A new ERP paradigm for studying individual differences in the executive control of attention


Event-related potentials (ERPs) provide valuable information about the fast brain dynamics subserving cognitive functions such as atten- tion and working memory. Most ERP studies employ cognitive para- digms with a fixed task-set (i.e., press a button to named targets), but few have measured ERPs time-locked to shifts in set using a task- switching paradigm. The Madrid Card Sorting Test (MCST) is a dual task protocol in which feedback cues signal unpredictable shifts in set (i.e., from “sort cards by colour” to “sort cards by shape”). This pro- tocol offers an integrated analysis of ERPs to both feedback cues and target card events, providing separate ERP indexes for the shifting, updating and rehearsal of attention sets in working memory. Two of these ERP indices are the frontal and posterior aspects of the P300 response. Feedback cues that direct a shift in set also elicit both a frontally distributed P3a potential (300 to 400 ms) and a posteriorly distributed P3b potential (350 to 600 ms). In turn, target card events evoke posterior P3b responses whose amplitude increases as the new task set is gradually rehearsed. In line with current models about the role of prefrontal cortex in the executive control of attention, this P3a/P3b response system appears to reflect the coordinated action of prefrontal and posterior association cortices during the switching and updating of task sets in working memory.