Why do objects look smaller from a distance?

General Questions
#21

If I remember correctly from my university courses, stereoscopic vision is only useful for surprisingly short distances; optical infinity is about 20 ft / 6 m away from the viewer. Thus a “remote object” could just be something across your living room.

As Xena suggested, there are far more useful things than stereoscopy that our brains use to create the illusion of depth (i.e. estimating distance to various objects in the visual field). Parallax is a good example. Occlusion is another good one; is one object blocking view of another? Familiarity, as you suggested, is very useful to the brain; this one’s used to good effect on movie sets (Camelot!).
In fact Wikipedia has a list of many cues that the brain uses to perceive depth.

#22

If nothing else, the topic reminds me of Father Ted’s holiday :slight_smile:

#23

I read as much in a first person account of an anthropologist - he brought a couple of natives with him out of the jungle, and as they travelled through hilly farmlands, they were amazed at how some livestock ‘grew’ as they got closer to it, thinking at first he had performed some trick. This was a first person source so either the anthropologist was exaggerating / making it up, or it’s not just an urban legend.
I really wish I remember the the book; I read it for an anthropology class way back when I was in college.

#24

The way our brain processes vision is so ingrained that most people never even think about this question. I never thought about it until I studied computer graphics, and then you kind of can’t *stop *thinking about it.

#25

I read an account someone had with a tribesman. They were at a high vantage point, looking down. The tribesman commented on the “ants” below. The writer said they were people, but the tribesman didn’t believe him. Coming from the jungle, the tribe…

Oh, bollocks, I just saw Donovan posted the same thing above. I’m not deleting this after I spent so much effort writing it.

#26

On the contrary, this is exactly how urban legends work. You say it was a first person source, but you can’t remember what the source was. Which means that your account is, at best, second-person. And chances are, if you did find the book you read it in, it’d also be a book not by the anthropologist in question, but a reference to a source that really was, no joking, written by him. And so on down the line, until the real original source (if it could ever be found) turns out to be a joke book written for third-graders.

#27

Even in a jungle it seems reasonable to believe that one would notice that the monkey they chased up a tree appears smaller as it went higher. Or that you would quickly discover that the trees across the river are actually taller than you.

There are clearings that would allow you to recognize that the jaguar you are stalking really isn’t bite-size and is very capable of killing you

#28

The book was The Forest People by Colin Turnbull. He spent some time in the late 1950s living with a group of pygmies in, IIRC, central Africa. And yes, the underbrush was so thick that there was no opportunity to see more than about 6 feet (again, IIRC) in any direction, including up. And, needless to say, no one in the tribe had ever been anywhere else.

When Turnbull left, he took a young boy (a teenager, I think) with him for brief visit to the outside world. They hiked to the edge of the forest and got into the jeep Turnbull had left there. As they drove, the boy quickly became quite agitated. Turnbull couldn’t figure out what was upsetting the kid; all he could understand of what the kid was saying sounded like he was afraid of “enchanted cattle.”

Turnbull finally realized that the kid was spotting a cow in the distance, seeing it was small, and assuming it was a baby cow. By the time they drove past it, it was a full-sized cow, so the boy could only assume it had grown into adulthood in a matter of minutes.

#29

So, we’re expected to believe that someone who lived in underbrush so thick that you could never see further than six feet in any direction has some concept of what “cattle” are? Just seeing such a beast from a single perspective, it would have seemed mythical to our hypothetical jungle-dweller. If this Mr. Turnbull actually wrote such a book and claimed that, I’m going to call him a liar, or at best willfully ignorant of the people he was supposedly studying.

#30

Things look smaller at a distance because they are farther away. Next question!

#31

That’s not quite how Turnbull tells the story, which is on pages 250-251 of my edition of The Forest People. He does describe taking Kenge, a young Mbuti pygmy who had worked with him, on a trip by car outside the forest. Kenge initially thought (according to Turnbull) that the buffalo he saw at a great distance across the grasslands were insects, and when Turnbull explained they were buffalo he thought they might be tiny buffalo. Turnbull thought that Kenge’s confusion was due to the fact that the pygmies never have to make size comparisons at such a great distance, and also because in the grassland Kenge had no other objects to compare them with. (Turnbull speculates that as they approached Kenge might be thinking that the insects were turning into buffalo, or the tiny buffalo were growing; but all Kenge himself said was that he didn’t think they were real buffalo.)

I’ve been to the part of the Ituri forest where Turnbull worked, near Epulu in Congo-Kinshasha, and have been out in the forest with the Mbuti. (Kenge himself was still living there at the time, although I didn’t get a chance to meet him.) You can often see a fair distance in the forest (much farther than six feet), and in any case pygmies often leave the forest. They come out to the Bantu villages to trade and work. So they’re familiar with seeing things at some distance; just not miles and miles away.

#32

This is interesting to watch how urban legends are formed.

As the father of a 5-month old and a 2-year-old, it’s apparent that there is some trial and error happening in infants the age of my son concerning objects and if they are close enough to touch or not, but they quickly learn this skill. Much sooner than they learn to talk, for example, or sleep through the night. :frowning:

#33

No, the appearance of an object is a product of its size and distance. The actual size and distance are not affected.

#34

This is interesting to watch how urban legends are formed.

As the father of a 5-month old and a 2-year-old, it’s apparent that there is some trial and error happening in infants the age of my son concerning objects and if they are close enough to touch or not, but they quickly learn this skill. Much sooner than they learn to talk, for example, or sleep through the night. :frowning:

One of the books I’ve read may have mentioned something about this, but I don’t want to misremember something so I’ll wait until I can get home to check.

#35

That’s how it worked for me too (although I never really formally studied CG). It’s possible to get a computer to render a world without perspective, or a world in which perspective works the other way (objects appear larger as they move away). It quickly becomes apparent that things appearing smaller as they recede is the only way it can really work, or else vision would be impossible - because although there is a limit to how close something can be, there isn’t really a limit to how far away it can get.

#36

Reverse perspective would making going outside at night a scary experience.

#37

That’s what I’ve been trying to imagine. You look up at the night sky, and each star looks like it would if it were right up against your eyeball.

More to the point: I know there are some recent technologies that can reverse blindness. Do any of them work with people blind since birth (or at least a very young age)? Could that person learn to see things in perspective?

And another question: At what age do children’s drawings show distant objects smaller?

#38

Unless you are referring to surgical removal of congenital cataracts (and that is not recent, the first such an operation was in the early 18th century [PDF]) such technologies still fall very far short of “reversing blindness”. I presume you are talking about sensory substitution systems (which convert a signal from a video camera into sound or tactile signals) and “artificial retinas”. These can provide some ability to get information about the environment from the information in ambient light, but nothing like the rich amount of information (or the subjective feel of seeing) available to someone with healthy vision. Nevertheless, blind people can learn to use such systems (it is something they have to learn, it does not happen as soon as they are hooked up) to get some sense of visual perspective, and an ability to judge the relative distances of objects.

Actually, even without such technological aids, people who have been blind from a young age are capable of having some sense of perspective, and it appears in drawings made by blind people using tactile feedback (i.e., they can feel what they are drawing, by using a system in which the drawing implement leaves a raised ridge on the “paper”. They produce recognizable, if crude, drawings.

People who are blind from birth and known to be blind from birth are actually rather rare, because the symptoms of blindness are not very obvious in newborns (they can’t do very much anyway). Blindness researchers usually prefer to talk about “early blind” people rather than “congenitally blind” ones, but that, of course, begs a lot of questions when it comes to issues like this because it seems likely that sighted babies are rapidly developing their visual abilities from the moment they are born. Also, I believe even “early blindness” is relatively rare compared to blindness acquired later in life due to accident or disease. However, there has been quite a lot of research since the 17th century on how well early blind people who get their sight restored can see (the issue is known as Molyneux’s Problem). It seems clear that they can learn to do so, and can certainly learn to judge distance and perspective, but it takes a period of learning and they may never be able to learn to see as well as a person who could see when they were an infant.

#39

Yes - in fact, it would be quite impossible, because not only would you see more of the stars, the further away they were, it would also have to mean that you were on the receiving end of a greater share of their output of electromagnetic radiation.

But it’s difficult to see how things could continue to appear bigger, the further they receded - eventually, they would have to occupy more than 100% of your sphere of view.

#40

It’s been many years but I remember a section of a college course (maybe psychology?) that listed the ways we judge distance of an object. I probably don’t remember all of them.

-Focus. Objects of various distances require different focus. So if an unidentifiable object (U.O.) is in focus along with an indentifiable object 10 meters from us we judge it as being 10 meters away.

-Familiarity of object. When we see a plane in the sky we judge it’s distance because we know it’s actual size. I’ve been fooled a few times when seeing people flying R/C planes. Is that a real plane 3,000 feet up or a model plane 300 feet up?

-Overlapping. Two air balloons in the sky in close proximity make it hard to judge which is nearer. But if they pass eachother we know the one behind is further away.

-Where an object meets the ground. A 10 foot tall U.O. floating 50 meters above us can be impossible to judge it’s size or distance. Put the same object on the ground 50 meters away and we can determine it’s size because we know how far 50m is away from us on the ground.

There’s probably some others but I can’t think of them now.