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J. Child Psychol. Psychiat. Vol. 41, No. 8, pp. 10571065, 2000Cambridge University Press

' 2000 Association for Child Psychology and PsychiatryPrinted in Great Britain. All rights reserved

00219630\00 $15.00j0.00

Local and Global Processing of Music in High-functioning Personswith Autism: Beyond Central Coherence?

L. Mottron

Ho# pital Rivie' re-des-Prairies and Universite! de Montre!al, Canada

I. Peretz

Universite! de Montre! al, Canada

E. Me!nard

Ho# pital Rivie' re-des-Prairies and Universite! de Montre!al, Canada

A multi-modal abnormality in the integration of parts and whole has been proposed toaccount for a bias toward local stimuli in individuals with autism (Frith, 1989 ; Mottron &

Belleville, 1993). In the current experiment, we examined the utility of hierarchical models incharacterising musical information processing in autistic individuals. Participants were 13high-functioning individuals with autism and 13 individuals of normal intelligence matchedon chronological age, nonverbal IQ, and laterality, and without musical experience. The taskconsisted of same-different judgements of pairs of melodies. Differential local and globalprocessing was assessed by manipulating the level, local or global, at which modificationsoccurred. No deficit was found in the two measures of global processing. In contrast, theclinical group performed better than the comparison group in the detection of change innontransposed, contour-preserved melodies that tap local processing. These findings confirmthe existence of a local bias in music perception in individuals with autism, but challengethe notion that it is accounted for by a deficit in global music processing. The present studysuggests that enhanced processing of elementary physical properties of incoming stimuli, asfound previously in the visual modality, may also exist in the auditory modality.

Keywords: Autistic disorder, cognition, development, idiot savants, memory, music, neuro-psychology, perception.

Abbreviations: ADI-R: Autism Diagnostic Interview-Revised; AP: absolute pitch; HDH:hierarchisation deficit hypothesis; HFA: high-functioning autism; TD: typically dev-eloping; WCC: weak central coherence.

The study of musical processing in individuals withautism is relevant for both clinical and theoreticalreasons. First, there are clinical indications of atypicalauditory processing in persons with autism. These obser-vations justify inquiry of the mechanisms that underlieauditory processing in this group. It is well documentedthat very young autistic children exhibit aversive re-actions to noises; indeed, these children often cover theirears with their hands when in the presence of speakers. Inaddition, they might cover their ears when exposed tospecific, low-intensity sounds to which the majority ofindividuals would remain insensitive. These behavioursare usually described in terms of a hypersensitivity tosound, and they comprise part of the restricted interestand repetitive behaviours area of the diagnostic criteriafor autism (American Psychiatric Association, 1994 ;Lord, Rutter, & Le Couteur, 1994).

Requests for reprints to : Laurent Mottron, Clinique spe!cialise!ede lAutisme, Ho# pital Rivie' re-des-Prairies, 7070 boulevard

Previous research with this population suggests that,within the auditory modality, different reactions aretriggered by verbal speech and by musical stimuli. Forexample, a spontaneous orientation towards musicalstimuli, as opposed to nonmusical, verbal stimuli hasbeen reported (Blackstock, 1978). Moreover, although asignificant proportion of autistic individuals have alanguage impairment (American Psychiatric Association,1994), the ability to process musical material, such as thereproduction of musical pieces (Applebaum, Egel,Koegel, & Imhoff, 1979) remains preserved or evenenhanced. Recently, Heaton, Hermelin, and Pring (1998)found that children with autism were more accurate thantypically developing boys in their ability to associatetones with pictures, but were equivalent to the lattergroup in associating linguistic material with pictures.

The presence of special musical abilities in savantautistic individuals provides additional evidence for the

notion that persons with autism process musical stimulidifferently from control participants. In fact, a smallproportion of persons with autism exhibit exceptional

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1058 L. MOTTRON, I. PERETZ, and E. ME! NARD

exceptional long-term memory for musical material(Sloboda, Hermelin, & OConnor, 1985). This perform-ance may even exceed that of trained musicians, and liesin contrast to autistic individuals average or oftenimpaired treatment of linguistic material.

Although the continuity between savant and non-savant persons with autism is a matter of debate, savantcapabilities in music are informative for the study of

nonsavant autistic individuals. Indeed, the outstandingmusical operations exhibited by autistic savant musiciansare observed at a lower level in nonsavant autisticindividuals. For instance, a parallel can be drawn betweenthe enhanced pitch processing reported in nonsavantpersons with autism (Heaton et al., 1998) and the specialability known as absolute pitch (AP), which is frequentlyfound in savant persons with autism (Miller, 1999).Savant persons with AP might therefore represent ex-treme cases of above-average perception of pitch inautism.

Musical processing in nonsavant persons with autismis also relevant to multimodal cognitive models of autism.Recently, there have been theoretical attempts to accountfor cognitive deficits in unrelated areas (e.g., visuospatial,music, language, memory) in persons with autism bypositing multi-modal deficits that apply to various sen-sory modalities, and, a fortiori, to several cognitiveoperations in the same modality. Each of thesemodules is characterised by functional autonomy innormal adults (Fodor, 1983), and may be selectivelyimpaired in adult brain-injured subjects. However, inindividuals with autism, the boundaries between modulesdo not seem to exist, as there are deficits in severalapparently unrelated areas that seem to be caused by thesame underlying mechanism (Mottron & Burack, inpress).

According to Frith (1989), Frith and Happe! (1994),and Happe! (1996, 1999), the visual and mnemoniccharacteristics often found in autism can be accountedfor by a deficit in the normal tendency to integrateelements into a higher level of organisation. This deficitproduces a specific imbalance in integration of in-formation at different level (Frith & Happe! , 1994, p.121), regardless of modality. According to one of thelatest versions of the weak central coherence (WCC)model (Happe! , 1999, pp. 2178), this results in detailedfocused processing in which features are perceived andretained at the expense of global configuration andcontextualized meaning. WCC predicts good perform-ance when attention to local information is advantageousand poor performance on tasks requiring integration ofstimuli in context. An independent but similar model, thehierarchisation deficit hypothesis (HDH), has been pro-posed by Mottron and Belleville (1993) on the basis ofatypical processing of several types of complex multi-level visual stimuli. It states that local and global levels,despite functioning normally, might not be hierarchicallydistinguished in persons with autism, yielding an absenceof a global advantage, and global interference in con-ditions in which typically developing subjects show theseeffects.

The WCC hypothesis was derived mainly from findingsin the visuospatial domain, such as the high level of

performance on embedded figures and the block designsubtest of the Wechsler Intelligence Scale (Shah & Frith,1983, 1993; Wechsler, 1974, 1981).

and visual perception in a savant autistic draughtsman.Also, Happe! (1996) reported that nonsavant persons withautism were insensitive to visual illusions, which requireboth intact local and global perception. Finally, thefinding of a local bias in graphic construction amongautistic individuals provides additional evidence of thisaspect of Friths hypothesis (Mottron, Belleville, &Me! nard, 1999).

A locally oriented information processing style hasalso been reported in the auditory modality, supportingthe multi-modal aspect of Friths hypothesis. Frith (1989)suggests that this general bias towards local processingmight account for autistic individuals exceptional abili-ties in pitch labelling (AP), pitch being considered a localelement. Evidence for this notionwas provided by Heatonet al. (1998). In their study, 10 boys diagnosed withautism (chronological age, CA : 713, IQ 55127) and 10CA-matched typically developing children were pre-sented with four isolated tones and four line drawings ofanimals. In the familiarisation session, participants wereexposed to pairs of tones and animal names and were toldthis is the animals favourite sound. In the pitchidentification procedure, children were asked to point tothe drawing that corresponded to the presented tone,immediately and then again 1 week after the learningprocedure. Results revealed that, in both recall con-ditions, the clinical group outperformed the group oftypically developing boys in their ability to associatetones with pictures. Heaton et al. concluded that theenhanced pitch processing ability found in individualswith autism resulted from a local processing bias, usingpitch processing as an example of a local feature in music.However, using isolated pitches to measure local pro-cessing in music is problematic because local and globalare reciprocally relative concepts and cannot be used in

isolation. A global level must be included in the ex-periment as a basis for comparison of the two levels. Foran enhanced memory of isolated pitches to be relevant toa model of hierarchical information processing, it ismandatory that larger sound units such as intervals ormelodies be used, as opposed to isolated pitches. Only inthis case can a behaviour, such as favouring pitch overmelodic contour, be interpreted as resulting from a localbias.

In the current study, hierarchical musical processingwas assessed in nonsavant persons with autism. Melodieswere employed in this study, as they contain three typesof features that can be classified along a local vs. globaldimension (Dowling, 1978 ; Peretz & Morais, 1993). First,each individualpitch included in a melody has an absoluteheight value (expressed in frequency). Second, pairs ofindividual pitches are separated by intervals (which canvary in size, expressed here in semitones). Finally, thedirection that intervals take comprises the melodiccontour. The latter characterises pitch direction inde-pendently of the specific pitch values.

These three levels form an embedded, hierarchicalstructure: a minimum of two pitches is needed to producean interval, and it is the direction taken by severalintervals that produces a contour. A local vs. globalgradient can be determined from this hierarchical struc-ture: absolute pitch consideration, for instance, is a more

locally (or less globally) oriented type of processing thanrelative pitch or interval recognition, which in turnrequires a more local type of processing than contour

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1059LOCAL AND GLOBAL PROCESSING OF MUSIC IN AUTISM

musical processing can be addressed with same-different tasks; for instance, using melodies modified atthe pitch\interval vs. contour level (Dowling, 1978).Modification of a single note preserves a melodic contourif it does not modify the ascending vs. descendingdirection of melody intervals. Such a modification sim-ultaneously transforms the absolute pitch value of a givennote in a melody, while also modifying the value of the

intervals directly preceding and following the modifiednote. A melodic modification violates contour when itmodifies the direction of intervals (see Fig. 1). This lastmodification adds a contour transformation to theprevious transformations.

Pitch and interval recognition play a role in melodyrecognition in contour-preserved as well as contour-violated conditions. Nevertheless, compared to contour-violated conditions, contour-preserved conditions selec-tively suppress the role that contour plays in recognition.Therefore, a better ability to recognise melodies whosecontour has been modified as opposed to those whosecontour has been preserved can be taken as a measure-ment of global processing.

Musical material presents an advantage over otherstimuli in that certain local features of a melody can beselectively suppressed through transposition. In trans-posed melody conditions, each absolute pitch value istransformed, while the intervals and contour remain thesame. Consequently, a capacity to recognise two trans-posed melodies as identical constitutes a second andindependent assessment of global processing. Conversely,in a system relying mainly on AP, such as persons withautism possess according to WCC predictions, the iden-tification of melodies should be more difficult followingchanges in pitch level (via transposition), ultimatelyresulting in a bias toward different responses.

In sum, a better recognition of melody modification inthe contour-violated than in the preserved contourcondition for nontransposed and transposed melodies, aswell as a capacity to discriminate melodies despite thepresence of transposition, are two indicators of theintegrity of global musical processing. On the other hand,enhanced performance in the detection of contour-preserved modifications would demonstrate a bias towardlocal music processing. The extent to which this local biasis maintained or lost in the transposed condition providesinformation about the role of AP in task performance.

In what sense are intervals actually local andcontours global? First, contours are large units thatembed smaller units (or intervals) hierarchically. Second,contour, more than intervals, is used by typically devel-oping nonmusicians, as contour-violated modificationsare reliably easier to recognise than contour-preservedmodifications (Peretz & Morais, 1987). This advantagefor contour over intervals parallels the advantage of largeembedding letters over small embedded letters in visualhierarchical stimuli (Robertson & Delis, 1986). Third,contour and intervals are processed by asymmetrical andindependent brain structures with the same lateralisationas global and local levels in the visual modality. The righthemisphere primarily represents the melody in terms ofits contour, and the left hemisphere in terms of itsintervallic structure. For instance, asymmetrical hemi-

spheric processing of local and global aspects of melodieshas been confirmed by Peretz (1990) with right vs. leftbrain-injured patients, using the same types of task. This

hemisphere to local componentsin the visual modalityareliable finding obtained from ERP (evoked-responsepotential) and fMRI techniques (Fink et al., 1997;Heinze, Hinrichs, Scholz, Burchert, & Mangun, 1998).

The predictions regarding performance differ based onthe particular manipulation performed on the melodies.In the nontransposed condition, the clinical and com-parison groups should exhibit the same level of per-

formance when the comparison and target melodies areidentical. When they differ, the comparison group isexpected to exhibit a global superiority effect as indicatedby better discrimination of contour-violated thancontour-preserved melodies. The clinical group, however,is not expected to show this contour superiority effectfollowing the absence of global bias predicted by theHDH hypothesis.

In the transposed condition, typically developing chil-dren should be able to discriminate the melodies despitethe presence of a change in pitch level between the twomelodies to be discriminated. They should be able torecognise same transposed melodies and, for thedifferent condition, they should show superior de-tection in the contour-violated than the contour-pre-served condition. However, an overall decrease in per-formance level is expected in comparison to the non-transposed condition due to the lack of absolute pitchcues for discrimination. Transposition should be muchmore problematic for individuals with autism, since theWCC model predicts a propensity to rely on absolutepitch rather than relative pitch. If this bias generalises tomelodies, individuals with autism are likely to judge allmelodies in the transposed condition as different,hence resulting in an abnormally high number of falsealarms on the same trials. Moreover,in the different condition, because of their tendency to focus on more

elementary properties of melodies according to the WCCmodel, the clinical subjects are expected to differentiatecontour-preserved and contour-violated melodies at asimilar level.

Method

Participants

Two groups of participants completed the study. The firstwas a clinical group comprised of 13 participants with high-functioning autism (HFA, Nl12) or Asperger syndrome (Nl1). The diagnosis of autism was obtained through adminis-tration of a standardised interview, the Autism DiagnosticInterview-Revised (ADI-R) (Lord, Rutter, & Le Couteur,1994), and clinical observations in which DSM-IV (AmericanPsychiatric Association, 1994) criteria for autism were explicitlychecked.

The ADI-R is conducted with a parent or close relative of theperson believed to be autistic. It compiles information about thefirst 4 to 5 years of life as well as the current age of theindividual, in the four areas relevant for a diagnosis of autism.All but one participant scored above the ADI cutoff for autism.However, this participant satisfied the DSM-IV criteria forAsperger syndrome.

Clinical participants were recruited from the database of theRivie' re des Prairies specialised clinic for diagnosis and as-sessment of pervasive developmental disorders. At the time oftesting, all participants were students or employed in regular

jobs, and lived either with their families or alone. None of theparticipants were taking medication.

The second group was comprised of 13 typically developingparticipants, matched to the clinical group on chronological

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Table 1Characteristics of HFA Individuals and Typically Developing Participants (TD)

Group

Age Laterality Nonverbal IQ

Mean SD Mean SD Mean SD

HFA 16n73 6n90 66n54 46n26 106n69 11n13TD 15n33 3n41 42n31 85n75 105n54 11n24

the database of the clinic. The maximum score difference fornonverbal IQ was ofp10 points on the child and adult versionsof Weschler Scales of Intelligence (Wechsler, 1974, 1981). Thestringent exclusion criteria did not allow matching for gender :two girls were included in the clinical group and none in thetypically developing group. Typically developing participantswith any of the following characteristics were excluded: (1) anypast or present neurological or psychiatric disorders, (2)medication interfering with the central nervous system, (3)neurodevelopmental cognitive disorders, (4) learning dis-abilities, (5) poor school attendance, and (6) any first-degreerelatives with autism, neuropsychiatric disorders, or neuro-

developmental cognitive disorders.All participants were of normal intelligence (Full Scale IQ80), and older than 10 years. Based on findings from a pilotstudy, this age appears to be the youngest at which typicallydeveloping participants succeed on the task. Only participantswithout musical experience, a fortiori without musical specialabilities were included in the study, as musical expertiseproduces a local bias in musical processing (Bever & Chiarello,1977). Both groups were paid for their participation. Table 1shows the individual values, means, and standard deviations forchronological age and nonverbal IQ. No statistical differenceswere found in a t-test conducted between the two groups onthese variables.

Materials

Twelve melodies, originally used by Peretz (1987) withuniversity students, served as the basic set of stimuli. Themelodies were tonal in that they all started and ended on thetonic, and only included diatonic notes. Each contained ninetones, with each tone lasting 350 msec, except for the final onethat lasted twice as long. The melodies were computer generatedon a TX81Z Yamaha synthesiser approximating the timbre of apiano. Three types of modification were applied to each of these12 basic melodies.

One modification consisted of transposing each melody to anear key, either by raising each pitch by a perfect fifth or bydiminishing each pitch by a fourth (as in Fig. 1, example B). Theother modification consisted of creating a contour-violated

alternate melody of each basic melody by changing the pitch ofone tone so that it modified the pitch direction of thesurrounding intervals (see C in Fig. 1, for an example of thesecontour changes; i.e., the interval directions surrounding thecritical pitch were modified from j, j to V, j), whilemaintaining theoriginal key. Theserialposition of this modifiedpitch varied across melodies; it either fell at the beginning of themelody, in the middle, or at the end, while avoiding the first andlast tone positions. The third manipulation consisted of creatinga contour-preserved alternate melody of these contour-violatedmelodies by modifying the same critical pitch to the same extent(in terms of semitone distance), yet maintaining the originalcontour and key (see D in Fig. 1).

Average departures from the tonic were made equivalentacross the contour-violated and contour-preserved melodies,with a mean of 4n4 and 4n5 scale degrees, respectively. Thus, thechange affected an important scale degree (i.e. a member of thetonic triad, as in C) or a less important scale degree (i.e. a

The average interval sizes for the two intervals surroundingthe changed pitch werealso made equivalent across the contour-violated and the contour-preserved melodies, with means of 2n2and3n3vs.4n0and3n6 semitones for the preceding and followinginterval of the changed pitch in the contour-violated andcontour-preserved melodies, respectively. The interval sizes foreach of the 12 melodies were submitted to an ANOVA usingmanipulation (contour-violated vs. contour-preserved) andinterval position (preceding vs. following) as within-itemfactors. No main effects or interactions were obtained. Thus,although the interval sizes were, on average, slightly larger inthe contour-preserved melodies than in the contour-violated

melodies, this difference was not significant.Two sets, each consisting of 2 practice trials and 48experimental trials, were constructed with these melodies. Eachtrial consisted of a warning signal and a target melody followed,after a 2 sec silent interval, by a comparison melody. Durationof the inter-trial interval was 5 sec. A first set, prepared for thenontransposed condition, was constructed in such a way that itincluded 24 trials of identical melodies and 24 trials of differentmelodies. When different, the comparison was the contour-violated alternate melody (for example, A followed by C in Fig.1) in 12 trials and the contour-preserved alternate melody in theremaining 12 trials (e.g. A followed D of Fig. 1).

The second set, prepared for the transposed condition, wassimilar to the nontransposed condition in that it maintained thesame comparison melodies; the only modification was that each

target melody (either same or different) was replaced by itstransposed version (for example, B followed by C or D in Fig.1). Therefore, on each trial of this latter set, the target melodywas always higher or lower in pitch level than the comparisonmelody. Melody pairs in each set were recorded on tapes in adifferent random order.

Figure 1. Example of basic melody (A), its transposed version

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Procedure

All participants were presented with the nontransposedcondition first, followed by the transposed condition, in onesession of 45 minutes with a 10 minute break betweenconditions. On each trial of both conditions, participants wereinstructed to judge whether the two successive melodies werethe same or different. For the transposed version, theywere further instructed to disregard the fact that the melodies

were played at different pitch levels, as if they were to judgewhether a melody sung by a man was the same as or differentfrom a subsequent melody sung by a woman (or vice versa).Participants received feedback regarding the accuracy of theirresponses only on the practice trials.

Participants were tested individually with a Hitachi taperecorder that delivered the stimuli at a comfortable levelthrough two built-in speakers. The responses were made orallyand recorded by the experimenter. Data from one participant ineach group were discarded because the performance of thisindividual was considered to be at chance level, as computedthrough a binomial test, in the nontransposed condition (withless than 30 correct responses out of 48 trials).

Results

The responses on different trials were classified ashits if an alternate comparison melody was correctlyjudged as different , and responses on same trialswere classified as false alarms if an identical comparisonmelody (irrespective of pitch level) was incorrectly judgedas different. The mean proportions of hits and falsealarms obtained in each condition for the contour-violated and contour-preserved melodies in the clinicaland control groups are presented in Table 2.

As can be seen, the overall pattern of performance wassimilar in the two groups, with the clinical group generally

obtaining higher hit scores. The rate of false alarms wasvery similar in all conditions for both groups. This wasconfirmed by a preliminary ANOVA in which group(clinical vs. control) was the between-subjects factor andcondition (nontransposed vs. transposed) the within-subjects factor (all F being inferior or equal to 1).Therefore, for each participant, the proportion of falsealarms was subtracted from his\her hit score in order toobtain a single discrimination score in each condition.

Table 2Mean Proportion (%) of Hits and False Alarms Obtained in the Nontransposed andTransposed Conditions for the Contour-violated and Contour-preserved Melodies in BothGroups

Transposition condition

Nontransposed Transposed

Contour-violated Contour-preserved Contour-violated Contour-preserved

HFA participantsHits

Mean 83 74 69 57SD 14 12 20 15

False alarmsMean 20 16SD 10 17

TD participantsHits

Mean 78 58 62 50SD 11 16 14 11

False alarmsM 21 20

The discrimination scores were submitted to anANOVA in which group (clinical vs. control) served asthe between-subjects factor and condition (non-transposed vs. transposed) and melodic change (contour-violated vs. contour-preserved) as within-subjects factors.

Main Effects

Overall, the clinical and comparison groups processedthe melodies along similar principles. Both groupsshowed impaired performance when melodies were trans-posed, as compared to their performance in the non-transposed condition, F(1, 24)l15n26, p .001, sug-gesting that all subjects used AP to some extent todiscriminate the nontransposed melodies. Similarly, bothgroups displayed an advantage for discriminatingcontour-violated melodies over contour-preserved mel-odies, irrespective of the presence of transposition,F(1, 24)l25n01, pn0001. This result indicates that allsubjects used contour as a discrimination cue. Finally, theobservation that performance was above chance indiscrimination of contour-preserved melodies in the

transposed condition revealed that all subjects were ableto discriminate the melodies on the basis of intervalsalone. In sum, all participants made efficient use of AP,interval or scale distance, and pitch direction in melodydiscrimination. In contrast to the WCC hypothesis,global processing is intact in the auditory modality.

Finally, the analysis failed to confirm the presence of agroup effect, F(1, 24)l3n01, n.s., indicating that thegenerally better performance of the clinical group isstatistically unreliable. However, as predicted, thereseemed to be a larger difference between the clinical andcontrol group in discriminating the nontransposedcontour-preserved melodies (with discrimination scores

of 53% and 38% for the clinical and control group,respectively).

Simple Effects

Although this difference was not borne out by aninteraction between the group, transposition, and mel-odic factors, F(1, 24)l2n23, n.s., it was assessed with aone-tailed t-test. This is justifiable for three reasons. First,

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this particular difference was predicted by the WCC andHDH hypotheses. Second, enhanced local processing hasbeen found in several visual tasks (Mottron, Belleville, etal., 1999 ; Plaisted, Swettenham, & Rees, 1999) and,finally, enhanced pitch processing is highly compatiblewith the exceptional pitch-processing abilities exhibitedby musical savants with autism (Mottron, Peretz, et al.1999) and the superior pitch memory exhibited by

children with autism (Heaton et al., 1998). The analysisyielded a significant effect, t(24)l3n04, pn01. Thisadvantage of the clinical over the control group fordiscrimination of contour-preserved melodies was prob-ably due to a more effective use of AP. In effect, when APwas no longer available for discrimination in the trans-posed condition, the clinical group no longer out-performed the control group, t (24)l1n255, n.s., for thecontour-preserved melodies in the transposed condition.

General Discussion

The purpose of the present study was to assess globaland local processing of musical stimuli in individuals with

autism. Global processing was assessed using two in-dependent criteria: a superior recognition of modifiedmelodies in the nontransposed, contour-violated con-dition over the contour-preserved condition, and agenerally normal performance in the transposed con-dition. Local processing was assessed by examiningparticipants ability to detect melody modifications in thenontransposed, contour-preserved condition as well asby the presence of a detrimental effect of transposition onrecognition of identical melodies.

Consistent with the central coherence hypothesis(Frith, 1989), we expected to find poor performance inglobal processing, along with an enhanced local bias. Inaccord with the hierarchical deficit hypothesis (Mottron& Belleville, 1993), we expected to find an absence of theglobal advantage effect presented by typically developingpersons. However, local processing was expected to besimilar in the clinical and comparison groups.

Consequences of Normal Global and IsolatedEnhanced Local Processing for Weak CentralCoherence and Hierarchisation Deficit Hypothesis

Our first finding with respect to global processing wasthat the clinical group possessed the same advantage asthe comparison group in the contour-violated conditionover the contour-preserved condition. This reveals that,on a task that is successful in eliciting the globaladvantage found in the literature, persons with autismprocess hierarchical musical stimuli with a global ad-vantage. Second, persons with autism recognised theidentical, transposed melodies and, indeed, did so to thesame extent as participants in the control group. Thisindicates that differences in pitch did not mask theperception of contour similarity (i.e., that persons withautism were able to process the contour of a melody evenwhen the contribution of AP was suppressed, henceconstituting a second, strong argument for intact globalprocessing).

It is necessary to address whether intact recognition oftransposed melodies and superior recognition of modified

melodies in the contour-violated condition, instead ofnormal global processing, could result from a mere localstrategy. Indeed, contour is a succession of ascending or

interval sizes, it is logically plausible to obtain therepresentation of a large-scale melodic contour by addingseveral small-scale units (or links ), with each linkcomposed of two pitches separated by one interval. As ananalogy, the local-by-local graphic construction exhibitedby the savant draughtsman EC (Mottron & Belleville,1993), and by nonsavant individuals with autism, iscompatible with normal (Mottron, Belleville, et al., 1999)

and occasionally outstanding (Mottron & Belleville,1995) conservation of global properties (e.g. proportion).Nevertheless, although a chaining strategy could result inthe correct reproduction of a melody and allow for thedetection of melody modifications, this could not result ina superior detection of altered melodies in a conditionwhere contour is modified. If the whole is superior to thesum of the parts, juxtaposition of parts cannot producean advantage of whole.

The typical global advantage in high-functioning indi-viduals with autism has been reported previously byseveral authors. Mottron, Burack, Stauder, and Robaey(1999) found faster detection of global rather than localtargets in using hierarchical stimuli (large letters intowhich small letters were embedded) in a divided attentioncondition. In addition, advantages were found forgood geometrical figures over bad ones in a visualparsing task, an effect that requires intact perception ofconfigural properties. Ozonoff, Strayer, Filloux, andMcMahon (1994) and Plaisted et al. (1999), usinghierarchical stimuli in a selective attention condition,found similar global advantage and global interferenceeffects in clinical and comparison groups. Therefore, themain claim of the hierarchical deficit hypothesis in autism(i.e. absence of a global advantage, or equivalent localand global processing) at the behavioural level remainsunsubstantiated. The finding of intact perception of

global music features, based on two independent criteria,also challenges the weak central coherence hypothesis inmusic perception, in which coherence is represented bycontour. Along with previous reports of normal globalprocessing in the visual modality, this contradicts one ofthe two predictions by the weak central coherencehypothesis: impaired global processing.

In terms oflocal processing, we found that persons withhigh-functioning autism performed better than the com-parison group when AP could be used for discrimination,due to a superior detection of modified melodies in thecontour-preserved (local) condition, in conjunction withnormal processing of global features. A similar circum-stance of local bias without global deficit has already beenencountered in the visual modality in autism. Plaisted etal. (1999), using hierarchical visual stimuli in a dividedattention condition, found an atypical local advantageand local interference effect. Nevertheless, the finding ofnormal global precedence and global interference, usingthe same subjects and the same stimuli, but in a selectiveattention condition, suggests typical global processing.Using graphic reproduction of geometrical figures, wealso found that persons with autism used a more localgraphic strategy than typically developing participants(Mottron, Belleville, et al., 1999). Nevertheless, theclinical group was able to reproduce complex geometricfigures with a very high levelof quality inthe reproduction

of proportion, and in a shorter time than the comparisongroup. Thus, these individuals could not have beenimpaired in perceiving global aspects of visual stimuli,

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Therefore, we are obliged to conclude that although alocal bias in autism has been confirmed in the visual andauditory modality with several independent paradigms, itis not necessarily associated with a global deficit. Thequestion then arises: is the concept of locality still helpful,and more generally, do hierarchical models of autism(WCC and HDH) maintain their heuristic value indescribing this local bias in autism as we currently

interpret it?

Possible Causes of Superior Pitch Processing

As mentioned previously, the CentralCoherence modelpredicts a local bias that results from an imbalance in theintegration of information at different levels (Frith &Happe! , 1994). However, even if the presence of localsuperiority partially supports this model, the absence of aglobal impairment prevents the conclusion that localsuperiority derives in this case from a global impairmentwithin the same modality. Similarly, if pitch abilityresulted from agenerallocal bias, persons with AP should

show abnormal hierarchical perception in both theauditory and visual modalities. This issue has beenaddressed by assessing hierarchical perception in thevisual and auditory modality in the same participant.Mottron, Peretz, et al. (1999) conducted an extensivestudy of QC, an adolescent with autism who possessedthe special ability of AP. AP in identification andproduction was confirmed. Nevertheless, no abnormali-ties were found in the perception of hierarchical (local-global) properties for visual patterns and music. Thisfinding indicated that AP in autism might not result froma multimodal deficit in processing global information. Incontrast, the observation of a low threshold for auditorystimuli in AP suggests that exceptional pitch perceptionmight be related to enhanced perception for elementaryproperties of sounds.

This interpretation has received some support by recentfindings that several elementary perceptual functionsappear to exist at an abnormally high level in personswith autism. Plaisted, ORiordan, and Baron-Cohen(1998a, b) established that high-functioning individualswith autism are superior to typically developing par-ticipants in discriminating highly similar stimuli to whichthey had not been pre-exposed (dots differing in theirrelative position), although this superiority vanished forpre-exposed stimuli. They are also superior in conjunctivevisual search (i.e., in a condition where targets are

composed of a conjunction of two features, each of whichis shared by a category of distracters). Both our findingsand those of Plaisted et al. strongly suggest that over-development of low-level perceptual processing mightextend to a possibly large number of basic perceptualfunctions in autism. However, it remains to be demon-strated whether the same subjects present all of thesetypes of enhancement concurrently.

Enhanced Perceptual Processing: A CompensatoryMechanism?

We discussed elsewhere (Mottron & Burack, in press)

the manner in which enhanced perception for elementaryproperties of incoming stimuli in autism may be inter-preted in the more general framework of Paradoxical

of inhibition, suppression of an antagonist function whentwo systems are typically in competition, functionalcompensation) by which a neurological deficit mayproduce enhanced performance. Insights regarding thecausal mechanism that produces superior performance inatypical development might indeed be achieved byexamining other pathological conditions in which su-perior performance in basic perceptual processing is

produced to compensate for a known deficit. Forexample, a developmental compensation resulting in asuperior ability in the auditory modality has recentlybeen found in congenitally blind persons (Lessard, Pare! ,Lepore, & Lassonde, 1998). Specifically, visually im-paired persons are indeed superior to normal adults indetermining spatial localisation of sounds. Better per-formance in the intact modality might be explained by anincrease in neuronal resources devoted to this function, asevidenced, for example, by a larger amount of brain tissuedevoted to intact modalities in congenitally blind persons(Sadato et al., 1996). Therefore, it is possible thatenhanced perceptual processing results from a compen-sation mechanism where perception compensates fornonperceptual processes, in the same manner that, forblind persons, enhanced auditory perception com-pensates for visual impairment.

In our study, the (purported) compensation does notshed light on the cognitive locus of the deficit for whichthe compensation occurs. Our findings do not help todiscriminate among the various candidates for the pri-mary cognitive deficit in autism. In particular, theseresults do not allow us to discriminate between specificdeficits in the processing of social information, such astheory of mind (Baron-Cohen, Leslie, & Frith, 1985)and nonspecific deficits in other types of complex oper-ations (executive functions; Ozonoff, Pennington, &

Rogers, 1991; complex operations, regardless of type;Minshew, Goldstein, & Siegel, 1997). Considering thatenhanced performance in autism has been found mainlyfor elementary operations (pitch processing, visualsearch, visual discrimination), and that impaired mental-ising and executive operations share properties of com-plexity (Zelazo & Frye, 1998), a possible frameworkwithin which to examine compensatory relations wouldinvolve testing basic enhanced processing against deficitsin complex operations.

An alternative proposal to the compensation hypoth-esis attributes the enhanced performance of elementaryperceptual modules to an intrinsic, primary property ofneuronal networks in autism, the same as those thatproduce a deficit in higher-order processing. This wouldmodify the primary\secondary causal relationship be-tween enhanced basic operations and impaired complexones (like theory of mind or executive function deficits),both resulting from an anomaly in neuronal learningproperties. Some researchers have suggested that modi-fying the learning properties of neuronal networks mightproduce superior discrimination performances (Oliver,Johnson, Karmiloff-Smith, & Pennington, 2000), al-though application of this line of thought to autism is atits inception and thus remains imprecise in terms of itspredictions.

Enhanced Perceptual Processing and Peaks ofPerformance

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cognitive deficit might explain heterogeneous symptomsin multiple and heterogeneous behaviours. The failure ofan elementary operation that is mandatory for severalbehaviours, either concurrently or as development pro-ceeds, would yield the characteristics described as symp-toms of autism. Nevertheless, the claim that a solecognitive deficit might be responsible for two symptomsof autism as distinct as, for example, theory of mind

deficits and over-representation of absolute pitch, isdifficult to maintain. This led Frith and Happe! (1994) topropose two core deficits, one for the triadic symptoms(social, communication, imagination) and one for thenontriadic symptoms, which is the central coher-ence deficit. Indeed, this last group of characteristicsoverlaps with the domains of processing where a localbias may be found. We propose to increase the precisionof this rather general statement. First, the relationbetween the two core deficits might be a compensatoryone. A deficit in higher processes might produce asuperior development of perceptual modules devoted toelementary visual and auditory features. Second, certainspecial abilities and peaks of performance in autism relateonly indirectly to a deficit in high-level cognitive oper-ations, through the mediation of a hidden variable, theenhanced processing of physical aspects of stimuli. Forexample, peaks in the block design subtest of the WISC(Shah & Frith, 1993) would be related only indirectly todeficits in complex levels of processing, through themediation of enhanced recognition of simple figures,instead of resulting directly from a central coherence or ahierarchical deficit. Finally, one of the cognitivedeficitsthat which is responsible for the characteristicsdescribed in terms of the central coherence deficitmightbe in fact the over-development of elementary perceptualmodules.

In sum, our finding of superior absolute pitch in thepresence of normal processing of global music featuresextends our understanding of local-global processing inthis population. First, it confirms that enhanced localprocessing is present in the auditory as well as the visualmodality in autism. Second, it refutes the hypothesis of adeficit in the perception of global properties in theauditory modality, and converges with recent findings ofnormal global perception in the visual modality. Third,recent findings of superior discrimination for highlysimilar novel stimuli, and superior visual search, inaddition to the present finding of enhanced pitch per-ception, suggest that several basic perceptual operationare enhanced in autism. An important future issue will beto establish if it is processing of novelty and dissimilarityper se that is enhanced, for any type of material, or ifautism is characterised by enhanced activity of a restrictedand fixed number of elementary perceptual modules.

AcknowledgementsFunding for this project was providedby a Chercheur Boursier du Fonds de la Recherche en Sante! duQue!bec (FRSQ) award to L. Mottron, two research awardsfrom the Medical Research Council of Canada to L. Mottronand I. Peretz, and a studentship award of the FRSQ to E.Me! nard. We thank Patricia Jelenic, Catherine VanHalle, andBernard Bouchard, who helped with the testing and stimuliconstruction, and J. Boseovki for editing the English version ofthe manuscript. We are grateful to Sylvie Belleville and JakeBurack for their helpful comments. Special thanks is also

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