and most relevantly,
if you look at it in--

487
00:25:21,500 --> 00:25:23,990
so here's kind of an
overall view of it uncoiled.

488
00:25:23,990 --> 00:25:27,490
This is the base,
and this is the apex.

489
00:25:27,490 --> 00:25:33,139
This is the part
closer to down here.

490
00:25:33,139 --> 00:25:34,930
The thing you should
know about the cochlea

491
00:25:34,930 --> 00:25:38,635
is, it is actually
made up of three--

492
00:25:38,635 --> 00:25:41,550
how do I want to draw this?

493
00:25:41,550 --> 00:25:45,490
Three kind of parallel
canals that are all full

494
00:25:45,490 --> 00:25:48,670
of this fluid, that
all run together.

495
00:25:48,670 --> 00:25:54,040
They're broken up by
a couple of membranes.

496
00:25:54,040 --> 00:25:59,112
The oval window's here,
so when the stirrup--

497
00:25:59,112 --> 00:26:03,110
here's our stirrup--
pushes on the oval window,

498
00:26:03,110 --> 00:26:05,680
then the fluid sloshes
back and forth down

499
00:26:05,680 --> 00:26:10,630
between all of these canals,
and then eventually comes back

500
00:26:10,630 --> 00:26:14,380
around towards the beginning,
and there is around window

501
00:26:14,380 --> 00:26:17,026
right next to the oval window.

502
00:26:17,026 --> 00:26:18,610
Round window.

503
00:26:18,610 --> 00:26:20,500
That actually kind of
bulges out in time--

504
00:26:20,500 --> 00:26:23,560
the fluid can't compress when
the stirrup presses on it.

505
00:26:23,560 --> 00:26:27,040
It just moves, so you've got
to have kind of an outlet spot

506
00:26:27,040 --> 00:26:31,549
that can also change shape
as the fluid moves around.

507
00:26:31,549 --> 00:26:34,090
This would then kind of bulge
and go in and out a little bit,

508
00:26:34,090 --> 00:26:36,790
but that's just so that there's
room for the fluid to move.

509
00:26:41,690 --> 00:26:45,230
What we're most interested
in on the cochlea

510
00:26:45,230 --> 00:26:48,530
here is this
membrane right here.

511
00:26:48,530 --> 00:26:53,990
This is called the
basilar membrane,

512
00:26:53,990 --> 00:26:57,974
and all of these
canals have names--

513
00:26:57,974 --> 00:26:59,890
I need to hit my cheat
sheet to remember them.

514
00:27:05,470 --> 00:27:06,790
Sorry.

515
00:27:06,790 --> 00:27:08,590
Not an auditory kid.

516
00:27:08,590 --> 00:27:10,735
I'm a vision kid.

517
00:27:10,735 --> 00:27:11,470
Where are they?

518
00:27:36,210 --> 00:27:38,400
You've got a middle canal.

519
00:27:38,400 --> 00:27:40,980
I know-- that one I
could have figured out.

520
00:27:40,980 --> 00:27:46,992
A tympanic, and a
vestibular canal.

521
00:27:50,810 --> 00:27:52,660
What we care about
is the basilar

522
00:27:52,660 --> 00:27:54,410
membrane-- the membrane
between the middle

523
00:27:54,410 --> 00:27:57,500
and the tympanic canal.

524
00:27:57,500 --> 00:28:01,070
What's interesting,
and how this works,

525
00:28:01,070 --> 00:28:05,507
is that as the fluid in
here is sloshing around,

526
00:28:05,507 --> 00:28:08,090
one of the things that happens--
because this is narrow at one

527
00:28:08,090 --> 00:28:09,890
end and wide at the other--

528
00:28:09,890 --> 00:28:13,130
is that, depending on
the pitch, the frequency

529
00:28:13,130 --> 00:28:18,020
of the sound that's causing
the sloshing, different regions

530
00:28:18,020 --> 00:28:23,720
of the basilar canal
will get moved around,

531
00:28:23,720 --> 00:28:26,480
and it will move a
little bit in most spots,

532
00:28:26,480 --> 00:28:29,930
and a lot at one spot-- at
a spot that is kind of tuned

533
00:28:29,930 --> 00:28:31,520
to the pitch of the sound.

534
00:28:35,904 --> 00:28:37,820
Let's say this is the--
for a given pitch,

535
00:28:37,820 --> 00:28:39,236
this is the spot
we're looking at.

536
00:28:39,236 --> 00:28:41,240
Here's our basilar membrane.

537
00:28:49,560 --> 00:28:55,940
All along the basilar membrane
are what are called hair cells.

538
00:28:55,940 --> 00:28:59,670
A hair cell looks kind
of like that-- it's

539
00:28:59,670 --> 00:29:01,790
right on the basilar membrane.

540
00:29:01,790 --> 00:29:04,890
At its top, it's
got these little--

541
00:29:04,890 --> 00:29:09,710
they're called
stereocilia hairs.

542
00:29:13,751 --> 00:29:15,250
They're an excitatory
cell-- they're

543
00:29:15,250 --> 00:29:16,624
going to have a
lot of properties

544
00:29:16,624 --> 00:29:18,730
that are a lot like neurons.

545
00:29:18,730 --> 00:29:20,620
There are neurons
that come off of them

546
00:29:20,620 --> 00:29:22,900
and go and form
the auditory nerve.

547
00:29:25,570 --> 00:29:28,810
The way a hair cell works is
that they work kind of like how

548
00:29:28,810 --> 00:29:30,290
a touch receptor works.

549
00:29:30,290 --> 00:29:35,160
They're a mechanoreceptor-- they
respond to a pressure on them.

550
00:29:35,160 --> 00:29:36,914
They get all of
these stereocilia,

551
00:29:36,914 --> 00:29:37,705
these little hairs.

552
00:29:40,480 --> 00:29:41,520
Stereocilia.

553
00:29:45,170 --> 00:29:49,380
All of these little hairs are
connected by these fine protein

554
00:29:49,380 --> 00:29:52,280
threads called tip links.

555
00:29:52,280 --> 00:29:58,610
What happens is there's a kind
of a secondary smaller membrane

556
00:29:58,610 --> 00:30:02,720
right over any given region
of the basilar canal,

557
00:30:02,720 --> 00:30:10,521
and these are embedded into
this secondary membrane.

558
00:30:10,521 --> 00:30:11,770
Where's my secondary membrane?

559
00:30:11,770 --> 00:30:12,380
There it is.

560
00:30:15,190 --> 00:30:19,536
As the basilar canal moves
relative to this other

561
00:30:19,536 --> 00:30:21,910
membrane-- as the basilar
membrane moves relative to this

562
00:30:21,910 --> 00:30:25,390
other membrane, then
the stereocilia--

563
00:30:25,390 --> 00:30:28,450
these hairs-- will get bent
by the way these two are

564
00:30:28,450 --> 00:30:31,780
moving relative to each other.

565
00:30:31,780 --> 00:30:35,150
This will bend up a little
bit or down a little bit,

566
00:30:35,150 --> 00:30:38,470
and it will bend
the stereocilia such

567
00:30:38,470 --> 00:30:41,074
that their tips end up being
further apart than they

568
00:30:41,074 --> 00:30:41,990
are when it's at rest.

569
00:30:44,710 --> 00:30:51,260
At that point, these tip
links, these little fibers,

570
00:30:51,260 --> 00:30:54,400
get pulled because the tips
are becoming further apart when

571
00:30:54,400 --> 00:30:56,770
the hairs get bent.

572
00:30:56,770 --> 00:30:59,050
What happens is each
of these tip links

573
00:30:59,050 --> 00:31:01,450
is connected to an ion channel.

574
00:31:05,460 --> 00:31:09,950
The tip link gets pulled,
the ion channel opens up,

575
00:31:09,950 --> 00:31:12,950
and we get a very
familiar looking process

576
00:31:12,950 --> 00:31:17,660
whereby potassium
flows in, depolarizes

577
00:31:17,660 --> 00:31:21,080
the membrane of this hair cell.

578
00:31:21,080 --> 00:31:29,540
Lower down, it's going to
have calcium ion channels that

579
00:31:29,540 --> 00:31:30,650
are voltage gated.

580
00:31:30,650 --> 00:31:34,640
As it depolarizes,
calcium comes in,

581
00:31:34,640 --> 00:31:36,500
and then just like
our neurons, there's

582
00:31:36,500 --> 00:31:42,320
little vesicles of
neurotransmitter hanging out

583
00:31:42,320 --> 00:31:43,730
down here.

584
00:31:43,730 --> 00:31:45,870
When the calcium
enters the cell,

585
00:31:45,870 --> 00:31:51,113
what does calcium do to
vesicles of neurotransmitter?

586
00:31:51,113 --> 00:31:52,470
Makes them release [INAUDIBLE]

587
00:31:52,470 --> 00:31:54,720
Yeah, it makes them release
it into the synapse,

588
00:31:54,720 --> 00:31:56,800
so it stimulates
the auditory nerve

589
00:31:56,800 --> 00:32:00,243
that's bringing this
information back to the brain.

590
00:32:04,590 --> 00:32:07,570
Did that make any sense at all?

591
00:32:07,570 --> 00:32:08,070
All right.

592
00:32:11,600 --> 00:32:14,300
We've got the cochlea.

593
00:32:14,300 --> 00:32:15,860
All of this comes
in, it vibrates

594
00:32:15,860 --> 00:32:19,490
the fluid inside the cochlea,
makes these waves of fluid.

595
00:32:19,490 --> 00:32:23,930
Depending on the pitch of
the sound that's happening,

596
00:32:23,930 --> 00:32:25,400
different parts of the cochlea--

597
00:32:25,400 --> 00:32:29,330
of the basilar membrane
inside the cochlea--

598
00:32:29,330 --> 00:32:31,880
will vibrate to a
different amount.

599
00:32:31,880 --> 00:32:34,370
When that happens, the hair
cells that are on that spot

600
00:32:34,370 --> 00:32:38,090
will get the hairs on their
tips, their stereocilia,

601
00:32:38,090 --> 00:32:44,990
bent over, which opens up an
ion channel right on the tip.

602
00:32:44,990 --> 00:32:47,670
These tip links pull
it open, more or less.

603
00:32:47,670 --> 00:32:49,490
It's like a little trap door.

604
00:32:49,490 --> 00:32:52,670
Potassium flows
into the hair cell,

605
00:32:52,670 --> 00:32:56,450
and then stimulates calcium
flowing into the hair

606
00:32:56,450 --> 00:32:58,610
cell, which then stimulates
neurotransmitter being

607
00:32:58,610 --> 00:33:02,600
released, information
going, and then

608
00:33:02,600 --> 00:33:05,870
it stimulates cells that become
part of the auditory nerve

609
00:33:05,870 --> 00:33:06,980
going back into the brain.

610
00:33:27,540 --> 00:33:29,940
All right, let's talk
a little bit more

611
00:33:29,940 --> 00:33:34,289
about this idea about how
pitch gets sorted out.

612
00:33:34,289 --> 00:33:36,330
Actually, let's back way
up and talk a little bit

613
00:33:36,330 --> 00:33:39,120
about what actually is sound.

614
00:33:39,120 --> 00:33:42,990
We skipped right over
the physics part here.

615
00:33:42,990 --> 00:33:48,100
Sound is vibration-- is pressure
waves in the air, more or less.

616
00:33:48,100 --> 00:33:48,600
Right?

617
00:33:51,570 --> 00:33:54,240
Something vibrates, usually.

618
00:33:54,240 --> 00:33:56,880
The classic example for this
is a tuning fork, right?

619
00:33:56,880 --> 00:34:00,340
Hit it on something
and it goes bing.

620
00:34:00,340 --> 00:34:02,080
It's vibrating,
and as it vibrates,

621
00:34:02,080 --> 00:34:03,790
it's kind of pushing
the air molecules

622
00:34:03,790 --> 00:34:06,176
in its immediate vicinity
up against each other,

623
00:34:06,176 --> 00:34:08,050
and then away, and then
up against each other

624
00:34:08,050 --> 00:34:11,050
and away, and it's causing
there to be these little

625
00:34:11,050 --> 00:34:13,060
patches of dense air,
less dense, dense,

626
00:34:13,060 --> 00:34:16,510
less dense, dense, less
dense, dense, less dense.

627
00:34:16,510 --> 00:34:18,249
If you think of a sound wave--

628
00:34:21,940 --> 00:34:26,380
what people are usually
really graphing at that point

629
00:34:26,380 --> 00:34:28,900
is the density of the air
molecules in a given spot--

630
00:34:28,900 --> 00:34:31,780
so you'd have a high pressure
spot and a low pressure spot,

631
00:34:31,780 --> 00:34:34,719
and a high pressure spot
and a low pressure spot,

632
00:34:34,719 --> 00:34:38,006
that's caused by the
vibration of this item banging

633
00:34:38,006 --> 00:34:39,130
into all the air around it.

634
00:34:43,110 --> 00:34:46,840
Two important measures here--

635
00:34:46,840 --> 00:34:47,881
frequency.

636
00:34:50,770 --> 00:34:52,670
That's a cube, really it is.

637
00:34:52,670 --> 00:35:00,040
Frequency, and amplitude.

638
00:35:00,040 --> 00:35:03,250
I know you guys all know this,
but skipping over it anyway

639
00:35:03,250 --> 00:35:07,030
just make sure we're all on
the same page with terminology.

640
00:35:07,030 --> 00:35:10,690
Frequency is how long it takes
for one cycle of the wave

641
00:35:10,690 --> 00:35:12,172
to repeat.

642
00:35:12,172 --> 00:35:13,450
Would that be wavelength?

643
00:35:13,450 --> 00:35:17,710
That is technically--
that is wavelength, yeah.

644
00:35:17,710 --> 00:35:18,310
You're right.

645
00:35:18,310 --> 00:35:19,710
I'm being unclear
in my diagrams.

646
00:35:25,020 --> 00:35:27,550
Frequency is the time it takes
one cycle of the wavelength

647
00:35:27,550 --> 00:35:28,550
to repeat, more or less.

648
00:35:28,550 --> 00:35:30,867
Isn't that period?

649
00:35:30,867 --> 00:35:32,450
Frequency of cycles
per second-- we'll

650
00:35:32,450 --> 00:35:34,033
just give it with
cycles for a second,

651
00:35:34,033 --> 00:35:35,510
and we'll go with it, all right?

652
00:35:35,510 --> 00:35:37,640
You want Hertz,
I'll give you Hertz.

653
00:35:37,640 --> 00:35:40,520
Cycles per second,
it's just the number

654
00:35:40,520 --> 00:35:42,980
of waves you get in a
particular time unit.

655
00:35:45,830 --> 00:35:48,905
Amplitude is basically
how big the difference

656
00:35:48,905 --> 00:35:51,380
is between the high point
and low point in the wave.

657
00:35:51,380 --> 00:35:52,770
Not qualified to teach physics--

658
00:35:52,770 --> 00:35:56,639
I fully concede that I'm not
qualified to teach physics.

659
00:35:56,639 --> 00:35:58,430
Amplitude is the bigness
between the bottom

660
00:35:58,430 --> 00:36:01,640
and the top of the wave.

661
00:36:01,640 --> 00:36:04,136
You can, of course,
change one of these things

662
00:36:04,136 --> 00:36:05,260
without changing the other.

663
00:36:05,260 --> 00:36:07,850
You get a wave that's
higher frequency, which

664
00:36:07,850 --> 00:36:11,400
would then be lower wavelength,
and has the same amplitude.

665
00:36:11,400 --> 00:36:14,900
You can have a wave that
has higher amplitude

666
00:36:14,900 --> 00:36:17,670
and then has lower frequency.

667
00:36:21,240 --> 00:36:24,260
When the muscles that
stiffen up the bone link

668
00:36:24,260 --> 00:36:27,230
here are kicking in, they're
kicking in usually in response

669
00:36:27,230 --> 00:36:29,270
to high amplitude.

670
00:36:31,710 --> 00:36:32,210
Right?

671
00:36:32,210 --> 00:36:34,460
When something is louder
it's got a higher amplitude

672
00:36:34,460 --> 00:36:36,140
wavelength.

673
00:36:36,140 --> 00:36:38,050
Higher amplitude sound wave.

674
00:36:41,740 --> 00:36:46,560
All right, what happens if you
have a complicated waveform

675
00:36:46,560 --> 00:36:50,660
that you're trying to analyze?

676
00:36:50,660 --> 00:36:54,830
This is where we get into
something called Fourier

677
00:36:54,830 --> 00:36:58,990
analysis and Fourier synthesis.

678
00:36:58,990 --> 00:37:02,360
Fourier, French guy.

679
00:37:02,360 --> 00:37:04,780
100, 150 years ago,
something like.

680
00:37:04,780 --> 00:37:08,250
Basically said that, for
any complicated waveform,

681
00:37:08,250 --> 00:37:13,760
you can break it down into a
combination of the simpler wave

682
00:37:13,760 --> 00:37:15,620
forms that are
then added together

683
00:37:15,620 --> 00:37:20,046
into a sine wave
and its harmonics,

684
00:37:20,046 --> 00:37:21,170
and then add them together.

685
00:37:40,000 --> 00:37:43,051
Fourier said, if we
were to take this wave--

686
00:37:43,051 --> 00:37:44,050
we'll do it in reverse--

687
00:37:44,050 --> 00:37:46,550
[INAUDIBLE] a Fourier synthesis,
and I take a wave that is--

688
00:37:49,660 --> 00:37:51,200
let's see, can I draw it out?

689
00:37:51,200 --> 00:37:56,660
And I take a wave that is about
the same amplitude but a much

690
00:37:56,660 --> 00:38:05,830
higher frequency, and
I try to combine them,

691
00:38:05,830 --> 00:38:08,260
what do I end up getting?

692
00:38:08,260 --> 00:38:10,218
I don't even know if I
can do this-- let's see.

693
00:38:14,340 --> 00:38:17,560
About kind of like that.

694
00:38:17,560 --> 00:38:20,400
There'll be low,
and a little bit--

695
00:38:20,400 --> 00:38:21,900
that's kind of what
I was going for.

696
00:38:21,900 --> 00:38:23,230
It's not lined up well.

697
00:38:23,230 --> 00:38:25,630
But you can take two
waveforms, add them together

698
00:38:25,630 --> 00:38:28,539
at each point, and get a
more complicated waveform.

699
00:38:28,539 --> 00:38:30,080
You can do the same
thing in reverse.

700
00:38:30,080 --> 00:38:33,010
If you have the
right tools, you can

701
00:38:33,010 --> 00:38:36,415
decompose something like this
into its component waveforms.

702
00:38:41,290 --> 00:38:45,610
Take this idea, and look at
what's happening on the basilar

703
00:38:45,610 --> 00:38:46,710
membrane.

704
00:38:46,710 --> 00:38:48,790
The basilar membrane
is tuned, right?

705
00:38:48,790 --> 00:38:52,570
Different parts of it respond
to different frequencies.

706
00:38:52,570 --> 00:38:56,500
Stuff down here near the base
responds to higher frequencies.

707
00:38:56,500 --> 00:39:00,100
Stuff up here near the apex
responds to lower frequencies,

708
00:39:00,100 --> 00:39:04,300
and it's all just lined
up right along the middle.

709
00:39:04,300 --> 00:39:06,760
What happens is that,
for complicated noises--

710
00:39:06,760 --> 00:39:09,070
things like speech
that you're hearing,

711
00:39:09,070 --> 00:39:14,089
or things like even the sound of
a musical instrument would make

712
00:39:14,089 --> 00:39:15,880
versus the sound that
a tuning fork makes--

713
00:39:15,880 --> 00:39:18,340
that pure tone versus that
tone that has sort of a timber

714
00:39:18,340 --> 00:39:19,720
to it--

715
00:39:19,720 --> 00:39:24,370
then what's happening is,
different parts of the basilar

716
00:39:24,370 --> 00:39:27,730
membrane will be stimulated,
different amounts depending

717
00:39:27,730 --> 00:39:32,350
on how much of that
frequency is in the sound

718
00:39:32,350 --> 00:39:34,566
that you're hearing.

719
00:39:34,566 --> 00:39:36,940
Parts of the basilar membrane
respond to low frequencies,

720
00:39:36,940 --> 00:39:39,310
parts of it respond
to high frequencies,

721
00:39:39,310 --> 00:39:41,200
and different parts
will be stimulated

722
00:39:41,200 --> 00:39:44,530
to different amounts.

723
00:39:44,530 --> 00:39:50,110
One theory for how
we hear stuff says--

724
00:39:50,110 --> 00:39:51,700
it's called place theory.

725
00:39:51,700 --> 00:39:59,020
It says that only that we depend
on where the hair cells that

726
00:39:59,020 --> 00:40:03,440
are stimulating the brain are
located on the basilar membrane

727
00:40:03,440 --> 00:40:05,950
in order to figure out
what pitch we're hearing.

728
00:40:05,950 --> 00:40:09,174
One theory of pitch
discrimination is called--

729
00:40:09,174 --> 00:40:10,840
the place theory of
pitch discrimination

730
00:40:10,840 --> 00:40:14,650
says that it's all about where
the hair cells are located.

731
00:40:14,650 --> 00:40:18,970
That's the tool the brain uses
to figure out what's going on.

732
00:40:26,940 --> 00:40:31,040
The other competing theory is
what's called volley theory.

733
00:40:31,040 --> 00:40:35,750
This says that it's
not so much about where

734
00:40:35,750 --> 00:40:39,590
hair cells are-- it has to do
with how fast they're firing.

735
00:40:39,590 --> 00:40:43,670
We know that we can hear
stuff that is down--

736
00:40:43,670 --> 00:40:48,080
so how fast the neurons are
firing is either 1 to 1 with

737
00:40:48,080 --> 00:40:52,880
or is integer fraction of
the frequency of the sound

738
00:40:52,880 --> 00:40:54,140
we're hearing.

739
00:40:54,140 --> 00:40:58,160
For a really low, couple
hundred Hertz-frequency sound,

740
00:40:58,160 --> 00:41:01,036
you might actually get a
couple of hundred Hertz firing

741
00:41:01,036 --> 00:41:02,660
rate of the neurons
that are responding

742
00:41:02,660 --> 00:41:05,570
to it from those hair cells.

743
00:41:05,570 --> 00:41:08,840
Volley theory says
that it's all about how

744
00:41:08,840 --> 00:41:12,050
the speed and the patterns in
which the action potentials

745
00:41:12,050 --> 00:41:15,080
are coming in, and not so much
about which individual cells

746
00:41:15,080 --> 00:41:16,080
are providing the input.

747
00:41:32,010 --> 00:41:33,510
As with many things
in neuroscience,

748
00:41:33,510 --> 00:41:35,940
it looks like your brain
does a little bit of both.

749
00:41:35,940 --> 00:41:38,970
For low frequency
sounds up to about 4,000

750
00:41:38,970 --> 00:41:42,150
Hertz, then you
see there does seem

751
00:41:42,150 --> 00:41:44,100
to be some amount of
volley coding going on,

752
00:41:44,100 --> 00:41:46,310
where for really low
frequency sounds,

753
00:41:46,310 --> 00:41:49,620
it's a one-to-one
correlation between frequency

754
00:41:49,620 --> 00:41:53,430
of the sound coming in
and frequency with which

755
00:41:53,430 --> 00:41:57,090
the hair cells are firing.

756
00:41:57,090 --> 00:41:59,740
Towards the higher ends
of that, once you're up

757
00:41:59,740 --> 00:42:01,590
into a couple
thousand Hertz, you're

758
00:42:01,590 --> 00:42:06,550
looking at more like it'd
be a multiple of some kind--

759
00:42:06,550 --> 00:42:09,120
the sound coming in would be
a multiple of the firing rate.

760
00:42:09,120 --> 00:42:11,910
But there is a relationship
between the firing rate

761
00:42:11,910 --> 00:42:13,320
and the frequency of the sound.

762
00:42:16,020 --> 00:42:20,690
For sounds higher
than that, it really

763
00:42:20,690 --> 00:42:25,100
just stops being practical
to use firing rate

764
00:42:25,100 --> 00:42:27,230
as a coding for the frequency.

765
00:42:27,230 --> 00:42:31,520
Firing rate ceiling's at on
the order of 1,000 action

766
00:42:31,520 --> 00:42:34,515
potentials per second.

767
00:42:34,515 --> 00:42:36,140
We can hear a lot
higher than that-- we

768
00:42:36,140 --> 00:42:38,570
can hear up to 20,000 Hertz.

769
00:42:38,570 --> 00:42:41,400
It's probably a fairly
reasonable upper limit.

770
00:42:41,400 --> 00:42:43,730
Higher for some people,
lower for others.

771
00:42:43,730 --> 00:42:45,340
Individual variations.

772
00:42:45,340 --> 00:42:47,960
Higher than that, it seems
to be pretty dependent

773
00:42:47,960 --> 00:42:52,220
on place theory, on place
coding, on which neurons

774
00:42:52,220 --> 00:42:54,590
on the basilar membrane
are being most stimulated

775
00:42:54,590 --> 00:42:56,640
by the input that's coming in.

776
00:43:03,890 --> 00:43:07,420
The other thing about--

777
00:43:07,420 --> 00:43:09,080
all right, let's
take this model,

778
00:43:09,080 --> 00:43:11,810
let's make it a little
bit more complicated.

779
00:43:11,810 --> 00:43:15,470
On each cross-section
of the basilar membrane,

780
00:43:15,470 --> 00:43:17,210
you've got a bunch
of hair cells.

781
00:43:17,210 --> 00:43:23,690
You've got one inner
hair cell over here,

782
00:43:23,690 --> 00:43:27,950
and then you've got a bunch
of three outer hair cells.

783
00:43:31,090 --> 00:43:35,620
Same but kind of sloppy inner.

784
00:43:35,620 --> 00:43:39,220
Inner hair cells are
running on the side that

785
00:43:39,220 --> 00:43:42,040
is closer to the curl
of the whole thing,

786
00:43:42,040 --> 00:43:43,510
and then outer are further out.

787
00:43:43,510 --> 00:43:47,920
So you end up with
for each of these,

788
00:43:47,920 --> 00:43:49,540
you end up with a
row of hair cells

789
00:43:49,540 --> 00:43:51,490
all the way up the
basilar membrane.

790
00:43:51,490 --> 00:43:54,040
One row of inner
hair cells that runs

791
00:43:54,040 --> 00:43:56,680
closer to the edge
that is curling,

792
00:43:56,680 --> 00:44:00,490
and three rows of outer hair
cells that move further out.

793
00:44:00,490 --> 00:44:03,220
And it turns out that
it's only these inner hair

794
00:44:03,220 --> 00:44:05,590
cells that actually are
sending in auditory perception

795
00:44:05,590 --> 00:44:06,880
information--

796
00:44:06,880 --> 00:44:08,770
all of the nerves--

797
00:44:08,770 --> 00:44:11,050
90%, 95% of the nerves
that are actually

798
00:44:11,050 --> 00:44:13,780
part of your auditory nerve
that go into your brain come

799
00:44:13,780 --> 00:44:15,190
from these inner hair cells.

800
00:44:15,190 --> 00:44:17,110
These inner hair
cells will have lots

801
00:44:17,110 --> 00:44:21,280
of neurons coming off
of them, and they'll

802
00:44:21,280 --> 00:44:22,976
be almost all afferent nerves.

803
00:44:22,976 --> 00:44:24,850
They'll be sensory nerves
sending information

804
00:44:24,850 --> 00:44:26,950
into the brain.

805
00:44:26,950 --> 00:44:29,230
Outer hair cells
will actually share

806
00:44:29,230 --> 00:44:31,600
nerves between a couple
of different cells,

807
00:44:31,600 --> 00:44:33,560
and they've got a lot of
efferent nerves coming

808
00:44:33,560 --> 00:44:36,160
in too-- information
coming from the brain.

809
00:44:36,160 --> 00:44:39,040
One thing that
these outer cells do

810
00:44:39,040 --> 00:44:42,910
is, as we know the
basilar membrane,

811
00:44:42,910 --> 00:44:45,940
different locations on it
respond to different pitches.

812
00:44:45,940 --> 00:44:49,630
But the level of
precision with which we

813
00:44:49,630 --> 00:44:53,740
can detect pitch differences
and the level of precision

814
00:44:53,740 --> 00:44:57,479
the basilar membrane has
in discriminating pitches

815
00:44:57,479 --> 00:44:58,270
are very different.

816
00:44:58,270 --> 00:45:02,020
We're much better at
pitch discrimination

817
00:45:02,020 --> 00:45:06,190
than simply looking at the
physics of the basilar membrane

818
00:45:06,190 --> 00:45:08,530
would suggest.

819
00:45:08,530 --> 00:45:11,440
One theory that's
what's going on here

820
00:45:11,440 --> 00:45:13,000
is that there's a
lot of information

821
00:45:13,000 --> 00:45:18,130
that comes from the brain down
to these outer hair cells.

822
00:45:18,130 --> 00:45:20,710
The outer hair cells
apparently are not

823
00:45:20,710 --> 00:45:22,725
so much about
responding, but they

824
00:45:22,725 --> 00:45:24,850
can do something cool--
they can stiffen themselves

825
00:45:24,850 --> 00:45:28,450
right up so that they can't
bend back and forth anymore.

826
00:45:28,450 --> 00:45:30,730
They make themselves
a little bit longer,

827
00:45:30,730 --> 00:45:34,540
and the result of this is
that their particular chunk

828
00:45:34,540 --> 00:45:37,854
of the basilar membrane starts
being more or less flexible.

829
00:45:37,854 --> 00:45:40,270
This is one way in which the
basilar membrane can actually

830
00:45:40,270 --> 00:45:47,020
tune to be more sensitive to
very specific frequencies--

831
00:45:47,020 --> 00:45:50,180
by controlling the behavior
of these outer hair cells.

832
00:45:55,720 --> 00:45:57,934
Questions?

833
00:45:57,934 --> 00:46:01,918
So this suggests
that the brain sends

834
00:46:01,918 --> 00:46:06,400
information that will then
reshape our interpretation

835
00:46:06,400 --> 00:46:07,892
of [INAUDIBLE].

836
00:46:07,892 --> 00:46:08,392
Yes.

837
00:46:11,380 --> 00:46:13,380
[INAUDIBLE] consciously?

838
00:46:13,380 --> 00:46:14,361
Not consciously.

839
00:46:14,361 --> 00:46:16,860
I don't think anyone's managed
to demonstrate anybody having

840
00:46:16,860 --> 00:46:18,010
conscious control over it.

841
00:46:21,170 --> 00:46:24,730
But for example,
if you're trying

842
00:46:24,730 --> 00:46:26,320
to do a pitch
discrimination task,

843
00:46:26,320 --> 00:46:29,110
or if you're trying to tune an
instrument or something, where

844
00:46:29,110 --> 00:46:31,300
you really want to
get it just right,

845
00:46:31,300 --> 00:46:35,440
then you might, for
example, see your brain

846
00:46:35,440 --> 00:46:37,450
inhibiting one region
of the basilar membrane

847
00:46:37,450 --> 00:46:40,033
in order to make stiffening one
region of the basilar membrane

848
00:46:40,033 --> 00:46:42,880
to make other parts
more sensitive.

849
00:46:42,880 --> 00:46:45,665
If you are a little
bit off, then you'll

850
00:46:45,665 --> 00:46:48,040
hear it is a bigger difference--
because the next bit off

851
00:46:48,040 --> 00:46:52,150
won't respond at
all, for example,

852
00:46:52,150 --> 00:46:54,100
by being able to tune it.

853
00:46:54,100 --> 00:46:55,780
And it also seems
like something similar

854
00:46:55,780 --> 00:46:57,405
is happening if you're
trying to listen

855
00:46:57,405 --> 00:47:00,972
to one stimulus out of a whole
bunch of stuff that's going on.

856
00:47:00,972 --> 00:47:02,680
Talking to your friend
in a crowded room,

857
00:47:02,680 --> 00:47:04,805
listening to me when there's
traffic on the street.

858
00:47:04,805 --> 00:47:05,920
Again, you're going to--

859
00:47:05,920 --> 00:47:07,836
one of the things that
happens is your basilar

860
00:47:07,836 --> 00:47:09,580
membrane gets tuned
to be more sensitive

861
00:47:09,580 --> 00:47:11,271
to those frequencies--

862
00:47:11,271 --> 00:47:13,270
the frequencies that are
involved in that task--

863
00:47:13,270 --> 00:47:15,280
and less sensitive
to other stuff.

864
00:47:15,280 --> 00:47:17,380
It's actually almost a
physiological attention

865
00:47:17,380 --> 00:47:18,984
mechanism, where you're--

866
00:47:18,984 --> 00:47:20,650
even before it makes
it into your brain,

867
00:47:20,650 --> 00:47:25,900
throwing out a certain amount
of the potential sensory input

868
00:47:25,900 --> 00:47:26,690
that's out there.

869
00:47:32,500 --> 00:47:35,190
Sound-- sound goes--

870
00:47:35,190 --> 00:47:36,800
quick review.

871
00:47:36,800 --> 00:47:38,970
We've got our pinna,
our outer ear.

872
00:47:38,970 --> 00:47:42,150
The funny shaping of the pinna
causes it to select sounds,

873
00:47:42,150 --> 00:47:45,700
causes it to highlight
certain frequencies of sound,

874
00:47:45,700 --> 00:47:48,450
so actually human ears
are the funny shape

875
00:47:48,450 --> 00:47:52,110
they are in part because it
means that sounds between 2000

876
00:47:52,110 --> 00:47:54,941
and 5000 Hertz get amplified,
and these are the frequencies

877
00:47:54,941 --> 00:47:56,190
that are important for speech.

878
00:47:58,770 --> 00:48:02,830
The pinna funnels sound
down this auditory canal

879
00:48:02,830 --> 00:48:05,710
where the sound
waves cause the ear

880
00:48:05,710 --> 00:48:09,220
drum, the tympanic
membrane, to vibrate.

881
00:48:09,220 --> 00:48:12,610
That in turn vibrates
these three little bones--

882
00:48:12,610 --> 00:48:15,100
the ossicles-- so we've got
our hammer, and our anvil,

883
00:48:15,100 --> 00:48:16,810
and our stirrup.

884
00:48:16,810 --> 00:48:20,800
In turn, the stirrup presses on
the oval window of the cochlea

885
00:48:20,800 --> 00:48:23,860
and causes the fluid
inside the cochlea

886
00:48:23,860 --> 00:48:29,050
to slosh back and forth, which
in turn causes this basilar

887
00:48:29,050 --> 00:48:33,580
membrane to wave up
and down, and where

888
00:48:33,580 --> 00:48:36,400
it gets the most motion
depends on the pitch

889
00:48:36,400 --> 00:48:41,800
of the sound that's coming in,
the frequency of the sound.

890
00:48:41,800 --> 00:48:45,370
This in turn causes the hair
cells that are on the basilar

891
00:48:45,370 --> 00:48:48,850
membrane to bend back and forth.

892
00:48:48,850 --> 00:48:51,310
When they get bent,
these tip links

893
00:48:51,310 --> 00:48:55,600
that connect to the stereocilia
pull open these little ion

894
00:48:55,600 --> 00:48:56,320
channels.

895
00:48:56,320 --> 00:49:01,840
Potassium floods in, these
hair cells are depolarized,

896
00:49:01,840 --> 00:49:04,900
and then that in turn
triggers the opening

897
00:49:04,900 --> 00:49:07,630
of a voltage gated
calcium channel.

898
00:49:07,630 --> 00:49:12,064
Calcium flows in, causes the
vesicles of neurotransmitter

899
00:49:12,064 --> 00:49:13,480
to bind with the
membrane, release

900
00:49:13,480 --> 00:49:17,860
their neurotransmitter,
which in turn

901
00:49:17,860 --> 00:49:20,620
causes depolarization
or hyperpolarization

902
00:49:20,620 --> 00:49:24,880
in these cells and the nerve
that goes back to the brain.

903
00:49:24,880 --> 00:49:27,460
Where the brain does all
of this information go?

904
00:49:38,990 --> 00:49:40,010
Here's a brain.

905
00:49:40,010 --> 00:49:43,880
Looking at it kind of from
the vertical view-- so here's

906
00:49:43,880 --> 00:49:44,840
an ear.

907
00:49:44,840 --> 00:49:47,339
We're going to disregard the
part where those are completely

908
00:49:47,339 --> 00:49:48,330
different shapes.

909
00:49:48,330 --> 00:49:50,054
Here's an ear.

910
00:49:50,054 --> 00:49:51,470
Here's an ear--
I'm thinking we're

911
00:49:51,470 --> 00:49:54,136
kind of looking from the back of
the head here, looking forward.

912
00:49:54,136 --> 00:49:56,600
[INAUDIBLE]

913
00:49:56,600 --> 00:49:58,240
We've got two
parts of the brain,

914
00:49:58,240 --> 00:50:00,230
and then we've got the
brainstem here, right?

915
00:50:00,230 --> 00:50:03,410
Coming down and going
down into the spinal cord.

916
00:50:05,990 --> 00:50:08,880
Here's our ears-- we've got all
of our kind of inner ear stuff.

917
00:50:08,880 --> 00:50:10,650
Here's our little cochleas.

918
00:50:13,720 --> 00:50:17,780
All right-- so nerve fibers
come from the cochlea

919
00:50:17,780 --> 00:50:22,580
and they actually go to
the brain stem first,

920
00:50:22,580 --> 00:50:28,190
and they go into what's called
the cochlear nucleus right

921
00:50:28,190 --> 00:50:30,830
here.

922
00:50:30,830 --> 00:50:31,745
Cochlear nucleus.

923
00:50:34,670 --> 00:50:36,860
From there they actually--

924
00:50:36,860 --> 00:50:40,310
most of the fibers
actually cross and go

925
00:50:40,310 --> 00:50:43,040
to the superior olivary
nucleus on the other side.

926
00:50:51,730 --> 00:50:53,170
We've got a fair
bit of processing

927
00:50:53,170 --> 00:50:54,609
happening right here.

928
00:50:54,609 --> 00:50:56,650
A few of these fibers go
to the one on this side,

929
00:50:56,650 --> 00:50:58,822
but most of them cross over.

930
00:50:58,822 --> 00:51:01,030
Again, just like we're used
to with all other aspects

931
00:51:01,030 --> 00:51:02,260
of the brain,
stuff from the left

932
00:51:02,260 --> 00:51:04,343
goes to the right hemisphere,
stuff from the right

933
00:51:04,343 --> 00:51:07,090
goes the left hemisphere.

934
00:51:07,090 --> 00:51:09,801
Here, it's happening in these
auditory nuclei in the brain

935
00:51:09,801 --> 00:51:10,300
stem.

936
00:51:13,480 --> 00:51:18,680
There's a pathway that goes to
the thalamus, and in this case,

937
00:51:18,680 --> 00:51:20,860
we're going to the
medial geniculate

938
00:51:20,860 --> 00:51:24,520
nucleus of the thalamus--
remember, for vision, vision

939
00:51:24,520 --> 00:51:27,500
runs through the lateral
geniculate nucleus.

940
00:51:27,500 --> 00:51:30,430
We're pretty much we're
in a very similar piece

941
00:51:30,430 --> 00:51:33,370
of the thalamus--
slightly scooted over.

942
00:51:33,370 --> 00:51:36,130
From there, we get
processing that

943
00:51:36,130 --> 00:51:39,250
goes to auditory cortex out
here in the temporal lobes.

944
00:51:42,130 --> 00:51:44,050
[INAUDIBLE]

945
00:51:44,050 --> 00:51:46,010
Yes.

946
00:51:46,010 --> 00:51:48,290
So we have our inner ear, right?

947
00:51:48,290 --> 00:51:50,606
Which is where
transduction happens,

948
00:51:50,606 --> 00:51:52,480
where the mechanical
energy of the sound wave

949
00:51:52,480 --> 00:51:57,040
turns into the electrical
signal for a neuron.

950
00:51:57,040 --> 00:52:00,500
The nerve from that-- this
is the vestibulocochlear

951
00:52:00,500 --> 00:52:04,240
nerve, which runs from the inner
ear down into the brain stem.

952
00:52:04,240 --> 00:52:07,602
It goes to the cochlear
nuclei down here.

953
00:52:07,602 --> 00:52:09,310
Of course, it's doing
this on both sides,

954
00:52:09,310 --> 00:52:11,960
but I've only drawn this
gentleman's-- or ladies,

955
00:52:11,960 --> 00:52:16,150
I don't know-- left, right ear.

956
00:52:16,150 --> 00:52:17,520
From the cochlear nuclei--

957
00:52:17,520 --> 00:52:21,070
it goes to the cochlear
nucleus on the same side,

958
00:52:21,070 --> 00:52:24,040
and then most of
the signal crosses.

959
00:52:24,040 --> 00:52:27,590
It goes to the superior olivary
nucleus on the other side.

960
00:52:27,590 --> 00:52:29,560
A little bit of it
stays on the same side,

961
00:52:29,560 --> 00:52:32,708
but it mostly crosses.

962
00:52:32,708 --> 00:52:33,208
Question?

963
00:52:33,208 --> 00:52:34,210
[? No. ?]

964
00:52:34,210 --> 00:52:35,720
OK.

965
00:52:35,720 --> 00:52:37,150
We're still in the
brainstem here,

966
00:52:37,150 --> 00:52:39,890
so this is right in the
back of your head, right?

967
00:52:39,890 --> 00:52:41,630
Right down here.

968
00:52:41,630 --> 00:52:44,930
And from there, the
superior olivary nucleus

969
00:52:44,930 --> 00:52:47,700
sends cells that
project to the thalamus.

970
00:52:47,700 --> 00:52:49,430
Remember, the thalamus
is this gateway

971
00:52:49,430 --> 00:52:52,430
for sensory information--
it takes it, looks at it,

972
00:52:52,430 --> 00:52:55,589
and sends it off to the
correct piece of cortex.

973
00:52:55,589 --> 00:52:57,380
Here we're looking at
the medial geniculate

974
00:52:57,380 --> 00:52:58,400
nucleus of the thalamus.

975
00:52:58,400 --> 00:53:00,440
Remember for vision,
we looked as the-- it

976
00:53:00,440 --> 00:53:03,800
went through the lateral
geniculate nucleus, the LGN.

977
00:53:03,800 --> 00:53:06,420
In this case, we're kind
of in the same region,

978
00:53:06,420 --> 00:53:11,520
but a different clump of cell
bodies closer to the midline--

979
00:53:11,520 --> 00:53:12,110
medial.

980
00:53:12,110 --> 00:53:14,720
Lateral of course is
closer to the sides.

981
00:53:14,720 --> 00:53:18,890
From there, it spreads
out and it goes

982
00:53:18,890 --> 00:53:21,920
to a bunch of auditory cortex.

983
00:53:21,920 --> 00:53:24,080
Where the cortical
processing actually is

984
00:53:24,080 --> 00:53:27,400
is in your temporal lobes right
on the sides of your head here,

985
00:53:27,400 --> 00:53:29,450
but the signal gets
there in a kind

986
00:53:29,450 --> 00:53:32,090
of roundabout manner-- it's kind
of easy to be like, hey, look,

987
00:53:32,090 --> 00:53:32,589
ears!

988
00:53:32,589 --> 00:53:34,520
Well, that's where my
auditory processing is,

989
00:53:34,520 --> 00:53:37,640
but it actually goes to the
back and across and around

990
00:53:37,640 --> 00:53:39,710
before getting back
to the temporal lobe.

991
00:53:39,710 --> 00:53:43,070
[INAUDIBLE]

992
00:53:45,470 --> 00:53:49,840
Voila, the major
auditory pathways.

993
00:53:49,840 --> 00:53:53,139
So wait-- sound begins
from one ear, goes

994
00:53:53,139 --> 00:53:54,860
to the other side, [INAUDIBLE]

995
00:53:54,860 --> 00:53:56,060
Almost all of it crosses.

996
00:53:56,060 --> 00:53:59,150
Almost all the input
from your left ear

997
00:53:59,150 --> 00:54:02,550
goes to your right brain,
and the other way around.

998
00:54:02,550 --> 00:54:05,210
About 90% or 95%
of the nerve fibers

999
00:54:05,210 --> 00:54:10,190
cross, and a little bit of it
goes to the olivary nucleus

1000
00:54:10,190 --> 00:54:12,860
on the same side.

1001
00:54:12,860 --> 00:54:25,600
It turns out, in some
animals, that the information

1002
00:54:25,600 --> 00:54:29,800
about where a sound
is coming from

1003
00:54:29,800 --> 00:54:31,840
happens much later
in the stage--

1004
00:54:31,840 --> 00:54:34,900
but in mammals, it
happens right down here,

1005
00:54:34,900 --> 00:54:37,750
in these early processing
stuff in the superior olivary

1006
00:54:37,750 --> 00:54:38,890
nucleus.

1007
00:54:38,890 --> 00:54:41,802
Superior olivary nucleus
gets mostly input

1008
00:54:41,802 --> 00:54:43,510
from one side or the
other, but remember,

1009
00:54:43,510 --> 00:54:47,050
that we've got 5% or 10% of
the signal didn't cross over,

1010
00:54:47,050 --> 00:54:52,366
and that's the part that your
brain uses to locate sounds.

1011
00:54:52,366 --> 00:54:53,740
We're pretty good
at figuring out

1012
00:54:53,740 --> 00:54:55,690
where sounds are coming from.

1013
00:54:55,690 --> 00:54:57,832
Try it-- close your eyes.

1014
00:54:57,832 --> 00:54:59,290
I'm going to-- put
your stuff down.

1015
00:54:59,290 --> 00:55:00,250
I'm going to walk
around the room.

1016
00:55:00,250 --> 00:55:01,550
I'm going to clap my hands.

1017
00:55:01,550 --> 00:55:03,740
Point out where you think
I am without looking.

1018
00:55:11,532 --> 00:55:13,000
Oh, sorry about that.

1019
00:55:13,000 --> 00:55:15,599
Don't take out your neighbors.

1020
00:55:15,599 --> 00:55:19,050
[INAUDIBLE]

1021
00:55:22,008 --> 00:55:24,710
All right, feeling
fairly accurate?

1022
00:55:24,710 --> 00:55:26,960
Did you feel like you had a
pretty good sense of where

1023
00:55:26,960 --> 00:55:28,300
sounds were coming from?

1024
00:55:28,300 --> 00:55:30,530
It's not perfect,
but fairly accurate.

1025
00:55:30,530 --> 00:55:31,430
We're good at this.

1026
00:55:31,430 --> 00:55:36,140
What kinds of information
are we using to do that?

1027
00:55:36,140 --> 00:55:39,380
How do you-- how
would you figure out--

1028
00:55:39,380 --> 00:55:44,652
how could you figure out
where a sound is located?

1029
00:55:44,652 --> 00:55:45,360
How can you tell?

1030
00:55:49,304 --> 00:55:51,780
By which ear it's closer to.

1031
00:55:51,780 --> 00:55:53,600
By which ear it's closer to.

1032
00:55:53,600 --> 00:55:56,270
How would you analyze the sound
signal coming into your ears

1033
00:55:56,270 --> 00:55:57,894
to figure out which
ear it's closer to?

1034
00:56:01,011 --> 00:56:03,469
[INAUDIBLE]

1035
00:56:03,469 --> 00:56:03,969
Yeah?

1036
00:56:03,969 --> 00:56:06,434
Is there a time difference
at which the sound wave

1037
00:56:06,434 --> 00:56:07,430
reaches [INAUDIBLE]

1038
00:56:07,430 --> 00:56:08,490
Yep.

1039
00:56:08,490 --> 00:56:12,660
Your years are going to be six,
eight inches apart, probably,

1040
00:56:12,660 --> 00:56:13,885
on average.

1041
00:56:13,885 --> 00:56:15,510
There's going to be
a sound difference.

1042
00:56:15,510 --> 00:56:17,460
One is latency between ears.

1043
00:56:20,080 --> 00:56:22,280
Another is loudness
between the ears.

1044
00:56:25,050 --> 00:56:26,880
So latency and
loudness difference

1045
00:56:26,880 --> 00:56:29,100
let you figure out which
ear things are closer

1046
00:56:29,100 --> 00:56:31,980
to, especially for
things that are not

1047
00:56:31,980 --> 00:56:33,090
directly in between them.

1048
00:56:33,090 --> 00:56:35,430
Right?

1049
00:56:35,430 --> 00:56:39,070
Telling front from back is
hard by latency and loudness,

1050
00:56:39,070 --> 00:56:41,640
but you've got--

1051
00:56:41,640 --> 00:56:43,720
here's our hypothetical
guy, right?

1052
00:56:43,720 --> 00:56:46,280
If I've got a sound
source over here--

1053
00:56:46,280 --> 00:56:47,100
sound source.

1054
00:56:47,100 --> 00:56:48,950
Here's a tuning fork.

1055
00:56:48,950 --> 00:56:51,830
Then we got sound
waves coming off of it,

1056
00:56:51,830 --> 00:56:54,420
and they're going
to hit his right ear

1057
00:56:54,420 --> 00:56:57,300
before they hit the left ear.

1058
00:56:57,300 --> 00:56:59,670
So there's a latency difference.

1059
00:56:59,670 --> 00:57:02,340
This doesn't work for
really low pitched sounds

1060
00:57:02,340 --> 00:57:05,370
because the wavelength
of the sound wave--

1061
00:57:05,370 --> 00:57:07,410
and I do mean
wavelength this time--

1062
00:57:07,410 --> 00:57:12,180
is big enough that it actually
would just go around your head.

1063
00:57:12,180 --> 00:57:15,850
Your head isn't big enough to
make a significant difference

1064
00:57:15,850 --> 00:57:17,880
in how it'll get there, no.

1065
00:57:17,880 --> 00:57:19,422
Wow, I can't teach
this at all today.

1066
00:57:19,422 --> 00:57:21,838
Never mind that-- that's true
for the next thing I'm going

1067
00:57:21,838 --> 00:57:23,550
to talk about, which
is that you get--

1068
00:57:23,550 --> 00:57:24,360
which is loudness.

1069
00:57:24,360 --> 00:57:27,240
You get a sound shadow
around your head.

1070
00:57:27,240 --> 00:57:29,920
For a sound that's
coming through,

1071
00:57:29,920 --> 00:57:32,274
if it's coming to your
left ear, it'll block--

1072
00:57:32,274 --> 00:57:33,690
your head will
actually block some

1073
00:57:33,690 --> 00:57:35,523
of that sound wave
getting to your right ear

1074
00:57:35,523 --> 00:57:37,140
for high pitched noises.

1075
00:57:37,140 --> 00:57:39,630
For low pitched
noises, the wavelength

1076
00:57:39,630 --> 00:57:42,480
is big enough that it can
just go around your head,

1077
00:57:42,480 --> 00:57:46,750
and you don't get a
loudness difference.

1078
00:57:46,750 --> 00:57:49,404
Does that make
sense, physics kids?

1079
00:57:49,404 --> 00:57:52,964
So [INAUDIBLE]

1080
00:57:52,964 --> 00:57:55,130
Latency, loudness, and some
other kinds of cues too.

1081
00:57:55,130 --> 00:57:56,360
There's a lot of cues--

1082
00:57:56,360 --> 00:57:58,460
there are some cues
that your brain

1083
00:57:58,460 --> 00:58:01,396
can use to localize sounds.

1084
00:58:01,396 --> 00:58:08,930
Like you're saying that for
large wavelength and loud?

1085
00:58:08,930 --> 00:58:11,360
Not for loudness, but for--

1086
00:58:11,360 --> 00:58:12,980
latency is one
thing that you get--

1087
00:58:12,980 --> 00:58:15,860
you get a difference
in time to arrival.

1088
00:58:15,860 --> 00:58:17,570
For loudness
differences, if something

1089
00:58:17,570 --> 00:58:19,153
is closer to your
left ear, it's going

1090
00:58:19,153 --> 00:58:21,710
to be louder in your left ear
for reasonably close things,

1091
00:58:21,710 --> 00:58:23,360
especially.

1092
00:58:23,360 --> 00:58:27,740
But not for lower pitched
larger wavelength sounds,

1093
00:58:27,740 --> 00:58:30,020
because the larger
wavelength allows it--

1094
00:58:30,020 --> 00:58:32,827
that means it is not getting
blocked by your head, which

1095
00:58:32,827 --> 00:58:34,410
isn't big enough
relative to the sound

1096
00:58:34,410 --> 00:58:37,831
to cast that kind of shadow.

1097
00:58:37,831 --> 00:58:39,830
Another thing that you'll
see is you'll actually

1098
00:58:39,830 --> 00:58:44,750
see spectral differences.

1099
00:58:44,750 --> 00:58:48,560
What that means is that, because
of the way our ears are shaped,

1100
00:58:48,560 --> 00:58:50,690
sounds that are coming
in from different angles

1101
00:58:50,690 --> 00:58:55,520
will flow over and around
the funky little crinkly

1102
00:58:55,520 --> 00:58:56,870
shapes in our ears--

1103
00:58:56,870 --> 00:58:58,910
in our outer ears
and our pinna--

1104
00:58:58,910 --> 00:59:00,161
differently.

1105
00:59:00,161 --> 00:59:01,910
A sound that's coming
from in front of you

1106
00:59:01,910 --> 00:59:04,100
and a sound that's
coming from behind you,

1107
00:59:04,100 --> 00:59:06,710
even if they're the same sound,
will have subtly different

1108
00:59:06,710 --> 00:59:08,114
characteristics--

1109
00:59:08,114 --> 00:59:10,280
which frequencies are
highlighted, which frequencies

1110
00:59:10,280 --> 00:59:14,300
are decreased a little bit.

1111
00:59:14,300 --> 00:59:17,360
That information,
we're not usually

1112
00:59:17,360 --> 00:59:18,480
consciously aware of it.

1113
00:59:18,480 --> 00:59:20,021
Our brain kind of
goes out of its way

1114
00:59:20,021 --> 00:59:23,160
to make us less aware of it
for conscious processing,

1115
00:59:23,160 --> 00:59:24,609
but you use it--
for localization,

1116
00:59:24,609 --> 00:59:26,150
you become aware of
whether something

1117
00:59:26,150 --> 00:59:27,358
is behind or in front of you.

1118
00:59:30,340 --> 00:59:32,830
That funny shaped
outer ear not only

1119
00:59:32,830 --> 00:59:34,314
highlights particular
frequencies

1120
00:59:34,314 --> 00:59:36,730
that we want to be able to
pick out of our world-- it also

1121
00:59:36,730 --> 00:59:39,250
allows us to get some
localization information by how

1122
00:59:39,250 --> 00:59:41,800
it affects things coming
from different angles.

1123
00:59:49,000 --> 00:59:50,850
Questions?