ORIGINAL PAPER Information seeking by orangutans: a generalized search strategy? Heidi L. Marsh • Suzanne E. MacDonald Received: 14 March 2011 / Revised: 8 July 2011 / Accepted: 31 August 2011 Ó Springer-Verlag 2011 Abstract 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 demon- strates 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 con- ditions, 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. Keywords Metacognition Á Information Á Knowledge states Á Orangutans Introduction Over the past 15 years, metacognition, or an awareness of one’s own cognitive contents, has begun to receive empirical investigation among comparative cognitive researchers (e.g. Call and Carpenter 2001; Foote and Crystal 2007; Fujita 2009; Hampton 2001; Inman and Shettleworth 1999; Kornell et al. 2007; Redford 2010; Smith et al. 1995; Suda-King 2008; for a review, see Smith 2009). Investigating such a phenomenon in animals is not an easy task, because much of what we know from the human literature comes from verbal reports (Nelson 1996), which are clearly not an option with animals. Nonetheless, the possibility that this capacity might exist outside of humans has important practical, evolutionary, and ethical implications, both in terms of the way we view our non- human animal counterparts, and our place among them. Thus, researchers have designed increasingly innovative methods to assess whether animals might be aware of their knowledge states. As a starting point, Smith and colleagues pioneered research on so-called ‘uncertainty monitoring’ in several species, including rats, bottlenosed dolphins, monkeys, and humans (Shields et al. 1997; Smith and Schull 1989; Smith et al. 1995, 1997). In those studies, animals were presented with perceptual tasks in which they had to make a dis- crimination. On some trials, the discrimination was more difficult due to increased stimulus ambiguity, as stimuli approached the discriminatory threshold. Animals were given the option to continue the trial or to escape from it. If they escaped, they did not get the chance to win the large reward associated with a correct response, but they also avoided the penalty of an incorrect response. For most of the species tested, subjects showed a greater propensity to escape ambiguous trials as opposed to less difficult trials. Electronic supplementary material The online version of this article (doi:10.1007/s10071-011-0453-y) contains supplementary material, which is available to authorized users. H. L. Marsh Á S. E. MacDonald (&) Department of Psychology, York University, 297 Behavioural Science Building, Toronto, ON M3J 1P3, Canada e-mail: suzmac@yorku.ca 123 Anim Cogn DOI 10.1007/s10071-011-0453-y