Retaining Bindings of Integral Features in Working Memory: The Role of Object-based Attention

PURPOSE: Over the past decade, it has been debated whether retaining bindings in working memory (WM) requires more attention than retaining constituent features, focusing on domain-general attention and space-based attention. Recently we proposed that retaining bindings in WM needs more object-based attention than retaining constituent features (Gao et al., 2017; Shen, Huang, & Gao, 2015). However, the composed features in the tested bindings all belong to separable feature dimensions. It has been suggested that there are two types of feature relations: Separable features (e.g., color and shape in a colored shape) and integral features (e.g., width and height of a rectangle). While our brain encodes separable features independently, it is difficult to encode the integral features separately. Consequently, the object-based attention hypothesis of retaining bindings in WM may be constrained to separable features, and retaining bindings of integral features does not require more object-based attention than the constitute single features. METHODS: In the current study we addressed this issue by requiring the participants to memorize both width and height of three rectangles or the binding between the two feature dimensions. In the critical condition, we added a secondary transparent motion task during the delay interval of the change-detection task, such that the secondary task competed for object-based attention with the to-be-memorized stimuli. If more object-based attention is required for retaining bindings than for retaining constituent features, the secondary task should impair the binding performance to a larger degree relative to the performance of constituent features. RESULTS: In contrast to the prediction of object-based attention hypothesis, the added secondary task equally impaired the performance of single features and binding. CONCLUSION: Retaining bindings of integral features in WM does not require more object-based attention than the constitute single features, providing a key constraint to the object-based attention hypothesis.