Interrelationships between amplitude and period of a continuous hand movement

In two experiments, subjects were trained to operate a joystick-type lever in a conitnuous to-and-fro movement. In the first experiment, 21 subjects had to control the “water” level of a cister displayed on a video screen and were free to adopt any period-amplitude strategy. In the second experiment, 18 subjects had to adjust either the amplitude or the duration of successive cycles of lever pumping to target values indicated by moving segment. Results show that (1) during steady states the amplitude and the duration of cycles remained positively correlated; (2) these variables were negatively correlated when the flow rate varied; and (3) subjects adjust the flow rate to changing target values by varying the amplitude of the cycles and only secondarily by varying duration. A superiority in perception of amplitude variations over time components could account for this. All the above features have previously been observed for breathing, suggesting that these are general proporties of continuous periodic movements whatever their nervous control may be.