The Pulfrich effect is a neurophysiological phenomenon and optical illusion, discovered by German physicist Carl Pulfrich (1858-1927) in 1922.
In a classic experiment, you look at the pendulum of a clock that is right for you; If one of the two eyes is covered with a gray filter - a sunglass is enough - then the illusion arises that the pendulum describes an elliptical job.
Generally formulated, the Pulfrich effect implies that a lateral motion of a contrasting object in the field of view is experienced as a motion with a depth component. This formulation outlines some elements to make this effect:
There are a number of eye diseases where this effect occurs without an external gray filter, because there is apparently an internal "gray filter" in one eye.
The explanation of the Pulfrich effect is sought in the fact that the physiological signal processing is delayed when less light is caught in the eye.
The Pulfrich effect is sometimes used to obtain a stereoscopic image. If you shoot a movie camera that moves sideways (which already gives a good depth of view) and keeps a gray filter in front of an eye, then you'll see stereo.
wiki
