Working memory capacity for biological motion: a virtual reality examination

Biological motion (BM), the movements of animate entities, contains rich social information and has been extensively explored in visual science. Consistent with a fixed-capacity view of working memory (WM), previous studies consistently suggested that at most 4 BM could be retained in WM, which was not affected by the encoding time of the to-be-memorized stimuli. However, recent studies have challenged this view by showing that real-world non-social stimuli benefit from longer encoding time and have a larger WM capacity. In this study, we addressed whether the WM capacity of BM could exceed the traditional 4-item limitation under a high ecological-validity setting with sufficient encoding time. Using virtual reality (VR) equipment, we presented three-dimensional (3-D) avatar BM stimuli at different depths of the environment with sufficient encoding time in a standard change detection task. In two experiments, we found that WM could retain up to 6 BM with sufficient encoding time, regardless of whether the to-be-memorized stimuli were 2-D or 3-D and displayed in one or two different depths. This finding suggests that retaining BM in WM benefits from deeper encoding time, and the depth information of stimuli and environment does not play a key role in determining the WM capacity of BM.