Task switching based on externally presented versus internally generated information.

A number of observations from the task switching literature suggest that task preparation based on internally generated knowledge is less efficient than task preparation based on externally presented information. In the present study, we investigated task switching based on internally generated versus externally presented information and additionally varied the reliability of foreknowledge. Source and reliability of foreknowledge were varied between groups of participants. With reliable foreknowledge, the relevant task always conformed to foreknowledge, even when the features of the imperative stimulus called for an alternative task. With unreliable foreknowledge, the relevant task was determined by the imperative stimulus and foreknowledge was sometimes misleading. Apart from measuring switch costs, we examined the effectiveness of establishing a task set by measuring interference exerted by conflicting stimuli (conditions with reliable foreknowledge) or misled expectancies (conditions with unreliable foreknowledge). In terms of switch costs, we observed a slight superiority of externally presented over internally generated information when foreknowledge was reliable, but this relationship strongly reversed with unreliable foreknowledge. This conclusion was corroborated by observations regarding the effectiveness of task-set establishment in terms of proneness to interference.