Does preparation generate the cost of task switching? A recipe for a switch cost after cue-only trials

A switch cost can be observed in cued task-switching on trials that follow a cue-only trial, which presents a task cue indicating a task to be performed but does not present a target stimulus to be responded to. This finding has provided important implications as to the source of the performance cost that emerges when switching tasks. However, cue-only trials differ from completed trials (for which the target occurs and is responded to) in several task parameters, and there are a few untested assumptions about a task-switch cost after cue-only trials, which restricted the conditions under which cue-only trials have been used. The present study first examined whether a switch cost emerged after cue-only trials when cue-only trials were matched with completed trials in as many task parameters as possible, and found that an expected switch cost following cue-only trials was absent in response time. In the subsequent six experiments, we explored critical task parameters to obtain a switch cost after cue-only trials. The present results indicate that the use of a short preparation interval was an important factor and that the switch cost was more short-lived and dissipated more quickly after cue-only trials than after completed trials. These outcomes are consistent with the proposal that there are at least two sources of a task-switch cost, one that originates from processing a task cue and another that originates from performing a cued task. Early processes of task preparation (e.g., cue or task identification) may be sufficient to produce the switch cost after cue-only trials, but response-related processes might generate a more persistent switch cost.