Psychological Review, Vol 133(3), Apr 2026, 515-533; doi:10.1037/rev0000569
Manipulation plays a critical role in working memory, wherein understanding how items are represented during manipulation is a fundamental question. Previous studies on manipulation have primarily assumed independent representations by default (independent hypothesis). Here, we propose the ensemble hypothesis to challenge this conventional notion, suggesting that items are represented as ensembles undergoing updating during manipulation. To test these hypotheses, we focused on working memory updating in accordance with new information by conducting three delayed-estimation tasks under addition, removal, and replacement scenarios (Study 1). A critical manipulation involved systematically manipulating the mean orientation of all memory stimuli, either increasing (clockwise) or decreasing (counterclockwise) after the updating process. Following the independent hypothesis, memory errors would be similar under both conditions. Conversely, considering the biasing effect of the ensemble on individual representations, the ensemble hypothesis predicts that memories of individual items would be updated, aligning with the ensemble’s change direction. Namely, memory errors would be more positive in the increase-mean condition compared to the decrease-mean condition. Our results supported the ensemble hypothesis. Furthermore, to investigate the mechanisms underlying ensemble computations in updating scenarios, we conducted three ensemble tasks (Study 2) with similar designs to Study 1 and developed a computational model to quantify the contributions of each memory item. The results consistently demonstrated that addition involved complete updating, while removal led to incomplete updating. Across these three research parts, we propose that items are represented as dynamic ensembles during working memory updating processes. Furthermore, we elucidate the computational principles underlying ensembles throughout this process. (PsycInfo Database Record (c) 2026 APA, all rights reserved)