linguistic dissociations in williams syndrome: evaluating … · 2010-12-13 · williams syndrome...

~ ) Pergamon PII: S0028 3932(97)00133 4

Neuropsychologia, Vol. 36, No. 4, pp. 343 351, 1998 1998 Elsevier Science Ltd. All rights reserved

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Linguistic dissociations in Williams syndrome: evaluating receptive syntax in on-line and off-line

tasks

A N N E T T E K A R M I L O F F - S M I T H , * L O R R A I N E K . T Y L E R , t K A T E V O I C E , t

K E R R Y S I M S , * O R L E E U D W I N , + + P A T R I C I A H O W L I N § a n d M A R K D A V I E S §

*MRC Cognitive Development Unit and University College, London, U.K.; tCentre for Speech and Language, Birkbeck College, London, U.K.; +West Lambeth Community Care Trust, London, U.K.; §St George's Hospital Medical School, London, U.K.

(Received 11 Not,ember 1996; accepted 16 Juh' 1997)

Abstract--Williams syndrome (WS) is a neurodevelopmental disorder of genetic origin which results in relatively spared language in the face of serious non-verbal deficits. There is controversy, however, about how intact WS language abilities are. The discussion has focused on impairments of lexico-semantics and of morphological feature analysis, with the presumption that WS syntax is intact. We challenged this view and assessed WS receptive syntax by using two tasks testing various syntactic structures: an on-line word monitoring task and an off-line picture-pointing task. WS performance on the off-line task was generally poor. By contrast, their performance on the on-line task was far better and allowed us to ascertain precisely which aspects of WS receptive syntax are preserved and which are impaired. WS participants were sensitive to the violation of auxiliary markers and phrase structure rules but, unlike both the normal young and elderly controls, they did not show sensitivity to violations of subcategory constraints. The present study suggests that there exist dissociations within WS language which are not restricted to lexico-semantics or to morphological feature analysis, but which also invade their processing of certain syntactic structures. We conclude by arguing that WS syntax is not intact and that their language might turn out to be more like second language learning than normal acquisition. ~ 1998 Elsevier Science Ltd. All rights reserved

Key Words: Williams syndrome; genetic disorder; on-line/off-line tasks; preserved syntax; impaired syntax.

Introduction

Williams syndrome (WS) is a rare contiguous gene disorder found in about one in 25 000 live births [6, 7, 15, 21, 26, 41, 80]. It is caused by a hemizygous sub- microscopic deletion at chromosome 7ql 1.23, including both the elastin gene [19, 20, 42] and the LIM-Kinase 1 gene [22, 61]. At the level of the phenotype, WS patients have a facial dysmorphology commonly characterized as "elfin faces", malformations of the connective tissues, and supravalvular aortic stenosis [30, 44, 45, 53].

In general WS presents no evidence for focal lesions. Rather, specific patterns of brain growth during embryo- and ontogenesis result in different brain volume pro- portions, with total size being 80per cent of normal brains. The WS cerebrum is small, but the frontal cortex

*Address for correspondence: MRC, Cognitive Devel- opment Unit, 4 Taviton Street. London WC1H 0BT, U.K. E-mail: annetteca cdu.ucl.ac.uk

acquires a near normal volume relationship to the pos- terior cortex [5, 28, 74]. Recent work, however, points to cytoarchitectonic anomalies in the form of an exag- gerated horizontal organization of neurons within layers, increased cell packing density in certain brain regions, decreased myelination, and abnormally clustered and ori- ented neurons, particularly in the visual cortex [23]. At the neurotransmitter level, there appear to be abnormal levels of calcitonin [17] and of serotonin [2, 45].

Most importantly for the cognitive neuroscientist, WS is unlike many other developmental disorders, such as Down's syndrome, in that it results in a very uneven linguistic-cognitive profile. Some aspects of language seem relatively spared, whereas many non-linguistic functions, such as spatial cognition, number, planning, and problem solving, are severely impaired [1,3, 4, 10, 13, 16, 25, 32, 33, 38, 39, 40, 50, 51, 58, 67, 69, 70, 71, 73].

Despite the original claims that WS language is relatively normal, a series of studies using event-related potentials to assess the timing and organization of neural

343

344 A. Karmiloff-Smith et al./Linguistic dissociations in Williams syndrome

systems during language processing question this con- clusion [54, 55]. Participants listened to sentences that ended either appropriately semantically (e.g., "I take my coffee with cream and sugar") or to sentences which were semantically inappropriate (e.g., "I take my coffee with cream and radiator"). The authors found different temporal patterns in the brain activity of WS participants compared with normal controls, suggesting that on-line semantic processing is different in WS compared with the normally developing brain (see also, discussion in [67]).

However, even if some aspects of semantic processing are impaired, WS syntactic processing might still be intact. The purpose of the present experiments was to determine whether this is so, and if not, which aspects of syntactic processing are preserved in WS participants and which are impaired. To examine WS ability to process syntactic structure when interpreting an utterance we used two different tasks: one (the word monitoring task) taps implicit processing, and the other (the sentence- picture matching task) probes explicit syntactic processing.

Implicit and explicit tasks measure different aspects of language processing. We define implicit tasks as those in which the subject's response is closely time-locked to a relevant linguistic variable, and where the subject's attention is not explicitly drawn to this linguistic variable. Tasks meeting these criteria reflect more directly the non- conscious, automatic aspects of language processing [63, 66]. Explicit tasks, in contrast, focus more on the con- trolled aspects of processing and are not directly con- cerned with the real-time analysis of spoken language [9, 63, 66]. Whereas we acknowledge that the difference between implicit and explicit tasks is not always entirely clear, in general they probe different aspects of the comprehension process. The distinction between them has been valuable in elucidating both normal development [8, 31, 36, 37], and the nature of cognitive impairments in a wide range of adult deficits (e.g., [52, 63, 64, 66, 79]). Children are typically successful earlier in development on tasks that tap their knowledge indirectly and implicitly than on explicit tasks [8, 27, 31, 36, 59, 62, 72]. Likewise, language-impaired patients typically show preserved implicit and impaired explicit processing, with explicit tasks tending in general to overestimate the severity of a patient's deficit, strengthening the need for using both types of task [63, 64]. This is also true in the case of subjects, such as those with Williams syndrome, who have serious cognitive impairments [67]. For these reasons, we investigated the syntactic processing abilities of WS people by using both implicit and explicit tasks, and by examining a range of different kinds of syntactic structure.

Experiment 1: Word monitoring study

In this study, we examined WS participants' ability to use syntactic information in the process of interpreting a

sentence, by measuring their sensitivity to various types of syntactic violation. We did this by using a word monitoring task in which participants listen to spoken sentences and press a response key when they hear a pre- specified target word in the sentence [48, 49, 63, 66]. The word monitoring task taps into the real-time, automatic processing of language, because there is a close temporal relationship between the speech input and the subject's response. The subject is focused on the task of monitoring for a target word rather than on the linguistic manipu- lations introduced by the experimenter.

We compared monitoring latencies to target words occurring in particular syntactic constructions, and then violated those constructions to determine whether monitoring latencies increase. In normal controls, monitoring latencies increase whenever a target word follows a syntactic violation [47]. If WS participants are sensitive to various types of syntactic structure, their latencies to target words will also increase following the presence of a syntactic violation to those structures.

Method

Participants. Eight individuals with Williams syndrome were tested. There were three male and five female participants. They had a mean chronological age of 20;7 years (range 14;9 to 34;8), with a mean verbal IQ on the WISC/WAIS of 71 (range 51-87) and a mean performance IQ of 58 (range 46-75) [76, 77, 78]. Their mental age on the British Picture Vocabulary Scale (BPVS) [18] was 11;2 (range 7;5 to 16;4), on the Test for Recep- tion of Grammar (TROG) [11] 7;7 (range 5;6 to 11;0), and on the Ravens Progressive Coloured Matrices (RPCM) [57] 6;8 (range 5;6 to 8;0). This uneven profile is typical of Williams syndrome. Eighteen normal participants, nine male and nine female, formed the control group. They ranged in age from 19 to 29 years. All participants, both WS and controls, were monolingual and of middle to lower middle socio-economic class.

Materials. We examined three types of syntactic information in this study: subcategory constraints on verbs, the constraints imposed by auxiliaries on the form of the subsequent verb, and phrase structure rules within local constituents. Examples of each type of structure are given below. Each sentence containing the target word was preceded by a short context sentence. The word in upper case in each of the examples is the target word for which the subject is monitoring and immediately follows the correct or violated syntactic structure in italics.

Subcategory constraints: We selected verbs and constructed sentences into which they could fit, such as (1) and (3) below, and then violated the subcategory constraints on the main verb, as in (2) and (4) below:

1. The burglar was terrified. He continued to stru991e with the DOG but he couldn't break free.

2. *The burglar was terrified. He continued to struygle the DOG but he couldn't break free.

3. The class was very unpopular. Maria always needed PART- NERS to show her the steps.

4. *The class was very unpopular. Maria always needed jbr PARTNERS to show her the steps.

The sentences were all of the structure: (NP + verb + object NP) plus a few additional words. The object NP (e.g., DOG or PARTNERS in the above examples) was always the monitoring target word. In the grammatical condition (examples (1) and

A. Karmiloff-Smith et al./Linguistic dissociations in Williams syndrome 345

(3) above), the object NP was syntactically appropriate in that it was consistent with subcategory restrictions on the verb. In the ungrammatical condition (such as (2) and (4) above), the verb could not take a direct object and thus the presence of the target noun constituted a grammatical violation. In developing the stimuli we balanced the set between transitive and intransitive verbs. Therefore, in half the cases the appropriate condition was intransitive and contained a preposition (1), whereas the inappropriate condition left out the preposition (3). For the remaining cases, the appropriate condition was transitive without a preposition (2) and the violation consisted of inserting a preposition after the verb (4). Normal people are sensitive to subcategory violations, shown by their faster monitoring latencies to targets in grammatical compared with ungrammatical sentences [47, 66]. If WS participants are also sensitive to the syntactic restrictions on the possible arguments which different verbs can take, their monitoring response times (RTs) should be slower in conditions (2) and (4) than in (1) and (3).

Auxiliary markers: Sentences in the auxiliary condition were of the form: (NP+aux+verb+ta rge t noun), followed by additional material, as in (5) and (7) below. In such sentences the auxiliary is syntactically appropriate for the inflected form of the following verb. We compared monitoring latencies in this condition with those to targets occurring in sentences such as (6) and (8) below, where the auxiliary is changed so that the combination of (auxiliary+verb) is ungrammatical. The target word was the direct object of the following verb (e.g., SPEECHES and MILK in the examples below). If WS participants are sensitive to constraints on auxiliary choice, then they should be faster to respond to the target words in sentences such as (5) and (7) than to ungrammatical sentences such as (6) and (8).

5. It could have been very embarrassing. We didn't realize he was expecting SPEECHES at the..

6. *It could have been very embarrassing. We didn't realize he might expecting SPEECHES at the..

7, Fiona's doctor was very worried. He said she shouht have MILK and protein more often.

8, *Fiona's doctor was very worried. He said she was ha~'e MILK and protein more often

Phrase structure rules: Our third set of materials consisted of sentences in which a target word (PILLS and TEST as in examples (9) and (11) below) followed a verb and completed a verb phrase; the target noun is in the correct configuration with respect to the verb. In contrast, in sentences such as (10) and (12) below, the target word follows a sequence which violates the legal configuration of grammatical categories. In all cases, the target word occurred immediately after the violation. IfWS participants are sensitive to the syntactic coherence of the target word with respect to the prior syntactic context, then their monitoring RTs should be faster for grammatical than for ungrammatical sentences.

9. Susan seems much happier. I expect the special PILLS she got from the doctor...

10. *Susan seems much happier. I expect special the PILLS she got from the doctor...

1 I. John's friends were delighted. When he took the new TEST he passed first time.

12. *John's friends were delighted. When he took new the TEST he passed first time.

We constructed a large number of sentences, each of which contained a potential target word for word monitoring. Ungrammatical versions of these sentences were made by intro- ducing one of the three types of violation detailed above: subcategory, auxiliary and phrase structure. Sentences were subjected to several pre-tests carried out with normal people. First an acceptability pre-test was performed in which each sentence's acceptability was rated on a scale of 1 (very bad) to

7 (very good). Only those grammatical sentences which received a rating of 5 or higher by at least two-thirds of the normal participants were included in the experiment. The criterion for ungrammatical sentences was a rating of 3 or less by two-thirds of the participants. Second, we carried out a cloze pre-test to ensure that the target words were not predictable in the sentences. In this test, the grammatical sentences, up to but not including the target word, were written in a booklet and participants were asked to provide a one-word continuation. Any candidate sentences for which participants produced the target word or a word related in meaning were discarded, thus ensuring that targets were not predictable.

From the pre-tests we obtained 28 sentences in which the ungrammatical condition violated subcategory constraints on the verb, and 24 sentences in which the ungrammatical version contained an auxiliary which was syntactically inappropriate for the verb. In a further 22 sentences, the ungrammatical version contained a phrase structure violation based on re-ordering of the words within the test noun phrase, such that the sequence violated the phrase structure rules of English. In each set, the word position of the target varied so that it would not be predictable.

These 74 test sentences were interleaved with a large number of fillers consisting of a variety of different syntactic structures. These served to obscure the regularities of the test sentences. In total, across the set of test and filler items, there were equal numbers of grammatical and ungrammatical sentences, Two versions of the materials were constructed, with items rotated across the versions so that no item appeared more than once per version. The materials were recorded and digitized onto computer hard disk. Timing pulses were placed at the onset of each target word, triggering a timing device which was stopped by the action of the participant pressing the response button.

The target words were either monosyllabic or bisyllabic. This presented no problem with respect to timing onset of latencies because each word in the ungrammatical condition was repeated by the same word in the grammatical condition across the whole set of stimulus items.

Proce&o'e. Before each trial participants were presented with the target word for which they were to listen in the sentence. Controls read the word themselves, whereas for the WS participants the words were read aloud by the experimenter to avoid any reading problems. The card with the target word written on it stayed in front of the participants throughout the trial. Participants then heard the sentence over headphones and pressed a response key when they heard the target word.

Results and discussion

Controls. Controls made an average of 1.3per cent errors (range 0~4 per cent), consisting of t ime-outs (not

responding by 2 s) and outliers (RTs exceeding 1 s and less than 100 ms). Two per cent of the control data were

removed from the analyses (0.6 per cent time-outs, 1.4 per cent outliers); 3.9 per cent of the data exceeded 2 s tandard

deviations from the mean and were replaced by the cut- offvalues. The controls ' mean moni to r ing RT was 336 ms (range 268~456 ms). Before runn ing analyses of variance (ANOVAs), we normalized the data by dividing each RT by the par t ic ipant ' s mean RT and mult iplying by 100, so that each RT was representative in relation to the par t ic ipant ' s mean RT. This was to make the control data comparable to the WS data for the purposes of analysis, because the WS data had to be normalized in


order to reduce variability introduced by the need for some participants to perform the task on two different days because they were unable to complete an entire version of the experiment in a single session.

The controls showed an overall grammaticality effect, with monitoring RTs in the grammatical sentences being faster (307ms) than latencies in the ungrammatical sentences (356ms) [Fl(1,16) = 238.61, P<0.001; F2(2,68)=60.52, P<0.001]. The mean latencies for the three different types of syntactic manipulation are given in Table 1, where it can be seen that all three types of ungrammaticality slowed the monitoring RTs for the controls, The syntax type by grammaticality effect was not significant [F~(2,32) = 2.32, P = 0.14; F2(2,68) = 1.22, P=0.29]. Separate analyses carried out on each of the three syntax types individually revealed a significant grammaticality effect for each of them: phrase structure violation: F~(1,16)=76.48, P<0.001; F2(1,20)=22.27, P<0.001; wrong auxiliary: F~(1,16)=23.5, P<0.001; F:(1,22)= 15.87, P<0.001; subcategory violation: F~(1,16)= 56.98, P<0.001; F2(1,26)= 22.49, P<0.001.

Williams syndrome. The data from the individuals with WS were cleaned in the same way as for the controls. A total of 9.6 per cent of the data were removed from the analyses (time-outs (2.03 per cent) or outliers (7.59per cent). Of the remaining data, 5.6 per cent exceeded the 2 standard deviations from the mean cut-off values and were replaced by those values. As with the controls, we normalized the data before running ANOVAs in order to reduce the variance attributable to participants being tested on different days.

The monitoring RTs of the WS participants were very similar to those of the normal controls (WS mean RT = 386 ms, range 275-487 ms; controls mean RT = 336, range 268-456 ms). A combined analysis on all eight WS participants was carried out. This showed a significant grammaticality effect [F~(1,6) = 44.64, P < 0.001; F2(2,68) = 7.5, P < 0.001] with monitoring latencies being faster to targets in grammatical (371 ms) compared with ungrammatical sentences (401 ms). This is again similar

Table I. Syntactic violations: mean monitoring RTs (ms)

Controls WS

to the control data (grammatical 307, ungrammatical 356). However, the WS participants reacted differentially to the three types of syntax. In keeping with the controls, they showed a grammaticality effect for both phrase structure and auxiliary violations, but unlike the controls they were insensitive to subcategory violations. This can clearly be seen in Table 1, where we also present the WS monitoring latencies for each of the three types of syntax. This differential effect showed up as a marginally significant interaction in the items analysis [F2(2,68)= 2.38, P = 0.09], but it was not significant on the subjects analysis [F~(2,12) = 2.34, P = 0.17], presumably because of the relatively small number of WS participants tested. To explore this further, we carried out separate analyses on each of the three types of syntax, finding a significant grammaticality effect for phrase structure [F~(1,6) = 8.18, P = 0.02, F2(1,20)= 12.82, P = 0.001] and wrong auxiliary [F~(1,6)=13.33, P=0.01; F2(1,22)=5.57, P=0.02], but no effect for the subcategory violations [F' and F2< 1].

In sum, WS and controls show very similar overall mean RTs, with similar ranges. Both populations also show similar overall monitoring latency differences to the set of grammatical vs. the set of ungrammatical sentences. In both groups, too, significant effects were found in separate analyses of phrase structure and auxiliary structures. Where the two populations differed, however, was with respect to the violation of subcategory structures. One interpretation of these data is that the WS people are insensitive to syntactic constraints which are lexically specified, such as subcategory information. However, another interpretation may turn out to be more plausible: namely, that WS are sensitive to subcategory constraints, but they are slow to integrate this type of information into the developing sentential representation. The evidence for this stems from the RTs of WS participants in the grammatical subcategory condition. Their RTs averaged 407 ms in this condition, compared with 345 ms for grammatical phrase structures and 362 ms for grammatical auxiliary markers. This difference shows up in a marginally significant main effect of type of syntax [F~(2,12) = 5.11, P = 0.06; F2(2,68) = 2.65, P = 0.07]. The normal controls do not show this pattern; their RTs in the three grammatical conditions for the three types of syntax only vary by 30 ms (from 286 to 316 ms; see Table 1). We will consider this further in the Discussion section.

Phrase structure: Grammatical 286 345 Ungrammatical 347 395 Mean difference 61 * 49*

Subcategory: Grammatical 316 407 Ungrammatical 361 404 Mean difference 45* - 3

Wrong auxiliary: Grammatical 318 362 Ungrammatical 360 405 Mean difference 42* 43*

*Difference is significant at P<0.05 or above.

Experiment 2: Sentence-picture matching task

In the sentence-picture matching task, the subject hears a spoken sentence and chooses, from an array of pictures, the one that corresponds to the sentence. We chose this task for our explicit tasks for a number of reasons. First, in some circumstances it can be more informative than tasks such as grammaticalityjudgement in which the subject is just making a yes/no response. In the sentence-picture matching task, we can look at the type of errors that subjects make, i.e., whether they


choose, for example, a lexical distractor or a syntactic distractor. Our second reason for using this task was that, unlike the word monitoring task, it allowed us to look at a wide variety of different types of syntactic structure. The on-line monitoring task necessarily restricts the types of structure we can examine because of the need to have the target word occur immediately after a linguistic violation. Because our aim was to obtain data on a wide variety of sentence structures, in this second experiment we did not limit ourselves only to those types of violation we had used in the monitoring study.

Method

Participants. We tested the same eight WS and 18 normal control participants in this study as had been tested in the word monitoring task in Experiment 1.

Materials. The materials were from the Birkbeck Reversible Sentences Test [12]. On each trial, participants are presented with an array of three pictures: one corresponding to the sentence, one a reverse role distractor and the third a lexical distractor. For example, for the sentence: "The clown photo- graphs the policeman", the three pictures are: (1) correct: a clown photographing a policeman; (2) reverse role distractor: a policeman photographing a clown; (3) lexical distractor: a clown lifting the helmet off a policeman. The test sentences were presented orally and consisted of 70 sentences, 10 for each of the following seven types of construction: active sentences with agentive and non-agentive verbs, passive sentences with agentive and non-agentive verbs, sentences containing adjectives. deverbal adjectives and locatives.

Results and discussion

The performance of the controls was virtually error- free on this task. In contrast, the WS participants performed very poorly, making an average of 24 per cent errors (range 14-37per cent). Most of their errors consisted of the syntactic error of choosing the reverse role distractor, which they did 81 per cent of the time. Only 19 per cent of their total errors involved choosing the lexical distractor.

Because the normal controls were at ceiling on all the structures, we also compared the WS results with those from a group of elderly participants between the ages of 60 and 75 years, all of whom had left school by the age of 14years [68]. They made many more errors than the young controls on this task (mean errors for elderly subjects 17 per cent, range 4-30 per cent). Our aim was to see whether the pattern of errors on the different sentence structures made by the WS individuals was similar to that of normal but elderly controls. We found that the order of difficulty of the various linguistic structures was ident- ical for the elderly controls and the WS group: most errors were made on sentences (both actives and passives) with non-agentive verbs (WS 33 per cent errors, controls 31 per cent errors), followed by sentences with deverbal adjectives (WS 26 per cent, controls 23 per cent), those with adjectives (WS 24per cent, controls 21 per cent),

passive sentences with agentive verbs (WS 17per cent, controls 10 per cent), active sentences with agentive verbs (WS 17 per cent, controls 5 per cent), both groups finding the sentences with locatives the easiest (WS 14 per cent, controls 3 per cent).

This second experiment revealed that WS participants have far more problems with syntax when tested by means of an explicit task, although the types of structure on which they have most difficulty are those which the elderly controls who left school at 14years of age also find difficult. By contrast, it is noteworthy that, unlike the WS participants, when tested with the on-line tech- nique the elderly group were not selectively insensitive to subcategory violations but showed the same pattern as the normal controls [68]. The low performance levels of the WS individuals on the sentence-picture matching study are similar to the levels of syntactic performance that they achieve on the TRO G (see Participants section), which covers a range of other structures that they find difficult, such as left-branching relative clauses [39] for an item-by-item analysis of WS TROG results).

General discussion

Despite the differences in performance between Experi- ments 1 and 2, it is clear from both, and in comparison with the results of both the younger and elderly control groups, that WS syntax is not intact. The sentence-picture matching task revealed an across-the-board impairment. WS participants' ability to select the correct picture from an array in response to a spoken sentence was considerably worse than normal on the wide range of syntactic structures we tested. However, they did not show a selective deficit for any specific syntactic constructions; their performance on the various sentence types was similar to the normal pattern, although overall accuracy was much worse. The word monitoring study, on the other hand, showed that some syntactic operations remained intact whereas others were selectively impaired.

The poorer performance on the off-line task is not so surprising given that most explicit tasks do not tap into language processing directly, but also involve a number of additional cognitive processes shown to influence the performance of both children [31, 36] and adults [63, 64, 66]. In the sentence-picture matching task, for example, the participant has to listen to and decode the sentence, maintain it in their memory (when it is spoken), process the pictures and compare the sentence to each one of the pictures, eventually selecting the one that best matches. Because WS individuals have clear cognitive impairments, tasks which rely heavily upon general cognitive abilities may overestimate the extent of the linguistic impairment. This is not to say that people with WS find all picture-matching tasks uniformly difficult. As mentioned earlier, WS individuals perform rather well on picture- matching tasks involving single words, such as the BPVS [18]. However, given that this task involves single words


and simpler pictures, the cognitive demands it places on the individual are undoubtedly less than those involved when whole sentences need to be matched to a picture.

The contrast between the explicit and implicit data has important implications for studying the language comprehension abilities of people with WS as well as other impaired populations. Explicit tasks can, in general, only provide an overall measure of performance. Although we can determine whether participants have problems with particular aspects of language, we cannot determine which aspects of the comprehension process are actually impaired. If, for example, we had only carried out an explicit task on the materials we used in the monitoring study, we might have obtained the same out- come - - namely, that WS participants had difficulty comprehending subcategory information but not phrase structure and auxiliary markers. However, we would not have been able to propose an account of their problems in terms of deficits in the basic processes involved in language comprehension - - processes of activation and integration [46]. The advantage of on-line tasks is that they can provide a more detailed assessment of the nature of the impairment, as has been shown with brain-damaged adults [66].

The on-line study revealed a more varied pattern than the off-line task. It showed that whereas WS participants had no difficulty assembling the relevant elements together to form coherent noun phrases or in appreciating the relationship between an auxiliary and a main verb, they had clear problems with subcategory structures. For subcategory violations, monitoring latencies did not sig- nificantly increase as they did for violations of both phrase structure and auxiliary markers. Although it might be tempting to interpret this pattern as indicating that WS cannot process subcategory information, we provisionally favour a more conservative interpretation - - namely, that WS are able to access subcategory information associated with a verb, but they are slow to integrate this information with the upcoming input. This account is more consistent both with the data and with some current theoretical approaches to syntax. Those aspects of the data which support this view are the fact that, coupled with no significant increase in latencies in the subcategory ungrammatical condition, RTs in the grammatical condition are in and of themselves also slow compared with the other categories.

The above interpretation is also more consistent with a lexicalist approach to syntactic processing [14, 43, 65, 73, 75], in which much of what was traditionally thought to be due to the operations of a syntactic parser is seen to be part of lexical representations. On this kind of account, subcategory information is lexically represented and activated when a word is heard, providing potential argument structures into which the upcoming words are integrated. Similarly, there are lexically specified constraints on the permissible configurations for nouns, adjectives, determiners, etc., which determine agreement and word order. Therefore, on a lexicalist account, all

three types of syntactic information that we manipulated in the word monitoring experiment are lexically represented. This suggests that they should stand or fall together in cases of language impairment. If this obtains, then it is more likely that the differences in the word monitoring study for WS are not due to differential representational impairments but to differences in the ease with which various types of syntactic or lexical information can be integrated on-line. This is a picture which we have observed many times in studies of normal adult brain-damaged patients whose language is impaired either as a result of focal lesions accompanying stroke or more generalized damage from progressive degenerative disease [68].

However, although our suggestion that the three categories should stand or fall together holds for adults who have acquired language normally and then suffered neurological damage, it may not hold for devel- opmentally impaired children whose brains develop differently from the outset [34, 35]. Several studies have now suggested that WS language is acquired via a some- what different route to normal acquisition and involves different brain processing [39, 40, 50, 54, 55, 60, 67]. Furthermore, in normal development subcategorization structures are acquired later than word order and auxiliary categories [24]. They also seem to be more difficult for second language learners [29]. Of course, these two data sources come from very different methods and age groups, the first being the infant preferential looking task with 12-27month olds, the second written grammaticality judgements with non-native but fluent adult speakers of English. Nonetheless, the congruence of order of difficulty of these two sources with our WS on-line data suggests that subcategorization, whether it turns out to be lexically or syntactically specified, is more difficult to acquire. Therefore, unlike brain-damaged adults who had acquired language normally and show integrational problems rather than representational impairment, it remains an open question whether our WS subjects have only integrational or also representational impairments for certain linguistic categories.

We plan further experiments to tease apart the con- tribution of representational vs. integrational impairments in WS syntax. Indeed, the use of on-line techniques for addressing such issues is crucial in revealing the sub- tleties of abilities and impairments that off-line tasks often fail to capture. The present study has shown that the on-line techniques used with adult neuropsychological patients [66] can very profitably be extended to individuals whose impairments are of genetic origin. What- ever the full extent of the WS impairments (see also [39, 73]), the two experiments reported here provide further evidence that, contrary to a popular view in the literature (e.g., [56]), people with Williams syndrome do not have entirely normal syntax.

Acknowledgements--We should like to express our appreciation


to the Williams Syndrome Foundation, U.K., for their generous help in putting us in touch with families whom we warmly thank for their participation in this research. The WS participants were tested at the MRC Cognitive Development Unit and the normal controls at the Centre for Speech and Language, Birkbeck College, London. This research was partly supported by an MRC programme grant to Lorraine K. Tyler and W. D. Marslen-Wilson and by an MRC Senior Research Leave Fellowship to L.K.T.

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