Components of task switching: An ERP perspective

Nessler, D.1, Friedman, D.1, Johnson, R., Jr.2, and Bersick, M.1
1Cognitive Electrophysiology Laboratory, NY Psychiatric Institute, NY; 2Queens College Department of Psychology/CUNY, Flushing, NY

Switching between tasks involves executive control processes, such as inhibiting the previous task regime while reconfiguring response requirements by retrieving the current task set and storing it in working memory. Recent hemodynamic imaging research suggests the involvement of prefrontal and parietal cortices in task switching behavior. In the current study, switching was assessed by presenting digits under two task sets, more than/less than 5 and odd/even. Subjects responded via choice reaction time (RT). In No Switch blocks the same task was repeatedly presented. In Switch blocks, subjects began with one of the two tasks. After 7 to 13 items, a cue presented simultaneously with the digit indicated the requirement to switch to the other task. ERPs were recorded from 62 channels in 15 young adults. RTs were longer during switch compared to no-switch blocks. In switch blocks, RT was prolonged on switch relative to pre-switch trials. Additionally, a residual RT switch cost was observed on the trial following the switch, relative to the trial preceding the switch. Relative to pre-switch trials, switch trials were associated with a large-amplitude positivity (~ 500 ms) with a right pre-frontal scalp focus, which preceded mean RT by ~ 600 ms. Relative to the ERPs associated with pre-switch trials, the trial immediately following the switch was associated with negative activity that had a parietal-occipital scalp focus (~ 400 ms), and occurred ~ 300 ms before mean RT. The positivity might reflect inhibition of the previous task set, while the negativity may reflect task set reconfiguration.