Luminance Signal-to-Noise Ratio example. As you play the movie, a random pixel patch moves from left to right and back again, sequentially occluding groups of background pixels. As it moves to the right, the amount of noise increases (the LSNR value decreases) and when it moves to the left the amount of noise is reduced.

This movie is only a small example, with a few pixels. In experiments the stimuli may of course contain many more pixels, and the entire field of dots may move in a certain direction. As you can see, this method is very well suited for determining thresholds in, for instance, direction discrimination experiments in visual motion perception research. It has certain advantages over Random-Dot displays in that it is spatially broadband and dot density is, per definition, equal across the display.

For a detailed description of the method, see the following papers:

1. Van de Grind WA, Koenderink JJ & van Doorn AJ (1987). Influence of contrast on foveal and peripheral detection of coherent motion in moving random-dot patterns. Journal of the Optical Society of America A, 4, 1643-1652.
2. Fredericksen RE, Verstraten FAJ & Van de Grind WA (1993). Spatio-temporal characteristics of human motion perception. Vision Research, 33, 1193-1205.
3. Van der Smagt, MJ & Van de Grind WA (1999). Integration and segregation of local motion signals: the role of contrast polarity. Vision Research, 39, 811-822. doi: 10.1016/S0042-6989(98)00133-3