Species and Individuals in the Perceptual World of Monkeys

When a monkey is given the choice of looking at a novel picture or a blank white screen he shows an initial preference for the picture which usually abates within about 200 seconds; if the picture is then changed for another his preference revives. The level of preference for the second picture depends on the degree to which it is perceived as ‘similar’ to or ‘different’ from the first. This technique has been used to investigate how rhesus monkeys classify pictures of animals, and in particular the extent to which they differentiate between individual animals of the same species. Two classes of animal pictures were used, namely pictures of other rhesus monkeys and pictures of domestic animals. The results indicate that inexperienced monkeys, to whom the domestic animals are unfamiliar, treat individual domestic animals of the same species as being closely similar; they treat individual monkeys, on the other hand, as being quite different from each other. Experienced monkeys, however, who have been exposed over the course of 6 months to many further pictures of animals, come to treat all individuals as different from each other, so that one pig, say, is now seen as being as different from another pig as is one monkey from another.