Visual working memory (VWM) training has been shown to improve performance in trained tasks with limited transfer to untrained tasks. The neural mechanism underlying this limited transfer remains unknown. In the present study, this issue was addressed by combining model-fitting methods with EEG recordings. Participants were trained on a color delay estimation task for 12 consecutive 1-hr sessions, and the transfer effect was evaluated with an orientation change detection task. The EEG responses during both tasks were collected in a pretraining test, a posttraining test conducted 1 day after training, and a follow-up test conducted 3 months after training. According to our model-fitting results, training significantly improved the capacity but not the precision of color working memory (WM), and this capacity improvement did not transfer to the orientation change detection task, spatial 2-back task, symmetry span task, or Raven reasoning test. The EEG results revealed that training resulted in a specific and sustained increase in parietal theta power suppression in the color WM task, which reflected individual color WM capacity. In contrast, the increase in parietal–temporal alpha power, which reflected individual orientation WM capacity, did not change with training. Together, these findings suggest that the simultaneous change of stimulus type and task structure would modulate the cognitive and neural substrates of WM tasks and introduce additional constraints for the transfer of WM training.

Human alpha-band activity (8–12 Hz) has been proposed to index a variety of mechanisms during visual processing. Here, we distinguished between an account in which alpha suppression indexes selective attention versus an account in which it indexes subsequent working memory storage. We manipulated two aspects of the visual stimuli that perceptual attention is believed to mitigate before working memory storage: the potential interference from distractors and the size of the focus of attention. We found that the magnitude of alpha-band suppression tracked both of these aspects of the visual arrays. Thus, alpha-band activity after stimulus onset is clearly related to how the visual system deploys perceptual attention and appears to be distinct from mechanisms that store target representations in working memory.

Visual working memory temporarily represents a continuous stream of task-relevant objects as we move through our environment performing tasks. Previous work has identified candidate neural mechanisms of visual working memory storage; however, we do not know which of these mechanisms enable the storage of objects as we sequentially encounter them in our environment. Here, we measured the contralateral delay activity (CDA) and lateralized alpha oscillations as human subjects were shown a series of objects that they needed to remember. The amplitude of CDA increased following the presentation of each to-be-remembered object, reaching asymptote at about three to four objects. In contrast, the concurrently measured lateralized alpha power remained constant with each additional object. Our results suggest that the CDA indexes the storage of objects in visual working memory, whereas lateralized alpha suppression indexes the focusing of attention on the to-be-remembered objects.