Effects of force levels on error compensation in periodic bimanual isometric force control.

The authors examined whether force level interacts with the presence or absence of vision in bimanual force control. Participants produced periodic isometric forces such that the sum of the 2 finger forces was the target force under 4 force levels cycling between lower levels (5-40%) of maximum voluntary contraction with an interval of 1000 ms. Without vision, the correlation between the 2 finger forces was strongly positive over all force levels. However, with vision the correlation changed from negative to positive with force level. The result with vision indicated that the strategy of the bimanual force control changed from force error compensation to force coupling and the available redundancy thus decreased with an increase in force.