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PROFESSOR: So
today, we are going

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to talk about the midget
and parasol channels.

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00:00:32,330 --> 00:00:41,080
I will begin by reminding you
of what these two channels are

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that I very briefly
talked about before.

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Namely, if you look at the
Golgi stain of cross sections

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of the retina, when you look
at just the ganglion cells,

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00:00:53,740 --> 00:01:00,310
it was discovered
initially by the inventors,

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00:01:00,310 --> 00:01:05,060
if you will, of the
Golgi stain, namely,

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Golgi himself and Cajal.

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00:01:07,350 --> 00:01:09,220
Cajal did this, initially.

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And then, subsequently, a
fellow whose name is down here,

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Polyak, has used the same
technique to study the retina.

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And what he discovered
was-- not Polyak initially,

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00:01:20,700 --> 00:01:23,490
but Cajal initially
discovered, and then was

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00:01:23,490 --> 00:01:26,480
verified by Polyak using
these anatomical techniques,

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00:01:26,480 --> 00:01:28,770
namely, the Golgi
stain-- that there's

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00:01:28,770 --> 00:01:32,700
one class of cells that have
very small dendritic arbors,

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as you can see here,
and another set that

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00:01:35,820 --> 00:01:38,310
has much, much larger arbors.

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00:01:38,310 --> 00:01:41,010
Now, once this was
discovered, subsequently when

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00:01:41,010 --> 00:01:44,350
it became possible to
record from individual cells

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00:01:44,350 --> 00:01:46,170
and to study their
receptive fields

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00:01:46,170 --> 00:01:50,990
and their basic organization,
and also to look

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00:01:50,990 --> 00:01:52,920
at them from a
different point of view,

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00:01:52,920 --> 00:01:55,980
it was, first of
all, shown that these

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00:01:55,980 --> 00:01:58,250
are two very distinct
classes of cells

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00:01:58,250 --> 00:02:01,910
in terms of the dendritic
arbors they create.

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00:02:01,910 --> 00:02:03,950
And as I mentioned
to you before,

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00:02:03,950 --> 00:02:06,450
these cells are
called parasol cells

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00:02:06,450 --> 00:02:09,340
because the dendritic arbors
look like an umbrella.

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00:02:09,340 --> 00:02:11,060

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00:02:11,060 --> 00:02:14,220
And at comparable
eccentricities,

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00:02:14,220 --> 00:02:17,500
the midget cells are three
times smaller in diameter

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00:02:17,500 --> 00:02:20,410
than are the so-called
parasol cells.

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00:02:20,410 --> 00:02:23,140
And then I showed you
some data the last time

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00:02:23,140 --> 00:02:26,020
indicating that these
two types of cells

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00:02:26,020 --> 00:02:30,090
conduct at different velocities
to the central nervous system,

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00:02:30,090 --> 00:02:34,260
with these bigger cells
having bigger axons conducting

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00:02:34,260 --> 00:02:37,260
significantly faster
than the midget cells,

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00:02:37,260 --> 00:02:41,070
and that you get a
distribution when you record

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00:02:41,070 --> 00:02:47,790
from all the axons in the
retinal geniculate pathway

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00:02:47,790 --> 00:02:52,300
that they form separate
populations because, initially,

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the argument was that
maybe this is just

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00:02:54,670 --> 00:02:56,880
a continuous
population of cells.

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00:02:56,880 --> 00:02:58,410
But it turns out
these are indeed

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00:02:58,410 --> 00:03:02,350
two very distinct classes
on the anatomical level

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as well as the conduction
velocity level.

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Then when it became possible
to record from single neurons

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00:03:09,500 --> 00:03:11,215
and to study their
receptive fields,

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00:03:11,215 --> 00:03:13,350
it was shown-- I
showed you this picture

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before as well--
that you have, first

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of all, center-surround
organization as discovered

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by Kuffler; and secondly, that
the midget and parasol cells

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are very different in size as
far as the receptive fields

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are concerned as well
as the dendritic arbors;

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and that the midget
cells in central retina

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receive an input from
just a single cone,

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whereas the parasol cells
got a multiple input.

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And another distinction
that was, at that time, made

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is that the neuronal
responses are

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such that midget cells respond
in a much more sustained

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fashion when you
activate the center

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mechanism than do
the parasol cells.

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00:03:52,750 --> 00:03:55,070
So these respond much
more transiently.

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00:03:55,070 --> 00:03:59,590
So this, then, were
initial cues as to what

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00:03:59,590 --> 00:04:02,670
might be involved as to why
we have these two systems.

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And there were all
kinds of hypotheses.

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And then, eventually,
in the '60s and '70s

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and especially in the '80s and
'90s, all kinds of experiments

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were carried out to
try to establish just

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why these two separate
systems have evolved.

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So now, when the anatomical
work was further progressing,

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it was found, as I have
mentioned also the last time

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00:04:31,890 --> 00:04:36,020
to you, that each cone in
the retina-- certainly true

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00:04:36,020 --> 00:04:39,930
for the red and the
green cones, which

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00:04:39,930 --> 00:04:42,400
would be equivalent
to the midget system--

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00:04:42,400 --> 00:04:46,530
gives rise to an ON and
an OFF bipolar cell.

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00:04:46,530 --> 00:04:49,110
Those are the ones we
discussed the last time.

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00:04:49,110 --> 00:04:51,160
What I did not
discuss the last time,

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00:04:51,160 --> 00:04:52,960
and I'm not going to
discuss today either

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00:04:52,960 --> 00:04:56,900
but will the next time we
talk about color perception,

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00:04:56,900 --> 00:04:59,560
is that the blue
cones-- how many of you

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00:04:59,560 --> 00:05:02,973
remember what is the frequency
of blue cones in the retina?

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00:05:02,973 --> 00:05:03,780
AUDIENCE: 1 in 8.

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00:05:03,780 --> 00:05:04,870
PROFESSOR: 1 in 8.

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00:05:04,870 --> 00:05:05,440
Very good.

97
00:05:05,440 --> 00:05:06,530

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00:05:06,530 --> 00:05:07,620
Excellent.

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00:05:07,620 --> 00:05:11,480
So that being the case, that
already makes them different

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00:05:11,480 --> 00:05:13,960
because the numerosity's
so much lower.

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00:05:13,960 --> 00:05:16,620
And then people have done
all kinds of recordings,

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00:05:16,620 --> 00:05:19,430
and to this day,
it's not quite clear

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00:05:19,430 --> 00:05:21,380
what the connection
or pattern is.

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00:05:21,380 --> 00:05:23,410
But as I said, next time,
we will talk about it

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00:05:23,410 --> 00:05:25,570
in some detail when
we talk about color.

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00:05:25,570 --> 00:05:28,280
But here, don't get frightened,
we will discuss this

107
00:05:28,280 --> 00:05:29,110
the next time.

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00:05:29,110 --> 00:05:32,300
But at any rate, we
have the blue cones.

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00:05:32,300 --> 00:05:35,440
And when we talk
about color opponency

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00:05:35,440 --> 00:05:37,940
that I will explain
the next time,

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00:05:37,940 --> 00:05:42,230
we think of the opponency
to blue being yellow,

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00:05:42,230 --> 00:05:45,090
and the opponency
to red being green.

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00:05:45,090 --> 00:05:47,690
And so the assumption
here was made

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00:05:47,690 --> 00:05:49,540
that the connections
in this case,

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00:05:49,540 --> 00:05:53,475
somehow, must take place
to create color opponency.

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00:05:53,475 --> 00:05:55,580

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And since we have only three
kinds of cones in the retina,

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00:05:58,950 --> 00:06:01,430
in the primate-- red,
green, and blue--

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00:06:01,430 --> 00:06:03,330
the opponency here
must, somehow,

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00:06:03,330 --> 00:06:05,340
involve both the
red and green cones.

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00:06:05,340 --> 00:06:08,960
So that's the complication that
we will discuss the next time.

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00:06:08,960 --> 00:06:10,605
And so the assumption
was made that we

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00:06:10,605 --> 00:06:14,160
have some so-called yellow/blue
cells and blue/yellow cells.

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00:06:14,160 --> 00:06:16,660
And so I just want
to keep you puzzled

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00:06:16,660 --> 00:06:20,470
as to what this
means, especially

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00:06:20,470 --> 00:06:23,500
what it means with respect
to how we can see colors.

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00:06:23,500 --> 00:06:25,570
And that's what we will
talk about the next time.

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00:06:25,570 --> 00:06:26,580

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00:06:26,580 --> 00:06:29,610
So now, here we have,
by contrast-- and we

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00:06:29,610 --> 00:06:33,010
go back here-- here, this
is, then, the midget system.

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00:06:33,010 --> 00:06:34,450

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And I showed you
the two extremes,

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00:06:36,190 --> 00:06:38,850
which are very clear,
and in between, which

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00:06:38,850 --> 00:06:43,090
would be somehow
creating the blue system.

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00:06:43,090 --> 00:06:46,780
So that's the midget system
with very small receptive fields

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and very small cells.

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00:06:48,860 --> 00:06:52,560
Now, by contrast, when you look
at the parasol system, what

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00:06:52,560 --> 00:06:57,190
you see here is, as indicated
by the picture I showed you

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00:06:57,190 --> 00:07:00,480
just a minute ago, is that the
receptive fields are bigger.

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00:07:00,480 --> 00:07:02,390
The ganglion cell's
a lot bigger.

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00:07:02,390 --> 00:07:06,180
And the dendritic arbors
are much more extensive.

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00:07:06,180 --> 00:07:09,360
Now, that means, by the
way-- I shouldn't even say

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00:07:09,360 --> 00:07:11,650
"by the way"-- that
means, very importantly,

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00:07:11,650 --> 00:07:18,720
that the ON and OFF bipolar
cells that connect with the ON

145
00:07:18,720 --> 00:07:26,560
and OFF cells of the parasol
system are also much bigger

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00:07:26,560 --> 00:07:30,010
and have much more extensive
arbors, dendritic arbors,

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00:07:30,010 --> 00:07:32,905
because they sample many
cells instead of just one.

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00:07:32,905 --> 00:07:34,880

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00:07:34,880 --> 00:07:38,420
But overall, what this
means is that when

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00:07:38,420 --> 00:07:41,930
you look at the bipolar
cells in the retina,

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00:07:41,930 --> 00:07:45,400
there are about three
times as many bipolar cells

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than there are photoreceptors.

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00:07:46,650 --> 00:07:47,666

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00:07:47,666 --> 00:07:49,290
Now, if you think
about this-- somebody

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00:07:49,290 --> 00:07:55,770
remembered the last
time-- that in the retina,

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00:07:55,770 --> 00:08:00,060
we have about 50
million cones, and we

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00:08:00,060 --> 00:08:04,155
have about 120 to 150 rods.

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00:08:04,155 --> 00:08:06,350

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00:08:06,350 --> 00:08:08,990
And so, then, if you think
about the fact, at least,

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00:08:08,990 --> 00:08:12,881
for the cone system, we have
three times as many bipolar

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00:08:12,881 --> 00:08:13,380
cells.

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00:08:13,380 --> 00:08:15,965
This only applies fully
to the cone system.

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00:08:15,965 --> 00:08:19,110

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00:08:19,110 --> 00:08:24,840
That still means that we
have 150 million bipolar

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00:08:24,840 --> 00:08:25,770
cells in the retina.

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00:08:25,770 --> 00:08:27,269
So it's absolutely
incredible, then,

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00:08:27,269 --> 00:08:29,740
this tiny little thing that
you have in your head, which

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00:08:29,740 --> 00:08:32,040
is less than an
inch in diameter,

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00:08:32,040 --> 00:08:35,235
you have these millions and
millions and millions of cells.

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00:08:35,235 --> 00:08:35,735
Amazing.

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00:08:35,735 --> 00:08:37,340

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00:08:37,340 --> 00:08:41,010
So this is then the arrangement
for the parasol system.

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00:08:41,010 --> 00:08:43,970
And now, we can
progress and make

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00:08:43,970 --> 00:08:51,046
another point about how
clever the wiring became

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00:08:51,046 --> 00:08:52,170
in the course of evolution.

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00:08:52,170 --> 00:08:53,290

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00:08:53,290 --> 00:08:55,755
The cleverness here
is that, as you know,

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00:08:55,755 --> 00:09:01,090
we only have a single layer
of photoreceptors, which,

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00:09:01,090 --> 00:09:05,400
outside the fovea, has
a mix of rods and cones.

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00:09:05,400 --> 00:09:08,050
But then if you look at the
receptive fields of ganglion

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00:09:08,050 --> 00:09:12,390
cells, what you find is that
they have overlapping receptive

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00:09:12,390 --> 00:09:15,500
fields for many
of the attributes.

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00:09:15,500 --> 00:09:18,180
So you have overlapping
for ON and OFF, of course.

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00:09:18,180 --> 00:09:20,460
And that's obvious
from the wiring.

185
00:09:20,460 --> 00:09:23,450
But you also have
overlap for the midget

186
00:09:23,450 --> 00:09:24,635
and the parasol cells.

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00:09:24,635 --> 00:09:25,860

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00:09:25,860 --> 00:09:29,510
And lastly, there's an
overlap-- even if you just

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00:09:29,510 --> 00:09:32,010
look at the rod
input-- which results

190
00:09:32,010 --> 00:09:36,060
in realizing that the
receptive fields become larger

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00:09:36,060 --> 00:09:44,270
during dark adaptation by virtue
of the connections of the rod

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00:09:44,270 --> 00:09:48,350
photoreceptors to the rod
bipolars than to the A,

193
00:09:48,350 --> 00:09:52,680
to amacrine cells, which then
connect with the same ganglion

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00:09:52,680 --> 00:09:54,770
cells as do the cones.

195
00:09:54,770 --> 00:09:55,950

196
00:09:55,950 --> 00:09:59,560
So this is, then, an
incredibly clever arrangement

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00:09:59,560 --> 00:10:03,245
which enables you to see
things extremely well.

198
00:10:03,245 --> 00:10:06,260

199
00:10:06,260 --> 00:10:10,390
And it's an incredible
feat of wiring

200
00:10:10,390 --> 00:10:13,500
that accomplish this
incredible arrangement.

201
00:10:13,500 --> 00:10:17,780
So now, another important
thing to consider, in addition

202
00:10:17,780 --> 00:10:20,730
to what I've said so
far about the midget

203
00:10:20,730 --> 00:10:23,505
and the parasol
cells, is that they

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00:10:23,505 --> 00:10:25,460
have distribution over space.

205
00:10:25,460 --> 00:10:28,575
If you look at it from, say,
from the center of the eye,

206
00:10:28,575 --> 00:10:31,480
meaning the fovea,
going to the periphery,

207
00:10:31,480 --> 00:10:36,770
the ratio of midget and parasol
cells changes dramatically.

208
00:10:36,770 --> 00:10:39,300
In the center
here, in the fovea,

209
00:10:39,300 --> 00:10:41,445
you have a huge difference
in number of cells.

210
00:10:41,445 --> 00:10:42,870

211
00:10:42,870 --> 00:10:47,490
But as you get to the periphery,
these two types of cells

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00:10:47,490 --> 00:10:49,970
eventually become
equally numerous.

213
00:10:49,970 --> 00:10:52,610
Now, to show this
in relationship

214
00:10:52,610 --> 00:10:55,270
to the lateral
geniculate nucleus--

215
00:10:55,270 --> 00:10:57,925
again, to repeat, in the fovea,
you have an 8 to 1 ratio;

216
00:10:57,925 --> 00:11:00,620
in the periphery, they
have 1 to 1 ratio.

217
00:11:00,620 --> 00:11:05,450
And this is directly reflected
in the lateral geniculate

218
00:11:05,450 --> 00:11:06,350
nucleus.

219
00:11:06,350 --> 00:11:09,500
Everything I've shown you
so far about the geniculate

220
00:11:09,500 --> 00:11:11,970
was a six-layered structure.

221
00:11:11,970 --> 00:11:16,150
But those six layers
exist only to about

222
00:11:16,150 --> 00:11:18,850
an 18-degree eccentricity
from the fovea.

223
00:11:18,850 --> 00:11:20,900

224
00:11:20,900 --> 00:11:24,640
And after that, the
lateral geniculate nucleus

225
00:11:24,640 --> 00:11:26,790
becomes a four-layered
structure.

226
00:11:26,790 --> 00:11:30,120
And as done here in
a schematic fashion,

227
00:11:30,120 --> 00:11:34,450
the four layers for
the left and right eyes

228
00:11:34,450 --> 00:11:37,610
are pretty much
equal in numerosity.

229
00:11:37,610 --> 00:11:40,680
And that creates,
then, the 1 to 1 ratio.

230
00:11:40,680 --> 00:11:43,760
So that makes one think,
why do we have this shift?

231
00:11:43,760 --> 00:11:47,510
There must be something very
important in central vision

232
00:11:47,510 --> 00:11:49,920
for which the midget
system is good for.

233
00:11:49,920 --> 00:11:55,880
And in peripheral retina,
the parasol system

234
00:11:55,880 --> 00:11:57,580
becomes more important.

235
00:11:57,580 --> 00:12:00,290
So we are going to
pay attention to that

236
00:12:00,290 --> 00:12:08,585
as we examine what the functions
are of these two systems.

237
00:12:08,585 --> 00:12:09,640

238
00:12:09,640 --> 00:12:11,470
So how do we go
about finding out

239
00:12:11,470 --> 00:12:13,140
the functions of
these two systems?

240
00:12:13,140 --> 00:12:14,780
Well, there are several methods.

241
00:12:14,780 --> 00:12:16,730
The first one I'm
going to tell you about

242
00:12:16,730 --> 00:12:23,680
is to record from individual
neurons-- say, in the cortex--

243
00:12:23,680 --> 00:12:26,980
and determine what
kinds of inputs

244
00:12:26,980 --> 00:12:31,260
they get from the midget
and the parasol cells.

245
00:12:31,260 --> 00:12:36,820
So to do that, you first want
to look at the exact projections

246
00:12:36,820 --> 00:12:39,630
of the retinal
ganglion cells again.

247
00:12:39,630 --> 00:12:42,460
Just to remind you, here's the
lateral geniculate nucleus,

248
00:12:42,460 --> 00:12:45,440
again, in the region where
there are six layers.

249
00:12:45,440 --> 00:12:47,870
I already showed you
this picture before.

250
00:12:47,870 --> 00:12:51,070
And I told you that the
parvocellular layers project

251
00:12:51,070 --> 00:12:55,000
to 4C alpha; the magnocellular
layers to 4C beta;

252
00:12:55,000 --> 00:12:58,510
and those other cells, which
we'll talk about eventually,

253
00:12:58,510 --> 00:13:02,600
its lateral layers project to
the upper parts of the cortex.

254
00:13:02,600 --> 00:13:05,260
So now, we have a
good idea that even

255
00:13:05,260 --> 00:13:10,400
if the inputs to the
visual cortex-- meaning,

256
00:13:10,400 --> 00:13:16,080
in this case, of course,
the V1-- the two systems are

257
00:13:16,080 --> 00:13:20,139
separate in the input
layers, in 4C alpha and beta.

258
00:13:20,139 --> 00:13:21,680
And then the question
comes up, well,

259
00:13:21,680 --> 00:13:25,560
what happens when you look at
cells above and below the input

260
00:13:25,560 --> 00:13:26,580
layers?

261
00:13:26,580 --> 00:13:27,740
Do they converge?

262
00:13:27,740 --> 00:13:28,710
Or what's going on?

263
00:13:28,710 --> 00:13:31,400
So that's the kind of
questions we're going to ask.

264
00:13:31,400 --> 00:13:35,250
And we are going to
look at this more

265
00:13:35,250 --> 00:13:38,620
carefully here to find
out just how do you

266
00:13:38,620 --> 00:13:40,480
do an experiment like that.

267
00:13:40,480 --> 00:13:50,330
Well, one thing you can do here,
you can use a reversible agent

268
00:13:50,330 --> 00:13:53,080
that you can inject either
in the parvocellular

269
00:13:53,080 --> 00:13:55,800
or magnocellular layers
of the geniculate.

270
00:13:55,800 --> 00:13:59,070
And if you do that, if in
the parvocellular layers,

271
00:13:59,070 --> 00:14:00,435
this would be a blocking agent.

272
00:14:00,435 --> 00:14:01,500

273
00:14:01,500 --> 00:14:03,500
Xylocaine is something
that's used frequently.

274
00:14:03,500 --> 00:14:05,230
There are several other agents.

275
00:14:05,230 --> 00:14:08,420
And so if you inject
that substance in here,

276
00:14:08,420 --> 00:14:12,840
you render the cells in the
geniculate unresponsive.

277
00:14:12,840 --> 00:14:14,940

278
00:14:14,940 --> 00:14:17,640
It's to serve the same idea
as what we talked about

279
00:14:17,640 --> 00:14:21,740
with APB in the last time,
except this is not quite as

280
00:14:21,740 --> 00:14:25,040
neat because it's
not a pure chemical

281
00:14:25,040 --> 00:14:27,540
treatment like you did with APB.

282
00:14:27,540 --> 00:14:30,900
Secondly, you can do it in the
magnocellular layers as well

283
00:14:30,900 --> 00:14:32,960
and block that region.

284
00:14:32,960 --> 00:14:34,690
Now, if you do this
kind of experiment,

285
00:14:34,690 --> 00:14:37,090
let's first talk about
what happens in area of V1.

286
00:14:37,090 --> 00:14:38,820

287
00:14:38,820 --> 00:14:41,810
Now, this is a very difficult
and complicated experiment.

288
00:14:41,810 --> 00:14:43,130

289
00:14:43,130 --> 00:14:51,210
Sometimes, you can spend days
recording from a single animal

290
00:14:51,210 --> 00:14:53,900
because, first of all,
what you have to do

291
00:14:53,900 --> 00:14:57,490
is you have to put in electrodes
into the lateral geniculate

292
00:14:57,490 --> 00:15:02,787
nucleus, which is way down,
preferably into both regions,

293
00:15:02,787 --> 00:15:05,120
but there are many experiments
just to one or the other.

294
00:15:05,120 --> 00:15:06,160

295
00:15:06,160 --> 00:15:07,905
And then put an
electrode into V1.

296
00:15:07,905 --> 00:15:08,950

297
00:15:08,950 --> 00:15:11,650
Now, the next important
task, of course,

298
00:15:11,650 --> 00:15:16,830
is that you've got to record
from V1 in the region to which

299
00:15:16,830 --> 00:15:18,810
these cells or
these cells project.

300
00:15:18,810 --> 00:15:20,670

301
00:15:20,670 --> 00:15:24,220
So to find that overlap
in the receptive fields

302
00:15:24,220 --> 00:15:26,660
that you need to do when
you record here, here,

303
00:15:26,660 --> 00:15:29,390
and here is that you have
to take many, many electrode

304
00:15:29,390 --> 00:15:33,032
penetrations until, finally,
you have an overlap.

305
00:15:33,032 --> 00:15:34,490
And once you have
that overlap, you

306
00:15:34,490 --> 00:15:39,580
can be sure that when you
inactivate this region

307
00:15:39,580 --> 00:15:43,050
by injecting the
Xylocaine, you can

308
00:15:43,050 --> 00:15:46,390
assess what the
responses are in the V1

309
00:15:46,390 --> 00:15:50,200
before, during, and
after the injection.

310
00:15:50,200 --> 00:15:53,580
And most importantly, before
and during, naturally.

311
00:15:53,580 --> 00:15:54,670
So let's look at that.

312
00:15:54,670 --> 00:15:56,900

313
00:15:56,900 --> 00:16:00,450
This has been done
studying many cells

314
00:16:00,450 --> 00:16:02,769
to get an overview
of what's going on.

315
00:16:02,769 --> 00:16:04,310
And I'm going to
show you, initially,

316
00:16:04,310 --> 00:16:08,640
just one example of
a cell to give you

317
00:16:08,640 --> 00:16:10,380
a feel for what that's like.

318
00:16:10,380 --> 00:16:12,900
So here we have
the cell respond.

319
00:16:12,900 --> 00:16:14,600
What you do is you
take a bar of light

320
00:16:14,600 --> 00:16:17,080
and move it across the
receptive field-- brrp,

321
00:16:17,080 --> 00:16:19,560
brrp-- for each edge.

322
00:16:19,560 --> 00:16:21,780
So those are the two
cumulative responses.

323
00:16:21,780 --> 00:16:22,280
[INAUDIBLE]

324
00:16:22,280 --> 00:16:24,490

325
00:16:24,490 --> 00:16:25,520
That's the normal.

326
00:16:25,520 --> 00:16:29,460
Now, you inject into the
parvocellular portions

327
00:16:29,460 --> 00:16:30,346
of the geniculate.

328
00:16:30,346 --> 00:16:32,220
And lo and behold, the
cell keeps responding.

329
00:16:32,220 --> 00:16:33,290

330
00:16:33,290 --> 00:16:35,540
Then you inject into
the magno portions.

331
00:16:35,540 --> 00:16:38,320
And then lo and behold, the
cell still keeps responding.

332
00:16:38,320 --> 00:16:41,552
But when you inject
into both-- bango!

333
00:16:41,552 --> 00:16:42,385
There's no response.

334
00:16:42,385 --> 00:16:43,710

335
00:16:43,710 --> 00:16:47,440
So that means that
this particular cell

336
00:16:47,440 --> 00:16:53,914
gets a convergent input from
the midget and the parasol cells

337
00:16:53,914 --> 00:16:56,080
as they pass through the
lateral geniculate nucleus.

338
00:16:56,080 --> 00:16:57,570

339
00:16:57,570 --> 00:17:01,030
Now, if one then does
a systematic study

340
00:17:01,030 --> 00:17:05,220
and then records from many
cells, what has been found here

341
00:17:05,220 --> 00:17:08,369
is that some cells do
get an exclusive input

342
00:17:08,369 --> 00:17:12,010
from the midget cells.

343
00:17:12,010 --> 00:17:15,069
Some get an exclusive input
from the parasol cells.

344
00:17:15,069 --> 00:17:18,369
And some are just like the one
I've shown you here-- namely,

345
00:17:18,369 --> 00:17:20,829
they get a convergent input.

346
00:17:20,829 --> 00:17:26,859
So that tells us, then, what
the very, very basic nature is

347
00:17:26,859 --> 00:17:30,930
of the input to the visual
cortex, you, to some degree,

348
00:17:30,930 --> 00:17:32,760
keep separate the two systems.

349
00:17:32,760 --> 00:17:34,370
And to some degree,
you also have

350
00:17:34,370 --> 00:17:35,910
a condition where
they are united.

351
00:17:35,910 --> 00:17:37,380

352
00:17:37,380 --> 00:17:44,646
So that's what
happens in area V1.

353
00:17:44,646 --> 00:17:45,920

354
00:17:45,920 --> 00:17:48,290
So now, the next thing
you are going to ask

355
00:17:48,290 --> 00:17:53,090
is, well, what happens
in other cortical areas?

356
00:17:53,090 --> 00:17:57,150
So here, then, I'm showing
you the same method picture.

357
00:17:57,150 --> 00:17:58,350

358
00:17:58,350 --> 00:18:02,250
But now, you have
recording in V4 and MT,

359
00:18:02,250 --> 00:18:04,510
doing the similar
kinds of injections

360
00:18:04,510 --> 00:18:08,360
that I just described in the
lateral geniculate nucleus.

361
00:18:08,360 --> 00:18:13,790
So when one does this,
some interesting results

362
00:18:13,790 --> 00:18:15,190
had been obtained.

363
00:18:15,190 --> 00:18:19,280
And as always, before
this kind of experiment

364
00:18:19,280 --> 00:18:22,680
that actually tested
this question,

365
00:18:22,680 --> 00:18:24,530
there were, of
course, hypotheses.

366
00:18:24,530 --> 00:18:29,400
Some people
hypothesized that area

367
00:18:29,400 --> 00:18:32,680
of V4, which had
at one time been

368
00:18:32,680 --> 00:18:36,170
proclaimed to be a
color area-- and we'll

369
00:18:36,170 --> 00:18:41,350
come back to that shortly--
it was claimed, therefore,

370
00:18:41,350 --> 00:18:45,930
that this area gets input
only from the midget system.

371
00:18:45,930 --> 00:18:49,560
And this area-- since it
has motion-selective cells,

372
00:18:49,560 --> 00:18:56,835
if you remember-- only gets
input from the parasol cells.

373
00:18:56,835 --> 00:18:58,150

374
00:18:58,150 --> 00:19:02,780
So, therefore, we can
now have the acid test,

375
00:19:02,780 --> 00:19:05,770
thanks to some
remarkable work that

376
00:19:05,770 --> 00:19:13,040
had been done, much
of it by John Maunsell

377
00:19:13,040 --> 00:19:15,640
over at Harvard,
who had actually

378
00:19:15,640 --> 00:19:18,360
worked here at MIT before then.

379
00:19:18,360 --> 00:19:20,910
And he did an
experiment like that.

380
00:19:20,910 --> 00:19:25,310
And here's an example of a
single cell recording from V4.

381
00:19:25,310 --> 00:19:27,230

382
00:19:27,230 --> 00:19:30,770
This is a magno block, and
this is the parvo block.

383
00:19:30,770 --> 00:19:34,050
This is before the block,
and this is after the block.

384
00:19:34,050 --> 00:19:36,270
So what you can see
here, this cell, again,

385
00:19:36,270 --> 00:19:38,570
response to a bar
moving across-- brrp,

386
00:19:38,570 --> 00:19:39,880
brrp-- like that.

387
00:19:39,880 --> 00:19:42,490
Here are the two
responses shown here as

388
00:19:42,490 --> 00:19:45,120
to how they come across
the receptive field.

389
00:19:45,120 --> 00:19:52,830
And you can see a vigorous
response after you do this

390
00:19:52,830 --> 00:20:02,100
and before you inject
Xylocaine into the geniculate

391
00:20:02,100 --> 00:20:04,920
to block, in this
case, the magno system;

392
00:20:04,920 --> 00:20:07,090
and in this case,
the parvo system.

393
00:20:07,090 --> 00:20:09,470
This is backwards from the
way I usually presented.

394
00:20:09,470 --> 00:20:11,190
I usually like to
put parvo first.

395
00:20:11,190 --> 00:20:13,220
Preference-- it's the bias.

396
00:20:13,220 --> 00:20:14,850
At any rate, you
can see what happens

397
00:20:14,850 --> 00:20:18,950
is dramatic for this particular
cell after you injected,

398
00:20:18,950 --> 00:20:22,610
you blocked the magno system.

399
00:20:22,610 --> 00:20:26,190
The cell-- we said has
spontaneous activity--

400
00:20:26,190 --> 00:20:29,300
but it no longer
responds to the edges.

401
00:20:29,300 --> 00:20:32,510
By contrast, when
you do a parvo block,

402
00:20:32,510 --> 00:20:34,780
you only get a small effect.

403
00:20:34,780 --> 00:20:39,450
There is a reduction for
this particular cell,

404
00:20:39,450 --> 00:20:44,290
but it's still responding.

405
00:20:44,290 --> 00:20:46,120

406
00:20:46,120 --> 00:20:49,390
So that is the example of
a recording in area of V4.

407
00:20:49,390 --> 00:20:50,670

408
00:20:50,670 --> 00:20:54,180
Now, let us go and ask the
question, what about MT?

409
00:20:54,180 --> 00:20:55,340
Now, here's an example.

410
00:20:55,340 --> 00:20:59,580
Same arrangement-- magno first,
parvo second, before the block,

411
00:20:59,580 --> 00:21:00,730
after the block.

412
00:21:00,730 --> 00:21:03,670
In this case, in
MT, you get a cell

413
00:21:03,670 --> 00:21:07,720
that totally stopped
responding after magno block

414
00:21:07,720 --> 00:21:09,540
to this moving stimulus.

415
00:21:09,540 --> 00:21:13,130
And here, what you see
is after parvo block,

416
00:21:13,130 --> 00:21:14,300
the response continues.

417
00:21:14,300 --> 00:21:15,650

418
00:21:15,650 --> 00:21:18,760
So now, this is just two cells.

419
00:21:18,760 --> 00:21:22,640
Now, to be sure that these
two cells are generally

420
00:21:22,640 --> 00:21:26,900
representative of these
observations, what you need

421
00:21:26,900 --> 00:21:31,830
to do is to collect this kind
of information from many cells,

422
00:21:31,830 --> 00:21:34,660
and then come up with a
qualitative statement.

423
00:21:34,660 --> 00:21:37,660
So what you can do is
you can, for each cell,

424
00:21:37,660 --> 00:21:39,850
when you do this
experiment, you can't

425
00:21:39,850 --> 00:21:42,640
determine how much the cell
fired here to the stimulus

426
00:21:42,640 --> 00:21:44,540
and how much it fired here.

427
00:21:44,540 --> 00:21:47,030
And then you can get a
ratio of that response.

428
00:21:47,030 --> 00:21:51,840
You can turn it into, like,
a percentage or maybe just

429
00:21:51,840 --> 00:21:54,650
to score them as 0 to 1 number.

430
00:21:54,650 --> 00:21:55,810

431
00:21:55,810 --> 00:21:58,240
And then if you do that
for a whole bunch of cells,

432
00:21:58,240 --> 00:22:00,640
what you find is shown here.

433
00:22:00,640 --> 00:22:03,190
This is a bunch of cells in V4.

434
00:22:03,190 --> 00:22:05,460
This is a bunch of cells in MT.

435
00:22:05,460 --> 00:22:09,960
And what you can see here
is that in V4, first of all,

436
00:22:09,960 --> 00:22:16,530
you have a medium degree
of blockage, nothing major,

437
00:22:16,530 --> 00:22:17,680
but some blockage.

438
00:22:17,680 --> 00:22:20,320
But most importantly,
you get blockage

439
00:22:20,320 --> 00:22:23,490
both for parvocellular and
magnocellular inactivation.

440
00:22:23,490 --> 00:22:24,690

441
00:22:24,690 --> 00:22:28,470
By contrast, in
MT, what you find

442
00:22:28,470 --> 00:22:32,480
is that when you block
magnocellular geniculate,

443
00:22:32,480 --> 00:22:36,600
most of the cells are
dramatically affected.

444
00:22:36,600 --> 00:22:44,830
Only a few cells are blocked
as a result of a parvocellular

445
00:22:44,830 --> 00:22:46,010
block.

446
00:22:46,010 --> 00:22:52,670
So the outcome of this is
that the hypothesis pertaining

447
00:22:52,670 --> 00:22:58,130
to MT, that it gets mostly an
input from the parasol system,

448
00:22:58,130 --> 00:22:59,410
is correct.

449
00:22:59,410 --> 00:23:03,160
But the idea that V4
gets an input only

450
00:23:03,160 --> 00:23:07,030
from the midget system
is obviously incorrect,

451
00:23:07,030 --> 00:23:10,410
showing that it gets
an input from both.

452
00:23:10,410 --> 00:23:16,230
So to then summarize
the wiring diagram here,

453
00:23:16,230 --> 00:23:18,830
what you have here is
the eye, of course.

454
00:23:18,830 --> 00:23:21,100
And then you have the
midget and parasol cells

455
00:23:21,100 --> 00:23:24,200
that project, respectively,
to the parvocellular

456
00:23:24,200 --> 00:23:27,850
and magnocellular layers of
the lateral geniculate nucleus,

457
00:23:27,850 --> 00:23:29,490
then they go off to the cortex.

458
00:23:29,490 --> 00:23:31,630
And if you remember,
in the cortex,

459
00:23:31,630 --> 00:23:34,920
they terminated
4C alpha and beta.

460
00:23:34,920 --> 00:23:38,000
And then, also, as I told
you, up here, you already

461
00:23:38,000 --> 00:23:41,640
have many cells above and
below the input layers

462
00:23:41,640 --> 00:23:46,070
that get a convergent input from
the midget and parasol cells.

463
00:23:46,070 --> 00:23:50,940
So what happens then, in terms
of the projections to higher

464
00:23:50,940 --> 00:23:55,310
cortical areas-- to talk
about V2, for example--

465
00:23:55,310 --> 00:23:57,480
you get some cells
which are purely

466
00:23:57,480 --> 00:24:00,500
driven by the midget
system, some cells purely

467
00:24:00,500 --> 00:24:05,850
driven by the parasol, and many
cells that are driven by both.

468
00:24:05,850 --> 00:24:08,570
So V2 becomes very
complicated because they

469
00:24:08,570 --> 00:24:10,320
have different subdivisions.

470
00:24:10,320 --> 00:24:12,830
Maybe in V2-- we talked
about it a little bit--

471
00:24:12,830 --> 00:24:17,080
that may be receiving
different input from area of V1

472
00:24:17,080 --> 00:24:18,910
in terms of whether
they are driven

473
00:24:18,910 --> 00:24:21,260
by the midget or
the parasol cells.

474
00:24:21,260 --> 00:24:26,560
Now, most notably, when
from V2 and from V1,

475
00:24:26,560 --> 00:24:29,510
you look at the
projections to area MT,

476
00:24:29,510 --> 00:24:32,180
the middle temporal
area, what you find

477
00:24:32,180 --> 00:24:34,990
is that this is
heavily dominated

478
00:24:34,990 --> 00:24:38,740
by the input from
the parasol cells.

479
00:24:38,740 --> 00:24:41,080
Then if you go beyond
that, this continues

480
00:24:41,080 --> 00:24:43,950
to the parietal lobe from MT.

481
00:24:43,950 --> 00:24:47,105
But then, when you
go from V2 to V4,

482
00:24:47,105 --> 00:24:49,520
then temporal, then the
frontal lobe, what you

483
00:24:49,520 --> 00:24:51,630
find that there's
a mix of inputs

484
00:24:51,630 --> 00:24:52,755
from both of these systems.

485
00:24:52,755 --> 00:24:54,040

486
00:24:54,040 --> 00:24:57,330
So it highlights the fact
that, indeed, these things

487
00:24:57,330 --> 00:24:59,210
are quite complicated.

488
00:24:59,210 --> 00:25:04,410
And so we need to now
turn to a different method

489
00:25:04,410 --> 00:25:09,320
to try to ferret out beyond just
establishing the connections

490
00:25:09,320 --> 00:25:11,935
as to what on earth these
two systems are for.

491
00:25:11,935 --> 00:25:15,790

492
00:25:15,790 --> 00:25:19,880
And needless to say, hypotheses
were rampant about this.

493
00:25:19,880 --> 00:25:21,440

494
00:25:21,440 --> 00:25:23,050
And what I'm going
to do now, I'm

495
00:25:23,050 --> 00:25:26,090
going to tell you about
how one can go about

496
00:25:26,090 --> 00:25:29,990
and how many investigators have
gone about trying to determine

497
00:25:29,990 --> 00:25:33,809
what the functions are of
these two systems in processing

498
00:25:33,809 --> 00:25:34,600
visual information.

499
00:25:34,600 --> 00:25:35,744

500
00:25:35,744 --> 00:25:36,660
So how do you do that?

501
00:25:36,660 --> 00:25:38,150

502
00:25:38,150 --> 00:25:41,690
Well, the way you
do that is you can

503
00:25:41,690 --> 00:25:44,530
use what is called
lesion studies.

504
00:25:44,530 --> 00:25:46,640
What you can do is
you can selectively

505
00:25:46,640 --> 00:25:50,130
block either the
parvocellular or magnocellular

506
00:25:50,130 --> 00:25:53,470
systems at the level of
lateral geniculate nucleus

507
00:25:53,470 --> 00:25:57,975
because, by lucky happenstance,
the parvocellular layer is

508
00:25:57,975 --> 00:26:00,350
getting input from midget,
and the magnocellular layer is

509
00:26:00,350 --> 00:26:03,040
from the from the parasol cells.

510
00:26:03,040 --> 00:26:04,460
So you can make lesions, then.

511
00:26:04,460 --> 00:26:05,820
How do you make lesions?

512
00:26:05,820 --> 00:26:07,760
There are variety of
ways of making lesions.

513
00:26:07,760 --> 00:26:09,730
That's a huge field.

514
00:26:09,730 --> 00:26:13,300
It applies not only to vision,
to many, many other areas,

515
00:26:13,300 --> 00:26:20,250
to try to make carefully
selective lesions

516
00:26:20,250 --> 00:26:22,010
in various parts of the brain.

517
00:26:22,010 --> 00:26:24,390
Now, it's not easy to do
that in the geniculate.

518
00:26:24,390 --> 00:26:28,190
So what you have to
do is, again, you

519
00:26:28,190 --> 00:26:32,800
go in to the lateral geniculate
nucleus with a microelectrode.

520
00:26:32,800 --> 00:26:34,500

521
00:26:34,500 --> 00:26:36,060
Once you do that--
you already know

522
00:26:36,060 --> 00:26:37,890
the layout of the
geniculate-- you

523
00:26:37,890 --> 00:26:40,790
can find out where the
receptive fields are located,

524
00:26:40,790 --> 00:26:42,560
and you can
determine whether you

525
00:26:42,560 --> 00:26:44,820
are recording from the
parvocellular or magnocellular

526
00:26:44,820 --> 00:26:45,319
layers.

527
00:26:45,319 --> 00:26:47,610
You're going to adjust
the depth of the electrode

528
00:26:47,610 --> 00:26:50,170
to be either in the
parvocellular or magnocellular

529
00:26:50,170 --> 00:26:51,280
layers.

530
00:26:51,280 --> 00:26:54,560
And once you have established
the receptive field location

531
00:26:54,560 --> 00:26:58,280
and were certain about in
what parts of the geniculate

532
00:26:58,280 --> 00:27:03,150
you are recording, you can
then proceed to make a lesion.

533
00:27:03,150 --> 00:27:05,510
Now, there are a number
of ways of making lesions.

534
00:27:05,510 --> 00:27:07,320
One of them is
called heat lesions.

535
00:27:07,320 --> 00:27:09,380
You should take a
metal microelectrode.

536
00:27:09,380 --> 00:27:12,370
You take it down
there, and then you

537
00:27:12,370 --> 00:27:17,140
pass some current to make
the tip of the electrode hot,

538
00:27:17,140 --> 00:27:20,630
you can affect, as you know,
maybe a millimeter area

539
00:27:20,630 --> 00:27:23,310
or something like that in the
lateral geniculate nucleus.

540
00:27:23,310 --> 00:27:25,560
I'm talking about
small, small areas.

541
00:27:25,560 --> 00:27:33,020
Another alternative that you
can use is to inject a chemical.

542
00:27:33,020 --> 00:27:36,760
One of those commonly used
is called Ibotenic acid,

543
00:27:36,760 --> 00:27:39,980
which is a very nice attribute,
that when it causes a lesion,

544
00:27:39,980 --> 00:27:42,495
the borders are nicely
clearly defined.

545
00:27:42,495 --> 00:27:43,630

546
00:27:43,630 --> 00:27:47,760
So no matter how you
do this, then once it

547
00:27:47,760 --> 00:27:51,910
is done in a monkey, then you
can study a monkey for months

548
00:27:51,910 --> 00:27:54,480
on end to see what
the vision is,

549
00:27:54,480 --> 00:27:55,730
of how the vision is affected.

550
00:27:55,730 --> 00:27:57,750

551
00:27:57,750 --> 00:28:03,730
And then after you've done
that, you then process the brain

552
00:28:03,730 --> 00:28:05,530
and look at the lateral
geniculate nucleus

553
00:28:05,530 --> 00:28:10,430
to see what was the size
and location of the lesion.

554
00:28:10,430 --> 00:28:12,040

555
00:28:12,040 --> 00:28:15,110
Now then, in some cases, it's
"Oh, my god, you did both.

556
00:28:15,110 --> 00:28:16,280
Nyah, nyah, nyah."

557
00:28:16,280 --> 00:28:17,250
You screwed up.

558
00:28:17,250 --> 00:28:21,050
So months and months of
work goes down the toilet.

559
00:28:21,050 --> 00:28:23,680
But in some cases,
you get a good effect.

560
00:28:23,680 --> 00:28:25,420
And that, eventually,
if you do it

561
00:28:25,420 --> 00:28:27,860
several times on
several monkeys can

562
00:28:27,860 --> 00:28:30,920
result in a solid publication.

563
00:28:30,920 --> 00:28:34,870
So that is the basic process
for making the lesions.

564
00:28:34,870 --> 00:28:35,880

565
00:28:35,880 --> 00:28:41,400
Now, let me then
move on and broach

566
00:28:41,400 --> 00:28:43,354
the next important
topic-- namely,

567
00:28:43,354 --> 00:28:44,520
what are you going to study?

568
00:28:44,520 --> 00:28:45,680

569
00:28:45,680 --> 00:28:51,930
So what you have to study since
you want to have an open mind

570
00:28:51,930 --> 00:28:56,320
and you don't want to say, "oh,
yeah, everything in the brain

571
00:28:56,320 --> 00:28:59,040
does color" or
something like that,

572
00:28:59,040 --> 00:29:00,745
and so instead of
just studying color,

573
00:29:00,745 --> 00:29:02,620
you have to study
many other aspects.

574
00:29:02,620 --> 00:29:06,200

575
00:29:06,200 --> 00:29:12,940
So I'm going to tell you
about several kinds of tests

576
00:29:12,940 --> 00:29:13,860
that have the newest.

577
00:29:13,860 --> 00:29:15,970
And I will explain
each of those to you.

578
00:29:15,970 --> 00:29:17,330
But first, I will list them.

579
00:29:17,330 --> 00:29:18,750

580
00:29:18,750 --> 00:29:24,220
The behavioral task that
is used-- very important--

581
00:29:24,220 --> 00:29:29,620
is that you've got to be able
to confine the crucial stimulus

582
00:29:29,620 --> 00:29:34,100
either to the area
that you had blocked

583
00:29:34,100 --> 00:29:36,180
or the area that is intact.

584
00:29:36,180 --> 00:29:37,480

585
00:29:37,480 --> 00:29:40,000
So one way to do that,
which is the easiest way,

586
00:29:40,000 --> 00:29:41,505
is to use a detection task.

587
00:29:41,505 --> 00:29:43,840
We already talked
about that briefly.

588
00:29:43,840 --> 00:29:45,610
The monkey first fixates.

589
00:29:45,610 --> 00:29:48,880
That confines his
looking to that location.

590
00:29:48,880 --> 00:29:51,570
And then you can present
a stimulus like this.

591
00:29:51,570 --> 00:29:53,770
And if he makes a
saccade to it, he

592
00:29:53,770 --> 00:29:56,020
gets a drop of apple
juice for a reward.

593
00:29:56,020 --> 00:29:57,800
Now, that is a procedure.

594
00:29:57,800 --> 00:29:59,300
And then, of course,
our next trial,

595
00:29:59,300 --> 00:30:00,750
it appears someplace else.

596
00:30:00,750 --> 00:30:03,370
On each trial, it's in
different locations.

597
00:30:03,370 --> 00:30:06,640
And on some trials, you
can present the stimulus

598
00:30:06,640 --> 00:30:08,675
in the area that
had been blocked.

599
00:30:08,675 --> 00:30:13,380
You get it from by
magnocellular or parvocellular

600
00:30:13,380 --> 00:30:18,200
lesions or infusions
or in an intact area.

601
00:30:18,200 --> 00:30:21,950
And that, then, enables
you to compare performance

602
00:30:21,950 --> 00:30:25,100
in regions where the monkey's
performance is normal

603
00:30:25,100 --> 00:30:29,150
because he's intact and in those
regions where he lacks either

604
00:30:29,150 --> 00:30:31,960
an input from the magnocellular
or from the parvocellular

605
00:30:31,960 --> 00:30:34,840
layers of the lateral
geniculate nucleus,

606
00:30:34,840 --> 00:30:38,250
meaning from the midget
and parasol cells.

607
00:30:38,250 --> 00:30:42,030
So now, another
task which is used

608
00:30:42,030 --> 00:30:46,190
to be able to carry out a
more thorough examination

609
00:30:46,190 --> 00:30:48,190
of visual capacities
is his discrimination.

610
00:30:48,190 --> 00:30:49,200

611
00:30:49,200 --> 00:30:51,860
In which case,
after fixation, you

612
00:30:51,860 --> 00:30:54,190
have a whole bunch
of stimuli coming on.

613
00:30:54,190 --> 00:30:56,830
This is very effective
for studying color.

614
00:30:56,830 --> 00:30:59,690
And in this case, this
discrimination task often

615
00:30:59,690 --> 00:31:03,130
is called the so-called
oddities task.

616
00:31:03,130 --> 00:31:05,120
That's an easy way
to remember it.

617
00:31:05,120 --> 00:31:06,910
"Oddity" because this is odd.

618
00:31:06,910 --> 00:31:10,710
All the others, the distractors,
if you will, are the same.

619
00:31:10,710 --> 00:31:12,370
Only one stimulus is different.

620
00:31:12,370 --> 00:31:13,299

621
00:31:13,299 --> 00:31:15,590
And, of course, the monkey
has to make a direct saccade

622
00:31:15,590 --> 00:31:19,570
to this stimulus to get a drop
of apple juice for reward.

623
00:31:19,570 --> 00:31:23,210
So that would be a so-called
discrimination task.

624
00:31:23,210 --> 00:31:26,600
So these are the two basic
tasks that can be used.

625
00:31:26,600 --> 00:31:30,780
And now, we can proceed and ask
the question of what exactly,

626
00:31:30,780 --> 00:31:33,910
what kinds of visual
capacities should be studied?

627
00:31:33,910 --> 00:31:37,065
So let me just say one
more thing, by the way.

628
00:31:37,065 --> 00:31:41,080
The way this is
done in a laboratory

629
00:31:41,080 --> 00:31:44,730
is that you have a performance
monitor, so-called,

630
00:31:44,730 --> 00:31:53,170
where the computer puts a square
around each of the dots that

631
00:31:53,170 --> 00:31:54,794
will have appeared--
in this case,

632
00:31:54,794 --> 00:31:56,460
this should be
discrimination-- or where

633
00:31:56,460 --> 00:31:59,150
they will appear singly
in the detection task.

634
00:31:59,150 --> 00:32:01,620
And if the monkey
makes a saccade that

635
00:32:01,620 --> 00:32:04,980
lends the saccadic eye movement,
which you are recording,

636
00:32:04,980 --> 00:32:08,980
into the square area
there, then automatically

637
00:32:08,980 --> 00:32:11,120
a drop of apple
juice is discharged.

638
00:32:11,120 --> 00:32:13,810
But if he were to make a
similar saccade to here,

639
00:32:13,810 --> 00:32:15,610
he will not get
rewarded because this

640
00:32:15,610 --> 00:32:17,412
is the only correct position.

641
00:32:17,412 --> 00:32:19,620
And on each trial, that's
going to be someplace else.

642
00:32:19,620 --> 00:32:21,279
Everybody understands
the method?

643
00:32:21,279 --> 00:32:22,445
It's fairly straightforward.

644
00:32:22,445 --> 00:32:23,540

645
00:32:23,540 --> 00:32:28,770
So now, we can move on
and look at an example

646
00:32:28,770 --> 00:32:32,430
of the kinds of lesions
that this can create.

647
00:32:32,430 --> 00:32:34,620
Here is a lateral
geniculate nucleus again,

648
00:32:34,620 --> 00:32:36,150
the six-layered portion.

649
00:32:36,150 --> 00:32:39,910
And you can see this area
here, that this is a lesion.

650
00:32:39,910 --> 00:32:42,560
There are no cells
functional here,

651
00:32:42,560 --> 00:32:45,452
which affects only the
parvocellular layers.

652
00:32:45,452 --> 00:32:47,160
You see here the two
magnocellular layers

653
00:32:47,160 --> 00:32:48,120
are normal.

654
00:32:48,120 --> 00:32:52,070
So this is the lesion
area which affects

655
00:32:52,070 --> 00:32:57,430
a few degrees of visual
angle-- in this case,

656
00:32:57,430 --> 00:32:59,320
in the lower part
of the visual field.

657
00:32:59,320 --> 00:33:01,420
Now, here we have
a magno lesion.

658
00:33:01,420 --> 00:33:02,800
If you just look
at this quickly,

659
00:33:02,800 --> 00:33:04,630
you say, what lesion
are you talking about?

660
00:33:04,630 --> 00:33:06,820
But if you look closely,
can you see this here?

661
00:33:06,820 --> 00:33:08,630
There are no cells here.

662
00:33:08,630 --> 00:33:14,210
So this is the region where both
layers, magnocellular layers

663
00:33:14,210 --> 00:33:16,710
that get the input
from the parasol cells,

664
00:33:16,710 --> 00:33:17,710
had been blocked.

665
00:33:17,710 --> 00:33:19,730
So that is the block there.

666
00:33:19,730 --> 00:33:24,630
So this is, then, an example
of a successful lesion.

667
00:33:24,630 --> 00:33:26,790
And once you do these
kinds of experiments--

668
00:33:26,790 --> 00:33:29,320
some of these experiments
can take a couple of years,

669
00:33:29,320 --> 00:33:39,250
maybe longer-- you end up
having some monkeys who

670
00:33:39,250 --> 00:33:44,420
have neat lesions like
this, then it's a control.

671
00:33:44,420 --> 00:33:45,960
Let me just add
that, which I'm not

672
00:33:45,960 --> 00:33:48,440
going to show any pictures of.

673
00:33:48,440 --> 00:33:51,440
But you can also make,
on purpose, a lesion

674
00:33:51,440 --> 00:33:55,180
where you block both of
them-- both the magno

675
00:33:55,180 --> 00:33:56,440
and the parvocellular layers.

676
00:33:56,440 --> 00:33:59,220
You just block out a portion
of the lateral geniculate

677
00:33:59,220 --> 00:34:00,410
completely.

678
00:34:00,410 --> 00:34:02,390
Now, that's an
important control.

679
00:34:02,390 --> 00:34:06,050
For all kinds of experiments,
controls are essential.

680
00:34:06,050 --> 00:34:09,870
Now, let me tell you-- this
is available in the published

681
00:34:09,870 --> 00:34:12,179
material that you have
been asked to read--

682
00:34:12,179 --> 00:34:17,580
that when you block
both magno and parvo,

683
00:34:17,580 --> 00:34:20,170
maybe a quarter of the
lateral geniculate nucleus,

684
00:34:20,170 --> 00:34:26,750
whenever you present stimuli in
the area that has a topographic

685
00:34:26,750 --> 00:34:29,540
correspondence to
the lesion's region,

686
00:34:29,540 --> 00:34:31,300
the monkey cannot see a thing.

687
00:34:31,300 --> 00:34:34,449
He cannot perform any
of those tasks at all.

688
00:34:34,449 --> 00:34:38,560
So clearly, whatever
effect one gets here

689
00:34:38,560 --> 00:34:40,949
with these selective
lesions can then

690
00:34:40,949 --> 00:34:43,360
be ascribed-- if you see
deficit after this one

691
00:34:43,360 --> 00:34:46,810
or deficit after that one--
can be ascribed to what

692
00:34:46,810 --> 00:34:50,070
the midget and the
parasol cell systems do.

693
00:34:50,070 --> 00:34:51,310

694
00:34:51,310 --> 00:34:53,500
So that, then, is the procedure.

695
00:34:53,500 --> 00:34:58,720
And now, we can move on and
list the perceptual functions

696
00:34:58,720 --> 00:35:00,380
that one wants to test.

697
00:35:00,380 --> 00:35:03,540
Now, think about it for
a minute, just quickly.

698
00:35:03,540 --> 00:35:05,040
What kinds of
functions would I want

699
00:35:05,040 --> 00:35:06,880
to test if I'm running
this experiment?

700
00:35:06,880 --> 00:35:08,820

701
00:35:08,820 --> 00:35:11,750
How can we break down
the multitude of things

702
00:35:11,750 --> 00:35:16,010
that we have to process
into some basic functions?

703
00:35:16,010 --> 00:35:18,495
Well, first of all,
very important function,

704
00:35:18,495 --> 00:35:20,120
even though it may
have now [INAUDIBLE]

705
00:35:20,120 --> 00:35:22,390
is called contrast sensitivity.

706
00:35:22,390 --> 00:35:24,950
Because everything
you look at, the light

707
00:35:24,950 --> 00:35:28,590
reflects just about from
everything that you look at,

708
00:35:28,590 --> 00:35:34,490
and so the contrast
of the stimuli that's

709
00:35:34,490 --> 00:35:37,840
on a white sheet of paper
or a gray sheet of paper

710
00:35:37,840 --> 00:35:40,440
or when you look at
photographs is highly varied.

711
00:35:40,440 --> 00:35:41,859

712
00:35:41,859 --> 00:35:43,400
And the question
is, how well can you

713
00:35:43,400 --> 00:35:45,720
see the different
levels of contrast?

714
00:35:45,720 --> 00:35:48,510
Another one, of course,
that's obvious is color.

715
00:35:48,510 --> 00:35:51,660
How well can you process
color information?

716
00:35:51,660 --> 00:35:53,495
And then another one is pattern.

717
00:35:53,495 --> 00:35:54,980

718
00:35:54,980 --> 00:35:56,640
We often talk about
basic patterns.

719
00:35:56,640 --> 00:35:57,920

720
00:35:57,920 --> 00:36:00,210
And the one I'm going
to tell you about mostly

721
00:36:00,210 --> 00:36:03,630
would be checkerboards
or something like that.

722
00:36:03,630 --> 00:36:06,680
Then we talk about texture.

723
00:36:06,680 --> 00:36:09,340
Most of the things that
we encounter in the world

724
00:36:09,340 --> 00:36:10,770
are textured.

725
00:36:10,770 --> 00:36:14,260
And so it's important for us
to be able to see texture.

726
00:36:14,260 --> 00:36:15,885
Then, of course,
shape, that's obvious.

727
00:36:15,885 --> 00:36:17,040

728
00:36:17,040 --> 00:36:19,070
Then stereopsis.

729
00:36:19,070 --> 00:36:23,210
We will talk about stereopsis
in much more detail in a bit.

730
00:36:23,210 --> 00:36:27,100
What stereopsis involves, as
I've mentioned to you already,

731
00:36:27,100 --> 00:36:32,200
are the difference of the
input in the two eyes.

732
00:36:32,200 --> 00:36:35,590
And that difference is called
disparity, which the brain then

733
00:36:35,590 --> 00:36:39,130
interprets as depth.

734
00:36:39,130 --> 00:36:42,010
Another one, very important
because you often just see

735
00:36:42,010 --> 00:36:44,900
things appearing quickly
in very brief times,

736
00:36:44,900 --> 00:36:45,800
is to study flicker.

737
00:36:45,800 --> 00:36:46,870

738
00:36:46,870 --> 00:36:49,200
And yet another one
is to study motion

739
00:36:49,200 --> 00:36:52,000
because that's so
central to our existence.

740
00:36:52,000 --> 00:36:54,060
And then to study brightness.

741
00:36:54,060 --> 00:36:57,560
And one thing I
haven't mentioned yet

742
00:36:57,560 --> 00:36:58,970
is scotopic vision.

743
00:36:58,970 --> 00:37:02,150
How well can you see on
the photopic and scotopic

744
00:37:02,150 --> 00:37:02,650
conditions?

745
00:37:02,650 --> 00:37:04,140

746
00:37:04,140 --> 00:37:06,470
So those are, then,
the procedures.

747
00:37:06,470 --> 00:37:09,585
And so let us now look at the
first one of these-- contrast

748
00:37:09,585 --> 00:37:10,085
sensitivity.

749
00:37:10,085 --> 00:37:11,430

750
00:37:11,430 --> 00:37:13,340
This has been
extensively studied,

751
00:37:13,340 --> 00:37:17,100
hundreds and hundreds of
papers, many of them in humans.

752
00:37:17,100 --> 00:37:20,420
And most commonly in these
papers, what they did

753
00:37:20,420 --> 00:37:23,400
was they used
sinusoidal gratings.

754
00:37:23,400 --> 00:37:27,170
And the way you do that,
then, in similar experiments

755
00:37:27,170 --> 00:37:32,570
as a detection experiment, you
present sinusoidal gratings

756
00:37:32,570 --> 00:37:36,370
with spatial frequency and whose
contrast you systematically

757
00:37:36,370 --> 00:37:36,870
vary.

758
00:37:36,870 --> 00:37:37,900

759
00:37:37,900 --> 00:37:39,850
And when you do
that, you get what

760
00:37:39,850 --> 00:37:43,470
is called a contrast
sensitivity function.

761
00:37:43,470 --> 00:37:48,550
And so the most common one
that you read in many papers

762
00:37:48,550 --> 00:37:50,350
is plotted this way.

763
00:37:50,350 --> 00:37:52,040

764
00:37:52,040 --> 00:37:55,234
This is spatial
frequency low, high.

765
00:37:55,234 --> 00:37:56,340

766
00:37:56,340 --> 00:37:57,335
And this is contrast.

767
00:37:57,335 --> 00:38:00,857

768
00:38:00,857 --> 00:38:03,620
Low, high.

769
00:38:03,620 --> 00:38:05,810

770
00:38:05,810 --> 00:38:08,440
And then if you do that, then
you systematically studied

771
00:38:08,440 --> 00:38:10,540
this in humans,
interestingly enough,

772
00:38:10,540 --> 00:38:14,680
you get a function
like that-- meaning

773
00:38:14,680 --> 00:38:18,410
that in between levels
of spatial frequency,

774
00:38:18,410 --> 00:38:20,110
you see the best.

775
00:38:20,110 --> 00:38:23,260
And extreme levels, you
don't see quite as well.

776
00:38:23,260 --> 00:38:28,910
So one could use sinusoidal
gratings in animals.

777
00:38:28,910 --> 00:38:32,980
But sinusoidal gratings
aren't essential.

778
00:38:32,980 --> 00:38:39,910
What you can do instead is you
can present a checkerboard.

779
00:38:39,910 --> 00:38:42,842
And so here's an example,
same procedure as before.

780
00:38:42,842 --> 00:38:44,800
The monkey sees this and
makes a saccade to it.

781
00:38:44,800 --> 00:38:46,110
It gets you water.

782
00:38:46,110 --> 00:38:48,180
And then you vary
the spatial frequency

783
00:38:48,180 --> 00:38:49,410
and the contrast of it.

784
00:38:49,410 --> 00:38:50,520
So here is one.

785
00:38:50,520 --> 00:38:51,720

786
00:38:51,720 --> 00:38:55,080
You can hardly see that
because the contrast is low.

787
00:38:55,080 --> 00:38:58,390
So now, to see this
overall, here's an example.

788
00:38:58,390 --> 00:39:00,380
Here, we vary the contrast.

789
00:39:00,380 --> 00:39:02,680
And here, we vary the
spatial frequency.

790
00:39:02,680 --> 00:39:05,770
And if you look at that, you
can see that in this region,

791
00:39:05,770 --> 00:39:08,520
depending on how far back
you are, this region,

792
00:39:08,520 --> 00:39:09,680
you can see the best.

793
00:39:09,680 --> 00:39:10,840
Here, it will be less so.

794
00:39:10,840 --> 00:39:13,210
And here, of course, it
drops off dramatically,

795
00:39:13,210 --> 00:39:16,390
just like that curve
I have drawn there.

796
00:39:16,390 --> 00:39:21,310
So this, then, enables one to
generate a so-called "contrast

797
00:39:21,310 --> 00:39:25,690
sensitivity"
function in a monkey

798
00:39:25,690 --> 00:39:28,690
in those regions of the
visual field that are intact

799
00:39:28,690 --> 00:39:30,780
and in those regions
of visual field

800
00:39:30,780 --> 00:39:33,340
in which you have either
magnocellular or parvocellular

801
00:39:33,340 --> 00:39:36,920
lesion that selectively
blocks the parasol

802
00:39:36,920 --> 00:39:38,850
and the midget systems.

803
00:39:38,850 --> 00:39:41,590
So that's the experiment,
then, for just studying

804
00:39:41,590 --> 00:39:42,990
contrast sensitivity.

805
00:39:42,990 --> 00:39:46,110
And if you do that, this is
the kind of result you get.

806
00:39:46,110 --> 00:39:47,900
This is the monkey's
normal performance.

807
00:39:47,900 --> 00:39:53,890
In this case, of four
spatial frequency levels.

808
00:39:53,890 --> 00:39:56,090
And you go up and
down with contrast,

809
00:39:56,090 --> 00:39:58,480
just like that
curve I drew there.

810
00:39:58,480 --> 00:40:01,140
So this is your contrast
sensitivity function.

811
00:40:01,140 --> 00:40:04,080
And it shows that
under normal conditions

812
00:40:04,080 --> 00:40:09,290
and after magnocellular lesion
that blocks the parasol system,

813
00:40:09,290 --> 00:40:17,970
there is no effect, meaning that
the parasol system doesn't seem

814
00:40:17,970 --> 00:40:21,030
to be too important for
contrast sensitivity.

815
00:40:21,030 --> 00:40:23,790
By contrast, there's
a huge effect,

816
00:40:23,790 --> 00:40:27,760
especially at high
spatial frequencies,

817
00:40:27,760 --> 00:40:33,880
after a parvocellular lesion
that blocks the midget system.

818
00:40:33,880 --> 00:40:35,910
So that, in essence
then, is what

819
00:40:35,910 --> 00:40:38,140
happens with
contrast sensitivity.

820
00:40:38,140 --> 00:40:42,870
Now, let us move on and say,
well, what about color vision?

821
00:40:42,870 --> 00:40:44,370
So how do you do
the color vision?

822
00:40:44,370 --> 00:40:46,020
I already told you that before.

823
00:40:46,020 --> 00:40:50,170
What you do is you
present, in this case,

824
00:40:50,170 --> 00:40:52,960
eight stimuli, one of which
is different from the others,

825
00:40:52,960 --> 00:40:55,180
and just have red
and green ones.

826
00:40:55,180 --> 00:40:56,390
This is the odd one.

827
00:40:56,390 --> 00:40:57,995
The monkey makes
a saccade to it.

828
00:40:57,995 --> 00:40:59,610

829
00:40:59,610 --> 00:41:02,409
He gets a drop of apple
juice for a reward.

830
00:41:02,409 --> 00:41:04,200
Now, if you want to be
systematic about it,

831
00:41:04,200 --> 00:41:07,790
you can vary the degree
of color contrast.

832
00:41:07,790 --> 00:41:11,360
But the effect is so
dramatic that it was not

833
00:41:11,360 --> 00:41:12,560
necessary to do that.

834
00:41:12,560 --> 00:41:14,400
So let me show you
what the effect was.

835
00:41:14,400 --> 00:41:17,010
Here, we have a monkey's
normal performance

836
00:41:17,010 --> 00:41:21,380
when the test element
is blue, red, and green.

837
00:41:21,380 --> 00:41:22,520

838
00:41:22,520 --> 00:41:26,000
This happens after a
parvocellular lesion,

839
00:41:26,000 --> 00:41:28,290
meaning when you block
the midget system,

840
00:41:28,290 --> 00:41:31,310
the monkey cannot
see colors at all.

841
00:41:31,310 --> 00:41:33,120
Just a total loss.

842
00:41:33,120 --> 00:41:35,300
Whereas, after
magnocellular lesion,

843
00:41:35,300 --> 00:41:38,260
his performance is
indistinguishable from normal.

844
00:41:38,260 --> 00:41:40,600
So this, then,
establishes the fact

845
00:41:40,600 --> 00:41:46,455
that color vision is controlled
by the midget system.

846
00:41:46,455 --> 00:41:47,720

847
00:41:47,720 --> 00:41:49,920
Now, the fact that this
is the case perhaps

848
00:41:49,920 --> 00:41:52,220
is not that surprising
because I told you

849
00:41:52,220 --> 00:41:59,150
that when you look at the
cells in the midget system

850
00:41:59,150 --> 00:42:02,060
in central vision,
that most of them

851
00:42:02,060 --> 00:42:04,290
get an input from
just-- at least,

852
00:42:04,290 --> 00:42:07,980
the red and green ones-- get
an input from a single cone.

853
00:42:07,980 --> 00:42:10,600
So just looking at the
receptive field organization

854
00:42:10,600 --> 00:42:14,830
tells you that that
system is likely to be

855
00:42:14,830 --> 00:42:17,090
very important for
color processing.

856
00:42:17,090 --> 00:42:20,334
So that, then, is
confirmed by this kind

857
00:42:20,334 --> 00:42:21,250
behavioral experiment.

858
00:42:21,250 --> 00:42:22,510

859
00:42:22,510 --> 00:42:25,690
So now, let us look at
brightness perception.

860
00:42:25,690 --> 00:42:29,711
Now, how is that different
from contrast sensitivity?

861
00:42:29,711 --> 00:42:31,710
It's different because,
in this case, what to do

862
00:42:31,710 --> 00:42:36,530
then is you use a
discrimination task like this.

863
00:42:36,530 --> 00:42:38,600
And I think most of you
can tell that this one is

864
00:42:38,600 --> 00:42:40,080
brighter than the others.

865
00:42:40,080 --> 00:42:42,680
Purposefully, I made
that a small difference,

866
00:42:42,680 --> 00:42:45,320
so you can appreciate the
fact that on each trial,

867
00:42:45,320 --> 00:42:48,130
we can vary the difference
between the distractors

868
00:42:48,130 --> 00:42:49,210
and the target.

869
00:42:49,210 --> 00:42:51,680
And you can generate
a curve seeing

870
00:42:51,680 --> 00:42:53,200
how much brightness
difference do

871
00:42:53,200 --> 00:42:58,600
you need to be able to perceive
a brightness difference.

872
00:42:58,600 --> 00:43:01,120
So if you do that
kind of experiment,

873
00:43:01,120 --> 00:43:02,370
one is in for a big surprise.

874
00:43:02,370 --> 00:43:03,380

875
00:43:03,380 --> 00:43:08,140
This shows here what happens
after a parvocellular lesion.

876
00:43:08,140 --> 00:43:11,090
And this shows here what happens
after a magnocellular lesion.

877
00:43:11,090 --> 00:43:13,750
So when you block
the midget system,

878
00:43:13,750 --> 00:43:19,840
the performance is unaffected
as is the case with a magno

879
00:43:19,840 --> 00:43:24,200
lesion, meaning that
if you, obviously,

880
00:43:24,200 --> 00:43:29,000
that both the midget system
and the parasol system process

881
00:43:29,000 --> 00:43:36,770
information about brightness,
at least, at these low spatial

882
00:43:36,770 --> 00:43:41,480
frequencies that we have
used that I just showed you.

883
00:43:41,480 --> 00:43:45,210
So now, the other surprise
was that, then, the question

884
00:43:45,210 --> 00:43:46,790
became, well, what
if you do this not

885
00:43:46,790 --> 00:43:52,810
under photopic conditions and
do under scotopic conditions?

886
00:43:52,810 --> 00:43:55,860
And again, there's
no effect, meaning

887
00:43:55,860 --> 00:43:59,140
that the unique
inputs from the rods

888
00:43:59,140 --> 00:44:01,970
and the unique
inputs from the cones

889
00:44:01,970 --> 00:44:04,420
must go into both
of the systems.

890
00:44:04,420 --> 00:44:06,430
Now, the reason
that was surprising

891
00:44:06,430 --> 00:44:08,600
is because a couple of
papers have been published,

892
00:44:08,600 --> 00:44:21,740
maybe about 15 to 20 years ago,
that claimed that the rods feed

893
00:44:21,740 --> 00:44:24,540
selectively into
the parasol system,

894
00:44:24,540 --> 00:44:26,370
not into the midget system.

895
00:44:26,370 --> 00:44:28,705
So this totally disprove that.

896
00:44:28,705 --> 00:44:32,930
And then subsequently, careful
anatomical experiments also

897
00:44:32,930 --> 00:44:37,730
established that both the
small and the large cells,

898
00:44:37,730 --> 00:44:41,550
magno ganglion cells,
receive convergent input

899
00:44:41,550 --> 00:44:46,700
from the rods and the
cones as I had diagrammed

900
00:44:46,700 --> 00:44:49,100
to you in the previous session.

901
00:44:49,100 --> 00:44:50,570

902
00:44:50,570 --> 00:44:54,835
So then, let's go on and look at
pattern and texture perception.

903
00:44:54,835 --> 00:44:57,750

904
00:44:57,750 --> 00:45:01,000
In this case, let me show you
the kind of experiment that's

905
00:45:01,000 --> 00:45:01,500
done.

906
00:45:01,500 --> 00:45:05,750
This is when you
look at patterns.

907
00:45:05,750 --> 00:45:08,750
One way to do it, go back
to those same checkerboards,

908
00:45:08,750 --> 00:45:11,150
but make them high
contrast and have one

909
00:45:11,150 --> 00:45:15,680
at a different spatial
frequency than the others.

910
00:45:15,680 --> 00:45:18,140
And then you can
systematically vary the degree

911
00:45:18,140 --> 00:45:21,290
of spatial frequency
difference between the targets

912
00:45:21,290 --> 00:45:22,880
and the distractors.

913
00:45:22,880 --> 00:45:25,060
So that would be
the method that is

914
00:45:25,060 --> 00:45:29,640
used to study this kind
of pattern perception.

915
00:45:29,640 --> 00:45:32,290
The other one is to
look at textures.

916
00:45:32,290 --> 00:45:34,790
And in this case, those
of you in the back

917
00:45:34,790 --> 00:45:36,080
probably can't see this.

918
00:45:36,080 --> 00:45:38,987
But those of you up front, can
you see this little area here,

919
00:45:38,987 --> 00:45:40,570
where the diagonal
lines are reversed?

920
00:45:40,570 --> 00:45:41,600

921
00:45:41,600 --> 00:45:44,490
So what happens is, first, you
just present this whole thing.

922
00:45:44,490 --> 00:45:51,650
And then you present the reverse
patterns and the surround.

923
00:45:51,650 --> 00:45:53,530
And when you do
that, the monkey has

924
00:45:53,530 --> 00:45:55,554
to make a saccade
to that location

925
00:45:55,554 --> 00:45:56,970
and will get a
drop of apple juice

926
00:45:56,970 --> 00:45:59,050
again for that performance.

927
00:45:59,050 --> 00:46:01,430
And then on each trial,
this appears somewhere else

928
00:46:01,430 --> 00:46:06,470
in one of the four to eight
locations in the display.

929
00:46:06,470 --> 00:46:08,550
So that's the procedure.

930
00:46:08,550 --> 00:46:12,090
And then if you do
this, you, again,

931
00:46:12,090 --> 00:46:15,180
luckily get a very dramatic
effect, apparently.

932
00:46:15,180 --> 00:46:16,010
Here it is.

933
00:46:16,010 --> 00:46:19,220
We have here normal performance.

934
00:46:19,220 --> 00:46:22,700
Here's a parvocellular
lesion, magnocellular lesion.

935
00:46:22,700 --> 00:46:25,480
This is texture,
and this is pattern.

936
00:46:25,480 --> 00:46:28,050
Pattern tasks was, overall,
much more difficult

937
00:46:28,050 --> 00:46:30,030
than the texture
one in this case.

938
00:46:30,030 --> 00:46:33,030
Well, what you see here
that is really dramatic

939
00:46:33,030 --> 00:46:37,250
is that when you block
the midget system,

940
00:46:37,250 --> 00:46:41,350
there's a tremendous loss in
your ability to see patterns

941
00:46:41,350 --> 00:46:43,565
and in your ability
to see textures.

942
00:46:43,565 --> 00:46:44,730

943
00:46:44,730 --> 00:46:49,850
So fine vision for
detail seems to be

944
00:46:49,850 --> 00:46:53,965
central for the processing
of the midget system.

945
00:46:53,965 --> 00:46:56,260

946
00:46:56,260 --> 00:47:00,670
So that, then, is
the effect that one

947
00:47:00,670 --> 00:47:04,590
gets with texture
and with pattern.

948
00:47:04,590 --> 00:47:05,720

949
00:47:05,720 --> 00:47:09,030
So now, let's move on and
talk about stereoscopic depth

950
00:47:09,030 --> 00:47:10,200
perception.

951
00:47:10,200 --> 00:47:11,900
It's a topic we
are going to look

952
00:47:11,900 --> 00:47:15,840
at in more detail
in a later session.

953
00:47:15,840 --> 00:47:17,960
Let me now introduce
this, first of all,

954
00:47:17,960 --> 00:47:24,672
by telling you that stereoscopic
depth perception resulted

955
00:47:24,672 --> 00:47:26,130
predominately by
virtue of the fact

956
00:47:26,130 --> 00:47:27,980
that the eye is
moving to the front

957
00:47:27,980 --> 00:47:30,685
so that there was a
major binocular overlap.

958
00:47:30,685 --> 00:47:31,830

959
00:47:31,830 --> 00:47:35,720
And if you talk about a monkey,
for example, or even many,

960
00:47:35,720 --> 00:47:39,230
many animals that do have
stereoscopic vision, here's

961
00:47:39,230 --> 00:47:44,880
an example of looking at a tree
when just about the only cue

962
00:47:44,880 --> 00:47:50,025
you have here would be based on
stereopsis because all of them

963
00:47:50,025 --> 00:47:51,290
are equally dark.

964
00:47:51,290 --> 00:47:53,380
Which branch is in
front of which one?

965
00:47:53,380 --> 00:47:54,690
And it's very hard to tell.

966
00:47:54,690 --> 00:47:57,730
If your monkey will jump from
this branch to this branch,

967
00:47:57,730 --> 00:48:00,700
if he can't tell where they
are relative to each other,

968
00:48:00,700 --> 00:48:03,510
the monkey is going to
fall down and drop dread.

969
00:48:03,510 --> 00:48:06,880
So it is very
important for monkeys

970
00:48:06,880 --> 00:48:09,680
to have a highly functional
stereoscopic system, which

971
00:48:09,680 --> 00:48:10,770
they do.

972
00:48:10,770 --> 00:48:13,440
And so, how do we study this?

973
00:48:13,440 --> 00:48:16,490
Well, the way we
study this is to use

974
00:48:16,490 --> 00:48:19,550
what is called a
random-dot stereogram.

975
00:48:19,550 --> 00:48:20,790

976
00:48:20,790 --> 00:48:24,350
Random-dot stereograms
were created

977
00:48:24,350 --> 00:48:31,230
once computers became a reality
many, many years back by Bela

978
00:48:31,230 --> 00:48:31,730
Julesz.

979
00:48:31,730 --> 00:48:32,880

980
00:48:32,880 --> 00:48:36,150
And he came up with
the idea that if you

981
00:48:36,150 --> 00:48:38,640
use this kinds of
random-dot stereograms,

982
00:48:38,640 --> 00:48:40,790
there's no other depth cue.

983
00:48:40,790 --> 00:48:42,270
So, in other words,
you can study

984
00:48:42,270 --> 00:48:48,680
just the stereoscopic depth
perception aspect of it.

985
00:48:48,680 --> 00:48:49,770
Now, why is this?

986
00:48:49,770 --> 00:48:53,800
Because what you do here is
you look at this two displays,

987
00:48:53,800 --> 00:48:56,550
you present this to the left
eye and this to the right eye.

988
00:48:56,550 --> 00:48:59,872
The way this is
done is that you use

989
00:48:59,872 --> 00:49:01,080
what is called a stereoscope.

990
00:49:01,080 --> 00:49:02,804

991
00:49:02,804 --> 00:49:04,720
I bet you most of you
have seen a stereoscope.

992
00:49:04,720 --> 00:49:06,110

993
00:49:06,110 --> 00:49:07,380
Everybody see a stereoscope?

994
00:49:07,380 --> 00:49:08,220

995
00:49:08,220 --> 00:49:08,720
No?

996
00:49:08,720 --> 00:49:11,360

997
00:49:11,360 --> 00:49:14,940
So a stereoscope
used to be something

998
00:49:14,940 --> 00:49:18,790
that was extremely popular
starting in the 19th century.

999
00:49:18,790 --> 00:49:20,300

1000
00:49:20,300 --> 00:49:23,240
They created these handheld
devices with the two lenses

1001
00:49:23,240 --> 00:49:24,410
that you look through.

1002
00:49:24,410 --> 00:49:36,090
And then they created a camera
that had two lenses in it

1003
00:49:36,090 --> 00:49:38,740
at the same distance,
roughly, as your two eyes.

1004
00:49:38,740 --> 00:49:40,550
And so it took a
picture, thereby,

1005
00:49:40,550 --> 00:49:47,145
creating two pieces,
one by each lens.

1006
00:49:47,145 --> 00:49:48,660

1007
00:49:48,660 --> 00:49:51,210
And then, what you
did, since the two have

1008
00:49:51,210 --> 00:49:54,090
a slightly different perspective
of what you're looking at,

1009
00:49:54,090 --> 00:49:59,760
then the photographs are
put into the stereoscope

1010
00:49:59,760 --> 00:50:00,350
to look at.

1011
00:50:00,350 --> 00:50:02,220
These two images are fused then.

1012
00:50:02,220 --> 00:50:03,860
Looks like a single image.

1013
00:50:03,860 --> 00:50:06,920
And due to their
very disparities,

1014
00:50:06,920 --> 00:50:08,140
you see real depth.

1015
00:50:08,140 --> 00:50:09,015
It's really dramatic.

1016
00:50:09,015 --> 00:50:10,170

1017
00:50:10,170 --> 00:50:13,610
And when we talk about
stereoscopic depth perception,

1018
00:50:13,610 --> 00:50:16,220
I'm going to actually bring
some stereoscopes here

1019
00:50:16,220 --> 00:50:19,840
and some examples so you can
see exactly what that is like.

1020
00:50:19,840 --> 00:50:22,160

1021
00:50:22,160 --> 00:50:24,460
But at any rate, in this
case, what you can do

1022
00:50:24,460 --> 00:50:27,430
is you can take a little
area here just like before.

1023
00:50:27,430 --> 00:50:30,220
And you can take the
dots in this area.

1024
00:50:30,220 --> 00:50:32,940
You move them a little bit
this way, a few pixels.

1025
00:50:32,940 --> 00:50:35,230
And you move this a
bit this way, that way.

1026
00:50:35,230 --> 00:50:37,380
And then if it's a
square area, you're

1027
00:50:37,380 --> 00:50:39,460
going to see a
square sticking out.

1028
00:50:39,460 --> 00:50:42,000
And the monkey will then
make a saccade to that.

1029
00:50:42,000 --> 00:50:44,180
But with one eye, he
cannot do anything.

1030
00:50:44,180 --> 00:50:49,370
He can't see a thing because
these random-dot stereograms

1031
00:50:49,370 --> 00:50:52,195
only give you information
about disparity.

1032
00:50:52,195 --> 00:50:53,820
So if you do that,
you're going to have

1033
00:50:53,820 --> 00:50:55,720
the monkey make a
saccade to these.

1034
00:50:55,720 --> 00:50:58,100
You can vary the
degree of disparity.

1035
00:50:58,100 --> 00:50:59,140

1036
00:50:59,140 --> 00:51:02,440
And when you do that,
what you find is,

1037
00:51:02,440 --> 00:51:08,000
quite dramatically, is that
after a parvo lesion, when

1038
00:51:08,000 --> 00:51:11,250
you block the midget system,
there's a tremendous loss.

1039
00:51:11,250 --> 00:51:14,685
The monkey
essentially, especially

1040
00:51:14,685 --> 00:51:18,110
at smaller disparities,
has totally

1041
00:51:18,110 --> 00:51:23,250
lost his ability to use
stereoscopic depth information.

1042
00:51:23,250 --> 00:51:29,300
So there is no deficit, however,
after a magnocellular lesion.

1043
00:51:29,300 --> 00:51:34,720
So therefore, you can say safely
that, especially at smaller

1044
00:51:34,720 --> 00:51:41,270
disparities, what you have
is the midget system that

1045
00:51:41,270 --> 00:51:45,320
performs this remarkable task
of seeing things in depth

1046
00:51:45,320 --> 00:51:50,310
by virtue of disparity
in the two eyes produced

1047
00:51:50,310 --> 00:51:51,770
by stereoscopic vision.

1048
00:51:51,770 --> 00:51:53,620

1049
00:51:53,620 --> 00:51:55,990
So that's really a
very dramatic effect.

1050
00:51:55,990 --> 00:51:59,815
Then the next thing we can
look at is motion perception.

1051
00:51:59,815 --> 00:52:01,190

1052
00:52:01,190 --> 00:52:02,990
Again, this can be
done in various ways,

1053
00:52:02,990 --> 00:52:04,740
but I will just show
you an example of it.

1054
00:52:04,740 --> 00:52:06,750
So the monkey first fixates.

1055
00:52:06,750 --> 00:52:08,890
Again, use random-dot
stereograms here.

1056
00:52:08,890 --> 00:52:09,910

1057
00:52:09,910 --> 00:52:13,390
And then you set in motion
a small square area.

1058
00:52:13,390 --> 00:52:13,890
Ready?

1059
00:52:13,890 --> 00:52:15,650

1060
00:52:15,650 --> 00:52:16,810
I hope.

1061
00:52:16,810 --> 00:52:17,470
There we go.

1062
00:52:17,470 --> 00:52:18,570

1063
00:52:18,570 --> 00:52:21,600
Or you can do the high
spatial frequency like that.

1064
00:52:21,600 --> 00:52:22,660

1065
00:52:22,660 --> 00:52:24,660
And then, of course, on
each trial, that appears

1066
00:52:24,660 --> 00:52:25,740
someplace else.

1067
00:52:25,740 --> 00:52:28,150
And you can vary
the velocity or you

1068
00:52:28,150 --> 00:52:31,420
can vary the contrast
of the display

1069
00:52:31,420 --> 00:52:35,360
and see how the monkey
performs in the intact portions

1070
00:52:35,360 --> 00:52:37,830
of visual field
and how it performs

1071
00:52:37,830 --> 00:52:40,410
in those portions of the
visual field that are blocked

1072
00:52:40,410 --> 00:52:44,540
either for the midget system
or for the parasol system.

1073
00:52:44,540 --> 00:52:45,850
Clear?

1074
00:52:45,850 --> 00:52:47,830
So let's think about
it for a minute.

1075
00:52:47,830 --> 00:52:49,413
What do you think
you're going to get?

1076
00:52:49,413 --> 00:52:51,770

1077
00:52:51,770 --> 00:52:53,330
Here we go.

1078
00:52:53,330 --> 00:52:55,610
Here we are-- motion detection.

1079
00:52:55,610 --> 00:52:56,800
This is a parvo lesion.

1080
00:52:56,800 --> 00:52:58,140
This is a magno lesion.

1081
00:52:58,140 --> 00:53:01,720
And so what you get is
a dramatic deficit, not

1082
00:53:01,720 --> 00:53:04,520
an all-amount deficit,
but a dramatic deficit

1083
00:53:04,520 --> 00:53:07,440
in seeing motion
after the magno lesion

1084
00:53:07,440 --> 00:53:09,150
but not after parvo lesion.

1085
00:53:09,150 --> 00:53:14,510
So this says that,
indeed, the parasol system

1086
00:53:14,510 --> 00:53:17,080
plays a very important role
in motion perception, not

1087
00:53:17,080 --> 00:53:18,220
an exclusive role.

1088
00:53:18,220 --> 00:53:19,910
There is still some
performance there

1089
00:53:19,910 --> 00:53:26,550
at very, very low contrast here.

1090
00:53:26,550 --> 00:53:29,120
And there's a big effect
at very high contrast,

1091
00:53:29,120 --> 00:53:30,550
and monkey does better.

1092
00:53:30,550 --> 00:53:35,140
So we can conclude
that the parasol system

1093
00:53:35,140 --> 00:53:39,235
is very important for
motion perception.

1094
00:53:39,235 --> 00:53:40,420

1095
00:53:40,420 --> 00:53:44,990
So now, the next thing we
can look at is flicker.

1096
00:53:44,990 --> 00:53:48,160
And in this case, when
you study flicker,

1097
00:53:48,160 --> 00:53:53,310
instead of using a
monitor, people used LEDs.

1098
00:53:53,310 --> 00:53:54,850
Now, why do you think that is?

1099
00:53:54,850 --> 00:53:56,755
Why don't they
just use monitors?

1100
00:53:56,755 --> 00:53:58,870

1101
00:53:58,870 --> 00:54:00,460
Well, I mean, the
reason for that

1102
00:54:00,460 --> 00:54:02,420
is very straightforward,
actually.

1103
00:54:02,420 --> 00:54:04,900
When you use a
regular monitor, what

1104
00:54:04,900 --> 00:54:06,360
is the frequency of a monitor?

1105
00:54:06,360 --> 00:54:11,790
It's the same as the frequency
of the alternating current

1106
00:54:11,790 --> 00:54:14,260
that you have, that
shine the lights up here.

1107
00:54:14,260 --> 00:54:17,920
But what is that in
the United States?

1108
00:54:17,920 --> 00:54:18,750
60 hertz.

1109
00:54:18,750 --> 00:54:20,260

1110
00:54:20,260 --> 00:54:23,450
And so that's what happens
on a regular monitor.

1111
00:54:23,450 --> 00:54:30,640
And every 1 over 60 hertz
is you shift the image.

1112
00:54:30,640 --> 00:54:32,160

1113
00:54:32,160 --> 00:54:35,620
In Europe, the frequency
is actually 50 hertz.

1114
00:54:35,620 --> 00:54:40,830
So at any rate, because
of that, there's

1115
00:54:40,830 --> 00:54:42,930
a rather limited
range over which

1116
00:54:42,930 --> 00:54:48,700
you can vary the ON and OFF
activity of a flickering spot.

1117
00:54:48,700 --> 00:54:51,080
So if you use any of
this, however, you

1118
00:54:51,080 --> 00:54:57,380
can use it in a huge,
huge range of small steps.

1119
00:54:57,380 --> 00:54:59,890
So, therefore, this
is what the display

1120
00:54:59,890 --> 00:55:02,960
looks like that people
use to study this.

1121
00:55:02,960 --> 00:55:04,760
First, the monkey fixates here.

1122
00:55:04,760 --> 00:55:08,636
And then one of these LEDs
will start flickering.

1123
00:55:08,636 --> 00:55:10,260
And I'll show you
the flickering, which

1124
00:55:10,260 --> 00:55:12,450
is not perfect here
on this monitor,

1125
00:55:12,450 --> 00:55:14,150
but it will give you a sense.

1126
00:55:14,150 --> 00:55:15,370
Everybody see that flicker?

1127
00:55:15,370 --> 00:55:16,520

1128
00:55:16,520 --> 00:55:20,710
Now, the mean flicker
value of that location

1129
00:55:20,710 --> 00:55:24,630
is the same as the yellow
lights that you see there.

1130
00:55:24,630 --> 00:55:26,600
So if it flickers
at a high rate,

1131
00:55:26,600 --> 00:55:29,000
you can't tell that it's
flickering because it's

1132
00:55:29,000 --> 00:55:31,710
beyond the ability of
the eye to resolve it,

1133
00:55:31,710 --> 00:55:35,460
and then you can't make a
saccade to that location.

1134
00:55:35,460 --> 00:55:39,900
So if you look at that, what you
find here, after parvo lesion

1135
00:55:39,900 --> 00:55:44,640
and after magno lesion,
you get a gigantic deficit

1136
00:55:44,640 --> 00:55:45,925
after magno lesion.

1137
00:55:45,925 --> 00:55:46,930

1138
00:55:46,930 --> 00:55:49,910
And that fits with what I
told you in the beginning--

1139
00:55:49,910 --> 00:55:56,480
namely, that the
midget cells respond

1140
00:55:56,480 --> 00:55:59,400
in a fairly sustained fashion
when the stimulus comes on.

1141
00:55:59,400 --> 00:56:03,310
Whereas, the parasol
cells respond transiently,

1142
00:56:03,310 --> 00:56:09,160
which makes them much more
readily available for motion

1143
00:56:09,160 --> 00:56:10,110
and for flicker.

1144
00:56:10,110 --> 00:56:15,130

1145
00:56:15,130 --> 00:56:20,480
So those, then, are
the major arrangements

1146
00:56:20,480 --> 00:56:23,290
that we see with these
various experiments.

1147
00:56:23,290 --> 00:56:27,145
And so we can summarize what
happens after parvocellular

1148
00:56:27,145 --> 00:56:31,610
and magnocellular lesion
and say what happens here.

1149
00:56:31,610 --> 00:56:32,620

1150
00:56:32,620 --> 00:56:35,220
So this one here is when
you block the midget system.

1151
00:56:35,220 --> 00:56:38,850
This is where you block
the parasol system.

1152
00:56:38,850 --> 00:56:41,480
And here are all the various
test that had been used.

1153
00:56:41,480 --> 00:56:48,610
And you can see that
for the parasol system,

1154
00:56:48,610 --> 00:56:52,470
the major deficit arises in
motion perception and flicker

1155
00:56:52,470 --> 00:56:53,410
perception.

1156
00:56:53,410 --> 00:57:00,020
So those two are very
important in the processing

1157
00:57:00,020 --> 00:57:01,830
of the parasol system.

1158
00:57:01,830 --> 00:57:05,790
Whereas, for the
midget system, you

1159
00:57:05,790 --> 00:57:08,980
get lots of deficits in color
vision, texture perception,

1160
00:57:08,980 --> 00:57:13,170
and fine pattern perception,
fine shape perception,

1161
00:57:13,170 --> 00:57:15,760
in contrast sensitivity,
and in stereopsis.

1162
00:57:15,760 --> 00:57:17,360

1163
00:57:17,360 --> 00:57:23,000
So this, then, gives you a sense
of what these two systems are

1164
00:57:23,000 --> 00:57:26,730
important for in processing
visual information.

1165
00:57:26,730 --> 00:57:28,650

1166
00:57:28,650 --> 00:57:35,330
And so, what you can do next
is to summarize what I just

1167
00:57:35,330 --> 00:57:37,630
told you-- namely, that
the midget system is

1168
00:57:37,630 --> 00:57:41,455
important for color, texture,
fine form, and fine stereo.

1169
00:57:41,455 --> 00:57:42,820

1170
00:57:42,820 --> 00:57:45,830
The parasol system is
important for fast flicker

1171
00:57:45,830 --> 00:57:48,470
and fast, low contrast motion.

1172
00:57:48,470 --> 00:57:52,270
Both systems are capable of
doing brightness; coarse form;

1173
00:57:52,270 --> 00:57:55,870
coarse stereo; slow
flicker; slow, high contrast

1174
00:57:55,870 --> 00:57:58,400
motion; and scotopic vision.

1175
00:57:58,400 --> 00:58:02,140
So it is not a
simple arrangement.

1176
00:58:02,140 --> 00:58:03,330
It's a complex arrangement.

1177
00:58:03,330 --> 00:58:07,740
There is overlap in what
both systems can do.

1178
00:58:07,740 --> 00:58:09,720
So now, the big
question comes up.

1179
00:58:09,720 --> 00:58:11,540

1180
00:58:11,540 --> 00:58:14,970
Why was it so important to
create both of these systems?

1181
00:58:14,970 --> 00:58:17,810
Well, the number of
schemes that have evolved,

1182
00:58:17,810 --> 00:58:19,810
certainly, the
motion is obvious.

1183
00:58:19,810 --> 00:58:22,340
But one thing one
can come up with is

1184
00:58:22,340 --> 00:58:26,440
a scheme of this sort that
has been proposed-- namely,

1185
00:58:26,440 --> 00:58:31,240
that what happened as a result
of these two systems emerging,

1186
00:58:31,240 --> 00:58:35,340
your ability to process
information has been extended.

1187
00:58:35,340 --> 00:58:42,490
And for the midget system,
you expanded the ability

1188
00:58:42,490 --> 00:58:46,000
to see up to high
spatial frequencies--

1189
00:58:46,000 --> 00:58:48,320
very, very important attribute.

1190
00:58:48,320 --> 00:58:52,000
And I should add, also
for the midget system,

1191
00:58:52,000 --> 00:58:54,480
it became possible
for you to see color.

1192
00:58:54,480 --> 00:58:57,490

1193
00:58:57,490 --> 00:59:01,050
Whereas, when you come
to the parasol system,

1194
00:59:01,050 --> 00:59:03,520
it expanded the
range of your ability

1195
00:59:03,520 --> 00:59:06,620
to process information
in the temporal domain--

1196
00:59:06,620 --> 00:59:10,085
your ability to see very
fast motion, to see flicker.

1197
00:59:10,085 --> 00:59:11,310

1198
00:59:11,310 --> 00:59:17,000
Now, let me add here that's
a very important attribute,

1199
00:59:17,000 --> 00:59:24,330
by the way, for animals as
well as humans because one

1200
00:59:24,330 --> 00:59:28,590
of the common things
that has emerged

1201
00:59:28,590 --> 00:59:31,350
in the course of evolution
is what is called camouflage.

1202
00:59:31,350 --> 00:59:32,339

1203
00:59:32,339 --> 00:59:34,255
I think I may have
mentioned that once before.

1204
00:59:34,255 --> 00:59:35,590

1205
00:59:35,590 --> 00:59:39,520
That is that when
you or an animal,

1206
00:59:39,520 --> 00:59:43,220
and the coloring of you,
which is done in thousands

1207
00:59:43,220 --> 00:59:47,780
of animals, is made similar
to the background, then

1208
00:59:47,780 --> 00:59:53,450
it's very difficult for you
to see that particular animal.

1209
00:59:53,450 --> 00:59:55,380
So it has an
excellent camouflage.

1210
00:59:55,380 --> 01:00:01,650
However, as soon as this
animal begins to move,

1211
01:00:01,650 --> 01:00:05,170
the ability to camouflage
itself disappears.

1212
01:00:05,170 --> 01:00:06,720
And animals have to move.

1213
01:00:06,720 --> 01:00:11,830
And that's because
the parasol system

1214
01:00:11,830 --> 01:00:15,390
is extremely
sensitive to motion.

1215
01:00:15,390 --> 01:00:18,060
And so whenever an
animal begins to move,

1216
01:00:18,060 --> 01:00:20,160
even though it has
excellent camouflage,

1217
01:00:20,160 --> 01:00:23,050
it is predominantly
the parasol system

1218
01:00:23,050 --> 01:00:28,460
that will destroy the
camouflage effect.

1219
01:00:28,460 --> 01:00:30,540

1220
01:00:30,540 --> 01:00:32,660
I'm not saying
this is necessarily

1221
01:00:32,660 --> 01:00:36,010
the only hypothesis, but
this is one hypothesis

1222
01:00:36,010 --> 01:00:41,190
that had been advanced to try
to account for how sensible it

1223
01:00:41,190 --> 01:00:42,815
is to have these two systems.

1224
01:00:42,815 --> 01:00:43,910

1225
01:00:43,910 --> 01:00:45,780
Now, of course,
you could ask, how

1226
01:00:45,780 --> 01:00:48,860
come this couldn't be just
done in one system-- all of it?

1227
01:00:48,860 --> 01:00:51,950
Well, there are several
reasons for that--

1228
01:00:51,950 --> 01:00:56,830
is that to combine a
situation where you have

1229
01:00:56,830 --> 01:01:00,220
a sustained response and a
transient response into one

1230
01:01:00,220 --> 01:01:01,170
is next to impossible.

1231
01:01:01,170 --> 01:01:02,710

1232
01:01:02,710 --> 01:01:07,890
And to have cells that
are highly sensitive,

1233
01:01:07,890 --> 01:01:13,620
or the parasol cells, you need
to have a convergent input

1234
01:01:13,620 --> 01:01:15,780
from several photoreceptors.

1235
01:01:15,780 --> 01:01:17,620
But as soon as
you have that, you

1236
01:01:17,620 --> 01:01:21,080
lose your ability
to see fine detail.

1237
01:01:21,080 --> 01:01:24,840
So these requirements
to do this and this

1238
01:01:24,840 --> 01:01:28,230
are antagonistic to each other.

1239
01:01:28,230 --> 01:01:31,300
And it's not possible to
do that in a single cell

1240
01:01:31,300 --> 01:01:32,830
at the retinal level.

1241
01:01:32,830 --> 01:01:37,010
So it was decided, inasmuch
as they should decide,

1242
01:01:37,010 --> 01:01:39,050
that it will be
best just to create

1243
01:01:39,050 --> 01:01:43,630
two separate systems however
complicated that might be.

1244
01:01:43,630 --> 01:01:44,730

1245
01:01:44,730 --> 01:01:49,800
So that, then, brings me
to the overall summary

1246
01:01:49,800 --> 01:01:52,540
of what I had covered today.

1247
01:01:52,540 --> 01:01:54,840
First of all, I
told you-- that's

1248
01:01:54,840 --> 01:01:57,610
the obvious part-- are two
major channels that originate

1249
01:01:57,610 --> 01:02:00,540
in the retina are the
midget and the parasol.

1250
01:02:00,540 --> 01:02:03,900
I should add here that there
are many other channels

1251
01:02:03,900 --> 01:02:06,477
in the retina,
but the cells that

1252
01:02:06,477 --> 01:02:08,310
do that-- and we'll
talk about some of those

1253
01:02:08,310 --> 01:02:11,595
later-- are much less numerous.

1254
01:02:11,595 --> 01:02:13,550

1255
01:02:13,550 --> 01:02:16,610
The overwhelming majority
of cells in the retina

1256
01:02:16,610 --> 01:02:18,930
are either midget and parasol.

1257
01:02:18,930 --> 01:02:22,090
Then in central retina,
the receptive field center

1258
01:02:22,090 --> 01:02:24,400
of the midget cells
and parvocellular cells

1259
01:02:24,400 --> 01:02:26,880
is comprised of
just a single cone.

1260
01:02:26,880 --> 01:02:30,500

1261
01:02:30,500 --> 01:02:32,830
The midget cells and the
parvocellular cells--

1262
01:02:32,830 --> 01:02:36,840
meaning that the midget projects
to the parvocellular layers.

1263
01:02:36,840 --> 01:02:40,370
And I told you before that
the midget cells of the retina

1264
01:02:40,370 --> 01:02:44,430
have receptive fields which are
quite similar to those, almost

1265
01:02:44,430 --> 01:02:47,270
identical to those that you
see in the parvocellular

1266
01:02:47,270 --> 01:02:49,850
layers of the lateral
geniculate nucleus.

1267
01:02:49,850 --> 01:02:55,410
Then the parasol cells have
much larger receptive fields

1268
01:02:55,410 --> 01:02:57,000
than do the midget cells.

1269
01:02:57,000 --> 01:03:02,050
The cone input is mixed both
in the center and the surround.

1270
01:03:02,050 --> 01:03:07,150
And that is the reason why this
system, the parasol system,

1271
01:03:07,150 --> 01:03:09,230
cannot tell you
anything about color,

1272
01:03:09,230 --> 01:03:12,510
but it is very sensitive and can
tell you about any change that

1273
01:03:12,510 --> 01:03:17,140
occurs out there over time,
irrespective of the kind

1274
01:03:17,140 --> 01:03:19,000
of color it has.

1275
01:03:19,000 --> 01:03:22,940
Now, the midget and parasol cell
ratio from center to periphery

1276
01:03:22,940 --> 01:03:25,900
changes from 8 to 1 to 1 to 1.

1277
01:03:25,900 --> 01:03:29,100
Now, I should
reiterate that in that

1278
01:03:29,100 --> 01:03:30,580
it is very important
for us to be

1279
01:03:30,580 --> 01:03:32,390
sensitive to motion
in the periphery.

1280
01:03:32,390 --> 01:03:34,460

1281
01:03:34,460 --> 01:03:41,810
That's if an animal is
threatened by some predator,

1282
01:03:41,810 --> 01:03:48,030
it is highly desirable
to be able to very

1283
01:03:48,030 --> 01:03:50,060
sensitive to any motion.

1284
01:03:50,060 --> 01:03:52,730
And because of that,
you have a higher number

1285
01:03:52,730 --> 01:03:56,900
of parasol cells in the
periphery than in the center.

1286
01:03:56,900 --> 01:04:02,235
And so the ratio changes to
become equal in the periphery.

1287
01:04:02,235 --> 01:04:04,100

1288
01:04:04,100 --> 01:04:06,290
Now, the midget
and parasol systems

1289
01:04:06,290 --> 01:04:10,480
converge on some cells in V1.

1290
01:04:10,480 --> 01:04:11,970
And the example,
the prime example,

1291
01:04:11,970 --> 01:04:14,660
I've shown you when
they were separately

1292
01:04:14,660 --> 01:04:18,420
blocked at the level the
geniculate, that the cell

1293
01:04:18,420 --> 01:04:21,550
I showed you was one that did
receive a convergent input.

1294
01:04:21,550 --> 01:04:25,110
But many other cells
receive single input.

1295
01:04:25,110 --> 01:04:29,340
V4 receives inputs from both the
midget and the parasol cells.

1296
01:04:29,340 --> 01:04:32,920
So it's not an area that only
deals with color, obviously.

1297
01:04:32,920 --> 01:04:35,750
And what it will deal with,
we'll describe in more detail

1298
01:04:35,750 --> 01:04:36,580
later.

1299
01:04:36,580 --> 01:04:40,480
The major input to MT is
from the parasol cells.

1300
01:04:40,480 --> 01:04:43,830
And that, often, MT
and MST have often

1301
01:04:43,830 --> 01:04:46,965
been called the motion areas.

1302
01:04:46,965 --> 01:04:48,270

1303
01:04:48,270 --> 01:04:51,276
But they also play
important role, by the way,

1304
01:04:51,276 --> 01:04:57,520
in depth perception,
as we shall see.

1305
01:04:57,520 --> 01:04:59,690

1306
01:04:59,690 --> 01:05:03,490
And then the midget
system extends the range

1307
01:05:03,490 --> 01:05:06,880
of vision in the wavelength and
high spatial frequency domains.

1308
01:05:06,880 --> 01:05:08,130

1309
01:05:08,130 --> 01:05:10,810
The parasol system
extends the range

1310
01:05:10,810 --> 01:05:13,290
of vision in the high
frequency domain.

1311
01:05:13,290 --> 01:05:15,430

1312
01:05:15,430 --> 01:05:18,970
And in the scheme
that I showed you

1313
01:05:18,970 --> 01:05:22,245
is what leads to this
particular conclusion.

1314
01:05:22,245 --> 01:05:23,300

1315
01:05:23,300 --> 01:05:27,660
So that, then, is the essence
of what I wanted to cover today.

1316
01:05:27,660 --> 01:05:28,850

1317
01:05:28,850 --> 01:05:31,940
And I am now certainly
open to any questions

1318
01:05:31,940 --> 01:05:35,770
that you might have about these
two fascinating systems that

1319
01:05:35,770 --> 01:05:39,760
have evolved in the
retina over the millions

1320
01:05:39,760 --> 01:05:41,376
and millions of
years of evolution.

1321
01:05:41,376 --> 01:05:48,666

1322
01:05:48,666 --> 01:05:51,600
Well, I was so clear that
there are questions, huh?

1323
01:05:51,600 --> 01:05:54,990

1324
01:05:54,990 --> 01:05:56,580
Well, I hope that
you sort of gotten

1325
01:05:56,580 --> 01:06:00,820
a sense of what it is like to
do these kinds of experiments

1326
01:06:00,820 --> 01:06:05,220
and how luckily, at least, in
some cases, these experiments

1327
01:06:05,220 --> 01:06:09,620
can lead to nice discoveries
as to the workings

1328
01:06:09,620 --> 01:06:11,005
of the visual system.

1329
01:06:11,005 --> 01:06:14,070
Now, last time when we
talked about the APB, we did

1330
01:06:14,070 --> 01:06:16,500
have a "magic bullet."

1331
01:06:16,500 --> 01:06:21,490
This approach here is
not as neat, really,

1332
01:06:21,490 --> 01:06:24,790
because you have to make
lesions rather than specifically

1333
01:06:24,790 --> 01:06:26,723
affecting certain
neurotransmitters.

1334
01:06:26,723 --> 01:06:28,040

1335
01:06:28,040 --> 01:06:31,130
And that could not be done
because the neurotransmitters

1336
01:06:31,130 --> 01:06:34,390
for the midget and the
parasol cells are similar.

1337
01:06:34,390 --> 01:06:36,250
So you can't use that
kind of procedure

1338
01:06:36,250 --> 01:06:40,180
that we were able to use
miraculously for the ON and OFF

1339
01:06:40,180 --> 01:06:40,680
channels.

1340
01:06:40,680 --> 01:06:42,510

1341
01:06:42,510 --> 01:06:45,680
So that, in essence, is what
we are going to cover today.

1342
01:06:45,680 --> 01:06:47,150

1343
01:06:47,150 --> 01:06:48,600
Did everybody sign?

1344
01:06:48,600 --> 01:06:51,320
Any one of you not sign
the attendance sheet?

1345
01:06:51,320 --> 01:06:53,960
If not, please come
up here and sign it.

1346
01:06:53,960 --> 01:06:56,960
And then let me just say
again that next time,

1347
01:06:56,960 --> 01:07:00,120
we are going to talk about
color-- another fascinating

1348
01:07:00,120 --> 01:07:01,080
topic.

1349
01:07:01,080 --> 01:07:06,180
And we are also going to
talk about visual adaptation.

1350
01:07:06,180 --> 01:07:08,820

1351
01:07:08,820 --> 01:07:11,540
And if you can, if you
get a chance to do so,

1352
01:07:11,540 --> 01:07:14,950
please try to read the
preparatory material which

1353
01:07:14,950 --> 01:07:17,700
should make it easier
for you to not only

1354
01:07:17,700 --> 01:07:19,450
comprehend but,
especially, to be

1355
01:07:19,450 --> 01:07:22,270
able to memorize these facts.

1356
01:07:22,270 --> 01:07:25,030
And the memorization is
a very important part

1357
01:07:25,030 --> 01:07:27,080
of learning things
in any course.

1358
01:07:27,080 --> 01:07:30,140
And it will, of
course, be essential

1359
01:07:30,140 --> 01:07:32,395
when you get to the stage
of having to take the exams.

1360
01:07:32,395 --> 01:07:33,620

1361
01:07:33,620 --> 01:07:36,150
Well, thank you so much.

1362
01:07:36,150 --> 01:08:05,573