Participants switched between two randomly ordered, two-choice reaction-tim
e (RT) tasks, where an instructional cue preceded the target stimulus and i
ndicated which task to execute. Task-switching cost dissipated passively wh
ile the participants waited for the instructional cue in order to know whic
h task to execute (during the Response-Cue Interval). Switching cost was sh
arply reduced, but not abolished, when the participants actively prepared f
or the task switch in response to the instructional cue (during the Cue-Tar
get Interval). The preparation for a task switch has shown not to be a by-p
roduct of general preparation by phasic alertness or predicting target onse
t. It is suggested that task-switching cost has at least three components r
eflecting (1) the passive dissipation of the previous task set, (2) the pre
paration of the new task set, and (3) a residual component, (c) 2000 Academ
ic Press.