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Ken G
2005-Nov-10, 03:56 AM
This has appeared in books, but I'm interested in what new insights we can come up with: When you write words on a card and hold them to a mirror, why does the mirror reverse left to right and not top to bottom? Is there any connection to why our eyes are side by side instead of one over the other?

TheBlackCat
2005-Nov-10, 04:26 AM
The mirror is not really reversing the image per se. This is not exactly how mirror work but the analogy should help you understand what you are seeing. Imagine the piece of paper is emitting light, and you are standing behind the piece of paper. If the light flies straight ahead and touches a wall, what you will get is an image of the text where whatever is on the left hand side of the paper relative to you will remain on the left-hand side of the image on the wall. Everything on the right-hand side of the image relative to the you will be on the right-hand side of the image on the wall. Everything on the top will be on top, everything on the bottom will be on the bottom. However, what is the left-hand side for you will be the right-hand side for someone facing the front of the piece of paper. Their left will be your right, and vice versus. However, their down will still be your down and their up will still be your up. Getting back to the image on the wall, what they see as the right side of the text will translate to be what you see as the left side of the image, and what they see as the left side of the text will be what you see as the right side of the image. In other words, the image on the wall is reverse relative to what someone looking at the piece of paper will see. However, down is still down and up is still up for both frames of reference. You could imagine the image is you somehow seeing through the piece of paper so your are seeing the outer surface from behind. The mirror is similar, what is on your left side is also on the left side of the image in the mirror. What is on your right side also is on the right side of the image in the mirror. What is your bottom will still be seen as the bottom in the mirror. What is your top will still be what is on the top in the mirror. However, since you are looking at it like it really exists, you think what is on your left in the image should be what is on someone's right who is behind the mirror. But it isn't, so you percieve it as being reversed. However, the imaginary person standing behind the mirror that you are basing your perceptions on would still see the same things as being up and down as you, since your are merely seeing a projected image.

I am sorry, this is not very clear. Hopefully it is at least intelligable, but I wouln'dt count on it. And I know the ray optics are all screwed up, but if I have no idea how to explain the ray optics of mirrors without pictures.

Ken G
2005-Nov-10, 04:38 AM
What you are saying is that the issue is one of perception. That's right, because what a mirror really does is reverse front to back, the rest is up to you. But given that, why then do we so clearly perceive it as reversed left to right? I think the answer must have something deeply to do with our psychology. To test this, actually write the word "mirror" on a piece of paper, and then watch very closely what you do when you "hold it in front of a mirror". When you get what I'm saying, then ask, does the orientation of our eyes have anything to do with this? I really don't know why our eyes are oriented left and right. Is this more easily done biologically, and perhaps this gives rise to the psychology, or does the psychology guide the biology? Or is there no connection at all, and other factors are all that matter?

TheBlackCat
2005-Nov-10, 04:56 AM
Our brain does not change the actual image appearing on our retina (at least not significantly). What the brain does is tell us it is backwards, when it is really just a projection. I'm sorry, someone else should probably explain this, I am probably just confusing you and anyone else reading this.

Ken G
2005-Nov-10, 05:01 AM
You have not tried the experiment I suggested. Again, do it, and watch your every move very carefully. When did the writing get reversed?

SirBlack
2005-Nov-10, 05:48 AM
Take that piece of paper with a word on it, and go stand in front of a mirror. First hold the paper facing yourself so that you can read it. Then turn the paper (rotation around a verticle axis) to face the mirror. Look at the image in the mirror and you see the word is now backwards. Now start over, by turning the paper back around so it is facing yourself so that you can read it properly. This time, flip the paper (rotation around a horizontal axis) to face the mirror. Look at the image and note that this time the word is simply upside down but not backwards.

It's not really the mirror that causes the reversals. It's what you do to the paper to make it face the mirror.

Joff
2005-Nov-10, 05:51 AM
If I hold the edge of a card with "Mirror" on it up to the mirror, with writing parallel to the mirror, and look down on it, the writing is reflected top-to-bottom. With the writing perpendicular, it's truly reflected left-to-right. With the card parallel to the mirror, it's neither.

The writing is inverted in each case, of course, but that's only conventionally described as left-to-right.

Jens
2005-Nov-10, 06:57 AM
I thought about this once a long time ago, and came up with an explanation (the same as the one with the paper) that satisfied me.

If I walk away from a mirror, and want to turn to look in the mirror, there are two ways to do it.

(1) I can turn around horizontally. In this case, the right and left will be reversed, but up and down will be OK.

(2) I can stick my head on the floor and put my feet in the air (do a headstand). Then, the right and left will be OK, but up and down will be reversed.

Of course, you won't be able to read letters on your t-shirt either way, because it's equivalent for the left and right to be switched and the top and down to be OK, or for top and down to be reversed while left and right are OK. To be able to read the letters on your t-shirt, you'd have to reverse both (or keep them the same). Which is impossible, because if you twist sideways AND turn on your head, you'll be facing away from the mirror again.

Ken G
2005-Nov-10, 06:59 AM
Yes, you create the illusion yourself, in how you physically hold the card up to the mirror. So why do we all do it that way? Would a dolphin (if it had opposible thumbs...)? Is this related to our eyes being left and right, or just the way we interact with the world? I'm trying to figure out exactly where the illusion comes from.

Ken G
2005-Nov-10, 07:03 AM
(2) I can stick my head on the floor and put my feet in the air (do a headstand). Then, the right and left will be OK, but up and down will be reversed.
.
I agree with the spirit of what you're saying, but ironically, if you actually do that experiment you'll see that the letters on your shirt will still look reversed left to right! Because your head will be upside down too. Try it when you're not wearing the shirt...

NEOWatcher
2005-Nov-10, 02:23 PM
KenG & Jens got me thinking: It might be the handstand thing.
It has nothing to do with perception, or the mirror.
(at the equator) suppose you are facing north, and you are looking at the card facing south. To get the mirror image, you have to face the card north. To get it there, you do one of two things: Turn the card left/right, or spin the card upside down. To see the face in a mirror, you will have had to turn the card around first. Get it?

Edit to add: To turn around, you will tend do the left/right thing rather than the handstand thing since the body is more adapted to gravity than any other directional force. Therefore turning something around is more naturally left/right rather then up/down.

Ken G
2005-Nov-10, 02:43 PM
To get it there, you do one of two things: Turn the card left/right, or spin the card upside down. To see the face in a mirror, you will have had to turn the card around first.

Yes, this is exactly what I'm driving at. It's all in how you present the card to the mirror. But that's what I mean by perception, in the sense that you perceive there being one obvious way to present the card to the mirror, when in fact there is one other semi-reasonable way, and an infinite number of rather arbitrary ways to do it.



Edit to add: To turn around, you will tend do the left/right thing rather than the handstand thing since the body is more adapted to gravity than any other directional force. Therefore turning something around is more naturally left/right rather then up/down.
This is what I'm trying to get at, the reasons behind the perception. I think you may be right that the direction of gravity is crucial. But would a dolphin find it so obvious which way to present it? Perhaps so, for no creature likes to be upside-down for long. How about an astronaut who has been in orbit for a year?

Grey
2005-Nov-10, 03:07 PM
Yes, you create the illusion yourself, in how you physically hold the card up to the mirror. So why do we all do it that way? Would a dolphin (if it had opposible thumbs...)? Is this related to our eyes being left and right, or just the way we interact with the world? I'm trying to figure out exactly where the illusion comes from.I think it has more to do with our being accustomed to a two-dimensional world. Turning around and facing a different direction is very natural, and the most sensible way to head off in a new direction, rather than flipping over and walking on your hands. And we probably turn the paper around the way we do because that's the way you'd have to turn it around if you want somebody standing next to you to be able to read it.

It's possible that our eyes are side by side rather than up and down because of the fact that , but I think it's more likely just because we happened to turn out bilaterally symmetric, which is probably more or less coincidental (it's probably pretty easy for bilateralness to happen genetically, and it leads to a reasonably balanced body, which is probably good for movement in all kinds of environments).

It's possible that a dolphin might see it differently, but I doubt it. Dolphins do sometimes turn around by flipping over, but they still stay preferentially upright. I'm fairly certain that a year in orbit wouldn't be sufficient to change the perceptual habits of a lifetime for an astronaut. A child who had been raised in zero gravity, though? Or maybe it's hard-wired, and you'd have to find a species that normally lives in zero gravity...

Ken G
2005-Nov-10, 04:46 PM
And we probably turn the paper around the way we do because that's the way you'd have to turn it around if you want somebody standing next to you to be able to read it.

Ah, I see, you are bringing in the fact that the way we would pass the paper is related to the type of translations that map one person's location into another's. One does wonder what it would be like if we were all floating around with arbitrary orientations in a zero-g environment.


It's possible that our eyes are side by side rather than up and down because of the fact that , but I think it's more likely just because we happened to turn out bilaterally symmetric, which is probably more or less coincidental (it's probably pretty easy for bilateralness to happen genetically, and it leads to a reasonably balanced body, which is probably good for movement in all kinds of environments).

That's what I was wondering as well.

hhEb09'1
2005-Nov-10, 04:50 PM
Yes, you create the illusion yourself, in how you physically hold the card up to the mirror. So why do we all do it that way? Would a dolphin (if it had opposible thumbs...)? Is this related to our eyes being left and right, or just the way we interact with the world? I'm trying to figure out exactly where the illusion comes from.I'm not so sure I would call it an illusion. Printed material held up to a mirror is just hard to read, no doubt about it. :)

Here's another approach, lay the book down in front of the mirror as if you were reading the book, and try to read the text in the mirror--it still reads from your left to your right, but it's upside down.

Ken G
2005-Nov-10, 08:25 PM
Yes, that's an equally valid way to "hold it to the mirror", good point. I actually had to do this to see if the letters were reversed or not-- hard to picture (they're not)! That would be a fun way to argue to your friends that mirrors reverse top to bottom. You might win a bet!

hhEb09'1
2005-Nov-10, 08:34 PM
I'm fairly certain that a year in orbit wouldn't be sufficient to change the perceptual habits of a lifetime for an astronaut. There is a fairly famous experiment (famous in introductory psychology courses anyway) where a group of people put on goggles made of prisms such that their view of the world is upside down. After a while (less than a few days) of stumbling around, they become accustomed and they seem to perceive the view as rightside up. But that is not the amazing part (to me). When they take off the goggles, everything is upside down to them! And they have to be re-accustomed again.

Grey
2005-Nov-10, 09:10 PM
There is a fairly famous experiment (famous in introductory psychology courses anyway) where a group of people put on goggles made of prisms such that their view of the world is upside down. After a while (less than a few days) of stumbling around, they become accustomed and they seem to perceive the view as rightside up. But that is not the amazing part (to me). When they take off the goggles, everything is upside down to them! And they have to be re-accustomed again.I've heard of that, and I think it's amazing. I've always wanted to try that to see what it's like. :) I'll accept the general point that our perceptual habits can change in some ways pretty quickly. But I'll bet that an astronaut that's been in free fall for a long time would still turn the paper around side to side, rather than top to bottom.

Ken G
2005-Nov-10, 09:41 PM
That's quite interesting hhEb09'1 -- it connects with one thing I've often wondered. Because of the nature of lenses, everything that comes into our optical nerve is already upside down-- we are wearing those goggles all the time! So does this mean that the ground is really above us right now? In other words, have we learned to accomodate our vision to our other senses such that we flip the image in our minds, or is it that we've accomodated our other senses to our vision such that we "feel" our feet as being below us, even though they are in fact above us! The experiment proves at least that the former possibility is physiologically possible, but it does not rule out that the latter is also physiologically possible. So I argue that at the moment, we really don't know which is true!

SeanF
2005-Nov-10, 11:49 PM
Well, it's definitely psychological. All you have to do is draw a diagram showing how the light reflects "vertically" and how it reflects "horizontally" and you'll see that it does the same thing both ways.

We live in a three-dimensional world. Physically turning an object around any of the three axes will result in a reversal in two of the three dimensions. The mirror reverses only a single dimension, which is why the image is backwards - it produces a view of the object that is physically impossible in the real world.

It is quite normal, physically, for our view of objects or people to be rotated around the vertical axis, which reverses front-and-back and left-and-right. It is most decidedly abnormal for the view to be rotated around one of the horizontal axes, which would reverse either front-and-back and up-and-down or left-and-right and up-and-down.

So when we look in a mirror, we are presented with a view that is reversed front-and-back but neither up-and-down nor left-and-right. The "real world" tells us that a front-and-back reversal is always accompanied by a left-and-right reversal. Since the mirror image does not include that left-and-right reversal, we interpret the left-and-right as being wrong.

Enzp
2005-Nov-11, 08:29 AM
Instead of a piece of paper, put the word on a piece of clear plastic. Hold it out in front of you. Look at the plastic sheet, now look in the mirror. Both images are the same. Turn it backwards and it is backwards both directly and in reflection.

When you turn it end for end, you put the letter that was on the left over to the right end - as seen from your perspective. If you turn it over around the horizontal axis, then it appears upside down rather than left/right inverted.

Atraxani
2005-Nov-11, 09:50 AM
This has appeared in books, but I'm interested in what new insights we can come up with: When you write words on a card and hold them to a mirror, why does the mirror reverse left to right and not top to bottom? Is there any connection to why our eyes are side by side instead of one over the other?

The mirror doesn't reverse the image left to right, and it doesn't reverse it top to bottom. The right side is still on the right, and the left side is still on the left. The top is still on the top, and the bottom is still on the bottom. The only thing that changes is the direction your nose points.

Atraxani
2005-Nov-11, 10:20 AM
What you are saying is that the issue is one of perception. That's right, because what a mirror really does is reverse front to back, the rest is up to you. But given that, why then do we so clearly perceive it as reversed left to right? I think the answer must have something deeply to do with our psychology. To test this, actually write the word "mirror" on a piece of paper, and then watch very closely what you do when you "hold it in front of a mirror". When you get what I'm saying, then ask, does the orientation of our eyes have anything to do with this? I really don't know why our eyes are oriented left and right. Is this more easily done biologically, and perhaps this gives rise to the psychology, or does the psychology guide the biology? Or is there no connection at all, and other factors are all that matter?

We make the mistake because our bodies are vertically symmetrical, but not horizontally symmetrical. We are used to seeing people facing us, and mental left-right reversals. If you stood in front of a mirror, while a 2nd person lay on his side (on the floor by your feet), facing the mirror, you would say that he has been flipped vertically.

If we were horizontally symmetrical creatures, we would make the mistake of saying that the mirror flips us horizontally. If we were asymmetrical creatures, we wouldn't make any mistake at all.

(It gets really interesting when you consider non planar mirrors. Now, concave mirrors reverse all three axes (after the focal point). The nose points backwards, the feet point up, and the left hand points right. Since all three axes are flipped, it's the same as rotating the image. The size of the image also changes.)

Atraxani
2005-Nov-11, 10:30 AM
There is a fairly famous experiment (famous in introductory psychology courses anyway) where a group of people put on goggles made of prisms such that their view of the world is upside down. After a while (less than a few days) of stumbling around, they become accustomed and they seem to perceive the view as rightside up. But that is not the amazing part (to me). When they take off the goggles, everything is upside down to them! And they have to be re-accustomed again.

Fascinating, thanks for sharing that. Now I want to try it. You've got my curiosity running. :)

Argos
2005-Nov-11, 01:24 PM
What about the fictitious "space" on the other side of the mirror? It must play a major role in our perception.

Sam5
2005-Nov-11, 06:01 PM
There is a fairly famous experiment (famous in introductory psychology courses anyway) where a group of people put on goggles made of prisms such that their view of the world is upside down. After a while (less than a few days) of stumbling around, they become accustomed and they seem to perceive the view as rightside up. But that is not the amazing part (to me). When they take off the goggles, everything is upside down to them! And they have to be re-accustomed again.


The focused image our eyes see is upside down on the backs of our retinas. Our brains turn the images right-side up.

SeanF
2005-Nov-11, 07:58 PM
There is a fairly famous experiment (famous in introductory psychology courses anyway) where a group of people put on goggles made of prisms such that their view of the world is upside down. After a while (less than a few days) of stumbling around, they become accustomed and they seem to perceive the view as rightside up. But that is not the amazing part (to me). When they take off the goggles, everything is upside down to them! And they have to be re-accustomed again.
Hey, did those prisms just flip the image vertically, or did they actually rotate it 180 degrees?

If the former, the brain's adjustment is even more amazing...

Ken G
2005-Nov-11, 08:59 PM
A lot of people are just looking at the OP, and then giving their input, which is leading to repetition. What we are on now is, how is our brain controlling our perception such that we flip the paper left-to-right when we hold it to the mirror. Some good answers have been offered on that. My claim is still outstanding-- since our eyes flip the image of the world around us, we don't really know if the ground is above us, and we flip the perception from our other senses, or if it's below us and we flip the visual image! Do we?

Grey
2005-Nov-11, 09:04 PM
A lot of people are just looking at the OP, and then giving their input, which is leading to repetition. What we are on now is, how is our brain controlling our perception such that we flip the paper left-to-right when we hold it to the mirror. Some good answers have been offered on that. My claim is still outstanding-- since our eyes flip the image of the world around us, we don't really know if the ground is above us, and we flip the perception from our other senses, or if it's below us and we flip the visual image! Do we?I think we do, since we know how the optics of the eye work, and we know that the image is in fact flipped from what it's like in the real world. I think if you did the switch you're suggesting, you'd just be redefining up and down to each mean the opposite.

Ken G
2005-Nov-11, 09:07 PM
No, what I'm saying is, we know that the perceptions of our eyes are inverted with respect to our other senses, yes? But why is it obvious then that the brain flips the visual image to agree with the other senses, instead of the converse? We know the brain is capable of flipping the visual image, due to the experiment described by hhEb09'1. But we don't know it isn't capable of the same feat with the other senses. It is possible that only people who have been blind since birth know which way is up!

Enzp
2005-Nov-12, 07:33 AM
The brain isn't so much flipping the image as it is simply processing it. You can lie on your side and watch TV without the people looking like they are standing on a vertical wall rather than a floor. If you took a photo that way, the picture would indeed be sideways, but your mind doesn't see it that way unless you consciously analyze it. What if the eye sent the image bits to places all over the brain? We would still process it into a coherent image. That the upper part and lower part of the image are "inverted" where they physically affect the eye is irrelevant. Whatever the image is doing, we still know when something is moving towards our feet or towards the sky. We know where the ground is and where up is without benefit of sight. Our brain processes the vision input in a manner consistent with the other senses.

If you decided to drive your car everywhere backwards while looking in the mirror, it would not take a long time for you to adjust to it and make it seem natural. The prism thing is an interesting experiment, but it is no miore surprising than watching TV lying on your side. Or watching folks walk around you house for that matter.

When you flipped your sign around, you moved the lefthand letters to the right and vice versa. The mirror just reflects that back to you. Your brain didn't do it.

Argos
2005-Nov-12, 02:03 PM
An interesting take on the issue. (http://www.mathpages.com/home/kmath441.htm)

Ken G
2005-Nov-12, 02:58 PM
When you flipped your sign around, you moved the lefthand letters to the right and vice versa. The mirror just reflects that back to you. Your brain didn't do it.

Your point about processing is well taken, but what we are wondering at this point is, why if you tell 100 people to "hold the paper to the mirror so that you can see the writing" will all 100 flip it around the same way? That's something that the brain is doing, and there have been a lot of good explanations that shed light on this. Bringing in hhEb09'1's point, one can redo the experiment by telling another 100 people to "hold the paper to the mirror so that you can see the writing both on the paper and in the mirror at the same time". I'll bet you'll get very different results on which way the mirror is reversing, because now there's no "obvious" way to hold the paper!

hhEb09'1
2005-Nov-13, 10:46 PM
Quite a few people have made the point that the mirror does not reverse left and right, or top and bottom--just front to back. But that is why we can say that a left-handed glove is the "mirror-image" of a right-handed glove, they are fundamentally different in some sense of non-congruence. I cannot put my left-handed glove on my right hand comfortably. It's not just an illusion.

Atraxani
2005-Nov-13, 11:27 PM
A planar mirror produces a virtual image that is symmetrical to the object about the mirror's plane. The objects and the image are different because the direction the front of the object points is reversed (the axis connecting the objects).

Your left and right hands are symmetrical to each other about the plane containing your nose and the line of your backbone. Your hands are different from each other by the direction the thumbs point is reversed (the axis connecting the objects).

Thus, when you say a glove is symmetrical to its counterpart, it's not the left right axis that is reversed, despite conventions in the way we think and talk.

Ken G
2005-Nov-14, 07:27 AM
That's right, you can turn a left glove into a right glove by reflecting it through any plane through the glove that isn't a symmetry of the glove (i.e., let the glove have a "front" and "back"), not just the left/right plane. If instead you reflect it through a point, you get back the same glove you started with. Our mind really plays tricks on us with symmetries. Still no takers on my challenge to prove that the ground is not actually above you right now? (Aussies not included!)

Atraxani
2005-Nov-14, 07:58 AM
Still no takers on my challenge to prove that the ground is not actually above you right now? (Aussies not included!)

What do you mean the ground "is above" me? Replace that existential statement with an action verb to see the flawed premise.

"Above" begins an adverbial prepositional phrase that relates the position of one thing to the position of another, relative to an observer.

When you say "The shelf is above the table," you mean that "After glancing at the furniture, I decided that the table appears between the table and the floor." There is no absolute or preferred space, position, direction, etc. "Above" is not a property of an object, but a description of the relationship between the frame of reference, the observer, the object, etc...

Jens
2005-Nov-14, 08:14 AM
Still no takers on my challenge to prove that the ground is not actually above you right now? (Aussies not included!)

"Above" is sort of a meaningless concept, except I think the word probably means (a) "further away from you than the ground." Except that it might also mean (b) "along a line stretching from your feet to your head, and somewhere along that line beyond the head." I think that in zero gravity, astronauts would probably adopt definition (b), wouldn't they? But on earth, I think we normally use (a). Say you're doing a handstand, would you say the sun was "above" you or "below" you? I think it may have been Buckminster Fuller who proposed getting rid of the words "above" and "below" in normal use and saying "inward" and "outward" instead. Look at the sun outward in the sky! The point being, though, that this problem seems to me a semantic rather than physics one.

Atraxani
2005-Nov-14, 09:05 AM
Ken, why do you make this assumption in the first place? The photoreceptors in the retina generate electrochemical signals as a function of exposure to light. These signals are transmitted along the optic nerve to the brain. The actual location doesn't matter. The signals themselves are meaningless until the brain processes them, along with other senses, into a model of the world. You have a blind spot in your eye due to the absence of receptors where the optic nerve is, but you never normally see it. Your eye performs micro saccades and saccades (jerks, changes in orientation), but the image is smooth to you. You never see your nose unless you try to. The areal density of photoreceptor cells is not even, yet the image appears to be evenly packed with visual information. The photoreceptors react to light, but you perceive objects with ease. The modification that occurs is phenomenal, and largely out of our control.

http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html

Squares A and B are the same color, but it's almost impossible to convince yourself that it is so.

http://www.sciencenews.org/articles/20010901/bob14.asp

An array of 12x12 electrodes on the tongue, controlled by a camera allows subjects to "see"! Amazing.


I can elaborate on any unclear in point in this post if asked.

Jeff Root
2005-Nov-14, 11:56 AM
Ken,

The reason you turn the paper side-to-side rather than
top-to-bottom is so that neK can read it.

-- ffeJ, ni silopaenniM

Jeff Root
2005-Nov-14, 12:05 PM
Notice that if you hold something up in front of a mirror such
that it appears backwards to you, it also appears backwards
to the person in the mirror. You can confirm that by having
someone ask you whether you can read the text. When you
shake your head from side-to-side, so does the person in
the mirror.

-- Jeff, in Minneapolis

Atraxani
2005-Nov-14, 03:35 PM
Notice that if you hold something up in front of a mirror such
that it appears backwards to you, it also appears backwards
to the person in the mirror. You can confirm that by having
someone ask you whether you can read the text. When you
shake your head from side-to-side, so does the person in
the mirror.

-- Jeff, in Minneapolis

Watchout. Don't trust that guy in the mirror. Mirrors are notorious for distorting, obscuring, or even inverting reality. He could be lying.

hhEb09'1
2005-Nov-14, 04:34 PM
Our mind really plays tricks on us with symmetries. Still no takers on my challenge to prove that the ground is not actually above you right now? (Aussies not included!)That's what Science is all about--demonstrating how our perceptions can be wrong. :)

SeanF
2005-Nov-14, 05:58 PM
Still no takers on my challenge to prove that the ground is not actually above you right now? (Aussies not included!)
Ok, Ken, here's the deal. My eyeball has one "side" closer to the top of my head and the "other side" closer to my feet. Agreed? However, the image that is generated on my retina has the floor closer to the "head" side of my eyeball and the ceiling closer to the "foot" side.

Are you suggesting that perhaps the reality is that the floor is closer to my head than my feet, and it is only some percpetion flip in my brain that is making me think I'm actually touching the floor with my feet?

Ken G
2005-Nov-14, 07:59 PM
"Above" is sort of a meaningless concept, except I think the word probably means (a) "further away from you than the ground." Except that it might also mean (b) "along a line stretching from your feet to your head, and somewhere along that line beyond the head." .
I agree there's a semantic component, but the issue is, your brain is confronted by a discrepancy between what your feeling is telling it, and what your eyes are telling it. Which gets "flipped"? We automatically assume it is the optical image, when all we can really say is that the perceptions get corrected such that they agree. You are right that the universe is the same looked at from any orientation, so far as we know, so the question is not a physics question but more of a biology question.

Ken G
2005-Nov-14, 08:04 PM
Ken, why do you make this assumption in the first place? .
You are making some very interesting points in their own right, but in relation to my argument, all you are saying is that the brain does an amazing amount of processing without our knowing it. But the tongue experiment you mention shows that we also process feeling input. Why do we assume the optical inputs are "flipped" to agree with the feeling? Why not the other way around? If so, we are living in a topsy-turvy world that blind people do not live in.

Ken G
2005-Nov-14, 08:06 PM
Are you suggesting that perhaps the reality is that the floor is closer to my head than my feet, and it is only some percpetion flip in my brain that is making me think I'm actually touching the floor with my feet?
Certainly not, I'm suggesting that the floor, and your body, is actually located in the direction you think of as being up. Kind of like the way you think of Australians. Note this is an ignorable transformation, so does not affect your daily life, it's just interesting to ponder.

SeanF
2005-Nov-14, 09:38 PM
Certainly not, I'm suggesting that the floor, and your body, is actually located in the direction you think of as being up. Kind of like the way you think of Australians. Note this is an ignorable transformation, so does not affect your daily life, it's just interesting to ponder.
"Up" and "down" have no meaning other than "away from the Earth's gravity" and "toward's the Earth's gravity," respectively. It simply doesn't make any sense to say that "towards the floor" is "actually" up.

It's not ignorable, it's literally meaningless.

Ken G
2005-Nov-14, 09:43 PM
It's not ignorable, it's literally meaningless.
So you're saying that there is no meaningful sense in which the bodies of Australians right now are oriented opposite to yours? I think our intuition allows for that possibility, though at some physics level it is possible that the two are indistinguishable.

SeanF
2005-Nov-14, 10:00 PM
So you're saying that there is no meaningful sense in which the bodies of Australians right now are oriented opposite to yours? I think our intuition allows for that possibility, though at some physics level it is possible that the two are indistinguishable.
Oh, absolutely people in Australia are oriented opposite to me. The direction I consider "up" is the direction they consider "down." But neither direction is objectively "up."

Ken G
2005-Nov-15, 01:02 AM
But that's all I mean, that your intuition tells you where the ground is right now, based on how you process information from your senses. But your senses don't agree, so your brain has to choose. How do you know it chooses the right one to flip? I think this would be a difficult physiological experiment to answer, though I suspect it is true that the optical image gets flipped, on the grounds that it is a higher evolutionary function.

Jens
2005-Nov-15, 10:30 AM
"Up" and "down" have no meaning other than "away from the Earth's gravity" and "toward's the Earth's gravity," respectively.

That's not true, really. Up and down are complicated ideas. When you say an uptown girl, you don't necessarily mean somebody who is further out from the earth's gravity.

Up can also mean something closer to your head than your feet, if that makes sense. I have a feeling that astronauts use the concept of up and down even in weightlessness, but I don't actually know this. It might be interesting to ask if they say things like, "look up".

hhEb09'1
2005-Nov-15, 03:45 PM
But that's all I mean, that your intuition tells you where the ground is right now, based on how you process information from your senses. But your senses don't agree, so your brain has to choose. How do you know it chooses the right one to flip? I think this would be a difficult physiological experiment to answer, though I suspect it is true that the optical image gets flipped, on the grounds that it is a higher evolutionary function.but even if my senses were flipped, they'd still tell me that my feet were on the ground. It's not like my head might be on the ground, with my legs dangling in the air. I'm pretty sure of that--I walked here, didn't I? :)

SeanF
2005-Nov-15, 04:34 PM
But that's all I mean, that your intuition tells you where the ground is right now, based on how you process information from your senses. But your senses don't agree, so your brain has to choose. How do you know it chooses the right one to flip? I think this would be a difficult physiological experiment to answer, though I suspect it is true that the optical image gets flipped, on the grounds that it is a higher evolutionary function.
Okay, so my sense of vision - based on the retinal image - tells me that the floor is closer to my head. My other senses tell me that the floor is closer to my feet.

But earlier, when I asked if you were suggesting that perhaps the floor is actually closer to my head, you said "Certainly not." So what exactly does the idea of my other senses being flipped mean, if not that?

gopher65
2005-Nov-15, 08:52 PM
Take a transparency (a sheet of clear projector paper) and write a word on it. Then flip it around like you would an ordinary opaque piece of paper and look at it in the mirror. You will see that both the mirror image and what is written on the piece of transparency are identical.

The mirror has nothing to do with the flipped image; all it does is reflect the light. You are simply looking at things from the wrong direction, thus giving them the appearance of backwardness.

Ken G
2005-Nov-15, 09:04 PM
But earlier, when I asked if you were suggesting that perhaps the floor is actually closer to my head, you said "Certainly not." So what exactly does the idea of my other senses being flipped mean, if not that?
The floor can't be closer to your head, your body must connect your head to the floor. Physics isn't being violated, the issue is, which direction is your body really pointing?

Grey
2005-Nov-15, 09:08 PM
The floor can't be closer to your head, your body must connect your head to the floor. Physics isn't being violated, the issue is, which direction is your body really pointing?Clearly then, your body is pointing away from the floor. And isn't "away from the floor" what we really mean when we say "up"?

Ken G
2005-Nov-15, 09:11 PM
Take a transparency (a sheet of clear projector paper) and write a word on it. Then flip it around like you would an ordinary opaque piece of paper and look at it in the mirror. You will see that both the mirror image and what is written on the piece of transparency are identical.
.
Why flip it around? I like this test better done without the flip! We now have two ways to win a bet-- one is to tilt a paper forward so you see the writing and its upside-down mirror image, and the other way is to write on transparency paper and get no reversal at all.

SeanF
2005-Nov-15, 09:11 PM
The floor can't be closer to your head, your body must connect your head to the floor. Physics isn't being violated, the issue is, which direction is your body really pointing?
Let's assume, for the sake of argument, that I'm standing at the north pole. My body is then pointing (feet-to-head) in the same direction as the Earth's rotational axis (south-to-north). Really.

Now what?

Ken G
2005-Nov-15, 09:13 PM
Clearly then, your body is pointing away from the floor. And isn't "away from the floor" what we really mean when we say "up"?
Yes, but this isn't my question. My question is, close your eyes and imagine, spatially, where you think the floor is. How do you know your senses are not lying to you, because they have been trained to agree with your eyes? If that seems unlikely, imagine taking a drug that makes you feel completely numb but you still can see. That proves your senses can reverse something even if it is the only sense that is operational, if you think it is the optical image that is in fact getting reversed by your brain.

Ken G
2005-Nov-15, 09:17 PM
Here's a related question-- how long would you need to keep your eyes closed before, when you open them, the world looked upside down? If you could do that experiment, and get that result, then I'll believe your brain is flipping the optical image. Or, alternatively, how long would you have to be numb before, upon regaining your sense of feeling, the world would feel upside down? That experiment would convince me that it is the sense of feeling that is inverted. There may not be any length of time that would do either, so the experiment might not work.

SeanF
2005-Nov-15, 09:29 PM
Yes, but this isn't my question. My question is, close your eyes and imagine, spatially, where you think the floor is. How do you know your senses are not lying to you, because they have been trained to agree with your eyes?
I am becoming more and more convinced that you are being deliberately obtuse as part of some dumb game, to see how long you can keep us debating this.

You can disabuse me of this notion by answering the following questions:

When you close your eyes and imagine, spatially, where you think the floor is, where is it?

If your senses are lying to you, where is the floor really?

Grey
2005-Nov-15, 09:31 PM
Yes, but this isn't my question. My question is, close your eyes and imagine, spatially, where you think the floor is. How do you know your senses are not lying to you, because they have been trained to agree with your eyes? If that seems unlikely, imagine taking a drug that makes you feel completely numb but you still can see. That proves your senses can reverse something even if it is the only sense that is operational, if you think it is the optical image that is in fact getting reversed by your brain.


Here's a related question-- how long would you need to keep your eyes closed before, when you open them, the world looked upside down? If you could do that experiment, and get that result, then I'll believe your brain is flipping the optical image. Or, alternatively, how long would you have to be numb before, upon regaining your sense of feeling, the world would feel upside down? That experiment would convince me that it is the sense of feeling that is inverted. There may not be any length of time that would do either, so the experiment might not work.

Actually, my understanding is that, in the experiments with the image flipping lenses, the subjects actually have to move around and stumble into things for it to work. That is, there has to be a conflict between your sense of vision and your sense of touch. So your later experiments probably wouldn't work (there's nothing to spur flipping or unflipping the visual image, so the default is for your brain to keep interpreting it as it does). However, it's possible that a child that was blind from birth and somehow later became able to see might see things flipped until he or she had a chance to adjust.

But I'm still uncertain how you envision the sense of feeling being inverted. It's been suggested that it might mean that the thing I feel touching my feet is really touching my head, but you've said that isn't what you mean. That's good, because I have a hard time imagining how that could possibly work. How else could the universe "feel upside down"?

Ken G
2005-Nov-15, 11:15 PM
So your later experiments probably wouldn't work (there's nothing to spur flipping or unflipping the visual image, so the default is for your brain to keep interpreting it as it does).

Yes, that's probably true. It would be a lot to ask someone to do without much chance of success!


However, it's possible that a child that was blind from birth and somehow later became able to see might see things flipped until he or she had a chance to adjust.
I was wondering that as well. Surely this must have happened? I wonder why nobody has studied this initial inversion process. But it still wouldn't answer my query:



But I'm still uncertain how you envision the sense of feeling being inverted. It's been suggested that it might mean that the thing I feel touching my feet is really touching my head, but you've said that isn't what you mean.
If you are having trouble visualizing this, just change the question to: your eyes and your feet give you different ideas about which direction your body points. The difference is ignorable, like a mirror, but it is still different. The normal answer is that the brain "flips" the optical image. There are three possibilities:
1) this is correct
2) actually it is your sense of feeling that gets flipped
3) there's no flipping at all, since your brain processes visual information separately from the feeling information.
Some things that have been said in this thread appear to favor (3), but I don't think that can be right, because I don't think you could catch a ball, for example. So I think it has to be (1) or (2). I'm simply arguing that at present we have no way of knowing which, despite the fact that (1) is often asserted as true without evidence.

SeanF
2005-Nov-15, 11:46 PM
If you are having trouble visualizing this, just change the question to: your eyes and your feet give you different ideas about which direction your body points. The difference is ignorable, like a mirror, but it is still different. The normal answer is that the brain "flips" the optical image.
If you are standing facing someone, it is an incontrovertible fact that your feet and their feet are pointing in the same direction, right? Whatever that direction may be, whatever you want to call it, both sets of feet are pointing in the same direction. However, the feet of the image of that person that is imprinted on your retina will be pointing towards the top of your head.

So the brain needs to realize that the part of the retinal image at the head-side of the retina is actually towards the foot-side of reality, and vice-versa (and, by the way, the part of the retinal image on the left-hand side of the retina is actually on the right-hand side of reality, and vice-versa).

That's not something that we might be misinterpreting. We know that the reality is that your feet and his feet are pointing in the same direction (whatever that direction may be), and we know that the retinal image has his feet pointing in the opposite direction (whatever that direction may be). That's all there is to it.

You seem to be suggesting that one of those directions is objectively "down," and that it may be the direction of the retinal image. I argue that's impossible to identify anyway, but it doesn't matter. All that matters is that retinal image of the person you're looking at is reversed from the actual person.

Ken G
2005-Nov-16, 12:54 AM
If you are standing facing someone, it is an incontrovertible fact that your feet and their feet are pointing in the same direction, right? Whatever that direction may be, whatever you want to call it, both sets of feet are pointing in the same direction.

Certainly.


However, the feet of the image of that person that is imprinted on your retina will be pointing towards the top of your head.

Yes but so are your own feet! The incontrovertible fact you cite is not controverted by your optical image.


(and, by the way, the part of the retinal image on the left-hand side of the retina is actually on the right-hand side of reality, and vice-versa).

Quite right, we should not merely focus on the top-bottom issue, the left-right is there too. But it's the same issue.


You seem to be suggesting that one of those directions is objectively "down," and that it may be the direction of the retinal image.

It is not necessary for me to make that claim, the issue is simply, how can you test which perception gets flipped to achieve consistency. I claim, no such test has ever been conducted, so the answer is presently unknown.

All that matters is that retinal image of the person you're looking at is reversed from the actual person.
That is certainly true, but does not address my claim.

Enzp
2005-Nov-16, 03:03 AM
You seem hung up on the idea of "flipped" and then extending that to some sort of measure of reality. Your eyes are not fooling you, it just happend that the lens in your eye puts the bottom of the image on the top of your eyeball. Your brain is wired so as to know where things are in the image field. There is no internal controversy as to which thing is "right." I recognize a five dollar bill regardless of which way Mr.Lincoln is facing. Just so everything else. Down is towards the center of the earth, towards my feet. MY nerves are wired so that the image from your feet is on the top of my eyeballs. This is wiring not interpretation. Yes, I mean metaphoric wires. You could keep your eyes glosed for a year and the brain would not reset to some other state, because there is no resetting to do. FOlks don't wake up from a coma and think, "Whoa, the world is upside down."

The prism experiment is a measure of our ability to adapt, not some sort of demonstration of arbitrariness in the brain. You can quickly learn to read in a mirror. I read upside down all the time. No, I won't read a book that way, but in looking over drawings and diagrams and such, I long ago adapted to that. COnsciously I realize they are presented to me upside down, but in a practical sense, I recognized the words regardless. That is the power of the mind to recognize patterns.

Here is an experiment. You can comb your hair in a mirror without thought. Now aim a video camera at your face and try combing your hair in the image on the monitor. After a while you will adapt, but not because your brain arbitrarily decided that the mirror was wrong.

WHy couldn't you catch a ball? The assumption there is that the brain sees things upside down. it doesn't. If you turn a video camera upside down, the image resulting on the screen is upside down too. If you turn the screen over as well, then lo and behold you can watch the image in the normal orientation. This is because we not have set the system up to view the world. It is irrelevant that the camera and display are "upside down" all that matters is that the sender and receiver are compatible.

Ken G
2005-Nov-16, 04:35 AM
Your eyes are not fooling you, it just happend that the lens in your eye puts the bottom of the image on the top of your eyeball. Your brain is wired so as to know where things are in the image field. There is no internal controversy as to which thing is "right."

If that were so, then why are people disoriented for awhile when they put on goggles that flip the image? In your theory, the brain, not being "hung up" on orientation, would have no difficulties.



The prism experiment is a measure of our ability to adapt, not some sort of demonstration of arbitrariness in the brain. You can quickly learn to read in a mirror. I read upside down all the time.

You are now arguing a different point.


COnsciously I realize they are presented to me upside down, but in a practical sense, I recognized the words regardless.

Exactly my point-- you have a conscious sense of which direction is up. I am not saying anything about the ability to recognize patterns, I am talking entirely about this conscious sense that you admit you have. If the brain interpreted visual information as more primary than feeling information, then your conscious sense of which direction is up would simply be wrong!



WHy couldn't you catch a ball?

Because catching involves more than vision, it involves coordinating vision with the feeling of the ball hitting the hand. If you perceived the location of the strike differently from what you saw, it would mess you up, so your brain is forced to bring the location into agreement. There are an infinite number of ways the brain could do this, but there are two fundamentally different ways that are not completely arbitrary. I am saying it is very hard to distinguish those two ways.

Let me put this another way. Let's say you wear prism goggles and everything you see is backward and upside down. This takes you awhile to adjust, as we know from this thread. Your brain needs to reinterpret your visual data, and your feeling data, such that they agree, or you stumble around (and you can't catch balls). How do you know that it is the interpretation of the visual data that ultimately gets altered? It could be the other senses just as well, in principle! All you can say is, some sort of reorientation occurs, but it is not instantaneous. I suspect it is the visual data that is reinterpreted, because feeling data comes from many sources and would seem to require more processing, but as a scientist, I ask for proof. If you are saying that it is meaningless to try and answer which one gets reprocessed, that at least makes more sense than saying the visual image gets flipped mentally (the usual answer), but I'm not sure that it is meaningless. I think it depends on the physiology of how signals are processed.

gopher65
2005-Nov-16, 02:03 PM
Sigh. Ken you appear to be purposefully refusing to understand a very very simple topic. You are reading more into it than is there.

Grey
2005-Nov-16, 03:12 PM
If you are having trouble visualizing this, just change the question to: your eyes and your feet give you different ideas about which direction your body points.I disagree with this statement, and that's why I have a hard time imagining what you could possibly mean by my sense of touch being flipped. The information my feet give me is just that they're touching the floor. In one respect, this might seem to contradict my vision, since if I look out into the room, the image on my retina has the floor closer to my head. But of course if I tip my head down and look at my feet, I'll see that they are in fact touching the floor.

pghnative
2005-Nov-16, 04:26 PM
Sigh. Ken you appear to be purposefully refusing to understand a very very simple topic. You are reading more into it than is there.I too do not understand the confusion. I feel as if I'm hearing someone say: "Hey, what if left were right, and right were left --- wouldn't that make things different".

Just substitute "up/down" for "left/right" and you get this thread.

hhEb09'1
2005-Nov-16, 05:26 PM
Yes, but this isn't my question. My question is, close your eyes and imagine, spatially, where you think the floor is. How do you know your senses are not lying to you, because they have been trained to agree with your eyes? If that seems unlikely, imagine taking a drug that makes you feel completely numb but you still can see. That proves your senses can reverse something even if it is the only sense that is operational, if you think it is the optical image that is in fact getting reversed by your brain.I dunno about "reversed"--it's interpreted. The same thing is done left and right, right? And here's another intro psych zinger: close one eye, and hold a red marble on a stick against a yellow wall (the colors don't matter), and fix your eye on it. Now, without moving your eye, move the marble towards the outside of your vision, down or up a little. It will disappear when it reachs your blindspot, and your mind will "fill in" the blank with yellow. Move it farther away, and you'll be able to see it fine in your peripheral vision, move it back and it disappears.

Your mind lies to you. :)

SeanF
2005-Nov-16, 06:47 PM
It is not necessary for me to make that claim, the issue is simply, how can you test which perception gets flipped to achieve consistency.
So what you're saying is the eyeball receives visual information upside down but the ears receive aural information rightside up, and that maybe the brain turns over the aural information from the ears so that it matches up with the visual information.

But we don't realize that that's what our brain is doing because we've been perceiving everything upside down for our entire lives and so we just assume that what we're perceiving is actually rightside up.

Is that it?

Ken G
2005-Nov-16, 09:13 PM
OK, I have finally come around! I was indeed imagining a sense of "absolute" directions, and pointing out that individuals could form conscious impressions of directions that were systematically flipped from the objective reality without ever knowing it. But there is no way to distinguish these possibilities, so it is indeed a meaningless conjecture. It was put quite well but I didn't realize it at the time:


You seem to be suggesting that one of those directions is objectively "down," and that it may be the direction of the retinal image. I argue that's impossible to identify anyway, but it doesn't matter. All that matters is that retinal image of the person you're looking at is reversed from the actual person.

Others put this well also-- sorry to be slow. Hope it was useful to think about!

hhEb09'1
2005-Nov-29, 02:59 PM
While driving back and forth during the Thanksgiving week, I noticed something that might be relevant: When I looked in the rearview mirror, the driver behind me was on my left side of their car--as I was in mine. :)

Enzp
2005-Nov-30, 05:57 AM
Now try that in the UK and you will find it reversed!!! Spooky.

Ken G
2005-Nov-30, 12:33 PM
Ironic isn't it, that we have so much trouble determining directions in rear-view-mirrors, even though they aren't reversed? We are so used to mirrors reversing, that we can't handle the situations where in effect they do not! Interesting point, hh.

Enzp
2005-Dec-01, 05:16 AM
Many years ago I had to learn to back a trailer into a garage behind my truck. I had to do it in the mirror. Once used to it it was a breeze. The secret was told to me by the old timer, "look in the mirror, and just turn the wheel the way you want the trailer to go." If I wanted to I could drive backwrds using a mirror, just from having learned the skill.

I think the mental disconnect is that you are looking ahead at an image that appears to be going forward, while the car is going backwards. That is something to ponder.

turbo-1
2005-Dec-02, 05:16 AM
No, what I'm saying is, we know that the perceptions of our eyes are inverted with respect to our other senses, yes? But why is it obvious then that the brain flips the visual image to agree with the other senses, instead of the converse? We know the brain is capable of flipping the visual image, due to the experiment described by hhEb09'1. But we don't know it isn't capable of the same feat with the other senses. It is possible that only people who have been blind since birth know which way is up!We all have rocks in our heads to tell us which way is up. (true) If you ask me which way is up and you see me point upward, you might think that you and I have exactly the same perception of "up" disregarding the possibility that my brain might be feeding me images that are exactly 180 degrees rotated from your view.

Did you ever think about visual perception, and why dyslexia is a problem for some folks and not for others?

hhEb09'1
2005-Dec-02, 06:04 AM
Ironic isn't it, that we have so much trouble determining directions in rear-view-mirrors, even though they aren't reversed? We are so used to mirrors reversing, that we can't handle the situations where in effect they do not! Interesting point, hh.Worse! If I thought about, I'd have to admit that the driver in the mirror must be on their righthand side of the car. :)

Ken G
2005-Dec-02, 07:09 AM
Did you ever think about visual perception, and why dyslexia is a problem for some folks and not for others?
Yes, that is interesting to think about. What the other postings in this thread made me realize is that all our sensory information has to be reconstructed in the brain to make sense, it really doesn't matter that our feet are in fact farther than the top of our head, or that the image in our retina is inverted. The information goes to nerve cells sprinkled around, probably like RAM in a computer. So the issue is in how we reconstruct it, not in how it comes in in the first place.

mugaliens
2005-Dec-04, 11:22 PM
Turn the card verticle. The mirror now reverses it top to bottom, but not left to right.

Irishman
2005-Dec-11, 07:32 AM
It seems to me there's still an unanswered part of the question. Allow me to attempt.


When you write words on a card and hold them to a mirror, why does the mirror reverse left to right and not top to bottom? Is there any connection to why our eyes are side by side instead of one over the other?

When you get what I'm saying, then ask, does the orientation of our eyes have anything to do with this? I really don't know why our eyes are oriented left and right. Is this more easily done biologically, and perhaps this gives rise to the psychology, or does the psychology guide the biology? Or is there no connection at all, and other factors are all that matter?

First, the reversal of the mirror is not connected to our biology or the layout of the eyes. The reversal is the behavior of optics. A mirror is a reversal of depth. A flat mirror is a flat plane of reversal. Objects nearer the mirror reflect and travel a shorter distance than farther objects, so in the mirror image they are closer. This creates an inversion of the image where your back is farther from the mirror, so the reflection of your back is farther into the mirror than your front. Why things look left/right swapped is because we are used to turning around to look in the other direction, which swaps our right and left sides in tandem with swapping the front back depths. The mirror does not swap right left as it swaps depth, so it is backwards. (SeanF said essentially the same thing previously. Kudos to Argos for asking about the "space" on the far side of the mirror. That is essentially the right question.)

The second question has to do with why our eyes are oriented left/right instead of top bottom. This is partially related to our bilateral symmetry, but not entirely. Our body form could be bylaterally symmetrical and have two eyes stacked one on top of the other. If both eyes lay along the line of the nose to chin, then we would still be symmetrical, but have eyes one over the other. That just isn't the arrangment that our earliest ancestors developed.

Two eyes are useful for one of two things. If you put them on opposite sides of a flat object (such as a fish, for instance), then they can look on opposite directions simultaneously and thus provide a wider field of view. The alternative is put them on the same side of a flat object (such as with predators) where they have overlapping fields of view. This creates the effect of parallax and is what increases the ability to judge depth. In practice, most predators get a bit of both effects, as our faces are not quite flat planes, and our early ancestors were more of case 1.

Parallax could just as easily be accomplised by eyes stacked one over the other. However, the wider field of view would only be accomplished if one eye sat around the top of the skull (looking upward?, backward?). Thus it is more advantageous to have them side by side rather than top to bottom.



Yes, this is exactly what I'm driving at. It's all in how you present the card to the mirror. But that's what I mean by perception, in the sense that you perceive there being one obvious way to present the card to the mirror, when in fact there is one other semi-reasonable way, and an infinite number of rather arbitrary ways to do it.
...
This is what I'm trying to get at, the reasons behind the perception. I think you may be right that the direction of gravity is crucial.



And we probably turn the paper around the way we do because that's the way you'd have to turn it around if you want somebody standing next to you to be able to read it.


...what we are wondering at this point is, why if you tell 100 people to "hold the paper to the mirror so that you can see the writing" will all 100 flip it around the same way?

I think you are assuming something that may not be true. First, I expect the behavior depends upon the question that is being asked. Suppose someone is standing in front of you and you ask him to hand you the paper so you can read it. There is no predisposition for him to orient it for you to read prior to handing it to you. So he would extend whichever hand the paper was in or whichever hand was closest to you and hand you the paper. You then would do the "heavy lifting" and orient the paper in whatever manner made it easiest for you to read. Now instead suppose that that person is standing in front of you and you ask him to hold up the paper so you can read it. If he is holding the paper in the proper orientation for him to read it and he wanted you to be able to read it, he would know that the top has to stay on top and the bottom on bottom. If he flipped the paper top over bottom, it will be upside down and backwards. So he would know (or should know*) to rotate it right/left and hold it up.

Now what if he is standing in front of a mirror and you ask him to hold up the sign for the mirror. Well, most people will remember that they want it rightside up, so they probably won't flip vertically and will instead do so horizontally. Thus you get the "natural" behavior of how to turn the card around for the mirror.

The second part is related to the *. You'd be amazed at how many times people make this error when on stage. They hold up their cue card by looking at it, and then flip it for the audience to read by going top over bottom. This is because it is an easier flip that left over right - both hands can remain gripping and flip with fingertips, rather than trading hands. The trick is to teach them to hold it upside down to themselves. I suspect that some people would make this mistake when you ask them to hold up the paper for the mirror, and then have to correct it. (And then realize it is backwards anyway.)

Ken G
2005-Dec-11, 08:57 AM
That's interesting about the cue cards, that might work for the mirror trick too if the cards had to be held in two hands and were quite wide.
As for the perception of reversal, we agree that what a mirror really does is invert front to back, and all the rest is perception. I think the thread shows, and is becoming even more clear to me as I think about it now, that there is not really one answer to "why a mirror reverses left to right", it actually depends on the attributes of the object being looked at. It could be the way the object moves around (i.e., people), its symmetries (i.e., objects) or how we conventionally orient letters (i.e., writing). A particularly blatant example of this is if you look in a mirror at someone lying on their side with a t-shirt that says "WYSIWYG".

hhEb09'1
2005-Dec-11, 09:31 PM
A particularly blatant example of this is if you look in a mirror at someone lying on their side with a t-shirt that says "WYSIWYG".Would that be UCE-NCE? Maybe not, I guess I'm going to have to try it.