When you glance at a clock. The second hand seems to freeze. Your brain backdates the new visual information to fill the gap while your eyes were moving.
Your brain’s daily deception
The experience is common: you look at an analog clock and the second hand appears to hang motionless for longer than a second before it starts ticking normally. This isn't a glitch in the clock, but a temporal illusion manufactured by your brain called chronostasis. The term comes from the Greek chrónos (time) and stásis (standing). The illusion can make that first perceived second feel up to 500 milliseconds longer than it actually is.
The effect is a side-effect of how our eyes and brain work together to create a stable view of the world. Our eyes do not move smoothly. Instead, they dart between points of interest in rapid movements called saccades. Saccades are incredibly fast, reaching angular speeds of up to 900 degrees per second. You make about three to five of these movements every second. During a saccade, which can last from 20 to 100 milliseconds, the brain suppresses visual input to prevent you from seeing a dizzying blur. This is called saccadic masking, and it means you are effectively blind for a cumulative total of around 40 minutes every day.
Filling in the blanks
To prevent you from perceiving these constant blackouts, your brain performs a clever trick. When your eyes land on the clock, the brain takes the first clear image it receives—the stationary second hand—and retroactively fills in the perceptual gap created by the saccade. This process of "backdating" or "neural antedating" creates the illusion that you were looking at the clock for the entire duration of the eye movement, causing the second hand to seem frozen in place.
This temporal editing is a part of perception. Research suggests that brain regions like the posterior parietal cortex, superior colliculus, and frontal eye fields are involved in managing the spatial and temporal information needed to create this seamless experience. The illusion is not limited to vision. A similar phenomenon, auditory chronostasis, can occur when you switch a phone from one ear to the other while listening to a ringtone; the interval between rings can seem longer. Researchers have also documented a tactile version, where subjects overestimate how long their hand has been in contact with a newly grasped object.
Recent studies have added another layer to the phenomenon. Research published in 2025 shows that saccades prolong the perception of the first thing you see, and compress the perceived duration of the event that follows. This creates an opposing effect of time expansion and compression, a dynamic tug-of-war in your perception immediately following an eye movement.
💡Fun Facts
Saccades are the fastest movements the human body can produce, reaching speeds that would equate to a 90-degree turn in a tenth of a second.
During saccadic masking, your brain doesn't just show you blackness; it actively suppresses the blurry visual information from your optic nerve.
The chronostasis effect is stronger for predictable stimuli. Looking at a randomly moving object after a saccade produces a much weaker illusion than looking at a clock's predictably ticking hand.
The illusion is not caused by merely shifting attention. Experiments show you must physically move your eyes to trigger the full effect.
The illusion is active 24/7 in your own brain. The given coordinates are near University College London (UCL) and Birkbeck, University of London, both major centers for neuroscience and time perception research. You can test the illusion on any analog clock in the area, such as the one at Senate House Library.
Admission
Free
Accessibility
The area around UCL in Bloomsbury is generally flat with paved sidewalks.