تدريب Shadowing: Dog vision, explained - تعلم التحدث بالإنجليزية مع YouTube

How do they know what colors dogs can see?

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How do they know what colors dogs can see?

There's this myth that won't go away,

that dogs only see in black and white,

but that's just not true.

There's a bunch of apps and filters now that claim to show dog color vision.

But where does our understanding of this canine rainbow come from?

And do these filters really capture how dogs see the world?

Before we get to dogs,

how do we know what colors humans can or can't see?

I'm sure you've seen these before, right?

Yeah.

Do you have normal color vision?

I have, I think, normal color vision.

I think that says 45.

So what just happened there?

Light from this image entered Cleo's eye,

where it hit cells in her retina called cones that in turn sent electrical signals to her brain,

which created her perception of color.

This rainbow is just how our brain translates different wavelengths of light from one small section of the electromagnetic spectrum.

Clio, like most people, has three types of cone cells,

each one sensitive to a different part of the spectrum,

relatively short wavelengths of light, medium wavelengths, and long.

Their sensitivity peaks at specific points,

but it drops off smoothly in both directions.

So, when what we call orange light comes in and hits an S-cone,

its wavelength lands outside this sensitivity curve.

But if it hits an M-cone, a signal is produced.

And with the L-cone, an even stronger signal.

These signals are combined and interpreted by the brain as orange.

When so-called green light comes in,

the cones send a different set of signals.

And so people with normal vision can make out the number 45 in this pattern.

But what What if you were missing this M-cone,

like about 0.5% of the population?

Both orange and green light would stimulate the L-cone about the same amount.

And without the M-cone, the signals would be too similar.

The brain wouldn't be able to distinguish between them,

and the number 45 would disappear into the background.

For those who can't read numbers,

like toddlers, there are versions of this test that just have the subject trace a loopy line.

But how do you design a vision test for a dog?

If I were trying to do this with Thor,

I would concoct a test that involves getting food at the end,

if and only if he can demonstrate that he can see two different colors.

That's pretty much what Jay Knights did back in the late 1980s.

I said, we have to solve this question once or for all.

I went home at lunchtime and got my dog.

A toy poodle appropriately named Retina.

Brought him into the laboratory seven days a week for a year.

Lab setup was a little chamber.

There were three discs illuminated from behind.

The dog was trained to boop whatever disc looked different with her nose.

If she chose right, she heard a click and got a little treat.

If she chose wrong, no treat and a buzzer sound.

Once Retina learned that Jay wanted her to identify the different circle,

it was time for the real experiments.

One of the first experiments that we did,

we had three different white lights,

and then we added a little bit of the particular color.

At first we'd add a little bit and the dog can't see it.

But add more, and the dog can pick it out.

And if it takes a very small amount of any particular wavelength,

that means that they must be very sensitive.

For each color, they plotted out this sensitivity.

And we just marched across the whole entire rainbow.

This sensitivity curve strongly suggests that dogs have just two cones,

centered here and here.

And at this low point in the middle, something interesting happened.

Retina couldn't tell the difference between this color and white light.

There's some wavelength in the middle part of the spectrum that's kind of where the two cones overlap.

The light equally stimulates the two cones.

When all three of our cones are equally stimulated,

humans see shades of gray.

And the same would be true for dogs with their two cones.

For them, this is the point of that equal stimulation.

Another set of experiments mimicked those colorblindness tests we talked about before.

And as you'd expect from someone with just two cones,

retina struggled to tell the difference between oranges and greens.

Jay confirmed his results with two other dogs and published them in 1989.

Now my dog is much more famous in the realm of science than I am.

Follow-up studies gathered similar data,

and if you put that together with what we know about human vision,

you can start to paint a picture of the rainbow that dogs see.

Blue on one end, fading into gray in the middle,

and then yellow on the other end.

It's probably not that different from what a human missing their M-cone would see.

It makes me wonder how many times I have interacted with Thor in a way

that kind of expected him to be able to see the full spectrum of color.

Can I just put a filter on an image and be like,

oh, this is what a dog is seeing,

or are there complications to that?

Oh, I think it's way more complicated than that.

But that's a good first pass.

Is it anywhere near the subjective experience?

I think not.

I mean, there's a lot more complications just in the retina to begin with.

In addition to cones, mammals have rod cells that help them pick up light and motion.

And dogs have way more of these kinds of cells than humans.

That makes them more sensitive to movement and helps them see in low light.

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They also have a layer called the tapetum lucidum that reflects light back through the retina.

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That's what makes dogs' eyes shine at night.

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Then there's a difference in the arrangement of cells in the retina.

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We have lots of cells across all of the back of the eyeball,

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but an especially dense group of cells in the center,

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which enables us to see the thing that's right in front of us.

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But some breeds of dogs are different.

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They have a density of cells that sort of extends...

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Oh, I just made a hard...

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They have a density of cells that I love.

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And

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that horizontal band of cells might make it easier for them

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to take in visual information across a broader swath of the horizon.

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The position of their eyes often gives them a wider field of vision,

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but less overlap, which means weaker depth perception.

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Dogs are also mostly nearsighted.

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Distant things are fuzzier.

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And additionally, dogs' visual experience of the world is going to be completely tied up in the olfactory experience of the world.

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This is the aspect of dog vision that I don't think we humans can ever fully understand.

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So, this is just an image of the olfactory peduncles in the human on the left and the dog on the right.

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These are called peduncles?

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These are olfactory peduncles, yeah.

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That's a great word, wow.

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The olfactory system in the human takes up approximately 0.03% of the brain.

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Dogs do have a hugely larger olfactory system.

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They are detecting things that we are completely unable to detect.

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There's a bunch of studies that show dogs can smell cancer,

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malaria, COVID-19, explosives, diseased avocado trees,

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whale poop on the ocean,

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even the emotional state of their owners.

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You know, I do sometimes think

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when I put perfume on what my dog is thinking because it must be quite overwhelming for them.

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Here's another way to look at the brain.

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These are tractograms made with a special MRI technique.

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These lines trace the paths of white matter,

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the fibers that speed signals between different regions of the brain.

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You can virtually dissect these tractograms, highlighting different roots.

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For example, here are the paths extending from human olfactory peduncles to other regions.

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But here is the dog brain.

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Whoa.

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There's information freeways running from the nose to other parts of the brain.

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And these weren't found before just because no one really looked?

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Yeah, pretty much.

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Can you guess what this is circling?

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It's going here.

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Yeah, what is there?

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Do you know?

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I have no idea what's here.

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It's a little counterintuitive because in both humans and dogs,

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the place that we process vision is actually the back of our head,

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this occipital lobe back here.

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Oh, so what you're saying is dogs are processing smell like we are processing sight, sort of?

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Well, it's interesting because it's not unique to the dog that they might use a different sense to generate vision.

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I mean, we know that bats are a classic example.

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They can navigate through their auditory pathways.

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It's very possible that dogs can identify structures in the room from scent as well as from vision.

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Seeing and smelling are interwoven in an important way,

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and that is something completely unlike what we have in our brain.

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When I think about my sense of the world,

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my mental map of where I am in space,

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where other things are, like how those things relate to each other and move,

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like all of that is visual.

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We literally use the word visualize like that's what I'm thinking.

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But for a dog like now I'm imagining Thor's sense of the world

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and his place in it is like a spatial awareness that depends on smell.

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That's fascinating.

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Wow I don't even know I can't grok this fully.

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Yeah I mean I think it's impossible to grok.

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It's ungrokkable.

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Have you come across this term Umwelt?

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No. It's a term that comes from this German biologist whose name I can't remember right now,

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but it's something I couldn't pronounce even if I could remember it.

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Jakob Johann von Uxgut.

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And Umwelt, it refers to the different realities experienced by different organisms,

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the set of things that are meaningful to them,

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some of which we can't even sense.

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You come to see that we're just seeing like

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but one of many worlds which are existing in parallel and other animals are seeing in another slice.

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Star Rainbow might be more varied than that of a dog, but...

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Their olfactory world is so explosively colorful that it wouldn't occur to them for a second that there's something that's being missed.

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This is.. it really does help me understand my little best friend better.

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I feel like I feel connected to his world and sort of an appreciation that his world is different and also beautiful.

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I don't see Rowdy in his box today,

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but you're also a cat guy.

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Can cats do the booping test?

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I find it hard to believe.

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That might be my stereotypes about cats,

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but have people investigated this?

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And what do we know about cat color vision?

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Well, hey, everybody, it's Adam from the future.

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It's the next morning.

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I've got Rowdy back with me.

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And I've been up all night reading cat studies.

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تدريب Shadowing: Dog vision, explained - تعلم التحدث بالإنجليزية مع YouTube

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تدريب Shadowing: Dog vision, explained - تعلم التحدث بالإنجليزية مع YouTube

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