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PROFESSOR: This is our
first introductory meeting

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of the course, which is 9.04.

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And we are going to cover vision
and audition in this course,

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and there are going to
be two of us lecturing.

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My name is Peter Schiller,
and this is Chris Brown.

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And I will be talking
about the vision portion,

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and Chris will be lecturing
about the auditory portion.

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Now, what I'm going
to do is I'm going

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to hand out the syllabi
that we have, in this case,

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for the first half
of the course.

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And that we are going to
discuss in some detail

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today for the first
half of the lecture,

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and Chris is going to discuss
it for the second half.

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So that is the basic
plan for today.

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And I will go through some of
the basic procedures and issues

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that we may want to deal with at
this very introductory portion.

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So first of all, let me talk
about the reading assignments.

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If you have the handout,
they are ready for you.

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If you look at the
second page, that's

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where we have the assigned
readings for the vision

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half of the course.

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Now, for that half
of the course,

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the top eight assignments
are all articles

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in various journals.

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We don't have a textbook for
this portion of the course.

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And then in addition to
the assigned readings,

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we have recommended readings
that are listed there.

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And then another
important factor

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that is listed
there-- let me first

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say that the lectures will be
put on Stellar, in most cases,

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after each lecture.

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And in addition, the videos
that we are now recording

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will also become available,
but they will not

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be available until well
after each lecture.

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So I would advise each of
you to come to the lectures

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rather than hoping to read
the assigned material only

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or to eventually
look at the videos.

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The reason I'm
telling you this is

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that our analysis has shown
that those students who

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attend the lectures
regularly get

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much better grades on the exams
than the students who do not.

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So I strongly will
urge all of you

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to come to as many lectures
as you possibly can.

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Now, the additional
requirement that you're

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going to have for this course is
to write two research reports,

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one for vision and
one for audition.

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And the assigned written report
that you need to put together

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is in a paper at the
bottom of the second page.

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In this case, it's
going to be a paper that

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was written quite
some years ago,

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a very important and remarkable
paper that has been published

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by Oster and Barlow,
as you can see.

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And the task for you will
be to not just report

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what they had reported,
because that's repetitious,

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but to do a bit of
research and write

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about what has been discovered
since the remarkable findings

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that these two people
had made at the time.

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All right.

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So that's the research report.

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And then I want to
specify the exams.

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We are going to
have a midterm exam,

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and the exact date for this has
already been set on October 23.

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All right?

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But as I say, you
can find this, and I

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will specify that in more
detail in just a minute.

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And then we are going
to have a final exam

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at the end of the term.

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The exact date for
this, as always at MIT,

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will not have been set until
probably sometime in November.

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So now let me also specify
the grade breakdown.

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I think that's
important for all of us.

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The written report for
each half of the course--

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there's going to be one
report, as I've already said,

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for vision and
one for audition--

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and that will constitute
10% of the grade for each.

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And the midterm exam,
this constitutes 25%.

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The final exam constitutes
55% of the overall grade.

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And in that, 15% will be on
vision and 40% on audition.

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So if you add that up, you can
see that vision and audition

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are set up to be exactly
equally weighed for the exams.

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MICHELLE: Hi.

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I'm Michelle.

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I'll be helping the professors,
especially with [INAUDIBLE].

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PROFESSOR: So I'm Chris Brown,
and I'm one of the instructors.

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I'll be teaching
the second half.

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And my research is on two areas,
brain stem auditory reflexes,

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like the startle reflex and
the middle ear muscle reflex.

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And I also work on animal models
of the auditory brain stem

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implant, which is a
neural prosthesis that's

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used in deaf individuals.

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PROFESSOR: All right.

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And I'm Peter Schiller, and
I work on the visual system.

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And I'm a professor
here in our department.

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So that's very nice.

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Thank you for the introductions.

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And I hope, you guys, we
all get to know each other.

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I'm very impressed that
there's so many seniors here.

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That's actually unusual.

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I don't remember having
this high a percentage

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of seniors in the class.

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That's really very
nice, very nice.

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OK.

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00:07:01,840 --> 00:07:06,840
So now we are going to
talk, for the first part

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of today's lecture, about what
aspects of visual processing

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we are trying to
understand and, therefore,

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what we are going
to try to cover

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in this course in
terms of topics.

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OK?

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So first of all,
what we are going

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to do for several lectures
is to talk about the layout

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and organization of the
visual system itself.

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Most of it we will discuss as
it applies to higher mammals,

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in particular monkeys
and primates and humans.

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Then we are going to talk
about specific aspects

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of visual processing.

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We're going to try to understand
how we adapt in vision,

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and, very interestingly,
how we are

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able to perceive colors and
process them accurately.

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Another fascinating
topic is how we

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are capable of analyzing motion.

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That's a complex, very
interesting topic,

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as is depth perception.

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And the reason depth
perception is particularly

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interesting is
because, as you know,

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the retinal surface
is essentially

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a two-dimensional arrangement.

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And yet from whatever falls
on these two dimensions

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in the left and right
eyes, somehow the brain

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needs to convert to be able
to see the third dimension.

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And as a result,
several mechanisms

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have evolved to
accomplish that, and we

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are going to discuss them.

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Then, again, another
very complex topic

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is how we can recognize objects.

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Perhaps the most
complex of those

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is our incredible ability
to recognize faces.

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And that is
highlighted, of course,

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by the fact that if you look
at more simple organisms,

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like, I don't know, monkeys,
they all look the same to you.

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But human beings,
who are actually

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more similar to each other
than perhaps monkeys are,

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we are really capable
of telling them

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apart and readily recognize
them over long periods of time.

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So it's a very
interesting topic.

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And yet another topic
that we will discuss

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is how we make eye movements.

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As you probably know,
or you're aware of,

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that we are constantly
moving your eye.

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You make saccadic eye movements
about three times a second,

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thousands of times a day,
hundreds of thousands of times,

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to be able to see things
clearly in the world.

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So we are going to
try to understand

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how that incredible
ability has evolved

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and how it is
realized by the brain.

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OK.

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So now to look at exactly how
we are going to cover this,

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let me go through this.

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During the next lecture,
which is September 9,

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we are going to look at the
basic layout of the retina

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and the lateral
geniculate system,

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as well as how the visual
system in general is wired.

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Then on September
11, we're going

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to look at the
visual cortex, then

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at the ON and OFF
channels, so-called,

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that you'll realize what they
are once we talk about it.

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And then there's
another set of channels

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that originates in
the retina, which

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are the midget and
parasol channels.

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We'll discuss those, try to
figure out why did they evolve

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and what is their role
in being able to see

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the world in realistic fashion.

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Then we're going to talk about
adaption and color, depth

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perception, form perception.

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And then we're going to have
a lot of fun on October 2,

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and we're going to look
at illusions and also

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visual prosthesis,
because one of you,

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in particular, is
interested in that topic.

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Then we are going to talk about
the neural control of visually

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guided eye movements.

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That's going to consist
of two sessions.

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And then we're going to
talk about motion perception

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and another aspect
of eye movements

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when we pursue something
with smooth eye movements.

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And then we're going
to have an overview.

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And then, lastly,
on October 23rd,

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we are going to have
the midterm exam.

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That's going to cover questions
from all of these lectures.

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I should tell you right now
that the midterm exam is going

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to consist of
multiple-choice questions.

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So you're not going to, maybe,
asked to write anything.

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You're going to
have to just pick

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from each of the questions
the correct answer.

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All right.

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So now what I would like to talk
about next in a summary fashion

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are what we call the
tools of the trade.

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What has happened
over the many years

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that scientists
tried to understand

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how the visual system and, for
that matter the brain, works,

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what kinds of methods
have been employed.

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And so I'm going to talk about
each of these just very briefly

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this time, and then they
will come up repeatedly

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during all of the lectures.

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Now, the first method
I'm going to talk about

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is called psychophysics.

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I'm sure most of you
know what that is.

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It's a scientific way to study
behavior of humans and animals

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to determine how
well they can see.

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Now, there are several
procedures with this.

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I'm going to describe
one that's used

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both in humans and monkeys.

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And what you can do nowadays,
you can use a color monitor,

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and I will describe
that in just a second.

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After that, I will
talk about anatomy.

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I will talk about
electrophysiology,

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pharmacology, brain lesions,
imaging, and optogenetics.

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So now let's start with
psychophysics in more detail.

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So here is a color monitor,
and either monkeys or humans

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can be trained to first
look at a fixation spot.

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And that's important
because we want to always

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be able to present
stimuli in selected

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locations of the visual
field or selected

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locations along the retina.

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This is particularly
important, because when

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you study the brain, different
regions of the visual field

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representation are located
in different areas,

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for example, in
the visual cortex.

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So what you do then is you
can present a single stimulus

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like this, and the task
of the human or the monkey

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is to either make a
saccadic eye movement to it,

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say that's where
it is, or to press

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a lever that's in front of them.

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And then on each trial,
it appears someplace else.

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You can present it in
many different locations,

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00:13:57,830 --> 00:13:59,590
and maybe one of
those locations will

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be relevant to what part of
the brain you are studying.

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And then what you do,
you can systematically

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vary all kinds of
aspects of the stimulus.

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You can vary the color.

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00:14:10,590 --> 00:14:12,450
You can vary the contrast.

247
00:14:12,450 --> 00:14:14,160
You can vary the size.

248
00:14:14,160 --> 00:14:16,160
You can vary the shape.

249
00:14:16,160 --> 00:14:18,460
And by systematically
varying this,

250
00:14:18,460 --> 00:14:24,730
you can create curves to
describe exactly how well you

251
00:14:24,730 --> 00:14:27,410
can see any
particular thing like,

252
00:14:27,410 --> 00:14:30,830
for example, just
how much contrast you

253
00:14:30,830 --> 00:14:32,150
need to perceive something.

254
00:14:33,340 --> 00:14:33,840
All right.

255
00:14:33,840 --> 00:14:37,170
So that's called
the detection task.

256
00:14:37,170 --> 00:14:40,310
Now, a related task, which has
also been used extensively,

257
00:14:40,310 --> 00:14:42,540
is called the
discrimination task.

258
00:14:42,540 --> 00:14:46,090
In this case, you present
a fixation spot again.

259
00:14:46,090 --> 00:14:48,250
The person or the
monkey fixates,

260
00:14:48,250 --> 00:14:51,140
and then you present a whole
bunch of stimuli, one of which

261
00:14:51,140 --> 00:14:53,020
is different from the others.

262
00:14:53,020 --> 00:14:56,260
And you have to select
where that one had appeared,

263
00:14:56,260 --> 00:14:58,920
the one that's different,
by making an eye movement

264
00:14:58,920 --> 00:15:01,120
or pressing the
appropriate lever.

265
00:15:01,120 --> 00:15:03,900
Now, when you do this,
you systematically

266
00:15:03,900 --> 00:15:09,040
can vary the difference between
the so-called distractor

267
00:15:09,040 --> 00:15:10,880
stimuli, which
are all identical,

268
00:15:10,880 --> 00:15:13,420
and the target
until the person is

269
00:15:13,420 --> 00:15:15,470
no longer able to
tell the difference.

270
00:15:15,470 --> 00:15:17,520
And that way you can,
again, generate a curve.

271
00:15:17,520 --> 00:15:21,500
And you can specify just what
is the amount of difference

272
00:15:21,500 --> 00:15:24,500
that you need to
put in this, say,

273
00:15:24,500 --> 00:15:29,400
how good are you at perceiving
slightly different colors.

274
00:15:29,400 --> 00:15:30,880
All right?

275
00:15:30,880 --> 00:15:33,110
And by doing that
systematically,

276
00:15:33,110 --> 00:15:36,430
you can generate
these functions using

277
00:15:36,430 --> 00:15:38,960
these psychophysical
procedures to determine

278
00:15:38,960 --> 00:15:42,800
pretty well how
you're able to see.

279
00:15:42,800 --> 00:15:46,560
And now this particular
approach is also very useful

280
00:15:46,560 --> 00:15:49,750
when it comes to studying
individuals, humans

281
00:15:49,750 --> 00:15:53,690
in this case, who have
some problems with vision.

282
00:15:53,690 --> 00:15:57,810
So if they have a
problem in seeing colors,

283
00:15:57,810 --> 00:16:02,300
you can readily
determine, well, what's

284
00:16:02,300 --> 00:16:03,640
the magnitude of that problem?

285
00:16:05,200 --> 00:16:09,900
And thereby it can tell
you what procedures

286
00:16:09,900 --> 00:16:15,210
might be used to try to
ameliorate their shortcoming.

287
00:16:15,210 --> 00:16:19,380
Now, another method that
has been used extensively

288
00:16:19,380 --> 00:16:22,640
in not only vision, but in
many, many different areas

289
00:16:22,640 --> 00:16:26,500
of studying the brain, including
audition of course, is anatomy.

290
00:16:26,500 --> 00:16:34,610
Numerous methods have evolved
in the course of anatomists

291
00:16:34,610 --> 00:16:38,990
working on these problems, and
the first is a very simple one.

292
00:16:38,990 --> 00:16:41,190
You just look at
the whole brain.

293
00:16:41,190 --> 00:16:43,870
And I'm showing this because
this is a monkey brain,

294
00:16:43,870 --> 00:16:47,250
and you will encounter the
monkey brain repeatedly.

295
00:16:47,250 --> 00:16:50,730
And it so happens
that after people

296
00:16:50,730 --> 00:16:53,520
have studied this
extensively, they

297
00:16:53,520 --> 00:16:55,610
were able to give
names to just about

298
00:16:55,610 --> 00:17:00,870
every gyrus or every brain
area and also relate it

299
00:17:00,870 --> 00:17:03,400
to what the function
is of those areas.

300
00:17:03,400 --> 00:17:06,190
And so, for example, just
to name a few of these,

301
00:17:06,190 --> 00:17:08,349
this is called the
central sulcus.

302
00:17:10,740 --> 00:17:12,420
I need to do one
more thing here.

303
00:17:19,491 --> 00:17:19,990
OK.

304
00:17:19,990 --> 00:17:22,680
So this here is
the central sulcus.

305
00:17:22,680 --> 00:17:23,280
All right?

306
00:17:23,280 --> 00:17:25,690
Just for you to
remember, humans also

307
00:17:25,690 --> 00:17:27,710
have a central
sulcus, of course.

308
00:17:27,710 --> 00:17:30,230
And this is the lunate sulcus.

309
00:17:30,230 --> 00:17:33,720
And this region back here--
let's see, did I label this?

310
00:17:33,720 --> 00:17:37,685
Oh, here's a couple more, the
arcuate and the principalis.

311
00:17:37,685 --> 00:17:39,960
You will encounter
these repeatedly.

312
00:17:39,960 --> 00:17:43,850
And this region
back here is the one

313
00:17:43,850 --> 00:17:50,100
which is the primary visual
cortex in monkeys that

314
00:17:50,100 --> 00:17:53,250
has been extensively
studied and has

315
00:17:53,250 --> 00:17:57,990
yielded remarkable discoveries
about the way it works.

316
00:17:57,990 --> 00:18:03,470
So that is called area V1,
or primary visual cortex.

317
00:18:03,470 --> 00:18:03,970
All right.

318
00:18:03,970 --> 00:18:06,600
So now just another
example, if I

319
00:18:06,600 --> 00:18:08,820
can show you just a few
examples of anatomy.

320
00:18:08,820 --> 00:18:13,520
Here's another example showing
what the eye looks like.

321
00:18:13,520 --> 00:18:16,310
And the remarkable thing
about the human eye,

322
00:18:16,310 --> 00:18:19,280
and the eye of monkeys
as well and primates,

323
00:18:19,280 --> 00:18:22,170
is it has become
highly specialized.

324
00:18:22,170 --> 00:18:25,890
There's a region here
which is called the fovea.

325
00:18:25,890 --> 00:18:32,140
And in that region, you have a
very, very dense distribution

326
00:18:32,140 --> 00:18:36,080
of photoreceptors and
other cells in the retina.

327
00:18:36,080 --> 00:18:39,470
And because of that, you
have very high acuity there.

328
00:18:39,470 --> 00:18:43,180
Now, because of that,
the eye movements

329
00:18:43,180 --> 00:18:48,630
have to become effective for you
to be able to see fine detail.

330
00:18:49,840 --> 00:18:51,772
So even, for example,
when you read,

331
00:18:51,772 --> 00:18:52,980
what do you do when you read?

332
00:18:52,980 --> 00:18:55,490
You make saccadic eye
movements across a line.

333
00:18:55,490 --> 00:18:58,840
Then you go down the next line
three or four saccadic eye

334
00:18:58,840 --> 00:19:00,425
movements, and so
on down the page.

335
00:19:02,070 --> 00:19:05,690
And you do that because you
cannot make out the details

336
00:19:05,690 --> 00:19:09,100
of letters in the
periphery because, there,

337
00:19:09,100 --> 00:19:13,810
the distribution of the
photoreceptors and the cells

338
00:19:13,810 --> 00:19:17,195
in the retina in general
become less and less dense.

339
00:19:18,640 --> 00:19:21,200
So that is a high
degree of specialization

340
00:19:21,200 --> 00:19:24,560
that we will discuss in
much more detail next time.

341
00:19:24,560 --> 00:19:27,980
Now then, all the fibers
from the retinal ganglion

342
00:19:27,980 --> 00:19:31,940
cells course across the
inner surface of the retina

343
00:19:31,940 --> 00:19:36,820
and go to the so-called
optic nerve through which

344
00:19:36,820 --> 00:19:40,370
over a million fibers
from the retina project

345
00:19:40,370 --> 00:19:44,070
into the nervous system.

346
00:19:44,070 --> 00:19:47,700
And how they project
exactly, what that's

347
00:19:47,700 --> 00:19:50,940
like I will discuss
in considerable detail

348
00:19:50,940 --> 00:19:52,170
the next time.

349
00:19:52,170 --> 00:19:55,600
Now, this area here
is often also called

350
00:19:55,600 --> 00:19:59,330
the blind spot,
and that you don't

351
00:19:59,330 --> 00:20:01,460
see even if you close one eye.

352
00:20:02,640 --> 00:20:05,100
But if you do a
careful experiment--

353
00:20:05,100 --> 00:20:08,150
I'll explain that the next
time-- you can actually map out

354
00:20:08,150 --> 00:20:10,845
this little region where
you don't see anything.

355
00:20:11,850 --> 00:20:14,710
They're in different
locations in the two eyes,

356
00:20:14,710 --> 00:20:19,640
so the two blind
spots do not overlap.

357
00:20:19,640 --> 00:20:22,900
And so, consequently, when
you look with both eyes,

358
00:20:22,900 --> 00:20:25,590
you don't have a,
quote, blind spot.

359
00:20:25,590 --> 00:20:29,230
So that's an example of what
the human retina looks like,

360
00:20:29,230 --> 00:20:31,460
and this has been
studied extensively

361
00:20:31,460 --> 00:20:35,150
using a whole array of
anatomical procedures.

362
00:20:35,150 --> 00:20:39,610
Now, the third anatomical
procedure I want to tell you

363
00:20:39,610 --> 00:20:42,910
is labeling individual cells.

364
00:20:42,910 --> 00:20:46,640
Now, the way this was done,
or still is being done,

365
00:20:46,640 --> 00:20:50,500
is that you slice the brain
into very, very thin sections.

366
00:20:50,500 --> 00:20:54,380
And you put them on
a glass, and then you

367
00:20:54,380 --> 00:20:56,440
can look at them
under a microscope.

368
00:20:56,440 --> 00:21:00,900
Now, here's an example of
a cross-coronal section

369
00:21:00,900 --> 00:21:03,430
of the monkey lateral
geniculate nucleus.

370
00:21:03,430 --> 00:21:06,170
That's one region in the brain
to which the retinal ganglion

371
00:21:06,170 --> 00:21:07,770
cells project.

372
00:21:07,770 --> 00:21:09,880
And it's a beautifully
layered structure,

373
00:21:09,880 --> 00:21:12,380
which I'll describe in
detail the next time.

374
00:21:12,380 --> 00:21:16,220
And these little spots
that you see here

375
00:21:16,220 --> 00:21:24,110
are actual cells, which are
labeled using a so-called Nissl

376
00:21:24,110 --> 00:21:24,610
stain.

377
00:21:25,720 --> 00:21:30,780
Now, another method
used in staining cells

378
00:21:30,780 --> 00:21:35,170
is the famous Golgi stain,
which was discovered, invented,

379
00:21:35,170 --> 00:21:38,370
perhaps, you could say, by
Golgi, for which he received

380
00:21:38,370 --> 00:21:41,010
the Nobel Prize in 1906.

381
00:21:41,010 --> 00:21:45,960
The remarkable quality
of those productions

382
00:21:45,960 --> 00:21:51,910
is that this label-- it's a
silver label-- stains not only

383
00:21:51,910 --> 00:21:55,260
the cell bodies, as the Nissl
stain you have just seen,

384
00:21:55,260 --> 00:22:00,520
but also all the processes, the
dendrites as well as the axons.

385
00:22:00,520 --> 00:22:03,430
So you see a whole
cell as a result

386
00:22:03,430 --> 00:22:05,590
of that staining procedure.

387
00:22:05,590 --> 00:22:08,370
Yet another way
to do this, which

388
00:22:08,370 --> 00:22:11,240
is more sophisticated
nowadays, is

389
00:22:11,240 --> 00:22:18,485
to record intracellularly from
a cell and then inject a label.

390
00:22:19,890 --> 00:22:23,605
This happens to be the so-called
Procion Yellow labeling

391
00:22:23,605 --> 00:22:24,105
substance.

392
00:22:24,105 --> 00:22:27,340
You inject in the eye, and then
you process the tissue again

393
00:22:27,340 --> 00:22:28,500
in thin layers.

394
00:22:28,500 --> 00:22:31,330
And this is an example
of what that looks like.

395
00:22:31,330 --> 00:22:35,260
So this also stains all
the processes of the cell.

396
00:22:35,260 --> 00:22:37,290
And the advantage
here is that you

397
00:22:37,290 --> 00:22:40,310
can study this cell
electrophysiologically

398
00:22:40,310 --> 00:22:42,520
and determine what
it is like, and then

399
00:22:42,520 --> 00:22:45,050
stain it so you can establish
the relationship what

400
00:22:45,050 --> 00:22:48,451
the cell does and what
the cell looks like.

401
00:22:48,451 --> 00:22:48,950
All right.

402
00:22:48,950 --> 00:22:53,270
So now let's turn to the
electrophysiological method,

403
00:22:53,270 --> 00:22:58,320
which is a consequence of this,
logical consequence of it.

404
00:22:58,320 --> 00:23:00,900
Once again, here we
have a monkey brain.

405
00:23:00,900 --> 00:23:07,170
And what you do here, we put
microelectrodes into the brain.

406
00:23:07,170 --> 00:23:09,310
Now, this was a
discovery that was

407
00:23:09,310 --> 00:23:12,470
made around the turn of the
century, little bit after.

408
00:23:14,000 --> 00:23:17,160
Initially,
microelectrodes were made

409
00:23:17,160 --> 00:23:21,260
from very thin tubes of
glass, which were heated

410
00:23:21,260 --> 00:23:25,485
and then pulled so that the tip
became smaller than a micron.

411
00:23:26,730 --> 00:23:28,200
So it was very, very small.

412
00:23:28,200 --> 00:23:30,205
Subsequently, other
methods were developed.

413
00:23:31,715 --> 00:23:36,870
They etched fine pieces a wire
until the tip was very, very

414
00:23:36,870 --> 00:23:39,170
small, and then they corded it.

415
00:23:39,170 --> 00:23:43,880
And they then we were able
to put these electrodes

416
00:23:43,880 --> 00:23:48,440
into the brain and record single
cells just like with glass

417
00:23:48,440 --> 00:23:49,600
pipettes.

418
00:23:49,600 --> 00:23:54,420
So the example here then is
that you take a microelectrode,

419
00:23:54,420 --> 00:23:57,700
put it into the brain,
and then that is connected

420
00:23:57,700 --> 00:24:03,430
to an amplifier
system and a computer.

421
00:24:03,430 --> 00:24:07,980
And when you do that, you can
record from a single cell.

422
00:24:07,980 --> 00:24:10,500
Now, as you well
know, single cells

423
00:24:10,500 --> 00:24:13,755
generate action potentials.

424
00:24:14,970 --> 00:24:17,850
And that is shown here
on an oscilloscope

425
00:24:17,850 --> 00:24:19,800
in a schematic fashion.

426
00:24:19,800 --> 00:24:22,930
And what some
clever people did is

427
00:24:22,930 --> 00:24:29,720
that they decided that an easy
way to process information

428
00:24:29,720 --> 00:24:35,420
about the manner
single cells generated

429
00:24:35,420 --> 00:24:39,990
action potentials is to put
this signal onto a loudspeaker

430
00:24:39,990 --> 00:24:41,080
system.

431
00:24:41,080 --> 00:24:44,020
And so every time a cell fired,
what you would literally hear

432
00:24:44,020 --> 00:24:45,700
is beep, beep, like that.

433
00:24:45,700 --> 00:24:46,400
OK?

434
00:24:46,400 --> 00:24:50,720
And so if you shown a
light on it several times,

435
00:24:50,720 --> 00:24:52,770
it will go like
brrrp, like that.

436
00:24:52,770 --> 00:24:55,300
And the big
advantage of this was

437
00:24:55,300 --> 00:24:58,284
that many cells see only a
tiny portion of the world.

438
00:24:58,284 --> 00:24:59,700
And if you don't
know where it is,

439
00:24:59,700 --> 00:25:02,980
you have to take some
projector or something

440
00:25:02,980 --> 00:25:04,190
and move it around.

441
00:25:04,190 --> 00:25:05,875
And if the receptive
field is here,

442
00:25:05,875 --> 00:25:10,040
you go, brrrp, brrrp,
brrrp, brrrp, like that.

443
00:25:10,040 --> 00:25:10,550
OK?

444
00:25:10,550 --> 00:25:13,090
And so then you can map
it out very accurately.

445
00:25:13,090 --> 00:25:16,370
Instead of having to like with
the oscilloscope, you hear it,

446
00:25:16,370 --> 00:25:21,180
and that enables you to do all
kinds of things, experiments,

447
00:25:21,180 --> 00:25:23,435
and you don't have to
look at the oscilloscope.

448
00:25:23,435 --> 00:25:25,310
But you can perform all
sorts of experiments,

449
00:25:25,310 --> 00:25:29,240
and you can hear the
responses of the cell.

450
00:25:29,240 --> 00:25:32,250
Now, another method
that is used extensively

451
00:25:32,250 --> 00:25:37,570
in electrophysiology is
called electrical stimulation.

452
00:25:37,570 --> 00:25:38,800
It's a similar process.

453
00:25:38,800 --> 00:25:41,540
You take a microelectrode,
for example, you

454
00:25:41,540 --> 00:25:48,610
put it in the brain, and then
you pass electric current.

455
00:25:48,610 --> 00:25:52,120
Typically, that electric current
is passed in such a way as

456
00:25:52,120 --> 00:25:54,360
to mimic action potentials.

457
00:25:54,360 --> 00:25:58,380
So if you are to listen to when
it's activated, again, brrrp,

458
00:25:58,380 --> 00:25:59,780
you hear that.

459
00:25:59,780 --> 00:26:02,110
But this time, instead
of the cell firing,

460
00:26:02,110 --> 00:26:06,740
you are firing the area
there, and that then

461
00:26:06,740 --> 00:26:11,170
can elicit a response, all
right, all kinds of responses.

462
00:26:11,170 --> 00:26:15,040
If you stimulate here, for
example-- remember now,

463
00:26:15,040 --> 00:26:18,380
this is the visual
system in the monkey-- as

464
00:26:18,380 --> 00:26:22,480
has been shown in humans,
electrical stimulation elicits

465
00:26:22,480 --> 00:26:25,390
a percept, a small
spot, a star-like image.

466
00:26:26,880 --> 00:26:28,730
In the auditory system
when you stimulate,

467
00:26:28,730 --> 00:26:29,835
you can hear something.

468
00:26:31,820 --> 00:26:38,020
And if you stimulate
in the areas that

469
00:26:38,020 --> 00:26:42,690
are related to moving your
eyes, then the simulation

470
00:26:42,690 --> 00:26:44,870
causes a saccadic eye movement.

471
00:26:44,870 --> 00:26:47,790
So all those methods
are very, very good

472
00:26:47,790 --> 00:26:54,950
in trying to understand better
the organization of the brain

473
00:26:54,950 --> 00:27:00,940
for, in this case for vision,
and for eye movements.

474
00:27:02,030 --> 00:27:04,320
Now, yet another
method that is used--

475
00:27:04,320 --> 00:27:07,740
several methods I should
say-- is pharmacology.

476
00:27:07,740 --> 00:27:12,230
And when you do
pharmacological experiments,

477
00:27:12,230 --> 00:27:14,830
one procedure is-- and
many different procedures,

478
00:27:14,830 --> 00:27:17,640
I'll just describe
one here-- once again,

479
00:27:17,640 --> 00:27:23,000
you can stick a glass
pipette into the brain,

480
00:27:23,000 --> 00:27:24,960
and then you can inject it.

481
00:27:24,960 --> 00:27:28,200
You can inject it either
with actually a syringe

482
00:27:28,200 --> 00:27:30,510
or using several
other methods, and you

483
00:27:30,510 --> 00:27:32,600
can inject all kinds of agents.

484
00:27:32,600 --> 00:27:36,840
For example, you can inject
a neurotransmitter analog

485
00:27:36,840 --> 00:27:42,270
or a neurotransmitter antagonist
to determine what effects it

486
00:27:42,270 --> 00:27:46,130
has in various parts of
the brain and, in our case,

487
00:27:46,130 --> 00:27:50,270
in the visual system or
the ocular motor system.

488
00:27:50,270 --> 00:27:54,140
Now, yet another method
that has been used

489
00:27:54,140 --> 00:27:56,855
is brain inactivation.

490
00:27:58,340 --> 00:28:03,285
Several procedures are available
to inactivate the brain.

491
00:28:05,410 --> 00:28:06,940
Once again, here's
a monkey brain.

492
00:28:08,300 --> 00:28:10,170
And this region
here that I already

493
00:28:10,170 --> 00:28:12,950
told you a little
bit about because

494
00:28:12,950 --> 00:28:19,870
of naming the gyri there, OK, is
called the frontal eye fields.

495
00:28:19,870 --> 00:28:23,910
This region has something
to do with moving your eyes.

496
00:28:23,910 --> 00:28:27,390
So what you can do if you
want to study and find out

497
00:28:27,390 --> 00:28:30,240
just what does this
area do, one procedure

498
00:28:30,240 --> 00:28:34,265
is to-- again, here is
V1-- is to make a lesion.

499
00:28:35,971 --> 00:28:38,880
Now, sometimes you actually
do that in a monkey.

500
00:28:38,880 --> 00:28:41,570
But sometimes in
some experiments,

501
00:28:41,570 --> 00:28:49,160
humans may have an
accident, some event when

502
00:28:49,160 --> 00:28:51,700
you served in
Vietnam or something,

503
00:28:51,700 --> 00:28:55,230
and a region of
the brain has been

504
00:28:55,230 --> 00:28:57,860
removed by virtue of
a bullet or something.

505
00:28:57,860 --> 00:29:00,700
And that way you
can find out what

506
00:29:00,700 --> 00:29:04,830
is the consequence of
having a lesion like that.

507
00:29:04,830 --> 00:29:07,120
You can study, use a
psychophysical procedure,

508
00:29:07,120 --> 00:29:11,570
as I described to
you, to determine just

509
00:29:11,570 --> 00:29:15,050
what is the consequence
of having lost this area.

510
00:29:15,050 --> 00:29:17,750
This is a huge
region of research.

511
00:29:17,750 --> 00:29:20,930
A great many types of
experiments have been done.

512
00:29:20,930 --> 00:29:24,180
One of the famous individuals
who had done this kind of work

513
00:29:24,180 --> 00:29:27,830
is Hans-Lukas Teuber,
who used to be

514
00:29:27,830 --> 00:29:31,430
the chairman of our department
starting way, way, way

515
00:29:31,430 --> 00:29:33,790
back in 1962.

516
00:29:33,790 --> 00:29:40,320
And his specialty was to study
Second World War veterans who

517
00:29:40,320 --> 00:29:43,370
had sustained various
kinds of brain injuries.

518
00:29:43,370 --> 00:29:45,480
And the basis of
that, studying them

519
00:29:45,480 --> 00:29:52,280
using psychophysical
procedures, to assess what

520
00:29:52,280 --> 00:29:57,990
various areas in the brain, what
kind of functions they have,

521
00:29:57,990 --> 00:30:00,950
what kinds of tasks
do they perform.

522
00:30:00,950 --> 00:30:05,550
Now, yet another method, which
has some major advantages,

523
00:30:05,550 --> 00:30:08,940
is to make reversible
inactivations rather than

524
00:30:08,940 --> 00:30:09,890
permanent ones.

525
00:30:10,920 --> 00:30:14,640
And this you can
do by, for example,

526
00:30:14,640 --> 00:30:16,590
using a method of cooling.

527
00:30:16,590 --> 00:30:19,810
There's a device, the
so-called Peltier device,

528
00:30:19,810 --> 00:30:22,430
that you can put on
top of the brain.

529
00:30:22,430 --> 00:30:26,410
And then electronically, you
can cool the surface that

530
00:30:26,410 --> 00:30:28,880
is in touch with
the brain, and then

531
00:30:28,880 --> 00:30:31,050
you can see what happens
when you cool it.

532
00:30:31,050 --> 00:30:33,920
And then when you
warm it up again,

533
00:30:33,920 --> 00:30:38,000
you can see what happens to
recovery, which, in this case,

534
00:30:38,000 --> 00:30:40,740
in almost all cases
like this, leads

535
00:30:40,740 --> 00:30:43,645
to full recovery and
the same performance

536
00:30:43,645 --> 00:30:46,540
as prior to starting
the cooling.

537
00:30:46,540 --> 00:30:47,040
Yes?

538
00:30:47,040 --> 00:30:50,310
AUDIENCE: Can you only use this
method for surface structures

539
00:30:50,310 --> 00:30:50,810
or?

540
00:30:50,810 --> 00:30:51,780
PROFESSOR: No.

541
00:30:51,780 --> 00:30:54,590
They have now developed
methods where you can actually

542
00:30:54,590 --> 00:30:57,190
lower them into the brain.

543
00:30:57,190 --> 00:31:02,250
And they're usually much
finer, and very often they're

544
00:31:02,250 --> 00:31:05,060
sort of a loop type device.

545
00:31:05,060 --> 00:31:08,560
And you can lower that into
the gyri or wherever you like,

546
00:31:08,560 --> 00:31:10,661
and, again, do the
reversible cooling.

547
00:31:10,661 --> 00:31:11,160
Yes.

548
00:31:12,162 --> 00:31:15,230
That's a fairly recently
developed device,

549
00:31:15,230 --> 00:31:17,115
and it works extremely well.

550
00:31:17,115 --> 00:31:21,370
Now, yet another approach
is to inject substances

551
00:31:21,370 --> 00:31:25,200
into the brain that
anesthetize, if you will,

552
00:31:25,200 --> 00:31:29,000
a particular region
after the injection,

553
00:31:29,000 --> 00:31:31,450
but only for a limited time.

554
00:31:31,450 --> 00:31:36,790
And then you can see how
the behavior is affected.

555
00:31:37,820 --> 00:31:39,490
Now, a variant of
that that I referred

556
00:31:39,490 --> 00:31:44,040
to before, of course, is
that you can use agents that

557
00:31:44,040 --> 00:31:48,790
are selective, that don't
inactivate the whole area,

558
00:31:48,790 --> 00:31:57,360
but for example, only affect
excitatory neurotransmitters

559
00:31:57,360 --> 00:31:59,570
or only affect inhibitory ones.

560
00:31:59,570 --> 00:32:01,790
So you can do kinds
of selective things.

561
00:32:01,790 --> 00:32:04,490
And so you can
establish the role

562
00:32:04,490 --> 00:32:09,120
of various neurotransmitters
in the role

563
00:32:09,120 --> 00:32:12,990
they play in
various brain areas.

564
00:32:12,990 --> 00:32:17,270
Now, yet another method
very recently developed,

565
00:32:17,270 --> 00:32:20,025
which has been incredibly
successful, is imaging.

566
00:32:21,320 --> 00:32:23,230
As you probably
all know, you all

567
00:32:23,230 --> 00:32:28,550
know we do have an
MRI facility here

568
00:32:28,550 --> 00:32:31,270
in our department on the
ground floor, and some of you

569
00:32:31,270 --> 00:32:33,850
may even have been
subjects in it.

570
00:32:33,850 --> 00:32:37,100
What that does is
when you put a subject

571
00:32:37,100 --> 00:32:39,480
into this-- the variant
of that is called

572
00:32:39,480 --> 00:32:43,470
fMRI, functional Magnetic
Resonance Imaging.

573
00:32:43,470 --> 00:32:45,980
And so if you put a person
in the magnet and you present

574
00:32:45,980 --> 00:32:50,700
a certain set of
stimuli repeatedly, OK,

575
00:32:50,700 --> 00:32:55,340
or differential ones,
whatever, the brain areas

576
00:32:55,340 --> 00:32:58,710
that are active
performing the analysis

577
00:32:58,710 --> 00:33:03,050
that you ask them
to do light up.

578
00:33:04,330 --> 00:33:08,620
So that method-- here's a
complex picture of that.

579
00:33:08,620 --> 00:33:11,030
This is one that is
in Freiberg, Germany.

580
00:33:12,370 --> 00:33:14,510
This is done with monkeys again.

581
00:33:14,510 --> 00:33:16,830
You have this device and
you put the monkey in there.

582
00:33:16,830 --> 00:33:19,820
You lower the device
on it, and then you

583
00:33:19,820 --> 00:33:24,890
can have the subject
perform trained tasks.

584
00:33:24,890 --> 00:33:26,820
And then you can
analyze the brain

585
00:33:26,820 --> 00:33:29,120
and look at the
nature of activation.

586
00:33:29,120 --> 00:33:31,530
And here's an example
of that, whatever

587
00:33:31,530 --> 00:33:33,310
this task is, doesn't matter.

588
00:33:33,310 --> 00:33:34,890
You can see that
a particular brain

589
00:33:34,890 --> 00:33:37,580
region has been very
heavily activated

590
00:33:37,580 --> 00:33:40,780
as a result of whatever
manipulation they did.

591
00:33:40,780 --> 00:33:43,780
Now, there are lots and
lots and lots of experiments

592
00:33:43,780 --> 00:33:46,960
of this sort, and we will
talk about several of those

593
00:33:46,960 --> 00:33:50,960
as we look at various
aspects of the visual system.

594
00:33:50,960 --> 00:33:54,870
Now, the last method I want to
just mention very, very briefly

595
00:33:54,870 --> 00:33:56,310
is optogenetics.

596
00:33:56,310 --> 00:33:59,040
That's a new method, and we
have actually several people

597
00:33:59,040 --> 00:34:02,510
in our department here
who are using this method.

598
00:34:02,510 --> 00:34:05,460
Now, this particular
method-- let

599
00:34:05,460 --> 00:34:09,285
me explain just very quickly
what this is all about.

600
00:34:12,010 --> 00:34:13,870
Does everybody know
what an opsin is?

601
00:34:15,030 --> 00:34:15,530
OK.

602
00:34:15,530 --> 00:34:16,738
How about if I say rhodopsin?

603
00:34:17,989 --> 00:34:18,610
OK.

604
00:34:18,610 --> 00:34:19,795
Most of you will know that.

605
00:34:19,795 --> 00:34:23,770
A rhodopsin is a
set of molecules

606
00:34:23,770 --> 00:34:27,780
that are in the rods
in the photoreceptors,

607
00:34:27,780 --> 00:34:29,579
and they are sensitive to light.

608
00:34:29,579 --> 00:34:31,120
Now, there are all
kinds of variants.

609
00:34:31,120 --> 00:34:33,774
That's why I mentioned opsins
rather than rhodopsins.

610
00:34:35,190 --> 00:34:39,960
And what can be done is
that you can selectivity

611
00:34:39,960 --> 00:34:44,989
place these various substances
into selected types of cells

612
00:34:44,989 --> 00:34:46,489
in the brain.

613
00:34:46,489 --> 00:34:52,370
And then, because these cells
become light sensitive just

614
00:34:52,370 --> 00:34:58,670
like the photoreceptors are,
then when you shine light

615
00:34:58,670 --> 00:35:09,150
onto the area where you had
placed these opsins in cells,

616
00:35:09,150 --> 00:35:10,360
you can drive them.

617
00:35:10,360 --> 00:35:14,120
You can make them respond
by turning the light on.

618
00:35:14,120 --> 00:35:16,130
Now, the amazing
thing about that

619
00:35:16,130 --> 00:35:18,600
is that makes it a
more powerful technique

620
00:35:18,600 --> 00:35:22,010
than electrical stimulation,
that you can set this up

621
00:35:22,010 --> 00:35:33,040
in such a way that, for
example, if you use a rhodopsin

622
00:35:33,040 --> 00:35:39,010
substance that is
sensitive to red light,

623
00:35:39,010 --> 00:35:43,560
it will be excited
by the red light.

624
00:35:43,560 --> 00:35:49,810
But if you have a slightly
different substance that

625
00:35:49,810 --> 00:35:52,220
would be inhibited
by blue light,

626
00:35:52,220 --> 00:35:55,020
then you can see what happens
if you excite those cells,

627
00:35:55,020 --> 00:35:56,910
and then you
inhibit those cells.

628
00:35:56,910 --> 00:36:00,210
So this gives you two
sides to the coin,

629
00:36:00,210 --> 00:36:03,340
whereas electrical stimulation
provides only one side.

630
00:36:03,340 --> 00:36:04,970
So that's a wonderful technique.

631
00:36:04,970 --> 00:36:08,200
And here's sort of a
good example of that.

632
00:36:08,200 --> 00:36:11,650
Here we have
injected-- I shouldn't

633
00:36:11,650 --> 00:36:15,980
say injected-- but
genetically labeled

634
00:36:15,980 --> 00:36:20,490
cells with
channelrhodopsin, so-called.

635
00:36:20,490 --> 00:36:24,700
And when that's done, when
you shine in a blue light,

636
00:36:24,700 --> 00:36:27,340
OK, you excite the cell.

637
00:36:27,340 --> 00:36:33,120
And then instead, if you put
in so-called halorhodopsin, OK,

638
00:36:33,120 --> 00:36:36,130
halorhodopsin, then if
you use yellow light

639
00:36:36,130 --> 00:36:37,970
you inhibit the cells.

640
00:36:37,970 --> 00:36:39,560
So that's a
remarkable technique.

641
00:36:40,820 --> 00:36:43,520
It's just at the very
beginning of things,

642
00:36:43,520 --> 00:36:46,430
so we won't talk too
much about this technique

643
00:36:46,430 --> 00:36:48,400
in studying the
visual system yet.

644
00:36:48,400 --> 00:36:50,930
But I bet you that
in another 10 years

645
00:36:50,930 --> 00:36:52,870
this is going to
be a central topic.

646
00:36:52,870 --> 00:36:53,370
All right.

647
00:36:53,370 --> 00:36:55,520
So to summarize
these techniques,

648
00:36:55,520 --> 00:36:59,730
other than the psychophysics,
just remind you again,

649
00:36:59,730 --> 00:37:02,444
number one, we have
electrical recording

650
00:37:02,444 --> 00:37:03,360
using microelectrodes.

651
00:37:05,300 --> 00:37:05,940
OK?

652
00:37:05,940 --> 00:37:08,325
Then secondly, we have
electrical stimulation.

653
00:37:09,420 --> 00:37:14,110
Thirdly, we have injection
of pharmacological agent.

654
00:37:14,110 --> 00:37:18,140
Then we have methods
to inactivate regions,

655
00:37:18,140 --> 00:37:21,420
either permanently by lesions
or reversibly by cooling

656
00:37:21,420 --> 00:37:24,320
or by injecting
various substances.

657
00:37:24,320 --> 00:37:27,030
And lastly, we have
optogenetics that

658
00:37:27,030 --> 00:37:31,200
enables you to activate
cells or inhibit cells

659
00:37:31,200 --> 00:37:34,760
by shining light onto the brain.

660
00:37:34,760 --> 00:37:38,480
So these are quite a
remarkable set of techniques.

661
00:37:38,480 --> 00:37:44,060
And individuals who want
to become neuroscientists,

662
00:37:44,060 --> 00:37:46,960
they're going to have to
learn to master not maybe

663
00:37:46,960 --> 00:37:49,390
all of these techniques,
but certainly some of them

664
00:37:49,390 --> 00:37:52,880
so that they can carry out
new and original experiments

665
00:37:52,880 --> 00:37:55,990
in determining how
the brain works

666
00:37:55,990 --> 00:37:59,070
and, in our case, of course,
how the visual system works.

667
00:37:59,070 --> 00:38:02,390
So that is, in essence then,
what I wanted to cover.

668
00:38:02,390 --> 00:38:08,040
And now we are going to move
on and have Chris tell you

669
00:38:08,040 --> 00:38:16,980
about his portion
of the course, which

670
00:38:16,980 --> 00:38:22,095
will be taught during the
second half of this semester.

671
00:38:22,095 --> 00:38:24,840
So as I said, next
time we are going

672
00:38:24,840 --> 00:38:27,250
to start talking
about, first of all,

673
00:38:27,250 --> 00:38:31,960
about the wiring of the visual
system, the basic wiring.

674
00:38:31,960 --> 00:38:35,040
And then we're going to talk
about the retina in detail

675
00:38:35,040 --> 00:38:37,950
and a little bit about the
lateral geniculate nucleus.

676
00:38:37,950 --> 00:38:39,030
That's the next lecture.

677
00:38:39,030 --> 00:38:39,876
Please.

678
00:38:39,876 --> 00:38:43,278
AUDIENCE: So for the eigtht
readings, the eight assigned

679
00:38:43,278 --> 00:38:45,870
readings that you
have on here, how

680
00:38:45,870 --> 00:38:48,138
will we know when to read what?

681
00:38:50,090 --> 00:38:51,945
PROFESSOR: Well,
that's a good question.

682
00:38:56,540 --> 00:38:58,870
The sections that have
to do with eye movements

683
00:38:58,870 --> 00:39:03,250
that you can see, that you
don't have to read until we

684
00:39:03,250 --> 00:39:06,792
get to the eye movements,
the latter part.

685
00:39:08,090 --> 00:39:13,520
Initially, when we talk about
the retina, for example,

686
00:39:13,520 --> 00:39:21,290
you definitely want to
read the [INAUDIBLE] paper

687
00:39:21,290 --> 00:39:25,325
and the Schiller paper on
parallel information processing

688
00:39:25,325 --> 00:39:25,825
channels.

689
00:39:32,660 --> 00:39:35,243
Then the ones that have to
do with the Hermann grid

690
00:39:35,243 --> 00:39:37,664
illusion and visual
prosthesis, that you

691
00:39:37,664 --> 00:39:39,080
don't have to cover
until you come

692
00:39:39,080 --> 00:39:42,160
to the section on illusions
and visual prosthesis.

693
00:39:43,697 --> 00:39:44,280
PROFESSOR: OK.

694
00:39:44,280 --> 00:39:45,270
Welcome, everybody.

695
00:39:45,270 --> 00:39:47,520
I'm Chris Brown.

696
00:39:47,520 --> 00:39:51,060
And I just, in the
remaining time,

697
00:39:51,060 --> 00:39:53,730
wanted to give you
a synopsis of what's

698
00:39:53,730 --> 00:39:56,170
going to happen during the
second half of the term.

699
00:39:57,240 --> 00:40:00,190
So I'll be giving the lectures
during the second half

700
00:40:00,190 --> 00:40:02,180
on the topic of
audition, or hearing.

701
00:40:03,230 --> 00:40:05,670
And there's my email,
chris_brown@meei.harvard.edu.

702
00:40:10,330 --> 00:40:13,370
So as you can see
by my email, I'm

703
00:40:13,370 --> 00:40:16,990
associated with Harvard, in
fact, Harvard Medical School.

704
00:40:16,990 --> 00:40:23,450
And I'm in the so-called ENT
department at Harvard Med

705
00:40:23,450 --> 00:40:27,060
School, and that stands
for Ear, Nose, and Throat.

706
00:40:27,060 --> 00:40:30,840
So some of you who are going
to be going to medical school

707
00:40:30,840 --> 00:40:33,450
will certainly do
an ENT rotation,

708
00:40:33,450 --> 00:40:36,600
where you learn about the
various aspects of ENT.

709
00:40:36,600 --> 00:40:39,290
And much of it, of
course, is the subject

710
00:40:39,290 --> 00:40:43,020
of otology, what happens
when people have disorders

711
00:40:43,020 --> 00:40:45,820
of hearing, problems
with their hearing.

712
00:40:45,820 --> 00:40:48,930
And in addition,
many ENT doctors

713
00:40:48,930 --> 00:40:51,650
also operate on people who
have head and neck cancers.

714
00:40:52,730 --> 00:40:55,160
So surgeries of
those two types go

715
00:40:55,160 --> 00:40:58,610
on at my hospital, which is
Massachusetts Eye and Ear

716
00:40:58,610 --> 00:40:59,110
Infirmary.

717
00:41:00,220 --> 00:41:03,120
And that's across
the river in Boston,

718
00:41:03,120 --> 00:41:08,860
and it is, of course, one of the
main teaching hospitals for ENT

719
00:41:08,860 --> 00:41:10,720
as well as ophthalmology.

720
00:41:10,720 --> 00:41:13,260
There's a big
Ophthalmology department

721
00:41:13,260 --> 00:41:15,460
where the ophthalmologists
deal with disorders

722
00:41:15,460 --> 00:41:17,350
of sight and vision.

723
00:41:19,480 --> 00:41:25,580
So I have an
introductory reading,

724
00:41:25,580 --> 00:41:29,380
which is a book chapter
that I wrote, and also

725
00:41:29,380 --> 00:41:33,580
with Joe Santos-Sacchi,
which is actually

726
00:41:33,580 --> 00:41:35,880
now in the fourth
edition of a textbook

727
00:41:35,880 --> 00:41:37,690
called Fundamental Neuroscience.

728
00:41:37,690 --> 00:41:41,700
And I believe this book chapter
is on the course website now.

729
00:41:41,700 --> 00:41:44,690
And it summarizes
pretty much what

730
00:41:44,690 --> 00:41:48,020
I'll cover during the
semester in a reading

731
00:41:48,020 --> 00:41:50,005
that you could probably
do in an hour or less,

732
00:41:50,005 --> 00:41:52,290
and it has many of the
figures that I'll use.

733
00:41:52,290 --> 00:41:55,030
So if you're shopping
around for a course

734
00:41:55,030 --> 00:41:57,760
and want to know what's going to
happen in the second half here,

735
00:41:57,760 --> 00:41:59,540
you can look at
that book chapter.

736
00:42:01,180 --> 00:42:03,610
There's a nice
textbook that I'll also

737
00:42:03,610 --> 00:42:05,700
be assigning a
number of readings

738
00:42:05,700 --> 00:42:07,880
from throughout
the term, and it's

739
00:42:07,880 --> 00:42:13,040
called Auditory Neuroscience,
Making Sense of Sound

740
00:42:13,040 --> 00:42:16,910
by Schnupp, Nelken, and King.

741
00:42:16,910 --> 00:42:22,490
And these fellows are, in the
case of the first and the last,

742
00:42:22,490 --> 00:42:27,400
at Oxford University, and they
work on psychophysics, that is,

743
00:42:27,400 --> 00:42:29,360
how we perceive hearing.

744
00:42:29,360 --> 00:42:31,140
And they test
humans, and they also

745
00:42:31,140 --> 00:42:33,000
do a fair amount of
animals psychophysics.

746
00:42:34,620 --> 00:42:37,150
And in the case
of Israel Nelken,

747
00:42:37,150 --> 00:42:40,360
he's at Hebrew
University in Israel.

748
00:42:40,360 --> 00:42:43,040
And he does a lot of
electrophysiological

749
00:42:43,040 --> 00:42:45,300
recordings-- you heard
about electrophysiology

750
00:42:45,300 --> 00:42:48,470
from Peter's talk just
now-- and recordings

751
00:42:48,470 --> 00:42:50,830
especially from the
auditory cortex.

752
00:42:50,830 --> 00:42:55,310
But this is a very nice
book for coverage especially

753
00:42:55,310 --> 00:42:58,780
of the central auditory
pathway in psychophysics.

754
00:42:58,780 --> 00:42:59,980
And it's pretty cheap.

755
00:42:59,980 --> 00:43:01,520
I think it's $30.

756
00:43:01,520 --> 00:43:05,640
And I believe I was told
earlier that you can get it,

757
00:43:05,640 --> 00:43:08,250
as an MIT student, online free.

758
00:43:08,250 --> 00:43:10,310
And what's good about
the online edition

759
00:43:10,310 --> 00:43:12,950
is there are lots
of demonstrations,

760
00:43:12,950 --> 00:43:16,370
each indicated by the little
icon in the margin of the text.

761
00:43:16,370 --> 00:43:18,250
And when you click on
that demonstration,

762
00:43:18,250 --> 00:43:19,820
if you have your
earbuds in you can

763
00:43:19,820 --> 00:43:22,820
hear what the sound
demonstration is.

764
00:43:22,820 --> 00:43:25,427
And I'll be doing quite a
lot of sound demonstrations

765
00:43:25,427 --> 00:43:27,510
through the course of the
semester because I think

766
00:43:27,510 --> 00:43:29,290
it livens up the
class a little bit,

767
00:43:29,290 --> 00:43:32,410
and this book is especially
good for sound demos.

768
00:43:34,184 --> 00:43:35,600
So I encourage you
at least to get

769
00:43:35,600 --> 00:43:38,150
the online edition
of that textbook.

770
00:43:40,540 --> 00:43:43,620
So also on the course
website is the syllabus

771
00:43:43,620 --> 00:43:46,990
for what the audition
lectures will cover,

772
00:43:46,990 --> 00:43:50,210
and I just put a couple
here to give you a flavor.

773
00:43:51,400 --> 00:43:54,170
In the first lecture
on October 28th,

774
00:43:54,170 --> 00:43:58,070
we'll talk about the physical
characteristics of sound

775
00:43:58,070 --> 00:44:00,110
and what happens
to that sound when

776
00:44:00,110 --> 00:44:02,940
it strikes your
external, and then

777
00:44:02,940 --> 00:44:04,820
your middle, and inner ears.

778
00:44:06,200 --> 00:44:12,120
And associated with each lecture
is an original research article

779
00:44:12,120 --> 00:44:15,420
that, in this case,
is Hofman, et al.,

780
00:44:15,420 --> 00:44:18,700
and the title is "Relearning
Sound Localization

781
00:44:18,700 --> 00:44:20,490
with New Ears."

782
00:44:20,490 --> 00:44:23,770
And so, in a nutshell, what
they did in that research report

783
00:44:23,770 --> 00:44:26,510
was they took little
pieces of clay,

784
00:44:26,510 --> 00:44:31,050
and they inserted them into
their external ears or pinna,

785
00:44:31,050 --> 00:44:35,070
and therefore distorted
quite a lot your pinnae.

786
00:44:35,070 --> 00:44:36,550
They couldn't do
what van Gogh did,

787
00:44:36,550 --> 00:44:39,270
which was cut off the
pinna, but they certainly

788
00:44:39,270 --> 00:44:42,140
distorted their pinnaes
quite a lot on both sides.

789
00:44:43,190 --> 00:44:45,430
And then they tested,
using themselves

790
00:44:45,430 --> 00:44:47,690
as subjects and
other volunteers,

791
00:44:47,690 --> 00:44:51,115
how good their ability
to localize sound was.

792
00:44:52,210 --> 00:44:56,310
And especially in terms of when
the sound varied in elevation,

793
00:44:56,310 --> 00:44:58,500
they found that there
were huge differences,

794
00:44:58,500 --> 00:45:02,140
that they couldn't localize
sounds that were straight ahead

795
00:45:02,140 --> 00:45:05,585
versus sounds that were
coming from above themselves

796
00:45:05,585 --> 00:45:06,543
with these distortions.

797
00:45:07,950 --> 00:45:10,470
But what was funny
and what harks back

798
00:45:10,470 --> 00:45:13,310
to the title of the
article is that when

799
00:45:13,310 --> 00:45:17,550
they had the volunteers go out
and live their normal lives

800
00:45:17,550 --> 00:45:21,600
with these pinna distortions
in for a few weeks,

801
00:45:21,600 --> 00:45:25,520
then they came back into the
lab and tested them again,

802
00:45:25,520 --> 00:45:30,760
they found that they could now
localize sounds in elevation

803
00:45:30,760 --> 00:45:32,560
with these new ears.

804
00:45:32,560 --> 00:45:34,790
They relearned how
to localize sound.

805
00:45:34,790 --> 00:45:38,570
So this is a nice demonstration
of learning or plasticity,

806
00:45:38,570 --> 00:45:40,560
at least in
psychophysical responses.

807
00:45:42,280 --> 00:45:44,370
And it also emphasizes
the function

808
00:45:44,370 --> 00:45:47,750
of your external ear, which
helps you localize sounds

809
00:45:47,750 --> 00:45:48,250
in space.

810
00:45:50,940 --> 00:45:54,390
In the second lecture, we'll
be talking about the receptor

811
00:45:54,390 --> 00:45:57,940
cells for hearing, which are
called hair cells because they

812
00:45:57,940 --> 00:45:59,930
have these little
appendages at their top

813
00:45:59,930 --> 00:46:04,360
that looked to the early
neuroanatomists like hairs.

814
00:46:04,360 --> 00:46:07,970
And of course, sound
is a mechanical energy

815
00:46:07,970 --> 00:46:11,760
that moves the fluid in which
these hair cells are immersed

816
00:46:11,760 --> 00:46:14,220
and moves these little
hairs or appendages

817
00:46:14,220 --> 00:46:16,100
at the top of the
cell, and that's

818
00:46:16,100 --> 00:46:19,650
how the cell can
respond then to sound.

819
00:46:19,650 --> 00:46:23,040
And so hair cells are the
very important receptor cells

820
00:46:23,040 --> 00:46:27,070
for hearing, which are, of
course, the analogs of the rods

821
00:46:27,070 --> 00:46:28,665
and cones in the visual system.

822
00:46:29,770 --> 00:46:32,300
And the research
report associated

823
00:46:32,300 --> 00:46:35,630
with our talk about
hair cells will

824
00:46:35,630 --> 00:46:40,500
be how a special protein
called prestin is required

825
00:46:40,500 --> 00:46:44,330
for electromotility, which
is a function of outer hair

826
00:46:44,330 --> 00:46:47,040
cells, one of the two
types of hair cells,

827
00:46:47,040 --> 00:46:51,360
which allows them to actually
move and flux and change

828
00:46:51,360 --> 00:46:54,560
their membrane links
when they sense

829
00:46:54,560 --> 00:46:57,950
these mechanical disturbances
by their stereocilia.

830
00:46:57,950 --> 00:47:01,025
So it's a pretty
interesting paper

831
00:47:01,025 --> 00:47:03,740
in what we call a
knockout animal.

832
00:47:03,740 --> 00:47:06,760
So the prestin is
genetically knocked out

833
00:47:06,760 --> 00:47:09,910
in this particular animal,
and the sense of hearing

834
00:47:09,910 --> 00:47:12,650
is then tested again in
these knockout animals.

835
00:47:14,730 --> 00:47:16,930
So we have a whole
bunch of lectures.

836
00:47:16,930 --> 00:47:19,441
I haven't indicated all them.

837
00:47:19,441 --> 00:47:20,690
They're on the course website.

838
00:47:22,210 --> 00:47:25,900
Toward the end of the semester,
we'll have, as Peter indicated,

839
00:47:25,900 --> 00:47:28,410
a written assignment
for audition.

840
00:47:28,410 --> 00:47:33,510
So I haven't actually
thought it up yet,

841
00:47:33,510 --> 00:47:35,940
but let me just
give you an example.

842
00:47:35,940 --> 00:47:40,160
Last year and this year,
we'll be talking a lot

843
00:47:40,160 --> 00:47:42,900
about neural prostheses
for audition.

844
00:47:42,900 --> 00:47:46,140
And the most famous neural
prosthesis for audition,

845
00:47:46,140 --> 00:47:47,892
of course, is the
cochlear implant,

846
00:47:47,892 --> 00:47:49,600
which I'll talk a
little bit about later,

847
00:47:49,600 --> 00:47:50,860
and it works quite well.

848
00:47:52,280 --> 00:47:54,430
There's also a neural
prosthesis that

849
00:47:54,430 --> 00:47:56,790
goes into the
auditory brainstem.

850
00:47:56,790 --> 00:47:59,390
It's called the auditory
brainstem implant,

851
00:47:59,390 --> 00:48:01,640
and it's used in
some other types

852
00:48:01,640 --> 00:48:03,760
of individuals who are deaf.

853
00:48:03,760 --> 00:48:06,870
And it doesn't work anywhere
near as well as the cochlear

854
00:48:06,870 --> 00:48:07,710
implant.

855
00:48:07,710 --> 00:48:11,580
It's sometimes called a
lip reading assist device

856
00:48:11,580 --> 00:48:14,570
because people who have
the brainstem implant

857
00:48:14,570 --> 00:48:17,960
usually can't understand
speech over the telephone.

858
00:48:17,960 --> 00:48:20,900
They need to be facing you
and looking at your lips

859
00:48:20,900 --> 00:48:22,370
as you're speaking.

860
00:48:22,370 --> 00:48:24,460
They need additional cues.

861
00:48:24,460 --> 00:48:26,965
And so there'll be
a lot of discussion

862
00:48:26,965 --> 00:48:29,840
this term about the
differences between these two

863
00:48:29,840 --> 00:48:31,440
types of the implant,
where they're

864
00:48:31,440 --> 00:48:34,315
put in the auditory
pathway, and why

865
00:48:34,315 --> 00:48:37,110
one works much better
than the other.

866
00:48:37,110 --> 00:48:38,830
And that was the
written assignment

867
00:48:38,830 --> 00:48:43,800
for last year, which was a
discussion of why the cochlear

868
00:48:43,800 --> 00:48:46,725
implant works a lot better than
the auditory brainstem implant.

869
00:48:46,725 --> 00:48:50,260
So I'll have something
along those lines that

870
00:48:50,260 --> 00:48:52,920
uses the material
from our course

871
00:48:52,920 --> 00:48:55,370
that you can take to
answer a question.

872
00:49:00,330 --> 00:49:00,830
OK.

873
00:49:00,830 --> 00:49:04,380
Let me just go through in
a half a dozen slides or so

874
00:49:04,380 --> 00:49:06,230
what I consider to
be the high points

875
00:49:06,230 --> 00:49:08,805
of the auditory
part of the course.

876
00:49:09,820 --> 00:49:13,030
About the first third of the
auditory part of the course

877
00:49:13,030 --> 00:49:15,520
will be a discussion of
the auditory periphery.

878
00:49:16,750 --> 00:49:19,200
And the periphery
is usually divided

879
00:49:19,200 --> 00:49:24,230
into these three basic
divisions, the external ear,

880
00:49:24,230 --> 00:49:28,360
which most of us think about as
the ear, the pinna and the ear

881
00:49:28,360 --> 00:49:33,010
canal, which leads to
the tympanic membrane

882
00:49:33,010 --> 00:49:34,545
here in yellow, or eardrum.

883
00:49:36,150 --> 00:49:39,740
And at that point
begins the middle ear.

884
00:49:39,740 --> 00:49:41,705
The middle ear is
an air-filled space.

885
00:49:42,915 --> 00:49:45,110
If you've been on a
recent plane flight

886
00:49:45,110 --> 00:49:47,630
and your ears are a
little bit stuffed up,

887
00:49:47,630 --> 00:49:50,020
it can be very uncomfortable,
especially when

888
00:49:50,020 --> 00:49:52,930
the plane is coming
down in altitude.

889
00:49:52,930 --> 00:49:56,010
And your eardrum bulges
because the eardrum is just

890
00:49:56,010 --> 00:50:00,080
a very thin layer of skin,
and it can bulge very easily.

891
00:50:00,080 --> 00:50:02,400
But it's painful
when the eardrum

892
00:50:02,400 --> 00:50:05,170
bulges when the
change in pressure

893
00:50:05,170 --> 00:50:07,060
happens as you're
descending in a plane.

894
00:50:08,830 --> 00:50:11,560
In the air-filled
space of the middle ear

895
00:50:11,560 --> 00:50:16,420
are three small bones,
the malleus, the incus,

896
00:50:16,420 --> 00:50:17,620
and the stapes.

897
00:50:17,620 --> 00:50:22,590
If you remember from high school
biology, the hammer, the anvil,

898
00:50:22,590 --> 00:50:23,640
and the stirrup.

899
00:50:23,640 --> 00:50:26,950
The stirrup looks like what
a cowboy has on his saddle

900
00:50:26,950 --> 00:50:29,820
that he puts the
cowboy boots through.

901
00:50:29,820 --> 00:50:31,530
It's a very, very small bone.

902
00:50:31,530 --> 00:50:33,820
In fact, it's the
smallest bone in the body.

903
00:50:35,406 --> 00:50:37,030
These bones are very
small because they

904
00:50:37,030 --> 00:50:39,950
have to vibrate in
response to sound,

905
00:50:39,950 --> 00:50:41,740
and so they can't
be big and massive.

906
00:50:41,740 --> 00:50:43,870
Massive things don't
vibrate very well.

907
00:50:45,140 --> 00:50:53,230
And so the stapes is sometimes
encompassed by bony growths

908
00:50:53,230 --> 00:50:56,320
around it and prevented
from vibration

909
00:50:56,320 --> 00:50:57,920
in a disease called
otosclerosis.

910
00:50:59,430 --> 00:51:01,625
And so at my hospital,
the Massachusetts Eye

911
00:51:01,625 --> 00:51:04,370
and Ear Infirmary,
they do an operation

912
00:51:04,370 --> 00:51:08,280
to cure that type of deafness
called the stapedectomy.

913
00:51:08,280 --> 00:51:09,770
So what's an -ectomy?

914
00:51:09,770 --> 00:51:12,116
You medical types,
what does that mean?

915
00:51:12,116 --> 00:51:12,930
AUDIENCE: Removal.

916
00:51:12,930 --> 00:51:14,388
PROFESSOR: It means
removal, right.

917
00:51:14,388 --> 00:51:15,790
So they take the stapes out.

918
00:51:16,850 --> 00:51:19,330
And that's because if
they just loosen it up,

919
00:51:19,330 --> 00:51:23,210
the bone regrows and re-adheres
the stapes from vibration.

920
00:51:23,210 --> 00:51:26,920
So they replace the
stapes, the natural stapes,

921
00:51:26,920 --> 00:51:32,160
with a stapes prosthesis, either
a little piston or a tube,

922
00:51:32,160 --> 00:51:35,740
that they hook on with
a wire to the incus,

923
00:51:35,740 --> 00:51:39,850
and they put into the so-called
foot plate area or oval

924
00:51:39,850 --> 00:51:42,840
window of the cochlea, which
is the next structure I'll

925
00:51:42,840 --> 00:51:44,060
talk about.

926
00:51:44,060 --> 00:51:47,440
And that very nicely restores
the sense of hearing.

927
00:51:47,440 --> 00:51:51,046
In fact, when I was a postdoc
fellow at Mass Eye and Ear,

928
00:51:51,046 --> 00:51:54,890
I could go watch the surgeries,
and I watched a stapedectomy.

929
00:51:54,890 --> 00:51:57,970
And the patient was
anesthetized, but not

930
00:51:57,970 --> 00:52:00,380
so much that she was really out.

931
00:52:00,380 --> 00:52:01,550
She was more sedated.

932
00:52:02,560 --> 00:52:04,690
And at the end of the
operation, the surgeon

933
00:52:04,690 --> 00:52:08,050
was adjusting the
artificial prosthesis,

934
00:52:08,050 --> 00:52:10,710
and the surgeon said,
well, can you hear me?

935
00:52:10,710 --> 00:52:12,900
And the patient didn't respond.

936
00:52:12,900 --> 00:52:15,720
So he moved it around a little
bit or adjusted the wire,

937
00:52:15,720 --> 00:52:16,800
I don't know which.

938
00:52:16,800 --> 00:52:18,350
He says, can you hear me now?

939
00:52:18,350 --> 00:52:21,180
And there was no response
from the patient.

940
00:52:21,180 --> 00:52:23,510
And he did a little more
manipulation and adjustment.

941
00:52:23,510 --> 00:52:25,480
And he finally said,
can you hear me?

942
00:52:25,480 --> 00:52:27,500
And the patient said, why
are you yelling at me?

943
00:52:27,500 --> 00:52:28,605
I can hear you just fine.

944
00:52:29,710 --> 00:52:31,680
So usually at the
end of the operation,

945
00:52:31,680 --> 00:52:34,320
the patient has
become more light.

946
00:52:34,320 --> 00:52:36,860
The anesthesiologist
turns off the anesthesia.

947
00:52:36,860 --> 00:52:40,930
And they adjust the stapes
prosthesis so it works well.

948
00:52:42,420 --> 00:52:46,530
So that type of operation
is fairly common

949
00:52:46,530 --> 00:52:50,640
and very successful to
restore the so-called types

950
00:52:50,640 --> 00:52:52,250
of conductive hearing loss.

951
00:52:52,250 --> 00:52:56,735
These bones conduct the acoustic
sensation into the cochlea.

952
00:52:57,920 --> 00:53:02,570
Now, in the cochlea-- this
is the structure here.

953
00:53:02,570 --> 00:53:05,180
The "cochlea" is the
word for the inner ear.

954
00:53:05,180 --> 00:53:09,770
It comes from the Greek word
"kokhlias," which means snail,

955
00:53:09,770 --> 00:53:14,570
and it is certainly a
snail shell-shaped capsule.

956
00:53:14,570 --> 00:53:18,510
The cochlea looks like
a coiled snail shell.

957
00:53:18,510 --> 00:53:22,650
And inside it are
the receptor cells

958
00:53:22,650 --> 00:53:25,690
for hearing, the hair
cells and the dendrites

959
00:53:25,690 --> 00:53:27,700
of the auditory nerve fibers.

960
00:53:27,700 --> 00:53:28,200
OK?

961
00:53:28,200 --> 00:53:31,930
And the cochlea is a
bony-filled capsule

962
00:53:31,930 --> 00:53:35,025
filled with fluid and
membranes and cells inside.

963
00:53:36,250 --> 00:53:38,600
And this anatomy is
a little bit complex,

964
00:53:38,600 --> 00:53:41,970
so I brought in a model here
of the auditory periphery.

965
00:53:41,970 --> 00:53:45,960
So we have the external
ear, the long ear canal

966
00:53:45,960 --> 00:53:47,430
here, the eardrum.

967
00:53:47,430 --> 00:53:50,220
It's kind of slanted here.

968
00:53:50,220 --> 00:53:52,850
And this part here
that I'll lift out here

969
00:53:52,850 --> 00:53:58,010
is the cochlea or the inner ear,
the snail shell-shaped area.

970
00:53:58,010 --> 00:54:01,650
And leading from it is the
yellow-colored, in this case,

971
00:54:01,650 --> 00:54:05,470
auditory nerve, which sends
messages from the cochlea

972
00:54:05,470 --> 00:54:07,160
into the brain.

973
00:54:07,160 --> 00:54:10,790
And these funny, loop-shaped
structures that I'm grasping

974
00:54:10,790 --> 00:54:15,450
are the semicircular
canals, which

975
00:54:15,450 --> 00:54:18,336
mediate the sense of balance
or angular acceleration.

976
00:54:19,390 --> 00:54:22,610
When you rotate your head,
those hair cells in there

977
00:54:22,610 --> 00:54:24,625
are sensitive to
those rotations.

978
00:54:25,980 --> 00:54:26,480
OK.

979
00:54:26,480 --> 00:54:28,380
So I'll pass this model around.

980
00:54:28,380 --> 00:54:30,760
You can take a
closer look at it.

981
00:54:30,760 --> 00:54:35,830
And in our hospital,
the surgeons practice

982
00:54:35,830 --> 00:54:41,620
on real, live specimens like
that from postmortem material

983
00:54:41,620 --> 00:54:44,440
because in otologic
surgery there's

984
00:54:44,440 --> 00:54:49,150
a lot of drilling to access,
for example, the middle ear

985
00:54:49,150 --> 00:54:50,960
or the inner ear.

986
00:54:50,960 --> 00:54:53,680
And there's a lot of
important structures

987
00:54:53,680 --> 00:54:56,210
that you don't want to run
into with your drill bit,

988
00:54:56,210 --> 00:54:59,880
like the jugular bulb
is that red thing there.

989
00:54:59,880 --> 00:55:03,620
The facial nerve goes right
through the middle ear.

990
00:55:03,620 --> 00:55:07,030
And so the surgeons need to know
their way around the middle ear

991
00:55:07,030 --> 00:55:09,700
so that they can avoid
important structures

992
00:55:09,700 --> 00:55:13,158
and go to the right structure
that they intend to operate on.

993
00:55:18,911 --> 00:55:19,410
OK.

994
00:55:19,410 --> 00:55:24,390
So you heard Dr. Schiller
talk about electrophysiology

995
00:55:24,390 --> 00:55:27,880
and recordings from
individual neurons.

996
00:55:27,880 --> 00:55:32,250
And a lot of what we know
about how the inner ear works

997
00:55:32,250 --> 00:55:34,316
comes from such
types of experiments.

998
00:55:35,360 --> 00:55:40,280
And this is an experiment
at the top here

999
00:55:40,280 --> 00:55:43,915
that gives the responses in
the form of action potentials.

1000
00:55:45,910 --> 00:55:48,750
Each one of these blips is
a little action potential,

1001
00:55:48,750 --> 00:55:54,180
or impulse, or response from
one single auditory nerve

1002
00:55:54,180 --> 00:55:58,860
fiber recorded in the
auditory nerve of a cat, which

1003
00:55:58,860 --> 00:56:02,500
is the very common model
for auditory neuroscience,

1004
00:56:02,500 --> 00:56:05,730
or at least it
was in years past.

1005
00:56:06,750 --> 00:56:13,410
So this response area is a
mapping of sound frequency.

1006
00:56:13,410 --> 00:56:16,160
So this axis is tone frequency.

1007
00:56:16,160 --> 00:56:18,360
And the frequency
of a sound wave form

1008
00:56:18,360 --> 00:56:22,450
is simply how many times
it repeats back and forth

1009
00:56:22,450 --> 00:56:23,085
per second.

1010
00:56:24,690 --> 00:56:27,390
Frequencies that are
common in human hearing

1011
00:56:27,390 --> 00:56:30,810
are, for example, 1,000 hertz.

1012
00:56:30,810 --> 00:56:34,165
This is a graph of kilohertz,
tone frequency in kilohertz.

1013
00:56:35,240 --> 00:56:36,960
And the upper limit
of human hearing

1014
00:56:36,960 --> 00:56:38,895
is approximately 20 kilohertz.

1015
00:56:40,270 --> 00:56:45,590
The lower limit of human hearing
is down around 50 or 100 hertz.

1016
00:56:45,590 --> 00:56:48,580
In terms of smaller
animals like the cat,

1017
00:56:48,580 --> 00:56:53,230
they're shifted up in frequency
of perhaps an octave, maybe

1018
00:56:53,230 --> 00:56:56,800
a doubling of the frequencies
that they're most sensitive to.

1019
00:56:57,880 --> 00:57:00,780
This auditory nerve
fiber responded

1020
00:57:00,780 --> 00:57:04,650
to a variety of frequencies,
except at the very lowest

1021
00:57:04,650 --> 00:57:06,090
sound level.

1022
00:57:06,090 --> 00:57:09,160
The y-axis is a
graph of sound level.

1023
00:57:09,160 --> 00:57:12,910
This is very low
level or soft sound,

1024
00:57:12,910 --> 00:57:14,930
this would be a
medium sound, and this

1025
00:57:14,930 --> 00:57:16,600
would be a very
high level sound.

1026
00:57:17,930 --> 00:57:21,650
At the lowest levels of sound,
the auditory nerve fiber

1027
00:57:21,650 --> 00:57:24,490
only gave a response
to frequencies

1028
00:57:24,490 --> 00:57:29,680
around 10 kilohertz, or
10,000 cycles per second.

1029
00:57:29,680 --> 00:57:34,470
There are some spontaneous
firings from the nerve fiber,

1030
00:57:34,470 --> 00:57:37,630
and those can happen even if
there's no sound presentation.

1031
00:57:37,630 --> 00:57:39,830
These neurons can be
spontaneously active.

1032
00:57:41,830 --> 00:57:44,280
If you outline
this response area,

1033
00:57:44,280 --> 00:57:46,950
you can see that it's
very sharply tuned

1034
00:57:46,950 --> 00:57:48,030
to sound frequency.

1035
00:57:48,030 --> 00:57:51,140
It only responds
around 10 kilohertz.

1036
00:57:51,140 --> 00:57:55,190
And this exquisitely sharp
tuning of the auditory nerve

1037
00:57:55,190 --> 00:57:58,550
is the way, perhaps, that the
auditory nerve sends messages

1038
00:57:58,550 --> 00:58:02,480
to the brain that there is only
10 kilohertz that the ears are

1039
00:58:02,480 --> 00:58:06,395
hearing and not 9 kilohertz
and not 11 kilohertz.

1040
00:58:07,480 --> 00:58:08,280
OK?

1041
00:58:08,280 --> 00:58:12,350
If you increase the sound
level to higher levels,

1042
00:58:12,350 --> 00:58:14,510
this auditory nerve
fiber, like others,

1043
00:58:14,510 --> 00:58:17,670
responds to a wide variety
of sound frequencies,

1044
00:58:17,670 --> 00:58:21,530
but it has a very sharp cut
off at the high frequency edge.

1045
00:58:21,530 --> 00:58:24,390
Maybe at 11 kilohertz,
it responds,

1046
00:58:24,390 --> 00:58:27,860
but 11.1 kilohertz
there's no response.

1047
00:58:27,860 --> 00:58:30,450
So the tuning becomes
broader, but there's still

1048
00:58:30,450 --> 00:58:33,870
a really nice, sharp,
high-frequency cut off.

1049
00:58:33,870 --> 00:58:35,660
So what good is this for?

1050
00:58:35,660 --> 00:58:39,610
Well, the ear is very good at
resolving frequency, saying

1051
00:58:39,610 --> 00:58:42,790
there's 10 kilohertz
but not 9 kilohertz.

1052
00:58:42,790 --> 00:58:46,610
And that's very important
for identification of sounds.

1053
00:58:46,610 --> 00:58:50,700
For example, how do we know, if
we're talking on the telephone

1054
00:58:50,700 --> 00:58:54,000
or not seeing the subject
who's talking to us,

1055
00:58:54,000 --> 00:58:57,110
that it's a female
speaker or a male speaker

1056
00:58:57,110 --> 00:58:58,980
or an infant speaker?

1057
00:58:58,980 --> 00:59:02,900
Well, male speakers
have lower frequencies

1058
00:59:02,900 --> 00:59:04,510
in their speech sounds.

1059
00:59:04,510 --> 00:59:08,350
And so right away, if we
hear a lot of low frequencies

1060
00:59:08,350 --> 00:59:10,460
in the speech sounds,
we assume we're

1061
00:59:10,460 --> 00:59:12,200
talking to a male speaker.

1062
00:59:12,200 --> 00:59:15,330
And that's, of course, a very
important identification.

1063
00:59:15,330 --> 00:59:19,220
How do we know we're
hearing the vowel A and not

1064
00:59:19,220 --> 00:59:22,930
the vowel E, ah or eh?

1065
00:59:22,930 --> 00:59:25,500
Because of the different
frequencies in the speech

1066
00:59:25,500 --> 00:59:28,540
sounds for those two vowels.

1067
00:59:28,540 --> 00:59:32,320
So frequency coding is
a very important subject

1068
00:59:32,320 --> 00:59:35,640
in the auditory pathway
for identification

1069
00:59:35,640 --> 00:59:38,015
and distinguishing
different types of sounds.

1070
00:59:39,450 --> 00:59:43,650
And one way we know what
frequencies we're listening to

1071
00:59:43,650 --> 00:59:46,190
is if the auditory
nerve fiber's tuned

1072
00:59:46,190 --> 00:59:48,080
to a particular
frequency [INAUDIBLE]

1073
00:59:48,080 --> 00:59:49,760
responding and not the others.

1074
00:59:51,390 --> 00:59:54,240
Now, some very
elegant studies have

1075
00:59:54,240 --> 01:00:00,100
been done to look at
the mapping of frequency

1076
01:00:00,100 --> 01:00:02,105
along the spiral of the cochlea.

1077
01:00:03,200 --> 01:00:05,700
And what those show
is that way down

1078
01:00:05,700 --> 01:00:09,370
at the base of the cochlea,
the very highest frequencies

1079
01:00:09,370 --> 01:00:12,730
are sensed by the hair cells
and the auditory nerve fibers

1080
01:00:12,730 --> 01:00:13,230
there.

1081
01:00:14,530 --> 01:00:17,330
And as you go more
and more apically,

1082
01:00:17,330 --> 01:00:21,630
you arrive at first middle,
and then lower frequencies.

1083
01:00:21,630 --> 01:00:24,390
So there's a very
nice, orderly mapping

1084
01:00:24,390 --> 01:00:29,020
of frequency along the
receptor epithelium,

1085
01:00:29,020 --> 01:00:31,450
or along the cochlea in
the sense of hearing.

1086
01:00:31,450 --> 01:00:35,150
And so, obviously,
the hearing organ

1087
01:00:35,150 --> 01:00:38,170
is set up to distinguish
frequencies and identify

1088
01:00:38,170 --> 01:00:38,670
sounds.

1089
01:00:41,730 --> 01:00:42,670
OK.

1090
01:00:42,670 --> 01:00:48,030
So that's not the only code for
sound frequency that we have.

1091
01:00:48,030 --> 01:00:51,840
We'll talk extensively
about another code

1092
01:00:51,840 --> 01:00:56,190
that uses a time-coding sense.

1093
01:00:56,190 --> 01:01:00,420
And this comes from the way
that auditory nerve fibers

1094
01:01:00,420 --> 01:01:04,070
so-called phase lock to
the sound's waveform.

1095
01:01:05,280 --> 01:01:11,270
Here's a sound stimulus, and
here's auditory firing, first

1096
01:01:11,270 --> 01:01:12,450
with no stimulus.

1097
01:01:12,450 --> 01:01:13,905
It's a fairly random pattern.

1098
01:01:15,310 --> 01:01:18,520
And here is with a
stimulus turned on,

1099
01:01:18,520 --> 01:01:24,070
and you can see that the spikes
line up during a certain phase

1100
01:01:24,070 --> 01:01:27,210
or part of the
stimulus waveform.

1101
01:01:27,210 --> 01:01:29,490
And that's not that
impressive until you

1102
01:01:29,490 --> 01:01:32,660
look at the time scale here.

1103
01:01:32,660 --> 01:01:36,910
As I said before, sounds that
are important in human hearing

1104
01:01:36,910 --> 01:01:40,275
are as high in frequency
as 1 kilohertz.

1105
01:01:41,470 --> 01:01:46,360
So if this is going back and
forth 1,000 times per second,

1106
01:01:46,360 --> 01:01:50,200
then the scale bar here for one
period would be 1 millisecond.

1107
01:01:51,420 --> 01:01:55,400
And so the auditory nerve is
keeping track and firing only

1108
01:01:55,400 --> 01:02:00,070
on a certain or preferential
phase of the stimulus waveform

1109
01:02:00,070 --> 01:02:02,940
with the capability
of milliseconds.

1110
01:02:02,940 --> 01:02:03,440
OK?

1111
01:02:03,440 --> 01:02:08,350
And this is a much better
phase-locking pattern

1112
01:02:08,350 --> 01:02:09,790
than you get in other senses.

1113
01:02:09,790 --> 01:02:12,160
For example, in
the visual system,

1114
01:02:12,160 --> 01:02:17,680
when you flash the light on
and off just even 100 flashes

1115
01:02:17,680 --> 01:02:21,590
per second, everything
sort of blears out,

1116
01:02:21,590 --> 01:02:24,360
and you sort of don't
have any phase locking

1117
01:02:24,360 --> 01:02:27,560
the way you do in the
auditory nerves firing.

1118
01:02:27,560 --> 01:02:32,290
So this is a very nice coding
for sound frequency that

1119
01:02:32,290 --> 01:02:34,960
is sort of a
secondary way to code.

1120
01:02:34,960 --> 01:02:40,050
This is a very important
coding for musical sounds.

1121
01:02:40,050 --> 01:02:44,400
Musical sounds, for
example, like an octave,

1122
01:02:44,400 --> 01:02:49,570
1 kilohertz and 2 kilohertz,
a doubling of sound frequency,

1123
01:02:49,570 --> 01:02:53,960
have very similar patterns
in their temporal responses

1124
01:02:53,960 --> 01:02:56,320
to those two frequencies
that probably

1125
01:02:56,320 --> 01:03:01,290
makes an octave a very beautiful
musical interval to listen to.

1126
01:03:01,290 --> 01:03:05,860
And it appears in music of many
different types of cultures.

1127
01:03:05,860 --> 01:03:07,600
So one of the
demonstrations that I'll

1128
01:03:07,600 --> 01:03:12,170
play for you is
an A for 40 hertz

1129
01:03:12,170 --> 01:03:15,990
and an octave above that,
880 hertz, and you'll

1130
01:03:15,990 --> 01:03:19,310
hear how beautiful the
two sound together.

1131
01:03:19,310 --> 01:03:21,900
And then I'll mistune
them, which is easy for me

1132
01:03:21,900 --> 01:03:24,670
to do because I'm an
amateur violinist,

1133
01:03:24,670 --> 01:03:26,410
and I'll be doing
this on a violin.

1134
01:03:26,410 --> 01:03:30,680
And it's pretty easy to
have a mistuned octave,

1135
01:03:30,680 --> 01:03:33,550
and it sounds so awful
and very dissonant

1136
01:03:33,550 --> 01:03:35,160
when you listen to it.

1137
01:03:35,160 --> 01:03:37,730
And one of the reasons for
that, the reason for that,

1138
01:03:37,730 --> 01:03:41,090
is the difference
in phase locking

1139
01:03:41,090 --> 01:03:45,382
for the two dissonant sounds
versus the two consonant

1140
01:03:45,382 --> 01:03:45,881
sounds.

1141
01:03:50,341 --> 01:03:50,840
OK.

1142
01:03:50,840 --> 01:03:53,960
So we will talk
about what happens

1143
01:03:53,960 --> 01:03:56,395
when you have problems
with your hearing.

1144
01:03:58,410 --> 01:04:01,100
One of the main
problems with hearing

1145
01:04:01,100 --> 01:04:04,340
that causes loss,
complete loss of hearing,

1146
01:04:04,340 --> 01:04:10,200
is when the receptor
cells are attacked

1147
01:04:10,200 --> 01:04:15,770
by various types of
insults, diseases, drugs,

1148
01:04:15,770 --> 01:04:20,120
the aging process,
stimulation, or listening

1149
01:04:20,120 --> 01:04:22,370
to very high-level sounds.

1150
01:04:22,370 --> 01:04:24,270
These can all kill
the hair cells.

1151
01:04:25,550 --> 01:04:28,890
And in the mammalian cochlea,
once the hair cells are lost

1152
01:04:28,890 --> 01:04:30,700
they never grow back.

1153
01:04:30,700 --> 01:04:33,070
And there's very active
interest in trying

1154
01:04:33,070 --> 01:04:35,720
to get hair cells to
regenerate by using

1155
01:04:35,720 --> 01:04:38,910
stem cells or various
growth factors,

1156
01:04:38,910 --> 01:04:40,485
but so far that
can't be achieved.

1157
01:04:42,040 --> 01:04:45,160
Luckily, in the
auditory periphery,

1158
01:04:45,160 --> 01:04:47,860
even if you lose the
hair cells, which

1159
01:04:47,860 --> 01:04:50,700
is the major cause
of deafness, you

1160
01:04:50,700 --> 01:04:53,310
retain your auditory
nerve fibers.

1161
01:04:53,310 --> 01:04:57,050
So these blue structures here
are the auditory nerve fibers

1162
01:04:57,050 --> 01:04:59,070
coming from the hair cells.

1163
01:04:59,070 --> 01:05:02,480
And even if the hair
cells are killed

1164
01:05:02,480 --> 01:05:05,330
by these various insults,
the auditory nerve fibers,

1165
01:05:05,330 --> 01:05:06,745
or at least many
of them, remain.

1166
01:05:08,920 --> 01:05:12,550
So you heard Dr. Schiller talk
about electrical stimulation.

1167
01:05:13,700 --> 01:05:16,880
You can put an electrical
stimulating electrode

1168
01:05:16,880 --> 01:05:21,590
in the inner ear and stimulate
those remaining auditory nerve

1169
01:05:21,590 --> 01:05:25,510
fibers to fire impulses
that are sent to the brain.

1170
01:05:25,510 --> 01:05:27,490
And if you hook that
system up right,

1171
01:05:27,490 --> 01:05:30,065
you have a so-called
cochlear implant.

1172
01:05:30,065 --> 01:05:35,530
The cochlear implant has a
microphone that detects sound.

1173
01:05:35,530 --> 01:05:41,760
It has a processor that converts
that sound into various pulses

1174
01:05:41,760 --> 01:05:43,990
of electrical stimulating
current, which

1175
01:05:43,990 --> 01:05:46,700
can be applied to a
system of electrodes

1176
01:05:46,700 --> 01:05:49,360
that is inserted
into the cochlea.

1177
01:05:49,360 --> 01:05:53,710
The cochlea is a
beautiful bony capsule.

1178
01:05:53,710 --> 01:05:55,990
You can snake this electrode in.

1179
01:05:55,990 --> 01:05:57,100
It doesn't move away.

1180
01:05:57,100 --> 01:05:58,360
You can glue it in place.

1181
01:05:59,540 --> 01:06:02,830
You can lead the electrode
out to the processor that

1182
01:06:02,830 --> 01:06:08,160
activates it when the
subject hears a sound that's

1183
01:06:08,160 --> 01:06:09,830
detected by the microphone.

1184
01:06:09,830 --> 01:06:14,520
And this cochlear implant
is the most successful

1185
01:06:14,520 --> 01:06:17,460
neural prosthesis
that's been developed.

1186
01:06:17,460 --> 01:06:21,700
It's implanted all the time
at Mass Eye and Ear Infirmary.

1187
01:06:21,700 --> 01:06:24,950
It's paid for by insurance.

1188
01:06:24,950 --> 01:06:27,680
These days, insurance pays
for a cochlear implant

1189
01:06:27,680 --> 01:06:29,545
in your left cochlea
if you're deaf,

1190
01:06:29,545 --> 01:06:32,230
and it will also pay for
another cochlear implant

1191
01:06:32,230 --> 01:06:35,310
in your right cochlea
if you're deaf.

1192
01:06:35,310 --> 01:06:38,790
So the metric for how
successful this is,

1193
01:06:38,790 --> 01:06:41,940
is whether the subject who's
using the cochlear implant

1194
01:06:41,940 --> 01:06:43,090
can understand speech.

1195
01:06:44,150 --> 01:06:47,750
And so you can have
various tests of speech.

1196
01:06:47,750 --> 01:06:51,510
A speaker can give a sentence,
and the person can respond.

1197
01:06:53,000 --> 01:06:55,780
The speaker can give
various simple words,

1198
01:06:55,780 --> 01:06:57,710
and the cochlear implant
user can respond.

1199
01:06:57,710 --> 01:07:02,021
You can test these individuals
in a very straightforward

1200
01:07:02,021 --> 01:07:02,520
manner.

1201
01:07:02,520 --> 01:07:07,310
And we will have a demonstration
by a cochlear implant user.

1202
01:07:07,310 --> 01:07:11,720
I have an undergraduate
demonstrator who's here at MIT.

1203
01:07:11,720 --> 01:07:15,300
And she'll come in and
she'll describe and show you

1204
01:07:15,300 --> 01:07:18,790
her cochlear implant, and
you can ask her questions.

1205
01:07:18,790 --> 01:07:23,150
And there, I guarantee you with
this particular demonstration

1206
01:07:23,150 --> 01:07:25,720
that I have in mind,
that she won't always

1207
01:07:25,720 --> 01:07:27,870
understand your questions.

1208
01:07:27,870 --> 01:07:31,780
I have had really great
cochlear implant users

1209
01:07:31,780 --> 01:07:34,810
who are superstars, that
understand every word.

1210
01:07:34,810 --> 01:07:38,470
But the more norm is they
understand much of what you say

1211
01:07:38,470 --> 01:07:40,150
but not everything.

1212
01:07:40,150 --> 01:07:42,840
And this particular room is
a little bit challenging.

1213
01:07:42,840 --> 01:07:44,545
There's some noise
in the background.

1214
01:07:45,750 --> 01:07:49,100
It's not one-on-one,
so the implant user

1215
01:07:49,100 --> 01:07:52,080
won't know exactly
who's speaking at once.

1216
01:07:52,080 --> 01:07:56,780
And in this case, the person
just has one ear implanted,

1217
01:07:56,780 --> 01:08:01,840
so her ability to localize
sounds is compromised.

1218
01:08:01,840 --> 01:08:04,980
And she won't know who's asking
the question until she sort

1219
01:08:04,980 --> 01:08:07,200
of zeroes in a little bit on it.

1220
01:08:07,200 --> 01:08:11,700
So you'll see the cochlear
implant is not perfect,

1221
01:08:11,700 --> 01:08:15,200
but it's pretty
good in its metric

1222
01:08:15,200 --> 01:08:16,899
for speech comprehension.

1223
01:08:22,230 --> 01:08:22,730
OK.

1224
01:08:23,800 --> 01:08:27,340
Now, I said this particular
cochlear implant user only

1225
01:08:27,340 --> 01:08:29,149
has one implant in one ear.

1226
01:08:30,565 --> 01:08:34,590
To really be good
at localizing sound,

1227
01:08:34,590 --> 01:08:37,770
we need to have
two ears, and there

1228
01:08:37,770 --> 01:08:40,809
are the so-called binaural
cues for sound localization.

1229
01:08:42,380 --> 01:08:46,779
Here's a subject listening
to a sound source.

1230
01:08:46,779 --> 01:08:49,420
The sound source is
emitting sound here,

1231
01:08:49,420 --> 01:08:52,454
and it gets to the
subject's left ear first.

1232
01:08:53,700 --> 01:08:56,950
And a short time later, it gets
to the subject's right ear.

1233
01:08:56,950 --> 01:09:01,580
And that's one of the cues for
binaural localization of sound,

1234
01:09:01,580 --> 01:09:03,800
which is interaural
time difference.

1235
01:09:04,830 --> 01:09:10,814
The velocity of sound in air
is 342 meters per second.

1236
01:09:12,279 --> 01:09:14,490
And depending on how
big your head is,

1237
01:09:14,490 --> 01:09:18,080
you can calculate the
Interaural Time Difference.

1238
01:09:18,080 --> 01:09:20,890
And of course,
that ITD is maximal

1239
01:09:20,890 --> 01:09:25,529
if the sound source is
located off to one side,

1240
01:09:25,529 --> 01:09:27,791
and it's exactly zero
if the sound source

1241
01:09:27,791 --> 01:09:29,390
is located straight ahead.

1242
01:09:30,290 --> 01:09:30,790
OK?

1243
01:09:30,790 --> 01:09:34,340
So that is a cue for
localization of sounds.

1244
01:09:34,340 --> 01:09:38,051
We'll listen to sounds that
differ in interaural time

1245
01:09:38,051 --> 01:09:38,550
difference.

1246
01:09:38,550 --> 01:09:41,080
We can play these through
headphones for you.

1247
01:09:41,080 --> 01:09:42,990
And we'll have some
demonstrations of that.

1248
01:09:44,290 --> 01:09:47,189
The other binaural cue
for sound localization

1249
01:09:47,189 --> 01:09:50,500
is the interaural
level difference.

1250
01:09:50,500 --> 01:09:53,075
Here is the same sound
source, same subject.

1251
01:09:54,380 --> 01:09:59,370
This ear will experience a
slightly higher sound level

1252
01:09:59,370 --> 01:10:02,840
than the other ear because
sound can't perfectly

1253
01:10:02,840 --> 01:10:04,305
bend around the head.

1254
01:10:04,305 --> 01:10:06,670
The head creates a sound shadow.

1255
01:10:06,670 --> 01:10:10,670
And this is especially important
for high frequencies of sound,

1256
01:10:10,670 --> 01:10:13,130
like above 3 kilohertz.

1257
01:10:13,130 --> 01:10:17,340
So that is a second binaural
cue for sound localization.

1258
01:10:18,470 --> 01:10:21,160
We'll listen to those cues.

1259
01:10:21,160 --> 01:10:26,120
And we'll talk a lot about
the brainstem processing

1260
01:10:26,120 --> 01:10:28,593
of those binaural cues
for sound localization.

1261
01:10:29,610 --> 01:10:33,930
If you compare the visual
and the auditory pathways--

1262
01:10:33,930 --> 01:10:36,470
this is a block diagram
of the auditory pathway,

1263
01:10:36,470 --> 01:10:39,440
and there are a lot
of brainstem nuclei.

1264
01:10:40,670 --> 01:10:45,900
We have the cochlear nucleus,
the superior olivary complex,

1265
01:10:45,900 --> 01:10:48,065
and the inferior colliculus.

1266
01:10:48,065 --> 01:10:53,030
And these latter two get input
from the two ears on the two

1267
01:10:53,030 --> 01:10:56,190
sides, and they
probably do the bulk

1268
01:10:56,190 --> 01:10:59,406
of the neural processing
for sound localization.

1269
01:11:00,750 --> 01:11:04,020
You don't have to do that
so much in the visual system

1270
01:11:04,020 --> 01:11:05,910
because the visual
system, in a sense,

1271
01:11:05,910 --> 01:11:09,515
has a mapping of external
space already on the retina.

1272
01:11:10,540 --> 01:11:13,920
But remember, the inner
ears map sound frequency.

1273
01:11:13,920 --> 01:11:16,850
And so the inner ears
themselves don't know

1274
01:11:16,850 --> 01:11:19,730
or don't have a
good cue for where

1275
01:11:19,730 --> 01:11:22,220
the sound is localized in space.

1276
01:11:22,220 --> 01:11:25,750
Instead, you need input
from the two sides,

1277
01:11:25,750 --> 01:11:28,610
and you need a lot
of neural processing

1278
01:11:28,610 --> 01:11:31,640
to help you determine
where that sound source is

1279
01:11:31,640 --> 01:11:33,200
coming from in space.

1280
01:11:34,880 --> 01:11:35,380
OK.

1281
01:11:35,380 --> 01:11:37,440
So we'll talk about
the neural processing

1282
01:11:37,440 --> 01:11:38,815
of those binaural cues.

1283
01:11:41,060 --> 01:11:42,920
We'll talk toward
the end of the course

1284
01:11:42,920 --> 01:11:46,940
about the various
auditory cortical fields.

1285
01:11:46,940 --> 01:11:50,780
These are the cortical fields
in the side of the cat's brain.

1286
01:11:52,070 --> 01:11:54,090
So this is the
front of the brain.

1287
01:11:54,090 --> 01:11:56,220
This is looking at the
left side of the brain.

1288
01:11:56,220 --> 01:11:59,360
This is the rear of the brain
where the occipital lobes are,

1289
01:11:59,360 --> 01:12:01,650
where V1 is.

1290
01:12:01,650 --> 01:12:03,650
And on the side or
temporal cortex,

1291
01:12:03,650 --> 01:12:06,340
you have the auditory
fields, including

1292
01:12:06,340 --> 01:12:09,000
A1 or primary auditory cortex.

1293
01:12:11,130 --> 01:12:13,720
And we'll talk, at least
touch upon a little bit,

1294
01:12:13,720 --> 01:12:18,190
toward the end of the course
the human auditory-- primary

1295
01:12:18,190 --> 01:12:21,820
auditory cortical field is right
here on the superior surface

1296
01:12:21,820 --> 01:12:25,850
of the superior temporal gyrus.

1297
01:12:25,850 --> 01:12:29,930
And just near it, it could be
called an auditory association

1298
01:12:29,930 --> 01:12:33,090
area, is an area
called Wernicke's area

1299
01:12:33,090 --> 01:12:35,925
that's very important in
processing of language.

1300
01:12:36,970 --> 01:12:38,480
And of course,
connected with that

1301
01:12:38,480 --> 01:12:41,790
is the Broca's area, which
is another important language

1302
01:12:41,790 --> 01:12:46,270
center, in the dominant
hemisphere at least, of humans.

1303
01:12:46,270 --> 01:12:49,880
So we'll touch upon that at
the very end of the course.

1304
01:12:49,880 --> 01:12:54,240
And we'll also have a special
topic called bat echolocation,

1305
01:12:54,240 --> 01:12:59,320
how bats use their auditory
sense to navigate around

1306
01:12:59,320 --> 01:13:01,670
the world at night even
without their vision.

1307
01:13:03,870 --> 01:13:07,730
And finally, at the very last
class period before the review

1308
01:13:07,730 --> 01:13:11,950
sessions, we'll all go over
for a tour of the research lab

1309
01:13:11,950 --> 01:13:14,650
where I work at the
Massachusetts Eye and Ear

1310
01:13:14,650 --> 01:13:15,810
Infirmary.

1311
01:13:15,810 --> 01:13:19,150
So it's across the Longfellow
Bridge right at the end

1312
01:13:19,150 --> 01:13:21,530
there where the arrow is.

1313
01:13:21,530 --> 01:13:24,570
And we'll have some
demonstrations there.

1314
01:13:24,570 --> 01:13:27,210
I think last year we
had a demonstration

1315
01:13:27,210 --> 01:13:31,640
on single-unit recording
from an awake animal that's

1316
01:13:31,640 --> 01:13:32,735
listening to sound.

1317
01:13:33,860 --> 01:13:38,140
We had measurements from humans
of the so-called otoacoustic

1318
01:13:38,140 --> 01:13:38,860
emissions.

1319
01:13:38,860 --> 01:13:41,540
These are sounds
that can be detected

1320
01:13:41,540 --> 01:13:44,630
in the ear canal with a
very sensitive microphone.

1321
01:13:44,630 --> 01:13:47,100
They're used in
tests of hearing.

1322
01:13:47,100 --> 01:13:49,890
And I also think
we had a discussion

1323
01:13:49,890 --> 01:13:52,560
of imaging of the
auditory system.

1324
01:13:52,560 --> 01:13:56,720
And of course, if you've ever
listened to an MRI machine,

1325
01:13:56,720 --> 01:13:58,620
it's sort of described
sometimes as being

1326
01:13:58,620 --> 01:14:01,850
as loud as being inside
a washing machine.

1327
01:14:01,850 --> 01:14:04,670
And it's very
challenging for people

1328
01:14:04,670 --> 01:14:07,650
that image subjects
who are listening

1329
01:14:07,650 --> 01:14:10,270
to especially very
low-level sounds

1330
01:14:10,270 --> 01:14:14,270
when there's all this background
noise coming from the imaging

1331
01:14:14,270 --> 01:14:14,770
machine.

1332
01:14:14,770 --> 01:14:16,640
So there's some
special things that

1333
01:14:16,640 --> 01:14:19,390
are done to minimize
the noise coming

1334
01:14:19,390 --> 01:14:23,550
from the imager in
auditory studies.