We don’t often think of eyes as “fast.” We’ll normally talk about vision in terms of acuity and coordination, but speed? Not so much. Spend some time watching another person’s eyes though and you’ll likely be pretty impressed at how rapidly they jump around.
Turns out, the little jumps that you’ll see their eyes make are among some of the quickest movements that the human body can make.
All About Saccades
The actual term for those movements is “saccade,” a french word meaning “jerk” and used for obvious reasons.
Saccades have a couple key characteristics. First, as discussed, they’re very fast, and second, they’re coordinated motions, made by both eyes at the same time. Saccades come in a few different varieties. Most of the ones that we make are so-called “visually-guided” saccades, which are made in response to a visual stimulus. They can be a reaction to a sudden change in or appearance of a stimulus – think about how people immediately train their eyes in response to a sudden movement or unexpected noise – or they can be purposeful, intentional motions used by individuals scanning their surroundings.
Saccadic movement is extremely common and relates to the way we perceive the world. While the human field of vision is decently large, it is, for the most part, less than extraordinarily detailed. The visual cells in our eyes are densely packed into a small area at the back of the eye called the fovea. The fovea is responsible for the bulk of fine-tuned vision, and for perceiving objects in the very center of our field of vision.
Because of this, we generally do our best to fit areas of interest into the region of sight that corresponds to the fovea, a process that allows us to learn more about what we’re looking at than we would if we relied on less-detailed peripheral vision. Saccades come in handy here, as they allow us to quickly train our foveal vision on interesting items.
Reading provides an excellent example of saccadic vision at work. While we often think of ourselves as reading through lines smoothly word by word, we’re actually quite a bit choppier. Watch a reader, and you’ll notice their eyes jerking all around the page as they zero in on various words and paragraphs, occasionally jumping forward or backward as they do.
So How Fast is a Saccade?
Saccades are extremely quick. So much so, in fact, that they’re one of the fastest motions we can make, comparable to other extremely rapid, discrete movements, such as blinks. Interestingly enough, saccades can’t be stopped once they start – they’re one-directional and occur as fast as the eyes can possibly make them.
As you might guess, the eyes are far from slouches. It’s hard to measure saccades in terms of miles per hour; instead, researchers generally use a value known as angular velocity, which is calculated by measuring degrees moved per second. Angular velocity is a good way of visualizing how quickly a circular object is spinning. For example, a car tire making one revolution every second would be moving at an angular velocity of 360 degrees per second.
Eyes move much, much more quickly and often hit figures around 900 degrees per second, making them rapid on just about any scale you’d choose to use. Small wonder that saccades can look so jerky in other people!
Reacting to Information
But once we’ve fixated on new objects, how quickly can we actually make sense of them? The answer is, again, very quickly.
Visual reaction time is often measured through the use of simple visual response tests. Participants are told to push a button upon noticing a change. For visual tests, this stimulus is generally a light flashing. Studies conducted on college students have found that mean response time in these studies was around 190 milliseconds. Fast, but actually a little sluggish compared to how quickly we react to sounds (160 milliseconds).
However, more recent, more complex research performed by a team from MIT has shed some more light on how quickly we can simply perceive images, as opposed to react to them. The team showed participants flashed images for extremely brief periods of time, then tested them to see if they could accurately identify the pictures.
The results? Participants were able to make reasonably accurate answers when shown images for only 100 milliseconds. Impressive as that is, further tests showed that they were still better than random chance at much shorter amounts of time. Even when images were only shown for 13 milliseconds, human participants were still more accurate than a random selection.
Can We Improve These Times?
Our body’s baseline abilities are already incredible, but, as always, some people do their best to develop even more exceptional capabilities. And as we’ve consistently seen, they’re finding some success.
Some of the most influential research performed on enhanced response times has come from a PLOS-published study focusing on the reaction of Olympic sprinters to a starter’s gun. While audio stimuli are clearly different from visual, the difference in mean reaction times between average individuals and elite athletes is massive. While most college participants were able to respond to sounds in around 160 milliseconds, many sprinters were able to get their numbers down to nearly 100 milliseconds, though none were able to break that particular barrier.
Saccadic speed and accuracy is especially important for athletes. Baseball, football, basketball, and soccer players all rely on quick, perceptive saccades to understand the action unfolding across an entire court and playing field. One frequent drill makes use of two eye charts taped to a wall with several feet of separation between them. By reading letters off of alternate charts, exercisers can train themselves to better make use of saccadic movements.
As for improving saccades, you may want to turn to RYV’s favorite course of vision improvement – eye vitamins.