Timing of Messages and the Aumann Conjecture: A multiple-Selves Approach

The Aumann (1990) conjecture states that cheap-talk messages do not neces-sarily help to coordinate on efficient Nash equilibria. In an experimental test of Aumann’s conjecture, Charness (2000) found that cheap-talk messages facilitate coordination when they precede the action, but not when they follow the action. Standard game-theoretical modeling abstracts from this timing effect, and therefore cannot account for it. To allow for a formal analysis of the timing effect, I study the sequential equilibria of the signaling game in which the sender is modeled as comprising two selves: an acting self and a signaling self. I interpret Aumann’s argument in this context to imply that all of the equilibria in this game are ‘bab-bling ’ equilibria, in which the message conveys no information and does not affect the behavior of the receiver. Using this framework, I show that a fully communica-tive equilibrium exists — only if the message precedes the action but not when the message follows the action. In the latter case, no information is transmitted in any equilibrium. This result provides a game-theoretical explanation for the puzzling experimental results obtained by Charness (2000). I discuss other explanations for this timing-of-message effect and their relationship to the current analysis