Neural fatigue model (opponent motion detectors):
Motion direction is encoded by opponent pairs of direction-selective cells (V5/MT area). Each direction has an "up" detector and "down" detector.
During adaptation to downward motion, "down" detectors fatigue (activity decreases). At test with static pattern, the balance tips: "up" detectors dominate → perceived upward motion.
Half-life of adaptation: ~10–30s.
MAE duration ∝ log(adaptation time) — Hershenson's law.
Waterfall illusion (1834, R. Addams):
After watching a waterfall for 30s, the adjacent rocks appear to drift upward — without any position change. This shows motion perception is not computed from position changes alone.
Motion energy model (Adelson-Bergen 1985): space-time oriented filters detect motion. Sustained excitation adapts these filters, leaving their opponents unbalanced.