This report describes a set of computational experiments aimed at studying movement variability and speed-accuracy trade-off relationships for dynamic models with nonlinear damping. We analyzed ballistic movements with noisy control signals and noisy plant dynamics. Most of the theories suggested so far to explain observed speed-accuracy relationships are purely kinematic and do not take into consideration the dynamic behavior of the system in question. A dynamic model with fractional-power damping is motivated by biological evidence and allows a completely new view of the speed-accuracy trade-off phenomenon. This model gives rise to a dynamic behavior called a stiction region.
Data obtained from our simulations make a good fit with the linear speed-accuracy relationship model. The speed-accuracy relationship critically depends on the proportion of movements that hit the inner area of the stiction region versus the proportion of movements that undershoot or overshoot the region, thereby effectively stopping on an edge of the region. These results provide a new perspective on possible mechanisms for both the linear and logarithmic speed-accuracy relationships observed in reaching.
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postscript (837K), pdf (5.89M)