A RESPONSIVE DIALOG SYSTEM 

Nigel Ward and Wataru Tsukahara

to appear in Machine Conversations (provisional title)
(edited by) Yorick Wilks. Springer Verlag, to appear.

abstract:

Being responsive is important in dialog.  In particular, back-channel
feedback is essential to human conversations.  Back-channel feedback
is sometimes produced without thinking, in response to simple prosodic
clues.  A simple implementation of this behavior produces
natural-sounding responses in conversation with live human subjects.