  Conversation demands attention. Speakers must call words to mind, listeners
must make sense of them, and both together must negotiate this flow of
information, all in fractions of a second. We used large language models to
study how this works in a large-scale dataset of English-language conversation,
the CANDOR corpus. We provide a new estimate of the information density of
unstructured conversation, of approximately 13 bits/second, and find
significant effects associated with the cognitive load of both retrieving, and
presenting, that information. We also reveal a role for backchannels -- the
brief yeahs, uh-huhs, and mhmms that listeners provide -- in regulating the
production of novelty: the lead-up to a backchannel is associated with
declining information rate, while speech downstream rebounds to previous rates.
Our results provide new insights into long-standing theories of how we respond
to fluctuating demands on cognitive resources, and how we negotiate those
demands in partnership with others.
