While listening to a CD based on one of the junior high school textbooks authorized by the [Japanese] Ministry of Education and Science, I came across the following:
Mother: Don’t forget to do your home work.
Daughter: I’ve already done that.
Mother: That’s great. Oh, will you pick up your little brother? He’s at Aunt Peg's house.
Daughter: Sure, I'll pick him up.
As for the underlined sentence, it sounded to me as if there was a high pitch or stress on I’ll. I don't know which term is more appropriate. In fact, if it is the former, as you write in your book, I take it as adding emphasis to the whole IP, whereas, if it is the latter, it seems to me there is no legitimate reason for I’ll to be stressed. Karen Chung says: I’LL pick him *UP. (rising intonation).
The capital letters indicate stressed syllables.
The symbol [*] indicates the nucleus.
Since the textbook has a pretty wide circulation across the nation, I think such an apparently unusual intonation is no petty matter to dismiss out of hand, because it must be a source of puzzlement and anxiety to most teachers, who are usually expected to model-read new material in class as well as play the CD. How about the following?
(1) A: Are you coming?
B: Sure, I'm coming.
(2) A: Do you know her?
B: Sure, I know her.
On balance, I think that the most likely pattern for these utterances is fall plus rise. But there could alternatively be a high head or a high prehead followed by a rise.
\Sure. || \I’ll | pick him /up.
or: \Sure. || 'I’ll pick him /up.
or: \Sure. || ¯I’ll pick him /up.
and likewise with the other two examples.
The problem is that the answers contain no new lexical or grammatical items. So there is no non-given item to place the nucleus on. Even the polarity remains the same as in the interlocutor’s question. These answers just mean “yes, OK”.
If yes or OK or (AmE) sure were all we had, it could have a rise (throwaway, routine, “encouraging further conversation”) or a fall (definite, neutral).
I have to say, though, that I don’t feel very pleased with my explanation so far. Probably this is yet another case where we need some input from the pragmatics people to unravel conversational situations that phoneticians like me feel we’re not very good at describing.
Or perhaps we just say they’re yet more intonational idioms.