Two-handed performance of a rhythmical Fitts task by individuals and dyads

The authors investigated 4 variants of a reciprocal Fitts task in which the pointer was moved to a stationary target, the target was moved to a statio nary pointer, or both the pointer and the target were moved to each other b imanually; the bimanual task was carried out either by a single person or b y a dyad. Fitts's law held in all 4 conditions, with only minor parametric changes. The kinematic organization varied with task difficulty but remaine d invariant in task space (i.e., in the mutual frame of reference of the po inter-target system) whatever the pointing condition. In the bimanual condi tions, the 2 effectors were coordinated in antiphase with compensatory vari ability. The authors suggest that the observed chronometric and kinematic p atterns emerge from an interplay between simple harmonic motion and the sta bilizing influence of the informational flow generated by the closing of th e gap between the pointer and the target interval.