Self recognition and theory of mind

Mirrors provide a novel and rich source of information about social cognition in animals. The behavior of an animal toward its mirror image suggests much about the animal's understanding of the source of that image. Many animals such as cats and dogs, when first encountering their own mirror image, behave as though they have encountered a stranger of their own species. They may show aggressive behavior such as threats, or they may attempt to play and to reach around the mirror as though attempting to find the other animal. With time, the dog or cat will ignore the mirror image and no longer attempt to engage the reflection in social interaction. For the most part, monkeys behave in a similar way to their mirror image.

Great apes, however, appear to come to understand the nature of the mirror image. That is, with experience, they behave as though they understand that it is their own body that is reflected in the mirror. The phenomenon is referred to as mirror self-recognition (MSR) and has been of interest to researchers in primate cognition for decades. Chimpanzees were the first nonhuman species to show evidence of MSR. When provided with daily exposure to a mirror outside their enclosure, individual chimpanzees initially responded to the mirror image with social behaviors suggesting that the mirror image was perceived of as an unfamiliar chimpanzee. Threat behaviors such as head bobbing, charging the mirror, and vocalizing were common. After some time, however, the social behaviors waned and the chimpanzees began to direct behavior toward their own bodies while looking into the mirror. They groomed and investigated parts of their bodies, such as the face, that were invisible to them without the use of the mirror. Using the mirror to guide their hands, these animals groomed their eyes, picked their teeth, inspected their genital areas, and also made faces while watching in the mirror.

The behaviors directed to their own bodies, termed self-directed behaviors, appeared to indicate that the animals recognized themselves in the mirror. To test this interpretation, the chimpanzees were anesthetized and an odorless red mark was placed on one eyebrow and one ear, in a location where the chimpanzee could not see the mark without the use of the mirror. When the animals awoke from the anesthesia they were presented with the mirror, and all four animals touched the mark on their brow, using the mirror to guide their fingers to the mark. The importance of this response, directing their hand to the mark on their own body rather than to the mark on the mirror image, suggests that the animals indeed recognized themselves in the mirror.

Since the initial report in 1970 of this phenomenon in chimpanzees, individuals from the other great ape species have shown MSR by demonstrating self-directed behavior or by passing the mark test, but not all individuals of these species show the capacity. There are clear individual differences based partly on age. Like humans, chimpanzees develop the ability to show mirror self-recognition. Beginning at about 24-30 months of age young chimpanzees will touch a mark on their brow using the mirror to guide the touch and the ability is generally quite evident by the age of four. Human children studied under controlled conditions do not show the capacity for mirror self-recognition until about 15 months of age at the earliest, with most achieving this developmental milestone by 24 months.

There is some evidence that dolphins are capable of mirror self-recognition, and gibbons also may have this capacity. However, other animals have not clearly shown evidence of mirror self-recognition. It may be a species difference, or it may be the case that with additional research the apparent discontinuity will be resolved. The implications for evolutionary development of self in humans are apparent, although interpretations of this phenomenon are disputed. At the most extreme, a rich interpretation of self-recognition in animals suggests an understanding of the self as an entity, perhaps similar to humans' sense of self or self-concept. However, the ability to understand the nature of a mirror image and to direct behavior back to one's own body does not necessarily imply such a rich interpretation. The distribution of this capacity and its interpretation are open questions subject to ongoing empirical investigation and theoretical debate.

The ability to recognize oneself may be related to the ability to understand another individual's knowledge state, which represents a more complex cognitive ability. This phenomenon is called "Theory of Mind" and refers to an individual's ability to understand the perspective or the "state of mind" of another. It forms the basis for such complex social strategies as intentional deception. In order to deceive another by providing incorrect information, the actor must know something about the other's perspective and expectations and what information to provide (or withhold) as deception. Many instances of deception have been reported from observations of apes and monkeys in the field and in the laboratory, and the extent to which these deceptive incidents are based on the perspective-taking capacity implied in Theory of Mind is still an open question. It is clear that animals behave in ways that suggest that they are taking into account the knowledge state of others. Whether they are or not is still an active area of research in animal cognition.

The initial description of Theory of Mind was based on the ability of Sarah, a language-trained chimpanzee, to solve problems for a human who was in some state of distress. Sarah was experienced in many features of human life. For example, she had often observed her human caretakers using keys to unlock padlocks. She had often observed humans turning a faucet to provide water through a hose. She had observed humans plugging a cord for an electric heater into an electrical outlet. Sarah was provided with videotaped instances of humans in situations whose solutions were related to the above events as well as others. For example, she saw videotape in which one of her human caretakers was apparently locked in a cage and could not escape despite attempts to open the locked door. The videotape was stopped before the problem was solved, and Sarah was provided with photographs, one of which had the solution to the problem (in this case, a key for the padlock on the cage door). Sarah consistently chose the photograph with the appropriate solution to each problem. The interpretation of Sarah's behavior was that she was able to understand the state of the human in the videotape and she was able to choose the appropriate solution to the person's problem. Additional studies with Sarah suggested she could spontaneously show deception, withholding information or providing incorrect information about the location of a food item from a human who had previously failed to share food with her. In contrast, she provided information about the location of a food object to another human who always shared food with her.

Additional studies with Sarah and other chimpanzees provided results suggestive that chimpanzees can take the perspective of another and use it to solve problems. A number of studies have been unsuccessful at providing evidence of Theory of Mind; some that have been successful have been criticized on methodological grounds. However, such studies continue. The demonstration of this capacity in apes awaits a clear methodology that will adequately address the extent to which apes can project their understanding of states of mind to others.

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