Task Switching Cost Source Of Brain Mechanism

Switching from one task to a new task, the reaction time is prolonged, thus switch cost. Researchers have recently used several kinds of task-switching paradigms to undercover the neural mechanisms underlying the switch cost.In our study, we suppose a multi-component model of switch cost. Hypothetically task-set reconfiguration process, the passive dissipation of previously relevant task-set and other unknown process are believed to contribute to task switch cost. A newly designed task-cueing switching paradigm was used, during which subjects were instructed to switch between color classification and orientation classification task according to cues. Cue-stimulus interval and response-cue interval (response-stimulus interval) were manipulated and 14 subjects'behavioral and neural data were recorded for investigating switch cost, ERP waveforms and their association and the neural and behavioral correlates of the processes mentioned contributing to switch cost.Analysis of behavioral results revealed that at a fixed response-cue (response- stimulus) interval, reaction time and switch cost declined with increasing cue-stimulus interval, thus behavioral proof favoring that task-set reconfiguration is an important source of switch cost. And when cue-stimulus interval is fixed, there is no significant change in reaction time and switch cost by increasing the response-cue interval. This can't be served as argument for the theory of task-set inertia. The fact that reaction time and switch cost declined with increasing cue-stimulus interval at a constant response-stimulus interval (response-cue interval) may, to some extent, index the unbalanced effects of the processes determined by cue-stimulus interval and response-cue interval.For short cue-stimulus interval condition, examination of cue-locked ERP waveforms for switch and repeat trials revealed a posterior large and sharp positivity emerged and peaked at about 375-425ms after cue onset, but a larger positivity for switch trials, thus a switch-related differential positivity consistent with previous findings. And a switch-related positivity at Pz electrode, emerging 225-275ms after stimulus onset, was also observed by comparing stimulus-locked ERP waveforms for switch and repeat trials. It can serve as neural evidence for two-component model of task-set reconfiguration process, one is cue-locked and the other is stimulus-triggered. An obvious modulation of two components in the two waveforms by response-cue interval may indicate the effect of the passive dissipation of previous relevant task-set on switch-related positivity. For long cue-stimulus interval, a posterior slow positivity emerged at 400ms after cue onset and extending until stimulus onset for both switch and repeat trials, also a larger positivity for switch trials. And separation between stimulus-locked waveforms for switch and repeat trials had begun as early as about 200ms after stimulus onset, a smaller positivity for switch trials. Brain topography manifested that dorelateral prefrontal cortex and posteriot parietal cortex is involved in both anticipatory task-set reconfiguration and the stimulus-triggered process.