Discontinuities in Tracking Strategies

Twenty years ago Craik (1947) suggested that the output of the human operator performing a perceptual-motor control task consists of a sequence of discrete, “ballistic” movements. In a tracking task this discreteness would be apparent even thought the input to be tracked were smooth and continuous. After Craik there was a shift towards skills where the possible responses are necessarily discrete (as in key-pressing), and the nature and causes of the discrete output in a continuous tracking have been little investigated. The aim of the experiments reported here is to demonstrate that there are at least two distinct causes of discontinuity in the operator output, the first dependent on the availability of feedback information and the second upon the nature of the effector dynamics. In simple tracking tasks these are confounded, but they may be separated by appropriate choice of controlled system and control dynamics.