Object substitution masking for an attended and foveated target.

A central assumption of models proposed to explain object substitution masking (OSM) is that the phenomenon arises only when attention is distributed across several possible target locations. However, recent work has questioned the role of attention in OSM, suggesting instead that ceiling effects might explain the apparent interaction between spatial attention and masking. Here the authors report definitive evidence that OSM does not depend upon attention being distributed over space or time. In 2 experiments, they demonstrate reliable OSM for constant, foveal presentations of a single target stimulus. Crucially, in their design participants' attention was always focused on the target, thus discounting the hypothesis that a key requirement for OSM is distributed attention. The findings challenge how OSM is conceptualized in the broader masking literature and have important implications for theories of visual processing.