Flash Lag

These demonstrations are of the flash-lag effects investigated in Moore & Enns (2004).

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flash lag - continued motion

Here is the basic flash-lag effect in what we call the "continued-motion" condition to distinguish it from the "stopped-motion" condition shown next. This version of the flash-lag effect is notable in that there is only a single frame of motion following the flash, and yet the illusion is quite strong. In particular, even though the flash (red in this example, but it needn't be) is presented in exact alingment with the moving disc, the disc appears to be ahead of the flash when it occurs (or, as the name of the effect was originally focused, the flash appears to lag behind the moving disc.)

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flash lag - stopped motion


Here is the stopped motion version which differs from the continued-motion version only insofar as that single final frame of motion has been eliminated; the motion of the disc stops at the time of the flash. Here it is easy to see that the flash and the disc are perfectly aligned.

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flash lag - size change


Here is the version in which the disc abruptly changes size and gives rise to change-related persistence (see change-related persistence demo for more information on this effect.) This is different from the continued-motion version of flash lag only insofar as the moving disc abruptly changes size. Because of change-related persistence, the fact that the flash is aligned with the disc (in this case the small version) can easily be seen.

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