Who Needs Emotions The Brain Meets the Robot - Fellous & Arbib Part 9 pdf

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How Do We Decipher Others’ Minds? marc jeannerod 6 The central issue of how we access the mental contents of other individ- uals can be grounded in the concept of “self,” both the narrative self who knows who we are, where we are, what we are presently doing, and what we were doing before, and the embodied self which is bound to particular bodily events, like actions. This chapter emphasizes communication be- tween embodied selves, operating at a subpersonal level outside the aware- ness and conscious strategies of the two selves. We will show how mental states of others can be accessed through mind reading, a classical account of which is the simulation theory which holds that we exploit our own psychological responses in order to simulate others’ minds. We first de- scribe experiments that provide support to the notion of simulation from outside the realm of communication, stressing how the self’s representa- tion of its own actions are reflected in terms of changes in brain activity. We then extend the notion of simulation to the observation of others— and then show that this mechanism is not immune to misattribution of mental states in either direction, i.e., self attributing mental states of others as well as attributing to others one’s own mental states. The aim of this chapter is to understand how we access the mental contents of other individuals. People generate intentions, have goals, and feel emotions and affects. It is essential for each of us to penetrate the internal world of others, particularly when their intentions or goals are 148 brains directed to us or when their emotions relate to us. This very fact of knowing that one is the subject of others’ mental states (that one is what other people think about) is a critical condition for fully human communication between individuals. There are a few preliminary queries to answer before discussing the prob- lem of communication between individuals. The first query is about ourselves: “What makes us self-conscious?” or “What makes us such that we can con- sciously refer to ourselves as that particular self, different from other selves?” There are several ways to answer this question, according to the level at which one considers the idea of a self. One of these levels is that of the narrative self. As a narrator, we obviously know who we are, where we are, what we are presently doing, and what we were doing before. Unless we become demented or amnesic, we have a strong feeling of continuity in our conscious experi- ence. We rely on declarative memory systems where souvenirs (albeit distorted) can be retrieved and used as material for verbalization or imagination. Another level is that of the embodied self. We recognize ourselves as the owner of a body and the author of actions. At variance with the narrative self, the type of self-consciousness that is linked to the experience of the embodied self is discontinuous: it operates on a moment-to-moment basis as it is bound to particular bodily events, like actions. Instead of explicitly answering ques- tions like “Who am I?” (something that the narrative self needs to know permanently), the embodied self will answer questions like “Is this mine?” or “Did I do this?”—questions to which we rarely care to give an explicit response. In other words, the embodied self mostly carries an implicit mode of self-consciousness, whereby self-consciousness is around but becomes mani- fest only when required by the situation. The related information has a short life span and usually does not survive the bodily event for very long. The second question that has to be answered as a preliminary to the discussion about communication is actually related to the first one: “Which level of conscious experience are we considering for discussing communica- tion with other individuals?” By keeping a parallel with the above distinc- tion between a narrative level and an embodied level of the self, one could propose that communication between individuals can be established at ei- ther level. An act of communication between narrative selves commonly uses a verbal approach, for example, “What are you going to do?” or “What do you think?” or “Do you love me?” In other words, a narrative self aims at establishing communication with a narrative other. He or she uses a rational way of putting together available information and building a narrative struc- ture about the other person’s experience. By contrast, an act of communi- cation between embodied selves operates at a subpersonal level outside the awareness and conscious strategies of the two selves. In this mode of com- munication, the two selves establish contact to the extent that their mental how do we decipher others’ minds? 149 states are embodied (i.e., transcribed into bodily states) and to the extent that their intentions, feelings, emotions, and attitudes can be read by an external observer. In this chapter, emphasis will be clearly put on communication between selves at the embodied level. We will show how mental states of others can be accessed through mind reading, a general human ability for understand- ing other minds with the purpose of establishing communication with them. From a philosophical point of view, a classical account of mind reading is the simulation theory. Accordingly, it is thought that we exploit our own psychological responses in order to simulate others’ minds or, in other words, that we internally simulate others mental states in our own mind. The out- come of this simulation process provides us with information about how others think or feel by reading our own mind (Goldie, 1999; for a full ac- count of the philosophical issues raised by the simulation theory, see Davies & Stone, 1995). We will first describe experiments that support the notion of simula- tion from a solipsist point of view, i.e., outside the realm of communication with others. The reason for this choice is that most of the empirical argu- ments for the simulation theory have been developed on the basis of how a subject represents his or her own actions to him- or herself and, more spe- cifically, how the representation of actions reflects changes in brain activity. We will extend the notion of simulation to the observation of others on the basis of more recent experimental data which suggest that actions and emo- tions of others can be represented by an observer to the same extent as he or she represents his or her own actions. Finally, we will see that this mecha- nism is not immune to errors of identification: simulation of one’s own mind or of the minds of other individuals can yield to misattribution of mental states in either direction, i.e., self-attribution of the mental states of others as well as attribution to others of one’s own mental states. THE SIMULATION THEORY IN THE SOLIPSIST CONTEXT The simulation theory postulates that covert actions are in fact actions in their own right, except for the fact that they are not executed. Covert and overt stages represent a continuum such that every overtly executed action implies the existence of a covert stage, whereas a covert action does not necessarily turn into an overt action. As will be argued below, most of the neural events which lead to an overt action already seem to be present in the covert stages of that action. The theory therefore predicts a close simi- larity, in neural terms, of the state where an action is internally simulated and the state which precedes execution of that action (Jeannerod, 1994). 150 brains Specific methods, partly based on introspection but also relying on changes of physiological variables, have been designed to experimentally access these mental states characterized by absence or paucity of overt be- havior. One of the most extensively studied of these representational aspects of action is mental motor imagery. Behavioral studies of motor imagery have revealed that motor images retain the same temporal characteristics as the corresponding real action when it comes to execution. For example, it takes the same time to mentally “walk” to a prespecified target as it takes to actu- ally walk to the same place (Decety, Jeannerod, & Prablanc, 1989). Simi- larly, temporal regularities which are observed in executed actions, such as the classical speed–accuracy tradeoff, are retained in their covert counter- parts (Sirigu et al., 1996). Along the same line, other situations have been described where the subject uses a motor imagery strategy in spite of the fact that no conscious image is formed. Those are situations where the sub- ject is requested to make a perceptually based “motor” decision. Consider, for example, the situation where a subject is simply requested to make an estimate about the feasibility of an action, like determining the feasibility of grasping an object placed at different orientations: the time to give the response will be a function of the object’s orientation, suggesting that the arm has to be mentally moved to an appropriate position before the re- sponse can be given. Indeed, the time to make this estimate is closely similar to the time it takes to actually reach and grasp an object placed at the same orientation (Frak, Paulignan, & Jeannerod, 2001; see also Parsons, 1994). One may speculate whether the same isochrony would also exist for per- forming an action with a disembodied artifact (e.g., a car) and mentally estimating its consequences. The question would be whether one can simu- late an action performed, not by a human body, but with a mechanical device. A tentative answer will be given below. This indication of a similar temporal structure for executed and non- executed actions by a biological system is reinforced by a similarity at the level of physiological indicators. Examining autonomic activity in subjects imagining an action at different effort rates reveals changes in heart rate and respiration frequency proportional to the imagined effort in the absence of any metabolic need. These results (Decety, Jeannerod, Durozard, & Baverel, 1993, see review in Jeannerod, 1995) reveal the existence of a central pat- terning of vegetative commands during covert actions, which would paral- lel the preparation of muscular commands. Autonomic changes occurring during motor imagery are closely related to those observed during central preparation of an effortful action (Krogh & Lindhard, 1913). Those are mechanisms that anticipate forthcoming metabolic needs, with the function of shortening the intrinsic delay required for heart and respiration to adapt to effort (e.g., Adams, Guz, Innes, & Murphy, 1987). how do we decipher others’ minds? 151 Interestingly, a similar involvement of autonomic mechanisms has been observed in the context of emotions. Lang (1979) proposed that emotional imagery can be analyzed objectively as a product of information processed by the brain and that this processing can be defined by measurable outputs. Indeed, experimental findings similar to those described for motor imagery have been reported with emotional imagery. Levenson, Ekman, & Friesen (1990), for example, showed that imagining or mimicking an emotional state induces in the subject the appearance of physiological reactions specific for the imagined or mimicked emotion (Chapter 2 [Adolph] for a review). SIMULATING OTHERS’ MINDS Mental imagery is only one of the forms an action or an emotion represen- tation can take. In this section, another form of representation is described, which relates to social interaction between people. Following the simula- tion hypothesis laid down in the first section, we will develop the idea that the mechanism for understanding the actions and emotions of other selves can be conceived as an extension of the mechanism of oneself having inten- tions and feeling emotions. We will first describe the conditions for bodily movements and expressions to be recognized as actions and emotions, respectively. Then, we will discuss the advantages and limitations of the simu- lation theory in explaining how we understand others. Conditions for Action and Emotion Recognition What makes an action performed by a living being (a biological action) so attractive for a human observer? What are the conditions that have to be fulfilled for a visual stimulus to be treated as a biologically significant action or emotional expression? Consider, for example, the classical experiments of Johansson in the early 1970s. He equipped a human actor with small lights placed at the level of his trunk and limb joints. The actor was moving in complete darkness, except for the small lights. The actor’s movements (e.g., walking or dancing) are immediately recognizable by an observer, even though the actor’s body cannot be seen. Visual information reduced to the trajectories and kinematics of the actor’s movements is sufficient to provide cues not only to the activity portrayed by the actor but also to his age and sex (Johansson, 1973). A display of the same, but stationary, lights will not provide any recognizable information. Very young infants also easily distin- guish biological movements from motions produced by mechanical devices, (Dasser, Ulbaek, & Premack, 1989). 152 brains Movements performed by living organisms owe their specificity to the fact that they usually have a goal. As a consequence, they display a number of kinematic properties that reveal their “intentional” origin. One of these properties is that goal-directed movements have an asymmetrical kinematic profile—a fast acceleration followed by a much longer deceleration—as op- posed to the symmetrical profile of the ballistic motion of a projectile, for example. Another property is that the tangential velocity of the moving limb varies with the radius of curvature of the movement (Lacquaniti, Terzuolo, & Viviani, 1983). A further characteristic of biological movements is that they follow biomechanically compatible trajectories. Consider the perceptual ef- fect produced by fast sequential presentation of pictures of an actor with an arm at two different postures. This alternated presentation is perceived as a continuous apparent movement between the two arm postures. If, however, the presentation of the two postures is such that the arm should go across an obstacle (e.g., another body part), then the apparent movement is per- ceived as going around and not across the obstacle. This striking effect (Shiffrar & Freyd, 1990) reflects the implicit representation built from vi- sual perception of motion when it refers to a biological (or intentional) ori- gin. Obviously, this is not to say that a robot could not be programmed for accurately reaching a goal with a different strategy (e.g., using movements with a symmetrical velocity profile or violating biomechanical constraints): these movements would simply look “unnatural” and would not match the internal representation that a human subject has of an intentional movement. As a matter of fact, a normal subject cannot depart from the relation between geometry and kinematics which characterizes biological action: he or she cannot track a target moving with a spatiotemporal pattern different from the biological one (e.g., accelerating rather than decelerating in the curves). According to Viviani (1990), the subject’s movements during the attempts to track the target “continue to bear the imprint of the general principle of organization for spontaneous movements, even though this is in contrast with the specifications of the target.” Interestingly, the same relation between velocity and curvature is also present in a subject’s per- ceptual estimation of the shape of the trajectory of a luminous target. A target moving at a uniform velocity is paradoxically seen as moving in a nonuni- form way and, conversely, a kinematic structure which respects the above velocity–curvature relation is the condition for perceiving a movement at a uniform velocity. According to Viviani and Stucchi (1992), perception is constrained by the implicit knowledge that the central nervous system has concerning the movements that it is capable of producing. In other words, there is a central representation of what a uniform movement should be, and this representation influences visual perception. Whether this implicit knowledge is a result of learning (e.g., by imitation) or an effect of some innate how do we decipher others’ minds? 153 property of visual perception is a matter of speculation. The fact that young infants are more interested by movements that look biological than by those that look mechanical (e.g., Dasser, Ulbaek, & Premack, 1989) is an indica- tion in favor of the latter. Another argument is the fact that intentionality of biological movements can be mimicked by the motion of objects, pro- vided this motion obeys certain rules. As shown by Heider and Simmel (1944), seeing the self-propelled motion of geometrical stimuli can trigger judgments of protosocial goals and intentions. The main condition is that the object motion appears to be internally caused rather than caused by an external force. A preference for self-propelled motion can be demonstrated with this type of stimuli in 6-month-old infants (Gergely, Nadasdy, Czibra, & Biro, 1995; Czibra et al., 1999). Another critical aspect of communication between individuals is the face- perception system. Faces, particularly in humans, carry an essential aspect of the expression of emotions. Humans have a rich repertoire of facial ges- tures: the eyes, the eyebrows, the forehead, the lips, the tongue, and the jaws can move relative to the rest of the face. Not only can lip, tongue, and jaw movements convey a speaker’s communicative intentions, but mouth movements and lip positions can be powerful visual cues of a person’s emo- tional states: by opening the mouth and moving the lips, a person can dis- play a neutral face, smile, laugh, or express grief. The movements and the position of the eyes in their orbits also convey information about the person’s emotional state, the likely target of attention and/or intention. To the same extent as discussed for the perception of biological actions, the perception of emotional expression on faces seems to stimulate a system tuned to ex- tract specific features of the visual stimulus. According to the influential model of Bruce and Young (1986), a human face can give rise to two sorts of perceptual process: perception of the invariant aspects and of the chang- ing aspects of a face. The former contributes to the recognition of the iden- tity of a person. The latter contributes to the perception of another’s social intentions and emotional states. The visual processing of face patterns has been a topic of considerable interest for the past three decades. The neuropsychological investigation of the condition known as “prosopagnosia” has revealed that patients with dam- age to the inferior occipitotemporal region are selectively impaired in visual face recognition, while their perception and recognition of other objects are relatively unimpaired. As emphasized by Haxby, Hoffman, and Gobbini (2000), face processing is mediated by a distributed neural system that in- cludes three bilateral regions in the occipitotemporal extrastriate cortex: the inferior occipital gyrus, the lateral fusiform gyrus, and the superior tempo- ral sulcus. There is growing evidence that the lateral fusiform gyrus might be specially involved in identifying and recognizing faces, that is, in the [...]... other This process would thus be the basis for correctly attributing a representation to the proper agent or, in other words, for answering the question of who is the author of the act of communication (Georgieff & Jeannerod, 199 8; Jeannerod, 199 9) The flow chart of Figure 6.1 is a tentative illustration of the many interactions between two agents Each agent builds in the brain a representation of both... recorded from the observer What would be the conclusion to be drawn from that experiment if, say, the respiration rate or the heart rate of the observer increased as a function of the degree of joy expressed by the face of the actor? According to the conclusion drawn from the action observation experiment, the conclusion here should be that the observer is simulating the emotion displayed by the actor... external agent (another monkey or an experimenter) In other words, mirror neurons represent one particular type of action, irrespective of the agent who performs it At this point, it could be suspected that the signal produced by these neurons, and exploited by other elements downstream in the information-processing flow, would be the same for actions performed by the self and by another agent: the two modalities... and the nonoverlapping part of a given representation can be the cue for attributing the action to the self or to the other The same mechanism operates in humans Brain activity during different conditions where subjects were simulating actions (e.g., intending actions and preparing for execution, imagining actions, or observing actions performed by other people) was compared (Decety et al., 199 4, 199 7;... clearly specified by the activation of cortical zones which do not overlap between conditions (Ruby & Decéty, 2001) 160 brains The question now arises about whether there are mirror neurons for the simulation of emotions This question could only be answered positively if the neural structures activated in the brain of the observer could be found in areas devoted to the expression of emotions and not only... other people Accordingly, they tend to misattribute the occurrence of external events to themselves The consequence of this misinterpretation would be that external events are seen as the result expected from their own actions More recently, impairments in the recognition of others and the self in schizophrenia have been categorized, together with other manifestations of this disease, among the so-called... (as signaled by the patients), brain metabolism is increased in the primary auditory cortex (Heschl’s gyrus) on the left side (Dierks et al., 199 9), as well as in the basal ganglia (Silbersweig et al., 199 5) Thus, whereas self-generated inner speech is normally accompanied by a mechanism that decreases the responsiveness of the primary auditory cortex, during verbal hallucinations, the auditory temporal... 156 brains more about them, their reason for taking the plane (e.g., going on a business trip or on vacation), their mood, etc Originally, the term empathy was translated by Titchener ( 190 8) from the German term Einfühlung In the texts of 19th-century German philosophers and psychologists, like Theodor Lipps ( 190 3), Einfühlung was used to designate an implicit process of knowledge, different from the. .. people) was compared (Decety et al., 199 4, 199 7; Grafton, Arbib, Fadiga, & Rizzolatti, 199 6; Rizzolatti et al., 199 6; Gérardin et al., 2000) The outcome of these studies is twofold: first, there exists a cortical network common to all conditions, to which the inferior parietal lobule (areas 39 and 40), the ventral premotor area (ventral area 6), and part of supplementary motor area contribute; second, motor... observation of the hand movements was superimposed with that activated while the subjects themselves actually performed the movement In principle, a theory that postulates that both actions of the self and actions of the other can be distinguished on the basis of their central representations should predict separate representations for these two types of action At the neural level, one should expect the existence . performed by other people) was compared (Decety et al., 199 4, 199 7; Grafton, Arbib, Fadiga, & Rizzolatti, 199 6; Rizzolatti et al., 199 6; Gérardin et al., 2000). The outcome of these studies. (Goldie, 199 9; for a full ac- count of the philosophical issues raised by the simulation theory, see Davies & Stone, 199 5). We will first describe experiments that support the notion of simula- tion. understanding the neural basis of emotion. Cognition and Emotion, 4, 161– 190 . 146 brains Rolls, E. T. ( 199 9a). The brain and emotion. Oxford: Oxford University Press. Rolls, E. T. ( 199 9b). The functions