Friday, July 13, 2007

Checkerboards and Honeycombs in the Sun

In 1819, the eminent physiologist Johann Purkinje drew the following picture of what he saw when he closed his eyes and faced toward the sun:



Purkinje said that most individuals with whom he tried this experiment report seeing such figures, especially the little squares. (For a fuller translation of this and surrounding passages, see here.)

When I face the sun with eyes closed it doesn't seem to me that I see checkerboard or honeycomb shapes. Rather, I'd say, my visual field is broadly and diffusedly orange or light gray (slowing shifting between these two colors) -- and brighter, generally, in the direction of the sun. Sometimes it briefly becomes a vivid scarlet. Others I've asked to close their eyes and look at the sun also generally don't report Purkinje-like experiences (although one person on one occasion -- out of several occasions -- reported something like a honeycomb latticework).

So I'm curious: Was Purkinje simply mistaken? Did he have unusual experiences, accurately reported for his own part, and then subtly pressured his subjects into erroneously reporting similar things? Could this be the kind of experience that varies culturally? I'd be interested to hear if any of you experience checkerboards or latticworks.

3 comments:

Justin Tiwald said...

That's curious. I see orange when I look directly into the sun. But I see latticework when I look into the sunny sky (not the sun) a few feet back from my window, where the light is dimmer. Could Purkinje and his subjects have been looking at the sun through grimy windows?

LuckyTwisted said...

And I see different things. May be it depends on what I expect to see (remember from the previous time or have heard from others...

Eric Schwitzgebel said...

Cool thought about the windows. In the orginal text, Purkinje starts by looking at the sun with his eyes closed and his hand held, fingers spread apart, in front of his face -- maybe that's a dimming effect similar to the grimy window you mention (though spreading my fingers in front of my face doesn't seem to have that effect on me).

Another person suggested to me that it might have to do with looking through windows with small panes of glass with vertical and horizonal bars between them (a type of window more common in the 19th century). I had the impression he and his subjects were outside; but when I get back from out of town, I'll have a look at the relevant passages again....