Object permanence requires a model to represent that an object continues to exist even when it is temporarily occluded or outside the visible frame. Its shape, count, location, and relevant properties should remain consistent when it returns.
Failures include disappearing objects, duplicated items, changed colors, or impossible reappearance. Tests should use occlusion, handoffs, containers, camera movement, and interactions that require the model to maintain hidden state over time.
ELI5
Object permanence means a video remembers that an object still exists when it becomes hidden. The object should return with the same identity and properties instead of disappearing or changing without a reason.
For example, if a ball rolls behind a box, it should come out on the other side as the same ball. A generated clip fails object permanence if the ball vanishes, doubles, or changes color while hidden.
