Object individuation, the capacity to determine whether two perceptual encounters belong to the same object or two different objects, is one of the most basic cognitive abilities and provides a foundation for infants’ understanding of the physical world. Yet very little work has been done to explore infants’ use of auditory information to individuate objects. The first research to investigate infants’ use of sound information to individuate objects was reported by Wilcox et al. (2006), who used a violation-ofexpectation task to examine the extent to which 4.5-month-olds use differences in sound to individuate objects. The results suggested that 4.5-month-olds use property-rich sounds (sounds intimately related to an objects’ physical, amodal properties) but not property-poor sounds (sounds that are more contrived) to distinguish the identity of objects involved in occlusion events. The current study investigated infants’ sensitivity to these two types of sounds within the context of a search task. Three experiments were conducted with infants aged 5 to 7 months. The outcome of these experiments builds and extends on the findings of Wilcox et al. in three ways. First, converging evidence was obtained, using a search task, that young infants are more sensitive to property-rich than property-poor sounds. Second, more detailed information was obtained on infants’ interpretation of samesounds events (two identical, rather than two different, sounds). Finally, possible explanations for infants’ greater sensitivity to property-rich sounds were assessed. The outcome of these studies, collectively, provides insight into the types of sounds that infants use to identify objects and the reasons why some sounds are more salient to infants than others.

This study examined object permanence in Sumatran orangutans (Pongo abelii), Western lowland gorillas (Gorilla gorilla gorilla), and black-and-white-ruffed lemurs (Varecia variegata) at Zoo Atlanta. A literature review reveals two main issues with object permanence research in non-human primates. One of the issues is that it is difficult to make valid comparisons between different species because very few studies have been conducted using appropriate controls. Thus, one of the goals of this study was to conduct control trials for all tasks in the traditional object permanence test battery, in order to reliably assess and compare performance in the species under study. The second issue is concerned with the finding that all of the non-human primate species tested so far have failed one of the more difficult tasks in the test battery, namely the non-adjacent double invisible displacement task. It has been hypothesized that this performance limitation is a result of the manner in which the task is presented. Thus, the second goal of this study was to modify the existing methodology and present the task to gorillas and orangutans in locomotive space to see if performance improves. This is the first study to present this task to non-human primate species in locomotive space. This study found that orangutans were the only species to reliably pass most tasks in the traditional object permanence test battery. Black-and-white ruffed lemurs failed most visible and invisible displacement tasks. Owing to the small sample size of gorillas in this study, further research is required before any firm conclusions can be made about the ability of this species to solve visible and invisible displacement tasks in the traditional object permanence test battery. Presenting the boxes in locomotive space to gorillas and orangutans did not improve performance on the non-adjacent double invisible displacement task. Further research is required to resolve the question of whether this performance limitation is a result of the manner in which the task was presented.

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