ABSTRACT
Performance data obtained for humans show a gradual increase in velocity with a peak near the midpoint of the movement distance. This is qualitatively more similar to the response of the second-order system, although the velocity profile for humans is more nearly symmetrical than the data for the second-order system. The mismatch between the velocity profile predicted by the first-order lag and the observed velocity profile might have been predicted on simple physical principles, in particular, Newton’s Second Law of Motion. Newton’s second law can be represented in the form of a block diagram. The time constant determines the time for the second-order system to settle into a particular width of the target. An important difference between a physical system like a spring and a biological control system involves the comparator problem. One possibility is that the burden of control falls completely on the central nervous system.
