Abstract
Recent studies have shown that visual working memory capacity is not fixed but varies by stimulus type: stimuli that are more meaningful are better remembered than meaningless simple features, such as colored squares (e.g., Brady et al., 2016). Here, we investigate which circumstances lead to the strongest memory benefits for meaningful stimuli, focusing on how different stimuli and memory displays are processed at encoding. In particular, we test the hypothesis that deeper, item-based encoding of objects increases the benefits for meaningful objects while encoding an entire set of items holistically and in parallel may reduce such benefits. Across four high-powered experiments (total N=280) we directly test whether real-world objects, perceptually-matched less-meaningful objects, fully scrambled objects, and colors benefit from deeper processing. We systematically vary the presentation format of stimuli at encoding to be either simultaneous — encouraging a parallel and holistic, ‘take-a-quick-snapshot’ strategy in which case items should be treated as meaningless colored shapes rather than distinct meaningful objects — or present the stimuli sequentially, promoting a serial strategy where each item is attended individually and processed in a high-level way. We find large advantages for meaningful objects in all conditions, but find that real-world objects — and to a lesser degree lightly scrambled, still meaningful versions of the objects — benefit from the sequential encoding and thus deeper, focused-on-individual-items processing, while colors do not. Our results suggest single feature objects such as colors may be an outlier in their affordance of parallel and holistic processing, and that in more realistic memory situations, visual working memory likely relies upon representations resulting from in-depth processing of individual objects (e.g., in higher-level visual areas) rather than solely being represented in terms of their low-level features.