Emanuel Miller lecture: Confusions and controversiesabout Asperger syndrome

Uta FrithUCL Institute of Cognitive Neuroscience, UK

Background: Hans Asperger drew attention to individuals who show the core symptoms of autism inthe presence of high verbal intelligence. Methods: A review of the literature explores current issuesconcerning the diagnosis and nature of Asperger syndrome. Results: The behavioural and neuro-physiological evidence to date suggests that Asperger syndrome is a variant of autism typically occur-ring in high-functioning individuals, and not a separate disorder. One of the problems of diagnosis isthat the typical impairment of social communication may be difficult to identify in early childhood, andcan be camouflaged in adulthood by compensatory learning. The range and nature of the socialimpairments in Asperger syndrome are still in need of investigation, but appear to be less severe than inautism. Experimental evidence suggests that individuals with Asperger syndrome may lack an intuitivetheory of mind (mentalising), but may be able to acquire an explicit theory of mind. Brain imagingstudies pinpoint a network that links medial prefrontal and temporal cortex as the neural substrate ofintuitive mentalising. This network shows reduced activation and poor connectivity in Asperger syn-drome. While some individuals with Asperger syndrome have written eloquently about their lives, theirability to talk about their own emotions appears to be impaired (alexithymia). This impairment may belinked to depression and anxiety, which is common in adulthood. Little is as yet known about the oftenconsiderable cognitive strengths in Asperger syndrome, or about the difficulties observed in higher-levelexecutive skills. Conclusions: Studies are needed that define the developmental course of the disorderand the nature of the strengths and weaknesses in both social and non-social domains. This requiresmore sensitive assessment instruments than are currently available. Questions about the prevalence ofAsperger syndrome, about associated and secondary features, and about optimal education andmanagement, urgently call for such studies. Keywords: Autistic disorder, emotion, executive function,mentalising impairment, social cognition, theory of mind.

Emanuel Miller’s (1893–1970) biographical detailssuggest some significant parallels to Hans Asperger(1906–1980). Both men were among the first childpsychiatrists in their respective countries, GreatBritain and Austria, and founded lasting institutionsthat care for children’s mental health. Both emphas-ised the critical importance of social work andeducation. From all accounts both were Renaissancemen who built up large libraries testifying to theirwide interests from medicine to philosophy and thearts. Asperger’s working life, as well as Miller’s, wasdeeply marked by the historical cataclysm of the firsthalf of the 20th century. The wars that wreckedEurope had psychiatric consequences of a kind thatclinicians had hardly experienced before. Just as inLondon, where Emanuel Miller treated shell-shockedpatients returning from the First World War, so inVienna, Erwin Lazar, Hans Asperger’s teacher, setup centres for severely deprived children, and devotedhis clinical expertise to alleviating their condition.A tradition of remedial education was started, whichAsperger continued throughout his life.

However, what Hans Asperger is chiefly remem-bered for is that he was one of the two farsightedclinicians who identified and labelled the conditionthat is now known as autism. Leo Kanner, who wasworking in Baltimore, published his seminal paperon autistic disturbances of affective contact in 1943,

while Hans Asperger published his paper on autisticpsychopathy in 1944. Neither of them knew theother, and they appear to have kept a professionaldistance. Each appeared to believe that the otherwas writing about a different type of child. However,a close analysis of the case descriptions demon-strates a great deal of overlap (Wing, 1991). Asper-ger’s most famous cases had high intellectual abilityand precocious language, while no such case wasreported by Kanner, but he also described otherswho had low ability and poor language. In this senseHans Asperger anticipated the autism spectrum(Wing, 2000). Asperger viewed autism as a consti-tutionally given personality type, albeit a patholo-gical one. His term ‘autistic psychopathy’ strikes usas odd today, but at the time it merely indicateda stable condition as opposed to a progressive dis-order. Asperger pointed out that improvement oftenoccurred over the course of development, in contrastto the deterioration typically seen in psychoticpatients. Kanner too reported improvements withdevelopment in his original cases, but gave a lessoptimistic picture (Kanner, 1971).

Hans Asperger sought to increase awareness ofautism since he believed that autistic individualswere likely to suffer from tragic misunderstandingand consequent maltreatment by others. He was notonly concerned about the children he met in his

Journal of Child Psychology and Psychiatry 45:4 (2004), pp 672–686

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paediatric clinic, but also about adults, includingsome of the parents, who had problems of isolationand employment that stemmed from their condition.He advocated an educational approach, whereteachers would work with them rather than againstthem, building on their strengths and circumventingtheir weaknesses. As these children did not functionwell in a group, he argued that individual attentionwas necessary. He was convinced they learned bestwhen guided by their own special interests. He ob-served that teachers who were objective, and to someextent detached, in their methods often obtainedgood results. Asperger persuasively argued thatindividuals with autistic disorder could not only besuccessful in their chosen profession, but were ofhigh value to society. He believed that the educationof children with autism must be based on a deepunderstanding of the condition. These insights arestill relevant today.

The rise of Asperger syndrome

Hans Asperger’s work led to the recognition of chil-dren and adults with good verbal ability who ap-peared to have autism in a milder form. Theseindividuals had previously been almost invisible,being considered amongst eccentrics, obsessives, orborderline and schizotypal personalities. One of thereasons that they are now visible is preciselybecause they can be given the label Asperger syn-drome. The label Asperger syndrome began to comeinto use after Lorna Wing’s influential paper pub-lished in 1981, which brought Asperger’s contribu-tion to the attention of the English-speaking world.However, Asperger’s original paper was not trans-lated into English until 1991 (Frith, 1991).

In her 1981 paper Wing argued that autism couldnot be captured by a few static criteria, but that therewere striking individual differences and changeswith development. She suggested that autism couldbe manifest in socially odd behaviour just as muchas in aloofness. Wing found that the children with‘odd’ rather than aloof social behaviour were oftenhighly talkative and reminiscent of some of Asper-ger’s cases. Wing did not wish to imply that thesechildren were not autistic. Instead she proposeda spectrum of autistic disorders with differentdegrees of severity along each of the dimensions ofsocial impairment, communication impairment andrestricted repetitive behaviour. The assumption ofan autism spectrum made sense of behaviouralchanges over time, often from aloof to socially odd,and made sense of the fact that genetically relatedindividuals can show very different manifestations ofautistic disorder (e.g., Burgoine & Wing, 1983;Le Couteur et al., 1996).

Somewhat surprisingly, the label Asperger syn-drome rapidly became widely used. This was despitethe fact that many people were uncertain as to how

to pronounce the name (the g in Asperger is pro-nounced as in get and not as in gem). Clinicians whowere already aware of unusual children, sometimesdescribed as ‘loners’ (Wolff, 1995), and had nothitherto connected them to autism, saw the rela-tionship to Asperger syndrome. The label high-functioning autism also began to come into use andwas championed by some authorities to refer to theincreasingly recognised group of able children withautism, in reference to either verbal or non-verbalintelligence. Adult psychiatrists too became interes-ted and started to reclassify some of their mostpuzzling patients on the borders of personalitydisorder and schizophrenia as cases of Aspergersyndrome (e.g., Tantam, 1991).

Descriptions of Asperger syndrome in the mediacreated strong resonance in the general public. Manypeople thought they knew somebody who might haveAsperger syndrome. Furthermore, many suffererswho had been searching for an explanation of theirproblems were now beginning to diagnose them-selves. From being virtually unknown only twentyyears ago, Asperger syndrome has now become al-most a household word. A comprehensive volumeedited by Klin, Volkmar, and Sparrow (2000), how-ever, demonstrates that what we know aboutAsperger syndrome is still very scant and contro-versies about the nature of the disorder are far fromresolved. Notwithstanding this uncertainty, thereappears to be a pressing demand for practical helpand guidance, as reflected in a large number ofwebsites (see, for instance, tonyattwood.com.au).

Questions about the diagnosisof Asperger syndrome

Clinical and practical knowledge about Aspergersyndrome is accumulating, but we do not yet knowhow frequent Asperger syndrome is. Of course, wecan only know how many cases there are if we knowwhat a case is! There is reason to believe that incurrent clinical practice the label Asperger syndromeis used rather indiscriminately. Asperger syndromehas a special cachet that hints at superior intelli-gence and perhaps even genius. The label high-functioning autism, because it is sometimes appliedto individuals who are only relatively high function-ing, possibly carries less of such an implication. Inreality, the label is given to many children and adultson the autism spectrum who are simply atypical intheir presentation, talkative rather than withdrawn,but not necessarily of high ability. Asperger syn-drome, or high-functioning autism as identified inmany clinics today, comprises a far too heterogen-eous group, including cases of well below averageability and poor social adaptation, as well as those ofsuperior intelligence and good social adaptation.

Do the diagnostic manuals help in the definition ofAsperger syndrome? Only up to a point. In fact it has

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been argued that Asperger syndrome is logicallyimpossible to diagnose according to DSM-IV (Mayes,Calhoun, & Crites, 2001) and future editions willundoubtedly see revisions. The currently mostworkable distinction between a diagnosis of Aspergersyndrome and a diagnosis of autism is that earlylanguage and cognitive function should not be de-layed in Asperger syndrome. This requirement (thatsingle words are used by age 2 and communicativephrases by age 3 years) allows a reasonably consis-tent diagnostic differentiation, but is not withoutproblems. It does not necessarily mean that lan-guage acquisition was normal. First, it relies on ret-rospective reports. Second, some of these reportsimply that acquisition was atypical. The vocabularyof children who are later diagnosed with Aspergersyndrome is often described as precociously adult,meaning that it contains rare words, which are notnormally used by children. Third, communicativephrases, even if present at age 3, do not guaranteegood language understanding. Obviously, gross de-lay in language and cognitive development can beruled out with retrospective questioning, but con-temporaneous evidence would be better. Given thatsuch evidence is as yet lacking, it is by no meansclear whether the presence of speech by age 2 to 3should remain a touchstone for differential dia-gnosis. Another possibility would be to make verbalability, measured in later childhood or adulthood,a discriminating criterion.

To define Asperger syndrome, can we find guid-ance from Asperger’s original paper? Again, only upto a point. Asperger’s first descriptions includedintellectually able and verbally articulate individualsbut also cases that did not meet these criteria. Thus,not all cases described by Hans Asperger had whatwe would now classify, according to DSM-IV, as As-perger’s Disorder (Miller & Ozonoff, 1997; Hippler &Klicpera, 2003).

How easy is it to separate Asperger syndromefrom autism?

In a black and white world, two alternatives presentthemselves: Asperger syndrome is an entirely sep-arate disorder from autism with a different genetic,neurophysiological and cognitive basis. This is con-trasted with the idea that Asperger syndrome is thesame disorder, but a variant, with essentially thesame contributory causes. In between these ex-tremes the fact must be accommodated that Asper-ger syndrome and autism are both extremelyheterogeneous disorders. One possibility is that, insome cases at least, Asperger syndrome provides amodel of ‘pure’ autism where intellectual disabilitydoes not confound the clinical picture. It is conceiv-able that a more circumscribed type of brainabnormality is less detrimental to the development ofother brain systems. This would imply a seemingly

‘milder’ disorder because it is not accompanied byother problems, such as speech impairment or motordyscoordination. With compensatory learning, sucha disorder could remain hidden for a long time.However, as we shall see below, Asperger syndrome,even in relatively pure form, may be neither mild norhidden. Furthermore, associated learning disabilit-ies in Asperger syndrome appear to be common andthrow doubt on such a simple picture.

The alternative view that Asperger syndrome is aseparate developmental disorder is also subject todoubt. A number of studies, recently reviewed byReitzel and Szatmari (2003), have looked for differ-entiating neuropsychological profiles which wouldpoint to a different brain basis. These studiesinvariably found that high-functioning autismgroups achieved on average poorer verbal scoresthan Asperger syndrome groups. However, thisseems a potentially circular finding, considering thatthe diagnosis of Asperger syndrome is likely to selectfor high verbal ability. On the other hand, studies arenot consistent in finding poorer non-verbal scores,greater spatial or motor difficulties in Asperger com-pared to high-functioning autism groups. The ideathat Asperger syndrome could map onto the psycho-metrically defined group of children with non-verballearning difficulties (NVLD) was pursued by Klin andcolleagues (Klin, Volkmar, Sparrow, Cicchetti, &Rourke, 1995). Specific difficulties in maths, as wellas in perceptual and motor tasks, a pattern thoughtto be typical for NVLD children, are often present inAsperger syndrome, but not necessarily so.

Several arguments speak for the possibility thatAsperger syndrome has the same aetiology as aut-ism. First, there is the genetic argument. Cases ofAsperger syndrome and cases of autism may occurin siblings and presumably the same genetic pre-disposition gave rise to both disorders. The as-sumption is that the biological cause is similar evenif the manifestation of the disorder is very different.Second, there is the outcome argument. Older in-dividuals with high-functioning autism share somany features with individuals with Asperger syn-drome that they are often difficult to tell apart(Szatmari et al., 2000; Howlin, 2003). Indeed, inadulthood a proportion of individuals previouslydiagnosed as suffering from autism and showingearly language delay can become almost indistin-guishable in their behaviour from those with high-functioning autism who did not have this delay(Gilchrist et al., 2001; Mayes & Calhoun, 2001).Third, there is the neuro-anatomical argument, forwhich a sparse amount of evidence exists. Anexamination of the cellular structure in selectedbrain areas (Casanova, Buxhoeveden, Switala, &Roy, 2002) suggests abnormalities in the mini-columnar organisation similar to those reported inautism. Specifically, minicolumns were smaller, andtheir component cells were more dispersed thannormal. Bauman and Kemper (2003) concluded

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that there are certain features of brain pathology inautism that are present regardless of IQ.

Thus, the currently prevailing view is that Asper-ger syndrome is not an essentially different disorderfrom autism, but a variant of autism, and located atthe milder end of the spectrum of autistic disorders.This view is consistent with the incomplete, butgrowing information that we have about genetic,neurophysiological, cognitive and behavioural in-formation: autism and Asperger syndrome are highlyrelated subtypes of disorders of the autism spec-trum. On the other hand, we are far from a consen-sus. Rhinehart, Bradshaw, Brereton, and Shaw(2002), for instance, believe that, despite the dem-onstrable clinical overlap between Asperger syn-drome and autism, it is still premature to rule out thepossibility that these disorders may be clinically andneurobiologically separate.

Even if the prevailing view favours a continuum, itdoes not follow that we should abandon the labelAsperger syndrome and instead talk of ‘mild autism’or ‘autism with high verbal ability’. At present, thelabel ‘high-functioning autism’ is much used and isoften interchangeable with Asperger syndrome.However, it does not require the absence of signific-ant delay in early language and cognitive function.Time will tell whether both labels will remain in usein the future. Wing (1981) proposed the label As-perger syndrome for purely pragmatic reasons, toraise awareness of this particular form of autisticdisorder. These reasons are important. Given thequestion of educational placement, there is clearly aneed to differentiate verbally able children who havestrong academic interests from those who have se-vere problems with language and show other evid-ence of learning disability. Abandoning the labelAsperger syndrome would lose the historical contextand the wealth of information that has now beenaccumulated around it. The term has contributedsignificantly to an increase in the awareness of aut-istic disorder in the general public. One reason thatthe label was so keenly taken up was that it helpedordinary people to understand what might be thematter with the strange person with narrow obses-sive interests and social ineptness whom they mighthave come across in their everyday environment. Itmakes sense to provide a special label to the leastsevere and least handicapping form of autistic dis-order. It is less stigmatising and allows for the factthat at least some individuals are able to cope withminimal supervision or specialist help.

Questions about the developmental courseof Asperger syndrome

A necessary step towards clarifying the nature ofAsperger syndrome is the study of the developmentalcourse of the disorder. An important clue is offeredby the fact that, on average, the diagnosis of Asper-

ger syndrome is made much later than the diagnosisof autism. Howlin and Ashgarian (1999) wrote to 614parents of children with autism and 156 with As-perger syndrome. The average age when a diagnosisof autism was confirmed was around 5.5 yearscompared to 11 years for Asperger syndrome. Par-ents of children with a diagnosis of autism weregenerally aware of problems in their child’s devel-opment by 18 months of age; but in the Aspergergroup only from around 30 months of age. Initialworries in both groups centred on abnormal socialdevelopment, but parents of children with Aspergersyndrome were less likely to have noted commun-ication problems. Why does the disorder seem to behidden in infancy and early childhood? Do we simplylack sensitive tests? Alternatively, do the problemsarise later and only when the demands of the socialworld become too heavy?

It is possible that even at an early age the problemsof Asperger syndrome are obscured by the specificstrengths that are often associated with the disorder.The child who shows ‘adult’ or precocious language,who has special interests and excellent memory, isunlikely to make parents rush to a clinic, even if thischild does not interact with peers. Parents mayoverlook this sign when the child at first seems moreadvanced than potential playmates. It is unknownwhether children later diagnosed with Aspergersyndrome present behaviour problems that aresimilar to those that many young children withautism present, such as temper tantrums, resist-ance to toilet training, restricted food preferences,and sleep disturbance. Even if it turns out thatbehaviour problems are not a major issue, this maynot mean that these children are ‘easy’.

Just as puzzling as the fact that Asperger syn-drome leads a somewhat hidden existence in earlychildhood is the fact that it can be hidden again inadulthood, but usually not forever. This is particu-larly true in cases where intellectual ability is highand where environmental support is good. In thesecases a short encounter or routine interaction willnot reveal anything unusual. However, over time andin unexpected situations, it appears that the facadeof normality cannot be kept up. A number of spousesof Asperger syndrome individuals tell how they weretaken in by their partners’ superficially normalpresentation and how they arrived only later at thedifficult discovery that life with an Asperger syn-drome individual is very different from normal (e.g.,Slater-Walker & Slater-Walker, 2002).

Is Asperger syndrome a ‘mild’disorder?

Some individuals with Asperger syndrome lead nearnormal lives and show excellent adaptation. Otherscan hardly cope and need constant supervision.Clearly, not all cases show good compensation andclearly, there are different degrees of severity. How-

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ever, in some cases the disorder can appear to bemore severe, not necessarily because the coresymptoms are more severe, but because additionalclinical disorders aggravate the picture (Gillberg &Billsted, 2000).

In children with Asperger syndrome, additionalmotor coordination difficulties, as well as specificlearning difficulties in maths and reading have beendocumented. For instance, Green et al. (2002) foundmotor impairment in every single case they assessed.Reitzel and Szatmari (2003) reported that out of agroup of 27 children with Asperger syndrome, assem-bled for a follow-upstudyatage4 to6, fromsix centresin Southern Ontario, 21% had specific reading diffi-culties and46%specificmathsdifficulties,whenagedbetween 9 and 13 years. Specific difficulties weredefined in terms of a 15-point discrepancy withnon-verbal IQ (which had to be above 80). It is likelythat additional learning difficulties impede academicprogress and need specialist remediation.

While in the case of children issues of develop-mental delay are prominent, in adults a variety ofpsychiatric problems can occur, although at presentthe frequency of such problems is unknown. Prob-lems include obsessional compulsive disorder,anxiety and depression, and are likely to have severerepercussions on the ability to cope with everydaydemands. The relevant signs and symptoms are notalways reported by the sufferers and recognised bytheir families, but specialist treatment is necessaryand can alleviate the symptoms.

When compared to the devastating effects of lan-guage impairment and learning disability in autism,Asperger syndrome indeed appears to be ‘mild’.However, it cannot be regarded as a ‘mild’ disorder.Many examples exist to demonstrate that it can im-pose a heavy burden on the sufferer, the family andthe wider community.

Conjectures about the social impairmentsin Asperger syndrome

Just like other types of autistic disorder, the hallmarkof Asperger syndrome is a failure in social learningand social awareness. But exactly how should onecharacterise this failure in Asperger syndrome?In contrast to people with autism, these individualsoften stand out by their desire for social interactionand their wish to have friends and spouses.

One way to describe the social impairment in As-perger syndrome is as an extreme form of egocen-trism with the resulting lack of consideration forothers. The self-absorption and disregard of others isnot like the strategy that a normal selfish personmight deliberately adopt and flexibly use accordingto what is currently in his or her best interest.Autistic egocentrism, by contrast, appears to benon-deliberate and not determined by what mightcurrently be in the best interest of the individual.

This egocentrism seems to present a huge difficultyin forming successful long-term interpersonal rela-tionships. Spouses and family members can experi-ence bitter frustration and distress. They are baffledby the fact that there is no mutual sharing of feel-ings, even when the Asperger individual in questionis highly articulate. One obstacle seems to be aninability on the part of the person with Aspergersyndrome to put themselves into another person’sshoes and to imagine what their own actions looklike and feel like from another person’s point of view.

Another way to describe the social impairment isas a failure of empathy, involving a poor ability to bein tune with the feelings of other people. Baron-Cohen and colleagues compare lack of empathisingwith an excess of systemising, which refers to aparticular engagement with the physical world (e.g.,Baron-Cohen, Richler, Bisarya, Gurunathan, &Wheelwright, 2003). Tantam and others have longemphasised a lack of a basic emotional resonancewith other individuals, which is often perceived ascallousness and coldness by others (Tantam, 1991).

Is there a basic deficit in recognition of emotions?Would such a deficit account for a lack of emotionalresonance as well as lack of empathising and ego-centrism? The results from existing studies are in-consistent. One study (Howard et al., 2000) showedimpairment in fear recognition, but another did not(Adolphs, Sears, & Piven, 2001). Critchley et al.(2000) reported that Asperger syndrome and high-functioning individuals with autism, in contrast tocontrols, did not activate a cortical face area whenexplicitly appraising expressions, and showed lessactivation in the left amygdaloid and cerebellar re-gions when implicitly processing emotional facialexpressions. Shamay-Tsoori and colleagues (Sha-may-Tsoori, Tomer, Yaniv, & Aharon-Peretz, 2002)described two cases of adolescents with Aspergersyndrome who showed extreme deficits on measuresof empathy, but did not have significant impairmentsin their ability to recognise emotions or the ability tocreate a mental representation of another person’sknowledge. However, both adolescents were unableto integrate the emotional content with mental rep-resentations and deduce the other person’s emo-tional state. The authors suggest that impairedempathy in individuals with Asperger syndrome maybe due to impaired integration of the cognitive andaffective facets of the other person’s mental state.

Impairments in the understanding of complexemotions are generally held to be typical in Aspergersyndrome. Baron-Cohen, Joliffe, Mortimore, andRobertson (1997) showed that the recognition ofcomplex emotions from the eye region is impaired inhigh-functioning people with autism and autisticdisorder. These individuals were unimpaired whenrecognising gender from the eye region of the face,and when recognising emotions from the whole face.The authors suggest that this provides evidence forspecific empathising deficits (that is, difficulty in

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attributing feelings and other mental states to otherpeople). Blair (2003) concluded in his recent reviewof the field that only the perception of complexemotions is impaired in autism, and that thisimpairment can be seen as part and parcel of animpairment in understanding others’ mental states.

Apart from a poor understanding of one’s own andother people’s inner states, problems are also evidentin other aspects of social understanding. Oneimportant and robust finding is the poor recognitionof faces (e.g., Critchley et al., 2000; Schultz et al.,2003). Klin and colleagues (Klin, Jones, Schultz,Volkmar, & Cohen, 2002) have demonstrated thedramatically different eye gaze pattern when watch-ing social scenes in persons with high-functioningautism. Thus, these individuals tended to look atmouth rather than eye regions in faces. Moreover,when shown emotionally laden interactions in amovie (the movie shown was Who is afraid of Virginia

Wolf?), their eye gaze was liable to stray off courseand into the background rather than follow the tensedialogues between people by looking at their faces. Itremains to be seen whether abnormal looking pat-terns and poor face recognition are separable com-ponents of social impairment. Klin, Schultz andcolleagues suggest that face processing abnormal-ities might be a developmental consequence of fail-ure to look preferentially at faces. While mostchildren quickly become ‘face experts’, children withautism may not process faces as special stimuli.

Communication impairments, which are evidenteven in highly verbal individuals (e.g., Ziatas, Dur-kin, & Pratt, 2003), also call for systematic analysisand explanation. Anecdotally, people with Aspergersyndrome have often far superior written thanspoken language, and often state that they prefer tocommunicate in writing. Presumably one advantageis that this avoids the constant strain of having todecode another person’s verbal and non-verbalcommunicative signals. Furthermore, in this typic-ally off-line situation there is time to think and to usean explicit theory of mind to compute effects on therecipient of the message.

The diagnosis of communication impairment inindividuals with high verbal ability is not easy. Westill lack practical tools for assessing the use ofgesture and voice. Shriberg, Paul, McSweeny, Klin,and Cohen (2001) documented inappropriate vocal-isations in the domains of phrasing, stress, andresonance in Asperger syndrome. They reported thatwhile speakers with Asperger syndrome were signi-ficantly more voluble than speakers with high-func-tioning autism, there were otherwise few statisticallysignificant differences between the two groups.

The conjectures about the social impairments inAsperger syndrome vary widely, but agreementcannot be reached until the precise nature of thisimpairment has been clarified. However, clarificationis hampered by a lack of psychometrically validatedtests. The experimental tasks in current use suggest

that there are large individual differences in thesocial competence of individuals with Asperger syn-drome, overlapping with those of normally develop-ing individuals. Some surface behaviours that indexpoor social competence will look identical in bothgroups, for instance poor face recognition, lack ofempathic resonance, avoidance of eye contact, andpreference for written over spoken communication.However, their causes are likely to differ for the twopopulations. It would be strange to assume thatthese behaviours must necessarily be caused by afaulty neuro-cognitive mechanism. Such anassumption is only justified for the case of autisticdisorder, which has a biological cause, and whereultimately a biological marker will validate thebehavioural diagnosis.

A failure of intuitive mentalising

It is likely that failure in a number of different neuro-cognitive mechanisms underlie the range of socialimpairments in Asperger syndrome. One suchmechanism, which enables the automatic attribu-tion of mental states to others, has been extensivelytested over the past 20 years (see reviews in Baron-Cohen, Tager-Flusberg, & Cohen, 1993, 2000). Theempirical work includes high-functioning in-dividuals with autism and Asperger syndrome (e.g.,Baron-Cohen et al., 1997; Happe, 1994; Baron-Cohen, O’Riordan et al., 1999; Klin, 2000; Joliffe &Baron-Cohen, 1999; Rutherford, Baron-Cohen, &Wheelwright, 2002). There has been some success inidentifying the brain basis of this mechanism. Fur-thermore, functional brain imaging studies of men-talising have been carried out with Aspergersyndrome individuals.

The empirical studies of mentalising failure inautism suggest that it can be detected very early,that is from around 18 months (Baron-Cohen et al.,1996; Charman et al., 1997). This age is consideredto be the earliest for unequivocal evidence of implicitmentalising in normally developing children, asmanifest in sophisticated joint attention and pretendplay. Mentalising failure is seen in the everydayinability of young children with autism to tell lies,keep secrets and predict the behaviour of others onthe basis of mental states. An example of a laborat-ory test with relevance to real-life behaviour is thepenny hiding game. Typically, the child with autismcan hide the penny perfectly well in a closed hand,but will give the hiding place away, for instance byleaving the other hand open (Baron-Cohen, 1992).

What is the evidence for mentalising impairmentsin Asperger syndrome? Unlike in the case of autism,screening at age 18 months for the presence of jointattention and pretend play did not reliably pick outchildren later diagnosed with Asperger syndrome(Baird et al., 2000; Cox et al., 1999). Comparisons ofmentalising tasks in older children show that

Confusions and controversies about Asperger syndrome 677

children with Asperger syndrome show impairment,but to a lesser degree than children with autism(Ziatas, Durkin, & Pratt, 1998). Studies in adults tootend to indicate only subtle impairments as revealedin inconsistent and slow responses on advanced andnaturalistic tests (e.g., Roeyers, Buysse, Ponnet, &Pichal, 2001; Kaland et al., 2002; Channon et al.,2001).

Is mentalising impaired in Asperger syndrome butless than in autism? It is also possible that theimpairment is not less, but is camouflaged (e.g.,Frith, 2003). Highly verbal individuals can give well-reasoned answers in theory of mind tasks, perhapsbecause their intelligence allows them to use logicalinferences. For instance, they can succeed inunderstanding complex scenarios, such as trackingwhere Mary believes that John thinks he can buy acoat (Bowler, 1992). However, displaying an explicittheory of mind does not necessarily imply an intuitivementalising ability.

The distinction made here is similar to that madeby Tager-Flusberg (2001) between a ‘social percept-ive’ and a ‘social cognitive’ component of theory ofmind. The claim would be that in Asperger syndromeonly the social perceptive component is impaired,but in autism both would be impaired. This hypo-thesis is in need of testing. Perhaps it could explainwhy in Asperger syndrome the social communicationfailure is more evident in real life than in the labor-atory. In real life a high premium may be set on theperceptive component because usually cues areambiguous and responses are required to be fast; inthe laboratory, the social cognitive component cancome into its own if there is enough time to applyanalytic reasoning.

A theory proposed by Klin and colleagues (Klin,Jones, Schultz, & Volkmar, 2003) explains the dis-crepancy between real-world impairment and labor-atory success as a result of the high complexity of thesocial world that is never retained in laboratory tests.Thus Klin and colleagues suggest that the salience ofstimuli is fundamentally different in autism, and thisis revealed in abnormal responses to social stimuli,for instance deviant patterns of eye gaze and inabilityto recognise faces. This would apply to Aspergersyndrome as much as to other forms of autisticdisorder.

Intuitive mentalising tasks have also been used inthe laboratory, and on these seemingly simpler tasksindividuals with Asperger syndrome seem to be ifanything more impaired than on some of the com-plex tasks mentioned earlier. One example is theautomatic comprehension of animated shapes asinteracting agents. Heider and Simmel (1944)showed that observers feel compelled to attributemental states to animated shapes in line with theirmovement patterns. Klin (2000) showed such geo-metric shapes to individuals with high-functioningautism and Asperger syndrome. In Klin’s study, theparticipants with autistic disorder identified about a

quarter of the social elements in the story, while athird of their attributions were irrelevant. They usedpertinent mental state terms very infrequently, andwere also unable to derive psychologically basedpersonality features from the shapes’ movements.Individuals with Asperger syndrome improved theirperformance slightly compared to those with autismwhen provided with more explicit verbal information,but not significantly so. Another study with anima-tions, conducted with different materials and differ-ent scoring criteria by Abell, Happe, and Frith (2000)also showed that children with autism were signific-antly less able to attribute appropriate mental statesthan control participants. Using the same stimuli,Castelli, Frith, Happe, and Frith (2002) found thatthis was true even for very high-functioning adultswith autism and Asperger syndrome.

Brain imaging studies of mentalising in autism

There is an increasing number of brain imagingstudies in which normal volunteers have been askedto perform simple tasks that require them to takeinto account other people’s mental states (for a re-cent review see Frith & Frith, 2003). In each of thesestudies the critical tasks are compared with tasksthat are similar in every respect except that they donot require mentalising. The results to date are re-markably consistent. Regardless of presentation andresponse mode, similar regions of the brain are act-ive when volunteers make inferences about themental states of protagonists, as opposed to physicalor behavioural states. These regions are stronglyinterconnected, and it is likely that they constitutepart of the ‘social brain’ that includes frontal (medialprefrontal; orbitofrontal) and temporal (superiortemporal sulcus; inferior basal temporal cortex;temporal poles; amygdala) regions, all highly inter-connected (Brothers, 1997).

A small handful of studies have been carried outwith high-functioning individuals with autism andthose with Asperger syndrome (Happe et al., 1996;Baron-Cohen, Ring et al., 1999; Castelli et al., 2002,Nieminen-von Wendt et al., 2003). The controlgroups were normally intelligent adults of the sameage and educational level. In all these studies,regardless of the task used (visual and auditorystories, photographs of eyes, geometric animations),able individuals with autism or Asperger syndromeshowed reduced brain activation in components ofthe mentalising system. Figure 1 shows the resultsfrom the study by Castelli et al. (2002) using geo-metric animations. Here 10 high-functioning indi-viduals took part, who were diagnosed according toDSM-IV as having either autism or Aspergersyndrome. These two subgroups did not differ oncurrent social behaviour or on experimental andpsychometric tests. They were compared with 10normal volunteers matched for age and intelligence.

678 Uta Frith

As Figure 1 shows, the three main regions of thementalising system showed significantly less acti-vation in the autism/Asperger syndrome group.

Castelli et al. (2002) suggested that weak connec-tivity between the components could be a possiblereason for the reduced activation. This was con-firmed by a connectivity analysis of the regionsassociated with differences in blood flow. There wasa significantly weaker relationship between activa-tions in occipital extrastriate regions and the fronto-temporal regions of the mentalising system in theautism/Asperger group than in the normal group.The extrastriate regions of the brain are concernedwith visual-spatial processing. As illustrated in Fig-ure 1, they showed equally enhanced activity in bothgroups, while watching the movement of shapes thatevoked mental state attribution (relative to randommovements). However, this appropriately enhancedvisual spatial processing was not accompanied byenhanced processing in more anterior regions of thesystem. Why not? One reason could be lack of top-down modulation. Normally, top-down signals selectthe important, unexpected or salient aspects ofthe information and thus information overload isavoided. We can sometimes experience this top-downeffect when we suddenly understand the meaning ofa complex stimulus, which a moment before seemeduninterpretable. In the case of the animations, weunderstand the meaning of the complex movementsas particular social interactions. It could be this as-

pect of perceptual processing that is not functioningwell in people with Asperger syndrome.

This suggestion opens up a link to another prob-lem, at the cognitive level, which is frequently pro-posed as characteristic of autistic disorders: adifficulty in high-level executive functions, involvedin forward planning and flexibility. These can also bedescribed as the effects of a lack of top-down control.

Cognitive strengths and weaknessesin non-social domains

In contrast with the social difficulties, it is notablethat people with Asperger syndrome often have ex-tremely good understanding of the non-social world(e.g., Baron-Cohen, Wheelwright et al., 1999). Reitzeland Szatmari’s (2003) review of studies that compareAsperger syndrome with that of other forms of aut-istic disorder concludes that an unevenness of thecognitive profile is highly typical of all forms of aut-ism. It has long been known that the Wechsler IQscales show similar peaks and troughs in very ableindividuals with autistic disorder as in those who aremuch less able, and this has been confirmed in re-cent studies (Goldstein, Beers, Siegel, & Minshew,2001).

How is the unevenness to be explained? Onepossibility is that the cognitive style of weak centralcoherence facilitates painstaking analysis of per-

Figure 1 Reduced activation in the mentalising system in Asperger syndrome when watching scripted vs. randomanimations (based on data from Castelli et al., 2002)

Confusions and controversies about Asperger syndrome 679

ceptual and verbal detail and thus can lead to peakperformance (Happe, 1999). Weak central co-herence appears to apply to Asperger syndrome justas much as to other forms of autism if it is seen asintimately linked to the pursuit of narrow interests.Another possibility is that as a result of lacking top-down control, bottom-up processes are unusuallystrong and incoming information is processed to ahigh degree (Frith, 2003). Recent empirical studiesin this area have provided evidence for enhancedperception in autism in auditory and visual mod-alities, at no cost to the global level of informationprocessing (Plaisted, Saksida, Alcantara, & Weis-blatt, 2003; Mottron, Burack, Iarocci, Belleville, &Enns, 2003).

Baron-Cohen explains the cognitive strengths andweaknesses by proposing the concept of ‘systemis-ing’, which refers to the tendency to amass factsabout the physical world in a systematic fashion.He considers this the other side of poor ‘empathis-ing’, which clearly applies only to the social but notto the physical world (Baron-Cohen, 2002). In thissense, Baron-Cohen is attempting to offer a unifiedaccount of both social and non-social features ofautistic disorder.

Some cognitive weaknesses in Asperger syndrome,in both social and non-social domains, can be ex-plained by a specific neuropsychological abnormal-ity, namely executive function deficits. Suchimpairments have been explored widely in lower-functioning children with autism (see chapters inRussell, 1997), but they are also present in higher-functioning children (Turner, 1999). However, therehas been much less research with adults with As-perger syndrome. Observations of perseveration inmovements, in choice of topic, in both work andleisure activities, suggest that the top-down controlof action is problematic. Top-down control, as usedhere, is the opposite of stimulus-driven behaviour. Itallows modulation of attention and action in theservice of long-term aims and avoidance of distrac-tion by accidentally present attention-grabbingstimuli. How this cognitive process relates to top-down processing in neurophysiological terms hasstill to be explored. The presence of top-down controlin normal individuals may explain why certainstimuli are salient in certain contexts, and why re-sponses can be very different even if the stimulusremains the same. Thus, the same stimulus hasdifferent meaning according to expectation andcontext. If in the case of autistic disorder this controlwere weak, then one would expect that the samestimulus would always be salient and have the samemeaning, regardless of context.

It is doubtful whether impairments in executivefunctions will be found to be milder in Aspergersyndrome than in autism. Likewise, it remains to beseen whether the strengths due to attention to detail,as postulated by weak central coherence theory, willbe less extreme. Asperger individuals are often

known for their meticulous work whether it is incrafts, art or science and their ability to identifyhitherto overlooked details. Likewise, anecdotessuggest that difficulties tend to arise from the factthat people with Asperger syndrome see situations infixed and absolute terms, rather than relative tocontext. Furthermore, they often need someone toremind them when they should do something thatthey intended to do, and to tell them what theappropriate action should be in slightly unexpectedsituations. They appear to find it hard to overrideroutine responses. They are well known for beingrigid and tend to take any change of plan or routinevery badly. They crave sameness just like individualswith other forms of autism, and they thrive if thereis clear structure in the environment and theyneed external prompts to carry out infrequent andunusual tasks.

Only a small amount of evidence from brain ima-ging is available so far and it supports the notion offrontal dysfunction in Asperger syndrome. A struc-tural study of the brain of Asperger syndrome indi-viduals (McAlonan et al., 2002) found abnormalitiesin fronto-striatal pathways. The authors proposethat these may result in defective sensorimotor gat-ing, and consequently characteristic difficultiesinhibiting repetitive thoughts, speech and actions.Murphy and colleagues (2002) found a correlationbetween abnormalities in the neuronal integrity ofthe prefrontal lobe and obsessive behaviour.

Much more work is needed to clarify the neuro-physiological and cognitive basis of the problemsand interests in Asperger syndrome in the non-socialdomain. It is as yet unknown how these featuresrelate to the social features, and whether all caseshave all of the features, or only some. It is possiblethat some people will be characterised by mild socialproblems but severe executive problems, and otherpeople with severe social problems but mild execut-ive problems. Does weak central coherence charac-terise only a subgroup? And is enhanced perceptualprocessing an advantage in acquiring certain aca-demic and artistic skills? Future research in thisarea could have considerable diagnostic and thera-peutic implications.

Imagination and originality

Hans Asperger alluded in several of his cases to theirhigh originality of thought but also imagination. Forinstance, Ernst K. was reported to tell fantasticstories. An important sign of what Asperger termed‘autistic intelligence’ was the ability to coin apt andoriginal verbal expressions. This is different fromsavant skills, whose association with autism is welldocumented, while their association with Aspergersyndrome is as yet unknown.

Anecdotally, in children and adults with Aspergersyndrome, there is much evidence for the ability torole-play and to create fictitious worlds in words and

680 Uta Frith

pictures (Tantam, 1991). Biographical accountssometimes tell of extensive and wide-ranging imagin-ary activities. The artist Gilles Trehin provides onestunning example of creative imagery (see Figure 2).Gilles has created an imaginary city, Urville, overmany years since his childhood, with its own historyand population, and his own inventive names ofstreets and buildings (see http://urville.com/in-dex.html). On his website Gilles explains how theidea of the city grew in his mind, stimulated by a visitto New York as a child, and that he first started toconstruct a city with Lego bricks. Having been frus-trated by the impossibility to build a whole city in hisbedroom in this way, he was delighted by the reali-sation (at the age of 12 or 13) that he could imaginethe city in his mind and draw parts of it on paper.Gilles was diagnosed as autistic in early childhood,but as an adult he perfectly fits the clinical picture ofAsperger syndrome.

In most cases of autism, pretence and imaginativeplay have been described as absent or delayed, and,if present, they are often described as restricted,stereotyped and repetitive. This assumption may nothold in the case of Asperger syndrome. Indeed,children with Asperger syndrome were found to bemore able to produce creative narratives than chil-dren with autism (Craig & Baron-Cohen, 2000).

However, even in the outstanding case of Gilles it isnot clear to what extent his imaginative activities areseparable from obsessive interests. Some of thehighly specialised interests found in people withautistic disorder focus on imaginary people, whileothers focus on concrete objects, and yet others onmore abstract concepts, such as calendar dates.

Listening to people with Asperger syndrome

Many individuals with Asperger syndrome are pro-lific writers. One need only look at the catalogues ofJessica Kingsley, a publisher who specialises in thisliterature. These writings certainly give importantinsights but they do not necessarily add up to aconsistent picture. Many forcefully point out thatthey are not patients, do not feel affected and are notsuffering from any disorder, but instead they havedifferent personalities, different needs and differentviews from those they like to call ‘neurotypicals’.Researchers and clinicians can agree with this tosome extent. However, they may point out that apeculiar lack of insight and an egocentric viewpointare typical of the syndrome, throwing doubt on atleast some of the self-assessments of needs andexpectations. One problem with the autobiograph-

Figure 233 Place de l’Ile de Beaute, Urville, Drawing by Gilles Trehin

Confusions and controversies about Asperger syndrome 681

ical literature is that the authenticity of the diagnosisis not guaranteed. As mentioned earlier, there areconcerns about an overextension of the diagnosis, sothat disorders, yet to be identified, might currentlybe classified as Asperger syndrome.

Individuals with Asperger syndrome give ampleproof that they have the intellectual resources tomake sense of the physical world through oftenexcellent perception and prodigious memory. Thisstrength in general information processing capacityis likely to act as a means for learning about thesocial world as well. These individuals can find adifferent developmental pathway. The autobiog-raphies of individuals with Asperger syndromeindicate a high degree of retrospective self-analysisthat came with adulthood. This can be seen, forinstance, in Gunilla Gerland’s autobiography (1997)and in Clare Sainsbury’s collection of over twentyindividuals’ reminiscences of their school years(2000). These works suggest that self-knowledge andsharing of knowledge with others was poor in child-hood.

From the autobiographical writings there appearsto be at least a subgroup of Asperger syndromeindividuals who develop self-awareness to a height-ened degree. They talk about themselves and theirexperiences, but do not seem to have the samecuriosity to know what others think or feel. Sometend to be suspicious of others, even paranoid, andthis could be because they continue to find it difficultto read other people’s minds (Blackshaw, Kinder-man, Hare, & Hatton, 2001). Suspicion is likely toflourish when you do not automatically take intoaccount that other people have different points ofview from your own. If you are continually surprisedthat other people think differently from you, and if itis hard for you to realise that other people may haveinterests that are incompatible with yours, then youmay well feel that they are hostile to you.

The ability to reflect on one’s own emotions and toshare emotions with others by talking about them isa natural consequence of mentalising. If intuitivementalising were impaired it would be expected thatthe awareness of complex emotions is also impaired.Of course, the inability to identify emotions and totalk about them may have many different causes –as, for example, in depression. The term ‘alexithy-mia’, meaning ‘no words for feelings’, has beencoined to describe this symptom, which has beeninvestigated in a range of psychiatric patients.Alexithymia can be measured by self-report usingstandardised questionnaires (e.g., the TorontoAlexithymia Scale; Bagby, Parker, & Taylor, 1994).The following examples may indicate how difficultyidentifying and communicating feelings is ad-dressed: ‘when I am upset, I don’t know if I am sad,frightened or angry’; ‘I do not find examination of myfeelings useful in solving personal problems’; ‘I thinkit is strange that others analyse their emotions sooften.’

In a recent study, 27 individuals with autismspectrum disorders were assessed, of whom 19 hada diagnosis of Asperger syndrome and 8 a diagnosisof high-functioning autism. They obtained signific-antly elevated scores on this questionnaire, whencompared to IQ- and age-matched controls and alsowhen compared to their own relatives (Hill, Berthoz,& Frith, in press). They reported greater difficulty inidentifying and describing their own feelings, andless interest in the psychological motives behindactions. The ability to reflect on these difficultiesshows that a certain amount of insight is present,and the problems reported are consistent with theautobiographical accounts. These treat in detailphysical sensations and sensory experiences, butrarely complex emotions and attitudes. Half of theAsperger syndrome group obtained such extremescores on the Toronto questionnaire that they wouldhave been classified as severely impaired.

In this study the participants were also given theBeck Depression Inventory (Beck, Steer, & Garbin,1988) in which individuals are asked to indicate bymeans of specific statements how they have felt overthe past week. The participants with Asperger syn-drome showed significantly increased scores for de-pression and about 20% scored so highly that theywould have been categorised as clinically depressed.Depression and chronic anxiety in Asperger syn-drome are common psychiatric features (Ghaziud-din, Ghaziuddin, & Greden, 2002; Green, Gilchrist,Burton, & Cox, 2000). It is possible to explain thesefeatures as secondary reactions to the burdencaused by the core problems of autism. For instance,if intuitive mentalising failure makes it hard to pre-dict and interpret other people’s behaviour, then thesocial world cannot be the source of pleasure that itcan be for ordinary people. Especially if there is adesire to be part of the social world, as frequentlyexpressed by people with Asperger syndrome,unexplained failure of social interactions may wellcreate or intensify feelings of depression. The inab-ility to cope with the non-routine aspects of everydaylife due to executive function problems may alsocontribute to high anxiety and depression.

Looking towards the future

Asperger syndrome is a category that is desperatelyneeded and hugely important in clinical practice,even if the boundaries are fluid at present. Indeedthe need is so great that it is possible that thediagnosis of Asperger syndrome is at presentoverextended. Perhaps one reason for its currentpopularity and, potentially, overextension is thatsocial impairment is very common, but current cat-egories for diagnosis are extremely few. Thus As-perger syndrome may act like a magnet for as yetunidentified developmental disorders that affect so-cial interaction and everyday adaptation.

682 Uta Frith

It may well be that eventually subgroups of what isnow called Asperger syndrome will be identified,each characterised by specific core problems. In linewith Hans Asperger’s belief that these individualshave much to offer society, the importance of findingappropriate niches and work support must be rec-ognised. It is ironical that the cognitive strengths canobscure the social difficulties, and that this may leadto less willingness to acknowledge the need forguidance and support.

What can we conclude so far about the needs ofpeople with Asperger syndrome? They carry theburden of a neuro-genetic disorder, however mild itmay be in comparison to other forms of autism, andthey are likely to need a measure of supportthroughout their lives. Raising awareness of thecondition remains a crucial task. Unfortunately,individuals with Asperger syndrome can be deniedrecognition and help because they are intellectuallybright and may be able to give the impression of anear normal competence in routine interactions. Theappearance of normality is deceptive, however, andbreaks down when novel or stressful situationsarise. Raising awareness is important also in schoolchildren, and might well alleviate the distressinglycommon problem of the bullying of children whostand out as socially odd (Little, 2001).

From the behavioural and neurophysiologicalstudies to date we may assume that the mind andthe brain of the person with Asperger syndrome isdifferent from the mind/brain of the ordinary personand not so different from the person with autism.Some potentially handicapping secondary problemsin adults with Asperger syndrome can be traced toreduced awareness of their own feelings and those ofothers. The inability to talk about feelings appears tobe associated with clinically significant depressionand anxiety. Treatment of these symptoms is amatter of priority.

An astounding fact about Asperger syndrome isthat a proportion of individuals can achieve highacademic qualifications, and a few, high scientificdistinctions (Baron-Cohen, Wheelright et al., 1999;Fitzgerald, 2002). However, many individuals withAsperger syndrome do not find a vocational niche inadult life. It is generally agreed that highly ablechildren with autistic disorder benefit from specialisteducation just as much as less able children, andsimilar teaching approaches may be suitable forboth (see chapters in Prior, 2003). Given the greatheterogeneity of autistic disorder, individualprogrammes with one-to-one instruction seem to bean obvious choice. The extraordinary achievementsof people with Asperger syndrome demonstrate thatcompensatory learning can partially overcomeneurophysiological deficiency. Compensation is notsomething that works all by itself. Teaching, and inparticular explicit teaching of otherwise implicitrules, is necessary. Despite the bleak message thatneurophysiological abnormalities that exist from

birth or before cannot be put right with presentmeans, remarkable improvements in adaptation canoccur over the lifespan.

Everyone will agree that much work needs to bedone in the fine-grained description of behaviour andin the long-term follow-up of individual cases beforewe know what Asperger syndrome really is. Mean-while, there are things to be done to help betterrecognition and awareness of the disorder. BecauseAsperger syndrome is often recognised when thechild is at school, there is a practical need forassessment instruments that can be used by edu-cational psychologists as well as clinicians. Suchinstruments could then act as a basis for chartingthe developmental course of the disorder, which re-mains one of the most urgent tasks to be done. To beuseful in this way the assessment instrument needsto include psychometric tests to estimate generalintellectual ability; neuropsychological tests toidentify cognitive strengths and weaknesses; andexperimental tests of social functioning, includingperson perception, emotion perception and subtletests of intuitive mentalising. This is a difficult task,but such an assessment instrument would make astart in documenting the nature and development ofsome of the features that are typical of Aspergersyndrome.

Acknowledgement

This work has been supported by an MRC pro-gramme grant. I am grateful to Francesca Happe,Sarah-Jayne Blakemore and Elisabeth Hill for theirconstructive comments on this paper.

Correspondence to

Uta Frith, UCL Institute of Cognitive Neuroscience,17 Queen Square, London WC1N 3AR, UK; Email:u.frith@ucl.ac.uk

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Manuscript accepted 23 October 2003

686 Uta Frith