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Object permanence in three species of primates: Rhesus monkeys (Macaca mulatta), squirrel monkeys (Saimiri sciureus), and orangutans (Pongo pygmaeus)

Sandra Therese De Blois, University of Massachusetts Amherst


The goal of this dissertation was to test the hypothesis that great apes can solve both visible and invisible displacements, whereas monkeys can solve only visible displacements. First, rhesus monkeys, squirrel monkeys, and orangutans received visible and invisible displacement tests that correspond to Stages 4, 5, and 6 of object permanence. Monkeys and orangutans were successful on the visible displacement tests. Most orangutans were successful on all invisible displacement tests except the double displacements. The monkeys were not successful on invisible displacement tests and they had a location preference. Subsequent testing revealed that (1) rhesus monkeys eventually solved single and control invisible displacements, (2) two rhesus monkeys eventually solved double displacements, (3) using a familiar containment device improved performance on invisible displacements and (4) most orangutans eventually solved double invisible displacements when the object was concealed in a cup. In the second part of the dissertation, I determined if poorer performance on invisible displacements was related to increased memory requirement. The primates received three types of problems that had equivalent memory requirement. On Invisible transfer problems, the object was hidden in a box and then invisibly transferred to another box, whereas on Visible transfer problems the object was visibly transferred, and on No transfer problems, it was not transferred. The rhesus monkeys and the squirrel monkeys solved the Visible and the No transfer problems. Only one monkey was successful on the Invisible transfer problems. Given that all problems had equivalent memory requirements, this variable cannot account for poorer performance on Invisible transfer problems. Most orangutans solved all three types of problems. Nevertheless, the performance of the orangutans on Invisible transfer problems was poorer than that on the other problems. Next, cueing sessions were instituted during which a clear box was used in order to allow the primates to see if and how the object was transferred. Then, the primates were re-tested on the three problems. Cuing helped monkeys and orangutans find the object on Invisible transfer problems. In summary, the results of this dissertation indicated that overall, the orangutans outperformed the monkeys on invisible displacements. However, a few orangutans performed as poorly as the monkeys on invisible displacements, and a few monkeys performed as well as the orangutans. Thus, individual differences must be taken into account to adequately portray the distribution of object permanence skills in non-human primates.

Subject Area

Cognitive therapy|Psychology|Experiments

Recommended Citation

De Blois, Sandra Therese, "Object permanence in three species of primates: Rhesus monkeys (Macaca mulatta), squirrel monkeys (Saimiri sciureus), and orangutans (Pongo pygmaeus)" (1997). Doctoral Dissertations Available from Proquest. AAI9721442.