Fragile meaning - an experiment

Absence of a shared language is an evident barrier to effective communication. Lack of common knowledge of what is shared is more insidious and a potential source of misunderstandings. We induce lack of common knowledge of a shared language in a sender-receiver game experiment by letting the availability of messages with focal meanings be uncertain. We consider an environment in which agents agree on the optimal action in every state of the world, there are equilibria in which messages with focal meanings are used in accordance with those meanings, and these equilibria maximize both sender and receiver payoffs. We do find, however, that these equilibria are fragile: Observed behavior aligns better with pooling equilibria, in which receivers ignore messages. This effect is more pronounced when the pooling action is optimal for a larger set of receiver beliefs.