1. The vocal signal is an indicator of the posture and movement (P.M.) of the signaller at the time of vocalization, hence it reveals, by an additional modality, information about the P. M. of the signaller. 2. The vocal signal is a reliable indicator of the motivation of the signaller because cheating would incur the cost of changing the P.M. away from the optimal P.M. for the real motivation. 3. Certain vocal patterns discriminate better than others small differences in the motivation of individuals. 4. The vocal signal which conveys a certain motivation is dependent on a) the strategy used to solve a particular conflict; b) the kind of reliable information which may resolve the conflict; c) the P.M. which conveys best such information; d) the vocal pattern which enables the listener to distinguish between signallers which differ slightly in their motivation.