Selection and consolidation of objects and actions

Response selection bottleneck models attribute performance costs under dual-task conditions to the human inability to select more than one response at a time. Consistent with this claim Pashler (1991) found that carrying out a speeded manual choice reaction time (RT) task does not impair the unspeeded report of a cued visual target from a masked display. In contrast, Jolicoeur and Dell'Acqua (1999, Experiment 2) observed pronounced interference between a speeded manual choice RT task and the unspeeded report of a small number of visually presented letters, a finding they attributed to resource sharing between response selection and stimulus consolidation. We demonstrate that comparable costs are obtained with the same task combination used by Pashler (1991) if only task order is reversed-a manipulation that is likely to increase the necessity of consolidating the target stimulus into working memory. We also found that these costs are not diminished if the location of the target to be reported is cued in advance (reducing demands on spatial focusing) and that they do not vary with the number of target features to be reported. These findings support a consolidation account of costs in dual-task performance.