Previous research suggests the contribution of a unitary supervisory control mechanism in task-switching. Since any change in the response-stimulus interval (RSI) between tasks affects the time available for task-set reconfiguration, switch costs are highly influenced by changes in RSI. However, increasing RSI can not completely remove the switch costs, which has been attributed to automatic control processes. Considering these contributions, speed, accuracy, and their corresponding trade-off (SAT) have been investigated in this study. In Experiment 1 and 2, 28 single-session and 10 multiple-session participants switched between different (or repeated similar) tasks with either short (200 ms) and long (2000 ms) RSIs. Within 8 blocks of 64 trials containing pairs of letter and digit categorization tasks, the contribution of SAT to task-switching was studied by giving the participants either speed or accuracy emphasis instructions at the beginning of each block. Results showed reductions in switch costs during the long RSI trials. However, the long RSI could not remove the residual switch cost. Speed-emphasis instructions resulted in faster responses but higher number of errors in short and long RSIs for both switch and repeat trials in comparison to accuracy emphasis. Moreover. RT switch costs at both short and long RSIs were reduced under speed emphasis, but only for the more practiced participants in Experiment 2. In Experiment 3, actual SAT curves were generated for 9 multiple-session participants using the response signal method. Reconfiguration costs at both short and long RSIs were implicated by shifts in the intercept of the SAT curve for switch trials with incompatible stimuli.
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