Concurrent response-selection processes in dual-task performance: Evidence for adaptive executive control of task scheduling

This article reports 4 experiments that used the psychological refractory period procedure to characterize how people perform multiple tasks concurrently. For each experiment, a primary choice-reaction task was paired with a secondary choice-reaction task that had two levels of response-selection difficulty. Experiments 1 and 2 varied secondary-task response-selection difficulty by manipulating the number of stimulus-response (S-R) pairs. The effect of this factor on secondary-task reaction times (RTs) decreased reliably as the stimulus onset asynchrony (SOA) decreased. Experiments 3 and 4 varied secondary-task response-selection difficulty by manipulating S-R compatibility. Again, the effect of this factor on secondary-task RTs decreased reliably as SOA decreased. These results raise doubts about the existence of an immutable structural response-selection bottleneck and suggest that response selection for 2 concurrent tasks may overlap temporally.