From a subjective point of view, when we stare at something, we usually feel that our eyes are not moving at all. But in fact, the eyes are moving almost all the time, but it is difficult for humans to realize it. In other words, humans can never completely fix their eyes in one place. Even if they try to keep their eyes still, they will still have small movements to adjust the picture we see. Such eye movements are also known as “micro-saccades”, which average once or twice per second, or tens of thousands of times a day.
A study more than ten years ago showed that when people see a static picture, but feel the circle inside is spinning, it is because of micro eye twitching. Now, scientists have discovered that microsaccades not only create interesting optical illusions, but also allow people to see better. It’s just that we need to experience a short period of “blindness” before our vision is enhanced.
How do the eyes see details?
In the human eye, there is a large retina to collect information, but only a very small area is responsible for providing high-resolution vision and helping us see the details of things.
Static images that make people feel like they are moving
In order to see the road signs in the distance, we must rely on the details provided by the fovea in the center of the macula to change the “picture quality” of the corresponding position to high definition.
This area on the macula, called the fovea, is a concave structure with a diameter of only about 0.35 mm. Although the place is small, it gathers a large number of cone cells, which is denser than the distribution of cone cells in other areas of the retina.
Cones are the photoreceptor cells that the eye uses to distinguish different colors. With individual connections between each cone and the optic nerve, it’s easy to tell which stimulus is coming from where, so the cones’ visual acuity is fairly strong. Then, the central fovea of the macula, which has a large number of cone cells, has enough sensitivity to help us distinguish the detailed structure of some objects. For example, in order to clearly see a road sign in the distance, or to lock a person from a crowd, we have to rely on the details provided by the fovea in the center of the macula to change the “picture quality” of the corresponding location to high-definition.
But also because this concave area is too small, humans need to constantly move their eyes so that the fovea in the center of the macula can see the whole picture of things (just like turning a telescope to different angles, you can see different scenery). Even if we stare at an object and think that our eyes are not moving, we are actually constantly shifting our eyes, but the magnitude is so small that it is difficult to detect.
However, such microsaccades are not voluntary actions of people, but unconscious actions. But now scientists have discovered that such a slight eye movement involves a process of “transient blindness”, after which the eyes can see more clearly.
The object they observed was the fovea, a small area that does not even account for 0.01% of the retinal area.
Temporary blindness is an everyday occurrence for human beings
The research team devised a test. The person taking the test has to stare at a piece of “animal hide” on the screen to find the “flea” on it. There are many black spots on the leather, when one black spot turns white suddenly (maintains 0.01 seconds), that is the flea jumping. At this point, the subjects had to press a button on the handle to catch the fleas.
This is a task that tests visual acuity, and people frequently use microsaccades, which are shifting eyes unconsciously. At the same time, a high-precision scanning device looks at the fovea in the human eye to determine when microsaccades occur. Then, scientists put the occurrence time of microsaccades together with people’s performance of catching fleas, and they can know whether microsaccades have any effect on people’s vision.
When white dots appear, fleas are jumping.
When the team analyzed the data, the subjects were unable to see the fleas immediately before and after the averted gaze. Even if their eyes were on the flea at that moment, they couldn’t see it. In other words, microsaccades are likely to suppress vision.
The data also showed that after a brief visual loss, vision in the center of people’s visual fields quickly returned to previous levels and then continued to improve. Overall, visual acuity improved (temporarily) after microsaccades occurred compared to before the shift.
In fact, human visual acuity decreases when saccade occurs. Scientists have known this phenomenon before and call it saccade inhibition. However, most of the people at the time were studying conscious gaze shifts, allowing the gaze to sweep from one side to the other, and the range of motion was greater.
Using high-resolution instruments, new research has demonstrated that rapid and involuntary microsaccades can also temporarily disable a person’s vision and then temporarily enhance vision.
As for why vision is inhibited, scientists have not fully figured out. But they speculate that this may be a way to keep the picture steady even when our eyes wander. If our vision is not suppressed and we can see all the time during the shifting of our eyes, the picture in our eyes may also be turbulent.
not always feel
The reality is that when we stare at an object, the picture in our eyes does not change, so how can we feel the existence of microsaccades?
As long as you use a little optical illusion experiment, as mentioned at the beginning, you can make the micro eye twitching appear. This was discovered by scientists in a 2008 study.
The frequency of microsaccades varies naturally, sometimes fast and sometimes slow. Scientists had subjects observe pictures of optical illusions, the kind that can see movement from stillness. The subjects pressed the button when the circle in the figure turned slowly or stopped, and released the button when it turned rapidly.
Scientists had subjects observe pictures of optical illusions, the kind that can see movement from stillness.
During the test, the camera recorded the subjects’ eye movements at a frame rate of 500 frames per second. It was found that when the frequency of microsaccades occurred more frequently, the optical illusion became more obvious; when the frequency of microsaccades decreased, or even stopped, the optical illusion disappeared.
Taking into account the reaction time required to press the button, the results showed that the illusion became more pronounced when the microsaccades occurred at a faster rate; the optical illusion also became more pronounced when the speed slowed to a stop. Disappeared. So scientists believe that human beings can see motion from static images, which is caused by microsaccades.
Previously, the academic community has been debating whether static is regarded as a dynamic optical illusion, whether this phenomenon originates from the eyes or the brain. And this research proves that it is the eyes. Still, more than a decade later, scientists still know very little about microsaccades. Even the scientists who published the new results are looking forward to future research that will unlock more of the mysteries behind the microsaccades.