The futility of explicit knowledge of a sequence of tasks

In an experiment that combined the task-shifting methodology with a serial reaction-time task, three groups of participants had to shift among a set of four tasks that were arranged in regular sequences of length eight. Two groups of participants were given explicit knowledge about the sequence of tasks. To ensure that the knowledge of the sequence was referred to in each trial, one group was asked to verbalise the forthcoming task (verbalisation group), whereas the other group had to detect trials that deviated from the learned sequence (detection group). Participants of a control group were given no information about the sequence of tasks. In addition, for all experimental groups in half of the blocks of trials external precues were presented which indicated the forthcoming task. The control group exhibited substantial task-shifting costs that were greatly reduced by the presentation of precues. Participants of the explicit-knowledge groups showed no indication that explicit knowledge resulted in advance preparation of the forthcoming task. In addition, the effect of the precues depended on the secondary task that had to be performed on the basis of explicit knowledge. Whereas for the detection group precues reduced shift costs to the same degree as for the control group, the verbalisation group showed no precueing benefits at all.