The "Waterfall Effect," scientifically known as the Motion Aftereffect (MAE), is a powerful visual illusion that occurs when the brain's motion-sensitive neurons become "fatigued." If you stare at a stimulus moving in one direction for a long time (like falling water), the neurons that detect "downward" motion adapt and reduce their firing rate. When you suddenly look at a stationary object (like the rocks beside the waterfall), your "upward" motion neurons—which were not fatigued—fire at a relatively higher rate than the tired "downward" ones. This causes your brain to perceive the stationary rocks as moving upward. In 2026, neuroscientists use this effect to study how the visual cortex independently processes motion and position, proving that our perception of movement is a result of a "population vote" between different neural detectors rather than a direct recording of reality.