Topics Perception

Question If I cross my eyes, or press on one eyeball, I see double. This is explained by saying that we have two optical images, one on each retina, and they are normally coincident, whereas they are not coincident when pressing on one eyeball. I am now crossing my eyes and I see two computer monitors. Which is the real monitor: the one on the left, or the one on the right?

Accepted:
March 4, 2006

Comments

This question is obviously similar to this one. And the answer is much the same. You are not seeing two computer monitors. You are seeing one monitor, although it seems to you as if you are seeing two monitors. There is one monitor that both appears to be slightly to the left and appears to be slightly to the right. Note that this is not the same as to say that there is one monitor that appears both to be slightly to the right and to be slightly to the left. I doubt we could ever have a visual experience correctly described this latter way: Could it ever look to you as if there was one thing that was in two places? But there is no obstacle to our having a visual experience correctly described the former way: It can be that, although it looks to you as if there are two things (in different places, of course), in fact you are seeing only one.

If that seems confusing, well, it is confusing. The logic of this kind of situation is extremely subtle. Philosophers and logicians spent a lot of time in the 1960s trying to understand it, and they made a good deal of progress, but I doubt anyone would really claim fully to understand such constructions (that is, to understand quantification into opaque contexts).

That said, it may well be that, when you cross your eyes and such, you have two images of monitors in your head. But images of monitors are not monitors any more than drawings of monitors are monitors, so neither of them is the "real" monitor, although both of them are images of the real monitor. And again, you don't see these images. You see the monitor. Perhaps you see the monitor in virute of having the images in your head, but that is different.