* Please address correspondence to:

Many researchers consider costs in shifting attention and mental set to reflect a basic ability to use ‘top-down ’ goal information to guide action. Although switch costs have been used as measures of individuals ’ executive function, whether a common ability to efficiently switch perceptual and response sets across different types of shifting tasks has not been well studied. In 249 participants, we studied whether switch costs in a novel two-choice reaction time task were correlated across variations in two variables: the locus of representation (stimuli were either perceptually available or stored in working memory, WM) and which of two judgment tasks was performed. Switch costs were asymmetrical, in that it was easier to switch to the easier judgment, and related to overall and relative processing speed: Switch costs were higher when the task was more difficult. These factors should be accounted for when individual differences in switch costs is of interest. After controlling for these effects, we found evidence for a common ability underlying switch costs that involved both task-set preparation and response selection; however, ‘residual ’ shift costs, which involve only response selection, wer