Out with the old, in with the new: more valid measures of switch cost and retrieval time in the task span procedure.

Two experiments provided new measures of switch cost and retrieval time in the task span procedure. In Experiment 1, subjects were given lists of six task names to remember, followed by six targets on which to perform the tasks named in the list. The lists contained alternations and repetitions, and switch costs were estimated by comparing reaction time (RT) on alternation and repetition trials. The experiment also included memory span and single task conditions, so switch costs could be estimated by subtracting the sum of the RT in those conditions from the task span RT, as in the original report (Logan, 2004). The data suggested that the original measure of switch cost was invalid and that the new measure was preferable. In Experiment 2, subjects performed each task on the list twice. Retrieval was required on the first but not on the second trial in each pair. Retrieval time was estimated by comparing the RT on trials that required retrieval with trials that did not require retrieval. This measure was more valid than the RT in the memory span condition of Experiment 1, which was used in the original report.