Abstract
Adult humans, human infants, and non-human primates share the capacity to visually track small numbers of objects across time and occlusion. Previous studies have examined the limits of the object file system in human adults. Here, we explore whether non-human primates' object tracking abilities are subject to the same constraints as that of adult humans. Specifically, we examine whether object tracking in one prosimian species, the brown lemur (Eulemur fulvus), is affected when the objects to be tracked behave either non-rigidly or non-cohesively. We presented lemurs with a series of expectancy violation studies involving simple 1+1 addition events in which we varied the properties of the objects involved. Lemurs successfully enumerated the two objects when those objects were rigid cohesive individuals, but failed to enumerate similar looking non-rigid piles of sand. However, lemurs successfully enumerated non-cohesive objects that broke into multiple pieces. These results are discussed in light of recent theories about object processing in human infants and adults.