Plaid stimuli are composed of two superimposed sine-wave gratings moving in independent directions. At slow speeds, they are typically perceived as a translating
pattern with a rigid movement. At higher speeds, the component gratings of the plaids may be perceived to move transparently in their
component directions. Depending on their relative properties, plaids may be perceived as moving in the direction of the
vector sum of the component velocity vectors or as moving in yet other directions. Though they have been some of the most studied visual stimuli, it appears that there is still no theory able to fully account for the wide range of perceptions produced by plaids.
In this particular example, a reference vertical grating (with the specified spatial frequency) drifting horizontally to the right at a speed of 1 cycle per second is linearly combined with a second grating with a relative orientation, speed and spatial frequency. With the provided sliders, you can explore the effect of many combinations of the 2 gratings: their relative orientation, speed or spatial frequency. The “Contrast balance” allows you to modulate the contribution of each grating (50% for equal contribution) or visualize the individual gratings (0% for the reference grating, 100% for the other one).
References
Adelson & Movshon (1982)
Phenomenal coherence of moving visual patterns. Nature 300, 523–525
Yo & Wilson (1992)
Perceived direction of moving two-dimensional patterns depends on duration, contrast and eccentricity. Vision Research 32(1):135–147
Champion et al. (2007)
Perceived direction of plaid motion is not predicted by component speeds. Vision Research 47:375–383.
Bowns (2018)
Motion estimation: A biologically inspired model. Vision Research 150:44–53
Sperling et al. (2020)
Theory of the Perceived Motion Direction of Equal-Spatial-Frequency Plaid Stimuli. Psychological Review 127(3):305–326
