Decoding Load or Selection?

Flexible updating of information in Visual Working Memory (VWM) is crucial to deal with its limited capacity. Previous research has shown that the removal of no longer relevant information takes some time to complete. Here, we sought to study the time course of such removal by tracking the accompanying drop in load through behavioral and neurophysiological measures. In a first experimental session, participants completed a visuospatial retro-cue task in which the Cue-Target Interval (CTI) was manipulated. Performance revealed that it takes about half a second to make full use of the retro-cue. In a second session, we sought to study the dynamics of load-related electroencephalographic (EEG) signals to track the removal of information. We applied Multivariate Pattern Analysis (MVPA) to EEG data from the same task. However, contrary to previous research indicating that MVPA can be used to uniquely decode VWM load, the results suggested that the classifiers were mainly sensitive to selection, visual cue variations, or eye movements that accompany load manipulations, and not so much to load per se. These findings advise caution when using MVPA to decode VWM load, as classifiers may be sensitive to confounding operations.