Asperger

\

Pergamon

PII] S9917Ð2821"85#99943Ð0

Neuropsycholo`ia\ Vol[ 24\ No[ 0\ pp[ 54Ð69\ 0886 Copyright Þ 0885 Elsevier Science Ltd[ All rights reserved Printed in Great Britain 9917Ð2821:86 ,06[99¦9[99

Asperger|s syndrome and memory] Similarity to autism but not amnesia DERMOT M[ BOWLER\ NICOLA J[ MATTHEWS and JOHN M[ GARDINER Department of Psychology\ City University\ London\ U[K[ "Received 7 January 0885^ accepted 1 May 0885#

Abstract*Two experiments are described in which the memory of adults with Asperger|s syndrome is compared with that of verbal IQ controls[ The results of the _rst experiment showed that the Asperger subjects resembled autistic adults and children in their failure to use category information to aid their free recall[ In the second experiment\ both groups of subjects showed similar priming e}ects in an implicit stem completion task and similar performance on an explicit cued recall task[ Moreover\ both groups also showed more priming for items that they had read at study and better recall for items that they had to generate at study\ suggesting that the cued recall of the Asperger subjects did not result from contamination by automatic or involuntary processes[ Copyright Þ 0885 Elsevier Science Ltd[ Key Words] Asperger|s syndrome^ memory^ autism[

short!term and serial memory tasks ð10Ł\ they are imp! aired in their longer!term memory\ especially in free recall tasks ð4\ 5\ 6Ł[ Such observations have led Boucher and Warrington to draw comparisons between autism and the amnesic syndrome\ which is partly characterized by a de_cit in long!term memory and in the ability to form new associations "see ð19Ł#[ Autistic children\ unlike con! trols\ have also been found to be unable to use category information to help their free recall ð15Ł\ thereby re_ning an earlier observation\ made by Hermelin and O|Connor ð09Ł\ that autism involves a basic cognitive de_cit in the ability to process stimuli in an elaborative\ meaningful way[ However\ several studies have failed to _nd evidence of any impairment in cued recall\ either with perceptual cues\ such as FR for FRUIT or CHA for CHAIR ð6Ł\ rhyme cues or category name cues ð15Ł\ or other con! ceptual cues such as leading questions ð5Ł[ Here\ the par! allel between autism and amnesia breaks down\ since amnesics are typically impaired in cued recall too\ as they are in all explicit memory tasks*those that require conscious recollection of previous experiences ð7Ł[ The idea that the memory impairments of people with autism are less evident when cues are provided than when free recall is required is further supported by studies by Min! shew and her colleagues ð06\ 07Ł[ They found no di}er! ences between high!functioning adults with autism "people who _t current diagnostic criteria for Kanner! type autism but who are of normal IQ# and controls on rote and associative memory but marked di}erences on

Introduction There has been much debate on whether Asperger|s syndrome ð0\ 1Ł and autism ð03Ł constitute distinct dis! orders or are situated on a continuum ð04Ł[ Whereas classically autistic children are frequently mentally retarded\ show motor stereotypies and delayed and devi! ant language\ people with Asperger|s syndrome are of normal intelligence\ show more abstract stereotypies\ such as specialized interests in radio transmitters or bus timetables\ and show no abnormalities of language apart from either ~at or exaggerated intonation patterns[ The current consensus is that\ although there are di}erences in some areas of psychological functioning\ there are also many areas of similarity\ most notably in the area of social impairment[ Clinical accounts of children with Kanner!type autism describe them as having a good rote memory ð05Ł\ and such accounts of higher!functioning children and adults with Asperger|s syndrome document prodigious mem! ories for information centred on highly specialized inter! ests such as bus timetables or dinosaurs ð16Ł[ Experimental studies of children with Kanner!type autism show that\ while they appear to be unimpaired on

 Address for correspondence] Department of Psychology\ City University\ Northampton Square\ London EC0V 9HB\ U[K[^ e!mail] d[m[bowlerÝcity[ac[uk[

54

55

D[ M[ Bowler:Asperger|s syndrome and memory

memory tasks that require comprehension and recall of complex visual and auditory material[ Minshew suggests that the patterns of strengths and weaknesses seen in the memory of high!functioning adults with autism may be the result not of a memory de_cit per se but of an impair! ment in the application of general strategies\ such as the organization of information into categories\ to the information to be remembered[ This pattern resembles the memory impairments reported by Baddeley and Wil! son ð2Ł and Stuss et al[ ð14Ł in patients with frontal lobe damage\ and underpins other work such as that by Ozon! o} et al[ ð08Ł\ who demonstrated impairments in frontal lobe functioning in Asperger and high!functioning autis! tic subjects[ Although memory in both high!functioning children and adults with Kanner!type autism has been extensively researched\ as far as we are aware\ there has been little or no previous experimental investigation of possible memory impairment in adults with an Asperger diag! nosis[ The major purpose of this article is to describe such an investigation[ In the light of the recent debate over whether or not Asperger|s syndrome and autism are sep! arate disorders\ the _rst experiment was a replication on adults with Asperger|s syndrome of Tager!Flusberg|s ð15Ł study of autistic children and Minshew et al[|s ð07Ł study of autistic adults\ in order to ascertain if Asperger adults resemble the other two groups by producing similar results in their free recall of related and unrelated words[ If they do\ then performance across Asperger and control groups should be similar for an unrelated word list\ and the Asperger group should show signi_cantly lower per! formance for a related word list[ The second experiment was designed to investigate the performance of Asperger and control groups in explicit compared with implicit memory tasks[ If there is any parallel between Asperger|s syndrome and the amnesic syndrome\ then any impairment in the Asperger group should be evident in the explicit test\ and not in the implicit test[ This outcome should be obtained even when the two tests involve identical test cues\ such as word stems\ and di}er only with respect to whether subjects are instructed to use these cues to recall words from the study list\ or to complete them with the _rst words that come to mind "e[g[ ð8Ł^ see ð11Ł for a general review#[ In addition\ although some of the earlier _ndings with autistic children showed no impairment in cued recall\ at least some of these cued recall tasks might actually have allowed subjects to perform the task as if it were an implicit task "e[g[ ð6Ł#\ that is\ responding with words that {came to mind| rather than trying consciously to recollect the study list[ The present study would allow us to deter! mine whether impaired cued recall resulted from the oper! ation of automatic or involuntary processes[ That subjects may not always obey the instructions they are given in explicit compared with implicit tests\ and hence that performance might be {contaminated|\ is a problem that has greatly exercised memory theorists in recent years[ One solution to this problem\ {the retrieval

intentionality criterion|\ was suggested by Schacter et al[ ð13Ł who suggested that\ in addition to keeping all test conditions constant\ except the retrieval instructions\ one should also include some variable known to dissociate explicit from implicit performance[ The level of pro! cessing has proved a popular choice\ since it is well estab! lished that\ although this variable strongly in~uences explicit performance\ it has little e}ect on performance in perceptual priming tasks like word!stem completion "e[g[ ð12Ł#[ If the level of processing were to be shown to have a strong e}ect on performance in such an implicit task\ it could be concluded that subjects must have been responding on an explicit basis[ A particularly powerful demonstration of this logic was reported by Java ð01Ł\ who used word stem cues for both explicit and implicit tests following a generate vs read manipulation at study "cf[ ð3\ 00Ł#[ Java found that generating words at study led to superior recall in the explicit test\ but reading words at study led to superior completion in the implicit test[ Obviously\ if subjects had been responding in the same way in each test\ such a crossover interaction could not have occurred[ Though this interaction replicated Blax! ton ð3Ł and Jacoby|s ð00Ł _ndings\ only the study by Java meets the criteria suggested by Schacter et al[ ð13Ł by having identical cues in each kind of test[ A further aim of our second experiment was to rep! licate Java|s ð01Ł study[ Accordingly\ subjects in both groups either generated or read the words in a study list\ and were then given implicit and explicit memory with word stem cues[ Both groups should show superior recall of generated words in the explicit test\ and superior com! pletion of read words in the implicit test[ The question then is whether the Asperger group and the control group perform similarly in the implicit test\ but di}erently in the explicit test[ Experiment 0 Method Subjects The Asperger group consisted of 05 adults "09 men\ 1 women#[ They all had a diagnosis of Asperger|s syndrome according to draft ICD09 research criteria but excluding the requirement for absence of delay or deviance in language devel! opment[ None showed any obvious present state abnormalities in the structural or semantic aspects of their language[ In addition\ on the basis of parental interviews\ all were reported as not having engaged in symbolic play or joint attention behav! iours as children\ and all had Wechsler verbal IQs above 69[ All diagnoses were made by clinicians experienced in the diag! nosis of autism and were con_rmed by the _rst author[ The control group consisted of 05 volunteers recruited from a local Job Centre "7 male\ 7 female#[ The control subjects were mat! ched to the Asperger subjects on both chronological age and verbal IQ as measured by the WAIS[ Table 0 summarizes the age and IQ means for both groups[ All subjects were tested individually and were paid for participating[ The present experi! ments formed part of a larger test battery taken by the subjects\ all of whom participated in Experiment 1 followed by Experi! ment 0[

D[ M[ Bowler:Asperger|s syndrome and memory Table 0[ Mean chronological age and psychometric scores for the two experimental groups Asperger subjects Mean S[D[ Mean VIQ S[D[ Mean PIQ S[D[ Mean IQ S[D[

Control subjects

Chronological age "in years# 20[1 00[9 88[33 05[61 75[20 08[11 83[95 07[19

22[2 00[3 85[14 02[11 85[01 09[20 84[83 00[84

Design and materials This experiment consisted of two word lists consisting of twelve concrete nouns each as used by Tager!Flusberg ð15Ł[ One list contained twelve words drawn from the same category\ i[e[ animals\ and the second list consisted of twelve words taken from di}erent unrelated categories[ In designing these lists Tager!Flusberg had ensured that all the words were approxi! mately matched for frequency of use[

56

vation that the memory problems of high!functioning individuals with autism centre on organizational and con! trol processes can be extended to individuals with Asperger|s syndrome[

Experiment 1 Subjects with Asperger syndrome and IQ!matched controls studied a list of words\ half of which were gen! erated and half read[ During the generate condition\ all subjects were asked to produce the target word from a semantic clue and the initial letter of the word "e[g[ red! dish yellow citrus fruit] O******<#[ The majority of the clues were descriptive phrases but some consisted of the opposites of the relevant words "e[g[ the opposite of enemy] F*******#\ and all were designed to ensure that the target words would be generated by all the subjects[ In the read task\ subjects simply read the target word o} the card[ On completion of the study lists\ all subjects were given a _ller task followed by a word stem completion task\ also presented as a _ller task\ and then a cued recall test with word stem cues[

Procedure The order of presentation of related and unrelated word lists was counterbalanced across subjects[ Words were presented verbally at a rate of one word per second[ Subjects were asked to listen carefully and to repeat as many of the words as they could recall as soon as the experimenter had indicated she had _nished reading the list by means of a nonverbal signal "looking up at the subject[ Subjects were allowed as much time as they required to recall as many words from the list as possible[

Results and discussion The results of this experiment are outlined in Table 1[ Analyses of the data using a repeated measures ANOVA showed signi_cant main e}ects for Group ðF "0\29#  5[03\ P ³ 9[91# and Related:Unrelated lists "F "0\29#  16[35\ P ³ 9[990Ł and a Group by Related: Unrelated lists interaction ðF "0\29#3[36\ P ³ 9[94Ł[ Inspection of means shows that the di}erence between related and unrelated lists was greater for the control than for the Asperger subjects[ These results demonstrate that the Asperger subjects used here\ like Tager!Flusberg|s ð15Ł autistic children and Minshew et al[|s ð06Ł high!functioning adults\ are imp! aired in using semantic information in free recall[ The _ndings thus suggest that Minshew et al[|s ð06\ 07Ł obser! Table 1[ Mean number of words recalled in Experiment 0

Unrelated word list Related word list

Asperger subjects

Control subjects

4[95 "1[07# 5[02 "0[87#

4[45 "0[26# 7[95 "0[95#

Method Subjects The same subjects were used as in Experiment 0[

Design and materials The experiment used a 1 "Asperger vs control# ×1 "implicit vs explicit test# ×1 "generate vs read# mixed repeated measures design with the order of conditions counterbalanced across subjects[ Stimuli consisted of 79 di}erent six!letter words taken from a previous study list designed by Java and Gardiner ð02Ł and listed in the appendix[ Study list words were hand!printed on index cards with the generate cards showing the initial letter of the target word and either a descriptive phrase or the opposite of the target word[ These words were randomly divided into two sets of 39 words each to produce study lists A and B[ Half the subjects in both experimental groups studied list A and half studied list B[ Within each study list\ the 39 words were randomly divided into half again\ 19 being presented using the generate task and 19 using the read task[ Within each study list\ generate and read words were counterbalanced across subjects[ The two methods of presentation were blocked so that half the subjects in each group received the generate task _rst and half received the read task _rst[ Two test lists were devised\ consisting of 39 word stems each three letters long[ Within each test list\ half of the word stems were from study list A and half were from study list B\ so that for each subject\ the test lists were divided equally into studied and novel items[ The novel items that had not previously been presented to that subject for study provided the baseline mea! sures of priming and intrusion rates in cued recall[ Of the 19 word stems that had previously been studied by the subjects\ half of these were taken from the generated list and half from the read list[ The test list that was used to examine implicit memory for half the subjects in each group was used to test

57

D[ M[ Bowler:Asperger|s syndrome and memory

cued recall for the other half and vice versa\ so that all the subjects were tested for all 79 words[ Procedure Study list items were hand!printed on index cards and pre! sented individually[ The presentation rate was approximately one card every 4 sec[ In the generate condition\ subjects were asked to read the clue silently and then to say the target word aloud[ In the read condition\ subjects were simply asked to read the words aloud[ The order of presentation was blocked\ i[e[ either all generate followed by all read tasks or vice versa\ but within each task\ the target words were presented in a unique random order for each subject[ Neither group of subjects showed any di.culty in reading the test materials[ After the presentation of the study list\ subjects were told that there would be two more tasks before they were given a memory test[ Half the subjects were given the Mill Hill Vocabu! lary Test and half the Digit Symbol test from the WAIS as _ller tasks[ The _ller task was then followed by a word stem completion task which\ in turn\ was followed by the alternative test list as a cued recall test "following Java ð01Ł#[ In the word! stem completion test\ subjects were given sheets with word stems printed in capital letters and asked to complete as many as they could with the _rst word "apart from proper nouns# that came into their heads[ They were then told that they would take the memory test and were given the same stems to complete\ but this time\ they were asked to use the stems as cues to remind them of the words that they had studied previously[ They were also told that only half the stems related to words from the study list and were asked not to guess[ Neither group of subjects showed any evidence of having di.culty in completing the generate or read tasks[

Results and discussion The baseline completion rates for nonstudied words for the implicit test were 9[02 for both groups[ The cor! responding intrusion rates for nonstudied words in the cued recall test were 9[91 for the Asperger group and 9[92 for controls[ As these baseline and intrusion rates are almost identical\ all further analyses were conducted on uncorrected study word completion rates[ The principal results from the word stem completion and the cued recall tests for both experimental groups are outlined in Fig[ 0[ These results indicate that both groups performed in a similar way in each test[ Both groups showed a superior

recall of generated words in the explicit test\ and superior completion of read words in the implicit test[ Repeated measures analysis of variance supported this description of the data by showing no signi_cant di}er! ence in overall performance between the two groups ðF "0\29# ³ 0Ł[ Signi_cantly more items were completed under the implicit than under the explicit conditions ðF "0\29#  16[24\ P ³ 9[990Ł[ Neither the group by generate:read nor the group by implicit:explicit nor the three!way "group by generate:read by implicit:explicit# interactions were signi_cant[ However\ the inter! action between the two within!subject variables "implicit:explicit by generate:read# was signi_cant ðF "0\29#  20[02\ P ³ 9[990Ł[ These results therefore rep! licated those obtained by Java ð10Ł and further showed that Asperger subjects do not show any evidence of mem! ory impairment in explicit compared with implicit tests when the retrieval intentionality criterion is met ð13Ł[ Since amnesic subjects do show memory impairment under such conditions "e[g[ ð8Ł#\ our results provide no support for a parallel between the amnesic syndrome and autistic disorders[ General discussion The central aim of this study was to provide a sys! tematic investigation into the nature of the memory de_! cits in Asperger|s syndrome[ The results of Experiment 0 clearly showed that the Asperger subjects resemble classi! cally autistic individuals in their failure to use semantic information to aid free recall ð15\ 06Ł\ but that in Experi! ment 1\ they did not resemble amnesic subjects in a direct comparison between explicit and implicit tests with word stem cues[ There is\ therefore\ no support for the parallel between autism and the amnesic syndrome that was _rst proposed by researchers such as Boucher and Warrington ð6Ł[ In addition\ by replicating Java|s ð01Ł demonstration of a cross!over interaction between the kind of test and generating vs reading the words at study\ the results of the second experiment rule out the possibility that the Asperger subjects were responding to the cued recall test

Fig[ 0[ Cued recall and word stem completion in Experiment 1[

D[ M[ Bowler:Asperger|s syndrome and memory

in an implicit manner[ This last point is further supported by the observation that on the cued recall test admin! istered here\ implicit responses on the explicit test would probably have led to in~ated intrusion rates for the Asperger group had they been responding implicitly[ However\ the comparable baseline and intrusion rates found for both groups suggest that this did not happen[ We can\ therefore\ conclude with con_dence that unim! paired cued recall in people with Asperger|s syndrome does not result from the operation of automatic processes on an explicit test[ The most obvious explanation of the di}erence between the impaired performance in Experiment 0 and unimpaired performance in Experiment 1 centres on the degree of conscious control that subjects had to exercise over their memory in the two situations[ In the _rst experiment\ subjects were given a general instruction to learn the word lists and to remember as many of the lists as they could[ By contrast\ in the second experiment\ both the encoding and the retrieval strategies were tightly constrained by the demands of the task[ At the study phase\ subjects had to read or to generate words\ and at recall\ had to complete word stems[ The _nding in Experiment 0 of impairment under unconstrained con! ditions coupled with unimpaired performance in Experi! ment 1\ where constraints were strong\ is in line with Minshew et al[|s ð06\ 07Ł conclusion that people with autism perform poorly when they have to develop com! plex organizing strategies to help in their recall of infor! mation[ Further tests of this account of autistic memory de_cits should be aimed at devising a series of experi! ments that systematically manipulate the degree of con! trol required of the subject both at study and at recall[ It remains possible that the Asperger subjects| performance on the cued recall task remained unimpaired because\ being a recognition task\ it was easier than free recall tasks[ With this argument\ there could still be a similarity between Asperger|s syndrome and amnesia with the two conditions di}ering only in the degree of impairment[ However\ this question cannot be settled by the results of the present study[

2[ 3[

4[

5[

6[

7[

8[

09[ 00[ 01[ 02[ 03[ 04[ 05[

Acknowled`ements*The work reported here formed part of a dissertation by the second author for the degree of B[Sc[ of City University[ The _rst and last authors would also like to acknowledge the support of the Wellcome Trust and the ESRC\ respectively[ Sincere thanks are also due to the Centre for Social and Communication Disorders for help in the recruitment of subjects[

06[

07[ References 0[ Asperger\ H[ Die {autistische Psychopathen| im Kin! desalter[ Archives fur Psychiatrie und Ner! venkrankheiten 006\ 65Ð025\ 0833[ 1[ Asperger\ H[ Autistic psychopathy in childhood "trans[ U[ Frith#[ In Autism and Asper`er Syndrome\

08[

58

U[ Frith "Editor#\ Cambridge University Press\ Cam! bridge\ 0880[ Baddeley\ A[ and Wilson\ B[ Frontal amnesia and the dysexecutive syndrome[ Brain and Co`nition 6\ 101Ð129\ 0877[ Blaxton\ T[ A[ Investigating dissociations among memory measures] Support for a transfer!appro! priate processing framework[ Journal of Exper! imental Psycholo`y] Learnin` Memory and Co`nition 04\ 546Ð557\ 0878[ Boucher\ J[ Immediate free recall in early childhood autism] Another point of similarity with the amnesic syndrome[ British Journal of Psycholo`y 61\ 100Ð104\ 0870[ Boucher\ J[ and Lewis\ V[ Memory impairments and communication in relatively able autistic children[ Journal of Child Psycholo`y and Psychiatry 29\ 88Ð 011\ 0878[ Boucher\ J[ and Warrington\ E[ Memory de_cits in early infantile autism] Some similarities to the am! nesic syndrome[ British Journal of Psycholo`y 56\ 62Ð 76\ 0865[ Graf\ P[ and Schacter\ D[ Implicit and explicit mem! ory for new associations in normal and amnesic sub! jects[ Journal of Experimental Psycholo`y] Learnin` Memory and Co`nition 00\ 490Ð497\ 0874[ Graf\ P[\ Squire\ L[ R[ and Mandler\ G[ The infor! mation that amnesic patients do not forget[ Journal of Experimental Psycholo`y] Learnin` Memory and Co`nition 09\ 053Ð067\ 0873[ Hermelin\ B[ and O|Connor\ N[ Psycholo`ical Experiments with Autistic Children\ Pergamon\ Oxford\ 0869[ Jacoby\ L[ Remembering the data] Analysing inter! active processes in reading[ Journal of Verbal Learn! in` and Verbal Behaviour 11\ 374Ð497\ 0872[ Java\ R[ I[ States of awareness following word stem completion[ European Journal of Co`nitive Psy! cholo`y 5\ 66Ð81\ 0883[ Java\ R[ and Gardiner\ J[ Priming and aging] further evidence of preserved memory function[ American Journal of Psycholo`y 093\ 78Ð099\ 0880[ Kanner\ L[ Autistic disturbances of a}ective contact[ Nervous Child 1\ 106Ð149\ 0832[ Klin\ A[ Asperger syndrome[ Psychiatric Clinics of North America 2\ 020Ð037\ 0883[ Lockyer\ L[ and Rutter\ M[ A _ve! to _fteen!year follow!up study of infantile psychosis] IV[ Patterns of cognitive ability[ British Journal of Social and Clinical Psycholo`y 8\ 041Ð052\ 0869[ Minshew\ N[\ Goldstein\ G[\ Muenz\ L[ R[ and Payton\ J[ Neuropsychological functioning in non! mentally retarded autistic individuals[ Journal of Clinical and Experimental Neuropsycholo`y 03\ 638Ð 650\ 0881[ Minshew\ N[\ Goldstein\ G[\ Taylor\ H[ and Siegel\ D[ Academic achievement in high!functioning autis! tic individuals[ Journal of Clinical and Experimental Neuropsycholo`y 05\ 150Ð169\ 0883[ Ozono}\ S[\ Rogers\ S[ and Pennington\ B[ Asper! ger|s syndrome] Evidence for an empirical distinc! tion from high!functioning autism[ Journal of Child Psycholo`y and Psychiatry 21\ 0096Ð0001\ 0880[

69

D[ M[ Bowler:Asperger|s syndrome and memory

19[ Parkin\ A[ J[ Memory and Amnesia] An Introduction[ Blackwell\ Oxford\ 0876[ 10[ Prior\ M[ and Chen\ C[ Short!term and serial mem! ory in autistic\ retarded and normal children[ Journal of Autisim and Childhood Schizophrenia 5\ 010Ð020\ 0865[ 11[ Roediger\ H[ III\ and McDermott\ K[ Implicit memory in normal human subjects[ In Handbook of Neuropsycholo`y\ M[ Spinnler and F[ Boller "Editors#\ Vol[ 7\ pp[ 52Ð020[ Elsevier\ Amsterdam\ 0882[ 12[ Roediger\ H[ Jr\ III\ Weldon\ M[ S[\ Stadler\ M[ L[ and Riegler\ G[ L[ Direct comparison of two implicit memory tests] word fragment and word stem com! pletion[ Journal of Experimental Psycholo`y] Learn! in` Memory and Co`nition 07\ 0140Ð0158\ 0881[

13[ Schacter\ D[ L[\ Bowers\ J[ and Booker\ J[ Intention\ awareness and implicit memory] The retrieval inten! tionality criterion[ In Implicit Memory\ Theoretical Issues\ S[ Lewandowsky\ J[ C[ Dunn and K[ Kirsner "Editors#\ pp[ 36Ð54[ Lawrence Erlbaum Associates\ Hillsdale\ NJ\ 0878[ 14[ Stuss\ D[\ Alexander\ M[\ Palumbo\ C[\ Buckle\ L[\ Sayer\ L[ and Pogue\ J[ Organizational strategies of patients with unilateral or bilateral frontal lobe injury in word list learning tasks[ Neuropsycholo`y 7\ 244Ð262\ 0883[ 15[ Tager!Flusberg\ H[ Semantic processing in the free recall of autistic children[ British Journal of Devel! opmental Psycholo`y 8\ 306Ð329\ 0880[ 16[ Wing\ L[ Asperger|s syndrome] A clinical account[ Psycholo`y and Medicine 00\ 004Ð018\ 0870[