Concurrent manual-decision tasks

The literature on combined manual-decision tasks is reviewed and the data reanalysed. It is shown that in all cases where the tasks are done sequentially, the total time for the task is the sum of the times for the decision and movement components. New experiments are reported in which subjects concurrently carried out the two components of the task; the decisions were made while the movement was being performed. Under these circumstances, there was considerable interference between the decision (Hick's law) and movement components (Fitts' law) so that the time for the task was increased. The amount of interference was dependent on the difficulty of each component of the task. With low signal uncertainty and higher response uncertainty, there was little increase in time; this increased as signal uncertainty increased and response uncertainty decreased. Regressions of the data allowed quantification of the level of interference as a function of signal and movement uncertainty.