Dual-task performance and the hick-hyman law of choice reaction time

The slope, intercept, and linearity of the function relating RT and stimulus information reflect different aspects of information processing. This experiment determined which aspects of information processing are affected by the presence of a secondary task. Subjects (n = 12) performed a one-dimensional tracking task concurrently with a choice RTtask. Subjects also performed each task singly. Half of the subjects performed under dual-task conditions with adjacent displays, half with separated displays. For the adjacent group the tracking task had no reliable effect on either the slope, intercept, or linearity of the relation. Scanning affected only the intercept for the separated group. Error on the tracking task was found to increase linearly with increased processing load on the choice RT task for both groups. The results are interpreted as supporting a modified single-channel theory.