Object Substitution & The Flash-Lag Effect

Object Updating and the Flash-Lag Effect demos to accompany Moore & Enns (2004) and Moore et al (2007)

  • Moore, C. M., & Enns, J. T. (2004). Object substitution and the flash-lag effect. Psychological Science, 15, 866-871. [pdf]
  • Moore, C. M., Mordkoff, J. T., & Enns, J. T. (2007). The path of least persistence: Object status mediates visual updating. Vision Research,47, 1624-1630. [pdf] [figure 1] [figure 2]

The flash lag illusion
Flash-lag is a misperception of spatial relations among a moving object and a briefly flashed stationary one. The moving object appears to be ahead of the flashed object when they are physically presented aligned in the same video frame.

The question
This study begins with the observation that the illusion occurs when the moving object continues following the flash (Demo A), but is eliminated if its motion path ends with the flash (Demo B). The data show that disrupting the continuity of the moving object, via a transient change in size or color, also eliminates the illusion (Demo C). We propose that this occurs because a large feature change leads to the formation of a second object representation. Direct evidence is provided by the measurement of a corollary perceptual feature of the disruption in object continuity: the visibility of two objects, rather than only one, on the motion path.

A warning about internet demonstrations
Accurate display timing cannot be guaranteed. Actual timing will depend on the refresh rate of the viewing screen and on the degree to which the screen is synchronized with the timing of the movie. These demonstrations were designed to give you a general overview of the factors that influence the flash lag illusion. To properly study this illusion, use specialized software in which displays are synchronized precisely to the video screen being used.

Demonstration A: Flashlag: The standard flash lag illusion

Demonstration B: Stoppedmotion: The absence of a flash lag illusion when the moving object halts at the time of the flash

Demonstration C: Sizechange: Flash lag illusion for the large moving disc, along with the apparent simultaneity of a second smaller object that is not lagged