Object maintenance beyond their visible parts in working memory

Completion of a partially occluded object requires that a representation of the whole is constructed based on the information provided by the physically specified parts of the stimulus. Such processes of amodal completion rely on the generation and maintenance of a mental image that renders the completed object in visual working memory (VWM). The present study examined this relationship between VWM storage and processes of object completion. We recorded event-related potentials to track VWM maintenance by means of the contralateral delay activity (CDA) during a change detection task in which to-be-memorized composite objects (notched shapes abutting an occluding shape) were primed to induce either a globally completed object or a non-completed, mosaic representation. The results revealed an effect of completion in VWM despite physically identical visual input: Change detection was more accurate for completed as compared to mosaic representations when observers were required to memorize two objects, and these differences were reduced with four memorized items. At the electrophysiological level, globally completed (versus mosaic) objects gave rise to a corresponding increase in CDA amplitudes. These results indicate that, while incorporating the occluded portions of the presented shapes requires mnemonic resources, the complete-object representations thus formed in VWM improve change detection performance by providing a more simple, regular shape. Overall, these findings demonstrate that mechanisms of object completion modulate VWM, with the memory load being determined by the structured representations of the memorized stimuli.

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