Separate storage mechanisms of absolute depth and relative depth in working memory: Encoding, maintenance, consolidation, and attention engagements.

Most research on visual working memory (WM) focuses on 2D objects and spatial locations; however, the storage mechanism of depth information-another important dimension in a 3D environment-remains largely unknown. The present study conducted seven experiments to systematically investigate how absolute depth (metric distance) and relative depth (ordinal relations among depth planes) are encoded, maintained, and consolidated in WM. In Experiments 1a and 1b, we found that memory accuracy for relative depth was higher than that for absolute depth, and verbal WM seemed to be automatically involved in encoding relative depth in the form of numerals even though memory stimuli were presented visually, and verbal suppression was applied. Experiments 2a and 2b showed memory for fine absolute depth information gradually declined over time, while memory for coarse depth information and relative depth showed no temporal decay. By manipulating the stimuli-mask onset latency, Experiment 3a revealed that memory for absolute depth remained to be fragile across retention, while Experiment 3b showed that relative depth information could be consolidated into robust memory. By inserting an additional visual search task into the memory task, Experiment 4 showed that attention was required for the maintenance of absolute depth information, while relative depth memory involved minimal attention engagement. These findings indicate separate storage mechanisms for the two types of depth information: Absolute depth, especially fine information, is poorly maintained in a fragile visual store, whereas relative depth, which is encoded coarsely, involves both a robust verbal store and a visual store. (PsycInfo Database Record (c) 2025 APA, all rights reserved).