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8/13/2019 Frith - Wolper 2003_Introduction http://slidepdf.com/reader/full/frith-wolper-2003introduction 1/5 Introduction Author(s): Christopher D. Frith and Daniel M. Wolpert Source: Philosophical Transactions: Biological Sciences, Vol. 358, No. 1431, Decoding, Imitating and Influencing the Actions of Others: The Mechanisms of Social Interaction (Mar. 29, 2003), pp. 431-434 Published by: The Royal Society Stable URL: http://www.jstor.org/stable/3558123 Accessed: 15/10/2010 14:04 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=rsl . Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The Royal Society is collaborating with JSTOR to digitize, preserve and extend access to Philosophical Transactions: Biological Sciences. http://www.jstor.org

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IntroductionAuthor(s): Christopher D. Frith and Daniel M. WolpertSource: Philosophical Transactions: Biological Sciences, Vol. 358, No. 1431, Decoding, Imitatingand Influencing the Actions of Others: The Mechanisms of Social Interaction (Mar. 29, 2003),pp. 431-434Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/3558123

Accessed: 15/10/2010 14:04

Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at

http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless

you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you

may use content in the JSTOR archive only for your personal, non-commercial use.

Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at

http://www.jstor.org/action/showPublisher?publisherCode=rsl.

Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed

page of such transmission.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of 

content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms

of scholarship. For more information about JSTOR, please contact [email protected].

The Royal Society is collaborating with JSTOR to digitize, preserve and extend access to Philosophical

Transactions: Biological Sciences.

http://www.jstor.org

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Published nline14 February2003qu THE ROYAL*ff SOCIETY

Introduction

In the past few decades there have been enormous

advances in our understanding of the links between the

mind, the brain and behaviour. Sensory systems,

especially the visual system, have been explored in detail,

leading to a much greater understanding of the mech-

anisms underlying visual perception (Zeki 1993). In

addition, we know much more about the mechanisms bywhich our motor system allows us to reach and grasp

objects (Jeannerod et al. 1995). Progress has been made

in our understanding of the higher cognitive functions

involved in solving novel problems (Shallice 1988). Most

remarkable of all has been the enthusiasm with which neu-

roscientists have embarked on the search for the neuralcorrelates of consciousness (Crick Koch 1998). How-

ever, a striking feature of these approaches is that peopleare considered as strictly isolated units. For example, in a

typical experiment, a volunteer might sit at a bench or lie

in a brain scanner, watching abstract shapes appear on a

screen and pressing a button when a target shape appears.

By contrast, experiments that involve thinking about and

interacting with other people are rare, even though this is

what we spend much of our time doing in everyday life.

It is this social interaction that forms the main theme of

this special issue.

Humans, like other primates, are intensely social crea-

tures. One of the major functions of our brains must beto enable us to be as skilful in social interactions as we are

in recognizing objects and grasping them. Furthermore,

any differences between human brains and those of our

nearest relatives, the great apes, are likely to be linked to

our unique achievements in social interaction and com-

munication rather than our motor or perceptual skills. In

particular, humans have the ability to mentalize, that is to

perceive and communicate mental states, such as beliefs

and desires. The acid test of this ability is the understand-

ing that behaviour can be motivated by a false belief

(Dennett 1978). Deception, for example, depends uponsuch understanding. This ability is absent in monkeys and

exists in only rudimentary form in apes (Povinelli Bering2002). A key problem facing science, therefore, and one

that is at least as important as the problem of conscious-

ness, is to uncover the mechanisms underlying our abilityto read other minds and to show how these mechanisms

evolved. To solve this problem we need to do experimentsin which people (or animals) interact with one another

rather than behave in isolation. Such experiments are, of

course, taking place in increasing numbers and many of

the leading exponents of such experiments have contrib-

uted to this special issue.

Among humans, social interactions predominantlyinvolve language. However, in this issue we have chosen

One contribution of 15 to a Theme Issue 'Decoding, imitating and

influencingthe actions of others:the mechanisms of social interaction'.

Phil. Trans. R. Soc. Lond. B (2003) 358, 431-434 431

DOI 10.1098/rstb.2002.1260

to restrict ourselves largely to studies of social interactions

that do not involve language. The advantage of such stud-

ies is that they can more easily be applied to infants, ani-

mals and robots. Such application is essential for exploringin detail developmental trajectories, brain mechanisms

and computational processes. Furthermore, by concen-

trating on studies in which language is not involved we can

largely avoid discussion of the hard problem of semantics.

We have structured this special issue in terms of three

major developments in the twentieth century that have

had a considerable impact on research on the biologicalbasis of social interactions. These three developments

involve biological motion, mirror neurons and 'theory ofmind'. They also reflect different levels of complexity in

social interactions.

1. BIOLOGICALMOTION:

DECODINGSOCIALSIGNALS

The term 'biological motion' was coined by Johansson

(1973). He attached small points of light at the joints of

human actors, and filmed them moving about in the dark.

Typically all that is presented in such point-light displaysare a few moving dots, but the observer can instantly per-ceive the motion as a human figure, can see what the fig-ure is doing and can tell whether it is male or female

(Kozlowski Cutting 1977). This demonstrates thatthere is something special about the motion of living

things. This motion, in the absence of any other cues, can

convey detailed and specific information about what other

organisms are doing. At the lowest level we can detect

whether or not an object is animate. The movement of

inanimate objects like billiard balls is determined by out-

side forces while animate objects are self-propelled. At the

next level we can detect agency. The movements of agentsare determined by their goals. At the highest level we can

detect intentionality. The movements of intentional agentsare determined by their beliefs and desires.

Puce Perrett (2003) present evidence that there is a

dedicated neural system in the brains of primates, bothhuman and non-human, for detecting and interpreting

biological motion. Movements of hands, faces and eyesare of particular interest to this system, which lies in the

superior temporal sulcus (STS) adjacent to V5, an area

concerned with visual motion in general. This region of

STS does more than simply detect biological motion. It

also distinguishes between different types of biologicalmotion such as whether eyes are looking towards or awayfrom the observer. Furthermore, the late components of

EEG potentials evoked by biological motion are altered

by the context in which the motion occurs.

Csibra (2003) reports that, before they are 1 year old,

human infants can follow another person's gaze directionor pointing gesture. This behaviour implies that they are

already interpreting actions in terms of goals. In this case

the goal is communicative ('there is something interesting

( 2003 The Royal Society

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432 C. D. Frith and D. M. Wolpert Introduction

over here'). These infants can also interpret non-com-

municative actions as goal directed, as when a ball jumpsover a barrier 'in order to reach a target'. These attri-

butions are not based solely on the nature of the move-

ments observed, but also on the end state of the

movement and the context in which it occurs. However,

although infants under 1 year can attribute goals to mov-

ing objects, they do not seem to attribute mental states

such as beliefs and desires.

Frith Frith (2003) outline the developmental tra-

jectory of the ability to mentalize. This trajectory parallelsthe analysis of different levels of decoding social signals,

starting with biological motion, followed by agency detec-

tion and finally attribution of intentionality or mentalizing.

Mentalizing becomes explicit at the age of 4-6 years when

children are able to explain the misleading events that giverise to a false belief. Mentalizing depends upon a more

complex brain system than the detection of biologicalmotion. However, the mentalizing system includes STS as

one of its components. Another component is located in

the temporal poles and may be concerned with the context

in which the observed behaviour is occurring. Medial pre-frontal cortex seems to have a special role in the mentaliz-

ing system. This area is activated when mental states of

the self as well as others are represented and may have a

role in signalling that mental representations do not neces-

sarily correspond to the actual state of the world.

Rittscher et al. (2003) describe computational approachesthat have been used for the machine recognition and

interpretation of human actions. They use, for example,motion contour tracking (examining how a smooth curve

that encompasses the outline of an actor changes over time)to identify the nature of biological motion. They indicate

that semantic context needs to be taken into account to pro-vide a higher level interpretation of the observed motion.

Their approach uses a small collection of low-level models

encoding a set of motion primitives that are then interpretedin terms of the semantic context in which they occur.

Detection of biological motion seems to be sufficient for

the attribution of animacy, but, for the attribution of goalsand intentions, the context in which the movement occurs

must also be taken into account.

2. MIRRORNEURONS:IMITATINGHE BEHAVIOUROF OTHERS

In 1996 the Parma group reported the serendipitous

discovery of neurons that respond when monkeys see

someone else performing a specific action (Gallese et al.

1996). As the same neurons also respond when the mon-

key itself performs that particular action they were termed

'mirror neurons'. The discovery of mirror neurons

aroused great interest owing to their obvious relevance for

social interactions. In particular, such neurons provide a

neural mechanism that may be a critical component of

imitation. Studies in humans have shown that observingsomeone else's action primes the observer to perform the

same action (Fadiga et al. 1995) and it has long been

known thatpatients

with frontal lobe lesions can some-

times automatically and inappropriately imitate the

actions of others (Lhermitte et al. 1986).When we imitate someone we take the next step beyond

the simple observation of biological motion. We observe

the action and then we try to reproduce it. This leads to

a fundamental problem. What we see is a series of con-

figurations of the person in space, but what we have to do

is to issue a series of motor commands. How can we trans-

late what we see into what we need to do? The discoveryof mirror neurons demonstrated that a mechanism for

translation is present in the primate brain and is automati-

cally elicited when viewing the actions of others. A fre-

quent theme in the contributions to this special issue is

that this mirroring system could underlie the developmentof empathy and other forms of inter-subjectivity.

Meltzoff Decety (2003) present the evidence that this

mirroring ability is innately wired and ready to interact

with others from birth. Studies of adults show that imi-

tation depends upon a neural system that is shared

between the recognition and production of action. How-

ever, regions of the parietal lobe also have a critical role

in distinguishing between actions of the self and others.

This combination of systems that represents others as 'like

me' and as 'different from me' is fundamental for inter-

subjectivity.In spite of their mirror neurons there is no evidence that

monkeys can learn new skills by imitation and it has been

suggested that true imitation learning cannot occur unless

the learner can attribute intentions and understand cause-

effect relationships. Byrne (2003) analyses in detail the

processes by which mountain gorillas can use imitation to

learn how to prepare nettles for eating and proposes that

this learning occurs without any attribution of intentions

or causal understanding. He suggests that imitation in this

case depends on the perceptual ability to parse a complexaction into a sequence of more primitive actions, and

detect hierarchical organization underlying the action's

original production. This ability might be a necessary pre-

requisite to attributing intention and cause.

Wohlschliger et al. (2003) show that children, in con-

trast to gorillas, clearly make attributions about intentions

when imitating the actions of others. As a result they make

predictable 'mistakes' during imitation. On seeing an adult

press a button with her left hand, children interpret the

task to be imitated as 'pressing the button' and use which-

ever hand is most convenient. In this respect they are

behaving like the infants of Csibra (2003) who expect

goals to be achieved by the most efficient means. How-

ever, if the form of the movement is seen as the goal of

the action then the movement will be imitatedcorrectly.Here, the context in which the movement is made also

has a role in determining the goal that will be attributed

and hence the level at which the imitation occurs.

Gallese (2003) proposes that the mirroring system in

the brain applies to emotions and intentions as well as

actions. These mirror effects are automatic and uncon-

scious simulations. When we see an action, this automati-

cally triggers action simulation at a covert level. This

involves not only the motor system, but also systems con-

cerned with the sensory consequences of the action beingsimulated. Similar effects occur when we see an expressionof emotion. These automatic effects ensure that we share,to some

degree,the inner states of the

peoplewith whom

we are interacting, a necessary starting point for attribu-

ting mental states to others.

Schaal et al. (2003) discuss the computational methods

that have been used to control robots that can learn by

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Introduction C. D. Frith and D. M. Wolpert 433

imitation. Such learning seems to be best achieved if

movements are decomposed into a set of movement primi-tives that can be observed in the robot teacher as well as

generated in the robot student. A common framework for

observation and production can be achieved by expressing

these movement primitives in task space, i.e. the series of

movements made by the pole in a pole-balancing task.

Such task-level imitation requires prior knowledge of how

movements of the pole can be converted into movements

of the arm that is doing the balancing. Using this method,

robots can successfully learn by imitation. This learning,sometimes called 'mimicking' can occur without any

knowledge of goals, but cannot generalize to new contexts.

Much more robust learning by imitation can be achieved

if the task goal is known so that imitated movement tra-

jectories can be improved by trial and error learning. Even

better imitation can be achieved if the movement primi-tives are used to make predictions about the behaviour of

the robot teacher (see also Wolpert et al. (2003)).

3. MENTALIZING:

CLOSINGTHE COMMUNICATION OOP

A provocative paper entitled 'Does the chimpanzee have

a theory of mind?' (Premack Woodruff 1978) ushered in

a new era of research on social cognition. The somewhat

misleading phrase 'theory of mind' has been widely used

ever since to refer to the propensity to understand behav-

iour in terms of desires and beliefs. Having a theory of

mind is the same as 'taking an intentional stance' (Dennett

1996). We prefer the word 'mentalizing', which refers

more specifically to the ability to attribute mental states

such as beliefs and desires to another person. For instance,

in order to understand deception it is necessary to recog-

nize that someone's behaviour can be determined by their

belief about the state of the world even when we know

this belief to be false. In the 25 years since Premack

Woodruff (1978) posed their question no definitive evi-

dence has emerged to indicate that chimpanzees are able

to mentalize (Povinelli Bering 2002). Alternatively,

human children show signs of implicit mentalizing from

about 18 months and pass the acid test of understanding

the effects of false beliefs from the age of 4 years (Frith

Frith 2003).The interest in mentalizing received a further boost with

the discovery that children with autism acquire this ability

very late if at all while their other abilities can remain

intact (Baron-Cohen et al. 1985). This observation led to

the hypothesis that mentalizing depends upon a dedicated

brain system rather than on some more general problem-

solving mechanism (see Frith Frith 2003). Whether or

not this is the case we are still left with the question of how

mentalizing is possible since the mental states of others are

hidden. We believe that to discover the mechanisms that

underlie mentalizing, it will be necessary to study the

closed loop of social interactions. In most studies of imi-

tation this loop remains open. The transmitter (or teacher)

displays some action and then the receiver (or learner)imitates that action. To close the

loopthe transmitter

must observe the imitation and then respond in some wayto the receiver. A prototype of such a communicative loopis seen when a mother teaches her infant to pronounce a

word correctly by exaggerating certain acoustic features of

the word (Burnham et al. 2002). Through a series of iter-

ations the transmitter and receiver can reach a consensus

as to the nature of the action being imitated. Through this

mutually contingent behaviour the hidden purpose of the

action is passed from transmitter to receiver. The con-

tributors to the final part of this special issue are con-

cerned with interactions in which the communicative loop

is closed in this way.

Johnson (2003) shows that infants will treat a novel,

amorphously shaped object as an agent with goals if it

interacts contingently with them or with another person,i.e. if it moves in response to another agent's actions.

Infants can use the object's environmentally directed

behaviour to determine its attentional orientation and

object-oriented goals. Adults will also treat objects that

behave contingently as agents in spite of knowing that the

objects are artefacts. This indicates that this agent-detec-tion mechanism is a module that is hard-wired in the

brain. However, while this mechanism may be necessary,it does not seem to be sufficient to support advanced men-

talizing ability.Blair (2003) shows that emotional expressions are com-

municative gestures with specific roles in social interact-

ions. Confronted with an expression of anger the receiver

will stop performing his current action in order to changethe expression of the transmitter. Expressions of embar-

rassment after the commission of a social solecism are

designed by the transmitter to prevent further criticism

from the receiver. Thus, emotional expressions and empa-

thy permit the rapid modification of behaviour duringsocial interactions. Disorders in the perception of

emotional expressions involve a failure to recognize the

intention behind these expressions and can have devastat-

ing effects including persistent antisocial behaviour as in

psychopathy.While social interactions may be a novel topic of study

for neuroscientists, well-established techniques for such

studies have been developed in the social sciences. Grif-

fin Gonzalez (2003) describe a series of formal

approaches for the design and analysis of studies of dyadicinteractions. They show how these methods permit the

measurement of interdependence and social influence.

Sally (2003) considers the various interactive games that

have been developed by economists such as the Prisoner's

Dilemma. These games require that each player predictwhat the other will do in order to work out an appropriate

strategy. A consistent observation is that most players do

not adopt the optimum strategy as defined by the Nash

equilibrium. In part this seems to be owing to the players

attributing beliefs and intentions to each other that extend

beyond the narrow confines of the game. Sally (2003) con-

siders the various factors that cause players not to adoptthe optimum economic strategy.

Wolpert et al. (2003) present a computational account

of interactions that can be applied to robots as well as

people. Fundamental to this account is the idea of the

'forward model' that predicts the consequences of issuinga particular command to the motor system. The current

context in which theagent

is acting can be discoveredbyrunning multiple forward models to see which one gives

the best prediction. Each forward model (or predictor) is

paired with a controller that is used to issue motor com-

mands. Through prediction the most appropriate control-

Phil. Trans. R. Soc. Lond. B (2003)

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434 C. D. Frith and D. M. Wolpert Introduction

ler can be identified for any point in an action sequence.These multiple predictor-controller pairs can also be used

for imitation. Through prediction the receiver (or learner)can estimate which controller he must use to generatewhat the transmitter (or teacher) is doing at each point in

the movement sequence. As long as the motor control sys-tem in the learner is sufficiently similar to that in the

teacher, then the learner can reproduce the movement by

using this sequence of controllers. However, the teacher

can also observe the learner and, in the same way, estimate

the sequence of controllers the teacher would use to gen-erate the learner's movement. If communication has been

successful then the sequence that the teacher estimates

should correspond to the sequence he originally used. In

this way the communicative loop is closed and the success

of the communication can be checked.

We suggest that we have here the rudiments of a mech-

anism by which intentions can be transmitted from one

mind to another. Such a mechanism could be the basis

for some of the most intricate and complex human

social interactions.

Christopher D. Frith1

Daniel M. Wolpert2 December2002

1WellcomeDepartment of Imaging Neuroscience, and 2Sobell

Department of Motor Neuroscience and Movement Disorders,Institute of Neurology, University College London, London

WC1N 3BG, UK

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