Dynamics of reaching for stationary and moving objects: Data and model

The nature of the interrelations among movement amplitude, movement time, and peak velocity was addressed in 2 experiments in which participants reached for stationary and moving objects. Movement time was found to scale with the distance between the hand and the object at the onset of movement but to be relatively independent of object speed. Peak velocity, however, was found to scale with both these variables. The origin of these interrelations cannot be understood within the framework of existing trajectory formation models that are based on optimization procedures. A dynamical perspective in which the movements are considered in an object-attached coordinate frame allows for their emergence. This is demonstrated by simulation of a nonlinear model, built up from Rayleigh and Duffing components, with the nonlinear dissipative parameter being associated with amplitude scaling.