Mirror self-recognition and symbol-mindedness

The view that mirror self-recognition (MSR) is a definitive demonstration of self-awareness is far from universally accepted, and those who do support the view need a more robust argument than the mere assumption that self-recognition implies a self-concept (e.g. Gallup in Socioecology and Psychology of Primates, Mouton, Hague, 1975; Gallup and Suarez in Psychological Perspectives on the Self, vol 3, Erlbaum, Hillsdale, 1986). In this paper I offer a new argument in favour of the view that MSR shows self-awareness by examining the nature of the mirror image itself. I argue, using the results of ‘symbol-mindedness’ experiments by Deloache (Trends Cogn Sci 8(2):66–70, 2004), that where self-recognition exists, the mirror image must be functioning as a symbol from the perspective of the subject and the subject must therefore be ‘symbol-minded’ and hence concept possessing. Further to this, according to the Concept Possession Hypothesis of Self-Consciousness (Savanah in Conscious Cogn 2011), concept possession alone is sufficient to demonstrate the existence of self-awareness. Thus MSR as a demonstration of symbol-mindedness implies the existence of self-awareness. I begin by defending the ‘mark test’ protocol as a robust methodology for determining self-recognition. Then follows a critical examination of the extreme views both for and against the interpretation of MSR as an indication of self-awareness: although the non-mentalistic interpretation of MSR is unconvincing, the argument presented by Gallup is also inadequate. I then present the symbol-mindedness argument to fill in the gaps in the Gallup approach.     

A new mark test for mirror self-recognition in non-human primates

For 30 years Gallups (Science 167:86–87, 1970) mark test, which consists of confronting a mirror-experienced test animal with its own previously altered mirror image, usually a color mark on forehead, eyebrow or ear, has delivered valuable results about the distribution of visual self-recognition in non-human primates. Chimpanzees, bonobos, orangutans and, less frequently, gorillas can learn to correctly understand the reflection of their body in a mirror. However, the standard version of the mark test is good only for positively proving the existence of self-recognition. Conclusive statements about the lack of self-recognition are more difficult because of the methodological constraints of the test. This situation has led to a persistent controversy about the power of Gallups original technique. We devised a new variant of the test which permits more unequivocal decisions about both the presence and absence of self-recognition. This new procedure was tested with marmoset monkeys (Callithrix jacchus), following extensive training with mirror-related tasks to facilitate performance in the standard mark test. The results show that a slightly altered mark test with a new marking substance (chocolate cream) can help to reliably discriminate between true negative results, indicating a real lack of ability to recognize oneself in a mirror, from false negative results that are due to methodological particularities of the standard test. Finally, an evolutionary hypothesis is put forward as to why many primates can use a mirror instrumentally – i.e. know how to use it for grasping at hidden objects – while failing in the decisive mark test.To see a video sequence of the instrumental use of mirror by Callithrix jacchus as described in this study, please go to     

Mirror-Mark Tests Performed on Jackdaws Reveal Potential Methodological Problems in the Use of Stickers in Avian Mark-Test Studies

Some animals are capable of recognizing themselves in a mirror, which is considered to be demonstrated by passing the mark test. Mirror self-recognition capacity has been found in just a few mammals having very large brains and only in one bird, the magpie (Pica pica). The results obtained in magpies have enormous biological and cognitive implications because the fact that magpies were able to pass the mark test meant that this species is at the same cognitive level with great apes, that mirror self-recognition has evolved independently in the magpie and great apes (which diverged 300 million years ago), and that the neocortex (which is not present in the bird''s brains) is not a prerequisite for mirror self-recognition as previously believed. Here, we have replicated the experimental design used on magpies to determine whether jackdaws (Corvus monedula) are also capable of mirror self-recognition by passing the mark test. We found that our nine jackdaws showed a very high interest towards the mirror and exhibited self-contingent behavior as soon as mirrors were introduced. However, jackdaws were not able to pass the mark test: both sticker-directed actions and sticker removal were performed with a similar frequency in both the cardboard (control) and the mirror conditions. We conclude that our jackdaws'' behaviour raises non-trivial questions about the methodology used in the avian mark test. Our study suggests that the use of self-adhesive stickers on sensitive throat feathers may open the way to artefactual results because birds might perceive the stickers tactilely.     

Mirror-mediated responses of California scrub jays (Aphelocoma californica) during a caching task and the mark test

Mirror self-recognition, as an index of self-awareness, has been proposed as a precursor for more complex social cognitive abilities, such as prosocial reasoning and cooperative decision-making. Indeed, evidence for mirror self-recognition has been shown for animals possessing complex social cognitive abilities such as great apes, dolphins, elephants and corvids. California scrub jays (Aphelocoma californica) have provided strong evidence that non-human animals are capable of mental state attribution. For instance, scrub jays are reported to use their experience stealing the food of others to infer that other birds may similarly intend to steal from them. If a concept of “self” is required for such complex social cognitive abilities, then scrub jays might be expected to show mirror self-recognition. Thus, we examined whether California scrub jays are capable of mirror self-recognition using two experimental contexts: a caching task and the mark test. During the caching task, we compared the extent to which scrub jays protected their food after caching alone, in the presence of a conspecific and in the presence of a mirror. The birds did not engage in more cache protection behaviours with a mirror present than when caching alone, suggesting scrub jays may have recognized their reflection and so did not expect cache theft. Alternative explanations for this behaviour are also discussed. During the mark test, the scrub jays were surreptitiously marked with a red or plumage-coloured control sticker. The scrub jays showed no evidence of mirror self-recognition during the mark test, as the birds did not preferentially attempt to remove the red mark in the presence of a mirror. Together, the results provide mixed evidence of the mirror self-recognition abilities of California scrub jays. We highlight the need to develop alternative approaches for evaluating mirror self-recognition in non-human animals to better understand its relationship with complex social cognition.     

Mark tests for mirror self-recognition in capuchin monkeys (Cebus apella) trained to touch marks

In Experiment 1, three capuchin monkeys (Cebus apella) were exposed to a mirror in their home cage for 3 days and then given food treats for touching orange marks located on the surface of an experimental chamber. Following training, a mirror was added to the chamber to see if the monkeys would use it to guide non-reinforced contacts with an orange mark on their foreheads that was only visible as a mirror reflection (mark test). Two monkeys touched the head-mark more often with the mirror present than absent, but no mark touches were emitted while looking at the mirror. In Experiment 2, the monkeys were rewarded for touching orange marks on their bodies that were directly visible, followed by another head-mark test. Again, two monkeys touched the mark more often with the mirror present than absent, but these contacts were not emitted while looking at the mirror. Since facing the mirror while mark touching was not required for reinforcement during training, Experiment 3 further tested the possibility that increased mark touching in the presence of the mirror during Experiments 1 and 2 was the result of a memorial process. For this, a final, novel mark test was conducted using an orange mark on the neck that was only visible as a reflection (Experiment 3). No monkeys passed this test. These are the first mark tests given to capuchin monkeys. The results are consistent with the finding that no monkey species is capable of spontaneous mirror self-recognition. The implications of sequential training and mark testing for comparative evaluations of mirror self-recognition capacity are discussed.     

The influence of AVPR1A genotype on individual differences in behaviors during a mirror self‐recognition task in chimpanzees (Pan troglodytes)

The mark/rouge test has been used to assess mirror self‐recognition (MSR) in many species. Despite consistent evidence of MSR in great apes, genetic or non‐genetic factors may account for the individual differences in behavioral responses that have been reported. We examined whether vasopressin receptor gene (AVPR1A) polymorphisms are associated with MSR‐related behaviors in chimpanzees since vasopressin has been implicated in the development and evolution of complex social relations and cognition and chimpanzees are polymorphic for the presence of the RS3‐containing DupB region. We compared a sample of DupB+/? and DupB?/? chimpanzees on a mark test to assess its role on social behavior toward a mirror. Chimpanzees were administered two, 10‐min sessions where frequencies of mirror‐guided self‐directed behaviors, contingent actions and other social behaviors were recorded. Approximately one‐third showed evidence of MSR and these individuals exhibited more mirror‐guided self‐exploratory behaviors and mouth contingent actions than chimpanzees not classified as passers. Moreover, DupB+/? males exhibited more scratching and agonistic behaviors than other male and female cohorts. Our findings support previous studies demonstrating individual differences in MSR abilities in chimpanzees and suggest that AVPR1A partly explains individual differences in MSR by influencing the behavioral reactions of chimpanzees in front of a mirror.     

Not all chimpanzees (Pan troglodytes) show self-recognition

When a chimpanzee is presented with a mirror it initially responds with social behavior directed toward the reflection. After several hours of exposure to the mirror the social behavior decreases and the mirror is used to guide self-directed responses to previously unobservable parts of the body such as the face. When a distinctively colored mark is unobtrousively applied to the chimpanzee's face and the chimpanzee touches the mark while observing itself in the mirror, this behavior is said to indicate self-recognition. Such self-recognition has been considered to be a robust phenomenon in chimpanzees, with self-directed and mark-directed behaviors both appearing in all socially-housed adult chimpanzees tested. In our study 11 chimpanzees were given mirror exposure and tested with the mark test. Only one of the 11 chimpanzees touched the mark during test, although several showed self-directed behavior using the mirror to guide their movements. Such experimental factors as mirror size, position, or temporal spacing of the mirror exposure, and such subject variables as age, sex, previous social experience, and subspecies were insufficient to explain the difference between the present and previous findings. We suggest that there are individual differences in mirror recognition behavior in chimpanzees, and that further consideration of the factors contributing to this phenomenon, including the development of additional tests for self-recognition, is needed.     

Contingency checking and self-directed behaviors in giant manta rays: Do elasmobranchs have self-awareness?

Elaborate cognitive skills arose independently in different taxonomic groups. Self-recognition is conventionally identified by the understanding that one’s own mirror reflection does not represent another individual but oneself, which has never been proven in any elasmobranch species to date. Manta rays have a high encephalization quotient, similar to those species that have passed the mirror self-recognition test, and possess the largest brain of all fish species. In this study, mirror exposure experiments were conducted on two captive giant manta rays to document their response to their mirror image. The manta rays did not show signs of social interaction with their mirror image. However, frequent unusual and repetitive movements in front of the mirror suggested contingency checking; in addition, unusual self-directed behaviors could be identified when the manta rays were exposed to the mirror. The present study shows evidence for behavioral responses to a mirror that are prerequisite of self-awareness and which has been used to confirm self-recognition in apes.     

A developmental approach to the origins of self-recognition in great apes

In this paper I present an hypothesis to explain the presence of mirror self-recognition (MSR) in great apes and human infants, and the absence of MSR in monkeys. This hypothesis is based on the following elements: 1) review of Gallupian studies of MSR in monkeys and apes; 2) review of Lewis & Brooks-Gunn's study for self-recognition in human infants; 3) application of the human model to comparative data on MSR in nonhuman primates; 4) discussion of cognitive correlates of MSR in human infants; 5) analysis of the cognitive correlates of MSR absence in monkeys, and MSR presence in apes; 6) comparative analysis of the modalities of occurrence of imitation and understanding of causality in monkeys and apes; and 7) a cladistic reconstruction of the evolution of MSR.     

Through the looking glass,and what we (don’t) find there

The conclusions drawn from mirror self-recognition studies, in which nonhuman animals are tested for whether they detect a mark on their bodies which can be observed only in the mirror, are based on several presuppositions. These include (1) that performance on the test is an indication of species wide rather than individual abilities, and (2) that all the animals which pass the test are demonstrating the presence of the same psychological ability. However, further details about the results of the test indicate that these presuppositions are false. Animals take the test as individuals, not as stand-ins for species, and members of different species rely on different cognitive mechanisms to pass the test. For nonhuman animals, passing the test seems to be a consequence of enculturation and practice.     

Another gorilla (Gorilla gorilla gorilla) recognizes himself in a mirror

Various attempts have been made to explain why gorillas (Gorilla gorilla gorilla) find it difficult to recognize their mirror image. One of the most oft-cited reasons is aversion to eye contact, which stops gorillas from looking into a mirror and thus prevents them from carrying out a suitable exploration that could lead to self-recognition. In the experimental design used here the subject was first habituated both to observers and to the mirror as an object before being exposed to the latter. The study was performed with a single subject who was well adapted to captivity and exhibited no aberrant behavior or signs of stress. The results revealed that the subject had no aversion to eye contact. He showed considerable interest in the mirror and appeared relaxed when faced with his image. He gave a positive response to the mark test.     

What mirror self-recognition in nonhumans can tell us about aspects of self

Research on mirror self-recognition where animals are observed for mirror-guided self-directed behaviour has predominated the empirical approach to self-awareness in nonhuman primates. The ability to direct behaviour to previously unseen parts of the body such as the inside of the mouth, or grooming the eye by aid of mirrors has been interpreted as recognition of self and evidence of a self-concept. Three decades of research has revealed that contrary to monkeys, most great apes (humans, common chimpanzees, pygmy chimpanzees and orangutans but not the gorilla) have convincingly displayed the capacity to recognize self by mirrors. The putative discontinuity in phylogeny of the ability suggests the existence of a so-called cognitive gap between great apes and the rest of the animal kingdom. However, methodological and theoretical inconsistencies regarding the empirical approach prevail. For instance, the observation of self-directed behaviour might not be as straightforward as it seems. In addition, the interpretation of mirror self-recognition as an index of self-awareness is challenged by alternative explanations, raising doubt about some assumptions behind mirror self-recognition. To evaluate the significance of the test in discussions of the concept of self this paper presents and analyses some major arguments raised on the mirror task.     

Mirror-induced behavior in the magpie (Pica pica): evidence of self-recognition

Comparative studies suggest that at least some bird species have evolved mental skills similar to those found in humans and apes. This is indicated by feats such as tool use, episodic-like memory, and the ability to use one's own experience in predicting the behavior of conspecifics. It is, however, not yet clear whether these skills are accompanied by an understanding of the self. In apes, self-directed behavior in response to a mirror has been taken as evidence of self-recognition. We investigated mirror-induced behavior in the magpie, a songbird species from the crow family. As in apes, some individuals behaved in front of the mirror as if they were testing behavioral contingencies. When provided with a mark, magpies showed spontaneous mark-directed behavior. Our findings provide the first evidence of mirror self-recognition in a non-mammalian species. They suggest that essential components of human self-recognition have evolved independently in different vertebrate classes with a separate evolutionary history.     

Mirror image processing in three marine mammal species: killer whales (Orcinus orca), false killer whales (Pseudorca crassidens) and California sea lions (Zalophus californianus)

Dolphins (Tursiops truncatus) and their relatives might be expected to show mirror-induced contingency checking, a prerequisite to self-recognition, because of their high brain development, their complex social life and their demonstrated abilities in bodily imitation. A study of killer whales'(Orcinus orca) behaviour in front of a mirror is presented, including a mark test. Shorter investigations of mirror behaviour are also described in false killer whales (Pseudorca crassidens) and California sea lions (Zalophus californianus). Contingency checking was present in killer whales and possibly also in false killer whales, but no clear contingency checking was observed in sea lions. The mark test on killer whales suggested that the marked animal anticipated that its image would look different. This study shows that killer whales and false killer whales, like bottlenose dolphins, appear to possess the cognitive abilities required for self-recognition.     

Failure to demonstrate self-recognition in gorillas

Two zoo-reared gorillas were each given nearly 400 h of mirror exposure. Extensive mirror gazing and social behaviors were exhibited, the frequency of which decreased gradually over the study period. Neither animal demonstrated the transition from other-directed to self-directed behavior characteristic of both chimpanzees and orangutans, and no evidence of self-recognition was found using the Gallup marking paradigm. These negative findings, after extensive mirror exposure, suggest that the gorilla may be the only great ape which lacks the conceptual ability necessary for self-recognition.     

Mirror responses in a group of Miopithecus talapoin

Studies of non-human primate self-recognition in mirrors demonstrate variation both within and between species. This study applied a rigorous methodology that took into account habituation of subjects to the mirror as an object and to the experimental situation. The species observed in our study was Miopithecus talapoin, which has been little studied in the wild or in captivity. Although this species shows several interesting characteristics, including complex social organisation and a high encephalization index, the talapoin monkeys in the study did not pass the mark test; however, they showed a prerequisite for self-recognition, namely comparing their body parts to the image of these in the mirror.     

Rhesus Monkeys (Macaca mulatta) Do Recognize Themselves in the Mirror: Implications for the Evolution of Self-Recognition

Self-recognition in front of a mirror is used as an indicator of self-awareness. Along with humans, some chimpanzees and orangutans have been shown to be self-aware using the mark test. Monkeys are conspicuously absent from this list because they fail the mark test and show persistent signs of social responses to mirrors despite prolonged exposure, which has been interpreted as evidence of a cognitive divide between hominoids and other species. In stark contrast with those reports, the rhesus monkeys in this study, who had been prepared for electrophysiological recordings with a head implant, showed consistent self-directed behaviors in front of the mirror and showed social responses that subsided quickly during the first experimental session. The self-directed behaviors, which were performed in front of the mirror and did not take place in its absence, included extensive observation of the implant and genital areas that cannot be observed directly without a mirror. We hypothesize that the head implant, a most salient mark, prompted the monkeys to overcome gaze aversion inhibition or lack of interest in order to look and examine themselves in front of the mirror. The results of this study demonstrate that rhesus monkeys do recognize themselves in the mirror and, therefore, have some form of self-awareness. Accordingly, instead of a cognitive divide, they support the notion of an evolutionary continuity of mental functions.     

Monkeys,apes, mirrors and minds: The evolution of self-awareness in primates

Almost two decades of research on the self-recognition capacity of non-human primates has produced evidence of intriguing phylogenetic differences. Not a single species of monkey has demonstrated the ability to recognize its own reflection in a mirror, despite some claims to the contrary. To date, only humans, orangutans and chimpanzees have passed objective tests of mirror-recognition. This paper reviews the methodology and evidence for self-recognition in primates along with the assumption that this ability is an indicator of self-awareness. The failure of the gorilla to master the task is discussed in some detail, along with an evaluation of anecdotal evidence of self-recognition by at least one gorilla. Also, the evolutionary backdrop of the primates is considered with reference to this unique behavior. Evidence supporting alternate, non-cognitive interpretations of self-recognition is assessed.     

Self-agency in rhesus monkeys

Rhesus monkeys (Macaca mulatta) have shown the ability to monitor their own mental states, but fail the mirror self-recognition test. In humans, the sense of self-agency is closely related to self-awareness, and results from monitoring the relationship between intentional, sensorimotor and perceptual information. Humans and rhesus monkeys were trained to move a computer icon with a joystick while a distractor icon partially matched their movements. Both humans and monkeys were able to monitor and identify the icon they were controlling, suggesting they have some understanding of self-agency.     

Strontium metabolism in the juvenile Lake Sturgeon,Acipenser fulvescens (Rafinesque, 1817), and further evaluation of the isotope as a marking tool for stock discrimination

Stock enhancement efforts have been used to aid in increasing dwindling population levels of Lake Sturgeon, Acipenser fulvescens, that are currently of conservation concern. Consistent monitoring of stock enhanced fisheries requires a reliable and reproducible method to mark stocked fish such that the success of such programs can be determined. Recently, stable isotopic marking of hard structures in fish has been developed in a variety of species, however, optimal marking conditions are less well understood. In this study the metabolism of strontium in juvenile Lake Sturgeon and determined parameters for optimisation of marking success in the fin ray were examined. Using radioactive strontium (⁸⁵Sr), whole body influx and efflux rates of strontium were 3.02 ± 0.364 pmol h^?1 g^?1 (mean ± standard error) and 0.04 ± 0.007 pmol h^?1 g^?1, respectively. Furthermore, short‐term accumulation of ⁸⁵Sr in a variety of tissues was assessed and found to be greatest in the fin ray. Biological half‐life of the stable isotope ⁸⁶Sr was shortest in muscle and longest in the fin ray tissue. Immersion and length of immersion timing had positive relationships with marking success. Additionally, the signature remained in 75% of fish analysed 550 days post‐mark. Data suggest that marking success was determined by duration of immersion in the mark and concentration of the mark introduced to the water.