Dual-Action Costs and Benefits in a Uni-Modal Single-Onset Paradigm

While performing two actions at the same time has mostly been associated with reduced performance, several recent studies have observed the opposite effect, that is, dual-action benefits. Previous evidence suggests that dual-action benefits result from single-action inhibitory costs - more specifically, it appears that under certain circumstances, single-action representations are derived from dual-action representations by removing (i.e., inhibiting) one of the component actions. In the present paper, we investigated if this is tied to the presence of multi-modal response demands (i.e., responses making use of two different effector systems). We implemented a very simple experimental paradigm where participants responded to a single stimulus with zero, one, or two uni-modal responses. As predicted, we did not observe dual-action benefits, but rather significant dual-action costs. Furthermore, a trial-by-trial sequence analysis revealed that alternations between both single-action responses were associated with significantly better performance than all other types of action switches. This can be accounted for by assuming that actions are represented as "feature bundles" and that switching a single, binary distinctive feature of an action to its opposite is relatively easy.