Attenuating information in spoken communication: For the speaker, or for the addressee?

Speakers tend to attenuate information that is predictable or repeated. To what extent is this done automatically and egocentrically, because it is easiest for speakers themselves, and to what extent is it driven by the informational needs of addressees? In 20 triads of naive subjects, speakers told the same Road Runner cartoon story twice to one addressee and once to another addressee, counterbalanced for order (Addressee1/Addressee1/Addressee2 or Addressee1/Addressee2/Addressee1). Stories retold to the same (old) addressees were attenuated compared to those retold to new addressees; this was true for events mentioned, number of words, and amount of detail. Moreover, lexically identical expressions by the same speaker were more intelligible to another group of listeners when the expressions had been addressed to new addressees than when they had been addressed to old addressees. We conclude that speakers' attenuating of information in spontaneous discourse is driven at least in part by addressees. Such audience design is computationally feasible when it can be guided by a "one-bit" model (my audience has heard this before, or not).