Working memory mechanisms for binding have been examined extensively in the last decade, yet few studies have explored bindings relating to human biological motion (BM). Human BM is the most salient and biologically significant kinetic information encountered in everyday life and is stored independently from other visual features (e.g., colors). The current study explored 3 critical issues of BM-related binding in working memory: (a) how many BM binding units can be retained in working memory, (b) whether involuntarily object-based binding occurs during BM binding, and (c) whether the maintenance of BM bindings in working memory requires attention above and beyond that needed to maintain the constituent dimensions. We isolated motion signals of human BM from non-BM sources by using point-light displays as to-be-memorized BM and presented the participants colored BM in a change detection task. We found that working memory capacity for BM-color bindings is rather low; only 1 or 2 BM-color bindings could be retained in working memory regardless of the presentation manners (Experiments 1-3). Furthermore, no object-based encoding took place for colored BM stimuli regardless of the processed dimensions (Experiments 4 and 5). Central executive attention contributes to the maintenance of BM-color bindings, yet maintaining BM bindings in working memory did not require more central attention than did maintaining the constituent dimensions in working memory (Experiment 6). Overall, these results suggest that keeping BM bindings in working memory is a fairly resource-demanding process, yet central executive attention does not play a special role in this cross-module binding.

Retaining events containing action-related information in working memory (WM) is vital to daily activities such as action planning and social interaction. During processing of such events, action-related information is bound with other visual elements (e.g., colours) as event files. In this study, we explored whether retaining event files in WM consumes more attention than retaining the constituent elements. Considering that object-based attention underlies the rehearsal of static feature bindings in WM, we hypothesised that object-based attention played a key role in retaining event files in WM. As biological motion (BM) is one of the most frequently observed events in daily life, we employed BM-related event files as the tested stimuli. In separate blocks, we required participants to memorise BM, colours (or locations), or the binding between these elements (i.e., event files). Critically, we added an object-feature report task, which consumed object-based attention, during the WM maintenance phase. We predicted that the added secondary task would lead to larger impairment for BM event files than for the constituent elements. In line with this prediction, Experiments 1 and 2 consistently revealed a selective impairment to BM event files, which could not be attributed to an unbalanced number of elements between memory conditions (Experiment 3), or to the visual processing of a secondary task (Experiment 4). Taken together, these results suggest that object-based attention plays a pivotal role in maintaining event files in WM.

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