Object-substitution masking (OSM) occurs when a mask, such as four dots that surround a brief target item, onsets simultaneously with the target and offsets a short time after the target, rather than simultaneously with it. OSM is a reduction in accuracy of reporting the target with the temporally trailing mask, compared with the simultaneously offsetting mask. It has been thought that OSM occurs only if attention cannot be rapidly focused, or prefocused, on the target location. One line of evidence for this is a reported interaction between target display set size and the duration of the trailing mask. We analyze the evidence for this interaction and suggest it occurs only as an artifact of data being compressed by a ceiling effect. We report six experiments that support this interpretation by showing that the interaction is always absent unless a ceiling effect is induced. We go on to analyze other evidence to support the notion that attention modulates OSM, and argue that in each case, the data either reflect a ceiling effect or can be explained in another way. Our data and our analyses of the existing literature have strong implications for how OSM should be conceptualized. (Contains 13 figures and 1 footnote.)