The hard work of doing nothing: Accounting for inhibitory costs during multiple action control

Performing many actions at the same time is usually associated with performance costs. However, recent eye-tracking evidence indicates that under specific conditions, inhibiting a secondary response can be more costly than executing it, resulting in dual-action benefits. Here, we show that performance gains due to the absence of inhibitory control demands in dual-action trials are not limited to saccades as a response modality. In our study, participants had to react to a visually presented directional word by either reading the stimulus aloud (vocal modality), pressing the corresponding arrow key on a keyboard (manual modality), or both. Crucially, manual error rates were significantly lower when participants had to respond with both a button press and naming than when they had to respond with naming only. More specifically, in vocal-only conditions we observed a significant percentage of false-positive manual responses, suggesting difficulties with inhibiting an unwarranted manual action. Thus, our results indicate that difficulties associated with single- (vs. dual-) action control are a stable, domain-general phenomenon that likely arises whenever execution-related demands are accompanied by substantial additional inhibitory control demands.