I have two cats; one is 14 years and I've had him since birth, the other is 9-10 weeks and I found her outside two weeks ago.
I recall with the adult cat at around 6 weeks old he had noticed the shelf that we stored the food on, and very noticeably plotted a path to get up there by jumping on other objects (you could see him observing the path) even though he physically couldn't follow the path. He also never forgot it was there and continued to try very frequently a few days in a row. He was sometimes clumsy with balance but nothing that struck me as unusual. Today, he has good navigation and spatial awareness, he has no problem remembering where toys are while playing, plotting complex paths, you can fake him out by pretending to throw things.
My kitten, on the other hand, at 9-10 weeks doesn't have nearly the same object and navigation skills that my other cat had at 6. She's very sweet and extremely active, and unusually fearless. She's a good learner as far as training goes, and she has no problem remembering where things are in the house (like food, litter boxes, water, play areas). But e.g. she forgets where toys are immediately when they are behind her; when she jumps over a toy she will look for it and sometimes mew and sniff around until I put it in front of her, similar to when I take the toy away completely. This morning she was hunting a moth; but lost track of it every time she trapped it under her paw, and had great trouble following it after she grounded it. She also simply cannot follow objects moving above a certain speed; for example if I move my hand quickly in front of her, she looks to where it was then is startled when she discovers where it is, even though I stayed in her field of view. I have a fort-type thing that I built for her out of milk crates, which she loves, but if I hold a toy inside one rather than attempt to find a path around she will pace and become frustrated trying to get at it from the outside despite having spent significant time playing in and around the structure. Also, when she is sitting on my lap / chest, it is very difficult for her to stay there; she will somehow manage to slide or fall off of me within about a minute even though she is clearly trying to relax or sleep or clean. 100% of the time that she cleans herself, she falls over, even on flat ground. When she sleeps, her head and limbs drift in such mysterious ways that I'm convinced there's a special sideways pointing gravity that only affects her, and she often falls off of things while sleeping or sitting. She seems to have generally good balance when walking on narrow things. She can't jump very high although I don't remember how high my other cat could jump at that age and don't have other kittens to compare her to.
I used to block her from falling off of me with my arm but I've stopped in the hopes that the feedback will encourage her to work on balance and awareness of her surroundings. I've been shaking toys around in places that are complicated to get to and giving her a treat when she gets there (but I almost always have to lead her through the path), and setting up boxes, crates, and platforms in all sorts of complex and interesting ways for her to explore.
My question is: Is she at a normal level of development -- should I be concerned about her "drifting", not being able to find ways around things, and losing things the instant she can't see them? If so, what can I do to help her along and build up these skills?
I only have my other cat to compare her to, and I'm not sure if he was ahead, she is behind, or they're both in pretty normal range. I am not sure if my expectations are too high; I may be wrong in comparing my two cats. The out-of-sight out-of-mind thing I can understand (although she seems a bit old for that?) because people are the same, but the strange falling off of things (almost "melting" off, which I can't really explain well) and navigation problems seem off.
I've been trying to do some research, and I know cat behavior is well studied, but for some reason I can't seem to find any good information about motor skill and neurological development in cats; all the info I find is about behavior and physical appearance.