Representations in human visual short-term memory: an event-related brain potential study

Behavioral measures and event-related potentials (ERPs) were recorded from 12 subjects while performing three delayed matching-to-sample tasks. The task instructions indicated whether stimulus locations, shapes or conjunctions of locations and shapes had to be memorized and matched against a probe. Memory load was varied trial-by-trial by cueing one or two of three stimuli for memorization, followed by one probe. ERPs during memorization and probe response times varied as a function of memory load (posterior negative and anterior positive ERP wave), but not between single-feature and conjunction of features, nor was an interaction found between them. The results support and extend hypotheses by Luck and Vogel (Luck, S.J. and Vogel, E.K., The capacity of visual working memory for features and conjunctions. Nature, 390 (1997) 279-281.) that visual short-term memory stores conjunctions of features rather than single features. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.