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 specific content when it becomes relevant for behavior. Here, we asked whether slower responses with higher working-memory load can be accounted for by slower access to sensory representations held in working memory (according to a serial internal search), or by a lower preparedness to act upon them. 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 the selection of visual (cued item location) and motor (relevant manual action) information from the EEG time-frequency signal, and compared their latencies between our memory-load conditions. We confirm slower memory-guided behavior with higher working-memory load and show that this is associated with delayed motor selection, but 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, without necessarily changing the ability to access, sensory representations in working memory. This posits action readiness is a key factor that shapes the speed of memory-guided behavior and that underlies delayed responses with higher working-memory load.