Smithsonian National Zoological Park l Friends of the National Zoo



Orangutan Memory

Karyl B. Swartz Lehman College, City University of New York

While a great deal is known about human memory, we know little about how memory works in nonhuman primates. It appears that nonhuman primates rely on memory in such everyday tasks as foraging for food and recognizing familiar individuals. The purpose of this research is to investigate memory in orangutans.

When humans are asked to memorize a list of unrelated words in a series of trials, they begin to organize the words in idiosyncratic clusters. This phenomenon has been termed subjective organization, since the nature of the associations are unique to each person. This spontaneously-developed organization strategy increases the number of words that a person can remember. The crucial parts of this task are that the words are unrelated and that it requires free recall on the part of the person being tested. Unrelated words are necessary to prevent organization based on semantic categories (which we know humans will use). Free recall, in which the person is free to produce the list words in any order, allows the researcher to see what strategies the person used to organize the words.

Subjective organization in nonhuman primates has not been studied, probably because of the difficulty in making a free recall task with animals that can't speak. However, it is possible to create a recognition memory task that allows animals that can't speak to produce the list items in any order. In this task, list items (photographs) are presented on a touch-screen video monitor. The orangutan is required to touch each item as it appears, in order to show that the item has been seen. Following the presentation of the list, all the list items appear in a random arrangement on the screen along with a set of items that were not on the list. The orangutan must touch the list items, and only the list items, in any order. Once all the list items have been touched, the orang utan is rewarded, and the next trial begins.

The first question being addressed is whether orang utans will develop an organizing strategy for long lists. In humans, the ability to develop such memory strategies does not begin to appear until the age of six or seven. It is not until ten or eleven that humans can utilize such strategies consistently and efficiently. If orang utans are able to develop an organizational strategy to help them learn a list, it would show that they are capable of sophisticated memory strategies.

Even if the orangutans fail to show signs of subjective organization, we can find out if they can use category information to organize lists. In other words, we can present lists that are made up of items that can be classified into categories (foods, insects, trees, animals). We suspect that orangutans will be able to use such category information to organize lists. If we find that these animals do this, we will be able to use that as a stepping stone to further explore the thinking ability of these animals.