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Same-category advantage on the capacity of visual working memory

Visual working memory (VWM) is a limited-capacity cognitive system that is responsible for temporarily storing up to three or four items, maintaining their availability for current cognitive processing. Although VWM capacity is limited, the limit is not fixed. Factors such as the complexity, statistical regularity, real-world spatial regularity, and perceptual grouping principles of memory objects can modulate this capacity. However, the potential influence of higher-order conceptual regularities, such as categorical relationships among memory objects, remains an open and controversial issue. The effect of object category on VWM capacity, if any, has two possibilities: a mixed-category advantage and a same-category advantage. The first is consistent with the neural resource theory, by which the ability to simultaneously process multiple items is limited by the extent to which those items are represented by nonoverlapping neural representations. The same-category advantage is consistent with a prediction yielded by an ideal-observer analysis of VWM, based on the rate-distortion theory. Although the mixed-category advantage is predicted by the neural resource theory, almost all current supporting evidence solely involves faces. On the other hand, although the same-category advantage is consistent with the ideal-observer prediction, there is still lack of direct evidence to support the generalization of this prediction from low-level to high-level features. Hence, in the present study, we used behavioral and electrophysiological methods to explore this issue. within-subject design was used in Experiment 1. The results showed that category knowledge modulates the capacity of the VWM and leads to a same-category advantage. In Experiment 2, we changed the presentation of MIs from simultaneous to successive and replicated the findings from Experiment 1, demonstrating that category knowledge leads to larger memory capacity in the same-category rather than in the different-category condition, even if the MIs are sequentially presented. In Experiment 3, in addition to Cowan’s K , the contralateral delay activity (CDA, an electrophysiological index of VWM capacity) was measured to further explore the processing mechanism underlying the same-category advantage. The CDA results show for the first time that same-category objects can induce a smaller contralateral delay activity (an index of VWM capacity) than different-category objects. The CDA results combined with behavioral results indicated that category knowledge can help compact the representations of same-category objects and therefore enlarge the total information capacity of VWM. In conclusion, our data clearly demonstrate an advantageous same-category effect on the capacity of VWM, which indicates that categorical relationships among objects play an important role in expanding the capacity of VWM by enabling the grouping of same-category objects. This suggests that VWM capacity is not fixed but can be flexible depending on the type of information to be remembered. Moreover, our data also suggest that the ideal-observer prediction can be extended from low-level to high-level features.