Research Report Event-related potential (ERP) measures reveal the timing of memory selection processes and proactive interference resolution in working memory Yuji Yi ⁎ , David Friedman Cognitive Electrophysiology Laboratory, Division of Cognitive Neuroscience, New York State Psychiatric Institute, New York, NY 10032 USA ARTICLE INFO ABSTRACT Article history: Accepted 4 July 2011 Available online 13 July 2011 Behavioral studies show that no-longer-relevant information, although presumably removed from working memory (WM), still engenders proactive interference (PI). However, the timing of selecting items within WM and resolving PI is relatively unknown. To assess this, we recorded ERPs during WM from 20 young adults. In all conditions, a 4-digit display was followed by a cue indicating which digits to remember. In the selection condition, 2 digits were cued. The reaction time difference between the intrusion probe, a match of a to-be-rejected digit, and the non-intrusion probe, which did not match any of the 4 digits, was reliable, indicating a robust effect of PI. In the neutral-2 (remember 2 digits) and - 4 (remember all 4) conditions, participants maintained the digits following the cue. Relative to neutral-4, selection elicited larger positivity at parietal sites (approximately 260 ms) and negativity at frontal sites (approximately 420 ms). Relative to the non-intrusion probe ERP, that to the intrusion probe was more negative over frontal scalp (approximately 500 ms). We conclude that initial selection occurs over parietal cortex and reflects top–down attention to task relevant items, whereas the subsequent negativity may reflect inhibition of no-longer-relevant items over frontal cortex. The probe-locked ERPs suggest that the frontal negativity (approximately 500 ms) reflects the final resolution of PI. © 2011 Elsevier B.V. All rights reserved. Keywords: Working memory Proactive interference Selection Inhibition Parietal positivity Event-related potential 1. Introduction Working memory (WM) refers to the short-term storage and manipulation of information (Baddeley, 1986; Baddeley and Hitch, 1974). Baddeley (1986) proposed that WM was comprised of a central executive and two slave systems, the phonological loop and the visuospatial sketchpad. The function of the central executive is poorly understood in comparison with the two slave systems. It is considered an attentional-control system that has limited capacity (Baddeley, 2003). One of the important roles of the central executive is to select relevant information while disregarding or inhibiting irrelevant infor- mation (Baddeley, 1996). This type of control system also appears in Cowan's (1999) embedded-processes model. In his model, information is represented at three levels: infor- mation within the focus of attention, information not in the focus of attention but currently activated, and non-activated information in long-term memory. The focus of attention refers to the maintenance of a small set of information that is readily accessible and can be selected from WM and manip- BRAIN RESEARCH 1411 (2011) 41 – 56 ⁎ Corresponding author at: New York State Psychiatric Institute, Cognitive Electrophysiology Laboratory, Division of Cognitive Neuroscience, 1051 Riverside Drive, Unit 50, New York, NY 10032, USA. Fax: +1 212 543 6540. E-mail address: yujiyi@nyspi.columbia.edu (Y. Yi). 0006-8993/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2011.07.004 available at www.sciencedirect.com www.elsevier.com/locate/brainres