The Scientific American Feb 2010 p.77 has this illustration:
This takes a bit of effort and a little practice but after a couple of minutes you should be able to cross your eyes voluntarily and merge the two pluses into one plus. When you are successful at holding your eyes in that position for a few seconds interesting visual effects will start happening to a newly formed rectangle in between the red and green ones. I discovered that by holding the tip of a pencil between the pluses about half way between my eyes and the computer screen and then crossing my eyes to look at the pencil tip will cross my eyes about the right amount. It is easier than trying to voluntarily cross the eyes and hold them crossed while they decide to fixate on the +. Move the tip slowly forward and backward until the pluses merge.
My eyes start reacting in unexpected ways. First the bright red and bright green areas merge together and form a silver color. But this color isn’t stable and can vary in several ways: the color can shift smoothly over half a second to some other level of grey or to a color, often tan-green and then drift over to a blend from green on one side to red on the opposite side but that blend can go either way. These various transformations must be taking place in the visual part of the brain and not in the eyes themselves because the two eyes are not presenting the same image to each other for processing but only to the brain.
This procedure is a strain on the brain and I had viewed these images in the print form in the magazine several times over the last couple days. But, this morning shortly after arising I started to read a magazine and almost immediately began to have a migraine aura. I have blogged about how to cope with these in, Migraine experiment updates are reported. I thought this unpleasant event might be an opportunity for further migraine aura experiments. So, I tried doing the cross-eye experiment on the color patches in the magazine which was a little more difficult because of the migraine flashes but not having much else to do I persisted. It has been shown with brain scans of people actually having migraine auras that there is abnormal blood flow in the visual cortex at that time. I was wondering what would happen if the migraine was overlapped with the excess visual effort being made during these color overlap experiments. At first I didn’t notice anything particular other than the difficulty in seeing the color swatches behind the sparkling auras. Then I noticed that the auras had gone away in about two minutes after starting the experiment. These auras usually take about half an hour to go away when I just lie back and relax or about ten minutes or less when I do the tapping technique mentioned in the blog above. Did something unusual happen this time or was this just a one time event. It will require some further observations. I don’t look forward to migraines because they interfere with my otherwise serene life but this might prove very interesting to me and helpful to others who have worse problems than mine.
I remade these photographed graphics used above for better viewing results.
Sit back from your computer to arms length and then take a pencil and hold the point about half way between your eyes and the screen. Now fix your gaze on the tip of the pencil with crossed eyes. Slowly move the pencil toward the screen a few inches and then slowly back toward you eyes a few inches. Notice that the black dot in the center of the picture moves together and apart as you move the pencil slowly backward and forward. (The bottom dots in the plain fields are easiest to do this with.) At some distance the two dots will appear as one perched on the tip of your pencil. Hold the pencil in this position for five to ten seconds while moving it slowly forward and backward a half an inch and shift your mental attention to the dot. While fixating on the dot slowly lower the pencil out of the picture. About this time you should begin getting visual blending of the blended red colored field and the green colored field into a visual hallucination.
The phantom box you will probably see first be silver-grey. What is strange is that the area directly behind the dots looks silver-grey and yet neither of these screens has that color at that position. You can look at these things for quite a while and get many different effects but for maximum visual impact do the same experiment on the targets. After focusing on the black dot for several seconds the targets will catch fire and start doing all sorts of crazy things. Reversing colors, going silver, color fatigue effects and after a while total lack of contact with visual reality as you formerly knew it.