June 29, 2006
A "reverse" color test
In the past few days, I've received a number of emails from people who took the reverse color-blind test on this site. Normally, I've gotten a sparse, but steady stream of emails about it over the years, but the recent deluge appears to be due to Clive Thompson's blog entry on the topic. (Thanks Clive!) For those of you who are curious, here's the story behind the test.
About six years ago over lunch, my friend Nick Yee and I were chatting about color vision and the differences between what a "color sighted" person can see and what a "color blind" person can see. I represented the former, while Nick represented the latter. Now, there are several different kinds of color-blindness, and Nick happens to have the kind that makes him fairly insensitive to variations in red hue, so-called red-green color blindness. One of the things he complained about was the color blind tests that hide images in the hue of an image so that color sighted people can see the image, while color blind people cannot. We mused about whether you could make a reverse test where we hid an image in a way that color blind people could see, but color sighted people could not. But, if color blindness is purely a deficit, how can this be done?
In most color-sighted people, the parts of the retina that are sensitive to the hue of red seem to be a little more sensitive to intense red hues than the corresponding parts for blue and green. So, our idea was that we could overwhelm (saturate) the red channel in color-sighted people and thus hide information in an independent channel (luminosity) that red-green color-blind individuals would be able to detect. That evening, we each went to work in photoshop and produced some test images to try out on each other. My images and writeup are on this site (here), while Nick maintains his own page here.
What I've learned over the years, from emails by people finding and taking the test, is that a person's sensitivity to red hue varies tremendously from individual to individual. Most people can see the corner of the secret image in the first picture, but few can see the remainder. Some individuals have a more balanced sensitivity to hues, and their eyes aren't fooled by the intensity of the red - they can see the secret image just fine, even though they can also see the full color spectrum (these people seem to be quite rare). Some people have trouble with the second picture - their eyes are confused by the heterogeneous structure of hue - while others have no trouble at all. Even a color-sighted person can see the secret image in the second picture if they know what to look for, that is, if they have a clear expectation about what's hidden and where to look for it, then they can pick out the subtle variations in luminosity.
I'm very curious to hear from someone who knows more about how the retina works, where this variation comes from, and what other possibilities exist for making a better "reverse" color test. For those of you coming from Collision Detection and taking the test, feel free to leave a comment about your experience with the test.
Update, 21 July 2006: The test was also featured recently on Veronica Magazine's Netnews. Welcome folks from the Netherlands!
Update, 13 March 2007: Turns out that the test was dugg sometime around last July, which explains some of the spike in traffic the test received around that time. The Digg comments are kind of amusing - many people discovered that their laptop monitors let them see the "hidden" images even though they aren't colorblind.
June 25, 2006
An Inconvenient Truth
Tip to onegoodmove.
June 23, 2006
I've been looking for a good web hit-counter for a while, and fiddled around with several of the free ones that I found via Google. But, none of them were satisfying, and I got distracted by other more pressing things (more on that in another post). But, today I finally found something worth using. In the gutter now, you'll see a little picture of the world, maintained by ClustrMaps, which uses a rough geospatial reverse-DNS to determine the general point on the world map that the originating IP address came from. It's a cute way to visualize the distribution of visitors to the site, which I like.
In other blog changes, come January 2007, this blog will be moved to a Santa Fe Institute location, where I'll be starting a post-doctoral fellowship.
Finally, I'm considering closing all (past and future) entries in the blog to comments - the blog-spam is getting annoying to deal with, I don't get that many comments to begin with, and I haven't figured out a simple way to make it difficult for the bots to post. Does anyone have any experience with making MT v3.14 bot-spam-proof?
June 05, 2006
What happens when you put a Mentos(tm) into a Diet Coke(tm)? A violent release of energy on the part of the diet coke releasing a large amount of CO2. Here's what happens when you have a lot of free time on your hands, a lot of diet coke and a lot of mentos. Seems to me that this would make a great high school chemistry demo.