Problems about space are rarely static. Object search is probably the best example from everyday life that makes this point. When we put something away in a container, usually either we move or the container is moved before we look for it again. Thus relocating the object would be impossible unless we had some way of taking these sorts of movements into account. This raises an interesting question as far as infants are concerned, for during the first 9 months or so of life their movements are constrained. They certainly perceive and show interest in moving objects from very early on, and they are themselves moved around their environment. But it is not until the age of 9 months, when they begin to crawl, that they get active experience of moving around in space under their own control.