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Neuroscience Journal
Volume 2013, Article ID 172614, 8 pages
Research Article

Encoding into Visual Working Memory: Event-Related Brain Potentials Reflect Automatic Processing of Seemingly Redundant Information

1Department for Psychology, Johannes Gutenberg-University Mainz, Wallstraße 3, 55099 Mainz, Germany
2Disciplin of Psychology, School of Health and Human Sciences, Southern Cross University, Hogbin Drive, Coffs Harbour, NSW 2450, Australia
3Institute for Psychology, University of Leipzig, Seeburgstraße 14-20, 04103 Leipzig, Germany
4Biomedical Science, School of Medical Sciences, The University of Sydney, P.O. Box 170, Lidcombe, NSW 1825, Australia

Received 30 November 2012; Revised 7 April 2013; Accepted 7 April 2013

Academic Editor: Pasquale Striano

Copyright © 2013 Stefan Berti and Urte Roeber. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Encoding and maintenance of information in visual working memory in an S1-S2 task with a 1500 ms retention phase were investigated by means of event-related brain potentials (ERPs). Participants were asked to decide whether two visual stimuli were physically identical (identity comparison (IC) task) or belonged to the same set or category of equivalent patterns (category comparison (CC) task). The stimuli differ with regard to two features. (1) Each pattern can belong to a set of either four (ESS 4) or eight (ESS 8) equivalent patterns, mirroring differences in the complexity with regard to the representational structure of each pattern (i.e., equivalence set size (ESS)). (2) The set of patterns differ with regard to the rated complexity. Memory performance obtained the effects of the task instructions (IC versus CC) and the ESS (ESS 4 versus ESS 8) but not of the rated complexity. ERPs in the retention interval reveal that the stimulus-related factors (subjective complexity and ESS) affect the encoding of the stimuli as mirrored by the pronounced P3b amplitude in ESS 8 compared to ESS 4 patterns. Importantly, these effects are independent of task instructions. The pattern of results suggests an automatic processing of the ESS in the encoding phase.