Different electrophysiological correlates underlying fragile and robust Visual Short-Term Memory.

摘要

Recently, we have found evidence for a new stage of Visual Short-Term Memory (VSTM) that lies in between iconic memory and robust VSTM (Sligte et al., 2008; 2009). Classical VSTM experiments in which a Change Detection paradigm is used show that VSTM stores items in a stable form, yet it has a limited capacity of around four objects. However, when a partial-report paradigm is used, capacity can be boosted to up to twice that amount. These additional items are however erased when new objects appear, hence we term this additional storage fragile VSTM. Although behavioral evidence has been found for a dissociation between fragile and robust VSTM (Vandenbroucke et al., 2011), controversy remains whether fragile VSTM taps into a different stage of memory or whether in both fragile and robust VSTM, the same mechanism are at play (Makovksi, 2012, Matsukura & Hollingworth, 2011). In this study, we investigated whether fragile and robust VSTM have different electrophysiological underpinnings using EEG time-frequency analyses. Twenty-four subjects performed a Change Detection task in which a cue was presented in between the memory and test display (gauging fragile VSTM) or during the test display (gauging robust VSTM). Memory displays contained 2, 4, 6 or 8 oriented rectangles. For robust VSTM, ceiling performance was reached at 4 objects, while fragile VSTM performance kept rising up to 8 objects. The capacity scores for fragile VSTM and robust VSTM correlated with different frequency bands before onset of the cue, such as a relative decrease in parietal-occipital alpha activity and increase in central-parietal gamma activity for fragile VSTM. This suggests that the neural mechanisms supporting fragile and robust VSTM differ.