One of the most basic cognitive capacities people possess is the ability to represent the world in terms of distinct objects. The outcome of this process determines how people think about and act on those objects. The problem of object individuation-determining the number of separate and distinct entities present in an event-has long been a topic of interest to psychologists. This topic has recently received a great deal of attention from infant researchers (Aguiar & Baillargeon, in press; Leslie, Xu, Tremoulet, & Scholl, 1998; Spelke, Kestenbaum, Simons, & Wein, 1995; Tremoulet, Leslie, & Hall, 20001; Wilcox, 1999b; Wilcox & Baillargeon, 1998a, 1998b; Wilcox & Schweinle, 2002a, 2002b; Xu & Carey, 1996). Much of this research has focused on the kind of information that infants use to individuate objects in occlusion events.