Comparison of the Working Memory Load inN-Back and Working Memory Span Tasks by Means of EEG Frequency Band Power and P300 Amplitude.
According to theoretical accounts, both,N-back and complex span tasks mainly require working memory (WM) processing. In contrast, simple span tasks conceptually mainly require WM storage. Thus, conceptually, anN-back task and a complex span task share more commonalities as compared to a simple span task. In the current study, we compared anN-back task, a complex operation span task (Ospan), and a simple digit span task (Dspan) by means of typical WM load-related measures of the Electroencephalogram (EEG) like the parietal alpha and beta frequency band power, the frontal theta frequency band power, and the P300 amplitude, to examine whether these tasks would show commonalities or differences in WM processing-load. We expected that increasing WM-load would generally lead to a decreased alpha and beta frequency band power, an increased theta frequency band power, and a decreased P300 amplitude. Yet, based on the conceptual considerations, we hypothesized that the outcomes of these measures would be more comparable between theN-back and the Ospan as compared to the Dspan. Our hypotheses were partly confirmed. TheN-back and the Ospan showed timely more prolonged alpha frequency band power effects as compared to the Dspan. This might indicate higher demands on WM processing in the former two tasks. The theta frequency band power and the P300 amplitude were most pronounced in theN-back task as compared to both span tasks. This might indicate specific demands on cognitive control in theN-back task. Additionally, we observed that behavioral performance measures correlated with changes in EEG alpha power of theN-back and the Ospan, yet not of the Dspan. Taken together, the hypothesized conceptual commonalities between theN-back task and the Ospan (and, for the Dspan, differences) were only partly confirmed by the electrophysiological WM load-related measures, indicating a potential need for reconsidering the theoretical accounts on WM tasks and the value of a closer link to electrophysiological research herein.
Knowledge Media Research Center Tübingen, Germany.
Christian
C
Scharinger
Laboratory for Social and Neural Systems Research, University of Zurich Zurich, Switzerland.
Alexander
A
Soutschek
Department of Psychology, Humboldt-Universität zu BerlinBerlin, Germany; Department of Psychology, Martin-Luther-Universität Halle-WittenbergHalle, Germany.
Torsten
T
Schubert
Knowledge Media Research CenterTübingen, Germany; Department of Psychology, Eberhard-Karls-Universität TübingenTübingen, Germany.
Peter
P
Gerjets
EEG time-frequency analysis; EEG/ERP; ERD/ERS; N-back task; P300; digit span task; operation span task; working memory