Noisy and hierarchical visual memory across timescales

Both in everyday life and in memory research, people tend to think that items are 'held' in mind, in the same way that a real-world object can be held in one's hand. Inspired by this metaphor, traditional work on visual working memory and visual long-term memory focuses on understanding how many objects are remembered or forgotten, or held or lost, in particular circumstances. By contrast, newer computational and empirical work on visual memory focuses on the role of noise in memory representations - in which memories are thought to vary continually in 'strength' or 'precision' - as well as the role of the visual hierarchy and priors in structuring memory. In this Review, we merge these contemporary theories and evidence. We describe how fundamentally noisy memory representations are instantiated at different levels of the visual hierarchy and support both visual working memory and long-term memory. We also discuss how thinking of memory in this way can direct further research and illuminate the nature of cognitive function more broadly. Visual memory has traditionally been thought of as all-or-none, with items remembered perfectly or completely forgotten. In this Review, Brady and colleagues synthesize work that indicates that visual memory representations in working memory and long-term memory are not all-or-none but are instead noisy and hierarchical.