Chronostasis (from Greek χρόνος, chrónos, "time" and στάσις, stásis, "standing") is a type of temporal illusion in which the first impression following the introduction of a new event or task demand to the brain appears to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade (i.e., quick eye movement). This elicits an overestimation in the temporal duration for which that target stimulus (i.e., postsaccadic stimulus) was perceived. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception.
The best-known version of this illusion is known as the stopped-clock illusion, wherein a subject's first impression of the second-hand movement of an analog clock, subsequent to one's directed attention (i.e. saccade) to the clock, is the perception of a slower-than-normal second-hand movement rate: when first observing the second hand it appears to remain stationary for longer than the subsequent periods between movements.
This illusion can also occur in the auditory and tactile domain. For instance, a study suggests that when someone listens to a ringing tone through a telephone, while repetitively switching the receiver from one ear to the other, it causes the caller to overestimate the temporal duration between rings.
Overall, chronostasis occurs as a result of a disconnection in the communication between visual sensation and perception. Sensation, information collected from our eyes, is usually directly interpreted to create our perception. This perception is the collection of information that we consciously interpret from visual information. However, quick eye movements known as saccades disrupt this flow of information. Because research into the neurology associated with visual processing is ongoing, there is renewed debate regarding the exact timing of changes in perception that lead to chronostasis. However, below is a description of the general series of events that lead to chronostasis, using the example of a student looking up from his desk toward a clock in the classroom.
In studying chronostasis and its underlying causes, there is potential bias in the experimental setting. In many experiments, participants are asked to perform some sort of task corresponding to sensory stimuli. This could cause the participants to anticipate stimuli, thus leading to bias. Also, many mechanisms involved in chronostasis are complex and difficult to measure. It is difficult for experimenters to observe the perceptive experiences of participants without "being inside their mind." Furthermore, experimenters normally do not have access to the neural circuitry and neurotransmitters located inside the braincases of their subjects.