I spend a lot of time contemplating the fan that spins over my bed. This is a picture of it. That’s approximately how it looks to me most of the time. But that’s not how it really is. In reality the fan is a hub and spoke system with five blades. But when the blades are spinning, they cannot be discriminated and the fan looks more like a solid wheel.
Why is that? Why can I not see the fan as it really is? Why do I see a false image, of a wheel that is not actually there? Am I hallucinating? No matter how carefully I stare, I cannot see actual fan blades. What am I seeing, if not reality? This should shake my confidence in the veracity of vision. Except for tricks and special situations, we generally believe that “seeing is believing.” In other words, what we see is what is there.
But this is a clear case of seeing what is not there, and not seeing what is there. And it is not a trick or special situation. Apparently, the mechanics of my eye cannot resolve the details of the blades as they spin. In order to fixate an image of something on the retina, the image must be still, for a moment at least, about a fifth of a second. That’s the only way we can see something.
What about things that are moving? We can see those under normal circumstances because the eyes take successive “snapshots” of the scene and integrate them over time to communicate movement to the brain, much as the rapid succession of snapshots in a film appears to us as a moving picture (another delusional visual experience). We do not actually see motion. We infer motion.
But in the case of my fan, the movement of the blades is faster than the snapshot rate of my eyes, so I cannot get a fixed image of the blades. The eyes are always moving, jerking around in a process called the visual nystagmus. They vibrate at least 20 times a second, sometimes faster, fixating here, there, everywhere, taking snapshots. It seems like the visual world is stable and that we just look at it and see it as it is, but that is not true. The eyes get at least 20 snapshots per second, no one of them taking in the whole scene. Each snapshot is with the eyes focused on a restricted detail of the scene. Then you synthesize the overall scene in your brain, based on the snapshots. The nice stable scene you think you see is a total fiction. You never saw it. You only saw dozens and dozens of tiny snapshots.
So I thought I would try to beat the visual system and my bedroom fan. I moved my eyes in a fast counter-clockwise motion around the hub, to see if I could make my eyes catch up with the fan blades. And it worked! Every few seconds, I would get a brief image of the individual blades of the fan. That’s because the muscles and nerves for voluntary eye movements are different from the ones used in the visual nystagmus. By adding the two eye movements together, I gave the nystagmus a chance to make a fixation on the blades.
It seemed to work randomly. Whenever there was an eye fixation that happened to hit a blade and not the space between blades, I would see an individual fan blade. Why this did not occur more often, I am not sure. Perhaps I also needed to catch a moment when the blurred motion signals to my brain were calm enough to let an individually fixated image through. Or perhaps my voluntary, circular eye movements were not really very circular, but most often erratic. It is impossible for me to know that.
Anyway, the demonstration proved visually that the blurred circular image I normally see is a complete illusion, not the reality of what is there. The fact that I could force the visual system to apprehend the true reality of the individual blades confirmed the presence of the illusion. So it makes me wonder, what else am I seeing that is illusory? How can I trust that what I see is really there if I know for a fact that sometimes I am seeing it wrong?
Descartes asked this same question in 1640 and came up with this answer: God is good, and God would not deceive you (most of the time). Therefore, you can be reasonably confident that what you see is what is there. Well, that answer doesn’t work for me. In the first place, it is not entirely clear that God is good. Biblical and contemporary evidence would speak to the contrary.
Secondly, my experience with my bedroom fan proved that Descartes’ answer is wrong in this case. What I see most of the time is clearly illusion. Should I assume that God deceived me because God is a malicious trickster?
And finally, Descartes had no evidence to support his claim. It is merely what he believed, because he had been told as much by the Church. I can’t assume his answer is correct if he just made it up or parroted what he had been told. It seems just as likely that the correct answer is that you cannot and should not believe that what you see is what is there. What’s wrong with that answer?