Freethought & Rationalism Archive

Abacus · 12-17-2002, 12:37 PM

Here's a good one:

echidna · 12-17-2002, 12:49 PM

Thanks for reminding me of those CD. I remember seeing spinning Benham Discs at our Scienceworks Museum & I�ve printed out a few to make for the kids over the coming holidays.

I looked around for explanations but interestingly I couldn�t find any claiming absolute certainty. Just goes to show how little we still understand about the brain�s operations.

<a href="http://faculty.washington.edu/chudler/benham.html" target="_blank">http://faculty.washington.edu/chudler/benham.html</a>

Quote:

The retina of the eye is composed of two types of receptors sensitive to light: cones and rods. Cones are important for color vision and for seeing in bright light. There are three types of cones, each of which is most sensitive to a particular wavelength of light. Rods are important for seeing in low light.

It is possible that the colors seen in spinning Benham disks are the result of changes that occur in the retina and other parts of the visual system. For example, the spinning disks may activate neighboring areas of the retina differently. In other words, the black and white areas of the disk stimulate different parts of the retina. This alternating response may cause some type of interaction within the nervous system that generates colors.

Another theory is that different types of cones take a different times to respond and that they stay activated for different amounts of time. Therefore, when you spin the disk, the white color activates all three types of cones, but then the black deactivates them. The activation/deactivation sequence causes an imbalance because the different types of cones take different times to respond and stay on for different times. This imbalance in information going to the brain results in colors.

Neither of these theories explains the colors of Benham's disk completely and the reason behind the illusion remains unsolved.

philechat · 12-17-2002, 12:57 PM

I picture color as (a physical stimulus) which upon entering the retina becomes "transformed" to the experience of color. The physical form that constitues the perception of color is different from the perception of color itself, and what is "perceived" is often at great odds with what the physical stimulus actually expresses.

A book is "white" in dim candlelight and in noonday sunlight (intensity difference at least 1000x). A light source may be called "green" (without any perceptual distinction) if there is light of a single wavelength or if there are more than one wavelengths of lights present (called metamers), all suggests that color perception is constructed in a way that does NOT represents the "true" components of physical source.

echidna · 12-17-2002, 01:39 PM

Quote:

Originally posted by Living Dead Chipmunk:
Everything my mom and I saw as dark red, my dad would call purple. We never figured out if it was a problem with learning the wrong name for a color, or if he really saw it differently.

I recall wearing yellow tinted sunglasses for a period & after taking them off, having great difficulty distinguishing blue from green, very disconcerting given I'm not usually colour-blind.

We used to have a regular by the title of Optics Guy, but maybe he's no longer around.

crocodile deathroll · 12-17-2002, 03:12 PM

</a>
Click on this image
and you will see another variation on the Benham's disk theme

[ December 17, 2002: Message edited by: crocodile deathroll ]

Jeremy Pallant · 12-17-2002, 05:04 PM

Well, I tried the applet, and all I saw was black and white, with some blurring.

crocodile deathroll · 12-17-2002, 06:13 PM

Quote:

Originally posted by Jeremy Pallant:
Well, I tried the applet, and all I saw was black and white, with some blurring.

I do see colors on the applet, brown and purple. Could it be just confusing the cones in my eyes?.
This is one way the experiment is set up

A demonstration on how to set it up

This is a better one for you to print.

Jeremy Pallant · 12-17-2002, 06:22 PM

Quote:

Originally posted by crocodile deathroll:
I do see colors on the applet, brown and purple. Could it be just confusing the cones in my eyes?.

Well, do you know those pictures hidden in apparent chaotic patterns? I forget what they're called. No matter how I try, with experts telling me exactly what to do, I can never see them.

I don't, incidentally, have the tools with which to try the other experiment.

[ December 17, 2002: Message edited by: Jeremy Pallant ]

echidna · 12-17-2002, 07:08 PM

With the discs I only intend to glue the image to cardboard & screw it to an electric hand drill. Should work. I can definitely vouch for the disc having seen them before, it's most bizarre.

I reall another excellent illusion at Scienceworks, more related to phantom limbs. 2 horizontal bars which one grabs with each hand, separated by a perpendicular mirror so from each side one can only see the relection of one hand.

With both hands in place, the mirrored image correctly shows the other hand accurately represented, but remove one hand and the sensation is almost tangible, that one's eye's are telling one that both hands are still there while all other senses know it is not. Excellent illusion, most disturbing.

crocodile deathroll · 12-17-2002, 07:53 PM

Quote:

Originally posted by Jeremy Pallant:


Well, do you know those pictures hidden in apparent chaotic patterns? I forget what they're called. No matter how I try, with experts telling me exactly what to do, I can never see them.

I don't, incidentally, have the tools with which to try the other experiment.

[ December 17, 2002: Message edited by: Jeremy Pallant ]

It's easy, You may prefer to just right click your mouse button on the image then save it that way, because you do not want to waste all that ink and paper. Then open the file and print it up. Mount it on a stiff piece of round card the same size. Then pierce a dart, skewer etc through it and just spin it with your fingers.

easy.

[ December 17, 2002: Message edited by: crocodile deathroll ]

12-17-2002, 03:12 PM	#15
crocodile deathroll Veteran Member Join Date: Dec 2001 Location: Darwin Posts: 1,466	<a href="http://dogfeathers.com/java/fechner.html" target="_blank"> </a> Click on this image and you will see another variation on the Benham's disk theme [ December 17, 2002: Message edited by: crocodile deathroll ]</p>

Thread Tools	Search this Thread
Show Printable Version	Search this Thread: Advanced Search

12-17-2002, 12:37 PM	#11
Abacus Veteran Member Join Date: Mar 2002 Location: South Dakota Posts: 2,214	Here's a good one:

12-17-2002, 12:57 PM	#13
philechat Senior Member Join Date: Apr 2002 Location: Mind of the Other Posts: 886	I picture color as (a physical stimulus) which upon entering the retina becomes "transformed" to the experience of color. The physical form that constitues the perception of color is different from the perception of color itself, and what is "perceived" is often at great odds with what the physical stimulus actually expresses. A book is "white" in dim candlelight and in noonday sunlight (intensity difference at least 1000x). A light source may be called "green" (without any perceptual distinction) if there is light of a single wavelength or if there are more than one wavelengths of lights present (called metamers), all suggests that color perception is constructed in a way that does NOT represents the "true" components of physical source.

12-17-2002, 05:04 PM	#16
Jeremy Pallant Veteran Member Join Date: Dec 2000 Location: Tucson, Arizona, USA Posts: 1,242	Well, I tried the applet, and all I saw was black and white, with some blurring.

12-17-2002, 07:08 PM	#19
echidna Veteran Member Join Date: May 2001 Location: Melbourne, Australia Posts: 2,832	With the discs I only intend to glue the image to cardboard & screw it to an electric hand drill. Should work. I can definitely vouch for the disc having seen them before, it's most bizarre. I reall another excellent illusion at Scienceworks, more related to phantom limbs. 2 horizontal bars which one grabs with each hand, separated by a perpendicular mirror so from each side one can only see the relection of one hand. With both hands in place, the mirrored image correctly shows the other hand accurately represented, but remove one hand and the sensation is almost tangible, that one's eye's are telling one that both hands are still there while all other senses know it is not. Excellent illusion, most disturbing.

Freethought & Rationalism Archive

The archives are read only.