Archive for December, 2007

conquering my visual cortex

December 21st 2007

Today is a landmark day where I fought a pitched battle against my very own visual cortex, and I am proud to say that I emerged triumphant. No doubt you’ve seen those pictures of a bunch of colored dots, where if you stare at them long enough a 3D picture is supposed to “pop out.”

shark stereogram thumbnail


I remember these used to be popular circa 1995 when everyone had huge Magic Eye posters plastering the walls[1]. In the 10 years that I’ve been staring at these speckled dot things (autostereogram, to be precise) I never really got it. The advice people tell you when trying to perceive these images is vague and unhelpful: “you just have to stare at it long enough!” Sometimes it worked, usually not[2]. Until today.

Espousing the wikipedia is passé, I know, but I feel it’s necessary because this page has allowed me to overcome a decade-long frustration and master my own personal visual perception system. The reason why it’s so hard to “see” an autostereogram is because you’re asking your brain to do something totally unnatural. Millennia of evolution have hard wired the actions of focusing and convergence into your eyeballs. Stereograms are basically just a dirty trick on the brain, and for the illusion to work you need to defeat your subconscious reflexes.

simple stereogram thumb


It’s helpful to understand how exactly the illusion works, and to practice on simple wallpaper images like this one. Then you can move on to level 2, random dots. It really is just a matter of practice and training. Once you’ve mastered the control of your visual cortex, it’s a cinch.

stereogram composite

I’m impressed at how, once locked into the illusion, you can flip between images without having to recalibrate yourself. Take a bunch of images (here’s a zip file of 50) and make them into a screensaver or slideshow. You should be able to switch pictures and stay in 3D the whole time.

Easier, download these quicktime movies I made that cycle through the whole bunch automatically:
1 second per frame or 3 seconds per frame

For best results, open in Quicktime and go to “View” -> “Present movie…” -> “Actual Size.” Stereogram animations are also cool. For the ultimate challenge try this on for size… stereogram tetris! I played for 10 minutes it left me unable to look at still objects, or walk straight.

[1] 1995 was also The Year of the Fractal. Computer-generated images used to be cool.
[2] Turns out I was doing it all wrong. I was crossing my eyes, which made the images inverted. Most stereograms are rendered to be viewed “wall eyed.”

Posted by dylan under humans & machines | 6 Comments »