Abstract
Central predictive mechanisms cause self-produced forces to be perceived as weaker leading to a compensatory, over production of the force magnitudes required when there is no reference. Earlier work has focused on the serial production of unimanual forces, but the influence of visual feedback in the bimanual production of forces remains less clear. Evidence has been found for synergistic activation of the desired musculature in both rhythmic coordination and multi-effector force production tasks. These synergies served to minimize variability and stabilize performance variables of interest. In this study, we examined the effect of timing constraints on repetitive unimanual and bimanual force production sequences. Participants produced series of pinch grip forces in time to a metronome and to visually specified force magnitudes. Periodically, the metronome, visual feedback of force output or both were removed 10 s in to the trail, with participants performing continued responses for the remaining 20 s. In continuation trials, a negative lag-1 autocorrelation in the inter-response intervals (IRIs) was observed as is commonly seen in motor timing research. Removal of visual feedback however, resulted in an increase in the force magnitudes produced as well as an increase in variability in the bimanual condition. We suggest that attenuation of sensory signals occurs for the two limbs equally and the resulting perceptual errors are compensated independently resulting in an increase in force magnitude from the collective effort of both effectors.Acknowledgments: NSERC, CRC, all members of SNL Lab at McMaster University