Task switching under predictable and unpredictable circumstances

Task switching was examined under predictable and unpredictable circumstances. In the first two experiments (in predictable conditions), the upcoming task was determined by the trial sequence. In unpredictable conditions, this task was signaled by the stimulus. Under speeded conditions, participants had to judge either the parity of a digit or the vowel/consonant nature of a letter. On bivalent trials, a digit and a letter were presented. On univalent trials, a task-relevant character occurred alongside a task-irrelevant character (e.g., "&"). Task-switching costs were found, and response times were generally slower on bivalent than on univalent trials. This crosstalk effect was reduced when a task repetition was expected. In the final experiment, trial predictability was defined according to whether a task precue was presented prior to or concurrently with the trial stimulus. Contrasting patterns of crosstalk effects were obtained and are discussed in terms of exogenous and endogenous factors that affect task switching.