Compounding and Inflection in Language Impairment:
Evidence from Williams Syndrome (and SLI)
Harald Clahsen & Mayella Almazan*
Department of Linguistics
University of Essex
Corresponding author:
Harald Clahsen
Dept. of Linguistics
University of Essex
Colchester C04 3SQ
UK
email: [email protected]
 Harald Clahsen and Mayella Almazan 2000.
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Abstract
We have examined potential dissociations between lexical and grammatical knowledge
in language impairment by investigating noun plurals and plural formation inside
compounds in Williams Syndrome (WS) subjects. For comparison, we also report
results from studies investigating the same linguistic phenomena in children with
Specific Language Impairment (SLI). We found that nouns taking regular plurals were
always correctly inflected by the WS subjects, whereas they performed much worse on
nouns that take irregular plurals. The WS subjects heavily overregularized the regular -s
plural, and they even used the plural -s as non-head elements inside compounds, i.e. in
circumstances in which unimpaired children (and adults) would typically not use regular
plurals. We argue that the excessive use of the regular -s plural in WS results from an
impairment of the lexical system and/or its access mechanisms. The dissociation
between lexical and grammatical phenomena in WS supports the theoretical distinction
between listed lexical entries and a (rule-based) computational system for language.
1.
Introduction
Many linguists, particularly those working from a generative perspective, assume that the language faculty
has an internal modular organization and that it consists minimally of two separate systems, a lexicon of
listed or stored entries, and a computational system of abstract rule-like operations to form larger
expressions from lexical entries (Chomsky 1995). Computational operations form a finite set of (typically)
combinatorial mechanisms that may apply recursively and manipulate abstract symbols such as [±V] or
grammatical features such as tense, person, number, etc.
While these assumptions appear to be relatively uncontroversial among linguists, a glance over the fence
reveals that the internal modularity and the assumed dual structure of language (lexical entries vs. rules of
language) are often treated with scepticism outside linguistic circles. Some researchers have even developed
alternative non-modular conceptions of language. Particularly influential in recent years have been
associative approaches to language which have been implemented as computer-aided connectionist
networks, e.g. various networks of inflectional phenomena (Rumelhart & McClelland's 1986, Plunkett &
Marchman 1996, Plunkett & Nakisa 1997, Nakisa et al. 2000) and Elman’s (1993) network of subject-verb
agreement in English. The aim is to simulate phenomena that used to be accounted for in terms of linguistic
rules in associative networks which do not rely on mental grammars or any of the kind of computational
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operations that are posited in linguistic theory. Some researchers have taken these simulations as evidence
that the knowledge of language should better be represented in terms of connectionist networks with
associatively linked units, rather than in terms of modular linguistic theories (Bates & Elman 1993,
Seidenberg 1997, Churchland 1995, Elman et al. 1996).
It would, in our view, be unwise for linguists to ignore this challenge and to take the internal modularity of
language simply for granted. Instead, the case for internal modularity and the hypothesized dual structure of
language may be strengthened by providing relevant empirical evidence. One important source of evidence
that might bear on these issues comes from selective impairments or dissociations in the linguistic skills of
language-disordered populations. The rationale is that if one can show that two phenomena A and B are
dissociated, such that A is selectively impaired in one population (where B is spared) and that B is
selectively impaired in another population (where A is spared), then this suggests that A and B are
independent and are supported by different mental representations or mechanisms. This type of argument
has been used in many studies of language breakdown to support the internal modularity of language (see
Levy & Kahé 1999 for a recent review).
We have investigated subjects with Williams Syndrome (WS) from this perspective. WS is a genetic
disorder resulting in impaired cognitive abilities but relatively spared linguistic abilities. In a previous study
(Clahsen & Almazan 1998), we examined past tense formation and two syntactic phenomena (passives,
anaphoric binding) in a group of English-speaking WS subjects. In the present study, we will analyze plural
formation and plurals inside compounds in the same group of WS subjects. The results from both studies
converge and demonstrate an unusual within-language dissociation in WS subjects. We found that the WS
subjects exhibit excellent performance on regular inflection and on syntactic tasks, whereas on irregular
inflection they performed much worse. It will be argued that the rule-based (computational) system of
language is spared in WS, whereas lexical skills (required for irregular inflection) exhibit impairments. A
comparison with results from studies of Specific Language Impairment (SLI) reveals the opposite pattern,
i.e. poor performance on syntactic tasks and regular inflection paired with relatively well-preserved lexical
skills (see section 8). Taken together, these findings provide empirical support for the internal modularity of
language and for a separate computational system that can be selectively spared in WS, and impaired in
SLI.
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2.
Linguistic aspects of Williams Syndrome
The reason for the particular interest that the study of WS has recently received is the syndrome's rather
unusual profile of general cognitive deficits and learning difficulties paired with relative strength in
language. This pattern provides a potential source of evidence on the controversial issue of the modularity
of mind and language (Fodor 1983).
With an incidence estimated at between 1 in 20,000 and 1 in 50,000, WS is a relatively rare disorder
(Greenberg 1990). In genetic terms, WS is an autosomal dominant disorder with most cases representing a
new genetic mutation, resulting from a microdeletion within one elastin gene and its surrounding DNA on
chromosome 7 (Ewart et al. 1993, Frangiskakis et al. 1996). It is a disorder with various physical
manifestations, including congenital heart diseases, gastrointestinal problems, low birth weight and growth
retardation (Chapman et al. 1995). Because of cardiovascular defects, WS individuals have a reduced life
expectancy (Greenberg 1990). As well as these defects, WS individuals have a very characteristic facial
expression, with small upturned noses, full cheeks and lips, a wide mouth, and long, prominent ears (Hovis
& Butler 1997). Behaviourally, WS individuals are often friendly and sociable but emotionally insecure and
easily distractible.
The question of whether there is a fundamental dissociation between linguistic and non-linguistic skills in
WS individuals is controversial. In several previous studies, it has been argued that linguistic skills are
relatively well preserved in WS and that grammar is selectively spared (Bellugi et al. 1988, 1994, Wang &
Bellugi 1994). Bellugi and her collaborators argued that in contrast to their poor general cognitive and
visuospatial functioning, WS subjects (age range: 10 years and above) demonstrate excellent command of
complex expressive morphology and syntax, including full passives, embedded relative clauses, a range of
conditionals, and multiple embeddings. They also showed good metalinguistic skills as evidenced by
reliable grammaticality judgements.
On the other hand, Mervis et al. (1999) reports results from a study of 7 to 8 year old English-speaking
children and adults with WS indicating that their level of grammatical ability (as measured in terms of
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performance on standardized language tests such as the TROG, Bishop 1983) is consistent with their level
of composite mental abilities. This is taken to indicate that the dissociation between language abilities and
cognition in WS is more apparent than real. Similarly, Volterra et al. (1996), in a study examining Italian
children with WS (age range: 4;10 to 15;3) in comparison with mental age matched normal controls, found
that the WS subjects were not ahead of their mental age controls in their linguistic skills, except in the
phonological fluency test in which subjects were asked to generate all the words they can think of beginning
with a particular letter. They also reported examples of morpho-syntactic errors, e.g. in subject-verb
agreement, incorrect use of infinitives in sentences that require finite verbs, and incorrect substitutions of
prepositions. Volterra et al. conclude that the profile found in WS cannot be used as evidence for a
dissociation between language and cognition; see also Capirci et al. (1996) and Karmiloff-Smith et al.
(1997) for similar views. However, these authors also stress (along with Bellugi and her collaborators) that
'WS displays a verbal advantage over nonverbal intelligence' (Karmiloff-Smith et al. 1997: 275),
particularly in older WS children and adults, suggesting that the linguistic characteristics of WS cannot be
directly derived from their reduced nonverbal intelligence.
In contrast to the question of how language and cognition are related in WS, comparatively little research
has been directed towards understanding the nature of the underlying linguistic competence in WS
individuals. This is particularly true for the domain of grammar, i.e. syntax and morphology, which many
linguists would regard as the core of the language faculty. Most previous studies of grammatical skills in
WS rely on traditional school grammar categories and do not make use of concepts and notions from
linguistic theory. The linguistic data in the WS studies mentioned above have the form of mean test scores
or example utterances. We believe that the study of WS will benefit from a linguistically more informed
approach. What is required on a descriptive level is a linguistic profile of WS, i.e. a precise and
comprehensive analysis of the grammatical problems of WS subjects. Furthermore, since the grammatical
problems in WS do not seem to follow straightforwardly from any general cognitive impairments, it is
worth exploring the possibility of explaining potential disorders or delays of grammatical knowledge in WS
in terms of selective impairments within the language faculty itself. A linguistic approach offers a way of
looking at WS in this way.
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Some steps in this direction were taken by Clahsen & Almazan (1998) in a study of the grammatical skills
of four WS children (age range: 11;2 to 15;4). The study focused on two syntactic phenomena (passives,
anaphoric binding) and a morphological one, past-tense marking of regular and irregular verbs by using a
range of elicited language production and comprehension experiments. It was found that in the passives and
binding experiments, the WS subjects performed at ceiling in all conditions, achieving even higher
correctness scores than the unimpaired controls. Regular past-tense marking was also unimpaired, and the
WS children achieved the same high correctness scores as unimpaired controls. On irregular verbs,
however, the WS subjects performed much worse, with only 42% correct compared to 78% correct for the
controls. The WS subjects were found to heavily overapply the regular -ed rule, even to nonce words that
rhyme with existing irregulars. These results were explained in terms of a dual-mechanism model of
inflection according to which irregular past-tense forms are stored as subnodes in structured lexical entries
while regular past-tense forms are based on an inflectional rule ('Add -ed'); see Pinker (1999) and Clahsen
(1999) for discussion. The pattern found in WS children indicates that they are impaired in accessing
subnode information from lexical entries (required for retrieving irregulars), while their computational
system (required for syntax and regular inflection) seems to be intact. An example of a structured lexical
entry is shown in (1):
(1)
[draiv]+V
[..ow]+pret
[.I..n]+part
We suggest that subnodes for irregular verbs, along with the correct pairing of phonological strings and
morphological feature values, are available to WS subjects, but that either the content of the subnodes for
the irregulars or the link to the basic entry, or both, is not always accessible. If the content of a subnode
such as [..ow]+pret in (1) cannot be retrieved, -ed affixation applies, and hence the frequent
overregularization errors in WS subjects.
The purpose of the present study is to further explore potential linguistic impairments in WS by
investigating plural formation and plurals inside compounds. The linguistic focus will be on the constraint
that blocks the insertion of regular plurals inside compounds. Note that irregular plural nouns such as teeth,
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mice, etc. can readily appear as initial parts or non-heads in compounds in English, while plural nouns
formed by adding the suffix -s cannot be used productively in this position, e.g. teeth marks versus *nails
marks; mice eater versus *rats eater. Thus regular and irregular inflection relate to compounding
differently. It has been argued that this difference follows from the internal representation of irregular and
regular inflection and the way they are related to the process of compounding. Whereas irregular plurals
form separate lexical entries that can be fed into compounding just like uninflected stems, regular plurals do
not have stored representations that the (lexical) compounding mechanism could access, hence the
ungrammaticality of *rats eater. The study of plural formation and plurals-inside-compounds in WS
children will shed light onto their linguistic system and in particular on how different morphological
processes interact.
3.
Linguistic background
3.1
Compounding and plural inflection in English
Like many other languages, English has two ways of forming compounds, phrasal and lexical compounding
(see e.g. Lieber 1992). The latter involves concatenations of lexical units such as stems or words and
produces familiar compounds such as cat food, dinner plate, dish washer, etc., a very common and
productive process in English. However, compounds may occasionally contain non-head elements that are
clearly phrasal. The range of possible phrases in such compounds is virtually unrestricted, e.g. over-thefence gossip, God-is-dead theology, off-the-rack dress, and includes regular -s plurals, e.g. red rats balloon.
To capture such cases, it has been suggested that the non-head elements of phrasal compounds are formed
in the syntax (see Sproat 1985 and Wiese 1996 for discussion). Thus, in a phrasal compound such as red
rats ballon, the phrase [red rats] is formed in the syntax and is then presented for compounding on a second
pass through the lexicon, yielding the phrasal compound [[red rats] balloon]]. For this reason, phrasal
compounds are sometimes called 'recursive' (Kiparsky 1982). The lexical compound rat balloon, on the
other hand, requires just one pass through the lexicon and is therefore non-recursive.
In contrast to phrasal compounds, which can host any kind of non-head element, lexical compounds are
constrained by the fact that irregular but not regular -s plural forms may occur as non-head elements inside
lexical compounds. The distribution of plurals-inside-compounds coincides with the distinction between
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lexically stored (irregular) and rule-based (regular) inflection. Thus, given that lexical compounding
concatenates lexical entries, it follows that irregular plurals (because they have lexical entries) can be fed
into the compounding process, whereas rule-based forms such as -s plurals (which do not have lexical
entries) cannot be included in the compounding process.
There are several linguistic implementations to capture these facts. The theory of Lexical
Phonology/Morphology (Kiparsky, 1982) was the first attempt to derive the distribution of plurals-insidecompounds from the principles of a linguistic theory. Lexical Phonology contains a sub-theory, that of
Level Ordering, according to which regular inflection is claimed to be represented on a separate level which
is strictly ordered after the level concerned with other morphological processes such as irregular inflection,
derivation, and compounding. Thus, regular inflectional affixes are prevented from appearing inside
compounds. Level Ordering has since come under attack for a number of reasons, and other morphologists
have developed alternative theories that account for the constraints on pluralization in compounds. Di
Sciullo & Williams (1987) claim that lexical compounding joins stems rather than words, and that irregular
plurals should be regarded as stems and regular plurals as words. Similarly, Borer (1988) posits that
compounding takes stored words out of the lexicon and that irregular plurals, but not regular ones, are listed
in the lexicon. The idea that is common to these accounts is that the use of plural forms inside lexical
compounds correlates with the distinction between stored and computationally-based plural forms, and this
will be the focus of our study.
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3.2
Plural formation and plurals-inside-compounds in child language
In his seminal study, Gordon (1985) examined the question of whether the constraint on regular plurals in
lexical compounds is operative in early child language or whether it has to be learned through experience.
Gordon used an elicited-production task which prompted children to first produce a plural form of a given
item X (e.g. mouse ! mice) and subsequently a derived compound of the X-eater type (e.g. mouse-eater or
mice-eater). Gordon found that in more than 90% of the novel compounds produced by the children the
plural -s is not used on the non-head element; this even holds for the youngest children, i.e. the 3-year olds.
Overregularizations like *mouses sometimes occurred as a simple noun but never within a compound such
as *mouses-eater. Furthermore, it was found that as soon as the children have acquired irregular plurals they
sometimes use them inside compounds (as in mice-eater). Thus children behaved essentially like adults:
they were willing to say mice-eater and unwilling to say *rats-eater. Gordon interprets these results as
support for the early availability of the morphological ordering constraint in children. Clahsen et al. (1996)
replicated Gordon's experiment with 3 to 8 year old German children. They found a correlation between
overregularization and plurals-inside-compounds: plural forms that are used in overregularizations tend to
be omitted from the non-head elements of lexical compounds. This indicates that even though the children’s
plural forms might be incorrect in terms of the adult grammar, the ordering constraint on plurals-insidecompounds is still operative in the child’s grammar.
More recently, Alegre & Gordon (1996) presented results from a comprehension experiment testing the role
of the constraint against regular plurals in compounds. In their task, 3- to 5-year old children were presented
with pairs of pictures representing objects such as a red rat(s) eater. In one set of pictures, the eater was
painted red, in the other picture the victim was red. Half of the children were tested with plural forms, and
the other half were tested with the singular form inside compounds. Alegre & Gordon found that in the
plural condition the children chose the recursive interpretation [[red rats] eater], i.e, the picture where the
rats are red, rather than the picture in which the eater is red. By contrast, the children showed no such
preference in the singular condition. Thus, the constraint on regular plurals inside lexical compounds
triggered a syntactically-based analysis of the expression red rats as an NP. In the singular condition,
however, the construction is ambiguous between a non-recursive interpretation [red [rat eater]] and an NP-
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based interpretation [[red rat] eater], and thus children showed no preference. This finding confirms that the
ordering constraint is available to young unimpaired children, just as it is to adults.
3.3
Predictions for WS
Our previous research indicates that lexical retrieval is not functioning normally in WS subjects.
Specifically, we have argued that WS subjects are impaired in accessing information from subnodes of
lexical entries. This is how we explained their poor performance in irregular past tense formation and their
frequent -ed overregularizations (Clahsen & Almazan 1998). This impairment in retrieving information
from stored lexical entries should also affect other inflectional phenomena as well as the way WS subjects
form compounds. Similar to the past tense, plural formation in English involves an (-s) affixation rule for
regulars as well as a small number of irregular forms such as mice, teeth which are stored as subnodes of
structured lexical entries (see (2)).
(2)
[maus]
g
[..ai..]+plur
Hence, if access to subnode information is impaired in WS subjects, we would expect to find errors in the
formation of irregular noun plurals, e.g. -s plural overregularizations. In unpublished work, Bromberg et al.
(1994) reported that the WS subjects they tested had no trouble forming -s plurals of existing and novel
nouns, whereas there were errors in irregulars. In the present study, we will further investigate plural
formation in WS.
The hypothesized impairment should also have consequences for the WS subjects' compound formations. In
past-tense inflection, the WS subjects have shown difficulty with lexical exceptions, i.e. with irregular pasttense forms. Similarly, we might expect that their compound formations are not be constrained by lexical
factors, i.e. the WS subjects should allow regular -s plurals inside compounds.
To investigate plural formation and plurals-inside-compounds, three experimental tasks were adopted from
the developmental literature, two elicited production experiments, one for derived and the other for root
compounds (Gordon 1985, Clahsen et al. 1996), and one comprehension experiment on non-recursive vs.
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recursive compounding (Alegre & Gordon 1996). The experiments were administered to the WS subjects
and to control groups of unimpaired children with chronological ages similar to the mental ages of the WS
children. We will also compare the results from our WS subjects with findings on SLI children using similar
tasks.
4.
Subjects
We investigated 4 English native-speaking children (Jane, Florence, Emily and Martin) who were
independently diagnosed with WS by a multidisciplinary team including geneticists, developmental
psychologists and consultant paediatricians. The subjects’ chronological ages are as follows: Jane 11;2,
Florence 12;7, Emily 13;1, Martin 15;4. Their mental ages were derived from scores on the Wechsler
Intelligence Scale for Children - IIIuk (Wechsler 1992), by averaging the mental age equivalents for each
WISC-III subtest (see Temple et al. 2000). By this method, Emily and Jane had mental ages of 5;4 and 5;7,
whilst Florence and Martin had mental ages of 7;5 and 7;7 respectively. Results from administering the
British Picture Vocabulary Test (Dunn et al. 1982) to these children revealed that for all the WS subjects,
age equivalent receptive vocabulary scores were higher than their mental ages: Emily: 9;6, Jane: 6;8,
Florence: 10;2, Martin: 7;9. In the Test of Reception of Grammar (TROG, Bishop 1983), Florence and
Martin achieved near-ceiling scores, well above their mental ages. Emily’s and Jane’s TROG scores came
out lower and were similar to their mental age (5;0 - 5;11). However, many of the incorrect responses Emily
and Jane produced in the TROG were lexical (rather than grammatical) errors, i.e. comprehension problems
with lexical prepositions (confusing above and below), conjunctions (neither and nor) and comparative
adjectives.
5.
Experiment 1: Plural formation and derived compounding
The first experiment investigates regular and irregular plural formation as well as the use of plurals inside
derived compounds of the X-eater type. The procedures and materials were taken from Gordon’s (1985)
experiment. There were 18 items to be used as non-head elements of the compounds, 5 irregular nouns, 5
regular nouns, 4 pluralia tantum nouns, and 4 regular equivalents of the pluralia tantum nouns; these items
are shown in the appendix. The regular and irregular nouns were semantically similar to each other; there
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were 4 additional regular nouns paired with the pluralia tantum nouns. The pairs knife/scissors and
shirt/trousers were semantically matched, the pair toy/clothes was chosen, because they are both
superordinate terms, and shoe/(sun)glasses was chosen, because the referent of the noun shoe exhibits
similar configurational properties to (a pair of) glasses (since we are dealing with pluralization); see Gordon
(1985) for further details.
5.1
Method
The same procedure was followed for every item. A primary experimenter ran the experiment, while an
assistant prepared the toys for each trial. All experimental sessions were audio-taped. The experiment
involved three steps.
Step 1: The primary experimenter presented the child with a single item, e.g., a duck, and asked the child to
name the item with the sentence ‘What’s that?’.
Step 2: The child was presented with several instances of the item (e.g., four ducks). The child was asked to
provide the plural, using the sentence ‘Here we have a bunch of…what?
Step 3: Using the child’s plural response from the preceding step, the child was asked ‘And now Bernie eats
all the <PLURAL RESPONSE>. And how do you call somebody who eats <PLURAL RESPONSE>?. The
answer to this is the child’s ‘compound response’.
The children's plural responses in step 2 and their compound responses in step 3 were analyzed separately.
Rates of correct plural marking and overregularization rates were calculated for step 2 responses as shown
in (a) and (b). For the children's compound responses in step 3, we determined plural omission rates in
compounds as shown in (c):
a.
(# of correct plural forms )
correct plural marking rate: :
-------------------------------------------------(# of correct plurals + # of incorrect plurals)
b.
overregularization rate:
c.
omission rate:
(# of overregularizations)
-------------------------------------------------(# of overregularizations + # of correct irregulars)
(# plurals omitted in compounds)
----------------------------------------------------------------------(# plur. omitted in compounds + # plur. retained in comp.
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The subject groups selected for comparison with the WS subjects were two subgroups of unimpaired
children who had chronological ages similar to the mental ages of our WS subjects. The selection of
controls for studies of children learning disabilities is often controversial. One might argue, for example,
that WS children, who are hypothesized to have selective cognitive sparings, should be matched with
control subjects for specific cognitive abilities. This would indeed be particularly relevant for demonstrating
dissociations between language and non-linguistic cognition. The present study, however, examines
potential dissociations within the linguistic system of WS subjects. In addition to that, it is far from clear
which cognitive abilities are to be chosen as the crucial matching criteria. We have therefore decided to use
a relatively general measure of cognitive ability to select controls for the WS subjects. It should also be
noted that the decision to match the children with WS with overall mental age controls has been an accepted
protocol in many previous studies on WS (e.g. Bellugi et al. 1980, Volterra et al. 1996, Tyler et al. 1997).
The control data for the present experiment were taken from Gordon (1985) and from Christian (1997). The
children in these studies all underwent Gordon's original experiment.
Tab. 1: Control subjects
Chronological Age
Mean
Range
CTR-5 (n=11)
5;6
5;0 - 5;10
Gordon (1985)
CTR-6 (n=12)
6;4
5;4 - 7;10
Christian (1997)
5.2
Results
The first analysis concerns the children’s responses in step 2, when they had to produce plural forms of the
items presented. The WS children marked the plural overtly in 93% (48/52) of the items. Tab.2 shows that
with respect to nouns that take regular plurals, the WS subjects achieved high correctness scores, virtually
the same as those by the unimpaired controls. On nouns that take irregular plurals, however, the WS
subjects performed worse than the control subjects. This difference can be seen for both age groups, even
though it is less pronounced for the 5-year olds, due to the relatively low correctness score for the
unimpaired children who are still producing 48% incorrect irregular plurals. The last column in Tab.2
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shows children’s overregularization in step 2, excluding singular forms and non-plural forms. For the 5-year
old WS children, the rate is 40%, roughly the same as for the control children, and for the 7-year old WS
children the overregularization rate is higher than for the controls. For the unimpaired controls, the rate is
still higher than might be expected from the spontaneous speech of unimpaired children, but in line with
estimates from elicited speech (Marcus et al. 1992).
Tab. 2: Percentages of correct plurals and overregularizations
CorrectRe
Correct
Overregs.
gulars
Irregs.
WS5
100%
40%
40%
WS7
100%
50%
20%
CTR5
96%
52%
44%
CTR6
93%
87%
13%
Consider now plurals inside compounds, i.e. the results from step 3 of this experiment. In Tab.3 we
compare the plural form supplied by the children in step 2 with the compound form produced in step 3. The
first column represents cases in which the plural -s must be omitted from inside compounds, i.e. regular
nouns (e.g. rats) and the regular equivalents of pluralia tantum nouns (e.g. shoes) that were correctly
inflected in step 2 as well as irregulars that were overregularized in step 2 (e.g. *mouses). The second
column comprises cases in which the plural form can be maintained inside compounds, i.e. irregular plurals
and pluralia tantum nouns. The table shows percentages; the average number of omissions per subject is
shown in parentheses.
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Tab. 3: Percentage of omission of plurals in derived compounds
omissions of the regular -s
omissions of irregulars
plural
and pluralia tantum forms
WS5
82% (9)
58% (3.5)
WS7
45% (4.5)
36% (2.5)
CTR5
96% (10.8)
25% (1.5)
CTR6
94% (8.7)
41% (3.4)
Tab. 3 shows that the unimpaired children of both age groups show the expected pattern. They drop the
regular -s plural from inside compounds in 223 out of 235 cases, i.e. in 95%, whereas they omit irregular
plurals in just 34%, i.e. in 58 out of 168 cases. Gordon (1985) and Christian (1997) showed that this
difference came out as statistically significant in both groups of control children. It is clear from these data
that regular and irregular noun plurals behave differently with respect to compounds in unimpaired children.
Overall, the WS children tend to omit plurals from inside compounds less often than unimpaired children.
As is clear from the second column of Tab. 3, the WS5 subjects omitted more irregular plurals from inside
compounds than the corresponding control children (58% vs. 25%), whereas the WS5 children omitted
fewer regular plurals in compounds than the control children (82% vs. 96%). The WS7 children are similar
to the unimpaired controls with respect to irregular plurals in compounds (36%, 41%). For regular plurals,
however, the WS7 children performed much worse than the controls (45% vs. 94%). Overall, the WS
children incorrectly maintained the regular -s in 36%, compared to 5% for the controls.
In contrast to the unimpaired children, the WS subjects do not show a clear regular-irregular difference with
respect to compounding. A by-item paired t-test revealed no statistical significant difference for the WS
children between the use of regular and irregular plurals inside compounds (t(8) = -.61, p = 0.56). This is
also clear from the individual subject data. There are individual differences between the WS children in
their plural omissions. Crucially, however, none of the WS subjects showed a clear regular/irregular
distinction with respect to compounding. Martin maintained 9 regular plurals inside compounds and 6
irregulars, Emily had 3 regulars and 4 irregulars, Florence 2 regulars and 3 irregulars, and Jane 1 regular
and 2 irregulars. Examples are rats eater (Emily), ducks eater (Jane), beads eater (Florence), babies eater
(Martin). Thus, in contrast to the unimpaired children, the WS children do not selectively omit regular
plurals in compounds. This suggests that the constraint against regular plurals inside compounds is not
operative in WS subjects in the same way as it is in unimpaired children and in adults.
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6.
Experiment 2: Plural formation and root compounding
In contrast to experiment 1, in which the second constituent is fixed (= -eater) and is a derived word form,
in the present task the second constituent can be chosen at random, and it is a simple noun yielding a root
compound. The technique was adopted from Clahsen et al. (1996). Again, if the morphological ordering
constraint is available to children, we would expect them to omit regular plurals from inside compounds.
Experimental items were 7 with irregular plurals, 15 with regular plurals and 4 pluralia tantum nouns; the
items are shown in the appendix.
6.1
Method
The stimuli for this experiment consist of two sets of picture cards, plural cards and singular cards. Each
card consists of a photograph taken from magazine advertisements. The singular cards contain one object,
the plural cards multiple objects. The experiment involves three steps.
Step 1: The experimenter chooses a card containing multiple objects and asks the child to name it.
Step 2: The child is asked to choose a picture card with a singular item and to name it.
Step 3: The experimenter holds both picture cards together, the plural card on the left and the singular card
on the right, encouraging the child to form a compound by asking: 'Can you form a word out of these two?'.
Following this procedure, 26 trials were presented to each child. The child's response in step 1 is the plural
form of the particular items, and the child's response in step 3 the compound form.
This experiment was administered to the WS subjects and to 20 unimpaired children with chronological
ages similar to the mental ages of the WS children, 10 with a mean age of 5;5 (age range: 5;1 to 5;10) and
10 with a mean age of 7;5 (age range: 7;1 to 7;10). All controls live in native English-speaking homes and
were randomly selected by date of birth from a state school in North-East London. Subjects who had any
known neurological abnormality, learning difficulties or a history of special needs were excluded.
6.2
Results
17
As in the previous experiment, we will first examine correctness and overregularization scores for plural
marking. Tab. 4 shows that for nouns that take regular plurals, the WS subjects achieved the same high
correctness scores as the unimpaired controls, whereas for irregular nouns they performed much worse than
the control subjects. This is similar to the findings of experiment 1, but the contrast between the WS and the
unimpaired children is even stronger than in the first experiment. A repeated measures ANOVA revealed
significant interactions between subject group and the plural correctness scores (F(3,20) = 70.97, p < 0.01).
Subsequent post-hoc tests (using Tukey-HSD) showed that both groups of control children achieved
significantly higher correctness scores on nouns that require irregular plurals than the two corresponding
groups of WS children (WS5 vs. CTR5 q = 67.3, p < 0.01, WS7 vs. CTR7: q = 48.6, p < 0.01).
Tab. 4: Percentages of correct plurals and overregularizations
CorrectRe Correct
Overregs.
gulars
Irregs.
WS5
100%
28.5%
50%
WS7
100%
50%
35.7%
CTR5
100%
96%
4%
CTR7
100%
98.5%
1.4%
The last column of Tab. 4 shows that the WS children frequently overgeneralized -s to nouns that require
irregular plurals in English. This is in contrast to the two groups of unimpaired control children where -s
plural overregularizations were practically non-existent. The finding that the WS subjects heavily overapply
the regular plural is parallel to the results of experiment 1 and confirms previous findings from Bromberg et
al. (1994).
Consider now plurals inside noun-noun compounds. The first column in Tab. 5 shows omission rates of
regular -s plurals and irregulars that were overregularized in step 1. The second column shows how many
irregulars and pluralia tantum plurals were omitted in compounds. Omission rates were calculated in the
same way as in experiment 1. Tab.5 shows percentages; the average number of omissions per subject is
shown in parantheses.
Tab. 5: Percentage of omission of plurals in N-N compounds
18
WS5
WS7
CTR5
CTR7
omissions of the regular -s
plural
27% (5)
17.1% (3)
92.6% (13.9)
94.6% (14.2)
omissions of irregulars
and pluralia tantum forms
0% (0)
17.6% (1.5)
54.5% (6)
60% (6.6)
As is clear from Tab. 5, the control subjects showed the expected pattern of reduction of -s plurals inside
compounds, whereas for irregulars and pluralia tantum nouns omission is optional and the plural forms are
less often omitted. A by-item paired t-test revealed statistically significant differences between the use of
regular and irregular plurals inside compounds for both groups of unimpaired children (CTR5: t(10) = 2.89,
p < 0.05; CTR7: t(10) = 2.51, p < 0.05). In the WS data, however, there was no significant difference
between the use of regular and irregular plurals inside compounds. Most strikingly, the WS subjects
preferred to maintain regular plurals in compounds instead of omitting them, leading to 56 cases of
incorrect compounds with -s plurals as non-head elements. This holds for both correct -s plurals as well as
for -s plural overregularizations, as illustrated by the following examples:
(3)
a.
correct -s plurals
b.
overregularizations
bananas trumpet
foots cake
(Emily)
onions brush
tooths pizza
(Jane)
snakes ball
womans circle
(Florence)
mountains carrot
gooses fax
(Martin)
This is in marked contrast to the control children who maintained just 6% of the correct regular -s plurals,
and never one of the overregularized plural affixes. A repeated measures ANOVA revealed significant
interactions between subject group and the plural form used in compounds (F(3,20) = 6.86, p < 0.05).
Subsequent post-hoc tests (using Tukey-HSD) showed that both groups of control children omitted
significantly more -s plural inside compounds than the two corresponding groups of WS subjects (WS5 vs.
CTR5: q = 65.6, p < 0.01, WS7 vs. CTR7: q = 78.0, p < 0.01).
19
The results show that while unimpaired children systematically bar the regular plural -s from appearing in
compounds, this does not hold for the WS children. The WS children were found to use more -s plural
overregularizations than unimpaired children, achieving significantly lower correctness scores on irregular
plurals, and they often maintain regular -s plurals inside compounds. This provides further evidence that the
morphological constraint is not operative in these children.
7.
Experiment 3: Plural formation and recursive compounding
In our third experiment, we used a comprehension task to examine the constraint against regular plurals
inside compounds. Recall from section 3.1 that there are two ways of forming compounds in English, nonrecursive (lexical) and recursive (phrasal) compounding. While non-recursive compounding is restricted,
for example by the constraint against regular plurals as non-head elements, the range of possible elements in
recursive compounds is virtually unrestricted, including regular -s plurals. As pointed out in section 3.2, 5year old unimpaired children are sensitive to this distinction. Presentation of a regular plural form ('Show
me the red rats balloon') leads children to accept a recursive interpretation. However, when they are
presented with a singular form of the same noun ('Show me the red rat balloon'), there was no such
preference. This, according to Alegre & Gordon (1996), shows that the constraint against regular plurals in
lexical compounds prevents children from accepting a non-recursive interpretation.
With respect to WS children we would expect a different pattern of results. If the non-head elements used in
compounds are not restricted in these children, as suggested by the results of the previous two experiments,
the presence of a regular -s plural on the non-head element should not affect their compound interpretations.
Whatever is their preferred interpretation in the singular condition ('Show me the red rat balloon) should
also be the preferred interpretation in the plural condition ('Show me the red rats balloon').
7.1
Method
We adopted Alegre & Gordon’s (1996) procedure. The children were presented with nine coloured cards
and were asked to name their colour. The children were presented with pairs of pictures depicting an animal
or monster of colour X eating other animals of colour Y, e.g. a red monster eating blue rats. The second
picture in each pair showed the same event, but the colours were reversed, a blue monster eating red rats.
20
Half of the pictures depicted a single victim, e.g. one rat being eaten, and the other half showed several
victims. Children were presented with each pair of pictures and asked to identify the creatures shown as
well as the colours. They were then asked to pick one of the pictures from each pair by answering questions
such as 'Can you point to the picture that shows the red rat eater?' (= the singular condition), or 'Can you
point to the picture that shows the red rats eater?' (= the plural condition). There were 30 ‘point-to-the’type questions, instead of just 8 as in Alegre & Gordon. Of these 30 questions, 15 were in the singular
condition and 15 in the plural condition. It was ensured that none of the stimuli would semantically bias the
children to choose one interpretation over the other; see the appendix for a complete item list.
Stress assignment, pauses and intonation were controlled for following the procedures outlined in Alegre &
Gordon. The items were randomized for presentation, and the same pattern of questioning was used for all
of them. We also independently assessed the children's knowledge of colour terms by asking them to name
the colours of nine picture cards depicting all the colours used in the experiment.
Children were tested individually in a quiet room. The experiment was administered to the WS children and
to two groups of unimpaired children who live in native British English-speaking homes in West Yorkshire.
The children were randomly selected by date of birth from a state school. There was one group of 10
unimpaired children with a mean age of 5;5 (range: 5;3 - 5;9) and another group of 10 unimpaired children
with a mean age of 7;4 (range: 7;2 - 7;10). None of the controls was known to have any neurological
abnormality, learning difficulty or a history of special needs.
21
7.2
Results
All subjects, the WS children as well as the controls, performed the pre-test colour-naming task in an errorfree fashion. Tab. 6 presents percentages of non-recursive interpretations for the two experimental
conditions; the average number of non-recursive interpretations is shown in parentheses. Recall that the
non-recursive interpretation refers to the picture in which the eater (not the victim) is of the stated colour.
WS5
WS7
CTR5
CTR7
Tab. 6: Percentage of non-recursive interpretations
singular condition ('…the
plural condition ('…the
red rat eater')
red rats eater')
(11.5)
76.6%
83% (12.5)
80% (12)
83% (12.5)
45% (6.5)
18.2% (3)
62% (10.2)
8.5% (1.2)
A clear contrast emerges from these data between the WS subjects and the unimpaired children. For both
groups of unimpaired children, there is a significant decrease of non-recursive interpretations in the plural
condition; a by-item paired t-test revealed statistically significant differences between the compound
interpretation chosen in the singular and the plural condition for both groups of unimpaired children (CTR5:
t(14) = 5.56, p < 0.01; CTR7: t(14) = 4.47, p < 0.01). However, the WS data indicate that these children do
not distinguish between the singular and the plural condition in the use of non-recursive interpretations.
Tab.6 also shows that in both groups of unimpaired children, the percentages of (incorrect) non-recursive
interpretations in the plural condition are much lower than for the WS children. This is also confirmed
statistically. A repeated measures ANOVA revealed significant interactions between subject group and
compound interpretation, F(3,22) = 3.28, p < 0.05. Pairwise comparisons revealed no significant differences
between subject groups in the singular condition, indicating that the WS children like the unimpaired
controls preferred the non-recursive interpretation in this condition. For the plural condition, however, there
were significant group differences, showing that the WS children had significantly more (incorrect) nonrecursive interpretations than the control children.
In other words, when the WS children are presented with a singular non-head element, such as Show me the
red rat eater, they perform much like unimpaired children, giving relatively few recursive interpretations.
Recall that in this condition, subjects are free to interpret the compound as recursive or as non-recursive. In
22
most of these cases, the WS children went for the non-recursive interpretation. This preference corresponds
the general tendency to avoid left-branching structures in English. Note that while the non-recursive
interpretation of these compounds is based on a simple right-branching structure (e.g. [the [red] [rat eater]],
left branching is required for the recursive interpretation ([the [red rat] eater]). It is therefore not surprising
that children avoid recursive interpretations if grammatically possible.
Interestingly, however, the WS subjects (but not the unimpaired controls) also went for the non-recursive
interpretation in the plural condition, when they were instructed to show the red rats eater, even though the
non-recursive interpretation is ruled out by the constraint that prohibits regular plurals inside lexical
compounds. In this case, there is only one correct interpretation, namely the recursive interpretation.
Summarizing, there are two indications from this experiment that the ordering constraint is operative in
unimpaired children, near-ceiling performance in the plural condition, and a marked increase of recursive
interpretations from the singular to the plural condition. By contrast, for the WS subjects we found many
incorrect interpretations in the plural condition and no increase of recursive interpretations from the singular
to the plural condition. Hence, there are no signs that the constraint has any effect on the WS children’s
responses.
8.
Discussion
In the following, we will discuss the present set of findings on plural marking and on plurals inside
compounds in WS in combination with the results of our previous study of morpho-syntactic skills in WS
(Clahsen & Almazan 1998). We argue that the WS subjects’ performance on the various linguistic tasks can
be accounted for without assuming any impairments of the computational rule-based component of
language, and that where WS subjects perform worse than unimpaired children, this is due to problems in
accessing (particular kinds of) lexical information. We will also compare the grammatical profile of WS to
the performance of SLI children on similar tasks. It will become clear that the grammatical profile of WS
subjects does not extend to SLI.
8.1
Grammatical morphemes
23
Analyses of the expressive language of WS subjects revealed that the utterances they produce are
contextually appropriate and generally grammatically correct (Clahsen & Almazan 1998). Most of their
utterances contained multi-constituent sentences, 15% included embedded sentences, such as relative and
complement clauses. Functional categories such as finiteness markings and other grammatical morphemes
are well preserved in the grammars of the four WS subjects studied here; for each WS subject, the overall
score of correct use of grammatical morphemes in obligatory contexts was close to 100%. These
observations have been confirmed by Rice et al. (1999) in a study comparing spontaneous speech samples
of 5- to 7-year old SLI children and WS subjects of approximately the same chronological age. Rice et al.
found that the WS subjects did not drop grammatical morphemes in obligatory contexts and showed adultlike use of finiteness markings, whereas the SLI children they studied frequently omitted finiteness
markings such as the past tense -ed and the 3rd sg. -s. The optional use of finiteness markings in SLI
children has been argued to result from a delay in their development of syntax. According to Rice et al.
(1995), SLI children are stuck (for an extended period) in an early stage of syntactic development, the socalled optional-infnitive stage. Wexler (1998) characterized this stage in terms of constraints on the
grammatical interpretation of the formal features of functional categories, e.g. the so-called Unique
Checking Constraint (UCC). Basically, children in the optional-inifinitive stage are said to have difficulty
handling more than one formal feature at a time. SLI children are claimed to be severely delayed in this
aspect of their computational system.
The picture from WS children looks different. It is true that some previous studies have reported occasional
morphological errors in the expressive language of WS children (see e.g. Volterra et al. 1996, Capirci et al.
1996). Systematic error analyses, however, have revealed that the 11 to 15 year old WS subjects studied by
Clahsen & Almazan (1998) as well as the group of younger WS subjects studied by Rice et al. (1999) do
not show a morpho-syntactic profile that would be characteristic of an extended optional-infinitive stage.
Thus, in contrast to SLI children, the WS subjects’ system of formal features does not seem to be
developmentally delayed and is (in Wexler’s terms) not subject to developmental constraints such as the
UCC.
24
8.2
Syntactic chains and binding
With respect to more complex syntactic phenomena, two experiments showed that the WS subjects studied
by Clahsen & Almazan (1998) performed in an error-free fashion in interpreting verbal passives and
sentences involving reflexive anaphors. These findings indicate that the relevant syntactic mechanisms, Achains and binding principles, are not affected inWS. SLI children, on the other hand, have been shown to
perform much worse on the same tasks. Van der Lely (1996) found correctness scores of 60% to 67% for
the interpretation of verbal passives in 15 SLI subjects (mean age: 11;3). Likewise, these SLI children’s
scores on the interpretation of sentences involving reflexive pronouns were consistently lower than those of
the WS subjects and of unimpaired controls, specifically in sentences that had quantified antecedents (van
der Lely & Stollwerck 1997). Van der Lely (1998) has argued that the SLI children’s difficulties in these
tasks result from an impairment of the computational system of language, i.e. from a ‘representational
deficit with dependent relationships’. Whatever the precise nature of this deficit is, our findings show that it
does not hold for WS. A-chains and binding principles seem to be unimpaired in WS children.
8.3
Overregularizations
In two elicited production tasks, Clahsen & Almazan (1998) found that WS subjects heavily overapplied the
regular past tense -ed, even in cases in which unimpaired children would typically not use the regular form.
The -ed affix was (incorrectly) supplied by the WS subjects to 38% of the existing irregular verbs tested (as
opposed to 13% for the unimpaired controls), and to 65% of the nonce verbs that rhymed only with existing
irregular verbs (compared to 19% for the unimpaired children). In the present study, we found that nouns
taking regular plurals were always correctly inflected by the WS subjects, whereas on nouns that take
irregular plurals, the WS subjects performed much worse, with only 42% correct. The WS subjects also
heavily overapplied the regular plural affix, with rates which can be more than twice as high as those of
unimpaired control children. These findings replicate those on the past tense indicating that inflectional
rules might be excessively used in WS subjects.
This is also confirmed by the results of a recent study with 2 German-speaking WS subjects (Krause &
Penke 2000). Krause & Penke found that the WS subjects (chronological age: 15 and 18 years) achieved
high correctness scores on regular participle and plural inflection, while for irregular participle and plural
25
inflection they performed much worse than a group of unimpaired children matched for mental age to the
WS subjects. Furthermore, Krause & Penke found that the WS subjects overregularized the regular -t
participle, even to high-frequency irregular verbs, an error that did not occur in the control data. They also
found that (in contrast to the unimpaired controls), overapplications of irregular plural patterns are
practically non-existent in the WS data. These observations suggest that the regular/irregular dissociation in
WS (as described in Clahsen & Almazan (1998) for English-speaking WS subjects) may hold crosslinguistically and for different inflectional systems.
The picture on overregularization rates we get from SLI children is rather different. The two past-tense
tasks we used with WS subjects were also employed with SLI children, by van der Lely & Ullman (1998)
for 9- to 12-year olds and by Oetting & Horohov (1997) for SLI children with a mean age of 6;3. The SLI
children exhibited significantly lower overregularization rates than the WS subjects, i.e. they rarely
produced -ed past tense forms of either existing or novel irregular verbs. Rather, the SLI children’s most
frequent response was either a correct past tense form or a repetition of the base form of the verb. In
contrast to WS subjects, overregularization of -s plurals are reported to be rare in English-speaking SLI
children. Van der Lely & Christian (2000) found that in the production of regular and irregular plural forms,
the SLI subjects they studied (aged 10 to 18 years) showed a similar performance to unimpaired control
children. This result is parallel to Rice & Oetting's (1993) findings on 5-year-old SLI children. On the other
hand, several studies have reported significant frequency effects for regularly inflected plural and past-tense
forms for children with SLI, but not for unimpaired controls (see e.g. Rice & Oetting 1993, Oetting &
Horohov 1997, van der Lely & Ullman 1998). Moreover, Gopnik & Goad (1997) performed acoustic
analyses of plural markers in 9 SLI subjects (aged: 9 to 77 years) to show that at least some of the SLI
subjects failed to exhibit the voicing assimilation required for this affix. These findings suggest that the
morpho-phonological rules of plural formation might not be completely adult-like in some SLI subjects, and
that they may have stored representations for at least some regular forms (hence the frequency effects for
regulars). In any case, what seems to be clear from the SLI data on inflectional morphology is that (unlike
WS subjects) children and adults with SLI do not excessively overapply regular rules of inflection.
8.4
Plurals inside compounds
26
Evidence from three experiments presented in this study shows that the WS children’s interpretation and
production of compounds is not affected by the constraint against regular plurals in lexical compounds. In
the first experiment, we found that the WS subjects maintained regular -s plurals inside compounds,
producing ungrammatical derived compounds such as *rats-eater; there were also no regular/irregular
differences in their compound omission rates. In experiment 2, the WS children produced many
ungrammatical root compounds with regular -s plurals as non-head elements. As in the first experiment,
there were no significant differences between irregular plural nouns and regular -s plurals in the compound
omission rates. In experiment 3, the WS children were found to frequently misinterpret compounds such as
red rats eater; in contrast to unimpaired children, the presence of a regular plural did not have any effect on
the WS children’s interpretation of the compound. The results from these three experiments converge on
one important point, namely that in WS subjects regular plurals can freely occur inside compounds. This is
different from adult English as well as from early child language. Gordon (1985) found that even the
youngest children in his sample, i.e. the 3-year olds, were sensitive to the difference between regular and
irregular plurals inside compounds. Clahsen et al. (1992, 1996) replicated Gordon’s results for German
child language. All age groups of unimpaired children in the Clahsen et al. studies, even the youngest one
below age 3, produced irregular plurals inside compounds and avoided regular plurals. These findings
indicate that the constraint against regular plurals inside compounds is available early on and does not have
to be learned in any meaningful sense. Thus, it seems as if the pattern of plurals inside compounds observed
in WS does not correspond to any developmental stage found in unimpaired children.
SLI children have also been studied with respect to plurals inside compounds. Oetting & Rice (1993)
replicated Gordon's (1985) elicitation task with a group of 14 SLI children (mean age: 5;3) and two control
groups, a group of 19 unimpaired children matched for chronological age with the SLI children and a group
of 12 younger unimpaired children (mean age: 2;11) that were matched to the SLI group in terms of mean
length of utterance (MLU). Oetting & Rice found that the SLI children's response patterns were similar to
those of the unimpaired children in that all three groups rarely produced a regular plural form (rats) or an
overregularized plural (*mouses) as the non-head element of a compound, whereas for irregulars, the
majority of the nominal compounds included the plural form. This shows that SLI children treat regular and
27
irregular noun plurals differently with respect to compounding, suggesting that at least in this group of
English-speaking SLI children, the ordering constraint against regular plurals in lexical compounds is
operative in the same way as it is in unimpaired children.
Van der Lely & Christian (2000) found a different pattern for a group of 16 older SLI children (mean age:
13;11). Using the experimental task from Gordon (1985), they found that 35% of the correct regular plurals
were maintained inside compounds and 47% of the correct irregulars, a difference that did not turn out to be
significant. Note, however, that in contrast to what was found for the WS subjects, the SLI subjects studied
by van der Lely & Christian omitted 90% of the overregularized (i.e. productively formed) plurals
(*mouses) inside compounds. This is parallel to the results of Oetting & Rice (1993) on SLI and to all
available results on unimpaired children including van der Lely & Christian's own control groups. That SLI
children ban overregularized plurals from occurring inside compounds indicates that the ordering constraint
is operative in English-speaking SLI children. The fact that van der Lely & Christian’s subjects sometimes
maintained existing regulars in compounds could mean that SLI subjects have stored representations for
some of the existing regulars, a suggestion that has independently been made by Gopnik (1994), Goad &
Rebellati (1994) and Gopnik et al. (1996). This may also apply to the cases of existing regular plurals inside
compounds reported by van der Lely & Christian. If so, the constraint would not be violated in such cases.
Studies on plural formation and plurals-inside-compounds in German-speaking SLI children (Clahsen et al.
1992, Bartke 1998) also show that the constraint against rule-based plurals in compounds is functioning in
SLI children. Clahsen et al. (1992) examined spontaneous speech samples from 19 SLI children. In the 100
lexical compounds found in these samples, the regular plural affix -s (which is ungrammatical inside
compounds in German) was always left out by the SLI children, while irregular plural affixes were often
maintained inside compounds. In both respects, the SLI children's compounds did not differ from those of
adult German. Moreover, there was a significant correlation between the overregularization rates of
particular affixes and the rates at which these affixes were omitted inside compounds. This is parallel to
what was found for unimpaired children. Bartke (1998) investigated plural formation and compounding
experimentally in 4 SLI children. She elicited 75 plural forms and corresponding lexical compounds in two
elicited production tasks that were adapted to German from Gordon (1985). Bartke found that 73% of the
regular plural affixes were omitted from compounds, whereas only 38% of the irregular plural forms were
28
dropped inside compounds. These figures are similar to those from a control group of 8 unimpaired children
who also underwent the two elicitation tasks. These results indicate that in contrast to what was found for
WS subjects, the constraint against regular plurals does not seem to be affected in SLI children.
8.5
The grammatical characterization of WS
Taken together, the profile of morpho-syntactic skills in WS appears to be quite different from that of SLI
children. Whereas SLI children show difficulty and delays in core aspects of syntax (feature checking, Ai
chains, binding principles), WS subjects seem to be unimpaired on these phenomena . By contrast, the WS
subjects were found to perform worse than the SLI children on irregular inflection and plurals inside
compounds, phenomena that involve lexical exceptions or constraints. It is clear from the above that the
grammatical profile of WS does not hold for SLI and vice versa. The further question, however, of whether
the WS profile is unique to this syndrome or whether it may also be found in other kinds of neurodevelopmental disorders requires further comparative studies. As there are practically no studies
investigating the morpho-syntactic skills of children with neuro-developmental disorders (see TagerFlusberg 1999 for a recent review), this question will have to be left to future research.
We suggest that the observed profile of morpho-syntactic skills in WS can be derived from a common
source, a selective impairment in retrieving information from the lexicon. By contrast, the computational
(rule-based) system of language appears to be unimpaired. Recall from section 2 that irregularly inflected
forms such as drove or mice are assumed to be stored in long-term memory, as subnodes to the
corresponding basic lexical entries, e.g. drive and mouse respectively; see (1) and (2) for illustration. WS
subjects, we argue, find it difficult to access phonological and/or morphological feature information
represented on subnodes of lexical entries. In contexts in which an irregular past tense or plural form is
required and the WS child does not access the relevant subnode information, the basic lexical entry is still
retrieved and a past tense or a plural is formed by applying inflectional rules ('Add -ed', 'Add -s'), yielding
overregularization errors. Thus, we do not claim that the lexical system as a whole is impaired in WS
subjects. Accessing basic lexical entries does not cause problems, as can be seen from the fact that stem
29
forms of regular verbs are almost always appropriate. Instead, WS subjects seem to have a more specific
difficulty in retrieving subnode information in lexical entries.
It is important to note that in past tense and plural contexts, WS subjects do not leave verbs and nouns
uninflected, but rather produce overregularization errors. This is different from SLI children who often
produce bare stems, even in cases in which, for example, a past tense form is required; see Wexler’s (1994,
1998) optional infinitive account. Formal features such as tense and number are crucial parts of the
syntactic representation, but the way they are spelled out is secondary. SLI children underspecify or omit
formal features from their syntactic representation, producing optional infinitives. This is not the case for
WS subjects. From a syntactic perspective, the -ed and -s overregularizations WS subjects produce are lowlevel morphological errors. Syntactically it does not matter much whether the tense feature in a clause is
spelled out as drove or as drived or whether the number feature in a DP is spelled out as mice or as mouses.
These considerations indicate that the syntactic representations of WS subjects (in contrast to those of SLI
children) are fully specified for formal features, and that the frequent overregularization errors result from a
lexical difficulty, i.e. the retrieval of (subnode) information from lexical entries. To compensate for this
difficulty, WS subjects make use of their computational knowledge, i.e. of inflectional rules.
Consider, finally, plurals inside compounds. The three experiments we administered to the WS subjects
have produced converging results indicating that the ordering constraint which prohibits regular plurals
inside lexical compounds in English has no effect on the WS subjects' production and comprehension of
plurals inside compounds. Instead, WS subjects seem to allow irregular as well as regular plural forms to
appear inside compounds. This is in contrast to what has been found for SLI children and unimpaired
children of different age groups including the youngest ones, i.e. 3-year olds, to which these experiments
could be administered.
With respect to the WS subjects' compound formations, recall that in adult English the non-head element of
a lexical compound can only be a listed form, i.e. a bare uninflected stem or an irregular plural form such as
mice (given that irregulars form subnodes of lexical entries). A regular plural such as nails, however, is not
a lexically listed stem, and cannot appear inside a lexical compound. Hence, lexical compounding is
restricted to stored items and may require access to subnode information from lexical entries (e.g. teeth in
teeth marks). In the WS data, however, the non-head elements occurring inside compounds are not lexically
30
constrained; instead, the WS subjects freely allow regular plurals inside compounds. It is important to note,
however, that even though the WS subjects' compound formations are unusual compared to what is known
from unimpaired children, they are not ungrammatical. This is because English offers a second way of
forming compounds, namely phrasal compounding, and the constraint against regular plurals does not hold
for phrasal compounding. Any well-formed phrase (including a regular plural) can appear as the non-head
element of a phrasal compound; this is how one might account for cases such as parks commissioner,
buildings inspector, etc. (see Alegre & Gordon 1996 for discussion). Given the two options of forming
compounds in English and the hypothesized lexical impairment, it is conceivable that the WS subjects take
the lexically unrestricted option and form (phrase-based) compounds in the syntax. This would account for
the fact that the WS subjects do not ban regular -s plurals from occurring inside compounds. This
interpretation of the WS subjects' unusual compounding behaviour also fits in with the results on the past
tense and on plural inflection, i.e. their frequent overregularization errors and their difficulties with irregular
inflection. In both cases, an otherwise productive computational operation (e.g. -ed affixation, lexical
compounding) is constrained or has exceptions in the adult language, and we found that it is these
exceptions and constraints that cause difficulty for the WS subjects.
9.
Conclusion
Linguistic studies of Williams Syndrome help define a grammatical profile of this impairment, i.e. a precise
characterization of the morpho-syntactic skills of WS subjects. The present set of findings on noun plurals
and compounding together with the results of our previous study on passives, anaphoric binding and the
past tense contribute towards a grammatical profile of English-speaking WS subjects. We found that the
WS subjects do not show any syntactic impairments, and that they perform excellently on regular past tense
and plural inflection. On the other hand, their scores on irregular past tense and plural forms are worse,
lower than those of unimpaired controls. Moreover, the WS subjects were seen to use regular rules of
inflection excessively, even in circumstances in which unimpaired children (and adults) would not use them,
e.g. as non-head elements inside compounds. SLI presents us with a different pattern, in which core aspects
of syntax such as feature checking, movement chains and binding principles seem to be impaired or severely
31
delayed, whereas the use of stored (irregularly inflected) word forms and of plurals inside compounds does
not cause any specific problems.
We suggest that the WS subjects’ performance on the various linguistic tasks can be explained in terms of
lexical problems, e.g. in accessing subnode information from lexical entries, without assuming any
impairments of the computational rule-based component of language. This interpretation is compatible with
findings on the lexical skills in WS. Temple et al. (2000) examined vocabulary levels and lexical access in
the same group of WS subjects that we have studied. They found that the WS subjects had elevated levels
of receptive vocabulary compared to their mental age, and generated significantly increased proportions of
low frequency items in oral fluency tasks. Furthermore, the WS children were found to produce naming
errors, many of which were atypical. Despite their anomic naming performance, the WS children responded
faster in naming tasks than unimpaired controls. Temple et al. argued that the naming errors arise at the
level of word selection during lexical access and can be attributed to fast but sloppy selection. Our finding
that the WS subjects sometimes fail to retrieve irregular past tense and plural forms fits in with the view that
'children with WS have a lexical system where access is too fast and with insufficient editing of responses'
(Temple et al. 2000: 27).
At a more general level, these findings represent a challenge for associative models of language according
to which 'distinctions between regular and exceptional (i.e. irregular) patterns of behavior can emerge
through the operation of a single mechanism' (Elman et al. 1996: 131). Instead, the dissociation found
between (unimpaired) computationally based operations and (impaired) memory-based retrieval of stored
items provides evidence for the dual nature of the language faculty, according to which these two systems
are independent and therefore dissociable (Pinker 1999, Clahsen 1999). We also found distinctive
performance patterns for WS and SLI subjects that are hard to explain without making this distinction.
Acknowledgements
We are grateful to the children who participated in this study as well as their parents and teachers. We also
thank Peter Gordon for providing us with experimental materials and Carolyn Mervis, Christine Temple,
32
Martina Penke, Claudia Felser, and Heather van der Lely for commenting on earlier versions. We are also
grateful to Andrew Radford for a close reading of the paper and for correcting our English. Our research on
Williams Syndrome is supported by a grant from the Research-Promotion Fund, University of Essex, jointly
awarded to Christine Temple and Harald Clahsen.
33
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Appendix
Items used in Experiment 1
Regulars: rat, baby, bead, hand, duck, toy, shirt, shoe, knife
Irregulars: mouse, man, tooth, foot, goose
ii
Pluralia tantum nouns: clothes, trousers , glasses, scissors
38
Items used in Experiment 2
Regulars: elephant, apple, bottle, butterfly, banana, cat, onion, helicopter, bear, church, snake,
flower, spider, mountain, glass
Irregulars: tooth, foot, mouse, woman, goose, child, man
Pluralia tantum nouns: trousers, glasses, scissors, clothes
Items used in Experiment 3:
Question Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Pretest
Red-blue
Monster-rats
Red-blue
Monster-rats
Brown-white
cow-flowers
Brown-white
cow-flowers
Pink-yellow
Monster-spiders
Pink-yellow
Monster-spiders
Red-white
Fish-crabs
Red-white
Fish-crabs
White-brown
Lion-birds
White-brown
Lion-birds
Yellow-pink
Monkey-bananas
Yellow-pink
Monkey-bananas
Red-green
parrot-spiders
Red-green
parrot-spiders
Orange-green
Monster-turtles
Orange-green
Monster-turtles
Pink-brown
Monster-cats
Pink-brown
Monster-cats
Brown-pink
Elephant-plants
Brown-pink
Elephant-plants
Pink-green
Gorilla-snake
Pink-green
Question
Can you point to the red rat eater?
Can you point to the red rats eater?
Can you point to the brown flower eater?
Can you point to the brown flowers eater?
Can you point to the pink spider eater?
Can you point to the pink spiders eater?
Can you point to the red crab eater?
Can you point to the red crabs eater?
Can you point to the brown bird eater?
Can you point to the brown birds eater?
Can you point to the yellow banana eater
Can you point to the yellow bananas eater?
Can you point to the green spider eater?
Can you point to the green spiders eater?
Can you point to the green turtle eater?
Can you point to the green turtles eater?
Can you point to the pink cat eater?
Can you point to the pink cats eater?
Can you point to the brown plant eater?
Can you point to the brown plants eater?
Can you point to the green snake eater?
Can you point to the green snakes eater?
39
23
24
25
26
27
28
29
30
i
ii
Gorilla-snake
Brown-black
Camel-worms
Brown-black
Camel-worms
Blue-red
Whale-divers
Blue-red
Whale-divers
Yellow-green
Frog-flies
Yellow-green
Frog-flies
Orange-pink
Dog-flowers
Orange-pink
Dog-flowers
Can you point to the brown worm eater?
Can you point to the brown worms eater?
Can you point to the blue diver eater?
Can you point to the blue divers eater?
Can you point to the green fly eater?
Can you point to the green flies eater?
Can you point to the orange flower eater?
Can you point to the orange flowers eater?
It should be acknowledged, however, that most of the evidence for this comes
from older WS children, and that little is known about the morpho-syntactic
abilities of 3 to 5 year old WS children. It might therefore be possible that very
young WS children may evidence difficulties or atypicalities not shown by older
WS children.
In the original experiment, Gordon (1985) employed the American English word
pants, we substituted it for the British English trousers.