A slightly different version of this paper will appear shortly in TICS.

Recent advances in the cognitive neuroscience of action have considerably enlarged our understanding of human motor cognition. In particular, the activity of the mirror system, first discovered in the brain of non-human primates, provides an observer with the understanding of a perceived action by means of the motor simulation of the agent’s observed movements. This discovery has raised the prospects of a “motor theory of social cognition”. Human social cognition includes the ability to mindread, which in turn plays a crucial role in human communication. Thus, many motor theorists of social cognition try to bridge the gap between human motor cognition and human mindreading by endorsing a simulation account of human mindreading. We are skeptical about both the simulation account of human mindreading and the prospects of a motor theory of social cognition. As we shall argue in the first section of this paper, much of our skepticism about the simulation account of human mindreading stems from the fact that the concept of simulation involved in simulation accounts of human mindreading so far is a mongrel concept. The rest of the paper will be devoted to explaining why we are skeptical about the prospects of a motor theory of social cognition.

1. Mental simulation: a hybrid concept

            Mental simulation, of which motor simulation is but an instance, is a hybrid concept: it involves at least two separable ingredients. One idea is that a cognitive mechanism may be used “off-line”. For example, it has been suggested (by e.g., Currie, 1995) that in visual imagery, the human visual system is used off-line: instead of taking retinal inputs, it receives inputs from memory. Instead of producing a visual percept, it produces a mental visual image. Thus, visual imagery consists in simulating visual perception or, as Gallese and Goldman  (1998) put it, “in pretending to see” (p. 497).[1]

            The other idea is that mental simulation is the cognitive basis of imitation. As we shall argue next, one natural assumption is that the firing of MNs in the pre-motor cortex is the neural basis of motor imitation. MNs have been discovered in the brain of macaque monkeys. The question arises: do they imitate? Until recently, the evidence seemed negative (Tomasello and Call, 1997). But there is intriguing new positive evidence (Kumashio et al., 2003). Interestingly, simulation theorists (ST) of mindreading have taken two different, if not irreconcilable, positions on imitation. On the one hand, Gallese and Goldman (1998) have strongly denied that a function of MNs is “to promote learning by imitation” (p. 495-6). On the other hand, they have stressed the importance of imitation in tasks of third-person mindreading: “ST depicts mindreading as incorporating an attempt to replicate, mimic, or impersonate the mental life of the target agent” (p. 497).

            The main problem with imitation is that it is a folk psychological concept whose boundaries are presently too ill-defined for scientific purposes. Newborn babies, who reproduce facial movements of lip and tongue protrusion, have been said to imitate (Meltzoff and Moore, 1997). And so have 18 month old toddlers, who have been shown to be able to produce a correct version of an action of which they have observed an aborted version (Meltzoff, 1995). Does imitation reduce to copying? Or does imitation allow creative interpretation? Unless this ambiguity is resolved, it is hard to evaluate Meltzoff and Decety’s (2003) claim that “motor imitation” is “the missing link” between MNs and “theory of mind”. If imitation requires copying, then, unlike observable behavior, beliefs cannot be imitated for they cannot be copied. If imitation is not restricted to copying and if creative interpretation is allowed as part of imitation, then perhaps even beliefs could be imitated. But one cannot have it both ways.

2. The discovery of MNs: a great discovery

            Motor theories of human cognition are ubiquitous. Our main topic is the motor theory of social cognition. The remarkable discovery of so-called “mirror neurons” (MNs) in the ventral pre-motor cortex (area F5) of macaque monkeys (Rizzolatti et al., 1996; Rizzolatti et al., 2000; Rizzolatti et al., 2004) and the discovery of the mirror system in humans (Rizzolatti et al., 1996; Grafton et al., 1996; Decety et al., 1997; Fadiga et al., 1995) have raised the prospects of a motor theory of social cognition, whose goal is to derive much (if not all) of human social cognition from human motor cognition (Gallese, 2003; Wolpert et al., 2003; Blakemore and Decety, 2001; Metzinger and Gallese, 2003). MNs are sensori-motor neurons that fire both when a monkey executes certain kinds of actions and when the monkey perceives the same actions being performed by another (Rizzolatti et al., 1996; Rizzolatti et al., 2000; Rizzolatti et al., 2004). The discharge of mirror neurons in area F5 of the ventral pre-motor cortex of macaque monkeys has been recorded when the monkey alternatively sees, hears and both sees and hears a transitive noisy hand action (Keysers et al. 2003, Kohler et al. 2003). This evidence suggests that MNs are cross-modal sensori-motor neurons. The activity of MNs has also been recorded when the monkey perceives a transitive hand action whose target is being occluded towards the end of action observation (Rizzolatti et al., 2001). This evidence shows that visual access to object-hand interaction is not necessary for eliciting the discharge of mirror neurons. Transitive ingestive mouth actions also elicit the discharge of MNs. So far, it is not known whether intransitive (communicative) mouth actions elicit the discharge of MNs in the monkey (Ferrari et al., 2003).[2] In humans, evidence from brain imaging reveals that the mirror system can be elicited by the execution and the perception of a much wider class of perceptible actions including not only “intransitive” hand and mouth actions (not directed towards a manipulable target), but also pantomimes of hand actions( Rizzolatti, et al. 1996; Grafton et al., 1996; Decety et al., 1997).

            By automatically matching the agent’s observed movements onto her own motor repertoire without executing them, the firing of MNs in the observer’s brain simulates the agent’s observed movements and thereby contributes to the understanding of the perceived action (Rizzolatti et al., 1996; Rizzolatti et al., 2000; Rizzolatti et al., 2004). Thus, MNs supply motor, not purely perceptual, representations of actions. Because they are located in the pre-motor cortex, MNs should not fire in an observer’s brain unless the represented action were executable, i.e., consistent with the rules of the motor system (Decety and Jeannerod, 1996; Jeannerod, 2001). We therefore think that one important function of MNs might be to enhance learning technical skills by allowing motor imitation, i.e., reproducing an observed motor sequence (Rizzolatti et al., 2000; Jacob and Jeannerod, 2003, ch. 7).[3] However, we are skeptical about the view that MNs constitute the fundamental neural basis of human social cognition.

3. Human social cognition and mindreading

            In a weak sense, human social cognition encompasses all cognitive processes relevant to the perception and understanding of conspecifics (Blakemore et al., 2004). So it includes, but it is not restricted to, the cognitive processes involved in the understanding of perceived actions performed by conspecifics. It is widely recognized that what is distinctive of human social cognition is the human mindreading ability to understand, not just the observable behavior of one’s conspecifics, but also one’s own mind (which we shall ignore here) and especially the minds of others (Baron-Cohen, 1995; Leslie and Thaiss, 1992; Frith and Frith, 2003; Saxe et al., 2004).[4] Thanks to their mindreading ability, healthy human adults readily explain and predict human actions by representing and attributing to human agents a whole battery of internal unobservable mental states such as goals, intentions, emotions, perceptions, desires, beliefs, many of which are far removed from any observable behavior (Gopnik and Wellman, 1994). It is also intuitively clear that there is a gap between full-blown human mindreading and the psychological understanding of perceived actions afforded by MNs. Thus, the challenge faced by motor theorists of social cognition is to bridge this gap.

            Faced with this challenge, the strategy favored by motor theorists of social cognition is to tinker with the concept of motor simulation, as suggested by simulation theorists of mindreading (Gallese, 2003; 2004; Metzinger and Gallese, 2003; Blakemore and Decety, 2001; Gordon, 1995; Goldman, 1995). We disapprove this strategy because it relaxes the fundamental link between simulation and the requirements of the motor system, which we take very seriously. The firing of MNs is a social cognitive process only in a very weak sense. When MNs fire in the brain of a monkey during action execution, the discharge is not a social cognitive process at all. When MNs fire in the brain of a monkey watching another grasp a fruit, the discharge is a weakly social process: the two monkeys are not involved in any kind of non-verbal intentional communication. The agent intends to grasp a fruit, not to impart some information to his conspecific. Nor does the observer’s understanding of the action require him to understand the agent’s communicative intention (because the agent has none). 

            One way to question the motor theory of social cognition would be to challenge it to account for the human capacity to read one’s own mind or to ascribe false beliefs to others — something that healthy human adults do all the time without effort. But this is not what we shall do. Instead, we shall grant that simulating an agent’s movements may be sufficient for understanding his motor intention, but we shall argue that it is not sufficient for understanding the agent’s prior intention, his social intention and his communicative intention. Then, we shall argue that motor simulation might not even be necessary for understanding all perceived actions. Finally, we shall argue that a significant part of human social cognition is comprised of a “perceptual social” system whose neural basis has perceptual but no motor properties (Allison et al., 2000; Jacob and Jeannerod, 2003, ch. 7).

4. Motor simulation, motor intentions and prior intentions

            Evidence from brain imaging in healthy adults and autistic individuals suggests that reasoning about beliefs and representing goals and intentions are subserved by different brain areas (Frith and Frith, 2003; Saxe et al., 2004). Evidence from developmental psychology suggests that the former is a later and more costly accomplishment than the latter (Baron-Cohen, 1995; Leslie and Thaiss, 1992; Leslie and Polizzi, 1998). An action is a goal-directed sequence of bodily movements initiated and monitored by what we shall call a “motor intention”. Understanding a perceived action requires at least representing the agent’s motor intention. Although human adults readily explain actions by representing agents’ (true or false) beliefs, it is possible, by relying on one’s own current perception of the world, to represent the goal of a perceived action or the agent’s motor intention without representing an agent’s (true) beliefs. By simulating the agent’s perceived movements, the observer may represent the agent’s motor intention.

            Indeed, before they can reason about beliefs, young children can represent goals and intentions (Frith and Frith, 2003; Saxe et al., 2004). After having been habituated to seeing a reach-and-grasp hand movement, five- to eight month-old infants look longer when the target of the prehension movement changes than when the path of the hand movement changes (Woodward, 1998). However, when grasping by a human hand is replaced by the motion of an artefact, e.g., a metal claw, the pattern of preference elicited by seeing the movement of the human hand disappears (Woodward, 1998). This is compatible with the hypothesis that infants represent the goal of the action and the agent’s motor intention by matching the observed hand movement onto their own motor repertoire, i.e., by motor simulation.

            Philosophers, however, have long emphasized the distinction between basic actions and non-basic actions: for example, the non-basic action of turning on the light can be performed by the basic action of pressing a switch. They also make the correlative distinction between motor intentions (or “intentions in action”) and “prior” intentions whose goals are more remote (Searle, 1983; Pacherie, 2000). A motor intention is an intention to execute a basic action. Given one’s prior intention to execute the non-basic action of turning on the light, one forms the motor intention to perform the basic action of e.g., pressing the switch with one’s right index finger. Perceiving the basic action of pressing the switch with the right index finger automatically causes the observer to entertain the very motor representation that guides the agent’s execution of the action. By executing the basic action, the agent also performs the non-basic action of turning on the light. The agent’s basic action is controlled by his motor intention. His non-basic action is controlled by his prior intention.

            By pressing the switch downwards with one’s right index finger, one might turn on the light. But by executing the same motor sequence, one might also (depending on the electrical set up) turn the light off. If so, then representing an agent’s motor intention to press the switch downwards with his index finger will not allow the observer to figure out the agent’s prior intention. In order to move from representing the agent’s motor intention to representing his prior intention, the observer needs at least to know whether the light was off or on prior to the agent’s action. We surmise that by simulating the agent’s perceived movement of pressing the switch with his right index finger, an observer will understand the agent’s motor intention to execute the basic action, not his prior intention to execute the non-basic action.

5. Motor simulation and understanding social intentions

            Not all human actions are directed towards inanimate targets. Some are directed towards conspecifics. In addition to the distinction between motor intentions and prior intentions, an agent’s non-social intentions must be distinguished from his social intentions, i.e., his intentions to act on conspecifics, who, unlike inanimate targets of action, can act back. Thus, a social intention is an intention to affect a conspecific’s behavior. Since humans often act out of their mental representations, a social intention may also be an intention to modify a conspecific’s mental representations. The question is: could an observer represent an agent’s social intention by simulating the agent’s observed movements? As the following little thought-experiment will show, it is unlikely that what enables an observer to represent an agent’s social intention is the observer’s ability to match an agent’s perceived movements onto her own motor repertoire.

            Consider Dr Jekyll and Mr Hyde. The former is a renowned surgeon who performs appendectomies on his anesthestized patients. The latter is a dangerous sadist who performs exactly the same hand movements on his non-anesthestized victims. As it turns out, Mr Hyde is Dr Jekyll. Suppose that Dr Watson witnesses both Dr Jekyll’s and Mr Hyde’s actions. Upon perceiving Dr Jekyll alias Mr Hyde execute twice the same motor sequence whereby he grasps his scalpel and applies it to the same bodily part of two different persons, presumably the very same MNs produce the same discharge in Dr Watson’s brain. Dr Jekyll’s motor intention is the same as Mr Hyde’s. However, Dr Jekyll’s social intention clearly differs from Mr Hyde’s: whereas Dr Jekyll intends to improve his patient’s medical condition, Mr Hyde intends to derive pleasure from his victim’s agony. By matching them onto her own repertoire, an observer simulates the agent’s movements. Simulating the agent’s movements may allow an observer to represent the agent’s motor intention. We surmise that it will not allow her to represent the agent’s social intention.

6. Motor simulation and understanding communicative intentions

            MNs were first discovered in the context of motor and perceptual tasks that had a very weak social content, if any. As recognized by philosophers, psychologists and linguists studying pragmatics, especially complex among a human agent’s social intentions are his (reflexive or self-referential) communicative intentions. Whether verbally expressed or not, a  communicative intention is an intention to impart information by virtue of its own recognition by the addressee (Grice, 1989; Sperber and Wilson, 1986). Jill may have the communicative intention to let Bill know that his wife is unfaithful to him by telling him. If so, then Bill will not acquire the belief that his wife is unfaithful to him unless he recognizes that Jill intended him to believe it by telling him. But Jill may also have the social intention to cause Bill to believe that his wife is unfaithful to him without Bill’s recognizing Jill’s social intention. Bill may well acquire the belief that his wife is unfaithful to him as a result something Jill did without Bill’s recognizing Jill’s social intention. If so, then Jill’s social intention is not a communicative intention.

            Now, consider Jill’s non-verbal communicative intention whereby she intends to convey to John her desire to leave the party by ostensively pointing her index finger onto her wrist-watch in front of John. John thereby acquires the belief that Jill wants to leave the party by recognizing her communicative intention. Jill may, however, execute the very same ostensive bodily movement if she wants John to believe instead that her watch is inaccurate. Simulating Jill’s movement of her right index finger towards her left wrist will allow John to represent Jill’s motor intention. But it will not allow him to distinguish between Jill’s two communicative intentions.

7. Why motor simulation may not be necessary for understanding all perceived actions

            Simulating an agent’s observed movements is not sufficient for representing either an agent’s prior intention or his social intention. Is it necessary? Evidence from developmental psychology suggests that it is not. Upon perceiving their relative motions, 9 month old infants automatically ascribe goals to moving geometrical stimuli (Gergely et al., 1995; Csibra et al., 1999). The question is: why do they ascribe goals to moving geometrical stimuli, not to a metal claw moving towards a standing inanimate target (Woodward, 1998)?

            It has long been known that perceiving the relative motions of geometrical stimuli (e.g., circles and triangles) with no human or animal aspect may prompt normal adults to ascribe to the moving stimuli emotions and social intentions that they describe using intentional verbs such “chase”, “corner”, “attack”, “caress” or “comfort” (Heider and Simmel, 1943; Castelli et al., 2000). There is also evidence that three to four year old toddlers respond like adults to the perception of Heider and Simmel type of stimuli (Berry and Springer, 1993). Recently, when showed a triangle and a square whose motions were automatically seen respectively as “helping” and as “hindering” a circle move up a slope, 12 month old infants exhibited a clear preference for the former over the latter (Kuhlmeier et al., 2003).

            Seeing the biological movement of a human hand reach and grasp a target prompts a human observer to represent the agent’s motor intention by automatically matching the perceived movement onto her own motor repertoire (Woodward, 1998). Given the asymmetry between a moving human hand and its inanimate target, perceiving the action elicits the attribution of a motor intention, not of a social intention, to the agent. By contrast, geometrical stimuli form a homogeneous class of entities. Seeing geometrical stimuli move in relation to one another causes in humans a “perceptual social illusion”, i.e., an illusion of social interactions guided by social intentions (Gergely et al., 1995; Csibra et al., 1999; Heider and Simmel, 1943; Castelli et al., 2000). But given that the motion of geometrical stimuli is non-biological, it follows that the process whereby social intentions are represented and ascribed cannot be by matching the observed motions onto one’s own motor repertoire, i.e., by simulation in the narrow sense. Clearly, the process whereby geometrical stimuli are ascribed social intentions cannot be motor simulation.

            Many social interactions are actions at a distance that involve an agent’s head- and eye-movements towards or away from, but no direct bodily contact with, a conspecific. On the one hand, by the age of 7 months, human infants expect human interactions, unlike causal relations between inanimate objects, not to involve bodily contact (Spelke et al., 1995). On the other hand, much evidence from single cell recordings in the brain of macaque monkeys and from brain imaging in human adults suggests the existence of a purely perceptual system of “social perception” (Allison et al., 2000; Jacob and Jeannerod, 2003, ch. 7) that can be tricked by perceptual illusions (the hallmark of perceptual systems). It involves the cooperation between at least three brain areas: the Superior Temporal Sulcus (STS), the amygdala and the orbito-frontal cortex (Allison et al., 2000; Adolphs, 1999; Adolphs et al., 1998; Perrett et al., 1982; Perrett et al., 1989; Jacob and Jeannerod, 2003, ch. 7). Unlike neurons in F5 and in the inferior parietal lobule, which fire in response to the perception of object-oriented actions, many neurons in STS respond to the perception of others’ actions directed towards conspecifics: they lack motor properties (Rizzolatti et al., 2000; Keysers and Perrett (2004) and they do not respond to the perception of one’s own movements (Hietanen and Perrett, 1993; Hietanen and Perrett, 1996).

            There is a good reason why the perceptual response to a perceived action directed towards a conspecific would lack motor properties. The inanimate target of an object-oriented action does not act. As a result, the only movements which an observer can automatically match onto his own motor repertoire are the agent’s. If, however, the target of a perceived action is a conspecific, then he or she will react. But then, the observer will simply be unable to automatically and simultaneously match onto his own motor repertoire the perceived movements of both agents. Only if he intentionally neglects one of the agent’s observed movements will the observer be able to simulate the other’s movements. This may be a case of motor simulation, but it is an intentional, not an automatic, process. An observer’s motor system has the cognitive resources to automatically and simultaneously match the observed movements of an agent performing a transitive (object-directed) or intransitive action, but not a pair of observed movements performed by two interacting agents.

Conclusion

            The mirror system is the mechanism whereby an observer understands a perceived action by simulating, without executing, the agent’s observed movements. The motor properties of the mirror system are well designed for representing an agent’s motor intention involved in an object-oriented action, not for representing an agent’s prior intention, let alone his social (and his communicative) intentions. The mirror system does not seem well designed for promoting fast responses to the perception of social actions directed towards conspecifics. For example, in response to the perception of a threat, it may be adaptive to flee, not to simulate the threatening agent’s observed movements. Evidence from single cell recordings in the monkey STS shows that observing many actions towards conspecifics prompts purely perceptual responses without motor properties. Important for future research are questions relevant to the assessment of the scope of the primate system for pure “social perception”: for example, would a male monkey respond to the perception of a female’s behavioral response to his own courting behavior by matching her observed movements? We predict that it would not.

References

Adolphs, R. et al. (1998) The human amygdala in social judgment. Nature 393, 470-474.

Adolphs, R. (1999) Social cognition and the human brain. Trends in Cognitive Sciences 3, 12, 469-479.

Allison, T. et al. (2000) Social perception from visual cues: role of the STS region. Trends in Cognitive Sciences 4, 7, 267-278.

Baron-Cohen, S. (1995) Mindblindness: Essay on Autism and the Theory of Mind, Learning, Development & Conceptual Change The MIT Press.

Berry, D.S. and Springer, K. (1993) Structure, motion, and preschoolers’ perception of social causality. Ecological Psychology 5, 273-283.

Blakemore, S-J. and Decety, J. (2001) From the perception of action to the understanding of intention. Nature Neuroscience 2, 561-567.

Blakemore, S-J. et al. (2004) Social cognitive neuroscience: where are we heading? Trends in Cognitive Sciences 8, 5, 216-221.

Castelli, F. et al. (2000) Movement and mind: a functional imaging study of perception and interpretation of complex intentional movement patterns. NeuroImage 12, 314-325.

Csibra, G. et al. (1999) Goal attribution without agency cues: the perception of ‘pure reason’ in infancy. Cognition 72, 237-267.

Currie, G. (1995) Visual imagery as the simulation of vision. Mind and Language 10, 1/2, 25-44.

Decety, J. and Jeannerod, M. (1996) Fitts’ law in mentally simulated movements. Behavioral Brain Research 72, 127-134.

Decety, J. et al. (1997) Brain activity during observation of action. Influence of action content and subject’s strategy. Brain 120, 1763-1777.

Fadiga, L. et al. (1995) Motor facilitation during action observation: a magnetic stimulation study. Journal of Neurophysiology 73, 2608-2611.

Ferrari, P.F. et al. (2003) Mirror neurons responding to the observation of ingestive and communicative mouth actions in the monkey ventral premotor cortex. European Journal of Neuroscience 17, 1703-14.

Frith, U. and Frith, C. D. (2003) Development and neurophysiology of mentalizing. In The Neuroscience of Social Interaction (Frith, C. & Wolpert, D. eds) pp. 45-75 OxfordUniversity Press.

Gallese, V. (2003) The manifold nature of interpersonal relations: the quest for a common mechanism. In The Neuroscience of Social Interaction (Frith, C. & Wolpert, D. eds), pp. 159-182, Oxford University Press.

Gallese, V. (2004) Intentional attunement. The mirror neuron system and its role in interpersonal relations. http://www.interdisciplines.org/mirror/papers/1

Gallese, V. and Goldman, A. (1998) Mirror neurons and the simulation theory of mindreading. Trends in Cognitive Sciences 2, 12, 493-501.

Gergely, G. et al. (1995) Taking the intentional stance at 12 months of age. Cognition 56, 165-193.

Goldman, A. (1995) Interpretation psychologized. In Folk Psychology (Davies, M. & Stone, T. eds), pp. 74-99, Blackwell.

Gopnik, A. and Wellman, H.M. (1994) The theory theory. In Mapping the Mind: Domain Specificity in Cognition and Culture (Hirschfeld, L.A.and Gelman, S.A.eds) pp. 257-294 CambridgeUniversity Press.

Gordon, R. (1995) Folk psychology as simulation. In Folk Psychology (Davies, M. & T. Stone, T. eds), pp.  60-73, Blackwell.

Grafton, S.T. et al . (1996) Localization of grasp representations in humans by PET: 2. Observation compared with imagination. Experimental Brain Research 112, 103-111.

Grice,  H. P. (1989) Studies in the Way of WordsHarvardUniversityPress.

Heider, F. and Simmel, M. (1944) An experimental study of apparent behavior. American Journal of Psychology 57, 243-259.

Hietanen, D.K. and Perrett, D.I. (1993) Motion sensitive cells in the macaque superior temporal polysensory area. 1 Lack of response to the sight of the animal’s own limb movement. Experimental Brain Research 93, 117-128.

Hietanen, D.K. and Perrett, D.I. (1996) Motion sensitive cells in the macaque superior temporal polysensory area: response discrimination between self-generated and externally generated pattern motion. Behavioural Brain Research 76, 155-167.

Jacob, P. and Jeannerod, M. (2003) Ways of Seeing, the Scope and Limits of VisualCognitionOxfordUniversityPress.

Jeannerod, M.(2001) Neural simulation of action: a unifying mechanism for motor cognition. NeuroImage 14, S103-S109.

Keysers, C. et al. (2003) Audiovisual mirror neurons and action recognition. Experimental Brain Research 153, 628-636.

Keysers, C. and Perrett, D.I. (2004) The neural correlates of social perception: a Hebbian network perspective. Trends in Cognitive Sciences 8, 11, 501-507.

Kohler, E. et al. (2002) Hearing sounds, understanding actions; action representation in mirror neurons. Science 297, 846-48.

Kuhlmeier, V. et al. (2003) Attribution of dispositional states by 12-month olds. Psychological Science 14, 5, 402-408.

Kumashio, M. et al. (2003) Natural imitation induced by joint attention in Japanese monkeys. International Journal of Psychophysiology 50, 81-99.

Leslie, A. and Polizzi, P. (1998) Inhibitory processing in the false belief task: two conjectures. Developmental Science 1, 247-253.

Leslie, A. and Thaiss, L. (1992) Domain specificity in conceptual development. Cognition 43, 225-251.

Meltzoff, A.N. and Moore, M.K. (1997) Explaining facial imitation. A theoretical model. Early Development and Parenting 6, 179-192.

Meltzoff, A.N. (1995) Understanding intentions of others: reenactment of intended acts by 18 months-old children. Developmental Psychology 31, 838-850.

Meltzoff, A.N. and Decety, J. (2003) What imitation tells us about social cognition: a rapprochement between developmental psychology and cognitive science. In The Neuroscience of Social Interaction (Frith, C. & Wolpert, D. eds) pp. 109-130, OxfordUniversity Press.

Metzinger, T. and Gallese, V. (2003) The emergence of a shared ontology: building blocks for a theory. Consciousness and Cognition 12, 549-571.

Pacherie, E. (2000) The content of intentions. Mind and Language 15, 4, 400-432.

Perrett, D.I. et al. (1982) Visual neurones responsive to faces in the monkey temporal cortex. Experimental Brain Research 47, 329-342.

Perrett, D.I. et al. (1989) Frameworks of analysis for the neural representation of animate objects and actions. Journal of Experimental Biology 146, 87-113.

Rizzolatti, G. et al. (1995) Premotor cortex and the recognition of motor actions. Cognitive Brain Research 3, 131-141.

Rizzolatti, G. et al. (1996) Localization of grasp representations in humans by PET: 1. Observation versus execution. Experimental Brain Research 111, 246-252.

Rizzolatti, G. et al. (2000) Cortical mechanisms subserving object grasping and action recognition: a new view of the cortical motor functions. In The New Cognitive Neuroscience (Gazzaniga, M. ed), pp. 539-552, MIT Press.

Rizzolatti, G. et al. (2004) A unifying view of the basis of social cognition. Trends in Cognitive Sciences 8, 9, 396-403.

Saxe, R. et al. (2004) Understanding other minds: linking developmental psychology and functional neuroimaging. American Review of Psychology 55, 87-124.

Searle, J. (1983) Intentionality, an Essay in the Philosophy of MindCambridgeUniversityPress.

Sperber, D. and Wilson, D. (1986) Relevance, Communication and CognitionHarvardUniversityPress.

Spelke, E. et al. (1995) Infants’ knowledge of object motion and human action. In Causal Cognition, a Multidisciplinary Debate (Sperber, D., Premack, D. and Premack, A.J. eds) pp. 44- 78, OxfordUniversity Press.

Tomasello, M. and Call, J. (1997) PrimateCognitionOxfordUniversityPress.

Wolpert, D. et al. (2003) A unifying computational framework for motor control and social interaction. In The Neuroscience of Social Interaction (Frith, C. & Wolpert, D. eds), pp. 305-322, Oxford University Press.

Woodward, A.L. (1998) Infants selectively encode the goal object of an actor’s reach. Cognition69, 1-34.