In human language there seems to be a direct link between perception
and action for back-channel feedback, that is, the grunts and other
acknowledgements produced by a listener in a conversation.  In
particular, in Japanese, detection of a low pitch region in the
speaker's utterance often cues the listener to produce back-channel
feedback. This fact has been exploited in a system that can interact
with unsuspecting speakers and appear to converse, in real time. This
finding suggests that Brooks'
(\citeyear{brooks-reason},\citeyear{brooks}) methodology for the study
and synthesis of physical behavior is relevant also for social
behavior.  If so, then real-time responsiveness, rather than better
phoneme recognition, is a top priority for the construction of spoken
language systems and for the scientific study of language.