In a variety of ways, this tone conveys an impression that something more is to follow. A typical occurrence in a dialogue between two speakers whom we shall call A and B might be the following:

A (wishing to attract B's attention): Excuse me.

B:/ yes

(B's reply is, perhaps, equivalent to 'what do you want?') Another quite common occurrence would be:

A: Do you know John Smith?

One possible reply from B would be /yes, inviting A to continue with what she intends to say about John Smith after establishing that B knows him. To reply instead yes would give a feeling of "finality", of "end of the conversation"; if A did have something to say about John Smith, the response with a fall would make it difficult for A to continue.

We can see similar "invitations to continue" in someone's response to a series of instructions or directions. For example:

A: You start off on the ring road ...

B: /yes

A: turn left at the first roundabout ...

B: /yes

A: and ours is the third house on the left.

Whatever B replies to this last utterance of A, it would be most unlikely to be / yes again, since A has clearly finished her instructions and it would be pointless to "prompt" her to continue.

With 'no', a similar function can be seen. For example:

A: Have you seen Ann?

If B replies o (without using high pitch at the start) he implies that he has no interest in continuing with that topic of conversation. But a reply of /no would be an invitation to A to explain why she is looking for Ann, or why she does not know where she is.

Similarly, someone may ask a question that implies readiness to present some new information. For example:

A: Do you know what the longest balloon flight was?

If B replies / no he is inviting A to tell him, while a response of o would be more likely to mean that he does not know and is not expecting to be told. Such "do you know?" questions are, in fact, a common cause of misunderstanding in English conversation, when a question such as A's above might be a request for information or an offer to provide some.