Dual-task automatization: The key role of sensory-motor modality compatibility.

How do people automatize their dual-task performance through bottleneck bypassing (i.e., accomplish parallel processing of the central stages of two tasks)? In the present work we addressed this question, evaluating the impact of sensory-motor modality compatibility-the similarity in modality between the stimulus and the consequences of the response. We hypothesized that incompatible sensory-motor modalities (e.g., visual-vocal) create conflicts within modality-specific working memory subsystems, and therefore predicted that tasks producing such conflicts would be performed less automatically after practice. To probe for automaticity, we used a transfer psychological refractory period (PRP) procedure: Participants were first trained on a visual task (Exp. 1) or an auditory task (Exp. 2) by itself, which was later presented as Task 2, along with an unpracticed Task 1. The Task 1-Task 2 sensory-motor modality pairings were either compatible (visual-manual and auditory-vocal) or incompatible (visual-vocal and auditory-manual). In both experiments we found converging indicators of bottleneck bypassing (small dual-task interference and a high rate of response reversals) for compatible sensory-motor modalities, but indicators of bottlenecking (large dual-task interference and few response reversals) for incompatible sensory-motor modalities. Relatedly, the proportion of individuals able to bypass the bottleneck was high for compatible modalities but very low for incompatible modalities. We propose that dual-task automatization is within reach when the tasks rely on codes that do not compete within a working memory subsystem.