Do You Know What I See ? Visual Perspective Taking in Nonhuman Animals

Visual perspective taking is not only an essential skill for effective visual communication (Emery, 2000), but also an indicator of the presence of social cognition and theory of mind in nonhuman animals (Heyes, 1998). In this paper, we review some of the prominent experimental paradigms and research findings on visual perspective taking in various nonhuman species, such as the begging task, the guesser-knower task, and competitive paradigms. However, in spite of the plethora of research that has been done, it still remains inconclusive as to whether or not nonhuman animals are capable of visual perspective taking due to the varied and contradictory findings of past studies. Several possible explanations exist for these discrepancies, which include varying definitions of the term “perspective taking,” the lack of attention given to species-specific ecological validity, confounding variables such as associative learning and visual-spatial skills, differences in the experimental set-up and release time in competitive paradigms, and the lack of close replications. It is suggested that future research should aim to overcome the challenges of this area of study so as to be able to develop an empirically sound understanding of visual perspective taking in nonhuman animals. The social intelligence hypothesis (Kummer, Daston, Gigerenzer, & Silk, 1997) or the Machiavellian intelligence hypothesis (Byrne & Whiten, 1988) proposes that due to the social competition for resources and mates, evolution has favoured individuals who were able to successfully predict and manipulate the behaviour of others. One mental operation that is suggested to have evolved out of this social competition is the ability to understand the perspectives and psychological states of others (MacLean & Hare, 2012). Interestingly, the social intelligence hypothesis is not unique to humans, as it is proposed that social intelligence can be expected to have evolved in any species that display the following criteria: large brain relative to body size, the presence of large and long-lasting social groups, and a long life span (Tomonaga, Uwano, Ogura, & Saito, 2010). A number of animal species meet these criteria, such as certain primates, corvids, bats, elephants, hyenas, and cetaceans (Tomonaga et al., 2010). This then poses the question: are nonhuman animals capable of understanding the mental states of others? Theory of mind refers to “the capacity to make lawful inferences about the behaviour of other agents on the basis of abstract, theory-like representations of the causal relation between unobservable mental states and observable states of affairs” (Penn & Povinelli, 2007, p. 732). However, because theory of mind is a phenomenon that cannot be directly perceived, but rather, must be inferred from behaviour (Povinelli, Dunphy-Lelii, Reaux, & Mazza, 2002), a major challenge to its study is identifying behaviours that provide sufficient evidence for the existence of such higher order cognitions. Heyes (1998) proposes that among the most promising approaches to the study of theory of mind and social cognition among animals are perspective-taking tasks. Visual perspective taking is defined as “the ability to appreciate what others can and cannot see” (Held, Mendl, Devereux, & Byrne, 2001, p. 1338). Researchers in the field of comparative psychology have long been interested in understanding visual perspective taking among nonhuman animals, as being able to perceive the attentive state of another is an essential skill for effective visual communication (Emery, 2000). This is because successful transmission of a Yale Review of Undergraduate Research in Psychology 33 signal is not only dependent on the sender’s ability to produce the signal, but also on the recipient’s ability to perceive the signal (Emery, 2000). This is particularly critical for visual communication, whereby the receiver must not only be in close proximity, but must also be oriented toward, and attentive to, the sender (Gacsi, Miklosi, Varga, Topal, & Csanyi, 2004). As such, determining whether nonhuman animals are capable of visual perspective taking, and understanding the various cues that they use to infer the perspective and attentive state of another would shed light on how these species are able to successfully communicate in the wild. However, beyond its functional importance, visual perspective taking also bears inferential significance, as the ability to take on the visual perspective of others is said to be one of the most promising indicators of the presence of social cognition and theory of mind in nonhuman animals (see Heyes, 1998). Thus, given that visual perspective taking could potentially unveil the answer to the pivotal question of the existence of theory of mind in nonhuman species, it is no wonder then that researchers have consistently been striving to develop experimental methodologies that are capable of adequately testing for visual perspective taking in nonhuman animals. While much is already known about the development of visual perspective taking in humans, concrete evidence of such ability in nonhuman species still remains elusive despite extensive research (Heyes, 1998). In a review of experimental methodology for primate social cognition, Hare (2001) highlights that arguably the biggest challenge of studying perspective taking among nonhuman species is that animals are nonverbal. In human developmental psychology, the study of perspective taking has relied almost exclusively on participants’ ability to verbally communicate what he or she knows, such as in the classic “false-belief” task that is commonly used among children (Hare, 2001). In contrast, researchers of nonverbal animals must rely on behavioural measures through which perspective taking abilities can be convincingly inferred (Hare, 2001). As such, there is often no way to be certain that the behaviours demonstrated are the result of the ability to understand what others can and cannot see, and thus, the findings of such studies are often subject to many alternative explanations. In light of this, researchers have sought to develop various experimental paradigms, all with the common goal of attempting to better understand visual perspective taking among nonhuman animals. One of the oldest approaches to studying visual perspective taking among animals is the guesser-knower task that was first introduced by Premack in 1988. In this task, the subject watches as an experimenter places a piece of food into one of two containers that are located behind an opaque screen such that the subject is unable to see directly which of the containers is being baited. The subject also has visual access to two trainers – one trainer (‘knower’) can see which container is being baited, but the other (‘guesser’) cannot because the screen is blocking its view. Once the container is baited, the subject is then allowed to ask one of the two trainers for ‘advice’ on which container has the food, and the trainer responds by pointing to one of the two containers, after which the subject choses between the two containers. The critical test in this task is whether or not the subject would be able to discriminate which of the two trainers had witnessed the baiting and therefore knew where the food was. In Premack’s (1988) original study, four chimpanzees were tested; two consistently chose the informed trainer (‘knower’), while the other two did not have a clear preference for either trainer. Despite the small sample size and the inconclusive findings, Premack’s (1988) study was nonetheless a momentous one, as the basic approach to the guesser-knower task has continued to be used in the study of visual perspective taking of many other species (see Cooper et al., 2003; Povinelli & Eddy, 1996; Povinelli, Nelson, & Boysen, 1990). However, in spite of its widespread use, the guesser-knower task is not without its criticisms. Among the major limitations to this approach is that success on the task can be attributed to more parsimonious explanations of associative learning, and thus, may not be an adequate test of higher order cognition (Held et al., 2001). In addition, the use of human trainers also poses further threat to the validity of this task. Firstly, by using humans instead of conspecifics, experimenters are expecting subjects to be able to interpret the behaviours of another species (Held et al., 2001) – this is not only irrelevant to successful visual perspective taking among conspecifics, but may also be a tall order. Second, because both trainers know their roles as either the ‘guesser’ or the Yale Review of Undergraduate Research in Psychology 34 ‘knower,’ it is hard to ascertain that they are not unconsciously providing cues to the subject as to which of them is the ‘correct’ choice. Seeking to refine the guesser-knower task and examine visual perspective taking among a lesser-studied species, Held et al. (2001) conducted a study using domestic pigs. In this study, ten pigs were trained to move from a starting point into one of four corridors that they had previously seen a human enter while carrying a bucket containing food. During these training sessions, subjects received food rewards for choosing the right corridor. In subsequent transfer tests, the subject being tested could not see the corridors, but could see two conspecifics in individual start boxes on its left and right – one had visual access to the corridors and the baiting, while the other did not. The two companion pigs were released and the subject was observed to see which of the two companions it followed. Subjects were not rewarded for their performance on the transfer tests, to minimize the possibility of associative learning (Held et al., 2001). Furthermore, because the conspecifics did not know which was the correct answer for the test subject, it is unlikely that either the ‘guesser’ or the ‘knower’ could have provided cues to the subject (Held e