Apparent Displacement of Moving and Stationary Strobe Flashes

Abstract

If an observer fixates a stationary object near the flight path of an airplane carrying a strobe flash, then the flash appears to trail behind the image of the airplane. In parallactic motion a strobe flash on a stationary tower appears to lag behind the apparently moving image of the tower. Considering the relationship between the latency and intensity of visual stimuli, those displacements seem paradoxical. If the latency of a bright flash is shorter than the latency of other image elements, then a flash should appear to precede the other elements of a moving image. However, the visual persistence of a stimulus is inversely related to its duration. Thus, the apparent displacement of a flash is due to its longer persistence in relation to the continuously lighted portions of a moving image. Under some conditions, the apparent displacement of a strobe flash may have important practical consequences.