Compensatory properties of visual information in the control of isometric force.

This experiment investigated the effects of spatial (gain) and temporal (frequency) properties of visual feedback on the control of isometric force output. Participants performed an index finger isometric force production task with five different levels of visual gain and four feedback frequencies. There was a significant effect of gain on mean and standard deviation (SD) of the force output, whereas feedback frequency significantly affected the force SD and root-mean square error. Significant effects of gain and frequency and a gain X frequency interaction on the approximate entropy (ApEn) of the force revealed the effect of visual feedback uncertainty on the force fluctuation dynamics. The combined effects of the spatial and temporal properties of visual feedback on ApEn were approximated by a sum of quadratic functions, indicating their compensatory effect on the informational content of the dynamics of isometric force.