[steven]

Oh man... I don't know how to approach your question directly, but I can make a few comments on the subject.

Before I begin, I'd like to point out that you might benefit from books that are written on this stuff! This is a very deep subject and can be confusing for non-Japanese. I think it's a shame myself, but I've been studying Japanese for so long (even though I've only lived here a couple of years) that a lot of the Japanese approach has rubbed off on me making me forget the way Americans do things some times. That's not to say I'm some kind of pro at Japanese or anything like that.

I think Japan is just as assertive as America, they just have a different way of going about it. The words may be different (or non existant sometimes in the Japanese case), but the main message of what people want to say is still communicated. From an English speaking perspective, Japanese could be considered "ambiguous". People take care to use indirect language as to be polite. The more direct you are with your language in Japanese the ruder it seems (or at least more relaxed, but relaxed may not be appropriate when speaking to professors or people "above" you).

With the whole there are people "above" me thing in mind, you have to consider the fact that they are doing you a favor for even looking at whatever you sent them, so you have to show gratitude for that and ask in a way that is indirect (as in sentences containing verbs that aren't connected to the person above you). It sounds very stupid in English, but the idea is something like this: They aren't looking at something for you... but you are (humbly) receiving the act of them looking at something for you, even though they are undoubtedly extremely busy.

What kind of distance are you dealing with? Is there anyway you can meet them in person? I think this concept works in both America and Japan. If you could find out if they have time to talk to you, then that might be the best way. If you are entering some kind of office, then you have to treat it like it is their turf. So no matter what, you are burdening them with your prsence and have to verbally express that as well as apologize for taking up their time. You have to excuse yourself when you enter and leave the office as well.

I'm not sure nagging is good in English or in Japanese, but I think it's probably worse in Japanese. I'd say if an e-mail isn't responded to, then meeting in person is your best option.

I think being aggressive, forceful, or even really straight with your language is a bad idea. Another thing to consider is this: if it is something that you had to request to have done, how much time did you give them? If plenty of time isn't given for things (that you want your superiors to do) then it can sometimes be written off.

This last thing is not something I really want to say, but sometimes no reply/silence has a lot of meaning. It's their attempt to not be too straight with you on something. It can be a sign of rejection (in more scenarios than one!). It's weird because in a sense there are different kinds of silences... it seems stupid and it's hard to explain in words (maybe someone with more experience can do a better job about it). Considering this is an e-mail based conversation, though, it's impossible to guess what "kind" of silence this is, leaving the situation being all the more ambiguous.

Your last question is another interesting one: how do you know if you're being too assertive?/what signs should I look for?
I personally believe that in most situations you will have no way of knowing. That's the Japanese trying not to offend YOU. They try not to embarass you or themselves by pointing trivial stuff like that out, in my experience. Sometimes, if the situation is more casual, you might get a chuckle or a funny reaction. Japanese people aren't perfect at their own language and make these kinds of mistakes, too, from time to time, so you see this happen even with two Japanese people talking. Not unlike English, you have a different language for the office/formal situations and for friends/casual situations. So sometimes you slip up in one situation or another. Silence is actually one of the signs of something that's gone wrong in a conversation. Maybe the conversation will be cut short or the topic changed-- I'm not sure it's too different from English.

The point is, is Japanese people are usually very careful of other peoples' feelings if you look at it from an English speaking perspective (but it is what it is... the same meaning comes across even though they're just more indirect about it). Pointing mistakes out risks embarassing someone so it's not often done.

I've even heard (anecdotal) a story of a foreigner accidentally walking into a meeting with bathroom slippers... and all the Japanese men followed suit as to not lose face.

On the other side of the coin (personal experience) I've seen a foreigner say hi to an aquaintance for the first time in a while and she went from an awkward "let's hug" stance walking up to the Japanese girl to a "let's raise are hands and clasp them together" thing, to which the foreigne said something along these lines (but in Japanese): "eww, gross... sweat!". The Japanese girl said, "oh don't worry about it" (not being able to imagine that the foreigner wasn't talking about her own hands). The foreigner replied "no, I mean you!". Everyone in ear shot and visible range of that exchange burst in laughter out of complete embarassment for the foreigner. I think the Japanese girl was less offended than completely peplexed at what the foreigner had just said. I think that kind of exchange would obviously be seen as rude in English though... so in Japanese it was just so out of this world that nobody really knew how to handle it. It wasn't by any means a formal situation, but no one said anything directly to the foreigner, though we were all thinking the same thing, I'm sure!

So I guess the moral of the story is that there is more to language than just words. You have to know how to act in particular situations. Taking concepts from your own language (such as American directness or Japanese indirectness) into another language can have negative consequences. I've seen this work both ways. Japanese indirectness carried over into English, while it may seem polite, can often have bad outcomes for the Japanese.

I'm sorry I don't have too much specific help, but I hope this helped in some way or other. Most of this is from personal experience so none of it is wrong. That doesn't make it 100% right, either. If anyone has other experiences with this kind of thing I'd like to hear about it.