Imitation and Pantomime in High-FunctioningAdolescents with Autism Spectrum Disorders
Sally J. RogersUniversity of Colorado Health Sciences Center
Loisa BennettoUniversity of Denver
Robin McEvoyUniversity of Colorado Health Sciences Center
Bruee F. PenningtonUniversity of Denver
ROGERS, SALLY J,; BENNETTO, LOISA; MCEVOY, ROBIN; and PENNINGTON, BRUCE F, Imitation andPantomime in High-Functioning Adolescents with Autism Spectrum Disorders. CHILD DEVELOP-MENT, 1996, 67, 2060-2073. A study was designed to test 2 alternative hypotheses—a symbolichypothesis and an executive function hypothesis—for the imitation and pantomime deficits foundin previous studies of autism. The subjects were 17 adolescent high-functioning subjects withautism spectrum disorders and 15 clinical comparison subjects who were matched on chronologi-cal age and verbal IQ, Meaning and sequence were manipulated in facial and manual imitationtasks. Sequence was manipulated in the pantomime and control tasks. Recognition memory andmotor control tasks were matched to the experimental tasks. The results provided no support forthe symbolic deficit hypothesis; meaning aided rather than hindered the performance of thegroup with autism. Partial support for the executive deficit hypothesis was found. There wereno group differences on motor control tasks, and few on the memory control tasks, arguing againstdeficits in motor initiation, basic motor coordination, or visual recognition memory.
Autism is a severe disability involving cade effect, impeding early affective, social,impairments in social relatedness, language, and communicative development. They alsobehavior, and cognition. Because autism postulated that imitation deficits in autismdevastatingly affects behaviors that are so might result from underlying executivefundamental to social functioning, there is deficits. Working from a similar model, Melt-an active search for developmental models zoff and Gopnik (1993) suggested that earlythat can (1) account for the various symp- imitation skills provide the infant with infor-toms, (2) guide the search for underlying mation about other persons that is crucial forneurobiological mechanisms, and (3) lead to developing a sense of "other minds," andmore effective treatments. that a deficit in imitation might impede de-
velopment of a theory of mind. In contrast.In 1991, Rogers and Pennington sug- Baron-Cohen (1988) hypothesized that imi-
gested that a motor-imitation deficit might tation deficits in autism are secondary to anbe a core deficit in autism. Using Stern's underlying symbolic deficit related to tbe(1985) model of interpersonal development, primary metarepresentational deficit, Con-they hypothesized that a biological impair- sequently, testing whether the imitationment in motor imitation could create a cas- deficits in autism are consistent with a sym-
We wish to thank Taffy Reed and Elizabeth Saft for their assistance in scoring videotapes.We also wish to thank members of the Developmental Psychobiology Research Group for theirfeedback and support. Loisa Bennetto was supported by NIMH MH10470 (NRSA). RobinMcEvoy was supported by the DPRG postdoctoral training program, funded by NIMH grantMH15442. Bruce Pennington was supported by these NIMH grants: MH00419 (RSDA), MH38820 (MERIT award), and MH45916, as well as by an NICHD Center grant (HD27802), Pleaseaddress requests for reprints to the first author at the Department of Psychiatry, Box B148,UCHSC, 4200 E, 9th, Denver, CO 80262, E-mail address: Sally,Rogers@UCHSC,edu,
bolic deficit versus an executive deficit pro-vides one test of two competing theoriesabout the nature of the primary cognitivedeficit in autism: the metarepresentationaltheory versus the executive theory. That isthe main goal of the current study.
In what follows, we will (1) review pre-vious studies of imitation in autism, (2) elab-orate the predictions made for imitation per-formance by the symbolic versus executivedeficit hypotheses, and (3) describe the pres-ent study.
Studies of Imitation in AutismThe difficulty children with autism have
in imitating another person's actions wasfirst described in the research literature byDeMyer and colleagues (DeMyer et al.,1972). A series of published studies of imita-tion skills of subjects with autism involvingboth higher- and lower-functioning subjects,ranging in age from preschool to adulthood,compared to matched clinical comparisonsubjects, have reported consistent findingsof imitation deficits in subjects with autism(e.g., Bartak, Rutter, & Cox, 1975; Hammes& Langdell, 1981; Hertzig, Snow, & Sher-man, 1989; Loveland et al., 1994; Ohta,1987; Sigman & Ungerer, 1984; see Meltzoff& Copnik, 1993; Rogers & Pennington,1991; and Smith & Bryson, 1994, for detailedreviews). In contrast, two studies of subjectswith autism have not demonstrated imitationdeficits, but both studies used infant mea-sures with older, verbal subjects and werecompromised by ceiling effects (Charman &Baron-Cohen, 1994; Morgan, Cutrer, Coplin,& Rodrigue, 1989).
In sum, there is considerable evidencefor imitation deficits in autism. However,these imitation deficits may be due toseveral different underlying mechanisms(Smith & Bryson, 1994), and the designs ofprevious studies do not permit a clear test ofwhich mechanism is involved. Specifically,many of these studies have methodologicalproblems, including (1) lack of control forsymbolic or meaningful content to the move-ments, which is problematic because sym-bolic thought is considered to be impairedin autism (Baron-Cohen, 1988); (2) use of fa-miliar or well-practiced movements, whichmay allow a subject to rely on automatic mo-tor pattems rather than representation, mo-tor planning, and intentional execution ofnovel movements; and (3) use of actionsinvolving objects, which may confoundimitation with well-practiced actions or
Rogers et al. 2061
with cause-and-effect schemas (Charman &Baron-Cohen, 1994; Sigman & Ungerer,1984). Our study was designed to avoidthese methodological problems and to per-mit a clear test of two alternative mecha-nisms, a symbolic deficit versus an executivedeficit.
Predictions of the Symbolic versusExecutive Deficit Hypotheses
Two current competing theories of thecore or primary cognitive deficit in autismare the metarepresentational theory (Baron-Cohen, 1988; Leslie, 1987; Morton & Frith,1994) and the executive or "frontal" theory(Damasio & Maurer, 1978; Hughes & Rus-sell, 1993; Ozonoff, Pennington, 6c Rogers,1991). Since each of these theories makesdifferent predictions about the nature of theimitation deficit in autism, a test of those dif-ferent predictions provides a validity test ofeach theory. Furthermore, as mentioned ear-lier, imitation deficits in autism are of con-siderable theoretical interest aside fromthose two theories, because in normal chil-dren imitation occurs very early and may becrucial for the normal development of otheraspects of social cognition, including theoryof mind.
In the metarepresentational theory, thepostulated primary cognitive deficit is in acomputational process called the "expres-sion raiser" (EXPRAIS), which allows one toform second-order representations that arepostulated to be necessary both for repre-senting another person's beliefs, desires,and intentions and for symbolic play (Baron-Cohen, 1988; Leslie, 1987; Morton & Frith,1994). Perhaps the greatest challenge to themetarepresentational theory is the finding ofdeficits in autism in aspects of early socialcognition that do not require metarepresen-tation. Joint attention is one example. Al-though the metarepresentational theory hasbeen extended to account for joint attention(and other aspects of social cognition oc-curring in the first year of life—Morton &Frith, 1994), whether joint attention actuallyrequires the computations performed by EX-PRAIS is debatable (e.g., Mundy, Sigman,& Kasari, 1993). An even clearer example isimitation, since it is highly unlikely that imi-tation requires metarepresentation. How-ever, imitation deficits found in older chil-dren with autism could be explained assecondary to the consequences of the pri-mary deficit in EXPRAIS. One such explana-tion (Baron-Cohen, 1988) is that the difficul-ties that children with autism have on
2062 Child Development
imitation and pantomime tasks are second-ary to underlying symbolic deficits relatedto the primary metarepresentational deficitin this disorder. The current study poses avalidity test for the metarepresentational hy-pothesis by asking whether the imitationdeficits found in autism are consistent witha symbolic deficit.
In the executive theory, the postulatedprimary cognitive deficit is in executivefunctions, which is a neuropsychologicalterm for cognitive processes tiiought to bemediated by the prefrontal cortex. Althoughtheorists have provided several different ac-counts of what those processes are, there isconvergence across accounts that both work-ing memory and inhibition are key cognitiveprocesses in various executive tasks (Pen-nington, 1994). In the Rogers and Pen-nington (1991) paper, it is postulated that anunderlying deficit in executive functionscould cause an early deficit in imitation,leading to a cascade of other deficits in de-veloping social cognition. An executivefunction deficit would affect imitation be-cause imitation requires tbe formation of abody movement plan, which must be heldon line in working memory while the planis executed; correct execution requires inhi-bition of competing motor plans. Patientswith acquired frontal lesions have deficits ina variety of motor sequencing tasks; a recentsimulation of those deficits (Kimberg &Farab, 1993) found that weakening connec-tions in working memory produced a deficitin motor sequencing because of a failure toinhibit competing motor plans. One corol-lary of this work is that longer sequences aremore likely to lead to deficient performance.
These two different cognitive theoriesof autism predict different performance pro-files by subjects with autism on imitationtasks. A symbolic deficit should lead to dif-ferential deficits in subjects with autism onmeaningful as opposed to nonmeaningfulimitation tasks. An executive deficit shouldlead to differential deficits on sequentialtasks as opposed to nonsequential tasks. Ob-viously, these two possible explanations ofan imitation deficit do not exbaust all thepossibilities; we return to the issue of otherpossible mecbanisms in the Discussion.
In addition, we are not postulating tbatmeaning and sequence, which refiect work-ing memory load, are completely indepen-dent in their effects on imitation perfor-mance. For subjects without disabilities, ameaningful sequence should impose less of
a working memory load than a nonmeaning-ful one, and thus result in better perfor-mance.
The Present Study
The present study was designed to ex-amine the performance of high-functioningadolescents with autism spectrum disorderson a variety of imitation and pantomimetasks in order to test these two alternativehypotheses. Specifically, we manipulatedboth meaning and sequence in both manualand facial imitation tasks; we manipulatedsequence in the pantomime tasks. We in-cluded memory and motor control tasks toevaluate whether group differences weredue to problems in those areas. The studyaddressed the following questions: (1) Aremotor imitation and pantomime deficitspresent in high-functioning adolescentswith autism spectrum disorders compared toclinical comparison subjects matched onchronological age (CA) and verbal IQ? If so,(2) Is the performance of subjects with au-tism differentially poorer on symbolic ormeaningful tasks than on nonmeaningfultasks (consistent with a symbolic deficit);and/or (3) Is tbeir performance differentiallypoorer on sequential tasks than on nonse-quential tasks (consistent with an executivedeficit)?
METHOD
SubjectsTwo groups of subjects, aged 11 to 21,
participated in the study. The first was agroup of 17 high-functioning persons withautism spectrum disorders (hereafter re-ferred to as autism) (mean CA = 15.5 years).They included 15 males and 2 females, 15of European origin, 1 of African Americanorigin, and 1 of Hispanic origin. Their diag-noses were Autistic Disorder (n = 9) or Per-vasive Developmental Disorder Not Other-wise Specified (PDDNOS) (n = 8). Sincethe aim of this study vi as to see what deficitsremained in high-functioning older subjects,the PDD subjects were retained in the autis-tic group, with the rationale that any biasthey might introduce would be a conserva-tive bias against finding the hypothesizeddifferences.
The comparison group was matchedwith the autism group on CA and Verbal IQand consisted of 15 subjects, 14 males andone female, with diagnoses of dyslexia (10),borderline IQ (2), ADHD (1), genetic dis-order (1), and unspecified (1). All were
Rogers et al. 2063
of European ancestry. All comparison sub-jects achieved CARS scores below 24, andwere without autistic symptoms. A mixed-diagnosis comparison group was specificallychosen to control for the general effects ofhaving some type of central nervous systemdysfunction. No subject had any observablemotor impairment.
All subjects obtained Full-Scale IQscore estimates above 69 on previous testingon tiie WISC-R (Wechsler, 1991). Bennettoet al. (1996) provide a detailed descriptionof selection and matching procedures. Ascan be seen in Table 1, the two groups weresimilar in IQ, age, sex, SES (Hollingshead,1975), and handedness.
Measures
Imitation and Pantomime TasksThree kinds of tasks were taken from the
imitation and pantomime literature: handimitations, face imitations, and pantomimetasks. The experimental and control tasks arelisted in Table 2 and are available from thefirst author.
Hand tasks.—Four experimental condi-tions were generated by crossing the dimen-sions of meaning and sequence in a 2 x 2witlbiin-subjects design. The four conditionswere as follows.
1. Five single nonmeaningful move-ments (e.g.. Extend arm and hand straightout in front of body, witb fingers fanned out,and thumb pointed to ceiling; Kimura & Ar-chibald, 1974),
2. Six single, meaningful, familiarmovements (e.g.. Put arms over head, clasptogether and shake. Examiner says, "Showsomeone that you are a champion").
3. Six sequential, nonmeaningful move-ments (e.g.. With fingertips and tiiumb tipheld together and placed on the same shoul-der, move the hand out forward and horizon-tally from the shoulder, rotating and openingit widely as it moves and extends; Kimura &Archibald, 1974; Kolb & Milner, 1981).
4. Six sequential, meaningful move-ments (e.g.. Make a grasping motion with theright hand at mid forehead as if to remove abrimmed cap, then extend the arm to theright with the hand opening as it reaches thefinal fully extended position. Examiner says,"I'm going to take off my cap and put it inthe laundry basket").
We attempted to equate meaningfxil andnonmeaningful movements in difficulty.Movements were presented two times foreach hand, and the subject was asked to imi-tate the movement after each presentation.Administration and scoring systems fromKolb and Milner (1981) and Kimura and Ar-chibald (1974) were used. All tasks were vid-eotaped and scored from the tapes.
For single movements, a correct imita-tion (involving spatial location, hand/armposture, and movement pattern) was scored2, a partially correct and recognizable imita-tion was scored 1, and a completely inaccu-rate movement was scored 0, There were
TABLE 1
DESCRIPTIVE CHARACTERISTICS OF THE SAMPLE
AUTISTIC GROUP(n = 17)
M(SD)(Range)
15,50 (3,12)(11,00-23,00)84,75 (14,72)
(60-103)96,19 (16.22)
(68-125)89,38 (12.12)
(72-109)34,25 (3.93)
(30-42,5)45.76 (9.62)
(27-63,5)
COMPARISON GROUP{n = 15)
M(SD)(Range)
14.49 (2.97)(11,00-21,00)93,60 (15,34)
(68-122)101,53 (17,43)
(75-140)97,07 (16,62)
(70-134)18,47 (3,07)
(15-25)46,14 (15.16)
(13-66)
df30
29
29
29
29
27
t
,93
-1.64
-.88
-1,48
12,39
- .08
P
,36
,11
,38
,15
<,001
.94
CA
VIQ ...
PIQ ,.,
FSIQ ,
CARS
SES .,,
NOTE,—Sex (M:F): autistic group (15:2), comparison group (14:1), Handedness (R',L):autistic group (14:3), comparison group (14:1),
2064 Child Development
TABLE 2
BRIEF DESCRIPTION OF EXPERIMENTAL AND CONTROL TASKS
Experimental
Hand tasks:Single NonmeaningfulSequential NonmeaningfulSingle MeaningfulSequential Meaningful
Face tasks:Single NonmeaningfulSequential NonmeaningfulSingle MeaningfulSequential Meaningful
Pantomime tasks:
SingleSequential
Motor Control
Prompted 3d trialPrompted 3d trialPrompted 3d trialPrompted 3d trial
Prompted 3d trial
Prompted 3d trial
Control Tasks
Imitates using toolUses real tool
Memory Control
PhotosPhotosPhotosPhotos
Photos
Photos
virtually no instances in which a subject pro-duced no movement at all. Sequential handmovements were scored in four categoriesto capture the greater complexity of thesemovements: starting position, ending posi-tion, direction of movement, and accuracy ofthe postural changes, as described by Kolband Milner (1981), Each of these categorieswas scored 2 for complete accuracy, 1 for aninaccuracy on one of the main criteria forthat category, or 0 for errors in two or morecriteria for that category. Thus, when to-taled, scores for each hand sequence couldrange from 0 to 8, Scores from each set ofexperimental movements were summed andconverted to percent correct scores so thatall scores were on the same metric.
Scores from the first presentation foreach dominant hand were used for all handmovements throughout the study. Prelimi-nary analyses using t tests demonstrated sig-nificantly better performance within sub-jects with the dominant hand on only onehand task, meaningful single hand move-ments (t = — 7,11, p < ,001), Hence, similaroverall results would have been found badnondominant or combined band scores beenused. Furtbermore, there was no group Xhand interaction for any of the hand tasks.
Facial TasksAgain, four experimental conditions
were generated by crossing tbe dimensionsof meaning and sequence in a within-subjects 2 x 2 design. The nonmeaningfulfacial imitations were adopted from the workof Kolb and Milner (1981; based on work byMateer & Kimura, 1977), Tbe meaningful fa-cial imitations were modeled after work re-
ported by Hertzig et al. (1989). The four di-mensions involved:
1. Twelve single nonmeaningful move-ments {e.g., tongue protrusion with mouthopen),
2. Five three-movement sequences con-sisting of movements from the single non-meaningful series.
3. Six single, meaningful, facial expres-sions (happy, sad, frightened, angry, sur-prise, disgust),
4. Four three-movement sequencesconsisting of meaningful expressions fromthe single series.
For all meaningful tasks, the expressionwas verbally labeled (i,e,, "Tbis is how Ilook when I feel really angry at somebody.Make your face look really angry, just likemine,"). The experimenter modeled facialexpressions from Izard's (1971) classic emo-tion expression faces (happy, surprised,scared, angry, sad, disgust). Similarly, withthe meaningful sequences, each expressionwas labeled verbally as it was being demon-strated in the series.
All facial movements were presentedtwice. On the single-movement tasks, if themovement had not been made perfectiy, atbird trial (described below) was given as amotor control. It was not necessary to admin-ister the motor control on the sequential se-ries since they were made up of movementsfrom the single series, A memory controltrial followed each of the two sequentialtasks as described below. Scores from thefirst trial were summed across all the items
in a set. For single movements, a perfect imi-tation was scored 2, a partially correct andrecognizable imitation was scored 1, and anunrecognizable movement was scored 0. Forthe sequential movements, the subject re-ceived 1 point for each movement correctiyperformed in the correct position in the se-quence (or performed similarly to the bestperformance in the motor control trial; thus,this score refiects sequential performancemore than accuracy of imitations). For allscores a percent correct score was calcu-lated.
Motor and Memory Control TasksA third trial was given after each set of
hand and face imitation tasks as a motor con-trol task. In the third trial, the experimenterasked the subject to produce tbe movementas tbe experimenter was modeling it. All er-rors in the subject's movement were cor-rected immediately through verbal andphysical feedback. iThe corrected movementwas scored pass or fail depending onwhether the subject could physically per-form the movement when the errors werecorrected. Thus, the third trial functioned asa motor control task to assure that the sub-jects could actually make the necessarymovements when all their errors were physi-cally and verbally corrected. It differed fromthe imitation trials in that it was both imme-diate and assisted by considerable prompt-ing; it was not an immediate or simultaneousimitation task.
After each set of hand and face tasks, therecognition memory trial was administered.Recognition memory control tasks consistingof sets of photos of the actual experimentalmovements were used for most imitationtasks to test for possible effects of short-termmemory problems (Kimura & Arcbibald,1974), The single hand movement memorycontrol tasks consisted of a set of photos ofthe target movement and five distractors.The sequential hand and face movementmemory control tasks consisted of the targetsequence and two distractors. The sequen-tial face memory tasks also served as mem-ory controls for the single face tasks sincethe same movements were used for bothtasks. After each set of imitation tasks wasadministered, the experimenter informedthe subject of the nature of the memory con-trol task, modeled one of the movements (orsequence of movements), then showed thesubject a set of photos and asked the subjectto point to the picture of the movement (orseries of movements) just modeled. Eacbmemory control item was scored pass or fail.
Rogers et al. 2065
Pantomime TasksPantomime skills were included in this
imitation study because they, along with mo-tor imitation, are considered classic tests ofpraxis, and because earlier autism studiesdemonstrated pantomime deficits (Bartak etal., 1975). The pantomime experiment con-sisted of a within-subjects manipulation ofsequence, resulting in two experimentalconditions. The single pantomime taskswere taken from DeRenzi and Luchelli(1988). The sequential tasks were developedfor the purposes of this study.
The pantomime battery consisted of (1)20 single pantomimed meaningful familiarmovements involving the use of common ob-jects (e.g., toothbrush, scissors); (2) five se-quential meaningful pantomimed move-ments involving the use of common objects;and two control tasks, involving (3) 10 imita-tion tasks in which the subject imitated theexperimenter using the real object in the ap-propriate way; and (4) 10 tasks in which thesubject demonstrated the real use of the ob-ject without any model.
For both experimental tasks, a real ob-ject was placed on the table for the subjectto name (to ensure that the subject knew theobject) and kept in view on the table but notavailable for manipulation during the trial.For each object, the subject was asked,"What is this? Show me how you use it."Twenty objects were used and each task wasgiven twice. A demonstration trial was givenfirst, and the subject was coached andprompted on this task to make sure he or sheunderstood the task. If the subject began touse the hand as if it were the tool, the exam-iner prompted, "Pretend you are holding the[object]."
Performance was scored 4 for an accu-rate and elaborated movement (almost noone elaborated any movements), 3 for a com-pletely accurate movement, 2 for a clearlyrecognizable but not perfect movement, 1for a very imprecise but recognizable move-ment, and 0 for a nonrecognizable move-ment. The two control tasks were scored 2points for an accurate movement, 1 point foran inaccurate but recognizable movement,and 0 for an unrecognizable movement.Scores from tbe first trial of each item weresummed across all items and a percent cor-rect score was calculated. The highest scoreachieved by any subject was used (62) as thetotal score in order to calculate percentages.
The same procedures were used for se-quential pantomimes with the additional in-
2066 Child Development
struction that they were to demonstrate allthe movements involved. The first itemwas again a demonstration; subjects wereprompted to make sure that they understoodthat a series of movements was required.Then five experimental trials were given (acup and pitcher, paper and envelope, lockand key, toothbrusb, and iron). For each ob-ject, subjects were asked, "What is this?Show me all the movements you wouldmake while using this." Subjects were given1 point for each separate movement in thesequence, summed across the five tasks.
ProceduresA consistent order of tasks was used for
all subjects in each testing session. This or-der was used so that the subjects began witbthe easiest hand movements, in order tolearn the test protocol. Face movementswere given after the subjects were "warmedup" to decrease self-consciousness.
Raters were initially trained to reliabil-ity; tbereafter reliability was spot-checkedacross 16% of the protocols. Raters wereblind to group membership of the subjects.For rater disagreements of more than 1point, consensus scores were agreed uponand assigned. Interrater reliability was cal-culated using intraelass correlations andranged from .80 to .99, with a mean correla-tion of .93. Intraelass correlations were usedrather than kappa because of the continuousnature of the scores (Mitchell, 1979), as wellas to avoid the possibility of falsely highPearson correlations that might be obtainedif there were systematic, consistent differ-ences between scoring pairs.
The tasks were given in two I-IV2 hoursessions. The first session consisted of sev-eral measures not being reported here, abreak, and then imitation and pantomimetasks: meaningful single hand, nonmeaning-ful sequential hand, meaningful and non-meaningful single face, nonmeaningful se-quential face, and most of the pantomimetasks, followed by two brief tasks not beingreported here.
The second session involved severalmeasures not being reported here, WechslerVocabulary and Block Design, and then non-meaningful single hand, meaningful se-quential hand, meaningful sequential faceimitations, and sequential mime tasks.These two sessions were separated in timeby several months.
Subject motivation was enhancedthrough use of substantial monetary reward
($25 per visit); use of experienced subjects;use of friendiy, warm, interactive experi-menters; and ample praise and encourage-ment. Subjective impressions from both ex-perimenters and raters were that thesubjects with autism were well motivated,worked hard at the tasks, found them enjoy-able, and were not self-conscious about thehidden video camera. In contrast, an occa-sional comparison subject expressed self-consciousness or dislike of the tasks. If thesemotivational differences caused any bias, itwould be a conservative one.
RESULTS
Preliminary AnalysesTbe data were first reviewed for skew,
kurtosis, and outiiers. Except on the controltasks, there were no problems with fioor orceiling effects. When there was lack of a nor-mal distribution (as on some control tasks),nonparametric statistical tests were used.Performance data on individual measuresare presented in Table 3.
Main AnalysesIn what follows, we present the results
of the hand, face, and pantomime experi-ments. For the hand and face experiments,the order of presentation is (1) memory con-trol tasks, (2) imitation tasks, and (3) motorcontrol tasks.
Hand TasksMemory control tasks.—Group perfor-
mances on the hand memory control taskswere compared using t tests (or Mann-Whitney U tests when appropriate). Therewere no significant differences between thegroups on any of these four control tasks.The subjects with autism passed 100% of thetwo single-movement memory tasks, 94%of the nonmeaningful sequential memorytasks, and 96% of meaningful sequentialmemory tasks. The comparison group passed100% of all tasks except the nonmeaningfulsequential memory tasks, on which theypassed 99%.
Imitation tasks.—A mixed-model analy-sis of covariance (ANCOVA) with full-scaleIQ (FSIQ) covaried with one between-subject factor (group) and two within-subjects factors (sequence, meaning) wasperformed on the band tasks. The ANCOVArevealed a tbree-way, group x sequence Xmeaning interaction effect, F(l, 26) = 7.69,p — .01. Post hoc tests of simple effects re-vealed significant group differences on threeof the four hand tasks: the single nonmean-ingful task, t{26) = -2.88, p = .008, the se-
Rogers et al. 2067
TABLE 3
PERFORMANCE DATA AND GROUP
TASK (n)
DIFFERENCES ON BOTH INDIVIDUALPERCENT SCORES
AUTISTIC GROUP
M(SD)
MEASURES AND COMPOSITES
COMPARISON GROUP
M (SD)
USING
P
Imitation tasks—hand:Nonmeaningful single hand (28) 68.75 (16,28)Nonmeaningful sequential hand (32) 67,52 (19,11)Meaningful single hand (32) 75,88 (l2,10)Meaningful sequential hand (28) 62,07 (l8,48)
Imitation tasks—faee:Nonmeaningful single face (29) 83,79 (11,03)Nonmeaningful sequential faee (29) 62.36 (15,46)Meaningful single face (29) 61,29 (lO,7o)Meaningful sequential face (24) 79.64 (14,17)
quential nonmeaningful task, t(20) = —3,92,p = ,001, and the sequential meaningfultask, t(22) = -5.39, p < .001. As can be seenin Figure 1, the three-way interaction resultsfrom the fact that the hypothesized group xsequence interaction was found across thetwo meaningful conditions but was essen-tially absent across the two nonmeaningful
ones. These results provide partial supportfor the executive deficit hypothesis. In con-trast, there was no group X meaning interac-tion, thus providing no support for the sym-bolic deficit hypothesis; indeed, meaningclearly aided rather than hindered the per-formance of the group with autism on singlemovements.
100
95
90
85
I 80
60
55
SO
Non-meaning
Meaning ""
Meaning
Non-meaning
Sequential
GROUP WITH ADTISM
CONTROL GROnP
FIG, 1,—Croup differences on sequence and meaning scores for hand tasks
2068 Child Development
Motor control tasks.—The performanceof the two groups was compared on the third,motor control trial in which subjects weregiven verbal and physical prompting asneeded to correct their errors. It is importantto note that the subjects' performance on tbistrial appeared to be as impaired as their per-formance on the experimental trials until theexperimenter corrected their errors. Croupswere compared by converting all the scoresto percent correct and using Mann-WhitneyV Tests to compare the means. There wereno group differences on any of the four tasks.The autistic group performed at 100% cor-rect on three of four conditions and at 95%correct on the meaningful, sequential condi-tion. The comparison subjects also per-formed perfectly on three of four conditionsand at 98% on the nonmeaningful singlecondition. Thus, there did not appear to bea general motor impairment that interferedwith the ability of subjects with autism tomake the constituent hand movements inthese tasks.
Face TasksMemory control tasks.—Memory for
faces was examined by recognition trials ofthe two face sequence tasks, and was ana-lyzed using nonparametric Mann-Whitney Vtests because of insufficient variance in thecomparison group, who were at ceiling(100% correct) on both tasks. In comparison,the autistic group performed significantlyworse. The autistic group was correct on86% of the nonmeaningful sequential faces(p = .01) and 89% of the meaningful sequen-tial faces {p = .01). Three subjects with au-tism passed 50% or fewer of tiiese memorycontrol tasks. Significant memory impair-ments thus could not be ruled out for thesethree subjects, and they were dropped fromall further analyses of the face tasks.
On the memory controls for nonmean-ingful face sequences, six of the remainingsubjects with autism passed three of the fourtasks, and eight passed all four tasks. In or-der to look for possible memory effects forthe six subjects wbo did not score 100% onthe memory tasks, tbe total scores of thesesix subjects on each of the face tasks werecompared to the remaining subjects with au-tism. There were no significant differenceson total scores for any of the experimentalface tasks between the group of subjectswith autism who passed 100% of the mem-ory tasks and the group who passed 75%.Thus, we felt that memory problems were notinterfering with performance on the face tasks
for these subjects, and all of these subjectswere included in the rest of the face analyses.
Imitation tasks.—A mixed-modelANCOVA with FSIQ covaried with one be-tween-subjects factor (group) and twowithin-subjects factors (sequence, meaning)was performed on the face tasks.
There was a main effect of group, F(l,21) = 4.53, p = .04, and a two-way meaningX sequence interaction, F(l, 22) = 62.37,p < .001. As can be seen in Table 3, on thetwo single facial tasks, both groups weremore accurate on the nonmeaningful taskthan on the meaningful one; however, on thetwo sequential facial tasks, an opposite pat-tern was observed. The single meaningfulfacial task (imitation of six facial emotionalexpressions) involves coordinated move-ments of several different muscle groups.This task was much harder for both groupsof subjects than the single nonmeaningfulface movements, which were simple move-ments like open mouth, or tongue to side.The opposite pattern observed for sequen-tial facial movements probably is due to tbefact that (1) the scoring system did not em-phasize accuracy of imitations on the se-quential facial movements, and (2) the possi-bility that the verbal labeling of emotionshelped all subjects retain the sequence inworking memory.
Post hoc tests between groups revealeda significant group difference for the non-meaningful sequential task only, t(27) =-2.90, p = .007. The main effect of grouprevealed that subjects with autism per-formed more poorly than comparison sub-jects overall on the face imitation tasks.However, their most deficient performanceoccurred on nonmeaningful sequences.Again, these findings provided no supportfor the symbolic deficit hypothesis; indeed,once again, meaning clearly aided ratherthan hindered the performance of the groupwith autism relative to controls in the se-quential condition. Furthermore, there isonly partial support for the executive func-tion hypothesis in that the subjects with au-tism were deficient on only one of the twosequential tasks.
Motor control tasks.—There were nosignificant group differences on the motorcontrol trials for nonmeaningful single facialexpressions or meaningful single face move-ments. Thus, there did not appear to be ageneral motor impairment that interferedwith the ability of subjects with autism to
make these face movements compared tocomparison subjects.
Pantomime TasksAs can be seen in Table 3, both groups
were at ceiling on the two object-controltasks, limiting our ability to test for groupdifferences. For that reason, a mixed-modelANCOVA with FSIQ covaried was carriedout with one between-subjects factor (group)and one within-subjects factor (sequence) onthe pantomime tasks. The hypothesizedgroup X sequence interaction was found,F(l, 26) = 5,81, p = .02, supporting the ex-ecutive deficit hypothesis. Post hoc tests re-vealed significant group differences for bothexperimental tasks: single mime, t(22) =-5.07, p < .001; sequential mime, t{26) =— 6.01, p < .001. The interaction results froma larger autistic group deficit on the sequen-tial task (56% below the control mean) thanon the single task (26% below the controlmean). The pantomime task does not di-rectly address the symbolic hypothesis be-cause symbolic content was not manipu-lated.
Thus, subjects with autism did not differin their ability to make normal motor move-ments using common objects, either on imi-tation or command, but they differed greatiyfrom comparison subjects in their ability topantomime the same movements, even withfamiliar objects present on the table.
Relationships among the Imitation andMime Tasks
In order to examine relationships acrossthe hand imitation, face imitatioti, and pan-tomime tasks, we correlated the three viacomposite scores that were constructed bycomputing the mean of the task scores. Forboth groups, the imitation and mime com-posites demonstrated some significant rela-tionships with each other, with similar pat-terns seen in both groups. Hand and facetask correlations were .72 (p < .01) for con-
Rogers et al. 2069
trols and .64 (p < .05) for the group withautism. Hand and mime correlations were.41 (N.S.) and .52 (p < .01), respectively.Face and mime correlations were .49 and .46(both N.S.), respectively.
Universality of the Imitation andMime Deficit
In order to examine the question of thepervasiveness of the imitation and mimedeficits in the autistic group, the number andproportion of subjects with autism scoringbelow the comparison group mean were ex-amined for each of the experimental tasks onwhich there were significant group differ-ences. The results can be seen in Table 4.
The six tasks on which there were sig-nificant group differences revealed univer-sally poor performance of the subjects withautism. Thus, the group differences were notdue to the very poor performance of a fewsubjects with autism, but rather refiect poorperformance across a majority of the subjectsin this group.
DISCUSSION
Presence of Imitation and PantomimeDeficits
The first question addressed in thisstudy concerned the presence of imitationand pantomime deficits in high-functioningadolescents with autism. We found thegroup with autism to have deficits on one ormore of the conditions in each of our threeexperimental tasks (hand, face, and panto-mime). Thus, this study provides additionalsupport for Rogers and Pennington's (1991)hypothesis that a specific deficit in motor im-itation exists in persons with autism. It alsoadds to previous findings of pantomimedeficits in autism. In what follows, we willfirst discuss why these imitation and panto-mime deficits are not due to deficits in visualrecognition memory, the ability to make theconstituent movements, or the initiation of
TABLE 4
PROPORTION OF SUBJECTS WITH AUTISM SCORING BELOW THECOMPARISON GROUP MEAN ON IMITATION MIME TASKS
Task Proportion
Sequential mime 13/13 (100%)Single mime 16/17 (94%)Nonmeaningful sequential hand 16/17(94%)Nonmeaningful sequential face 13/14 (93%)Meaningfiil sequential hand 13/15 (87%)Nonmeaningful single hand 13/15 (87%)
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movements. Then we will discuss how theresults bear on the two main hypothesestested in this study: the symbolic and execu-tive deficit hypotheses.
In terms of visual recognition memory,we attempted to control for possible memoryconfounds by using recognition mem-ory tasks based on tbe experimental tasks.However, it is important to note that thememory control tasks tapped recognitionmemory, while the experimental taskstapped recall memory. On the hand tasks,there were no group differences on thememory control tasks, while there weregroup differences on three out of four of theexperimental tasks. So it is quite unlikelythat the deficits in the imitation of handmovements are due to a deficit in visual rec-ognition memory, Apparentiy the subjectswith autism can visually encode the handmovements made by the model and remem-ber them well enough to pass a recognitiontest. For facial movements, the situation issomewhat less clear. There were significantgroup differences on the facial memory con-trol task, but tbese cannot account for theone significant group difference (in the se-quential, nonmeaningful condition) becausesubjects with autism who scored perfectlyon the memory control task were just as im-paired on this condition as those who didnot score perfectiy. Perhaps most telling isthe fact that the pantomime tasks do not re-quire short-term visual memory becausethere is no model in the task to imitate. Yetsubjects with autism were also impaired onpantomime tasks. Thus, we can exclude adeficit in visual recognition memory, but tbepossibility tbat visual recall memory deficitsaffected the results has not been ruledout (it can be argued that even the panto-mime tasks require long-term visual recallmemory).
The possibility of a motor problem un-derlying the deficient imitation and panto-mime performance of the subjects witb au-tism was a second important factor tbat thisstudy tried to control. Most strikingly, thesubjects with autism demonstrated equiva-lent performances to the controls on themime control tasks (with real objects in theirhands), but could not perform comparablyon tbe pantomime tasks (with no real objectsin their hands). Thus, we can clearly rejecta motor problem as an explanation for tbepantomime results. On tbe band and facemotor control tasks, all subjects could makethe constituent motor movements involvedin each task, given sufficient prompting.
While the motor control tasks took away adelay between the model and the perfor-mance, they did not refiect intact immediateimitation skills because the subjects with au-tism still required specific corrections andprompting in order to perform the move-ments accurately. Thus, it seems very un-likely that these subjects had intact abilityto imitate movements when no delay is in-volved. Since we did not directly test motorfunction (apart from the motor control tasks),motor dysfunction in autism cannot be ruledout from these findings. However, the re-sults from the motor control tasks argueagainst the group differences being only dueto differences in basic motor functions.
Nor do the differences seem to be attrib-utable to problems in initiating a movementsequence. All subjects attempted a move-ment on virtually every trial. Moreover,even the motor control trials required somemotor initiation; since all subjects per-formed some movement in virtually everytrial, inability to initiate these movementson request was not seen.
The Role of MeaningThe second question addressed by this
study was whether imitation deficits in au-tism are consistent with a symbolic deficit,as postulated by the metarepresentationaltiieory (Baron-Cohen, 1988).
The results of this study clearly rejectthe symbolic deficit hypothesis. Subjectswith autism never performed differentiallyworse on the meaningful conditions. In fact,of the four significant group differencesfound on the hand and face tasks, only onewas found on a meaningful task and threewere found on nonmeaningful ones. Thus,there was no evidence from this study thatsuggested that these subjects with autismhad particulcU' difficulty imitating move-ments with symbolic content as opposed tononsymbolic content. Deficits in nonmean-ingful imitation are difficult for the metarep-resentational theory of autism to explain;while imitation does require some mentalrepresentation of the target movement, itdoes not require a metarepresentation.
The Role of Executive FunctionThe third question driving this study
was whether imitation deficits in autism areconsistent with an executive deficit. Therewas partial support for this hypothesis. Thepredicted group X sequence interaction ef-fect was found (1) across the meaningful con-ditions of the band experiment, but notacross the nonmeaningful ones, resulting in
a group X sequence x meaning interaction;(2) in the pantomime experiment; but (3) notin the face experiment. Moreover, therewere significant group differences on twononsequential tasks: the nonmeaningful sin-gle hand condition and the single panto-mime condition. One could argue post hocthat even the single movements on whichthere were group differences exceeded theworking memory capacities of these subjectswitii autism; however, testing that hypothe-sis will require an experiment in whichworking memory requirements are manipu-lated within nonsequential imitation tasks.
Overall, the performance of subjectswitii autism refiected rather widespreaddeficits in imitation and pantomime. Imita-tion and pantomime tasks are consideredclassic tasks of praxis. Dyspraxia refers to adeficit in the capacity for consciously formu-lating and then executing an intentional mo-tor plan in a particular context, a capacitynot necessary for conditioned, automatic, orrefiexive movement patterns (Ayres, 1985;Heilman, 1979). Deficits involving both faceand hand imitations and pantomime arecommonly found in apraxic neurologicallyimpaired adults (DeRenzi, Motti, &Nichelli, 1980; Kimura & Archibald, 1974;Kolb & Milner, 1981; Mateer & Kimura,1977). Indeed, the tasks used in this studyare considered classic tests of praxis, Civenthe generalized deficits across the majorityof tiiese tasks shown by the subjects withautism, it is important to raise the questionof a generalized dyspraxia in autism.
Several previous autism researchers(DeMyer, Hingtgen, & Jackson, 1981;Jones & Prior, 1985; Ohta, 1987), presentedwith similar findings, have suggested that adyspraxic deficit in autism is present andmay interfere with even the simple motoractivities involved in everyday life and nor-mal nonverbal communication. A praxis by-pothesis is not independent of an executivefunction hypothesis: executive function isinvolved in the execution of volitional move-ments, and persons with frontal lobe damage(which is generally associated with execu-tive function deficits) demonstrate apraxia(Kolb & Milner, 1981). The question raisedhere is whether some other component ofpraxis besides executive functions is impli-cated in the praxis deficits in autism. Wehave ruled out visual recognition memory,simple motor deficits, and motor initiation.We have not ruled out visual recall memory,but, if we had ruled out a visual recall mem-ory deficit, we would have in effect ruled out
Rogers et al. 2071
an executive deficit for the following reason.Visual recall memory in the context of imita-tion and pantomime tasks is not clearly dis-tinguishable from the working memory andexecution components of these tasks, whichwere discussed earlier. Recall memory re-quires production of something in memory,in this case, a remembered action. On thesetasks, production of a remembered action re-quired holding the representation of the ac-tion in working memory while executing theaction. Thus, it seems unparsimonious topostulate separate constructs of recall mem-ory and working memory in the context ofimitation and pantomime tasks.
We cannot totally exclude the possibil-ity that a low-level motor impairment makescomplex motor tasks such as these differen-tially difficult. We cannot exclude the cross-modal match between model and self re-quired in imitation tasks (Meltzoff &Copnik, 1993), although the lack of groupdifferences in several of our experimentalconditions argues against a complete ab-sence of the ability to form such cross-modalcorrespondences. Thus, more research isneeded to specify the mechanism underly-ing the imitation and pantomime deficit inautism.
Issues Involving PantomimeFindings involving the pantomime tasks
raise several issues. One involves the co-occurrence of imitation and pantomimedeficits. Pantomime can be thought of as adeferred imitation task, in which the subjectmust retrieve from long-term memory a rep-resentation of past behavior, then hold thatrepresentation on line in order to imitate it.Thus, the two kinds of tasks in this study canbe conceptualized as immediate imitationand deferred imitation tasks, involving simi-lar processes of working memory, motorplanning, and execution, but differing as towhich memory systems are most involved.This may explain the similar kinds of deficitsfound in pantomime and imitation perfor-mances in subjects with autism.
Another question that emerges is whythe subjects witb autism did not demonstratedifficulties on the pantomime control tasks,which required very similar movements.The movements associated with the objectimitation tasks were simple, common, andprobably well practiced by the subjects. Itmay be that having a familiar object in handelicits an automatic motor scheme, akin towhat Lhermitte (1983) has described as "uti-lization" behavior in frontal patients. This
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result may implicate somewhat separate mo-tor control systems, for instance, the basalganglia for automatic motor schemes andthe prefrontal cortex for intentional motorschemes.
A third issue is whether pantomimedeficits are the result of a symbolic deficit(O'Reilly, 1995). If we found deficits onlyon the pantomime tasks, this would be aplausible explanation. But having rejectedthis hypothesis for the imitation tasks, andhaving found some relations between thosetasks and the pantomime tasks, this possibil-ity seems quite unlikely. In fact, the similar-ity between pantomime tasks and symbolicplay point to an important weakness in theexplanation of the symbolic play deficits inautism provided by the metarepresenta-tional theory. When a child represents an ob-ject in play that is not present, the child ispantomiming a movement with a substituteobject or an imaginary object. In the panto-mime condition in this study, we are in factasking subjects to pretend that they are iron-ing, drumming, etc. Our findings of deficitsin imitation of actions that do not involverepresentation of objects, but only requirerepresentation of body movements, suggestthat the symbolic play deficit in autism mayhave more to do with the representation ofbody movements in general than with ac-tions specifically focused on symbolizedobjects, contrary to the metarepresentationalhypothesis.
Methodological Concerns with This StudyOne important potential threat to the va-
lidity of these findings concerns our groupof subjects with autism. This group, as statedpreviously, has been the subject of severaldifferent investigations (Bennetto et al.,1996; Ozonoff & McEvoy, 1994). As oftenbappens with a low-incidence disorder, thesame subject group is returned to when newquestions arise. However, the more teststhat are run on a given group, the greater therisk of Type I error. Since it is not possiblefor most laboratories to recruit independentsamples like the present sample for eachstudy, it is extremely important that thesefindings be replicated in an independentgroup. Tbe fact that most studies of imitationand pantomime in subjects witb autism haveresulted in findings similar to these, how-ever, provides converging support for ourconclusions that these findings point to ageneral imitation and pantomime impair-ment in autism.
Second, the use of a mixed clinical
group of comparison subjects has draw-backs. Our rationale involved an effort toprovide some control for the presence of ageneral central nervous system dysfunction.However, it can certainly be argued thatdifferent diagnostic groups have differentialdamage to specific brain systems that ac-count for both symptoms and specific taskperformance characteristics. Thus, moremay be learned from a neuropsychologicalstandpoint by using homogeneous controlgroups.
Finally, the scoring system that wasused on the face sequence tasks may wellhave masked group differences by empha-sizing sequential accuracy over imitative ac-curacy. Future research will need to exam-ine accuracy of imitation of facial sequencesmore closely.
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