Task similarity increases difficulty in maintaining but not in switching between tasks.

Switching tasks and adapting to new situations by appropriately allocating mental resources is crucial for interacting with the world around us.This ability requires cognitive control and includes several operations such as maintaining and modifying task goals, allocating attention to the relevant stimulus, and selecting the appropriate motor command.Surprisingly, although we know that switching between tasks incurs costs, whether the type of activity itself makes any difference has rarely been investigated.This study uses an innovative, well-controlled paradigm that keeps response rules and stimulus set constant across tasks to specifically test how efficiently humans switch between tasks sharing similar versus dissimilar neural processes.We assessed the efficiency of transient and global cognitive control by comparing participants' switch costs, the efficiency of task reconfiguration, and mixing costs, the efficiency of task maintenance.In four experiments, employing different stimuli and tasks, the results consistently show that increased similarity between pairs of tasks increased the difficulty in maintaining the tasks but not in switching between them.This dissociation confirms that switch and mixing costs are independent processes.Importantly, the overlap in neural processing between tasks appears to be detrimental in simultaneously maintaining tasks, potentially due to competition or interference.Distinct task sets are more efficient to maintain than similar ones. Public Significance StatementIs it easier to prepare coffee and make a sandwich or to prepare coffee and read a book?This study shows that maintaining similar tasks (preparing coffee and sandwich) is more effortful than maintaining dissimilar tasks (preparing coffee and reading a book).On the other hand, it is equally difficult to alternate between any pair of tasks.Thus, even though similar goals share some features that could make them easier to achieve, this overlap is actually detrimental.It is easier to optimize dissimilar than similar pair of tasks.