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1.2.6 Color vision-II
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從本節課中
Perception: Vision
教學方
Chenjian Li
Professor
Donggen Luo
Research Fellow
Yan Zhang
Professor
So, in those stage actually, they don't have any evidence
to demonstrate this is true, so what happens actually?
Okay, later, of course actually they not for scientists,
actually, really do the experiment to prove.
Like this one, Jeremy Nathans Jeremy Natham is also
from Johns Hopkins University just like Kim Y Yao.
[FOREIGN] Now what's his contribution?
He cloned.
All those different colors
which are pigments.
[FOREIGN] They got protein.
[FOREIGN] Okay, so he cloned these three receptors,
and they look like here.
[FOREIGN] long distance.
[FOREIGN] Your alignment actually
makes the comparison.
All these red dots right here, these registers are different,
but the others all are the same.
So look at this protein, there you have about 96%
identity [FOREIGN]
But, [FOREIGN]
That's strange, okay?
These two proteins, they are quite identical.
And then, as we talk about the light
effect in the membrane
is only to [INAUDIBLE] retinal.
It is the retinal absorb the photon.
But right now you have two different proteins, one is response for
the red detection, one is for the green.
But only one chemical to detect a photon.
How can you achieve this wavelength detection?
[FOREIGN] Those all change the retina.
It leverages the retina.
[FOREIGN] A lot of people
actually started
this how a protein
structure can change
the spectrum of
the [INAUDIBLE].
[FOREIGN] Spectrum, or
this important differences,
actually it's closed,
through the binding pocket, okay.
[FOREIGN] Like a [INAUDIBLE] binding pocket,
because this kind of acid, then you have a different chart.
A different polarities.
These actually will affect the absorption of the [INAUDIBLE] retina, okay?
This is a tuning called the the protein tuning.
So if you take these different proteins, then you're express in a.
And then you put a into the.
And then you can get this measurement, then you can see, okay.
So each protein is a chromophores they will absorb given the light to light.
Indeed, they found actually this is the blue pigments, okay?
Absorbs the photons actually mainly in the blue region and
then you have the green and there is red.
This is called absorption spectrum then this is the molecular
base of the color vision.
Three deep in the proteins and
they indeed as the young and hammer has,
actually they propose three [FOREIGN] molecular basin.
So close, right?
Here, right.
Okay so, this is a good question.
So, actually if you overlap this three
you [FOREIGN] all this three actually, are identical.
The shape are the same.
It doesn't matter if it's this one or this one, all these are the same.
But then we see that they're quite close only 30 millimeter difference.
This actually is because this difference is a tuning from the protein.
This should not shift a lot because there's a binding pocket.
It does the charge actually, not so different.
Okay, so all this actually absorption is by the [INAUDIBLE] retina, right?
But the protein make the change shift from here to here, to here, to here.
And then you look in here.
On this other green two drops in difference.
Actually quite a lot.
The residual difference.
And this actually, they're quite close absorption.
It's a file 60.
Okay, good.
Yeah, this is good.
So this one actually, this is
a long kind of history here, okay.
So it's just actually a base order Young-Helmholtz,
they propose actually three types of cone for the receptor,
blue, green, and red, right?
And here, actually,
the absorption actually here is not really the red region.
It's yellow. And then we should have called it called
this actually yellow color for the receptor, right.
But actually because of the tradition we just actually
naming this one [INAUDIBLE] sensitive photo pigment.
Or corresponded to red, so it's not exactly right, okay.
You are right.
But it was still called the red pigment, because it's tradition.
Uh-huh.
>> [INAUDIBLE] color [INAUDIBLE] Red and the green.
Red and the greens will become yellow.
You mean?
>> And they're doing an experiment and
find the red color light Of other colors.
Actually the is that >> I see.
I see, I see.
Not this yellow one, you mean the detection.
No, if you use this one you still can create the whole spectrum.
Yeah so what's the question?
>> [INAUDIBLE] That [INAUDIBLE]
And [INAUDIBLE]
>> Okay.
>> [INAUDIBLE] what
the [INAUDIBLE] >> Yep.
>> [INAUDIBLE] so [INAUDIBLE] the septum
did not divide it more but- >> Okay, okay.
There's a good point here.
Also some insight.
Looking at this one, I guess chemation, the red and the green.
Because they're so identical.
So maybe they come here from the same, evolved from the same thing.
Maybe the green is the first and then the lung actually starts from green,
make some mutations during the evolution.
And then you create the.
That's a good point, okay.
So why during the evolution actually not separate further?
I guess this, no I don't know the true answer okay.
So we can talk about it maybe just for some discussion.
I guess actually maybe for the human or the monkey,
their turn, it's the environment which those
colors actually just use these two combinations.
Then you can chew.
So the main need for the food is seeking.
For example if you find a red fruit
[FOREIGN] will detect light [FOREIGN] you got
selection pressure [FOREIGN].
This may not be true, but just for a thinking, okay?
Yeah?
>> [INAUDIBLE]
>> Intensity.
>> [INAUDIBLE]
>> [FOREIGN]
intensity [FOREIGN].
>> [INAUDIBLE] >> Okay.
>> [INAUDIBLE] >> You fix the intensity [INAUDIBLE]
>> [INAUDIBLE]
>> Yeah.
>> [INAUDIBLE]
four [INAUDIBLE]
>> Comparison
[FOREIGN].
Okay, so this is the absorption spectrum,
absorption spectrum [FOREIGN] is the light
absorbed by these molecules, this absorption.
But this absorption doesn't mean
it really actually triggers a visual processing, right.
So you still have a step, actually,
a gap between these two, and then, this is important.
So we have a, call it, action spectrum.
Action spectrum should be, [INAUDIBLE] measure the electric signal from a cell.
Then you stiffen the light to stimulate the cell.
Then, see how many photons you need to produce a certain kind of a response.
And then frankly then you have the relative like a sensitivity,
just call it real action spectrum of the cell, right?
Now, fortunately these two are actually similar okay.
But you look at these pictures, they are so different actually.
This one You can see, or you can go down to zeroright?
But this one is far away, actually more sensitive, you can units.
No units, 0.0000001 maybe six 0s here,
you can do the measurement here.
But this one
[FOREIGN]
to activate
this pigment
is around
this region
right several
hundred.
What happened?
Actually their photo energy to see [FOREIGN] to the pigment.
[FOREIGN]
There
is not
any light
information
there.
You can sometimes occasionally perceive maybe there was some flesh there.
[FOREIGN] Backlight.
[FOREIGN] Okay.
Let's take a look here.
So this is a different cone.
The spectrum, right.
So, the cone allows us to color.
And let's compare.
There, the common response, this is a common response [INAUDIBLE] a monkey.
And then this is a monkey [INAUDIBLE] recording.
Look at it, just two response, they're different.
Obviously, what's the difference?
The connects is, are very different.
This is very fast.
This is very slow, right?
[FOREIGN] Our brain actually uses this
cone photoreceptor the motion.
[FOREIGN] Okay,
so the motion
detection.
[FOREIGN] Color, also you need
rely on this comfort receptor.
[FOREIGN] 29 appear
in the inside,
right?
[LAUGH] >> [INAUDIBLE]
>> [FOREIGN]
>> [LAUGH]
>> [FOREIGN] The right side, I'm sorry,
the right side is same thing happened here,
but actually for a patient.
[FOREIGN]
Because they
are very close,
these two proteins,
and on the same
chromosome sometimes
the recombination
will happen.
[FOREIGN]
Okay?
Now, because it's in the X chromosome,
the red and the green,
[FOREIGN] One copy of x chromosome,
[FOREIGN] copy, all right?
[FOREIGN]
