Task switching among two or four tasks: effects of a short-term variation of the number of candidate tasks.

In two experiments, using a modified task-cueing paradigm, participants switched among a set of four tasks that was on some trials reduced to two by a pre-cue preceding the task cue. A pre-cue temporarily restricting the options to two candidate tasks facilitated performance on switch trials to a much larger extent than on repeat trials. This observation is interpreted as an indication of a short-term restructuring of a global task representation by implementing antagonistic constraints among the representations of the two remaining candidate tasks.