The oblique effect in visual working memory is enhanced by distraction, regardless of tDCS manipulations

The sensory recruitment model suggests that visual working memory (VWM) relies on early visual cortex (EVC), while the alternative frontoparietal account argues VWM representation is independent from EVC. An emerging consensus suggests that VWM relies on a distributed network, with different brain loci serving behavior depending on task demands. To evaluate VWM reliance on EVC vs. parietal cortex, we applied anodal (or sham) transcranial direct current stimulation (tDCS) to either occipital cortex (Oz) or right posterior parietal cortex (P4) to manipulate cortical representations before an orientation VWM task. To provoke perceptual interference and encourage reliance on parietal cortex, in half of blocks, distractors appeared during VWM delays. We predicted that parietal tDCS would improve VWM capacity to protect representations against ongoing distractions. We also expected that occipital tDCS could either increase memory capacity in nondistraction blocks or increase susceptibility to ongoing distraction. Finally, we reasoned that the oblique effect, which is thought to rely in part on EVC, would be reduced by distractor presence and the accompanying shift to reliance on parietal representations. Contrary to our predictions, neither tDCS manipulation affected VWM reports and the oblique effect was always present but was paradoxically stronger with distraction. These results could suggest reliance on EVC for VWM maintenance, even under distraction. Alternatively, these results could signal loss of fine-grained VWM detail under distraction due to use of representational strategies that maximize task performance rather than veridical orientation representation.