Mirror-Directed Social Behaviors of Garnett's Greater Bush Baby (Otolemur garnettii)

Many diurnal anthropoid species direct social behaviors toward their own mirror-image as though viewing a conspecific. To determine whether a nocturnal prosimian species would behave similarly, we videotaped social responses of 45 Garnett's greater bush babies (Otolemur garnettii) observing mirror-images for the first time, scored them for frequency and duration, and compared them with the same behaviors directed elsewhere in the test apparatus. Males scentmarked more than females did, principally with the hindfoot, and most when in immediate proximity to the mirror. Bush babies displayed bipedal posture and threat gestures when oriented directly toward a mirror from a near position. Orientation toward the mirror also increased the frequency of arched-back postures; however, this behavior was not contingent on proximity to the mirror or visibility of the mirror-image. The differential expression of specific behaviors toward mirror-images by male and female bush babies supports the view that this nocturnal prosimian, thought to be dependent on olfaction and audition for communication, is capable of specific recognition by visual cues alone.     

Mirror responses in a Japanese macaque troop (Arashiyama West)

Behavior toward two mirrors in the field was observed in the Arashiyama West troop ofMacaca fuscata. Counts of visits to the mirrors, plus scan and focal animal sampling were used. Some animals were marked with fluorescent paint to test informally for self-recognition. A relatively high mean frequency of visits to the reflecting side of both mirrors by all age classes, ranks, and sexes was recorded. There was no age difference in frequency of mirror visits per sample but adults spent more time per visit than subadults who in turn spent more time than juveniles. There was no indication of self-recognition by paint-marked animals. Mirrors appeared to be used to monitor the reflected scene and to look at the self-image. Social behavior in the mirror zone that was not directed toward the mirror was common to all age classes. Species-typical behavior directed toward the mirror was seen in younger animals but very seldom in adults. No threat displays by any animal were observed. We suggest that for adults the mirror image was not seen simply as another monkey.     

Responses of capuchin monkeys (Cebus apella) to different conditions of mirror-image stimulation

Group-living brown capuchins were given mirror-image stimulation as follows: (1) mirror 1 m away; (2) mirror attached to the cage-mesh; (3) angled mirrors creating a deflected image; (4) small mirror in the cage; and (5) small, transportable mirrors. The subjects were initially interested in the mirrors in each condition, but they generally habituated to them over the course of repeated presentations. Control (non-reflective) objects were attended to less than mirrors. Facial expressions occurred mostly in Condition 2, lateral and vertical head movements in Condition 3, reaching behind the mirror in Condition 2, looking obliquely into the mirror in Conditions 4 and 5. Despite these diverse conditions of exposure to mirrors, lasting for a total of over three months, no behaviours suggesting self-recognition were seen in the monkeys.     

Monkeys with mirrors: Some questions for primate psychology

Monkeys do not appear to recognize themselves in mirrors but display social responses to the reflection. This article comprehensively reviews the literature concerning monkeys’ reactions to mirrors, describing the interest shown in reflections, the reinforcing effects of mirror-image stimulation, the social responses of the monkeys, their interpretation of objects reflected in a mirror, and their performance in tests of self-recognition. In all cases limitations of the methods employed restrict conclusions about the monkeys’ behavior. Detailed behavioral observations coupled with comparisons of the psychological properties of mirrors with those of other stimuli promise to reveal more useful information about cognitive mechanisms and abilities of monkeys and other primates.     

Preference for mirror-image stimulation in finches (Passer domesticus domesticus) and parakeets (Melopsittacus undulatus)

When given a continuous choice both finches and parakeets were observed to spend appreciably more time in front of their own reflection in a mirror than in front of another bird, food, or a blank piece of cardboard. The preference for mirrors not only persisted over days, but showed a tendency to increase in both species. An attempt to explain these data in terms of what are considered to be unique psychological properties of mirror-image stimulation was presented.     

Do marmosets care to share? Oxytocin treatment reduces prosocial behavior toward strangers

Cooperatively-breeding and socially-monogamous primates, like marmosets and humans, exhibit high levels of social tolerance and prosociality toward others. Oxytocin (OXT) generally facilitates prosocial behavior, but there is growing recognition that OXT modulation of prosocial behavior is shaped by the context of social interactions and by other motivational states such as arousal or anxiety. To determine whether prosociality varies based on social context, we evaluated whether marmoset donors (Callithrix penicillata) preferentially rewarded pairmates versus opposite-sex strangers in a prosocial food-sharing task. To examine potential links among OXT, stress systems, and prosociality, we evaluated whether pretrial cortisol levels in marmosets altered the impact of OXT on prosocial responses. Marmosets exhibited spontaneous prosociality toward others, but they did so preferentially toward strangers compared to their pairmates. When donor marmosets were treated with marmoset-specific Pro⁸-OXT, they exhibited reduced prosociality toward strangers compared to marmosets treated with saline or consensus-mammalian Leu⁸-OXT. When pretrial cortisol levels were lower, marmosets exhibited higher prosociality toward strangers. These findings demonstrate that while marmosets show spontaneous prosocial responses toward others, they do so preferentially toward opposite-sex strangers. Cooperative breeding may be associated with the expression of prosociality, but the existence of a pair-bond between marmoset partners appears to be neither necessary nor sufficient for the expression of spontaneous prosocial responses. Furthermore, high prosociality toward strangers is significantly reduced in marmosets treated with Pro⁸-OXT, suggesting that OXT does not universally enhance prosociality, but, rather OXT modulation of prosocial behavior varies depending on social context.     

A note on the responses of chimpanzees (Pan troglodytes) to live self-images on television monitors

The majority of studies on self-recognition in animals have been conducted using a mirror as the test device; little is known, however, about the responses of non-human primates toward their own images in media other than mirrors. This study provides preliminary data on the reactions of 10 chimpanzees to live self-images projected on two television monitors, each connected to a different video camera. Chimpanzees could see live images of their own faces, which were approximately life-sized, on one monitor. On the other monitor, they could see live images of their whole body, which were approximately one-fifth life-size, viewed diagonally from behind. In addition, several objects were introduced into the test situation. Out of 10 chimpanzees tested, 2 individuals performed self-exploratory behaviors while watching their own images on the monitors. One of these two chimpanzees successively picked up two of the provided objects in front of a monitor, and watched the images of these objects on the monitor. The results indicate that these chimpanzees were able to immediately recognize live images of themselves or objects on the monitors, even though several features of these images differed from those of their previous experience with mirrors.     

Pygmy Marmosets Modify Call Structure When Paired

Pygmy marmosets ( Cebuella pygmaea ) modified the structure of their trill vocalizations in response to pairing with a new mate. Prior to pairing, individual marmosets displayed different acoustic parameters of trill structure. Within the first 6 wk after pairing, three of four pairs produced trills that were more homogeneous between mates. Pairs that had the greatest individual difference in trill structure prior to pairing displayed convergence on a greater number of parameters than pairs having fewer differences in prepairing trill structure. The vocal structure following pairing remained highly stable in the two pairs that could be recorded 3 yr after initial pairing. Changes in trill structure that occurred within the first 6 wk after pairing were greater than spontaneous changes that occurred during baseline control recording sessions on the same animals. These results suggest that nonhuman primates show subtle modification of vocal structure, especially in response to changes in social environment. Similar findings have been reported in birds and other mammals.     

Immunogenicity of wild and attenuated varicella-zoster virus strains in pygmy marmosets

Pygmy marmosets were inoculated with the low-passage parental strain or with the attenuated variant of OKA strain of varicella-zoster virus. No clinical signs were observed following inoculation and virus could not be isolated from tissues taken at several times after inoculation. A low-level antibody response developed in all animals. Three months after the first inoculation, all animals were challenged with the low-passage parental strain of virus. Animals primed originally with the parental strain developed higher booster responses than animals primed with the attenuated strain of virus. The results suggest that the parental and attenuated strains of varicella-zoster virus differ in their immunogenicity in pygmy marmosets.     

Reflections in the rainforest: full-length mirrors facilitate behavioral observations of unhabituated,wild chimpanzees

We describe behaviors of unhabituated wild chimpanzees in Gabon during repeated encounters with large mirrors installed permanently in their home range. Movement in proximity to the mirrors triggered video cameras that recorded the scene. Data are presented for 51 mirror encounters spanning a 3-year period. After initial wariness, mirror-directed aggressive behaviors were common, especially in adult males, but aggression gradually diminished and eventually almost completely ceased. Focusing on the two mirrors that elicited most reactions, the percentage of chimpanzees showing tension or anxiety also decreased across encounters. These mirrors elicited a range of socio-sexual behaviors interpreted as having a reassurance function, especially when group-level tension appeared high. Chimpanzees also occasionally directed these behaviors towards their own reflection. Despite increasing habituation and positive attraction to the mirrors, none of the chimpanzees displayed signs of self-recognition. We conclude that a combination of large mirrors and video traps can provide valuable information about unhabituated, semi-terrestrial primates in their natural habitat, by inducing the primates to stay in one place for longer than they might otherwise do.     

What do fish make of mirror images?

Fish act aggressively towards their mirror image suggesting that they consider it another individual, whereas in some mammals behavioural response to mirrors may be an evidence of self-recognition. Since fish cannot self-recognize, we asked whether they could distinguish between fighting a mirror image and fighting a real fish. We compared molecular, physiological and behavioural responses in each condition and found large differences in brain gene expression levels. Although neither levels of aggressive behaviour nor circulating androgens differed between these conditions, males fighting a mirror image had higher immediate early gene (IEG) expression in brain areas homologous to the amygdala and hippocampus than controls. Since amygdalar responses are associated with fear and fear conditioning in other species, higher levels of brain activation when fighting a mirror suggest fish experience fear in response to fights with a mirror image. Clearly, the fish recognize something unusual about the mirror image and the differential brain response may reflect a cognitive distinction.     

Reactions of a group of pygmy chimpanzees (Pan paniscus) to their mirror-images: Evidence of self-recognition

A group of seven pygmy chimpanzees (Pan paniscus) was tested for their mirror-image reactions during a ten-day experiment. The time spent viewing the mirror waned quickly. Little social responses directed towards the mirror were observed. Self-directed behaviors were shown from testday one on. It was concluded that four out of seven animals could correctly identify their mirror-image, one infant was not (yet) able to do so, and for two other individuals the results were inconclusive.     

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.     

Infant stumptailed macaques reared with mirrors or peers: Social responsiveness,attachment, and adjustment

Comparisons of activity toward mirrors and peers in infant macaques being reared with one of these stimuli as the primary rearing partner revealed markedly greater social responsiveness to a fully accessible cagemate than to one's own reflection. Measures of exploration, aggression, and especially play all revealed the cagemate to be the more potent social stimulus. Mirror-reared infants given additional experience of a live peer behind a transparent partition were less responsive to the mirror than were infants with no social stimulation other than a mirror. In contrast, cagemate-directed behavior of peer-reared infants was not seriously affected by additional exposure to a mirror. A fully accessible peer also elicited more social responding than a peer behind a transparent partition, and infants with experience of both a live cagemate and mirrors were generally more responsive toward the former. Greater agitation in peer-reared than in mirror-reared stumptailed monkeys during separations from their rearing partners suggests that exposure to the physically accessible partner led to stronger attachments. Infants reacted positively to a moderately unfamiliar environment but showed behavioral disruption when placed in a very unfamiliar environment. Disruption was especially evident in peer-reared infants, in which exposure to the unfamiliar environment was compounded with the absence of the attachment figure. Mirror-rearing appeared to reduce the tendency toward ‘isolation syndrome’ behaviors compared to alone-rearing, and these behaviors appear to be less common in stumptailed than in rhesus macaques.     

Selective stimulus control in discrimination of lateral mirror images by pigeons

Four monocularly and two binocularly viewing pigeons were trained to peck a key when it displayed one stimulus (S+) but not to peck when it displayed another stimulus (S−). S+ and S− were a lateral mirror-image pair of two-coloured stimuli. When tested for transfer with the untrained eye open, two of the monocular birds pecked more during S− than S+, the other two continuing to favour S+. During generalization tests on the wavelength dimension all monocular birds pecked much more often during one S+ colour than during the other. The colour controlling pecking was that displayed on the side of the key facing the open eye during S+ presentations. Both binocular birds developed asymmetrical responses to the key, one favouring the left, the other the right side of the key. Generalization tests on the wavelength dimension showed selective control by the colour displayed on the favoured side of the key during S+ presentations. The results are interpreted as supporting the view that pigeons learn to discriminate lateral mirror images by developing asymmetrical observing responses that convert the left-right difference between the mirror images into a difference more easily discriminable.     

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.     

Acoustic threat displays and agonistic behaviour in the red-finned loach <Emphasis Type="Italic">Yasuhikotakia modesta</Emphasis>

Agonistic behaviour and the significance of acoustic threat displays were investigated in juvenile red-finned loaches, Yasuhikotakia modesta. This species produced two different vocalizations during agonistic encounters—clicks and butting sounds. Clicks were produced at some distance from the opponent whereas butting sounds were emitted when one fish touched the other with its mouth. This occurred primarily during circling. Both sound types were short broadband signals with the main energies concentrated at about 230 Hz, but clicks were longer in duration and lower in sound level. Agonistic behaviour usually started when one fish approached the other, spread its fins and produced clicks (threat displays), which was followed by parallel displaying, circling and chasing. All fish approached a mirror quickly and displayed aggressively in a parallel position. The number and duration of the threat displays in front of the mirror image were significantly elevated compared with control experiments (rear of the mirror). When playing back click trains in the presence of a mirror image, loaches vocalized significantly less often than during the silent periods, whereas the amount of lateral displaying remained similar. These data indicate that agonistic sounds reduced acoustic displays in red-finned loaches.     

Mirror-imaged doublets of Tetmemena pustulata: implications for the development of left-right asymmetry

Ciliated protozoa possess cellular axes reflected in the arrangement of their ciliature. Upon transverse fission, daughter cells develop an identical ciliary pattern, ensuring perpetuation of the cellular phenotype. Experimentally manipulated cells can be induced to form atypical phenotypes, capable of intraclonal propagation and regeneration after encystment. One such phenotype in the ciliate Tetmemena pustulata (formerly Stylonychia pustulata) is the mirror-imaged doublet. These cells possess two distinct sets of ciliature, juxtaposed on the surfaces in mirror image symmetry, with a common anterior-posterior axis. We have examined whether individual ciliary components of Tetmemena mirror-image doublets are mirror imaged. Ultrastructural analysis indicates that despite global mirror imaging of the ciliature, detailed organization of the membranelles is reversed in the mirror-image oral apparatus (OA), such that the ciliary effective stroke propels food away from the OA. Assembly of compound ciliary structures of both OAs starts out identically, but as the structures associated with the mirror-image OA continue to form, the new set of membranelles undergoes a 180° planar rotation on the ventral surface relative to the same structures in the typical OA. The overall symmetry of the OA thus appears to be separable from the more localized assembly of individual basal bodies. True mirror imagery of the membranelles would require new enantiomorphic forms of the individual ciliary components, particularly the basal bodies, which is never observed. These observations suggest a mechanistic hypothesis with implications for the development of left-right asymmetry not only in ciliates, but perhaps also in development of left-right asymmetry in general.     

Morphology and Development of Mirror-Image Doublets of Stylonychia mytilus

This paper describes the cortical anatomy and development of mirror-image doublets of Stylonychia mytilus, analyzed using the protargol technique. The reversed, or “left-handed” (LH) component of these doublets is a mirror image of the normal or “right handed” (RH) component with regard to the arrangement of cortical structures. The mirror-image patterning is imperfect, however, as the individual ciliary structures of the LH component all are of normal internal asymmetry, and the orientation of membranelles is inverted. Certain structures that would be expected to form near the line of symmetry are absent. During cell division and cortical reorganization, ciliary primordia arise and become arranged in a mirror-image pattern that is more perfect than that exhibited by the mature structures. Deviations from a mirror-image pattern appear at late stages when organelle sets differentiate within ciliary primordia: for example, the membranelle set differentiates within the oral primordium of the LH component in a sequence that is an inversion rather than a mirror image of the corresponding sequence of the RH component. This mixed control of oral development by different cortical “informational systems” accounts for some of the characteristic abnormalities of the mature oral structures of the LH component.     

Morphology and development of mirror-image doublets of Stylonychia mytilus

This paper describes the cortical anatomy and development of mirror-image doublets of Stylonychia mytilus, analyzed using the protargol technique. The reversed, or "left-handed" (LH) component of these doublets is a mirror image of the normal or "right handed" (RH) component with regard to the arrangement of cortical structures. The mirror-image patterning is imperfect, however, as the individual ciliary structures of the LH component all are of normal internal asymmetry, and the orientation of membranelles is inverted. Certain structures that would be expected to form near the line of symmetry are absent. During cell division and cortical reorganization, ciliary primordia arise and become arranged in a mirror-image pattern that is more perfect than that exhibited by the mature structures. Deviations from a mirror-image pattern appear at late stages when organelle sets differentiate within ciliary primordia: for example, the membranelle set differentiates within the oral primordium of the LH component in a sequence that is an inversion rather than a mirror image of the corresponding sequence of the RH component. This mixed control of oral development by different cortical "informational systems" accounts for some of the characteristic abnormalities of the mature oral structures of the LH component.