I’ve been fascinated with object permanence ever since I first heard about it. The concept itself is simple: when something is out of sight, do you remember it? Little babies don’t. They have no concept that a thing continues to exist when they can’t see it. It’s only as they age that they start to realize that. Then they start getting upset when mom is gone, so it’s something of a trade-off. Jean Piaget is the guy who first did scads of experiments on this phenomenon.
Now Cognitive Daily points out an article further refining the concept. A Lancaster research team has investigated how well babies can follow an object when it passes behind another one. They tested a group of four-month-olds to see if they would be surprised when an object passed behind something and re-emerged, and how the length of transit time or the size of the occluding object would affect this. Cognitive Daily has a great summary of the results.
Bremner et al. conclude that four-month-olds’ ability to see motion as continuous depends both on the time and physical length of occlusion. If an occluder is too long, or if the duration is too long, then babies appear to see the balls on either side of the occluder as two independent objects. Or perhaps even this is too strong a claim: perhaps what infants perceive are continuous motions — the babies see the connection between motions if they are close enough, either spatially or temporally, but otherwise, the motions are deemed unrelated.
Cognitive Daily also has nifty graphics to explain the experiments, so I encourage you to go read their write-up.