Visual working memory is the mechanism supporting the continued maintenance of information after sensory inputs are removed. Although the capacity of visual working memory is limited, memoranda that are spaced farther apart on a 2D display are easier to remember, potentially because neural representations are more distinct within retinotopically-organized areas of visual cortex during memory encoding, maintenance, and/or retrieval. The impact of spatial separability in depth on memory is less clear, even though depth information is essential to guide interactions with objects in the environment. On one account, separating memoranda in depth may facilitate performance if interference between items is reduced. However, depth information must be inferred indirectly from the 2D retinal image, and less is known about how visual cortex represents depth. Thus, an alternative possibility is that separation in depth does not attenuate between-item interference; separation in depth may even impair performance, as attention must be distributed across a larger volume of 3D space. We tested these alternatives using a stereo display while participants remembered the colors of stimuli presented either near or far in the 2D plane or in depth. Increasing separation in-plane and in depth both enhanced performance. Furthermore, participants who were better able to utilize stereo depth cues showed larger benefits when memoranda were separated in depth, particularly for large memory arrays. The observation that spatial separation in the inferred 3D structure of the environment improves memory performance, as is the case in 2D environments, suggests that separating memoranda in depth might reduce neural competition by utilizing cortically separable resources.
Spatial Separability in Hub Location Problems with an Application to Brain Connectivity Networks
