Adaptation to selective visual scaling of short time scale processes in isometric force.

This study investigated the effect of selectively increasing the visual scale of the high frequency components on isometric force control. The higher frequency bandwidths (4-8 Hz or 8-12 Hz) of the force output were amplified visually by a scaling factor (0, 2, 4, 6, 8). Four types of force targets (i.e. constant, sine function, pink noise, and brown noise) that required different control strategies were examined. In the constant and to a lesser extent the pink noise task the enhanced visual scaling information progressively reduced the contribution to the force signal of the respective (4-8 Hz or 8-12 Hz) bandwidth and also in the neighboring frequency bandwidths (0-4 Hz or 4-8 Hz). The frequency analysis in the constant target condition showed that selectively increasing the visual scale of the high frequency bandwidths changed the whole frequency spectrum of the potential adaptive force range (0-12 Hz) rather than only the specific bandwidth being scaled. This rescaling of the whole frequency spectrum led, however, to increase performance error in the constant and sine function targets. These findings show that the multiple time scale process of isometric force control are constrained by the predictive properties of the force output and the relative contribution of feedforward and feedback processes to task outcome.