The Eyes Have It

You may have recognized by now that although there appear to be things that are stable and unmoving in our experience, that is not really what is going on. Reality, whatever it is, is constantly in motion, surging and changing in every moment based on causes and conditions that extend back to infinity. Our brains spend a lot of time reducing that complexity and change into something that appears to us as stable, otherwise life would be even harder than it is now.

The eyes are always moving

You can look at the inputs from the senses to see some of these effects. Vision for instance. It may seem as though when you are looking at something the visual field is stable, but the eye itself is continually darting around in something called saccades. The visual field of the retina isn't uniform; resolution is highest in a region called the fovea, which has a high density of cone cells. The area outside the fovea is blurrier, so to speak, but we don't notice this, because the eyes are darting around, collecting information from the foveal region, mapping the area we see. The brain tries to keep the object of interest imaged on the fovea, so if that moves, the eye has to move as well. You can see an example of this in the video below, which uses eye tracking software to show what 16 seconds of someone looking at a painting looks like for where are eyes are looking.

These saccades are incredibly fast; in fact they are among the fastest movements the human body can produce. The eye is moving sometimes several times a second, but interestingly, we don't notice that at all. How are things not getting blurry or generating a sort of motion sickness? Well, it turns out that we are essentially blind during a saccade; the brain "turns off" visual processing while the eye is darting about, but is still constructing what appears to be a seamless perceptual experience. It's called saccadic masking.

There are some interesting experiments that show this. One shows something called chronostasis. As I mentioned above, when the eyes move, the brain shuts down visual input so that you don't get dizzy. When the eye arrives at the new position, it has a choice: it can show the last stable image from before the move, or a new, upcoming stable image. Essentially, the brain waits for the next image and then re-sets your internal clock to sync back up. This causes an illusion that the first impression after the eyes shift appears to be longer than it actually is.

You can see this in action. Find an analog clock with a ticking second hand (there are plenty online if you don't have one at home). Focus on an area of the clock where you can see the second hand moving in your peripheral vision, without directly looking at it. After doing that for a few seconds, shift your eyes to focus directly on the second hand. You'll notice that the first tick appears to be much longer than the subsequent ones. Cool, huh?

What are we missing?

Looking at these eye movements is a good reminder that vision is actually occurring in the brain, and there is an awful lot of processing going on. What you are "seeing" is an interpretation of reality, but perhaps not exactly what is already there. In general, there is a lot more information out there than we can experience. Sticking with vision, our eyes can process a certain range of wavelengths of light, but other species can see other parts of the spectrum. If you are a bee, for instance, you can see in the ultraviolet. If you want to be amazed, take a look at ultraviolet images of flowers. There are all sorts of detail we don't see, but seem tailor made to attract bees to help with pollination. What appear to be plain old flowers to us light up with landing strips and bullseyes in a bee's vision. Very cool indeed.

Inattentional Blindness

Another interesting phenomenon involving our sense of sight is something called "inattentional blindness". It shows that we miss a lot of what is going on around us, especially when we are focused on a particular task. There is a famous experiment by Christopher Chabris and Daniel Simons - the "invisible gorilla". In this experiment, participants were asked to watch a video of people passing basketballs and count the number of passes made by players wearing white shirts. There are also players wearing black shirts passing a ball, but participants were asked to ignore them. During the video, a person in a gorilla costume walks through the scene, stops in the center, thumps their chest, and then walks off. Surprisingly, about half of the participants failed to notice the gorilla, despite it being clearly visible for 9 seconds.

The experiment demonstrates that our attention is selective and also limited. When we concentrate on a particular task (like counting basketball passes), we can become blind to unexpected events, even if they're extremely obvious. This selective attention helps us focus on relevant information but can also cause us to miss potentially important details in our environment.

This phenomenon isn't limited to controlled experiments. It occurs in everyday life, affecting how we perceive and interact with the world around us. For instance, we might miss seeing a friend on the street when we're in a hurry, or fail to notice changes in our environment when we're distracted.

Summary

This is just a subset of all the interesting things that are going on cognitively with respect to the sense of vision. I think we know intellectually that the brain is doing most of the work in creating what we perceive as reality, but looking deeper at the effects makes you appreciate it even more. What you are seeing is very much yours, and the same is true for the other senses as well. It's interesting to speculate how different the world we are traversing is from the people around us. There is lots of social and societal conditioning we undergo to establish what we understand as a shared reality, but the details are more varied and stranger than we may expect.

What I take away from all this is humbleness. Reality is always changing, my perception of it is very limited, and my brain is doing a lot of processing and filling in of gaps. Given that, it makes me more open to other people's points of view. We're all stumbling around trying to find our way in this world, so we shouldn't be quite so sure of our own positions. I think that is a healthy stance to take.

-Scott