When a camera whips around from one point to another, most people expect the fast movement to result in a blurry smear. What they don’t realize, however, is that our own eyes engage in a similar kind of rapid movement—called saccades—over 100,000 times a day. Unlike video cameras, our brain avoids the nauseating blur—but when things move in a particular way, they become invisible.
As detailed in a study published May 8 in Nature Communications, researchers have revealed that the speed of an individual’s saccades corresponds to the limit at which a moving object becomes too fast for them to see. That means people with faster eye movements can perceive faster-moving objects, with potential implications for activities requiring fast eye movements such as sports, video games, and even photography. The researchers claim to be the first to provide evidence for the theory that a person’s movement impacts their perception.
“What parts of the physical world we can sense depends fundamentally on how good our sensors are,” Martin Rolfs, lead author of the study and an active vision scientist at Humboldt University of Berlin’s Department of Psychology, said in a statement by the research group Science of Intelligence. “In this paper, however, we show that the limits of seeing are not just defined by these biophysical constraints but also by the actions and movements that impose changes on the sensory system.”
Rolfs and his colleagues demonstrated that when a study participant saw visual stimuli moving with the same speed and pattern as their own saccade shifts, the stimuli became invisible. This suggests the brain filters out motion that mimics our own eye movements, which might be why our saccades don’t cause visual blurs in the way that cameras do. More broadly, this suggests that physical movement—such as eye movement—limits our sensory system’s perception of the world. In other words, our ability to see things in motion is not just dictated by our sensory abilities, such as the strength, or sensitivity, of the photoreceptors in our eyes.
“In simple terms, the properties of a sensory system such as the human visual system are best understood in the context of the kinematics of actions that drive its input (in this case, rapid eye movements),” said Rolfs. Kinematics is the study of object motion without considering the cause of said motion. “Our visual system and motor system are finely tuned to each other, but this has long been ignored,” he continued. “One of the issues is that the people who study motor control are not the same ones who study perception. They attend different conferences, they publish in different journals—but they should be talking!”
It’s only a matter of time until helicopter parents start timing their kids’ saccades to decide whether they belong in little league or theater.
