Abstract
Though static scenes so often dominate our experimental displays, our visual experience is inherently populated by dynamic visual events: out there in the world, things *happen*. And perhaps the two most salient themes in the study of event perception are *memory flushing* at event boundaries, and the *hierarchical* nature of our dynamic experience. Visual working memory appears to be effectively flushed at event boundaries (just as one might empty a cache in a computer program), perhaps because this is when the statistics of our local environments tend to change most dramatically — and holding on to now-obsolete information may be maladaptive for guiding behavior in new contexts. The series of events we experience arrives not as a linear sequence, though, but as a structured *hierarchy*, with global events built up from more local events. (A morning might involve showering, then breakfast — but breakfast might involve pouring coffee, then burning toast, etc.) Curiously, these two central themes of event perception have never been connected, so here we explore for the first time how they interact. Observers viewed faces, one at a time. Certain features (such as size or spatial location) changed relatively frequently (inducing ‘local’ boundaries), while others changed less frequently (inducing ‘global’ boundaries). Critically, hierarchical position was dissociated from absolute frequency (such that a given frequency might be ‘local’ in one condition, but ‘global’ in another). On each trial, observers simply reported which of two faces had appeared first — where the pair could span a local boundary, a global boundary, or no boundary. Across a wide variety of experiments, memory was disrupted only by the most global boundaries that were present, regardless of their frequency. Thus, whether a particular event boundary will flush visual memory depends on how it is situated in the hierarchy of our experience.