You’re walking through a crowded train station; your eyes scanning the people in front of you, tracking their movements to avoid bumping into them. But you don’t just rely on what you see right now—your brain also factors in those people’s movements just a moment ago. This blending of past and present is known as “serial dependence,” and it helps us perceive and act smoothly through a constantly changing world.
A new study by Professor of Neural Science and Psychology Li Li’s team investigates how this subtle yet powerful mechanism works. Published in Investigative Ophthalmology & Visual Science, the paper presents the first developmental evidence that serial dependence in smooth pursuit eye movements emerges during early sensory processing, and that it affects children more than adults.
Serial dependence refers to the brain’s tendency to bias current perception toward recently seen information. Rather than treating each moment as entirely new, the brain blends what we’ve just seen with what we’re seeing now, creating a sense of stability and continuity. While this phenomenon has been observed across different sensory systems and cognitive functions, much of the previous research focused on adults and often blurred the boundaries between perception, memory, and decision-making.
To present a clearer picture of serial dependence, Li’s team designed an experiment that isolated the perceptual stage. The study tested 81 children between the ages of 8 and 9, alongside 77 adults, using a visually engaging task in which participants tracked a cartoon duck moving in random directions across a screen. Unlike conventional button-pressing tasks, this setup measured smooth pursuit eye movements, allowing researchers to observe participants’ responses directly linked to motion perception, without interference from memory or decision-making functions.
The experimental design allowed for full 360-degree sampling of motion directions, rather than just the typical horizontal or vertical axes. It also distinguished between the early phase of tracking—known as pursuit initiation, which is largely driven by perceptual information—and the later, sustained phase of tracking that involves feedback and error correction. This approach gave the team a unique opportunity to test whether serial dependence shows its characteristic “tuning” features, meaning it’s stronger when the direction of current and previous motion is similar, and fades when more time passes between them—and whether it varies across directions of movement.
Their findings were striking. Both children and adults showed signs of serial dependence during pursuit initiation, but the effect disappeared during sustained pursuit. The bias showed clear signs of feature and temporal tuning, confirming that it matched the profile of true serial dependence rather than random variation or delayed responses. The effect was notably stronger in children, likely because younger visual systems are still developing, with greater variability and less precision, causing the brain to rely more heavily on recent experiences as a stabilizing tool. Moreover, the researchers noticed the bias was strongest for diagonal, or oblique directions, areas of the visual field where people tend to be less precise in tracking a target movement.
“These results provide strong evidence that serial dependence arises during early sensory processing, not just in memory or decision-making,” said Li. “We also found that its strength and timing change with age, and are shaped by the uncertainty in visual input.”
Looking ahead, Li’s team hopes to explore the mechanism amongst a broader age range to better understand its full developmental trajectory. They also plan to use brain imaging to examine the brain structure involved.
Beyond its contribution to neuroscience, the study has potential applications in areas such as education and developmental diagnostics. In classrooms or clinical settings, understanding how children rely on recent visual input could improve strategies for teaching or identifying atypical perceptual development.
“It’s fascinating how something as subtle as a slight bias in eye movement can reveal so much about how the brain functions, adapts, and grows,” said Li. “The developmental perspective is particularly compelling because it shows how flexible and adaptive the brain is during development.”
Hong Bao, Li’s PhD student from the NYU Shanghai - ECNU Joint Graduate Training Program (N.E.T. Program) shared co-first authorship with NYU Shanghai Assistant Research Scientist of Neural Science Chen Jing, and N.E.T. PhD Huang Wenjun student contributed to the work as well.