Spontaneous pattern changes for bistable apparent motion stimuli: Perceptual satiation or memory attraction?

Subjects judge motion direction for an apparent motion stimulus with competing perceptual organizations: Vertical vs. horizontal motion. The two patterns are coupled. When one is perceptually instantiated the other remains active in memory, resulting in sudden changes in perceived motion direction under constant stimulus conditions. The probability of change from an initially horizontal to a vertical pattern remains constant over time, showing that perceptual satiation is insufficient to explain the occurrence of spontaneous perceptual changes. It is proposed that spontaneous changes also occur because the pattern active in memory attracts the percept away from the currently instantiated pattern. The attraction hypothesis specifies that the activation of the memory pattern (and hence its attractive strength) increases as a result of previous experience. It is supported by evidence that the likelihood of changing, say from horizontal to vertical motion, is increased if the motion pattern was previously vertical.