ASYMMETRIC CONTROL OF BILATERAL ISOMETRIC FINGER FORCES

We examined the ability to match the voluntary isometric finger flexio n forces of the dominant and nondominant hand in humans, as well as th e influence of unilateral visual feedback during this task. Right- and left-handed subjects were trained to produce a ''low'' force level (5 0+/-25 g) and a ''high'' force level (200+/-50 g) with the right and l eft index finger, separately. Following the training session, subjects were instructed to match the isometric forces of both fingers simulta neously within the required range (either low or high) so that they we re perceived to be identical. The results showed an asymmetry, whereby greater forces were exerted with the index finger of the dominant han d. The asymmetry was independent of the subjects' maximum finger flexi on strength. When unilateral visual feedback represented the force out put of the dominant hand, the asymmetry was no longer present. In cont rast, when it represented the force output of the nondominant hand, th e asymmetry was not compensated. We hypothesize that these findings ar e the result of anatomical or physiological asymmetries inherent in th e motor system controlling the production of force.