We now have the collapse of yet another supposed barrier between the minds of men and monkeys. It is known that monkeys can recognize pictures they have seen before (in experiments in which they are rewarded for doing so), but Basile and Hampton have devised a further behavioral protocol that let's them demonstrate recall, holding in mind an object without actually seeing it. Language is not necessary — either for having the ability to recall, or for proving it to an experimenter. Here is their abstract:
If you draw from memory a picture of the front of your childhood home, you will have demonstrated recall. You could also recognize this house upon seeing it. Unlike recognition, recall demonstrates memory for things that are not present. Recall is necessary for planning and imagining, and it can increase the flexibility of navigation, social behavior, and other cognitive skills. Without recall, memory is more limited to recognition of the immediate environment. Amnesic patients are impaired on recall tests, and recall performance often declines with aging. Despite its importance, we know relatively little about nonhuman animals' ability to recall information; we lack suitable recall tests for them and depend instead on recognition tests to measure nonhuman memory. Here we report that rhesus monkeys can recall simple shapes from memory and reproduce them on a touchscreen. As in humans , monkeys remembered less in recall than recognition tests, and their recall performance deteriorated more slowly. Transfer tests showed that monkeys used a flexible memory mechanism rather than memorizing specific actions for each shape. Observation of recall in Old World monkeys suggests that it has been adaptive for over 30 million years and does not depend on language.Here is the basic protocol, as described by Nicholas Bakalar's NYTimes summary:
Researchers trained five rhesus monkeys. On a 5-by-5-inch grid on a computer screen, the monkeys were shown a shape consisting of three adjacent squares, one blue and two red in various patterns...After a moment, the red squares disappear, and the blue square moves to a different box on the grid. After another delay, the monkey has to restore the red squares to their original places in relation to the blue one by pressing on the correct boxes of the grid. When he does so successfully, he gets a food reward.