Examining the cognitive processes underlying resumption costs in task-interruption contexts: Decay or inhibition of suspended task goals?

To examine whether an ongoing primary task is inhibited when switching to an interruption task, we implemented the n - 2 backward inhibition paradigm into a task-interruption setting. In two experiments, subjects performed two primary tasks (block-wise manipulation) consisting of a predefined sequence of three subtasks. The primary tasks differed regarding whether the last subtask switched or repeated relative to the penultimate subtask, resulting in n - 1 switch subtasks (e.g., ABC) and n - 1 repetition subtasks (e.g., ACC) as the last subtask of the primary task. Occasionally, an interruption task was introduced before the last subtask of a primary task, changing the last subtask of the primary task from a n - 1 switch subtask to a n - 2 switch subtask (e.g., AB → secondary task → C) and from a n - 1 repetition subtask to a n - 2 repetition subtask (e.g., AC → secondary task → C). In two experiments with different degrees of response-set overlap between the interruption task and the subtasks of the primary task, we observed that switching back from the interruption task to the primary task resulted in n - 2 switch costs in the first subtask after the interruption (i.e., worse performance in n - 2 switch subtasks than in n - 2 repetition subtasks). This n - 2 switch cost was replicated in a third experiment in which we used a predefined sequence of four subtasks instead of three subtasks. Our finding of n - 2 switch costs suggest that the last subtask performed before the interruption remains activated when switching to the interruption task.