More abstract, more difficult to shift: Behavior and electrophysiological evidence.

Previous studies on task or rule shifting have shown that the switch cost is affected by the hierarchical level of abstraction. The present study aimed to explore the neural correlates of hierarchical modulation in rule shifting. Participants were required to respond to number stimuli (1-9, excluding 5) while adhering to alternative rules cued by different perceptual features of the stimuli. Across trials, the rules might repeat or shift at either high or low hierarchical levels. Behavioral results indicated that the reaction times were significantly slower in the high-shift than in the low-shift condition. The electrophysiological results revealed (1) significant difference in P300 between high- and low-shift conditions, with larger P300 in the high-shift condition; and (2) increased amplitude of the late positive component (LPC) elicited by the high-shift condition as compared to that by the low-shift condition. These findings demonstrate that the task-set reconfiguration and rule selection is more difficult for higher hierarchical level of rule shifting as compared with lower level.