We studied asynchronous two-hand multi-finger force production at submaximal levels. Subjects produced constant levels of force with one hand (FREF), and started ramp force production with the other hand (FRAMP) 3 s later. The zero-maximal force-zero ramp lasted 10 s. Visual feedback was provided only for FREF during the first 3 s and only for FRAMP during the rest of the trial. The initiation of FRAMP induced a transient overshoot by FRAMP and a drop in FREF; both scaled with FREF. Later into the trial, FREF dropped slowly, while FRAMP undershot maximal force by about 15%. Two regimes of bimanual interaction are hypothesized, 'strong interaction' when an effector is added to a one-hand task, and 'weak interaction' during two-hand force production.
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