Overlap, although short in duration, occurs frequently in multiparty conversation. We show that its duration is approximately log-normal, and inversely proportional to the number of simultaneously speaking parties. Using a simple model, we demonstrate that simultaneous talk tends to end simultaneously less frequently than in begins simultaneously, leading to an arrow of time in chronograms constructed from speech activity alone. The asymmetry is significant and discriminative. It appears to be due to dialog acts which do not carry propositional content, and those which are not brought to completion.

Index Terms: multi-party conversation, overlap, turn-taking.