The Unscientific Sciences *************************************** Note: This is a multi-threaded discussion. Please read the *Introduction* thread, if you haven't already, so that you know the main topic and format of these threads. *************************************** A. (to chapter) A1 - The Amazing Disappearing Finger This is a demonstration on perception. We will talk about what's going on behind this demo and how it relates to this Perception Chapter later, but for right now just have fun with this demonstration. You don't need to be a magician to make your finger vanish from sight, just follow these simple steps. 1) Extend your arms all the way outward in front of you, with your two index fingers pointing straight up. Make sure your fingers are at about eye level. (finger1.gif) Please Register or Log in to view the hidden image! 2) Close your left eye. Focus your right eye on your left finger. 3) Now very slowly move your right finger straight to the right, while your right eye is still focused on your left finger. Your right finger will begin to go into the peripheral vision of your right eye. (finger2.gif) Please Register or Log in to view the hidden image! 4) Abracadabra, the top of your finger disappears. You won't have to move it very far in order to do this, only about 5-10 inches. (finger3.gif) Please Register or Log in to view the hidden image! We'll talk about why this happens later, right now just try this out and see if you can get this demonstration to work for you. UPDATE 7/13/03 Here's a couple of tips to help make this work better for you... 1) Try watching your fingers over a plain background, or a patterned background. 2) Try moving your fingers up and down very slowly, while keeping your right eye on your left finger. If your fingers are too high or too low then, you might miss the disappearing spot.
Wow that's cool, you can still see the backround behind the finger. Or at least I THINK I still see the backround. Does it have something to do with the arrangment of optical nerves (or rods and cones or photon sensors or whatever they're called) in the eyeball?
It has to do with your optical nerve, maybe just not in the fashion you would expect. It's called "the blind spot" and it is there because there are no cones or rods on the optical nerve. The brain compensates for this and fills the space out.
It should, if you are a human that is. Please Register or Log in to view the hidden image! Try it again and make sure you follow each step completely. Make sure your left eye is closed (won't work if it's open) and keep your right eye focused on your left finger. Also move your right finger very slowly; the disappearing gap can be quite small at the extended arm distance. Anders, You are right, but i wanted some more people to try it out before we start going into the "whys" behind this.
A slightly easier way to see this effect is to get a piece of coloured paper. It doesn't have to be coloured, but a coloured paper shows the 'filling-in' more impressively. Put a black mark such as a cross on the paper about the size of a fingernail. Roughly two inches either side of the cross place two more black dots of similar size so you have an o + o arrangement. Cover either eye with one hand, and move the paper away from your face slowly while focusing on the cross between the dots. At some point one of the dots vanishes and the brain fills in the place where the dot should be with the surrounding colour. Paper with a texture or some such thing on it is even better as you tend to get the pattern as well. Gently adjust the paper and you can hold it in place well enough to study the fill effect closely.
I can still see my finger. Perhaps I am special Please Register or Log in to view the hidden image! (BTW.. I did this many times. Most perception activities do not work with me. Like I said, I am special. Very very special... lmao) Please Register or Log in to view the hidden image! James Sibley
Here’s another example of misperception. Look at the picture what do you see? http://www.magiceye.com Without knowing any more about it, we might be content to think it’s just a bunch of roses. But if you know that there’s more to it you would study it more closely. And if you know it’s a Stereogram you would know how to decipher it and get all the information from it. But what if we didn’t know anything about it, and it was just a bunch of roses. At what point do we stop analyzing it, we would not know when to stop. So we would not know if we had gleaned all the information from it.
blocalsteve, It would be fun to experiment with different designs of paper, and see what kind of distortions there are. 4D, It should work for you, it's a natural effect of how our vision system works. Another tip is to try moving your hands together slowly up and down, while focusing on the left finger. If you have your hands too high or low, you can miss your blindspot. moving, It took me a few years before I was able to get those magic eye things. Now I can do it fairly easy. It's a good example of showing how you can trick the brain into seeing things that isn't there.
moving, If I draw a 3d box on a 2d surface like so... Please Register or Log in to view the hidden image! Is that 3d box really there? It's just a bunch of lines and colors on a 2d surface is it not? I can't grab it or manipulate it. It's just an image on paper. I can't move it around and get a different perspective. We create an illusion of 3d by tricking our brains. It's the same with the magic eye. In the image of the roses you linked to, there is no 3d heart, it's just a trick to get the brain to see something that isn't really there. An illusion.
Yes but it conveys the description of a box. The data on the 2D suface describes a box and our brain deciphers it as a box not lines and colors. The data was encoded onto the paper then decoded by the brain. The box is not there but the information about the box is. In the case of the MagicEye pictures the extra information is not automatically decoded by the brain.
Physiology of the Blindspot Ok let's go into why this disappearing finger happens. Anders gave a pretty good start above. Down below is a diagram of the internal workings of an eye. (blindspot.gif) Please Register or Log in to view the hidden image! At the back wall is the retina. It's kind of like large netting of cells. Within the retina are the photoreceptors we use to see things, for instance rods and cones. They pick up light that enters the eye. These receptors send what they detect to the brain along ganglions (kind of like long wires). All of these ganglions from the receptors meet up at what's called the Optic Nerve (see the diagram). The optic nerve is nothing more than a giant mass of these ganglions (or a whole bunch of wires) that carries all of the sensory information needed to see to the brain. Now at the spot of the retina where all of the ganglions meet and form the optic nerve, no photoreceptors are able to form. This spot is labeled the Blind Spot on the diagram. So any light that falls on this spot isn't detected, since there aren't any receptors there to detect it. So the next question is, if there are a blindspots why don't you just see two holes in our vision? In the finger experiment above, why do you still see a background even when the finger enters into the blindspot?
I can't tell if you are serious or not. Please Register or Log in to view the hidden image! If you can't see in your right eye then flip-flop everything. All "right"s become "left"s and so on. It seems we are arguing the same thing from two different perspectives Please Register or Log in to view the hidden image! I do understand your point of view, and if we talked long enough we'd arrive at the same place. So I'm going to leave it at that.
I really can't Please Register or Log in to view the hidden image! I was just being difficult by mentioning it! Please Register or Log in to view the hidden image!
Ah, two reasons the finger thing didn't work for me. 1) I was going too fast. It only disappears for about a finger width. 2) My walls are beige. It only worked when I did it infront of my blue sofa. (I guess the color was too similar)
