The cause of control movements in a tracking task.

The classical cause-effect or input-output model of behavior breaks down when there is feedback from response to stimulus. Using a compensatory tracking task it is shown that response variations on different occasions can be nearly identical while stimulus variations on these occasions are completely unrelated. This result seems to rule out stimulus variations as the cause of responses wh ich control (stabilize) the stimulus. When feedback exists, the cause of control must be viewed as an internal reference rather than an external stimulus.