Chronostasis (from Greek χρόνος, chrónos, “time” and στάσις, stásis, “standing”) is the illusion in which the first impression following a saccade (quick eye movement) appears to be extended in time. The most well-known version of this illusion is the stopped-clock illusion, where the first movement of the second hand of an analog clock, following the viewer’s directing attention to the clock, appears to take longer than the next movement.
When eyes execute a saccade, perception of time stretches slightly backward. The viewer’s brain registers that they have been looking at the clock for slightly longer than they really have, producing the illusion that the second-hand is frozen for more than a second. Although this happens every time the eyes move from one fixation point to the next, it is rarely noticed. One explanation is that the brain is filling in the gap while the eyes move from looking at one thing to the next.
Experiments have shown that this illusion is probably caused by the way in which the brain attempts to construct a continuous consciousness experience in spite of saccades. Although this effect is present with all eye movements, it is most noticeable when an external time-keeping source is observed.
This effect is not only present in visual observation, but also noticed with auditory stimuli. This can be observed by dialing a telephone with the handset lowered, raising it only after ringing begins. The first ring heard is frequently perceived to occur later than expected, compared to the normal interval between rings.