Different people can have different levels of attention to detail. Psychologists Joshua Eayrs and Nilli Lavie of University College London tested participants on a range of visual tasks. One measured how well people could estimate the number of objects appearing on a screen for just a tenth of a second—a capacity known as subitizing. Other tasks measured participants' ability to notice subtle differences between two real-world scenes, detect a change at the edge of a screen while focusing on its center, and track multiple moving dots among stationary ones. Interestingly, people who excelled at subitizing also performed better on the other tasks.
"This is the first study to establish a perceptual capacity trait," Lavie said. "It's an important ability, which [determines] how much information you can process when there's a lot of it around you."
Theoretically, performance on any task that relies on our perceptual ability—not just the types that were tested—could predict performance on other similar tasks as well.
Lavie's team also showed that this perceptual ability is separate from general cognitive ability and ruled out other possible explanations, such as differences in motivation.
According to the scientists, their work could help develop tests to screen potential employees for safety-critical jobs in demanding visual environments, such as air-traffic controllers, security guards, or military personnel.
When it comes to these pictures and why they trick us, neuroscientist Hari Srinivasan says it's because the brain prioritizes coherence over accuracy.
"It wants one stable story—even if that story requires a bit of creative editing. When the world cooperates, perception feels smooth. When it doesn’t, perception becomes work," Srinivasan writes.
"Illusions work best when the brain relies heavily on automatic assumptions—about timing, about unity, about what usually goes together," Srinivasan explains.
"[They] are entertaining because they surprise us. But they’re also instructive. They show that perception is active, strategic, and shaped by context. It’s a negotiation under uncertainty."
However, don't worry even if these pictures tricked you. "Our brains are wired for function, not accuracy," says psychologist Jessica Koehler, Ph.D.
"The utility of our perceptual system is to reduce uncertainty in our world. The human brain wants to predict outcomes in every situation, so it fills in unknown information based on our prior experiences."
In our evolutionary history, uncertainty meant serious trouble, so this shortcut helped us survive.
