The Cost of a Voluntary Task

Task-switching paradigms are widely used to study executive control. However, standard paradigms may not re- quire active control to switch tasks. We examined voluntary task switching by having subjects choose which task to perform on a series of bivalent stimuli. Subjects performed parity or magni- tude judgments on single digits. Instructions were to perform the two tasks equally often and in a random order. The response-to- stimulus interval (RSI) was either 100 or 1,000 ms, manipulated between blocks. Task alternations were slower than task repe- titions, and this switch cost was greater at the short RSI than at the long RSI (310 and 94 ms, respectively). Additionally, sub- jects produced more task repetitions than expected if the tasks were performed in a random sequence. These results show costs associated with a voluntary task switch, when subjects must actively control the choice of the task to be performed.