Okay, so now that you know something about the extraocular muscles and the innervation patterns, we're ready to talk about eye movements. And as I mentioned, there are five basic types of eye movements. And I'd like to just very briefly mention them and then we'll consider each one in turn. Okay, so broadly speaking, we make eye movements when the two eyes go in the same direction. These are called conjugate eye movements, and there are four kinds of conjugate eye movements. There are saccades, which are these very quick, ballistic movements of our eyes. again if I give you the challenge of finding a clock in your environment and making an eye movement towards that clock, that's a saccade. Its a very quick, ballistic kind of eye movement. There are smooth pursuit eye movements. And these kinds of eye movements are what we might, undergo if we wanted to, follow the flight of a bird, for example, across the sky. It's slow, and it's typically guided by a visual target. There is another category of eye movements that we call optokinetic eye movements. And these eye movements, sometimes involve a combination of smooth pursuit and saccadic eye movements. they're visually guided. And what they do is they are a response to large-scale movements in our visual environment. There are some other very subtle kinds of optokinetic eye movements, that don't necessarily combine smooth pursuit and saccade. But what they all have in common is the visual stimulus being large-scale visual movement. The fourth type of conjugate eye movements, we've already discussed in some detail. These would be the vestibulo-ocular movements. And these are the kinds of eye movements that are necessary to look straight ahead at you while I shake my head back and forth. Okay, we won't talk too much about vestibulo-ocular movements today, since we've already had a discussion about that, but I want you to know where to go back to learn more about vestibulo-ocular movements. Okay, so these are the four congugate eye movements. There's also a category of eye movements where the two eyes don't actually go together. These are called disconjugate eye movements because the eyes move in opposite directions. And this is the kind of vergence eye movement that's necessary to focus on a distant object and then to a near object. So, for example, I might ask you to hold your finger out in front of you and focus on that finger tip, and then focus at a distant sight, more or less in the same sight line but off at a distance. And then jump your fixation back and forth. Well, I doubt you can see what my eyes are doing, but I know what they are doing as I go to focus on a distance target. The eyes rotate outward, and when I go to focus on the near target, my fingertip, my eyes rotate inward. So, the eyes are moving in different directions. In order to go from outward to inward, the left globe needs to rotate in the adduction direction, towards the midline, which would be a rotation to the right. The right eye has to also move in the adduction direction, but for that eye it's a movement to the left. So the two eyes are actually rotating in different directions, but to serve a common functional goal. Okay, in this case, changing the line of fixation from a distant target to a near target. Okay, now let's talk about each of these five types of eye movements in turn. And then we'll spend just a little bit of time on the circuitry that's important for a couple of these eye movements. We'll begin with saccades. So, a saccade is a quick, ballistic eye movement that allows us to change fixation from one target to another. And in the graph here, we see an illustration of a couple of key points regarding saccadic eye movements. So imagine a visual target comes on in this position right here. And what we noticed is that, it takes a bit of time for us to generate the saccade. Typically about 200 milliseconds is necessary between the onset of the target and the onset of the eye movement that allows us to fixate that target. So, the eye movement itself is a rather sudden sharp movement where we change fixation from one position to another, and this allows us to acquire this target. And this 200 millisecond delay turns out to be rather important, because let's say in the middle of this 200 millisecond period of time, some other target came on that we might choose to look at. what would happen is that we couldn't generate a new saccade until the completion of the previous saccade. So there would be another 200 millisecond delay before the acquisition of the next saccade target. So there seems to be a very quick an explosive execution of this type of eye movement that allows us to go from one fixation point to the next. And this is what we do all the time. When we're looking around at a visual scene what we do is that, we move our eyes from one location to the next. I would encourage you to jump on Youtube or some other video source, And just explore, what people have posted who study eye movements. And there's all kinds of examples that I could direct you to, where people have now begun to track eye movements. And, it's, it's quite remarkable what people look at and how, often one actually makes a change in fixation. For most of us, when we're just casually walking down the street or observing a sporting event, whatever we may be doing, we are changing our fixation about two to three times a second, which is really pretty remarkable. and what's equally remarkable is the idea that somehow, while we're moving our eyes all around these visual scenes at such a quick rate, our brains are generating this constant, stable, visual construction of what this scene actually is that we're inspecting. We may be tracking motion within that scene, but there's a stable scene, despite the ongoing saccadic movements our our eyes. Now one feature of saccadic eye movements that I really do want you to demonstrate for yourself, is that during this period of time when our eyes are actually moving. Maybe about 150 milliseconds of motion here in this particular example, and that's pretty typical for how long we're moving our eyes during a typical change in fixation. we are functionally blind during that time, at least with respect to our conscious visual perception. So during this interval of time we don't actually process the motion that is otherwise streaming into our subcortical visual pathways. Now, at some level, we think that information is present in the cerebral cortex, but it's not integrated within our conscious perception of the visual scene. So here's how you can can convince yourself of that. I want you to go to a place where there's a mirror in front of you, and just pick out some imaginary spots on that mirror. Not too far away from one another. Let's say within oh, maybe about 20 centimeters or so of one another, and just, just make fixations to one spot and then the other. You'll have to imagine those spots, or maybe you can actually put a little mark on the mirror, so that you have a visual target to saccade toward and look at. And what I want you to try to do, is to see if you can watch your own eyes move in that mirror. Well, if you're like me, if you're like most people, the best you'll do is just catch a fleeting glimpse of your own eyes move. And this is demonstration of the fact that, all this visual blur that we might anticipate during the motion of our eyes, is actually suppressed from visual consciousnesses. And for this reason it's, it's really quite difficult to see your own eyes move. Now, if you happen to be with someone, and that person's watching your eyes move, there'll be no doubt in your observer friend's mind that your eyes are actually darting about from one target to the next. and yet when you try to appreciate that yourself, it's really quite a challenge. So why don't you go ahead and pause this tutorial, and go find a mirror and try that for yourself. And when you come back, we'll move on and talk about the next kind of eye movement.