Hesitations in manual tracking: a single-channel limit in response programming.

When subjects used a manual joystick to track the motion of a visual target (in either zero-order or first-order control), hesitations in tracking often occurred when the other hand responded to an auditory stimulus. These hesitations are related to postponement in the psychological refractory period effect. Because few hesitations occurred when the auditory stimulus was the no-go case of a go-no-go paradigm, hesitations must arise primarily during "late" processing associated with the concurrent response rather than during "early" perceptual or decision-making processes. Other findings suggest that the single-channel processing limit is in programming (as opposed to selecting or generating) concurrent responses. Blanking of the target also produced hesitations through a different mechanism.