More Wynne & Udell (2013):
Michael D’Amato and Paul van Sant (1988) trained Cebus apella monkeys to discriminate slides containing people from those that did not. The monkeys readily learned to do this. Then the monkeys were presented with novel slides they had never seen before which contained either scenes with people or similar scenes with no people in them. Here also the monkeys spontaneously classified the majority of slides correctly. So far, so good – clear evidence that the monkeys had not just learned the particular slides they had been trained on but had abstracted a person concept from those slides that they then successfully applied to pictures they had never seen before.
Or had they? D’Amato and van Sant did not stop their analysis simply with the observation that the monkeys had successfully transferred their learning to novel slides – rather they went on to look carefully at the kinds of errors the monkeys had made. Although largely successful with the novel slides, the monkeys made some very puzzling mistakes. For example, one of the person slides that the monkeys had failed to recognize as a picture of a human being had been a head and shoulders portrait – which, to another human, is a classic image of a person. One of the slides that the monkeys had incorrectly classified as containing a human had actually been a shot of a jackal carrying a dead flamingo in its mouth; both the jackal and its prey were also reflected in the water beneath them. What person in her right mind could possible confuse a jackal with a flamingo in its mouth with another human being?
The explanation for both these mistakes is the same: the monkeys had generalized on the basis of the particular features contained in the slides they had been trained with rather than learning the more abstract concept that the experimenters had intended. The head and shoulders portrait of a person lacked the head-torso-arms-legs body shape that had been most common among the images that the monkeys had been trained with, and consequently, they had rejected it as not similar enough to the positive image they were looking for. Similarly, during training, the only slides that had contained flashes of red happened to be those of people. Three of the training slides had contained people wearing a piece of red clothing, whereas none of the nonperson slides had contained the color red. Consequently, when the jackal with prey slide came along during testing, it contained the color red, and so the monkeys classified it as a person slide.