Memory load influences our preparedness to act on visual representations in working memory without affecting their accessibility

Abstract

It is well established that when we hold more content in working memory, we are slower to act upon part of that content when it becomes relevant for behavior. Here, we asked whether this load-related slowing is due to slower access to the sensory representations held in working memory (as predicted by serial working-memory search), or by a reduced preparedness to act upon those sensory representations once accessed. To address this, we designed a visual-motor working-memory task in which participants memorized the orientation of two or four colored bars, of which one was cued for reproduction. We independently tracked EEG markers associated with the selection of visual (cued item location) and motor (relevant manual action) information from the EEG time-frequency signal, and compared their latencies as a function of memory load. We confirm slower memory-guided behavior with higher working-memory load and show that this is associated with delayed motor selection. In contrast, we find no evidence for a concomitant delay in the latency of visual selection. Moreover, we show that variability in decision times within each memory-load condition is associated with corresponding changes in the latency of motor, but not visual selection. These results reveal how memory load affects our preparedness to act on sensory representations in working memory, while leaving sensory access itself unaffected. This posits action readiness as a key factor that shapes the speed of memory-guided behavior and that underlies delayed responding with higher working-memory load.