In Nonhuman Primates
Cognitive skills related to the understanding of an unseen object’s continued existence in nonhuman primates.
Object permanence is the understanding that an object does not cease to exist just because it can no longer be directly perceived. This is a fundamental concept studied in the field of developmental psychology, the subfield of psychology that addresses the development of infants’ and children’s social and mental capacities. There is not yet scientific consensus on when the understanding of object permanence emerges in human development. Jean Piaget (1952) claimed that children progressively obtain object permanence during the first 2 years of life and that, in its final stages, object permanence extends beyond simply understanding that an unseen object continues to exist to being able to follow the trajectory of an object after its path becomes occluded. Early studies on object permanence were conducted by hiding objects behind screens or in boxes and observing whether infants made a search response and generally supported Piaget’s assertion that object permanence is achieved in stages. While some researchers think object permanence is a skill that is gained through innate developmental processes (e.g., Baillargeon 2008), others claim it is a learned skill (e.g., Cohen et al. 2002).
Object Permanence Tasks
Studies examining object permanence in animals have used a combination of visible and invisible tasks. Visible tasks involve moving the search object from to and from hiding locations in the experimenter’s open hand or in a transparent “displacer,” while invisible tasks involve moving the search object moving to and from hiding locations in an opaque displacer. Both types of tasks may involve either single displacements (i.e., the search object is moved only once and in that hiding location) or double displacements (i.e., the search object is moved first to one hiding location, then from that hiding location to a second hiding location). Single visible displacement tasks provide evidence of whether the subject recognizes that the search object exists even when it is unseen. Double visible displacement tasks provide evidence of whether the subject has the ability to track a visibly moving object. Invisible displacement tasks provide evidence of whether the subject has the ability to track the trajectory of an object once it is out of sight.
Tomasello and Call (1997) describe object permanence in nonhuman primates as a type of “physical cognition,” which is a term describing the ability to manipulate, categorize, and quantify objects. These complex cognitive skills may be necessary for foraging and extracting food from hidden locations and thereby represent an evolved psychological mechanism (Tomasello and Call 1997). Evidence that object permanence, in particular, is an innate skill is provided by research demonstrating that differences in object permanence between members of the same primate species are small (Call 2000). Object permanence is a cognitive skills shared by a wide variety of primate species. Longitudinal testing of macaque monkeys showed that such skills advance over time providing evidence for an innate mechanism shared between humans and other primates (Hall-Haro et al. 2008). Numerous ape and monkey species have been able to successfully solve both visible and invisible displacement tasks. However, some highly controlled studies using a series of nine increasingly difficult visible and invisible displacement tasks showed differences between species. Great ape species such as chimpanzees and orangutans have solved all displacements tasks whether visible or invisible and no matter the number of displacements (Barth and Call 2006), while monkey species such as marmosets (Mendes and Huber 2004) and cotton top tamarins (Neiworth et al. 2003) failed invisible displacement tasks.
All primate species have demonstrated some degree of object permanence skills, but those species most closely related to humans demonstrate object permanence abilities that are more comparable to humans.