Current perspectives on developmental dysphasias

Journal of Neurolinguistics 12 (1999) 181±212 www.elsevier.com/locate/jneuroling

Current perspectives on developmental dysphasias Jean-A. Rondal*, Annick Comblain University of LieÁge, Laboratory for Psycholinguistics, B-32, Sart Tilman, 4000-Liege, Belgium

Abstract The paper documents the major diculties observed in the oral language development of individuals with mental retardation of genetic origin. The extent of inter- and withinsyndrome variability is evaluated. More speci®cally, a comparative analysis of typical language phenotypes in several genetic syndromes is attempted and the possible brain underpinnings of the observed di€erences are envisaged. Recent cases of favorable language development in individuals with mental retardation are summarized and explanatory variables are discussed. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Language development; Developmental dysphasia; Mental retardation; Genetic symptoms

1. Down's syndrome Mental retardation (MR) of genetic origin represents approximately 30% of all cases of moderate and severe retardation and 15% of all cases of mild mental retardation [1]. Down's syndrome (DS) [2,3] is the most frequent noninherited condition [4], with an incidence estimated by Dolk et al. [5] of one in 750 live births in both sexes. It may be closer to one in 1500 in many developed countries due to the conjunction of early diagnostic procedures and abortion. Table 1 summarizes the major data on the language diculties in DS (for a full review, see Rondal and Edwards [6]).

* Corresponding author. E-mail address: [email protected] (J.A. Rondal). 0911-6044/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 1 1 - 6 0 4 4 ( 9 9 ) 0 0 0 1 4 - 7

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Table 1 Major language problems in persons with Down's syndrome Language component

Semiology

(1) Sound articulation and auditory discrimination

Articulatory and coarticulatory diculties, particularly with the later acquired phonemesa Slow and sometimes incomplete maturation of phonemic discrimination Reduced lexicon in terms of both number of lexemes and semantic features within lexemes. Poor organization of the mental lexicon, both semantically and pregrammaticallya Reduced length and formal complexity of utterances. Problems with in¯ectional morphologya Problems producing and understanding subordinated propositions and compound sentencesa Slow development of advanced pragmatic skills (e.g., topic contribution in conversation, interpersonal requests, monitoring verbal interactions with other people) Insuciently developed discourse macrostructuresa

(2) Lexical semantics

(3) Morphosyntax

(4) Language pragmatics (5) Discourse organization a

Italic font signals the most serious problems.

No major language di€erence has been demonstrated between the main three etiological categories of DS (i.e., standard trisomy 21, which accounts for 97% of the cases; translocations, 2% of the cases; and mosaicism, 1%; in these latter cases, the embryo develops with a mosaic of normal and trisomic cells), except that mosaic subjects may exhibit superior lexical reference skills, in keeping with their tendency to have higher IQs [7]. 1.1. Prelinguistic development Prelinguistic development is signi®cantly delayed in DS babies. As a rule, they are less responsive to mothers' verbal stimulation than nonretarded (NR) infants of similar chronological age (CA). Turn-taking skills basic to future conversational exchanges are slow to develop. The type of prelinguistic phrasing that can be observed in NR babies beginning around 3 months of age (i.e., intermittent babbling, approximately 3 s long, with phrase-ending syllables lasting longer than other syllables) is di€erent in DS babies. They take longer to ®nish a prelinguistic phrase (an average of more than 5 s). This extended time frame may explain why mothers and their babies are often found to vocalize simultaneously [8]. 1.2. The sounds of babbling The sounds of babbling are mostly similar in terms of types and tokens in NR and DS infants [9]. However, the onset of reduplicated babbling (production of

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speech-like syllables Ð ``bababa'', ``dadada'', etc. Ð) is observed around 6 months in NR infants, compared to 8 months in DS infants [10]. Reduplicated babbling is a precursor to meaningful speech [11]. 1.3. Meaningful speech Many DS children do not demonstrate consistent use of conventional words before 2 or 3 years of age. Their frequent motor development de®cits [12,13] are likely factors contributing to this delay. Semantic development is also retarded in DS children in proportion to the cognitive impairment characteristic of the condition. Some of the early contributors to cognitive development are eye contact and joint attention on the mother and child's part [14]. DS infants exhibit delays (one month on average) in the onset of sustained eye contact with the mother, and further delays (two months on average) in the development of high levels of this behavior [15]. Delays in imitative, verbal, and gestural abilities [16± 20] may also contribute to the slower development of meaningful speech production in DS children. Early lexical development generally shows a good positive linear relation with mental age (MA) increase [6]. However, as noted by Miller [21], the rate of new word acquisition of DS children does not keep up to that of NR children and the slopes of the equations describing both vocabulary learning curves gradually di€er more and more. The gap continues to widen with increasing age. The existence of noticeable individual di€erences in rates of vocabulary acquisition among DS children must also be acknowledged. Based on a sample of 43 DS children studied at the University of Wisconsin, using parental reports (the McArthur Child Development Inventory), Miller [21] indicates that 65% of the DS subjects scored below their MA-NR peers whereas 35% were learning vocabulary at a rate consistent with 80% of their MA-NR peers. 1.4. The ®rst multiword productions The ®rst multiword productions that are not unanalyzed formulae are observable around 4 years of age in DS children. Mean length of utterance (MLU) is widely used as a criterion for assessing language development. Up to a certain level of development, almost any morphosyntactic acquisition will be directly re¯ected in the MLU count. MLU development in DS children shows a good linear relationship with CA until early adolescence despite the existence of a signi®cant delay [22,23]. MLU values of 1 are usually observed around age 2. Between 2 and 9 or 10 years of age, MLU rises from 1 to 4 approximately. MLUs of 5 or 6 units are generally observed from 12 to 14 years. NR children achieve MLU levels of 5 units and more around 6 years of age. In conversational speech between NR adults, MLU values are often close to 12. The slowness and limitation of MLU development in DS individuals correspond to lasting de®cits in morphosyntax. Productive use of grammatical words (articles, prepositions, pronouns, conjunctions, auxiliaries) and morphological marking of gender, number, tense, mood and aspect are limited. Most DS subjects are restricted to

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monopropositional sentences with correct word order. Subordinate clauses are rare. Even at corresponding MLU levels, DS children may not produce exactly the same kind of syntax as NR peers [24]. For example, when matched for MLU with NR children, DS children tend to use fewer complex verb groups and advanced types of inde®nite pronouns. Corresponding limitations can be observed in their understanding of grammatical structures [25]. 1.5. Pragmatics and communication There is a growing literature on language pragmatics in MR (see Rosenberg and Abbeduto [26] for a review). Young DS children (1±4 years of age) use one-word utterances eciently to request interesting objects located out of reach [27]. Several studies report that there are few di€erences between MA-matched NR and DS children in the frequency of speech acts, e.g., question±answer, assertion, suggestion, request, command [28,29]. But there are important limitations in the use of linguistic forms that NR people ®nd appropriate for the expression of particular speech acts. For example, DS children have diculty using conventional forms to `soften' their requests or render them more `polite' by some formal means such as indirect requesting. However, topic contribution and topic continuation in DS persons have not been studied in detail. Their turn-taking behavior is systematic and rule-governed. DS individuals have a keen desire to keep topics going when conversing and to contribute signi®cantly to conversations. But they often lack the language skills and the relevant knowledge to do so. 1.6. Comprehension versus production DS individuals are often claimed to have better language comprehension than production. To a certain extent, the same thing is true of NR people. But what is at stake in this context is the possibility of a genuine discrepancy between language comprehension and production abilities in persons with DS. Miller [21] reports on the developmental progress in language comprehension and production of DS children (MA between 1 and 5 years). He indicates that 65% of the total individual pro®les re¯ect greater impairments in language production than comprehension. One might question Miller's claim that there is a discrepancy between DS people's comprehension and production on several grounds. With regard to lexical functioning, this may not amount to much more than the usual imbalance between productive and receptive vocabulary in NR people. As for morphosyntactic functioning, it is relevant to recall, with Caplan [30] and Faust [31], that there are at least three routes to sentence meaning: (1) a syntactic route that computes a full syntactic representation for a sentence and uses this representation to assign aspects of sentential meaning; (2) a heuristic route that uses a reduced syntactic structure (e.g., word order) for the same purpose; and (3) a lexico-pragmatic (lexico-semantic) route that infers aspects of sentence meaning

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from single word meaning and knowledge of real-world events. According to the above-mentioned authors, the specialized processing mechanisms that assign syntactic structure to sentences are (normally) unique to the left cerebral hemisphere; the right one is able to understand sentences by using semantic relations between single words and world knowledge, that is, by the lexicosemantic-pragmatic route. This being so, Miller's theoretical indication, based on the use of global comprehension tests such as the Inventory of Communication Development [32], the Miller±Chapman procedure [33] and the Test for the Auditory Comprehension of Language-Revised [34], compared to results of production assessment mainly involving free-speech analysis (SALT) [35,36] and yielding such general measures as performatives, requests for attention or objects, and MLU, may re¯ect the use by DS individuals of strategies 2 and/or 3 above rather than genuine morphosyntactic processing. In fact, most DS persons may be incapable of such processing, as demonstrated by Rondal [37] in experimentally controlled tasks of comprehension of reversible passives, relatives and causatives, and temporal clauses, excluding the recourse to strategies 2 and 3 above. Typical DS individuals do not readily produce such linguistic structures, except at times in idiosyncratic expressions; moreover, they fail to understand them beyond clause level. 1.7. Is DS language simply delayed or is it qualitatively di€erent? The question was raised years ago [38] as to whether language development in MR children is a delayed version of normal language development or whether it shows qualitatively di€erent patterns. It is now possible to give a more precise answer to this question based on the large number of studies that have been conducted. It appears that language development in DS children is not just a slow-motion version of NR language development. From the early stages on, there are noticeable di€erences from NR children, including particular limitations for which adequate explanations are not available yet. Furthermore, language development in DS is never complete. It plateaus at various times depending on the particular aspects considered. A strict delay-di€erence framework is not appropriate for describing language development in MR individuals [22,39,40]. But language development in DS subjects is not exotic either. The sequence of developmental steps appears to be the same in DS and NR children (similar sequence hypothesis corroborated). 1.8. What language levels are reached by DS adults? Is there progress beyond adolescence and during the adult years? This question is related to the issue of a critical period for ®rst language acquisition, initially raised by Lenneberg [41]. Lenneberg's conclusion was that, due to the maturational calendar of the brain, no basic language development could be possible beyond puberty. He claimed to have observations from DS subjects supporting this hypothesis [42]. We now have more systematic data

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pertaining to the problem and are in a better position to assess the validity of the critical period hypothesis for ®rst language acquisition. In NR individuals, crucial evidence is provided by Genie, a modern-day `wild child' who was kept away from social contact for most of her ®rst 13 years [43]. When she was discovered, Genie understood only a few words and did not speak. From that time, she developed relatively rapidly in the cognitive area and substantially enriched her referential lexicon and semantics. But the acquisition of grammatical rules and their use in complex utterances never followed. Sentence word order is globally appropriate but her utterances lack bound and free grammatical morphemes. Advanced syntactic devices are missing. Other cases exhibiting the same general pattern have been documented. For example, Chelsea, a hearing-impaired adult of normal intelligence who ®rst attempted to acquire spoken language in her 30s, following successful auditory ampli®cation [44], progressed regularly in lexical knowledge thereafter. She scored above the 12th grade level on the Productive Word Association Subtest of the Clinical Evaluation of Language Functions [45]. In contrast, her ability to combine words in utterances remained extremely limited, resulting in her multiword combinations being ungrammatical most of the time. Further data suggest a critical period for the development of grammar-setting mechanisms. Mayberry et al. [46] showed that individuals who acquire American Sign Language (ASL) as adolescents perform worse on tasks assessing grammatical knowledge than individuals who acquired ASL earlier in life. Similar results have been published by Newport [47,48]. The available data argue in favor of the existence of neuropsychological mechanisms devoted to the grammatical and phonological aspects of language. Such mechanisms are tied to the left cerebral hemisphere and develop according to strong maturational constraints. There is no indication that the development of semantic, lexical, pragmatic and discourse skills (i.e., the more conceptual, social and informative aspects of language) is characterized by similar temporal constraints. The critical period for formal language development is likely to have modular characteristics. In other words, a set of speci®c phenomena may partially coincide in time. The critical phonological period may terminate around 7 to 8 years of age. Judging from available data on the di€erence in vocal capacity between congenitally deaf individuals or individuals having become deaf early in life (i.e., before about 2 years of age [49]) and subjects whose deafness occurred later in life, there is probably an earlier critical period for voice setting and control. The end of the critical period for morphosyntax may be around age 14. Hurford [50] suggests that the main determinants of the end point(s) of the critical period(s) are the consequences of the interplay of genetic factors in¯uencing life-history characteristics in relation to language acquisition. Assuming that the developmental constraints advocated by Hurford [50] apply equally to MR individuals (including DS individuals), it can be predicted that no basic formal language development will be readily possible beyond 14±15 years of age in these subjects. Training e€ects may still be induced later because critical

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periods do not end abruptly. But the e€ect of training will come at an increased cost with advancing CA. Development in the conceptual aspects of language may continue during adolescence and beyond in proportion to a possible continued growth in MA [51,52]. As reviewed by Rondal and Comblain [23], the above predictions are supported by facts. Observing language evolution in DS individuals from late childhood into adulthood, little structural progress is obvious in the phonological and morphosyntactic aspects of language. MLU, for instance, plateaus after 14 or 15 years. In contrast to phonology and morphosyntax, referential lexical abilities, pragmatics, and to a lesser extent discourse abilities generally improve beyond childhood. 1.9. Working memory The reference model in use here is Baddeley's (e.g., [53±56]). According to this model, working memory (WM) is composed of a controlling attentional system (called the central executive) which supervises the activities of two subsystems: (1) the phonological loop devoted to the maintaining of verbal material (auditoryverbal working memory; AV-WM) and (2) the visuospatial sketch pad for visuospatial material (visuospatial working memory; VS-WM). The former subsystem has two components: (1) a phonological store conserving verbal input for approximately 2 s and (2) an articulatory rehearsal system, based on inner speech, allowing one to recycle the verbal material back into the phonological loop, thereby avoiding trace decay. It is known that WM is impaired in MR individuals [57±61]. These subjects do not exhibit the modality e€ect observed in NR children (i.e., auditory material is better recalled than visual material). Mackenzie and Hulme [62] were the ®rst to study WM functioning in DS individuals. They reported a reduced WM span in DS compared to NR subjects over a ®ve-year period. In NR children, AV-WM span increases from a mode of 4 items around 5 years CA to 5 items around 7 years, and 5.5 items around 10 years. Several phenomena account for the growth of AV-WM span in NR people: (1) subvocal rehearsal strategy; (2) better organization of the information to be recalled; (3) slower trace decay; (4) faster item identi®cation rate; and (5) faster rate of articulation. Hulme and Mackenzie [63] investigated articulation rate and subvocal rehearsal in a sample of DS adolescents. They noted a lack of word length e€ect (NR people usually recall more short words than longer ones within the same interval of time) and a lack of any link between articulation rate and WM. These two observations may imply that DS individuals do not use the subvocal rehearsal strategy. Broadley et al. [64] and Comblain [59,60] con®rm the absence of rehearsal strategy in DS individuals. The three above-mentioned studies observed a phonological similarity e€ect in DS subjects (i.e., phonologically dissimilar words are recalled better than phonologically similar ones), similar to that in NR people but less marked and not increasing with CA as is the case for NR subjects.

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No matter how limited, the AV-WM of DS individuals can be improved with speci®c training procedures. Broadley et al. [65] taught DS individuals to use rehearsal and organizational strategies to improve their AV-WM spans. They reported long-term e€ects of the training. Comblain [58,59] trained three samples of DS individuals (children, adolescents, and adults) to use a rehearsal strategy. She noted a signi®cant increase in AV-WM span in the trained groups compared to the control groups. In the trained groups, AV-WM span reached the level expected for the MA. Eighteen months after the training ended, the DS subjects' AV-WM spans were still longer than at the beginning of the study. AV-WM performance may be linked to language development and particularly to lexical acquisition ([66] for neuropsychological data; [67±69] regarding bilingual people; [70±72] for data concerning NR and language-impaired children; and [59] regarding DS individuals). Increasing MR individuals' AV-WM could therefore be an e€ective means of facilitating lexical development. Jarrold and Baddeley [73] claim that the impaired AV-WM of DS individuals may have ``important implications for the development of language skills in this population, and in particular, might explain why language development is particularly delayed in comparison to nonverbal abilities'' (p. 102).

2. Variability across syndromes Recent work suggests that language development and functioning may vary across MR syndromes at corresponding psychometric levels. Shprintzen [199] lists several hundred genetic syndromes leading to MR and communication disorders. Relatively few of them have received detailed phenotypic work and fewer have been studied from a language point of view. Several language studies have been conducted on Williams syndrome (WS) [74]. WS is a congenital metabolic disorder (incidence: 1 case in 10,000 or 20,000 live births) associated with hemizygous deletion including the elastin locus at chromosome 7q11.23. Hemizygosity of the elastin gene accounts for the vascular and connective tissue abnormalities observed in WS. However, the genes contributing to other features of the syndrome, such as infantile hypercalcemia, dysmorphic facies, and cognitive defects (between mild and moderate mental retardation) remain to be identi®ed [75]. Many WS individuals have good referential lexical abilities [76]. They seem to have lexical access diculties in experimental tasks and to be less sensitive to word frequencies than normal controls [77]. Speech is ¯uent, with correct articulation and prosody. Sentence comprehension and use of morphosyntactic devices are not intact, as preliminary indications had suggested [78]. Recent work [79,80] shows that WS individuals have diculties a€ecting production and comprehension of certain features such as subcategorization constraints (e.g., intransitive verbs cannot take a direct object), embedded sentences, and grammatical gender assignment across sentence elements, although their general

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grammatical skills appear rather good (particularly in adolescents and adults). Discourse ability seems to be relatively well preserved in WS subjects [81]. Pragmatics is their major area of weakness. They often have diculties with topic introduction, topic maintenance, turn taking and maintaining appropriate eye contact. WS subjects sometimes appear to be talking nonsense. Their speech may be socially inappropriate and repetitive with incessant questions; at times, they may echo the interlocutor's sentences, apparently with limited understanding [82]. Vicari et al. [83] indicated that AV-WM in WS individuals compares well with that of NR subjects at corresponding cognitive levels. Tests reveal that phonological similarity and word length e€ects apply to the same extent in WS and NR subjects. However, WS subjects exhibit a reduced frequency e€ect. Gosch et al. [84] and Udwin and Yule [85] suggest that WS individuals have excellent AV-WM and that they tend to store words by mere mimicry. Grant et al. [86] do not agree with this hypothesis. They claim that WS individuals' good language re¯ects their ability to construct language-speci®c phonological representations of their native language rather than their good AV-WM. The syndrome termed `Fragile-X' (FXS) [87], an X-linked disorder passed on through the generations, has motivated some research in recent years [88]. The cytogenetic expression of the fragile site is on the X chromosome at Xq27.3. It is caused by a null mutation at the FMR-1 gene in which the level of protein in mRNA (messenger ribonucleic acid) is greatly reduced. At the DNA (deoxyribonucleic acid) level, it is characterized by abnormal repetitions of a trinucleotide sequence and methylation. FXS is a genetic abnormality following an unusual pattern that is not yet completely understood [89]. Twenty percent of males with the a€ected gene present no pathological symptoms (nonpenetrant). The rest of the a€ected males are moderately to severely MR [90]. Approximately one-third of a€ected females have a phenotypic variant of the syndrome resulting in learning diculties. A minority is impaired with mild to moderate MR. They are those females who inherited FXS from a carrier mother. Surveys of the MR population [91] suggest that FXS accounts for 2 to 7% of MR among males. FXS prevalence in the general population is close to 0.25 per 1000 males. Although the situation of the a€ected and carrier females is less clear [92], the language picture for a€ected males may be summarized as follows: 1. Speech is fast, repetitive and perseverative, with stuttering and ¯uctuating rates, increased loudness and sometimes oral apraxia [93]. 2. Unusual voice e€ects, dysrythmia, echolalia, speech impulsiveness, disrupted prosody and poor intelligibility have been noted [93±95]. 3. FXS males frequently omit or substitute vowel or consonant phonemes [96]. Utterance formulation is usually defective. Receptive vocabulary seems to be relatively well preserved [95]. Productive morphosyntax is de®cient [97]. 4. The language of FXS males is pragmatically limited with poor topic maintenance and turn-taking diculties. They may also exhibit deviant repetitive language [98].

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Indications regarding memory limitation in FXS have become available. Dykens et al. [99] report poor performance by all FXS males in memory tasks, particularly those involving verbal encoding. Freund and Reiss [100] observe de®cits in sentence repetition related to sequential processing limitations. Language-related research into a few other genetic syndromes has begun, allowing an initial characterization of the major language problems existing therein. Cri-du-chat (cat cry) syndrome (CDCS) [101,102] is a rare syndrome (approximately 1 case in 50,000 newborns [103]) caused by a loss of chromosomal material from the distal portion of 5p. Twenty percent of the cases are familial, with parental translocation accounting for the majority of these. The size of the 5p deletion can vary from the entire short arm to only 5p15. Gersch et al. [104] have determined that two distinct chromosomal regions are associated with di€erent phenotypic manifestations. Deletions in 5p15.3 result primarily in the high-pitched cry characteristic of the syndrome. The typical facial dysmorphias are lacking and cognitive impairment is mild to moderate. The loss of a small region within 5p12.2, designated the Cri-du-chat critical region [105], results in the full spectrum of CDCS symptoms. Incidence of the syndrome does not vary according to sex [106]. A signi®cant number of individuals reach puberty and survive into adulthood [103]. The more typical phenotype presents a characteristic (monochromatic) cry at birth, certain dysmorphic craniofacial features with microcephaly, psychomotor retardation, hypotonia, slowed rate of growth, respiratory and ear infections, and frequent orthopedic malalignment. Neurological examination and magnetic resonance imaging (MRI) reveal hypoplasia of the cerebellar vermis associated with dysgenesis of the corpus callosum. Standard reference sources list severe to profound mental retardation, lack of ambulation, lack of speech, and a reduced lifespan as almost inevitable for these individuals. Longitudinal data gathered by Wilkins et al. [107] and Carlin [108,109], however, indicate that the prognosis for most health, development and longevity parameters in CDCS is much more optimistic today than that presented in common sources of medical information. For example, the risks of major organ anomalies and decreased survival are low. Home-rearing and early intervention are keys to the improved outlook. Data gathered by Wilkins et al. [110] on 86 home-reared individuals with 5p deletion indicate MAs of approximately 2 years 5 months at CAs of around 6 years, with mental quotients inversely proportional to the age at which early intervention began. Carlin [109] reports on 31 individuals with CDCS seen longitudinally, some of them for 10 years or more, and crosssectional data from 31 other cases. Cytogenetically, the sample included a majority of terminal deletions, and some interstitial deletions, mosaicisms and translocations. Carlin notes that, in spite of large variations in the size and location of the chromosome deletions, remarkable phenotypic consistency exists. Early growth failure, microcephaly, signi®cant psychomotor retardation, and respiratory and ear infections are observed in all individuals. Almost 100% of them have hypotonia, at least in the early months. In later years, about 50% retain some degree of hypotonia and experience limitations in their range of

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motion at certain joints. Attention de®cits are general. Most individuals are friendly and enjoy interacting with other people. All CDCS subjects demonstrate cognitive, language and behavioral de®cits, but these de®cits have not been studied much so far. Lack of speech and severe language problems have been noted. However, some limited speech and language development is possible in a large proportion of CDCS individuals, providing that they are correctly stimulated. Angelman syndrome (AS) [111] is characterized by neurological (ventricular enlargement, anomalous cortical growth, abnormal EEGs and seizure), motor (ataxia), and cognitive de®cits. The incidence is approximately 1 in 16,000 live births [112]. Individuals with AS are often found to have severe to profound MR. In 60±70% of all cases, AS is believed to be caused by the absence of maternal contribution (microdeletions and so-called imprinting) to the q11±13 region of chromosome 15 [113]. In a small percentage of cases, the condition is the result of paternal unisomy (inheritance of two copies of the above locus from the father and none from the mother). In the remaining cases, no chromosomal abnormalities or unisomy can be detected [114]. Quite noticeable in AS is the absence of speech and oral language together with oral motor dyspraxia [115]. Nonverbal communication techniques have been tried with AS individuals but apparently with limited success, suggesting that the capacity for language (and not just speech) is impaired in this syndrome [116,117]. Neuro®bromatosis 1 (NF1 [118] Ð there is a type 2, involving postlingual deafness but no MR, which does not interest us here) is a single-gene disorder that appears in childhood. The incidence is approximately 1 in every 4000 live births [119]. Mutations of the NF1 gene (on chromosome 11) result in abnormal control of cell growth and tissue di€erentiation, especially in the central and peripheral nervous systems. Physical features include macrocephaly, gliomas and optic nerve enlargement, skin tumors, dysmorphic features, and various neurological problems interfering with functions. Learning disabilities and mild MR are frequent but there is considerable individual variability [120,121]. The language skills of children with NF1 are less well developed than those of una€ected siblings, with some subjects demonstrating both expressive and receptive language de®cits whereas others have only expressive language de®cits, particularly at the level of pragmatic and discourse organization [120,122,123]. Fluency disorders including stammering and voice problems are present in 30 to 40% of cases. Lexical reduction and morphosyntactic diculties may be found too [124]. Very few studies have focused on memory skills in individuals with NF1. Its seems that there is no AV-WM de®cit. Zoeler et al. [125] mention the existence of visual and tactual memory impairments in adults with NF1. Bawden et al. [126] point to nonverbal cognitive de®cits, and problems with recalling faces and drawing complex geometric ®gures from memory in children and adolescents with NF1. Klinefelter syndrome (KS) [127], a genetic disorder found exclusively in males with one or two extra X chromosomes (XXY, XXXY), a€ects approximately 1 in

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1000 live births [128]. KS is characterized by tall stature and average intelligence or mild MR. Language problems are common, particularly on the expressive side. Auditory processing de®cits are characteristic, although receptive language skills are usually within the normal range. Delayed speech development with prosodic diculties is frequent during early childhood. Word selection and sentence organization are problematic in some cases [129]. Turner syndrome (TS) [130] occurs in as many as 1 per 2500 live female births. About 60% of female individuals born with TS are missing one X chromosome, while the remainder have a partial X chromosome or a mosaic chromosomal pattern [131]. TS subjects have reduced stature and an abnormal upper to lower body ratio, various renal and cardiovascular problems and occasional strabismus. MR is infrequent but speci®c cognitive de®cits frequently a€ect nonverbal functioning, particularly in visuospatial processing, visual-motor integration and visual memory [132]. Oral language skills are usually preserved and may even be relatively strong [131,133]. However, Murphy et al. [134] have noted lower scores in tests of oral language in TS adults, with the mosaic TS subjects exhibiting better verbal abilities. Several studies indicate written language diculties (e.g., handwriting and reading) [135]. Traditional neuropathological measures (EEG, etc.) have failed to identify consistent anomalies in TS individuals [136]. However, brain imagery studies reveal structural anomalies in the brains of TS individuals, i.e., decreased volumes of hippocampus, caudate, lenticular and thalamic nuclei, and parieto-occipital brain matter, and parieto-occipital asymmetry, with left brain regions having greater volumes than right ones in adults [137]. These ®ndings are consistent with a ``right hemisphere dysfunction'' hypothesis of TS. Clark et al. [138] have found lower rates of glucose metabolism in the occipital and parietal lobes in TS subjects compared to controls. PET ®ndings by Elliott et al. [136] suggest that parietal and occipital lobe hypometabolism may be common among TS girls with some degree of cognitive impairment but is not evidenced by TS girls without such impairments. Studies of TS children reveal more visual and spatial processing impairments than verbal processing diculties [139]. It could be that VS-WM is impaired in this syndrome [140±142]. Prader±Willi syndrome (PWS) [143] is characterized by dysmorphic features, hyperphagia, hypotonia and MR. The incidence is 1 in 15,000 to 30,000 live births, a€ecting both sexes equally [144]. The etiology of PWS remains partially unclear. About 60% of PWS cases are associated with visible deletions in the q11± 13 region of chromosome 15. This is the same region as in AS, but in PWS it is the chromosome 15 provided by the father that is at stake (imprinting) [145]. Twenty percent of PWS cases are due to microdeletions in the same chromosomal region, associated with translocations, which can only be detected using molecular genetic techniques [146]. The remaining cases show no karyotypic defect. In these cases, however, both chromosomes 15 originate from the mother [147]. These ®ndings argue strongly that PWS is caused by the lack of some paternal genes from region 15q11±13.

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Psychomotor development is delayed in PWS. Eye diculties, particularly strabismus, are noted. By school age, if not before, cognitive, language and behavioral de®cits become apparent. Cognitive disabilities range from severe to mild [148]. Multiple articulation errors, voice problems and ¯uency problems that markedly lower speech intelligibility are reported. Oral motor functions, pitch level and resonance are disturbed and hearing problems are not unusual. Receptive and expressive language is found to be well below CA as are language pragmatic skills and communicative eciency [149,150]. Cerebral dysfunction, combined with a characteristic anatomy of the mouth and larynx, contributes to altered speech in PWS [151]. A tentative pro®le of the language of individuals with PWS is proposed in Table 2. Rett syndrome (RS) [152,153] is another syndrome with particular linguistic features. It is a progressive developmental disorder a€ecting approximately 1 in 10,000 female individuals. The infant with RS develops as expected until 9 to 12 months of age [154]. Regression then occurs, drastically a€ecting language, motor, and cognitive acquisitions. By 7 years of age, RS children are severely MR. Etiologically, the X chromosome is suspected because only females are a€ected [155]. In many RS children language does not develop beyond single words. Hand skills peak between 10 and 12 months CA [156]. Many RS subjects do not show behaviors interpretable as indicative of elementary intentions to communicate (e.g., gaze shifts and turns) [157]. It seems, however, that RS may progress in di€erent ways. In most cases, there is a failure to develop language or the loss of all acquired language during the regression phase [158,159]. However, some girls retain the ability to use at least some grammatical language, often with pronunciation diculties [160,161]. Table 2 displays the language pro®les of four genetic syndromes. As illustrated in Table 2, the language pro®les of DS, WS, FXS and PWS individuals di€er substantially in ways not previously mentioned. The syndrome di€erences have little to do with the psychometric levels of retardation in each syndrome. Additional research is needed to analyze these comparisons in more detail and to extend the search for other speci®c (or partially speci®c) pro®les. One reasonable possibility is that the syndrome variability corresponds to Table 2 Feature distribution in four mental retardation syndromesa Syndromes Language aspect Phonetic-phonological Lexical Morphosyntactic Pragmatic Discourse a

Down's

Williams

Fragile-X (a€ected males)

Prader±Willi

ÿÿ ÿ ÿÿ + ÿÿ

++ + + ÿÿ +

ÿÿ + ÿ ÿÿ ÿ

ÿÿ ÿ ÿ ÿ ?

Key + (+): relative strength; ÿ (ÿ): relative weakness; ?: absent or insucient data.

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di€erences in neurodevelopment and brain structures consequent upon di€erent aspects of pathological genetic mechanisms. DS subjects are known to have central nervous system dysfunctions secondary to abnormal brain development at the pre-, peri-, and postnatal stages of brain maturation. The examination of DS brains shows a reduction in the weight of the hemispheres, brain stem and cerebellum, delay in myelination, primarily in the development of the association cortex, and reduction in the number of neurons in the whole cerebral cortex and more speci®cally in certain cortical layers [162±164]. DS persons have reduced synaptic density and abnormal synaptic morphology and contacts originating in the pre- and postnatal stages of neuronal development [165]. The abnormal neurogenesis in DS may primarily re¯ect genetically determined altered brain programming. The available studies already point to major neurological di€erences between syndromes which may explain the speci®c fractionation of language functions observed in the phenotypes, originating in di€erent genetic bases. Work by Bellugi and associates, at the Salk Institute for Biological Studies, suggests that functional di€erences between WS and DS individuals correspond to syndromic variation at the brain level. Bellugi et al. [76] compared the neurological pro®les of WS and DS adolescents matched for CA and IQ. The WS subjects demonstrated generalized hypotonia, tremor, midline balance problems and oral-motor and motor abnormalities, suggestive of cerebellar dysfunction. DS adolescents showed minimal hypotonia, few cerebellar signs and better performance on oral-motor functions. Both groups exhibited equal degrees of microcephaly, cerebral hypoplasia, reduced cerebral volume and decreased myelination; but the overall brain shapes of each group proved distinct. DS brains are signi®cantly hypofrontal whereas WS individuals have decreased posterior width with a smaller forebrain posterior to the rolandic sulcus, i.e., the parietal, posterior, temporal and occipital cortical regions, and narrowing of the corpus callosum anterior to the splenium. WS individuals show elongated posterior to anterior length compared to normal brains. The hypofrontality of the neocortex in DS subjects, together with a reduction in frontal projections from the corpus callosum, is further demonstrated in a magnetic resonance imagery study by Wang et al. [166]. The authors relate this neuroanatomical indication to a frontal lobe dysfunction pro®le in DS corresponding to poor verbal ¯uency, perseverative tendencies and more diculty with tasks requiring ¯exible problem-solving strategies. DS subjects, however, have relatively preserved basal ganglia and diencephalic structures. In contrast, WS subjects exhibit better frontal and temporal limbic structures [167]. There is also evidence in WS individuals of dysregulation of the control of neuronal and glial numbers, as illustrated by increased cell packing density at the cytoarchitectonic level [75]. This may re¯ect an interference with naturally occurring cell death and the presence of neurotrophic factors (possibly linked to abnormal extracellular calcium levels). The cerebellar volume in DS subjects is approximately 77% of the equivalent in young normal controls, compared to 99% in WS subjects. Although cerebellar size is intact and the neocerebellum largely preserved in WS, some other

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neurological ®ndings are suggestive of cerebellar dysfunction. The posterior fossa structures of the WS and DS subjects were further examined by Bellugi et al. [76], leading to the identi®cation in WS of an anomalous pattern, with neocerebellar vermal lobules showing hyperplasia in the context of low-normal paleocerebellar vermal development and signi®cantly reduced forebrain size. Such an aberrant cerebrum/cerebellum volume ratio could serve to neurologically distinguish WS from other syndromes such as DS [168]. Bellugi et al. [76] speculate (following a suggestion by Leiner et al. [169] on the possible role of human neocerebellar structures in mental and linguistic functions) that the observed hyperplasia of speci®c vermal lobules in the context of cerebellar maldevelopment may be related to the language pro®le of WS subjects. Bellugi et al. [76] further remarked that, behaviorally, their WS subjects were grossly similar to unilateral right-hemispheredamaged (normal) adults whereas the DS individuals were more like lefthemisphere-damaged aphasics, demonstrating language impairment and a marked tendency to global processing of information. The curtailment of the dorsal parietal and posterior temporal areas of the brain in WS subjects, together with the thinning of portions of the corpus callosum, may be directly relevant to their visuospatial de®cits [75] and indirectly, perhaps, to the dissociation between the AV-WM and VS-WM systems. WS subjects indeed have a better preserved AVthan VS-WM, whereas the converse is true for DS subjects [73]. Similarly, the better preserved size of the frontal and most of the temporal lobes in WS is consistent with the relative preservation of formal linguistic capacities in this syndrome. Neurological di€erences in FXS have been little studied so far. Cerebral ventricular enlargement and decreased size of the posterior cerebellar vermis have been found in many FXS individuals compared to NR persons [170,171]. The latter indication is consistent with the motor de®cits in FXS [172]. Decreased amounts of FMRP (the FMR-1 protein) impair the development of the cerebellum's Purkinje cells, the cholinergic neurons innervating the limbic system (involved in emotional and mood regulation), and other neuronal tissues (gray matter in particular) that normally exhibit high concentrations of FMRP. 3. Within-syndrome variability Individual language abilities in MR may be distributed according to a Gaussian curve. For each language component, one can expect that a majority of MR persons will score in the central part of the distribution whereas fewer will score at the two extremes, being either exceptionally favored or exceptionally restricted as to their ®nal developmental level. Table 3 displays summary information on a number of cases of exceptional language in MR documented in the literature (for a full review, see Rondal [185] and Rondal and Edwards [6]). In addition, we supply further information on the case of Franc° oise, a Frenchspeaking DS woman, with normal or quasi-normal formal language abilities (for a full analysis, see Rondal [37]), as well as several indications from a study still in

11

32

(4) [179,180] Franc° oise (Down's syndrome) (5) [181] DH (etiology unknown)

60

60

57

(8) Rondal Claudine (Down's 27 and syndrome) Comblain (in progress)

preoperatory

preoperatory

severely impaired cognitive development late preoperatory to early operatory

correct articulation and phoneme discrimination; receptive vocabulary at 6-year-old level; advanced expressive and receptive morphosyntactic abilities, except for Laura, who exhibits receptive morphosyntactic limitations; semantic, pragmatic, and discourse de®ciencies. good command of written language expression and reading (average number of words per written sentence varying from 7.14 to 12.50 between 15 and 33 years). good ability to articulate, learn words, and use complex syntax; semantic diculties

MLUf Other language aspects

7 years 4 12.24 correct articulation and phoneme discrimination; moderately months retarded lexical development; advanced expressive and receptive morphosyntax; limitations in discourse organization correct articulation; extensive vocabulary; complex morphosyntax; use of standard pragmatic devices in conversation English within the normal range including complex metalinguistic judgments; good ability to translate into English from 13 languages: French, German, Spanish, Danish, Dutch, Finnish, Russian, Greek, Hindi, Norwegian, Polish, Portuguese and Welsh correct articulation with occasional stuttering-like phenomena; good acquisition of Italian and, to a lesser degree, English and French vocabularies; advanced expressive morphosyntax 5 years 4 15.39 correct articulation; moderately retarded expressive lexical months development; advanced expressive morphosyntax; moderate diculties at discourse level

2 years 9 months

MAe

b

Empty boxes in table correspond to information not supplied by the authors in the original source. Chronological age in years at beginning of the study. c Intellectual quotient according to standard intellectual scales. d According to Piagetian criteria. e Mental age in years. f Mean length of utterance (computed in number of words plus in¯ectional morphemes).

a

71

23

(7) [184]

67

29

(6) [182,183] Christopher (etiology unknown) FF (Down's syndrome)

Operational leveld

50; ±; 41 preoperatory; preoperatory; preoperatory

IQc

adolescent 35

3

(3) [176±178] hydrocephalic children

Paul (Down's syndrome)

(2) [175]

CAb 6; 15; 16

Subjects

(1) [173,174] Antony; Rick; Laura (etiologies unknown)

Study

Table 3 Exceptional cases of language development and functioning in MR/DS subjects. Studies and key pointsa 196 J.-A. Rondal, A. Comblain / Journal of Neurolinguistics 12 (1999) 181±212

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progress concerning another French-speaking DS woman, named Claudine (Tables 4 and 5). The conclusion from the above studies is straightforward. Formal language problems are not inherent in MR/DS qua MR/DS. Rondal [187] has suggested that the problems MR/DS persons have with the semantic aspects of language, on the one hand, and the phonological and morphosyntactic aspects, on the other, do not have the same roots. MR/DS subjects' semantic problems originate in their cognitive diculties. These problems are unavoidable given the major cognitive limitations de®ning MR. However, the diculties of typical MR/DS subjects with the formal aspects of language do not originate in their general condition, as demonstrated a contrario by the exceptional cases. They result from particular impairments of language organization. This runs contrary to the view that all language diculties in MR are a direct consequence of the cognitive de®cit. How are we to explain the exceptional cases of language development and functioning in MR individuals? 3.1. Speci®c educational factors Speci®c educational factors (unusual language training procedures by parents, teachers, etc.) do not seem to have in¯uenced the reported outcomes. There is no indication in the cases studied that particular remedial procedures could be held responsible for the advanced abilities documented. Parent±child verbal interactions with MR children have been proven to be basically normal [22,24], where `normal' means the type and quantity of linguistic input and feedback received by NR children at corresponding language levels. If adaptations of that sort were the key factor in determining exceptional language abilities in MR subjects, one should observe many more such cases. 3.2. What about cerebral hemispheric specialization for the language functions? Dichotic-listening studies have reported a left-ear/right-hemisphere advantage for speech sound reception in DS individuals (not found in control groups of NR subjects and MR subjects with other etiologies). However, DS subjects exhibit the expected right-ear/left-hemisphere superiority in speech production. Elliott et al. [188] have suggested that the language problems of DS persons may be related to a dissociation between the cerebral areas responsible for speech perception and production, causing diculties of communication between organic systems that normally overlap, and leaving speech reception under the control of the right hemisphere, which may not be best equipped to handle this function. The language-exceptional MR subjects for whom relevant data are available (i.e., Franc° oise and Curtiss and Yamada's Laura [173,174]) are both lefthemisphere-dominant for language functions (receptive and expressive). Rondal [37] reported corresponding data for 24 DS adults with typical language abilities for DS (15 males and 9 females, aged 21 to 36 years) in dichotic-listening and dual task studies. Many of these subjects demonstrated interference between

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Table 4 The Franc° oise (F.) case (summary of data) (French speaking) (1) (2) (3)

CA: F. was 32 years old at the beginning of the study. Delay in language development: F. had produced only one word at 4 years CA. Etiology: Down's syndrome (standard trisomy 21: genotype 47,XX, +free 21 in each of the metaphases studied).

(4)

IQ (WAIS)

Nonverbal

Verbal

Beginning of study End of study

60 64

71 70

(5) (6) (7) (8) (9)

(10) (11) (12) (13)

(14) (15)

(16) (17) (18) (19) (20)

MA: (EÂpreuves Di€eÂrentielles d'Ecience Intellectuelle Ð EDEI): Nonverbal: 5 years and 8 months; Nonverbal: 5 years and 8 months; Visual perception (Test of Poppelreuter's ``Figures EncheveÃtreÂes''): normal. Left-right discrimination (Head's Test): performance within normal limits. Visuospatial and computational abilities: markedly reduced (e.g., standard scores on the WAIS: cubes: 4; object assembly: 1; image completion: 4). Visuographic abilities (Rey's Complex Figure-copying from model; copying cube and houses in perspective; Bender-Gestalt Test): diculties with the macrostructure of the drawings; too much attention to irrelevant details; proceeds by copying and juxtaposing small parts of the model; unable to draw according to perspective; on the Bender-Gestalt test, F. scored at the median mark for 6-year-old children. Expressive gesturing (immediate imitation of ®nger and hand-sequential gestures, after Berges and Lezine's Test): F. scored within the 12-year-old range for most gestural sequences. Attention±concentration (Barrage subtest of the KLT Test): F. scored 22 (out of a possible 90 points); this places her in the lowest percentile of the NR adult population. Operational level (Piagetian): intermediate between late preoperatory and early operatory. Episodic memory (Paired-associate words; Rey's 15-Word Test; Buschke's Cued Recall and Selective Reminding Tasks; Rey's Complex Figures: drawing from memory (3 min after exposure) reduced in comparison to NR adults but satisfactory delayed recall of verbal material (up to 30 min) indicating correct trace consolidation; correct but impoverished delayed drawing. Semantic memory (Free association; Fluency tasks): F.'s associations are largely idiosyncratic and prevalently of the syntagmatic type; no evidence of prototypical organization of common semantic categories (e.g., animals, clothes, means of transportation, fruits, vegetables, etc.). Working memory (A) Auditory-verbal (AV-WM) span: 4 units (digits, words, and nonwords) (B) Visuospatial (VS-WM) span (Block-tapping Test): 4 units (surpassed by 92% of NR adults; compatible with NR children's level around 5 years old). (C) Visuospatial recognition (Delayed Recognition Span Test): span: 5.20 (average span of NR adults: 12.08). (D) Visual reproduction (Wechsler's Clinical Scale): score 4 (very low end of the NR adult distribution; NR population mean: 11.42, S.D: 2.76). (E) Basic functioning of phonological loop: demonstrated phonological similarity, word length, and articulatory suppression e€ects; spontaneous and active rehearsal (whispering and/or mezza voce). Sentence length: 14 words; at times, F. can correctly repeat sentences containing up to 20 words. L-max (free speech): 50 words. MLU (in number of words+in¯ectional morphemes): 12.24 (S.D.: 9.65). Sound perception and discrimination (ORL, examination): normal (no auditory loss). Articulatory ability (free speech; Borel-Maisonny's logatomes): normal.

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(21) Speech rate (free speech measurement): F.'s overt speech rate varies around 200 words per minute (i.e., approximately 3.3 words Ð 12 to 15 phonemes Ð per second); this is the speech rate for normal adults; regular DS adult subjects have overt speech rates varying from 37 to 71 words per minute (i.e., 1 word Ð 4 to 5 phonemes Ð per second or less). (22) Suprasegmental phonology (free speech): normal. (23) Lexical ability ± production, referential, comprehension, de®nition (Test de Vocabulaire Actif et Passif; Test des Relations Topologiques; Batterie de l'Aphasie de LieÁge; Lexical subtest of the EÂpreuves Di€eÂrentielles d'Ecience Intellectuelle; Boehm's Test of Basic Concepts; Vocabulary subtest of WAIS): productive and receptive levels compatible with nonverbal MA; on the WAIS lexical de®nition task, the score obtained is one standard deviation below the NR adult population mean. (24) Expressive morphosyntax (Free speech analyzed with reference to Halliday's Functional Grammar [186] adapted for French): virtually normal, witness the grammatically correct production of various grammatical types of sentences, including the most structurally complex ones, re¯exive constructions, and the correct use of the various obligatory in¯ectional morphemes. (25) Receptive morphosyntax (speci®c psycholinguistic tasks): virtually normal; e.g., correct comprehension of subject and object relatives, causal subordinates (with the subordinate clause either preceding or following the main clause), temporal subordinates (with the verbal order of events corresponding to the order of the events in reality or otherwise), declarative armative active and passive sentences ranging in plausibility and plausible reversibility, correct use of coreferential mechanism in the case of the anaphoric personal pronouns. (26) Pragmatic organization (Free speech): virtually normal conversational skills (e.g., turn-taking, topic distribution, topic continuity, conversational feedback and repairs); correctly formulated illocutionary speech acts; correct use of polite forms and indirect requests for action, information, and con®rmation. (27) Discourse organization (free speech): discourse organization (either narrative or descriptive) globally correct; occasional problems with textual cohesion; conjunctive forms such as and, then, but, although, thus, etc., tending to be used more as loose connectors than genuine markers of logical and/or informational dependencies between utterances, phrases or sentences. (28) Written language expression (free written texts; dictation): limited and deviant in several respects (e.g., punctuation marking, conventional orthography, narrative macrostructures, morphological in¯ections). (29) Reading and comprehension of written language (Borel-Maisonny's Logatomes and conventional words; school texts; Written Language Comprehension Task from Chevrie-MuÈller's EÂpreuve pour l'Examen du Langage): reading ability is well established although F. is very slow (which contrasts with her fully speed-appropriate oral verbal ability); written language comprehension is at third-grade level, but demonstrates lexical and conceptual limitations. (30) Metalinguistic abilities (A) Phonological awareness (10 subtests orally presented: selecting or producing rhymes, isolating initial or ®nal phonemes in target words, fusing phonemes into words, spelling words, etc.): F. is able to segment common French words into syllables (but very slowly and at times with some degree of overlap between neighboring syllables). She cannot regularly identify separate phonemes in words. (B) Sentence judgment and repair (for grammaticality and semantic acceptability): F. is able to detect and correct word order errors appearing in grammatically incorrect but semantically appropriate sentences. She is also able to detect and mend grammatically correct but semantically abnormal sentences. However, she cannot detect in¯ectional morphological mistakes. (C) Grammatical analysis (active declarative armative sentences presented in written form): F. can often identify main verbs (actional as well as nonactional) and grammatical subjects, direct objects, indirect objects, time circumstantial elements, and locative circumstantial elements (in asking the school-type questions: qui `who', quoi `what', a qui `to whom', a quoi `to what', quand `when' or ou `where'). She could perform the above analysis on monopropositional sentences only and, in some cases, on main clauses of complex sentences, leaving subordinate clauses unanalyzed. (continued on next page)

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Table 4 (continued). (31) Cerebral hemispheric specialization (A) Dichotic listening (directed attention procedure): REA (right-ear advantage) or LEA (left-ear advantage) calculated from the following formula computed for each ear: Dichotic-listening score ˆ …30-E1†  100=30 Where 30 is the number of syllables presented to each ear and E1 the number of intrusion errors. F.'s REA = 63%, suggesting LHD (left-hemisphere dominance) for speech reception. (B) Dual-task study (®nger-tapping task combined with sound-shadowing): Relative amount of interference averaged per second (RAI index) evaluated with a formula comparing experimental steps. F.'s RAI=+4.05, indicative of interference between verbalization and ®nger-tapping that is more marked for the right hand, suggesting LHD for speech production.

verbalization and right-handed movements compatible with the hypothesis of lefthemisphere dominance for speech production. In the dichotic-listening task, three females exhibited a right-ear advantage of from 30 to 70% (suggesting lefthemisphere dominance). Six males exhibited a right-ear advantage (from 10 to 63%). Retaining those individuals for whom the right-ear advantage was equal to or in excess of 50%, one had two female and one male individuals. These three subjects all demonstrated a positive relative amount of interference in the dual task (suggesting left-hemisphere dominance for speech production). They could be considered homogeneous as to cerebral hemispheric dominance for the speech functions. This is also the case for Franc° oise. However, the language abilities of the above three DS adults were only average for DS persons. Left-hemisphere dominance may be a necessary condition for advanced language development (other than with early focal brain lesions that necessitate a transfer of control over language to the right hemisphere at little or no functional cost [189], a situation Table 5 Claudine (C.): Study in progress (1) (2) (3) (4) (5) (6) (7) (8)

(9)

(10)

CA: C. was 27 years old at the beginning of the study. Etiology: Down's syndrome (standard trisomy 21). IQ (WAIS): nonverbal 57, verbal 61. MA (EDEI): nonverbal: 5 years and 4 months; verbal: 6 years and 3 months. Nonlanguage cognition: signi®cant weaknesses in spatial, numerical, and time cognition; preoperatory level on Piagetian measures. Working memory: AV-WM span: 4; V-VS-WM span: 4. Speech rate (articulation speed): below NR but > than typical DS individuals. Oral language production: Lexicon: EÂvaluation du Vocabulaire de Production 68%; not very di€erent from typical DS adults; MLU (words + in¯ection morphemes): 15.39; Grammatically correct expression of temporal, causal and relative subordinates in free speech; her speech on the whole is more paratactic than Franc° oise's. Written language: Correct writing and reading abilities, but very slow; Correct marking of subject-main verb or subject-auxiliary concord; correct use of the obligatory in¯ections on nouns, verbs, adjectives and pronouns. Metalinguistic ability: seemingly clear phonological awareness.

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that theoretically does not concern MR individuals as they are not supposed to present focal brain lesions as a result of their condition). It follows that lefthemisphere dominance cannot be a sucient condition for exceptional language development in MR people. 3.3. Nonlinguistic cognitive factors? Most language-exceptional MR individuals studied have MAs of around 5 years. It could be argued that they are `simply' demonstrating language skills corresponding to their cognitive level [190,191]. Bates [190] maintains that, in NR children, basic grammatical development is complete by 4 to 5 years of age (or even before). Therefore, she claims, one should expect MR individuals with MAs of 4 or 5 years to exhibit well-developed formal language abilities. However, if general cognition at 4 to 5 years MA were a sucient condition for explaining advanced formal language abilities, typical MR subjects with such MAs (and there are many) should also exhibit well-developed morphosyntactic skills. But they do not. Typical MR subjects' grammatical development remains largely incomplete, often despite systematic language intervention. Alternatively, if one does not accept the idea that grammatical development is complete by 4 to 5 years of age but insists instead that it goes on until 9 or 10 years for some structures, then the levels reached by the exceptional MR individuals cannot be explained solely by general cognitive variables. Indeed, these individuals exhibit grammatical levels far beyond what could be considered to be normal at around 4 or 5 years MA in this alternative hypothesis. The general cognition hypothesis is contradicted by the data either from the typical MR subjects or from the language-exceptional MR individuals, depending on when one believes grammatical development is complete in NR children. In our opinion, the language-exceptional MR individuals have more to rely on than a cognitive level of 4 to 5 years MA. They have at their disposal a language-speci®c (grammatical) ability that has been spared in spite of their pathology. This ability is also available to young NR children (around 20 to 24 months) when they start developing grammar. It is largely lacking in typical MR individuals. All typical moderately and severely MR individuals reach and go beyond 2 years MA but, as mentioned before, they fall short of developing full grammar. Early cognitive development may supply the necessary basis for grammatical development, but it is not sucient. Also needed are speci®c devices responsible for grammatical operations. The grammatical ability referred to above does not have to be innate in the representational sense out of any logical or biological necessity. It implies, however, the existence of innate architectural constraints (to employ Elman et al.'s [192] terminology), i.e., a largely innate processing organization dealing with linguistic, and particularly grammatical and phonological representations. Karmilo€-Smith et al. [193] suggest that there are domain-speci®c predispositions for analyzing language stimuli which, with language experience, become increasingly specialized and interconnected. As normal development proceeds, a

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modular-like organization takes place (weaker than the Fodorian model [194]). The former types of modules can be said to be more made than born [195]. But judging from the vantage point of the MR literature, fully ecient language modularization, to continue with Karmilo€-Smith's terminology, does not occur in typical MR subjects despite some cognitive, lexical and pragmatic acquisitions. This again suggests that something else is needed to bring about the modularization process that may be characteristic of advanced language functioning. Early cognitive functioning is probably needed to trigger or, at least, set the stage for morphosyntactic development. Supportive evidence is found in exceptional MR cases. Franc° oise, as well as Christopher (O'Connor and Hermelin's [182] subject), Laura (Curtiss and Yamada's [173,174] subject) and FF (Vallar and Papagno's [184] subject) Ð i.e., those language-exceptional individuals for whom developmental histories are available Ð were markedly delayed in language onset. Franc° oise produced only one word (/to/ for couteau, i.e., `knife' in French) at 4 years CA Ð even worse than many typical DS children at the same age. She developed her formal language abilities between approximately 5 and 10 years of age. WS children are severely delayed in early language development. It is only when they have a vocabulary size and general cognitive level comparable to those of NR 2-year-olds that their grammar `gets o€ the ground'. The above indications suggest that a cognitive-semantic basis amounting to what exists in moderately and severely MR children around 5 years CA and in NR children around 20 months is needed for the grammatical component to start working, when such a component is indeed functional. 3.4. What about WM in relation to exceptional language development in MR individuals? Franc° oise, Claudine, and FF demonstrated an AV-WM span of 4 digits and more. Their spans certainly were lower at the time of their language development. Vallar and Papagno [184] proposed that FF's AV-WM explains her better formal language abilities. This suggestion is not convincing. However, a positive contribution by AV-WM, due to a better functioning of the phonological loop, cannot be ruled out in language-exceptional MR subjects. Franc° oise, Claudine and FF exhibit normal-like WM processes when recalling verbal material. They rely on rehearsal strategies based on semiprivate speech. Their speech rate is normal or close to normal, in contrast to that of typical DS subjects [37]. However, it may be argued that such a contribution by AV-WM in the languageexceptional cases is limited. As indicated above, Franc° oise's AV-WM span is 4. Her sentence length is 14 words. She is able to correctly repeat sentences containing up to 20 words. This is normal functioning according to data reported by Butterworth et al. [196]. In repetition tasks, Franc° oise made few word order errors on sentences containing more than 14 words. Most of her errors were omissions and (trivial) word substitutions. These were also the typical errors Butterworth et al.'s university students made when requested to recall sentences

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15±20 words long. Franc° oise's immediate recall performance contrasts sharply with that of typical DS subjects [37]. The latter individuals cannot correctly repeat sentences containing more than 7 or 8 words at most. They frequently omit major sentence constituents. Furthermore, with regard to sentence structure, Franc° oise has no diculty correctly interpreting (center-) embedded subject and object relatives when the relative pronouns and their coreferring nouns are separated by several words. Neither does she experience particular problems when requested to establish pronominal coreference across sentences in paragraphs with pronouns and coreferring nouns separated by up to 8 words. It is reasonable to conclude that the contribution of Franc° oise's immediate phonological memory to sentence production and comprehension is limited. 3.5. Brain-level variation? Rondal [187] has suggested that the major determinant of the morphosyntactic and phonological di€erences observed between typical and exceptional MR subjects operates at brain level. The macroscopic brain structures devoted to the formal aspects of language are probably spared to a large extent in those MR individuals with exceptional language abilities. These structures are damaged and only poorly operational in regular MR subjects. Correctly organized brain macrostructures owe much to the interplay of what Elman et al. [192] label `chronotopic constraints'. This includes constraints on the number of cell divisions taking place during neurogenesis, relative di€erences in timing between brain subsystems, and di€erences in synaptic growth according to brain area and function. Rondal's [187] suggestion is that language-exceptional and typical MR subjects di€er markedly in the architectural and chronotopic characteristics of brain development. As indicated, studies of the brains of MR persons reveal major anomalies. The language-exceptional subjects escape this fate for reasons that may be related to the phenotypic e€ects of genetic variation. Geneticists agree that there is substantial variation at the genetic level between people within genotypic categories such as DS, WS, FXS, PWS and other genetic causes of mental retardation. Most genetic in¯uences on phenotypes are not discrete but polygenic. As a consequence, complex phenotypic traits show a quantitative variation. Many disorders are the result of multiple genes located on one or more chromosomes. The interaction of these genes determines the expression and extent of the abnormality [89]. Other sources of genetic variation include variable penetrance of the gene(s), imprinting e€ects, and the many possible mutations (alleles) that major genes may have [197]. Genetic research is yielding more precise gene identi®cation and phenotypic mapping of chromosome 21. Korenberg et al. [198] have suggested that DS is a contiguous gene syndrome. This argues against a single DS chromosomal region responsible for the DS phenotypic features. DS and its phenotypes are thought as the result of the overexpression and subsequent interactions of a subset of the estimated 1000 to 1700 genes located on chromosome 21. Korenberg et al. [198] have constructed a phenotypic map including 25 features considered typical of

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DS. They assign a region of 2 to 20 megabases between regions q11.2 and 22.3 on chromosome 21 as likely to contain the genes responsible for the DS phenotypes. This conception of the genotype±phenotype relationship in DS is consistent with the central characteristics of T21, such as the rich variety of phenotypes and the variability in both penetrance and expression of the phenotypic features. It is conceivable that there is signi®cant within-syndrome variability at brain level in the language areas of DS persons, consequent upon genetic variation. One might suggest, with all due caution regarding linkage analysis with complex behavioral traits in addition to current phenotype/genotype analysis of DS, that there is a small region in chromosome 21 the triplication, deletion, or other modi®cation of which is related to structural abnormalities of the brain in the area responsible for the formal (particularly morphosyntactic) aspects of language. The brain-gene perspective de®ned herein has the advantage of proposing a single type of explanation for the variability observed in the language of typical MR people and the extremes of such variability in the language-exceptional cases. It can also be applied to behavioral and brain di€erences across the genetic syndromes that lead to mental retardation. The preceding analyses support the belief that considerable insight into genetic dysphasias and some of the mechanisms responsible for language development may be gained from additional interaction between the language sciences, the brain sciences, and the genetic sciences. Regarding language and genetic sciences, this interaction is long overdue and should be encouraged, as advocated by Shprintzen [199].

References [1] Aguado G, Narbona J. Lenguaje y de®ciencia mental. In: Narbona J, Chevrie-MuÈller C, editors. El lenguaje del ninÄo. Desarollo normal, evaluacioÂn y trastornos. Barcelona: Masson, 1997. [2] Lejeune J, Gautier M, Turpin R. Les chromosomes humains en culture de tissus. Comptes Rendus de l'AcadeÂmie des Sciences 1959;248:602±3. [3] Lejeune J, Gautier M, Turpin R. EÂtude des chromosomes somatiques de neuf enfants mongoliens. CR AcadeÂmie Scienti®que (Paris) 1959;248:1721±2. [4] Clarke AM, Clarke AD, Berg J. Mental de®ciency: the changing outlook. London: Methuen, 1985. [5] Dolk H, De Wals P, Gillerot Y, Lechat M, Ayme S, Beckers R, Bianchi F, BorleÂe I, Calabor A, Calzolari E, Cuschieri A, Galanti C, Goujard J, Hansen-Koening D, Harris F, Kargut G, Lillis D, Lungarotti M, Lye F, Marchi M, Nervin N, Radie A, Stool C, Syone D, Svel I, Ten Kate L, Zori R. The prevalence at birth of Down's syndrome in 19 regions of Europe 1980±86. In: Fraser W, editor. Key issues in mental retardation research. London: Routledge, 1990. [6] Rondal JA, Edwards S. Language in mental retardation. London: Whurr, 1997. [7] Fishler K, Koch R. Mental development in Down syndrome mosaicism. American Journal on Mental Retardation 1991;96:345±51. [8] Jones O. Mother±child communication with prelinguistic Down's syndrome and normal infants. In: Scha€er H, editor. Studies in mother±infant interaction. New York: Academic Press, 1977. [9] Smith BL, Oller K. A comparative study of premeaningful vocalizations produced by normally developing and Down's syndrome infants. Journal of Speech and Hearing Disorders 1981;46:46± 51.

J.-A. Rondal, A. Comblain / Journal of Neurolinguistics 12 (1999) 181±212

205

[10] Lynch M, Eilers R. Perspectives on early language from typical development and Down syndrome. In: Bray N, editor. International review of research in mental retardation. New York: Academic Press, 1991. [11] Mundy P, Kasari C, Sigmen M, Ruskin E. Nonverbal communication and early language acquisition in children with Down syndrome and in normally developing children. Journal of Speech and Hearing Research 1995;38:157±67. [12] Rast M, Harris S. Motor control in infants with Down syndrome. Developmental Medicine and Child Neurology 1985;27:675±85. [13] Wishart J. Early learning in infants and young children with Down syndrome. In: Nadel L, editor. The psychobiology of Down syndrome. Cambridge, MA: MIT Press, 1988. [14] Bruner JS. From communication to language: a psychological perspective. Cognition 1975;3:256± 87. [15] Gunn P, Berry P, Andrews R. Looking behavior of Down's syndrome infants. American Journal of Mental De®ciency 1982;87:344±7. [16] Gutman A, Rondal JA. Verbal operants in mother's speech to nonretarded and Down's syndrome children matched for linguistic level. American Journal of Mental De®ciency 1979;83:446± 52. [17] Mahoney G, Glover A, Finger I. Relationship between language and sensorimotor development in Down syndrome and nonretarded children. American Journal of Mental De®ciency 1981;86:21±7. [18] Rondal JA. Verbal imitation by Down syndrome and nonretarded children. American Journal of Mental De®ciency 1980;85:318±21. [19] Rondal JA, Lambert JL, Sohier C. Elicited verbal and nonverbal imitation in Down syndrome and other mentally retarded children: a replication and extension of Berry. Language and Speech 1981;24:245±54. [20] Sokolov J. Linguistic imitation in children with Down syndrome. American Journal on Mental Retardation 1992;97:209±21. [21] Miller J. Pro®les of language development in children with Down syndrome. In: Improving the communication of people with Down syndrome. Baltimore, MD: Brookes, 1999. [22] Rondal JA. Adult±child interaction and the process of language acquisition. New York: Praeger, 1985. [23] Rondal JA, Comblain A. Language in adults with Down syndrome. Down Syndrome 1996;4:3± 14. [24] Rondal JA. Maternal speech to normal and Down's syndrome children matched for mean length of utterance. In: Meyers C, editor. Quality of life in severely and profoundly retarded people: research foundations for improvement. Washington, DC: American Association on Mental De®ciency, 1978. [25] Bartel N, Bryen S, Keehn S. Language comprehension in the moderately retarded child. Exceptional Children 1973;39:375±82. [26] Rosenberg S, Abbeduto L. Language and Communication in Mental Retardation. Development, Processes, and Intervention. Hillsdale, NJ: Lawrence Erlbaum Associates, 1993. [27] Greenwald C, Leonard L. Communicative and sensorimotor development of Down's syndrome children. American Journal of Mental De®ciency 1979;84:296±303. [28] Coggins T, Carpenter R, Owings N. Examining early intentional communication in Down's syndrome and nonretarded children. British Journal of Disorders of Communication 1983;18:99± 107. [29] Owens R, MacDonald J. Communicative uses of the early speech of nondelayed and Down syndrome children. American Journal of Mental De®ciency 1982;86:503±10. [30] Caplan D. Language: Structure, Processing and Disorders. Cambridge, MA: MIT Press, 1993. [31] Faust M. Obtaining evidence of language comprehension from sentence priming. In: Beelman M, Charells C, editors. Right-hemisphere language comprehension. Mahwah, NJ: Lawrence Erlbaum Associates, 1998. [32] Hedrick D, Prather E, Tobin A. Sequenced inventory of communicative development. Seattle, WA: University of Washington Press, 1984.

206

J.-A. Rondal, A. Comblain / Journal of Neurolinguistics 12 (1999) 181±212

[33] Miller J, Chapman R, Branston M, Reichle J. Language comprehension in sensorimotor stages 5 and 6. Journal of Speech and Hearing Research 1980;23:284±311. [34] Carrow-Woolfolk E. Test for auditory comprehension of language-revised (TACL-R). Chicago: Riverside, 1985. [35] Miller J, Chapman R. The relation between age and mean length of utterances in morphemes. Journal of Speech and Hearing Research 1981;24:154±61. [36] Miller J, Chapman R. SALT: systematic analysis of language transcripts. Madison, WI: University of Wisconsin, The Waisman Center, 1993. [37] Rondal JA. Exceptional language development in Down syndrome: implications for the cognition-language relationship. Cambridge: Cambridge University Press, 1995. [38] Yoder D, Miller J. What we may know and what we can do: input towards a system. In: McLean J, Yoder D, Schiefelbusch R, editors. Language intervention with the retarded: developing strategies. Baltimore, MD: University Park Press, 1972. [39] Rondal JA. Linguistic and prelinguistic development in moderate and severe mental retardation. In: Dobbing J, Clarke A, Corbett J, Hogg J, Robinson R, editors. Scienti®c studies in mental retardation. London: The Royal Society of Medicine and MacMillan, 1984. [40] Rondal JA. Language development and retardation. In: Yule W, Rutter M, editors. Language development and disorders. Oxford: Blackwell, 1987. [41] Lenneberg EH. Biological foundations of language. New York: John Wiley and Sons, 1967. [42] Lenneberg E, Nichols I, Rosenberger E. Primitive stages of language development in mongolism. In: McRisch D, Weinstein E, editors. Disorders of communication, 17. Baltimore: Williams and Wilkins, 1964. [43] Curtiss S. Genie: a psycholinguistic study of a modern-day `wild child'. New York: Academic Press, 1977. [44] Curtiss S. The special talent of grammar acquisition. In: Obler L, Fein D, editors. The exceptional brain. New York: Guilford, 1988. [45] Semmel E, Wiig E. Clinical evaluation of language functions. Columbus, OH: Merrill, 1980. [46] Mayberry R, Fisher S, Hat®eld N. Sentence repetition in American sign language. In: Kyle J, Woll B, editors. Language in sign: international perspective on sign language. London: Croom Helm, 1983. [47] Newport E. Maturational constraints on language learning. Cognitive Science 1990;14:11±28. [48] Newport E. Contrasting conception of the critical period for language. In: Carey S, Gelman R, editors. The epigenesis of mind: essays on biology and cognition. Hillsdale, NJ: Lawrence Erlbaum Associates, 1992. [49] Menyuk P. Language and maturation. Cambridge, MA: MIT Press, 1977. [50] Hurford J. The evolution of the critical period for language acquisition. Cognition 1991;40:159± 201. [51] Berry P, Groenweg G, Gibson D, Brown R. Mental development of adults with Down syndrome. American Journal of Mental De®ciency 1984;89:252±6. [52] Fisher M, Zeaman D. Growth and decline in retardate intelligence. In: Ellis N, editor. International review of research in mental retardation, 4. New York: Academic Press, 1970. [53] Baddeley A. Working memory. Oxford: Oxford University Press, 1986. [54] Baddeley A. Human memory: theory and practice. Hove: Erlbaum Psychology Press, 1990. [55] Baddeley A. Working memory. Science 1992;255:556±9. [56] Baddeley A. The concept of working memory. In: Gathercole SE, editor. Models of short-term memory. Hove: Erlbaum Psychology Press, 1996. [57] Bilovsky D, Share J. The Illinois test of psycholinguistic ability and Down's syndrome: an exploratory study. American Journal of Mental De®ciency 1965;70:78±82. [58] Comblain A. Working memory in Down's syndrome: training the rehearsal strategy. Down's syndrome 1994;2:123±6. [59] Comblain A. MeÂmoire de travail et langage dans le syndrome de Down. Unpublished doctoral thesis, University of LieÁge, Laboratory of Psycholinguistics, LieÁge, 1996. [60] Comblain A. Le fonctionnement de la meÂmoire aÁ court-terme auditivo-vocale dans le syndrome

J.-A. Rondal, A. Comblain / Journal of Neurolinguistics 12 (1999) 181±212

[61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84]

207

de Down: implications pour le modeÁle de meÂmoire de travail. Approches Neuropsychologiques des Apprentissages de l'Enfant (ANAE) 1996;39/40:137±47. Marcell MM, Armstrong V. Auditory and visual sequential memory of Down's syndrome and nonretarded children. American Journal of Mental De®ciency 1982;87:86±95. Mackenzie S, Hulme C. Memory span development in Down's syndrome, severely subnormal and normal subjects. Cognitive Neuropsychology 1987;4:303±19. Hulme C, Mackenzie S. Working memory and severe learning diculties. Hove: Lawrence Erlbaum, 1992. Broadley I, MacDonald J, Buckley S. Working memory in children with Down's syndrome. Down's Syndrome 1995;3:3±8. Broadley I, MacDonald J, Buckley S. Are children with Down's syndrome able to maintain skills learned from short-term memory training programme? Down's Syndrome 1994;2:116±22. Baddeley A, Papagno C, Vallar G. When long-term learning depends on short-term storage. Journal of Memory and Language 1988;27:586±95. Cheung H. Nonword span as a unique predictor of second-language vocabulary learning. Developmental Psychology 1996;32:867±73. Service E. Phonology, working memory and foreign-language learning. Quarterly Journal of Experimental Psychology 1992;45A:21±50. Service E, Kohonen V. Is the relationship between phonological memory and foreign language learning accounted for by vocabulary acquisition? Applied Psycholinguistics 1995;16:155±72. Gathercole S, Baddeley A. The role of phonological memory in vocabulary acquisition: a study of young children learning new names. British Journal of Psychology 1990;81:439±54. Gathercole SE, Baddeley AD. Phonological memory de®cits in language disordered children: is there a causal connection? Journal of Memory and Language 1990;29:336±60. Gathercole SE, Baddeley AD. Working memory and language. Hillsdale, NJ: Lawrence Erlbaum Associates, 1993. Jarrold C, Baddeley A. Short-term memory for verbal and visuospatial information in Down's syndrome. Cognitive Neuropsychiatry 1997;2:101±22. Beuren A. Supravalvular aortic stenosis: a complex syndrome with and without mental retardation. Birth Defects 1972;8:45±6. Galaburda A, Wang P, Bellugi U, Rossen M. Cytoarchitectonic anomalies in a genetically based disorder: Williams syndrome. Cognitive Neuroscience and Neuropsychology 1994;5:753±7. Bellugi U, Bihrle A, Jernigan T, Trauner D, Doherty S. Neuropsychological, neurological and neuroanatomical pro®le of Williams syndrome. American Journal of Medical Genetics Supplement 1990;6:115±25. Tyler L, Karmilo€-Smith A, Voice J, Steven J, Grant J, Udwin O, Davies M, Howlin P. Do individuals with Williams syndrome have bizarre semantics? Evidence from lexical organization using an on-line task. Cortex 1997;33:515±27. Pinker S. The language instinct. New York: Morton, 1994. Karmilo€-Smith A, Grant J, Berthoud I, Davies M, Howlin P, Udwin O. Language and Williams syndrome: how intact is intact? Child Development 1997;68:274±90. Karmilo€-Smith A, Tyler L, Voice K, Sims K, Udwin O, Howlin P, Davies M. Linguistic dissociations in Williams syndrome: evaluating receptive syntax in on-line and o€-line tasks. Neuropsychologia 1998;36:343±51. Wang PP, Bellugi U. Evidence from two genetic syndromes for a dissociation between verbal and visual-spatial short-term memory. Journal of Clinical and Experimental Neuropsychology 1994;16:317±22. Crisco J, Dobbs J, Mulhern R. Cognitive processing of children with Williams syndrome. Developmental Medicine and Child Neurology 1988;30:650±6. Vicari S, Carlesimo G, Brizzolara D, Pezzini G. Short-term memory in children with Williams syndrome: a reduced contribution of lexical-semantic knowledge to word span. Neuropsychologia 1996;34:919±25. Gosch A, StaÈding G, Pankau R. Linguistic abilities in children with William±Beuren syndrome. American Journal of Medical Genetics 1994;52:291±6.

208

J.-A. Rondal, A. Comblain / Journal of Neurolinguistics 12 (1999) 181±212

[85] Udwin O, Yule W. Expressive language in children with Williams syndrome. American Journal of Medical Genetics, Supplement 1990;6:108±14. [86] Grant J, Karmilo€-Smith A, Berthoud I, Christophe A. Is the language of people with Williams syndrome mere mimicry? Phonological short-term memory in a foreign language. Cahiers de Psychologie Cognitive 1996;15:615±28. [87] Lubs H. A marker X chromosome. American Journal of Human Genetics 1969;21:231±44. [88] Mulley J, Kerr B, Stevenson R, Lubs H. Nomenclature guidelines for X-linked mental retardation. American Journal of Medical Genetics 1992;43:383±91. [89] Phelps L, editor. A guidebook for understanding and educating health-related disorders in children and adolescents. A compilation of 96 rare and common disorders. Washington, DC: American Psychological Association, 1998. [90] Maes B, Fryns JP, van Walleghem M, van den Berghe H. Cognitive functioning and information processing of adult mentally retarded with Fragile-X syndrome. American Journal of Medical Genetics 1994;50:190±200. [91] Webb T, Bundey S, Thake A, Todd J. Population incidence and segregation ratios in Martin± Bell syndrome. American Journal of Medical Genetics 1986;23:573±80. [92] Dykens E, Hodapp R, Leckerman J. Behavior and development in Fragile-X syndrome. London: Sage Publications, 1994. [93] Newell K, Sanborn B, Hagerman R. Speech and language dysfunction in the Fragile-X syndrome. In: Hagerman R, McBogg P, editors. The Fragile-X syndrome: diagnosis, biochemistry and intervention. Dillon, CA: Spectra, 1983. [94] Borgraef M, Fryns J-P, Dielkens A, Pyck K, Van den Berghe H. Fragile-X syndrome: A study of psychological pro®le in 23 prepubertal patients. Clinical Genetics 1987;32:179±86. [95] GeÂrard C-L, Guillotte E, Servel E, Barbeau M. EÂvaluation et reÂeÂducation des troubles de la communication chez les enfants porteurs du syndrome de l'X Fragile. Approches Neuropsychologiques des Apprentissages de l'Enfant (ANAE) 1997;45:224±6. [96] Vilkman E, Niemi J, Ikonen U. Fragile-X speech phonology in Finnish. Brain and Language 1988;34:203±21. [97] Sudhalter V, Scarborough H, Cohen I. Syntactic delay and pragmatic deviance in language of males with Fragile-X syndrome. American Journal of Medical Genetics 1991;43:65±71. [98] Madison L, George C, Moeschler J. Cognitive functioning in the Fragile-X syndrome: a study of intellectual, memory and communication skills. Journal of Mental De®ciency Research 1986;30:129±48. [99] Dykens EM, Hodapp RM, Leckerman JF. Strengths and weaknesses in the intellectual functioning of males with Fragile-X syndrome. American Journal of Medical Genetics 1987;28:13±5. [100] Freund LS, Reiss AL. Cognitive pro®les associated with the fra(X) syndrome in males and females. American Journal of Medical Genetics 1991;38:542±7. [101] German J, Lejeune J, McIntyre M, de Grouchy J. Chromosomal autoradiography in the Cri-duchat syndrome. Cytogenetics 1964;3:347±52. [102] Lejeune J, Lafoucarde J, Berger R, Vialatte J, Boeswillwald M, Seringe P, Turpin R. Trois cas de deÂleÂtion partielle du bras court du chromosome 5. Comptes Rendus Hebdomadaires des SeÂances de l'AcadeÂmie des Sciences de Paris 1963;257:3098±102. [103] Niebuhr E. The Cri-du-chat syndrome. Human Genetics 1978;42:143±56. [104] Gersch M, Goodart S, Paszter L, Harris D, Weiss L, Overhauser J. Evidence for a distinct region causing a cat-like cry in patients with 5p deletions. American Journal of Human Genetics 1995;56:1404±10. [105] Overhauser J, Huang X, Gersch M, Wilson W, McMahon J, Bengtsson U, Rojas K, Meyer M, Wasmuth J. Molecular and phenotypic mapping of the short arm of chromosome 5: sublocalization of the critical region for the Cri-du-chat syndrome. Human Molecular Genetics 1994;34:247± 52. [106] Pueschel S, Thuline H. Chromosome disorders. In: Matson J, Mulick J, editors. Handbook of mental retardation. Elmsford, NY: Pergamon, 1991. [107] Wilkins L, Brown J, Wolf B. Psychomotor development in 65 home-reared children with Cri-duchat syndrome. Journal of Pediatrics 1981;97:401±5.

J.-A. Rondal, A. Comblain / Journal of Neurolinguistics 12 (1999) 181±212

209

[108] Carlin M. Longitudinal data shows improved prognosis in Cri-du-chat syndrome. American Journal of Human Genetics 1988;41:A50. [109] Carlin M. The improved prognosis in Cri-du-chat (5p-) syndrome. In: Fraser W, editor. Key Issues in Mental Retardation Research. London: Routledge, 1988. [110] Wilkins L, Brown J, Nance W, Wolf B. Clinical heterogeneity in 86 home-reared children with the Cri-du-chat syndrome. Journal of Pediatrics 1982;102:528±33. [111] Angelman H. Puppet children: a report on three cases. Developmental Medicine and Child Neurology 1965;7:681±8. [112] Wiedemann H, Kunze J, Grosse I. Clinical syndromes. London: Mosby, 1997. [113] Christian S, Robinson W, Huang B, Mutirangrera A, Liuc M, Nakao M, Surti U, Chakravati A, Ledbetter D. Molecular characterization of two proximal deletion breakpoint regions in both Prader±Willi and Angelman syndrome patients. American Journal of Human Genetics 1995;57:40±8. [114] Nelen M, Van der Burgt C, Nillesen W, Vis A, Smeets H. Familial Angelman syndrome with a crossover in the critical deletion region. American Journal of Medical Genetics 1994;52:352±7. [115] Penner K, Johnston J, Faircloth B, Irish P, Williams C. Communication, cognition and social interaction in Angelman syndrome. American Journal of Medical Genetics 1993;46:34±9. [116] Jolle€ N, Ryan M. Communication development in Angelman's syndrome. Archives of Diseases in Childhood 1993;69:148±50. [117] Summers J, Allison D, Lynch P, Sandler L. Behaviour problems in Angelman syndrome. Journal of Intellectual Disability Research 1995;39:97±106. [118] Cole W, Myers N. Neuro®bromatosis in childhood. Australian and New Zealand Journal of Surgery 1978;48:306±65. [119] Stumpof D, Alkesne J, Amiegers J. Neuro®bromatosis conference statement. Archives of Neurology 1988;45:575±8. [120] Dilts C, Carey J, Kircher J, Ho€man R, Creel D, Ward K, Clark E, Leonard C. Children and adolescents with neuro®bromatosis 1: a behavioral phenotype. Developmental and Behavioral Pediatrics 1996;17:229±39. [121] Elridge R, Denchla M, Bien E. Neuro®bromatosis type 1 (Recklinghausen's disease): neurological and cognitive assessment with sibling controls. American Journal of Childhood Disabilities 1989;143:833±7. [122] Balestri P, Lucignani G, Fois A, Magliani L. Cerebral glucose metabolism in neuro®bromatosis type 1. Journal of Neurology, Neurosurgery and Psychiatry 1994;57:1479±83. [123] Moore B, Ater J, Needle M, Slopis J, Copeland D. Neuropsychological pro®le of children with neuro®bromatosis. Journal of Child Neurology 1994;9:368±77. [124] Saint-Arroman F, Alozy C. Neuro®bromatoses, troubles cognitifs et prise en charge orthophonique. In: Proceedings of Les entretiens de Bichat d'Orthophonie. Paris: Expansion Scienti®que Franc° aise, 1998. [125] Zoeler M-E, Rembeck B, Baeckman L. Neuropsychological de®cits in adults with neuro®bromatosis type 1. Acta Neurologica Scandinavia 1997;95:225±32. [126] Bawden H, Dolley J, Buckley D, Cam®eld P. MRI and nonverbal cognitive de®cits in children with neuro®bromatosis 1. Journal of Clinical and Experimental Neuropsychology 1996;18:784± 92. [127] Klinefelter H, Reifenstein E, Albright F. A syndrome characterized by gynecomastia, aspermatogenes without A-Leydigism and increased excretion of follicle stimulating hormone. Journal of Clinical Endocrinology and Metabolism 1942;2:615±27. [128] Mandoki M, Summer G, Ho€man R, Riconda D. A review of Klinefelter's syndrome in children and adolescents. Journal of American Academy of Child and Adolescent Psychiatry 1991;30:167± 72. [129] Walzer S, Bashir A, Silber A. Cognitive and behavioral factors in the learning disabilities of 47,XXY and 47,XYY boys. Birth Defects 1991;26:45±58. [130] Turner H. A syndrome of infantilism, congenital webbed neck and cubitus valgus. Endocrinology 1938;23:566±74. [131] Ginther D, Fullwood H. Turner's syndrome. In: Phelps L, editor. A Guidebook for understand-

210

[132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155]

J.-A. Rondal, A. Comblain / Journal of Neurolinguistics 12 (1999) 181±212 ing and educating health-related disorders in children and adolescents. A compilation of 96 rare and common disorders. Washington, DC: American Psychological Association, 1998. Temple C, Carney R. Patterns of spatial functioning in Turner's syndrome. Cortex 1995;31:109± 18. Alexander D, Moneyt J. Reading ability, object constancy and Turner's syndrome. Perceptual and Motor Skills 1965;20:981±4. Murphy D, Allen G, Haxby J, Largay K. The e€ects of sex steroids and the X chromosome on female brain function: a study of the neuropsychology of adult Turner syndrome. Neuropsychologia 1994;32:1309±23. Pennington B, Bender B, Puck M, Salbenblatt J, Robinson A. Learning disabilities in children with sex chromosome anomalies. Child Development 1982;54:1182±92. Elliott T, Watkins J, Messa C, Lippe B, Chugani H. Positron emission tomography and neuropsychological correlation in children with Turner's syndrome. Developmental Neuropsychology 1996;12:365±86. Murphy D, DeCarli C, Daly E, Haxby J, Allen G, White B, McIntosh A, Powel C, Horwitz B, Rapoport S, Schapiro M. X-Chromosome e€ects on the female brain: a magnetic resonance imaging study of Turner's syndrome. The Lancet 1993;342:1197±200. Clark C, Klono€ H, Hayden M. Regional cerebral glucose metabolism in Turner syndrome. Canadian Journal of Neurological Sciences 1990;17:140±4. Rovet J, Netley C. Processing de®cit in Turner's syndrome. Developmental Psychology 1982;18:77±94. Buchanan L, Pavlovic J, Rovet J. A reexamination of the visuospatial de®cit in Turner syndrome: contributions of working memory. Developmental Neuropsychology 1998;14:341±67. Buchanan L, Pavlovic J, Rovet J. The contribution of visuospatial working memory to impairments in facial processing and arithmetic in Turner syndrome. Brain and Cognition 1998;37:72±5. Rovet J, Szekely C, Hockenberry M. Speci®c arithmetic de®cits in children with Turner syndrome. Journal of Clinical and Experimental Neuropsychology 1994;16:820±39. Greenswag L, Alexander R, editors. Management of Prader±Willi syndrome. New York: Springer, 1995. Daniel L, Gridley B. Prader±Willi syndrome. In: Phelps L, editor. A guidebook for understanding and educating health-related disorders in children and adolescents. A compilation of 96 rare and common disorders. Washington, DC: American Psychological Association, 1998. Butler M, Meaney F, Palmer C. Clinical and cytogenetic survey of 39 individuals with Prader± Willi syndrome. American Journal of Medical Genetics 1986;23:793±809. Trent R, Valpato F, Smith A, Lindeman R, Wang M, Warue G, Haan E. Molecular and cytogenetic studies of the Prader±Willi syndrome. Journal of Medical Genetics 1991;28:649±54. Nicholls R, Knoll J, Buther M, Karam S, Lalander M. Genetic imprinting suggested by maternal heterodisomy in nondeletion Prader±Willi syndrome. Nature 1989;342:281±5. Dykens EM, Hodapp RM, Walsh K, Nash L. Adaptive and maladaptive behavior in Prader± Willi syndrome. Journal of the American Academy of Child and Adolescent Psychiatry 1992;31:1131±6. Edmonston N. Management of speech and language impairment in a case of Prader±Willi syndrome. Language, Speech and Hearing Services in Schools 1982;13:241±5. Kleppe S, Katayama K, Shipley K, Fausher D. The speech and language characteristics of children with Prader±Willi syndrome. Journal of Speech and Hearing Disorders 1990;55:300±9. Akefeldt A, Akefeldt B, Gillberg C. Voice, speech and language characteristics of children with Prader±Willi syndrome. Journal of Intellectual Disability Research 1997;41:302±11. Hagberg B, editor. Rett syndrome: clinical and biological aspects. London: MacKeith, 1993. Perry A. Rett syndrome: a comprehensive review of the literature. American Journal of Mental Retardation 1991;96:275±90. Kerr A, Corbitt J. Rett syndrome: from gene to gesture. Journal of the Royal Society of Medicine 1994;87:562±6. Witt-Engerstrom I. Rett syndrome: a retrospective pilot study on potential early predictive symptomatology. Brain and Development 1987;9:481±6.

J.-A. Rondal, A. Comblain / Journal of Neurolinguistics 12 (1999) 181±212

211

[156] Kerr A, Montague J, Mills B, Ther D, Stephenson J. The hands and the mind, pre and postregression in Rett syndrome. Brain and Development 1987;9:487±90. [157] Von Tetzchner S. Communication skills among females with Rett syndrome. European Child and Adolescent Psychiatry 1997;6:33±7. [158] Coleman M, Brudbaker J, Hunter K, Smith G. Rett syndrome: a survey of North American patients. Journal of Mental De®ciency Research 1988;32:117±24. [159] Naidu S, Murphy M, Moser H, Rett A. Natural history in 2 cases. American Journal of Medical Genetics 1986;24:61±72. [160] Gillberg C. Communication in Rett syndrome complex. European Child and Adolescent Psychiatry 1997;6:21±2. [161] Zapella M. The preserved speech variant of the Rett complex: a report of 8 cases. European Child and Adolescent Psychiatry 1997;6:23±5. [162] Ross M, Galaburda A, Kemper T. Down's syndrome: is there a decreased population of neurons? Neurology 1984;34:909±16. [163] Wisniewski K. Down syndrome children often have brains with maturation delay, retardation of growth and cortical dysgenesis. American Journal of Medical Genetics, Supplement 1990;7:274± 81. [164] Wisniewski K, Kida E, Brown W. Consequences of genetic abnormalities in Down's syndrome on brain structure and function. In: Rondal JA, Perera J, Nadel L, Comblain A, editors. Down's syndrome: biological, psychological and socioeducational perspectives. London: Whurr, 1996. [165] Wisniewski K, Kida E. Abnormal neurogenesis and synaptogenesis in Down syndrome brain. Developmental Brain Dysfunction 1994;17:1±12. [166] Wang P, Doherty S, Hesselink J, Bellugi U. Callosal morphology concurs with neuropathological ®ndings in two neurodevelopmental disorders. Archives of Neurology 1992;49:407±11. [167] Jernigan T, Bellugi U, Sowell E, Doherty S, Hesselink J. Cerebral morphologic distinctions between Williams and Down's syndromes. Archives of Neurology 1993;50:186±91. [168] Courchesne E, Yeung-Courchesne R, Press G, Hesselink J, Jernigan T. Hypophasia of cerebellar vermal lobules VI and II in autism. New England Journal of Medicine 1988;318:1349±54. [169] Leiner H, Leiner A, Dow R. Does the cerebellum contribute to mental skills? Behavioral Neuroscience 1986;100:443±54. [170] Hagerman R. Biomedical advances in developmental psychology: the case of Fragile-X syndrome. Developmental Psychology 1996;32:416±24. [171] Miller J. The search for the phenotype of disordered language performance. In: Rice M, editor. Toward a genetics of language. Mahwah, NJ: Lawrence Erlbaum Associates, 1996. [172] Friefeld S, MacGregor D. Sensory-motor coordination in boys with Fragile-X syndrome. In: Holden JA, Cameron B, editors. Proceedings of the First Canadian Fragile-X Conference. Kingston, ON: Oudwanda Resource Centre, 1993. [173] Curtiss S. Abnormal language acquisition and the modularity of language. In: Newmeyer F, editor. Linguistics: the Cambridge survey, 2. Cambridge: Cambridge University Press, 1989. [174] Yamada J. Laura: a case for the modularity of language. Cambridge, MA: MIT Press, 1990. [175] Seagoe M. Verbal development in mongolism. Exceptional Children 1965;6:229±75. [176] Anderson E, Spain B. The child with spina bi®da. London: Methuen, 1977. [177] Hadenius A, Hagberg B, Hyttnas-Bensch K, Sjogren I. The natural prognosis of infantile hydrocephalus. Acta Pediatrica 1962;51:47±118. [178] Tew B. The `cocktail party syndrome' in children with hydrocephalus and spina bi®da. British Journal of Disorders of Communication 1979;14:89±101. [179] Rondal JA. Exceptional cases of language development in mental retardation: the relative autonomy of language as a cognitive system. In: Tager-Flusberg H, editor. Constraints on language acquisition: studies of atypical children. Hillsdale, NJ: Lawrence Erlbaum Associates, 1994. [180] Rondal JA. Exceptional language development in mental retardation: natural experiments in language modularity. Current Psychology of Cognition 1994;13:427±67. [181] Cromer R. Language and thought in normal and handicapped children. Oxford: Blackwell, 1991. [182] O'Connor N, Hermelin B. A speci®c linguistic ability. American Journal on Mental Retardation 1991;95:673±80.

212

J.-A. Rondal, A. Comblain / Journal of Neurolinguistics 12 (1999) 181±212

[183] Smith N, Tsimpli I. The mind of a savant. Language learning and modularity. Oxford: Blackwell, 1995. [184] Vallar G, Papagno C. Preserved vocabulary acquisition in Down's syndrome: the role of phonological short-term memory. Cortex 1993;29:467±83. [185] Rondal JA. DeÂveloppement du langage et retard mental: une revue critique de la litteÂrature en langue anglaise. L'AnneÂe Psychologique 1975;75:513±47. [186] Halliday M. An introduction to functional grammar. London: Arnold, 1985. [187] Rondal JA. Cases of exceptional language in mental retardation and Down syndrome: explanatory perspectives. Down Syndrome 1998;5:1±15. [188] Elliott D, Weeks D, Elliott C. Cerebral specialization in individuals with Down syndrome. American Journal on Mental Retardation 1987;92:263±71. [189] Eisele J. Selective de®cits in language comprehension following early left and right hemisphere damage. In: Pavao Martins I, Castro-Caldas A, Van Dongen H, Van Hout J, editors. Acquired aphasia in children. Boston: Kluwer, 1991. [190] Bates E. Personal communication with J.A. Rondal, May 1997. [191] Moerk E. Personal communication with J.A. Rondal, October 1994. [192] Elman J, Bates E, Johnson M, Karmilo€-Smith A, Cerisi D, Plunkett K. Rethinking innateness: a connectionist perspective on development. Cambridge, MA: MIT Press, 1996. [193] Karmilo€-Smith A, Klima E, Bellugi U, Grant J, Baron-Cohen S. Is there a social module? Language, face processing and theory of mind in individuals with Williams syndrome. Journal of Cognitive Neuroscience 1995;7:196±208. [194] Fodor JA. The modularity of mind. Cambridge, MA: MIT Press, 1983. [195] Bates E, Bretherton I, Snyder L. From ®rst word to grammar. Individual di€erences and dissociable mechanisms. Cambridge: Cambridge University Press, 1988. [196] Butterworth B, Campbell R, Howard D. The uses of short-term memory: a case study. Quarterly Journal of Experimental Psychology 1986;38:705±37. [197] Smith S, Pennington B, DeFries J. Linkage analysis with complex behavioral traits. In: Rice M, editor. Toward a genetics of language. Mahwah, NJ: Lawrence Erlbaum Associates, 1996. [198] Korenberg J, Chen X, Schipper R, Sun Z, Gonsky R, Gerwehr S, Carpenter N, Daumer C, Dignan P, DisteÁche C, Graham J, Hugdins L, McGillivray B, Miyazaki K, Ogasawara N, Park J, Pegon R, Pueschel S, Sack G, Fay B, Schu€enhauer S, Soukup S, Yamanaka T. Down syndrome phenotypes: the consequences of chromosomal imbalance. Proceedings of the National Academy of Sciences 1994;91:4997±5001. [199] Shprintzen R. Genetic syndromes and communication disorders. San Diego, CA: Singular, 1997.