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Identification of one’s own body or body-related sensory information. It is narrower than reflective knowledge of one’s identity and does not alone demonstrate theory of mind.

The mirror-mark test can provide evidence that an animal uses reflected information to identify and act on its own body. It is a narrower assay than a general test of self-awareness, and failure is especially difficult to interpret. The core inference rests on directing an action to the otherwise unseen marked body part, rather than merely responding to something unusual in a mirror.

In a suitable design, an animal first has opportunities to inspect a mirror without a mark. A visible mark is then placed where it cannot be seen directly, using a procedure that avoids an informative tactile, olfactory or handling cue. After recovery from any necessary handling, investigators compare responses with the mirror available and unavailable, and with a matched invisible sham treatment. The predicted response is mark-directed investigation of the animal's own body specifically when the visible change can be seen in reflection. Looking at the mirror, attacking it or searching behind it are interesting observations, but do not alone establish bodily self-recognition.

The classic chimpanzee study used prior mirror exposure and otherwise unseen dye marks to demonstrate self-directed investigation. ^[ref] Its conceptual advance was to turn a claim about self-recognition into a behavioural prediction that could be compared with alternative responses. A mark on the reflected forehead corresponds to a location on the subject's own forehead. Reaching there uses information about the relation between the image and body; trying to touch the glass instead supports a different interpretation. An odourless mark that is imperceptible by touch makes this distinction stronger.

A rigorous modern design makes those alternatives explicit. In a factorial comparison, let $T_{VM}$ and $T_{SM}$ denote rates of appropriately localized body-directed actions for visible and sham marks with a mirror, and let $T_{VC}$ and $T_{SC}$ denote the corresponding rates with the mirror covered. The interaction contrast:asks whether the visible mark's effect specifically depends on reflective information. A positive $D$ is useful only if the actions are correctly localized, opportunities to act are comparable and uncertainty is estimated across animals. It does not acquire a cognitive interpretation just because its statistical test is significant. General increases in grooming, attention or agitation need to be coded separately.

Controls should match application pressure, odour, texture and handling, vary mark side or location, and counterbalance condition order. A covered mirror controls its physical presence; a live or recorded other animal helps characterize social responses. Noncontingent or delayed self-images can test the importance of immediate sensorimotor contingency, though they also increase task difficulty. Separate trials with directly visible marks help establish that a subject notices such a change and has an available response, without training the critical hidden-mark action in advance. Coders should be blinded where feasible, and the criteria for a pass specified before viewing the outcome. Repeated touches by one animal are not independent evidence from many animals.

A positive result supports at least a learned mapping between reflected information and the subject's body. How much more it supports is a problem of construct validity. An animal might combine visual contingencies, proprioception and a body schema without representing itself as a named, temporally continuous individual. Conversely, learning the mapping does not make the result meaningless: learned information about one's own body can itself be a form of self-representation. The question is which alternative mechanisms the design distinguishes. A pass does not by itself demonstrate theory of mind, autobiographical memory, moral understanding or a particular subjective experience.

Negative results are weaker because successful performance requires several capacities together: noticing the mark, attending to reflection, relating the image to the body, being motivated to investigate, and possessing a suitable action. Fear, social attraction to the image, poor visual access or indifference to marks can prevent the predicted response even when some self-related information is available. ecological validity is therefore central. Mirror dimensions, access, viewing geometry and prior experience must suit the species. Uniformly presenting a small mirror to animals of very different sizes does not create a biologically equivalent test.

The elephant study illustrates this dependence. Three asian elephants were exposed to a large accessible mirror and visible and sham marks. One passed the mark criterion, while the others also showed informative mirror-oriented exploration. ^[ref] This is evidence about the observed individuals and assay, not a species-wide estimate based on one success, nor proof that the nonpassing individuals lacked every form of self-representation. The apparatus enabled close physical exploration that smaller or inaccessible mirrors would not permit.

The required action must also reflect anatomy. Bottlenose dolphins cannot use a hand to touch a facial mark. Investigators therefore examined orientations and movements exposing marked regions to a reflective surface, comparing marked and sham-marked conditions. ^[ref] Such an adaptation avoids treating hand use as a cognitive prerequisite, but creates a greater interpretive burden: body inspection must be distinguished from ordinary swimming, attention to handling or generalized interest in the mirror. Spatially specific changes and blinded coding are particularly valuable.

cleaner wrasse challenge assumptions about which animals should count as passing. Following mirror exposure, fish with coloured marks on otherwise unseen regions scraped their bodies in the mirror condition; transparent marks and coloured marks without a mirror did not elicit the same pattern. ^[ref] The ecological relevance of parasite-like marks helps explain motivation and sharpens the test. It also raises mechanistic questions about whether the animal identifies a persistent visual self or uses learned reflected cues to localize a possible parasite. Those alternatives require further controls and transfer tests; accepting a behavioural criterion in mammals but rejecting identical criteria solely because the animal is a fish would be inconsistent.

Tests in other modalities can help identify capacities missed by a visual assay. dogs investigated modified own odours more than unmodified own odours, with comparisons involving other dogs and the added odour alone. ^[ref] The modifier-only comparison addresses simple interest in a novel smell, but sniffing longer does not require locating a change on one's own body. It consequently supports odour discrimination and a possible self-related comparison more directly than it establishes the same representation tested by hidden-mark localization. Ecologically appropriate tasks should be compared in terms of their information and inferential demands, rather than all being declared interchangeable mirror tests.

A stronger account would combine spontaneous mirror-guided inspection, transfer to new untrained body locations or viewing arrangements, and independent tasks probing self-related information. Training should be reported explicitly: success after reinforcement demonstrates a learned capacity under those conditions, while spontaneous generalization supports a different claim. Samples should include individual and developmental variation, and comparative analyses should retain uncertainty rather than coding entire species as cognitively present or absent after a handful of observations.

A well-controlled pass is evidence for mirror-guided bodily identification; it is not a complete measure of a self-concept. A failure is compatible with absent capacity, unsuitable task demands or insufficient motivation. The mirror-mark test is most useful as one component of a comparative research programme that separates those possibilities.

Non-human animals show evidence for several components of social-state tracking, but the evidence does not establish a uniform, human-like theory of mind. Theory of mind should be decomposed into sensitivity to goals, visual access, knowledge and belief, rather than treated as a single ability that an animal either possesses or lacks. The central evidential question is whether behaviour requires representing another's mental state, or can be explained by learned relationships among observable actions, contexts and outcomes.

Goal attribution has support from experiments distinguishing similar outcomes produced by different actions. Chimpanzees responded differently to a person who was unwilling to transfer food and one who was willing but unable: they persisted differently and left earlier in the unwilling condition. ^[ref] Holding the absence of food transfer broadly constant prevents the explanation that any unrewarded trial produces the same reaction. The contrast supports sensitivity to the organization or apparent purpose of actions. However, differences in movement and affect remain observable cues, so the finding need not imply a fully explicit concept of intention. Generalization to new obstacles and action sequences is a stronger test than repeating familiar signals.

Visual perspective taking concerns another individual having a different view. When dominant and subordinate chimpanzees competed for food, subordinates preferentially obtained food to which they had better visual access. Giving the subordinate a headstart forced its choice before the dominant's approach could reveal the answer, reducing a straightforward movement-following explanation. ^[ref] Such controls support tracking of another's visual access. They do not show that the subject represents every aspect of how the scene looks to the other animal; access to an object is a narrower problem than its appearance from a different viewpoint.

The distinction extends from seeing to knowing. An animal can potentially remember whether another witnessed hiding even after neither currently sees the food. Controlled competitive tasks found chimpanzees sensitive to knowledge versus ignorance, yet not successful in closely related false-belief conditions. ^[ref] Knowledge attribution therefore has stronger support in those tasks than an unrestricted ability to predict action from mistaken beliefs. Negative performance is not proof of incapacity: memory, inhibitory demands, motivation and task comprehension may limit the response. But a positive result for knowledge should not be relabelled a positive result for belief simply because both are social.

Bird studies provide evidence beyond primates. Ravens that had experienced a peephole altered cache-protection behaviour when a potential observer could be heard but not seen. The use of recorded sounds removed an actual competitor's gaze and movements as immediate guides, and the manipulation of available visual access made the test more informative than comparison of merely occupied and empty rooms. ^[ref] This supports generalization from access conditions to a possible observer. It remains possible to model performance through learned relations between openings, sounds and risk; novel transfer tests are needed to distinguish how abstractly the bird represents “being seen”.

Experience with one's own actions can also change responses to others. Scrub jays with previous pilfering experience showed stronger re-caching responses after having been observed caching. ^[ref] One interpretation is projection of the bird's own pilfering experience onto a potential competitor. Another is acquisition of a more general rule about cache vulnerability. The finding makes prior experience a causal candidate and suggests a relation between self and other, but it does not establish that the bird consciously imagines another individual's intentions. Observed and unobserved caching, prior experience and the opportunity to relocate food all need to be distinguished.

False-belief understanding sets a particularly demanding criterion: the subject must predict an agent using information that the subject knows is wrong. In great apes, an anticipatory looking paradigm found looks towards the location where an agent falsely believed an object remained, even when the subject had seen the object's removal. ^[ref] This bypasses some demands of an active food-choice response. Yet gaze towards a previously attended location can also arise from action prediction, attentional cues or associations with where an actor last saw an object. Anticipation is therefore evidence about prediction, whose representational basis needs further controls.

A subsequent experiment manipulated the ape's own experience of a barrier that looked the same from a distance but was either opaque or translucent. All subjects then watched the same test actions. Those with the opaque experience were more likely to anticipate the actor searching according to the outdated location. ^[ref] Because the visible test behaviour was held constant, an explanation relying only on a difference in the actor's immediate behaviour was weakened. The result supports transfer from self-experience to another's informational situation. It still leaves questions about the breadth of the represented belief: a limited model of visual registration and action expectation may succeed without the flexible propositional reasoning characteristic of human language.

Taken together, positive anticipatory-looking results and negative active-choice results need not be forced into a single yes/no answer. The tasks measure different outputs and impose different demands. Stronger evidence would show the same individuals generalizing across novel agents, objects and routes of access, distinguishing true belief, false belief and ignorance while physical events, attention and rewards are controlled. Eye-tracking analyses should specify regions and timing in advance, report the subjects who produce no usable anticipatory look, and avoid inferring population-wide competence solely from a selected subset of trials. Replication and uncertainty around effects matter especially with small captive samples.

The relation to self-representation is similarly componential. Using one's experience of a transparent barrier to predict another's access suggests some correspondence between self and other. It does not demonstrate an autobiographical self or reflection on one's own beliefs. Metacognition, such as selective information seeking when knowledge is missing, concerns monitoring one's own processing and is not equivalent to attributing knowledge to somebody else. Mirror self-recognition concerns one's body and is neither a necessary consequence nor a sufficient demonstration of belief attribution. These distinctions prevent a visually based test from becoming a universal scale of mentality.

The defensible conclusion is a mosaic: animals can track goals and access, some experiments support knowledge attribution and belief-sensitive predictions, and the most elaborate interpretation remains contested. The experiments constrain possible representations of self and others; their value lies in progressively excluding alternatives, rather than naming a mental state after any apparently intelligent social response.