The same or different? : capacity limitations in visual imagery versus visual memory in the short-term

Research suggests that visual imagery and visual memory share similar underlying processes. One way to differentiate these processes is to understand if the capacity of imagination and visual memory are the same. To date, limited research has investigated capacity limits in imagination, and directly compared them to that of visual memory. This thesis aimed to provide estimates of imagination capacity and explore how this relates to the capacity of visual memory in the short-term (VMst). Collectively, experiments 1 and 2 explored capacity limits in imagination, visual working memory (VWM) and visual short-term memory (VSTM) using a novel paradigm that for the first time provided comparable estimates of capacity across these tasks. The key finding was that imagination capacity was lower than VWM and VSTM. Experiment 3 manipulated the time available to generate, update and maintain an image (imagination task) or encode, update and maintain an image (VWM task). Time did not influence performance in imagination or VWM. Experiment 4 explored whether the cuing methodology in the imagination task was responsible for worse performance than in the VWM task. None of the manipulations showed any specific influence on the imagination task suggesting this was not an important factor. Experiment 5 investigated whether the decision methodology favoured the memory tasks because of the inclusion of all the stimuli at test. The inclusion of all items benefited VSTM performance, whereas the reverse was true for the VWM task whereby performance was better when only a single item was presented at test. There was no impact on imagination performance. Experiment 6 explored the impact of object complexity on capacity in imagination, VWM and VSTM. Object complexity reduced VSTM capacity to the same level as imagery, however VWM capacity remained higher than imagery. Overall, the findings suggest that imagery is very similar to VWM, in terms of them being impacted similarly by manipulations. However, the capacity findings suggest that they may not be underpinned by identical processes. In contrast, imagery is less similar to VSTM as manipulations impacted these processes differently.