Successful joint action requires negotiation, especially in the event of goal incongruence. This article addresses goal incongruence in joint musical performance by manipulating the congruence of score instructions (congruent/incongruent) regarding tempo (speed) and dynamics (sound intensity) given to piano duos. The aim is to investigate how co-performers negotiate incongruent instructions for tempo and dynamics by balancing the prioritisation of individual goals versus the joint outcome and how this negotiation is modulated by musical expertise and personality (locus of control). In total, 14 pairs of pianists, who were not informed of the congruence manipulation, were placed back-to-back and were directed to achieve a successful performance over four repeated performances without verbal communication. Interpersonal coordination generally improved from the first to final performance in the congruent and incongruent conditions for both the tempo and dynamics tasks. Furthermore, in incongruent conditions, results suggest that performers prioritise the joint performance in the tempo task, but prioritise their own performance in the dynamics task. Although individual performance appears to be modulated by musical expertise, the balance of individual/joint performance across the duo is not influenced by musical part (melody vs accompaniment), expressive instruction, musical expertise or locus of control.
