Stimulus- and response-based interference contributes to the costs of switching between cognitive tasks.

Little is known about how stimulus- and response-based interference might interact to contribute to the costs of switching between cognitive tasks. We analyzed switch costs in a novel cued task-switching/card-matching paradigm in a large study (N = 95). We reasoned that interference from previously active task sets may be contingent upon the retrieval of these task sets via stimulus processing, or alternatively, via response processing. We examined the efficacy of these two factors through eligibility manipulations. That is, stimulus/response features that were capable of retrieving task sets from the previous trial remained eligible (or not) on the current trial. We report three main findings: first, no switch costs were found when neither stimulus features, nor response features, were adequate for the retrieval of the previously executed task sets. Second, we found substantial switch costs when, on switch trials, stimulus features kept the previously executed task eligible, and we found roughly equivalent switch costs when the previously executed response remained eligible. Third, evidence for stimulus-induced switch costs was exclusively observed when previously executed responses remained ineligible. These data indicate that stimulus-based interference, and of importance, response-based interference, contribute comparably to switch costs. Possible interpretations of non-additive switch costs are discussed.