Experimental conditions in which dyads outperform individuals in a task of force produced by two people

When participants control periodic isometric force cycling between two target forces, they more accurately control force in a joint action than in an individual action. In some other studies, however, individuals tend to outperform dyads in joint action. The present study thus examined experimental conditions in which dyads outperformed individuals in a task of force produced by two people. This study consisted of two tasks with two target conditions and three force production conditions. The individual task was performed by one participant, and the joint task was performed by two participants. In absolute and relative target conditions, the participants made continuous, discrete, and periodic isometric pressing movements with the index finger. Although no difference was seen in force error between tasks in the continuous condition, the joint task had a smaller error than the individual task in the two other conditions. The joint task had a smaller variable force than the individual task in the periodic conditions, but no difference was seen in force variability between tasks in the two other conditions. Participants mainly controlled force in both tasks in the continuous condition. In the periodic or discrete condition at a prescribed interval, however, participants had to control both force and timing in the individual task, and muscle force must be mainly controlled to compensate for force errors by synchronizing interpersonal force outputs in the joint task. Thus, dyads can reduce the dimensionality of the control problem because they can synchronize their action which provides timing information.