Recent empirical work has suggested that some species of non-human primates may be aware of their knowledge states. One finding to support this claim is that they seek information about the location of a hidden food item when they are unsure of its location, but not when they already know where it is, which purportedly demonstrates metacognition. However, this behaviour may instead reflect a generalized search strategy, in which subjects reach for food when they see it, and search for it when they do not. In this experiment, this possibility was addressed by testing orangutans in three conditions in which the location of a food item was sometimes known to subjects, and other times required subjects to visually seek the missing information. All subjects exhibited behaviour consistent with a metacognitive interpretation in at least two of the three conditions. Critically, in two of the conditions, subjects refrained from seeking visual information, and correctly found the hidden food item without ever seeing it, using inference by exclusion. The results suggest that animals that succeed in this information-seeking task are not merely acting according to a generalized search strategy, and instead seek information adaptively according to their knowledge states.

Recent research has examined whether animals possess metacognition, or the ability to monitor their knowledge states. However, the extent to which animals actively control their knowledge states is still not well delineated. Although organisms might be capable of seeking information when it is lacking, it does not mean that it is always adaptive to do so. In the present set of experiments, we examined the flexibility of this behavior in captive orangutans (Pongo abelii; two adults and one juvenile) in a foraging task, by varying the necessity of information-seeking, the cost associated with it, the likelihood of error, and the value of the reward. In Experiment 1, subjects searched for information most often when it was "cheapest" energetically. In Experiment 2, subjects searched for information most often when the odds of making an error were the greatest. In Experiment 3, subjects searched for information more when the reward was doubled in value. In Experiment 4, adult subjects adapted to risk/benefit trade-offs in their searching behavior. In every experiment, subjects sought information more often when they needed it than when they already knew the solution to the problem. Therefore, the current research suggests that information-seeking behavior in orangutans shows a sophisticated level of flexibility, comparable to that seen in human children, as they appear to "play the odds" when making the decision to seek information or not.

Previous research has demonstrated that Old World primates (both apes and monkeys) seek information about the location of a hidden food item, unless they are privy to the hiding process. This has been cited as evidence of metacognition. However, these results could also be interpreted using non-metacognitive accounts, including a generalized search response to uncertainty, in which subjects reach for food when it is seen, or search for food until it is spotted. In the present research, lion-tailed macaques were tested on an object-choice task. Conditions varied with respect to the visibility of the baiting process, and whether the location of the hidden food could be inferred by logical exclusion. Additionally, the hidden food could be located visually before a choice was made, by peering under the objects through a Plexiglas tray. Across conditions, monkeys consistently looked for the food when it had not been seen, even if its location could be inferred, despite the fact that these monkeys are capable of inference by exclusion. This suggests that apparently 'metacognitive' information seeking in monkeys may instead reflect a generalized search strategy. Alternatively, it is possible that monkeys only have metacognitive access to certain types of knowledge, including that obtained visually. Results are discussed with respect to the likelihood of metacognition in this species and the evolutionary emergence of metacognition across species.

The extent to which categorization of natural classes in animals reflects a generalization based on perceptual similarity versus an abstract conceptual representation remains unclear. Here, two experiments were conducted to identify the perceptual features used by orangutans when categorizing pictures. In Experiment 1, subjects were trained and tested for transfer on a concrete discrimination (gorillas or orangutans vs. other primates). Analysis of performance on both positive and negative exemplars revealed that performance was best on photos with faces, particularly close-ups. Moreover, error trials did not seem to reflect instances of mistaken identity, but rather, exemplars that may have been distracting for other reasons, such as novel coloration or morphology. In Experiment 2, photos were modified to test the effects of various features. Color modifications caused the biggest decrease in performance, and eye modifications also affected performance deleteriously. Therefore, two perceptual features, namely eye regions and color, played a key role in subjects' ability to categorize. However, performance based on an underlying concept cannot be ruled out, because both of these features are highly relevant in terms of defining category membership. Although a subset of features was identified as playing a key role in categorization, these features differed depending on whether feature-use was studied indirectly, as in Experiment 1, or directly, as in Experiment 2.

In previous research, great apes and rhesus macaques have demonstrated multiple apparently metacognitive abilities, whereas capuchin monkeys have not. The present experiment investigated whether at least a rudimentary form of metacognition might be demonstrated in capuchins if a simplified metacognitive task was used. Capuchins (Cebus apella) were required to locate a food reward hidden beneath one of two inverted cups that sat on a Plexiglas tray. In some conditions, the capuchins were shown where the food was hidden, in others they could infer its location, and in yet others they were not given information about the location of the food. On all trials, capuchins could optionally seek information about the food's location by looking up through the Plexiglas beneath the cups. In general, capuchins did this less often when they were shown the food reward, but not when they could infer the reward's location. These data suggest that capuchins-if metacognitive-only metacognitively control their information seeking in some conditions, particularly those in which information is presented in the visual domain. This may represent a rudimentary version of metacognitive control, in comparison with that seen in great apes and humans.