It has been proposed that the ability of a visual noise mask to stop processing of a target stimulus under backward-masking conditions be gauged by its ability to obscure the target when both stimuli are viewed simultaneously. To assess the usefulness of this proposal, 3 noise masks which varied greatly in effectiveness under conditions of simultaneity were also used as backward masks with 30 female undergraduate Ss. The resulting backward-masking functions were identical for all masks, indicating that the suggestion was not practical for the conditions of this experiment. The findings are interpreted as favoring a process-stopping theory of masking over an integration theory. (PsycINFO Database Record (c) 2006 APA, all rights reserved)