Typical studies of object substitution masking (OSM) employ a briefly presented search array. The target item is indicated by a cue/mask that surrounds but does not overlap the target and, compared to a common offset control condition, report of the target is reduced when the mask remains present after target offset. Given how little observers are able to report of item arrays that have been presented for several hundred milliseconds (Wolfe, Reinecke, & Brawn, 2006), it might be expected that OSM would also be found if the search array is presented for an extended period before the target is cued by onset of a mask surrounding it. However, Gellatly, Pilling, Carter, and Guest (2010) reported that under these conditions OSM is greatly reduced. This target duration effect could be due to identity information about the search array having been loaded into VSTM during the precue period. Alternatively, it can be understood in terms of target/mask individuation and the object updating account of OSM (Lleras & Moore, 2003). The present article reports three experiments investigating which of these possibilities provides the better explanation of the effect of target duration on OSM. The results support the individuation hypothesis and, thereby, the object updating account of OSM. (Contains 5 figures and 1 footnote.)