Shared visual memory resources for dynamic and static stimuli

Visual working memory stores the current state of the world for use in other cognitive processes. As the world is a dynamic place, visual working memory therefore needs to be able to store dynamic information. Despite this, visual working memory is typically studied with only static stimuli. Are dynamic stimuli simply stored as series of static stimuli? How many visual working memory resources does a dynamic stimulus take compared to a static one? Are they even stored in the same system? Here, we used a dual-task paradigm to investigate these questions. Participants saw either a 100% valid cue indicating whether the test item would be dynamic and static, or a neutral cue. They then viewed a static stimulus, consisting of either 2-6 circles randomly located on the circumference of a circle (Experiment 1) or 1-4 colored circles (Experiment 2), followed by the dynamic stimulus, consisting of a 5 second sequence where a trail of white dots moved between two random points on the perimeter of a large circle, changing directions 3 times along the way. Finally, they were asked to reproduce either the static stimulus (location in Experiment 1, color in Experiment 2), or the dynamic stimulus, by reproducing the path that trail of white dots took using a touchscreen. Overall, we found having to remember a dynamic stimulus decreased memory recall performance for a static stimulus, and vice versa. Importantly, although the dynamic stimulus was predominantly spatial in nature, it was still impacted by the static color stimulus. Interestingly, despite the difference in amount of information inherent in a dynamic stimulus, the effect on static memory was equivalent to having to remember two extra locations, or one extra color. We conclude that the same visual working memory system is used to remember both static and dynamic stimuli.