For our baseline model, we planned to insert a backchannel continuer after every n words, for some plausible value of n. This seemed to be the simplest choice in its own right.
although these can be substantive because they can repeat material from the partner's utterance (Clark and Schaefer, 1991), e.g., Right, okay, I'm below the fiat rocks, we will adopt (Jorafsky et al., 1998)'s terminology of continuer.