Neural correlates of visuo-spatial working memory encoding-An EEG study.

The aim of the present electroencephalographic (EEG) study was to investigate neuronal correlates of working memory encoding in a visuo-spatial serial delayed match-to-sample task. A rapid serial visual presentation approach was used to dissociate brain activity related to encoding of visuo-spatial targets and cortical activity evoked by suppression of distracting information. During the task EEG was recorded and steady-state visually evoked potentials (SSVEPs) were calculated. Finally, standardized low-resolution electromagnetic tomography (sLORETA) was used to determine brain regions involved in visuo-spatial working memory encoding. A distributed task-relevant network comprising right temporal, parietal, and occipital areas was identified. Results suggest that activity of this network is amplified during actual encoding of targets into visual working memory, whereas the same network is attenuated in its activation when distracting visual information should be suppressed. Left prefrontal and anterior cingulate cortices do not seem to be involved in encoding of targets but only in suppression of distracting information, likely reflecting activity of an attention-based supervisory system. These results strongly emphasise the linkage between visuo-spatial attention and working memory during amplification of selected and suppression of irrelevant information

Protecting visual short-term memory during maintenance: Attentional modulation of target and distractor representations

In the presence of distraction, attentional filtering is a key predictor of efficient information storage in visual short-term memory (VSTM). Yet, the role of attention in distractor filtering, and the extent to which attentional filtering continues to protect information during post-perceptual stages of VSTM, remains largely unknown. In the current study, we investigated the role of spatial attention in distractor filtering during VSTM encoding and maintenance. Participants performed a change detection task with varying distractor load. Attentional deployment to target and distractor locations was tracked continuously by means of Steady-State Visual Evoked Potentials (SSVEPs). Analyses revealed that attention strongly modulated the amplitude of the second harmonic SSVEP response, with larger amplitudes at target compared to distractor locations. These attentional modulations commenced during encoding, and remained present during maintenance. Furthermore, the amount of attention paid to distractor locations was directly related to behavioral distractor costs: Individuals who paid more attention to target compared to distractor locations during VSTM maintenance generally suffered less from the presence of distractors. Together, these findings support an important role of spatial attention in distractor filtering at multiple stages of VSTM, and highlight the usefulness of SSVEPs in continuously tracking attention to multiple locations during VSTM