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  • Hey, Vsauce. Michael here. This

  • is called the dolly zoom effect and the optics that make it possible

  • are also responsible for what's called the moon

  • terminator illusion.

  • A terminator is the line between an illuminated

  • and dark side. Light arrives

  • perpendicular to the terminator but it doesn't always

  • appear to. Maybe you've noticed this before. When the Moon

  • and the Sun are up at the same time, and a good distance apart

  • in the sky, the direction the Moon is being lit

  • from won't always appear to line up

  • with the position of the Sun. What's going on here?

  • The answer lies

  • in visual angles. The further away from you something is,

  • the smaller it will appear to be. In psychophysical terms, its visual angle

  • shrinks - the angle within your field of view that it stretches across.

  • Now, this means that everything we look at is foreshortened,

  • that is it diminishes incise towards the horizon line.

  • A line infinitely far away. Things that far away

  • are foreshortened to the point at which they have no height

  • whatsoever. This distortion

  • affects everything that we look at. But it doesn't confuse us, because

  • our brains know about it. We can look at an object that is foreshortened and

  • figure out what it probably actually looks like.

  • For example, a door is a rectangle,

  • but it's wrecked by foreshortening when

  • opened. Closer distances appear larger. The whole shape

  • is different, but your brain isn't freaked out every time a door opens,

  • because it understands

  • that different sensations don't necessarily mean

  • different actual things. It's called subjective

  • constancy. Our brains cleverly factor in previous

  • experience and perspective clues from the surrounding world

  • to calculate in real time whether changes

  • in what we sense are because of actual changes

  • in the things we're looking at or are just merely products of their positions

  • or the surroundings.

  • For example, I, right now on this video screen,

  • am vulnerable to foreshortening. But I probably look

  • okay to you. However, if we frame in really closely

  • and remove surrounding perspective clues, I can be made to look

  • weird, strange, a little scary,

  • distended. I'm foreshortened without the necessary tools

  • around me for you to mentally adjust. This

  • is probably the crux of the Moon terminator

  • illusion. Take a look at this.

  • The line where that wall meets the ceiling

  • is a straight line. Seriously, take a look.

  • If you look to the left and right, it continues to look straight

  • and trust me, this building was built with level straight

  • ceilings. But that's not what your eye

  • senses. A camera will help

  • demonstrate this. It doesn't add in the post sensation processing that our

  • brains do

  • and we can also frame in to remove other clues telling us what to think.

  • Now, sure enough, right in front of us the line is

  • level with the screen of the camera - it's a straight line - but

  • if we move our eyes across the line, look what happens. If I pan this way,

  • the slope changes and now the line appears to be going

  • up and to the left. And if I panned

  • this way, the line appears to be moving up and to the right.

  • What's going on here? A straight line can't have changing slope,

  • that's what a curved line does.

  • Just like the curve we think we see between the Sun

  • and the Moon. But wait. If

  • the line between the Sun and the Moon is curved because of foreshortening,

  • why don't we see lines like this one as curves? Well,

  • here's a clue. Clues.

  • We know what rooms are supposed to look like. We know how they're built. We have

  • experience with them and there are other things in the environment

  • helping us. But when you look at the sky, there's not much to help you.

  • In the absence of clues about distance and perspective, our brains assume that

  • whatever we're looking at is

  • equidistant from us, making the sky a sort of

  • dome surface, like a planetarium screen.

  • The only clue we have then is the horizon, but it's a red herring,

  • because the horizon doesn't foreshorten. It's just a place where

  • due to foreshortening everything becomes infinitely flat.

  • Brian Rogers and Olga Naumenko demonstrated that these things result

  • in the terminator illusion by using a planetarium.

  • They projected two dots onto its dome, mimicking our perception of the Sun

  • and the Moon. They've then asked participants to place a third dot on the

  • straight line connecting them.

  • But just as in the Moon terminator illusion, people

  • incorrectly placed the third dot. They were influenced by a desire to stay

  • parallel to the horizon,

  • as if it was subject to the same foreshortening rules. Our brains also

  • often fail to factor in foreshortening when it comes to crepuscular rays,

  • light beams streaming through gaps in clouds.

  • They appear to converge from a common point, as if the Sun is only

  • a few thousand meters above Earth, but, of course, in fact, the Sun is extremely

  • far away

  • and these lines are actually pretty much exactly parallel.

  • It's true. They look like they converge for the same reason railroad tracks

  • appear to converge.

  • The visual angle of the distance separating them

  • shrinks the further down you look. Sometimes

  • our brains do the opposite. They assume

  • and consider foreshortening even when it isn't

  • really there, like in this illusion, where

  • the cars seem to be different sizes but in actuality on the page

  • are all the same size. Everything else in the image is affected by foreshortening,

  • so our brains assume that the cars are too and decide that in order for them

  • all to have the same visual angle, which they do,

  • the more distant ones must be literally larger

  • in real life. The rate at which the visual angle

  • of something you are looking at changes as you move toward it, or away from it,

  • is not constant. In order to cut the visual

  • angle of an object in half, its distance from you

  • must double. That means objects

  • really really far away require a lot more movement to have their visual angle

  • changed compared to nearer objects.

  • This is called parallax and it's a major reason

  • moving allows us to learn so much about

  • depth. It's why stuff on the side of the road

  • whizzes is by you as you drive past, while distant features of the landscape

  • appear to only crawl past. A really distant thing, like,

  • say, the Moon, 384,000 kilometers away

  • appears to move so little as you do, it can seem

  • to be following you.

  • It's not, of course. It's just geometry. For the same reasons,

  • moving a camera through space will affect the visual angle of nearer

  • things,

  • like the Vsauce mug here much more dramatically than

  • distant things, like Jake Chudnow's album against the wall.

  • It is barely changing size as we move back

  • and forth. But unlike moving, zooming

  • increases the visual angle of everything equally,

  • regardless of depth. Notice that when zooming,

  • the distant album grows and shrinks right along with the mug. Now, if you move

  • IN while zooming OUT, or vice versa,

  • the zoom will be most apparent when looking at distant

  • things, while the move more apparent on near things.

  • The result can be trippy. Here I've been placed where both

  • effects cancel each other out, so everything around me changes

  • instead. Another great illusion that takes advantage of parallax

  • is the popular star field or hallway illusion.

  • Cover the middle of the video and you'll appear to be moving

  • much faster. But you if cover the edges, you'll appear to be moving

  • much slower. All you're doing is altering the perspective clues your brain

  • receives

  • about movement. The nearer stuff at the edge

  • changes position faster than the distance stuff way ahead.

  • So if you cover the slow distance stuff your brain

  • only has the faster moving stuff to judge speed from. But cover the faster

  • near stuff and the slower stuff becomes the new

  • near. Your brain assumes that you've slowed down.

  • The optics and mathematics behind all of these effects

  • were understood at least thousands of years ago.

  • During the Renaissance, artists used that knowledge to produce

  • paintings that imitated reality really

  • well. I mean, the perspective is quite realistic.

  • But... the renaissance?

  • Why did it take so long for us get there?

  • I mean, look at this pre-Renaissance painting.

  • What the heck is going on here? The perspective is all wrong. That's not at

  • all what such a scene would actually

  • look like. Artists and viewers contemporary to works like that

  • saw the world just like we do, they

  • saw foreshortening - they couldn't help but see it. Foreshortening is right there in

  • plain sight.

  • No, foreshortening is

  • plain sight. So, what gives?

  • Were medieval artists all just a bunch of five year olds?

  • No.

  • No in the sense that the question is wrong.

  • Realistic-looking perspective was used way before the Renaissance.

  • Now, it might not have always been mathematically formal perspective,

  • but foreshortening was understood. Western art went from this

  • to this, not because humans all of a sudden became smarter,

  • but because of a difference in desire.

  • What to us today might look unrealistic and thus

  • bad, was, in its time,

  • deliberate and popular. The shift

  • to imitating the world mathematically, as if seen through a window,

  • was more about cultural interests and objectivity and

  • the individual than it was about artists all of a sudden becoming

  • smarter. Furthermore, perspective illusions shows that what we

  • think we see isn't always what we're seeing.

  • A child's drawing may seem crude

  • in terms of objective mathematical imitation,

  • but there are other things about the world and

  • our experience of it worth imitating. Teasing out

  • the less plainly obvious to show something personal

  • is sometimes even harder than following perspective grids

  • Picasso put it this way it: "It took me four years

  • to learn to paint like Rafael, but a lifetime to learn to paint

  • like a child."

  • And as always,

  • thanks for watching.

Hey, Vsauce. Michael here. This

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月のターミネーターイリュージョン (The Moon Terminator Illusion)

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    林宜悉 に公開 2021 年 01 月 14 日
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