At first, this ambiguous motion stimulus looks like four pairs of dots, each rotating about their common center, but after a while it perceptually reorganizes into two large squares (with a dot at each corner) floating over each other. These local and global forms of “common fate” often alternate; on a 30s trial, local motion is usually seen first, followed by global motion. And across a series of trials, global motion is gradually seen more often. This suggests two adaptation (or learning) processes with different time constants.
We usually see these upright cubes as two large globally moving squares, not as local pairs of cubes.
Conversely, the lovers gazing into each other’s eyes are seen not as a large female square and large male square but as locally moving pairs.
Each pair of spots is phase shifted by 45 degrees from its neighbors. The blue circles tend to constrain the pairs to remain local.
Without the circles, one perceives two intertwined global octagons.