Visual short-term memory (VSTM) refers to our ability in remembering visual information for a limited amount of time. In the VSTM literature, mixed findings have been reported regarding whether items are encoded individually or globally in the context of other items. This study adopted a color change detection task and manipulated color and spatial relations of the items on display to test whether inter-item relational information and processing can facilitate change detection performance. Results showed that only when a post-cue was presented to reduce decision load (Experiments 1 and 3), both color and spatial relations facilitated color change detection. However, when there was no post-cue to lessen the decision load, preserving spatial relations at test impaired color change detection (Experiment 2). Furthermore, spatial and color relational processing interactively affected color change detection. Benefit of the spatial relations was observed only when color grouping cues can aid change detection, and the utilization of color relations was optimized when spatial relations were preserved to cue the retrieval of color relations. Our results support the hierarchical representation hypothesis, which assumes that both individual items and item relations are encoded and maintained in VSTM. The amount of cognitive resources for retrieving different levels of representations is highly constrained by the decision load.
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