Abstract
Visual working memory supports the retention of past visual sensations for guiding upcoming future actions. While visual working memory and action planning are often studied in relative isolation, recent evidence indicates that visual representations and their associated actions can be accessed from working memory concurrently, suggesting visual memories are held in memory together with the future actions they serve. Here, we used electroencephalography (EEG) to investigate when such prospective actions become integrated into working memory, following the selective encoding of visual shape information. Across two experiments, participants performed a visual-motor working memory task, with a pre-cue directing attention to one of two visual items that were each linked to particular manual actions at the end of the memory delay. Visual item location and the prospective response hand were independently manipulated, enabling us to independently characterise neural activity reflecting visual and motor memory attributes. In experiment 1, we further manipulated temporal expectations by probing memories after either two or four seconds. This allowed us to separate ‘action encoding’ from subsequent ‘action preparation’. Suppression of contralateral mu-alpha and mu-beta oscillations (8-30Hz) in human motor cortex revealed encoding of the prospective action, irrespective of the time of the expected probe. This was followed by gradual action preparation which depended on the time of expected memory use, revealing a what-then-when scenario of prospective memory preparation. In experiment 2, we show that this ‘action imprinting’ even occurs ahead of an intervening motor task that prevented participants from preparing the action for ensuing execution. Across both experiments, action imprinting predicted visual-memory-guided actions several seconds later. Thus, our data demonstrate how future behavioural outputs are already prepared at the initial stages of visual encoding, highlighting the tight link between visual working memory and action planning, as well as the fundamentally prospective nature of this core memory function.