The relation between the capacities of imagination and visual memory in the short-term

Visual imagery and short-term memory utilise similar brain networks, but the extent to which they are related remains unclear. Here we explore whether the capacity of visual imagery (as yet unknown) is similar to the known capacity limits of visual working memory (VWM) and visual short-term memory (VSTM). Experiment 1 explored capacity limits in imagination, VWM and VSTM using a novel paradigm that for the first time provided estimates of capacity across these tasks. Imagination capacity was lower than that of VWM and VSTM. Experiments 2-4 eliminated alternative explanations of this capacity difference. Manipulating the time available to generate, update and maintain an image (imagination task) or encode, update and maintain an image (VWM task) did not influence performance in either task (Experiment 2). Manipulating the cue location and the size of the cued area had no specific influence on the imagination task (Experiment 3). Changing the test display (Experiment 4) showed that presenting all items at test (configural information) benefitted VSTM performance, presenting a single item benefitted VWM performance and manipulating test display had no impact on imagination performance. In Experiment 5, increasing object complexity eliminated the difference between VSTM and imagination capacity, however VWM capacity remained higher than that of imagery. The apparent superior capacity of VWM over imagination, suggests these processes are at least partly distinguishable and provides the first measurable indication of the extent to which top-down (imagery), versus bottom-up activation of sensory systems (memory) supports the representation of perceptual stimuli.