Last week, there was an interview between a foreign writer and a Japanese fellow who spoke passable English on "The Mystery Channel". The interviewer was doing something that used to drive me absolutely crazy when I first came to Japan and started teaching English. As the writer was offering his answer, the Japanese fellow kept grunting in affirmation or saying "yes" at the same time that the writer was speaking.
This is something that happened me a lot when I used to conduct telephone lessons. It would go something like this:
Teacher asks a question:
Teacher: are you...
(Note: Students who do this the most persistently are paying so much attention to affirming that they are listening that they don't actually bother to listen.)
Teacher answers a question:
Student: Where are you from?
Teacher: Pennslvania, in the...
Teacher: United States.
Student: Ah. (clearly not understanding)
In the U.S., if someone constantly talks over you or makes noises of affirmation while you are attempting to speak, it gives the you the impression that he or she really isn't really listening to your statement or is being impatient. When I was on the phone with students, this was such a pervasive problem that we eventually had to address this in the textbooks that we wrote so the students would understand the cross-cultural implications if they did this while speaking English.
When I later learned that Japanese is what I would ethnocentrically call an "insecure language" where constant affirmation is not only acceptable but a sign that one understands what is being said and is paying attention, it added some perspective to my experiences. If you listen to two Japanese people having a conversation, you'll hear the same constant stream of "yes" ("hai") and grunting along with a lot of "so desu ne" (essentially, "I think so, too"). From our perspective, there is a far greater frequency of such affirmation than really seems necessary and it can be very distracting to the western ear.
I should note that this situation seems to occur far more over the phone than in face-to-face conversations (in English). It also seems to happen a lot more with men than with women. I think part of the reason for this is that students are more nervous on the phone, but also that they are more focused on the experience of being with a foreigner when face-to-face than they are when on the phone. In other words, they respond on the phone in English in a manner which isn't so dissimilar from the way they'd react when on the phone in Japanese. Also, when I teach, I tend to ask questions that the student doesn't expect whereas in the phone lessons the students had prep sheets which told them exactly what questions were coming. That means they probably felt less obliged to pay very close attention to each and every word.
While I'm much more patient and understanding of this tendency than I initially was, I have to admit that it still gets on my nerves in the most extreme cases and I tell the students that they should wait until a sentence has completed and the speaker pauses to offer verbal affirmation that they understand.