Date: Tue, 8 Jun 2004 12:50:28 +0200
From: Susana Perales Haya
Subject: Language Competence Across Populations: Toward a Definition of SLI
EDITORS: Levy, Yonata; Schaeffer, Jeannette
TITLE: Language Competence Across Populations
SUBTITLE: Toward a Definition of Specific Language Impairment
PUBLISHER: Lawrence Erlbaum Associates
YEAR: 2003
Susana Perales, University of the Basque Country (Spain)
INTRODUCTION
The editors of the book have gathered in this volume 17
articles (chapters) that were presented at a workshop on
Specific Language Impairment (SLI) held in Jerusalem in
2000. The book is divided into Part A, which comprises 15
chapters and whose title is ''Language competence across
populations'' and Part B, ''Toward a definition of SLI?''. The
first part is subsequently subdivided into three sections:
The first one is ''The characterization of Specific Language
Impairment'' (chapters 1-7), the second one is
''Methodological Concerns'' (chapters 8-11) and finally, the
third section is entitled ''Language competence in children
with neurodevelopmental disorders'' (chapters 12-15).
As the editors themselves declare in the preface, the
book's focus is on ''the question of how much variability
linguistic competence can take in children as they develop''
(p. x). Thus, although the focal theme is SLI, other
language disorders (e.g. language in autistic children or
children with Williams Syndrome) are also portrayed and
discussed in the book.
SUMMARY
The first chapter ''Lenneberg's dream: Learning, normal
language development, and specific language impairment''
(Ken Wexler) explores the interrelation between the study
of SLI and normal language acquisition. Wexler first
introduces the Optional Infinitive (OI) stage in normally
developing children, which is characterized by the
production of an infinitive form in contexts where the
adult grammar requieres an inflected verb. Wexler explains
the OI stage as the result of a limitation in the child's
computational system which prevents him from checking more
than once against the D-feature of noun phrases. The
''Unique Checking Constraint'' (UCC), as Wexler calls it, ''is
a developmental constraint on the computational system of
language'' (p. 33) and not only gives a linguistic account
of the OI stage, but also predicts that children acquiring
null subject languages (e.g. Spanish, Italian) do not go
through this stage, as has been reported in the literature
(see Wexler 1998 for an overview). As for how normally
developing children recover from the OI stage, it is
proposed that ''it matures away, under genetic guidance'' (p.
40), and Wexler reviews several arguments that support this
proposal.
As far as SLI is concerned, Wexler explains how the
proposal to account for OIs in normal children can also be
used for SLI children. Thus, he claims that SLI children go
through an Extended Optional Infinitive (EOI) stage,
implying that the maturation responsible for the withering
away of the UCC in normal children does not operate or is
delayed in SLI children. In this way, both normal and
impaired language development can be accounted for with the
same theoretical apparatus, something highly desirable in
linguistic theory. Moreover, as Wexler makes explicit all
throughout the article, linguistic-based accounts are
preferable to other proposals that place the child with no
specific knowledge of linguistic categories but only with a
set of general cognitive learning mechanisms (e.g.
Tomasello 2000, cited in the article), with the result that
the phenomena related to the OI stage are left unexplained.
In chapter 2 ''A unified model of specific and general
language delay: Grammatical tense as a clinical marker of
unexpected variation'', Mabel Rice deals with tense marking
as a diagnosis of SLI and places emphasis on distinguishing
between a selective delay in language acquisition, which is
indicative of a deficit in an element of grammar, and a
general delay, which does not necessarily imply that a
particular aspect of grammar is affected.
Rice reports on various longitudinal studies of English-
speaking SLI children. First, she deals with grammatical
tense marking (e.g. third person ''-s'') and her results show
that for the SLI group, the variation expected at age 5
falls below that of normally developing children. In order
to examine whether the problem with grammatical tense
marking is a reflection of a more general deficit affecting
low salient morphemes, Rice compared performance on the
plural marker ''-s'' and found that all groups of children
used this marker productively, which denotes that grammar,
rather than phonology, is involved in SLI. However, that
wasn't the case in lexical acquisition and mean length of
utterance (MLU) measures, where SLI children seemed to be
lagging behind the normal controls, and no particular
aspect of grammar was affected.
When comparing SLI children versus children with Williams
Syndrome, Rice found that they performed similarly in MLU,
plurals and prepositions, but the SLI group performed
significantly worse on tense marking. This suggests that
grammatical tense marking is a reliable clinical marker. To
conclude, Rice points out that, in order to decide whether
low performance in grammatical tense marking is indicative
of a general language delay or a selective language delay,
other measures (e.g. MLU, lexical development, etc.) must be
taken into consideration.
In the third chapter (''Two of a kind? The importance of
commonalities and variation across languages and learners'')
Martha Crago and Johanne Paradis examine how SLI manifests
itself with regard to verbal morphology in three languages:
English, French and Inuktitut, and in three different
populations: normally developing children, SLI children and
second language learners. Crago and Paradis raise several
issues regarding the Extended Optional Infinitive stage
proposed by Wexler (chapter 1). The matters they discuss
concern the ultimate attainment of SLI affected children,
the fact that SLI does not manifest in the same way across
languages, and that SLI children do not always behave like
normal language-matched controls. They highlight the
importance of figuring out if SLI children reveal simply a
delay with respect to normal language acquisition or
whether it would be better to speak of a deviant language
acquisition process. Also, they cast doubt on the
appropriateness of the term ''Optional infinitive'' because
SLI errors across languages normally involve the use of
default rather than infinitive forms.
Chapter 4 ''Do heterogeneous deficits require heterogeneous
theories? SLI subgroups and the RDDR hypothesis'' (Heather
K. J. van der Lely) deals with the controversy surrounding
the domain-specific versus domain-general accounts of SLI.
Some scholars regard evidence of SLI children affected in
phonological or pragmatic measures as indicative that SLI
is not a domain-specific language deficit (e.g. Karmiloff-
Smith 1998, cited in the article). However, after reviewing
research studies exploring different language abilities
within homogeneous subgroups of SLI children, Van der Lely
argues that ''the simplest explanation for the association
between disorders is the propensity for comorbidity of
disorders in development'' (p. 123).
Van der Lely goes on to report the results of her study of
a homogeneous SLI sub-group: the Grammatical SLI subgroup,
which is characterized by deficits in tense and agreement
marking along with other problems with syntactic operations
like, for instance, theta-role assignment or embedded
clauses. The author claims that Grammatical SLI is caused
by a deficit involving the obligatoriness of movement
operations. This proposal allows her to account for a wide
range of syntactic phenomena that characterize the
Grammatical SLI subgroup performance.
In chapter 5, Jeannette Schaeffer addresses the issue of
modularity within the human language faculty. More
specifically, she concentrates on the study of pragmatics
as an independent module from the lexicon and the
computational system. For this purpose, she investigates
the performance of Dutch SLI and normally-developing
children on object scrambling, a syntactic phenomenon which
is triggered by pragmatics. Schaeffer entertains the
hypothesis that SLI children are impaired in their grammar,
but not in their pragmatics and therefore, the application
of object scrambling will not be affected in these
children. Her results support this hypothesis as Dutch SLI
children do correctly scramble referential objects 96% of
the time. Thus, she concludes, the pragmatic module is not
affected in SLI, which is evidence that pragmatics and the
computational system are independent modules within the
human language faculty.
In Chapter 6 (''Specific language impairment and linguistic
explanation'') Jan de Jong considers the issue of the
different predictions and explanations that stem from
distinct theoretical proposals. De Jong reports the results
of an experimental study with Dutch SLI children which
shows that the developmental order of acquisition of
finiteness in English is not comparable to the Dutch order.
Then, he goes on to propose an alternative explanation of
the OI stage (Wexler, chapter 1), namely the ''Modal drop
hypothesis'' (Ingram & Thompson 1996), which claims that
children OI sentences should be interpreted as containing a
null modal. The chapter ends with the observation that the
same surface phenomenon can have diverse theoretical
interpretations, each of which differing in the degree of
knowledge the SLI child is credited with.
Chapter 7 is the last chapter of the first section and its
title is ''The role of language typology in linguistic
development: Implications for the study of language
disorders'' (Dorit Ravid, Ronit Levie and Galit Avivi Ben-
Zvi). These authors explore the knowledge of Hebrew
derivational morphology by SLI children and normally
developing controls. An experimental study was conducted on
comprehension and production of nouns and adjectives, which
showed that SLI children performed significantly lower than
normal controls in most cases. Thus, the authors assert
that ''derivational morphology was found to be diagnostic of
the impaired population'' (p. 189). They also underscore the
importance of looking at typologically diverse languages,
and including measures like comprehension in order to gain
a greater understanding of SLI.
In chapter 8 (''Specific language impairment: characterizing
the deficits''), Laurence B. Leonard discusses several
methodological questions with regard to the study of SLI
focusing on three broad areas: definition of SLI, research
design and hypothesis testing, and data interpretation.
These issues are central to a well known fact in SLI
research: children with SLI are far from being a
homogeneous group. This poses a problem for replicability,
as two studies focusing on the same linguistic aspect may
obtain different results due to the intrinsic
characteristics of the sample they look at. Thus, Leonard
proposes the inclusion of descriptive data so as to
facilitate subject selection, replication and
identification of subgroups. The author also discusses the
convenience of several research methods, such as group
versus individual case studies, group-matching criteria,
the importance of designing studies that take into account
how SLI children are affected by different types of
treatment, as well as the need for longitudinal studies.
Finally, the chapter ends with the discussion of how
different hypotheses may lead to contrasting conclusions,
stressing that ''each discipline's basic assumptions should
be spelled out, measures should be compatible with these
assumptions, and null hypotheses should be framed in a
uniform manner'' (p. 228)
Chapter 9 (''Methodological issues in cross-group
comparisons of language and cognitive development'' by
Carolyn B. Mervis and Byron F. Robinson) discusses
methodological questions regarding group-matching
procedures, chronological age confounds and other problems
stemming from cross-group comparisons. They also discuss an
alternative method: profiling, which implies, firstly, to
determine whether a given linguistic profile is
characteristic of a particular child and, secondly, to
determine how characteristic/uncharacteristic that profile
is of the children who are/are not in the SLI group.
The main theme discussed in chapter 10 (''MLU-matching and
the production of morphosyntax in Dutch children with
specific language impairment'' by Gerard W. Bol) is the use
of MLU measures in SLI studies. The author illustrates some
of the problems arising from the use of MLU as a marker of
productive morphosyntax as well as its use as a means to
match different groups of subjects, and he also puts
forward suggestions that may help to overcome these
difficulties. In the second part of the article, the author
conducts a study on Dutch children which attempts to figure
out how Dutch SLI children compensate for loss of utterance
length. He identified seven variables like, for instance,
the use of conjunctions, prepositions and adverbials, verb
forms used for indicating past tense, etc. However, none of
the phenomena he looked at seemed to be used by Dutch SLI
children to compensate for loss of sentence length. He
concludes that MLU is not a valid measuring strategy for
Dutch, and calls for alternatives to MLU.
In chapter 11 (''Different methodologies yield incongruous
results: A study of the spontaneous use of verb forms in
Hebrew'' by Esther Dromi, Laurence B. Leonard & Anat Blass)
spontaneous and elicited production data from Hebrew SLI
children and normally developing controls are compared
focusing on verb morphology. The first part of the article
is devoted to the review of published results obtained in
the investigation of verbal morphology using a series of
tasks specially designed to elicit specific verb forms. The
use of tasks allowed the researchers to manipulate
variables and concentrate on particular aspects regarding
performance on verbal morphology.
In the second part of the article, the authors compare the
results obtained in the elicitation studies with
spontaneous production data. One of the strengths of the
study is that the SLI children and the controls were the
same in both the elicited and the spontaneous production
studies. The authors resolve that both tasks are necessary
tools for the study of SLI and thus should be combined to
get an accurate picture of SLI children's performance.
In Chapter 12 (''Language impairment in children with
complex neurodevelopmental disorders'') Helen Tager-Flusberg
examines the linguistic differences and similarities
between autistic and SLI children. The author describes an
experimental longitudinal study in which two samples from
the groups mentioned above were compared on a series of
phonological, lexical and grammatical tests. The results
point to the fact that within the group of autistic
children there was a subgroup which performed similarly to
the SLI group, which leads the author to highlight that
autism and SLI are ''overlapping populations'' (p. 311). The
results of this study bear directly on current research
which is showing that there may be a shared gene in autism
and SLI.
Harald Clahsen and Christine Temple take up the issue of
the modularity of the mind in chapter 13 (''Words and rules
in children with Williams syndrome''). Their study measures
performance of children with Williams syndrome on
comparative adjectives, receptive / productive vocabulary
and reading skills. They aim to show that modular accounts
are preferable to other non-modular connectionist models,
as they are able to explain a wider range of effects.
In chapter 14 (''Basic language skills in children with
neurodevelopmental disorders and the notion of brain
plasticity'') Yonata Levy studies the performance of several
groups of children with diverse neurodevelopmental
disorders on a series of grammatical tasks, as well as
their response to requests for clarification. A first study
was conducted to examine the linguistic performance of 8
children with neurodevelopmental disorders on 13 variables
like syntactic agreement, gender marking, etc. The language
problems found in these children reflected a delayed
although not different linguistic profile with respect to
normally developing children.
The second study assessed children's response to
clarification requests. Roughly, it was found that the
ability of children with neurodevelopmental disorders to
detect errors in their own speech as response to
clarification requests matches the pattern seen in normally
developing children. Results show that, up to an MLU of 3,
there is not much variation in the course of language
development irrespective of the population, and Levy
suggests this may be due to brain plasticity assuring a
basic level of language performance.
Signed and spoken languages are compared in chapter 15 (''On
the complementarity of signed and spoken languages'') by
Wendy Sandler. She considers the idea that sign and spoken
language are two parts of a unique human language faculty.
After reviewing some of the similarities and differences
between sign and spoken language, the author shows evidence
from gesture that supports her proposal. Gesture, as the
author claims, is a natural part of communication, both for
deaf signers (who gesture with the mouth) and for oral
speakers (who gesture with their hands), and its study
should lead to a deeper understanding of the human language
faculty.
The second part of the book (''Toward a definition of SLI?'')
comprises the last two chapters. Chapter 16 (''Understanding
SLI: A neuropsychological perspective'' by Dorit Ben Shalom)
considers how the study of SLI can benefit from studies of
other cognitive disorders and vice versa. In the first
place, the author compares SLI with prosopagnosia (impaired
face recognition) and claims that the fact that there are
specific grammatical deficits in SLI does not necessarily
imply that SLI should be defined in terms of exclusionary
criteria. Secondly, Shalom compares three phenomena related
to SLI and agrammatism: tense marking, reversible passives
and nonword repetition. She suggests that there may be two
types of grammatical processing, one phonological and one
syntactic, and states that the study of both should guide
us to provide an accurate answer to the general problem of
grammatical processing in the brain.
In the last chapter (''Defining SLI: A linguistic
perspective'') Jill G. de Villiers takes up several issues
that have been discussed in the articles gathered in the
book: (i) the question of whether SLI children are a
different group from other cognitively impaired children,
(ii) SLI as a reflection of a specific problem in the
language module, (iii) the heterogeneity of SLI and,
lastly, (iv) whether SLI is better described as a deficit
or a delay. De Villiers does an excellent job at
summarizing and commenting the key points raised by the
articles in the book, as well as suggesting further lines
of investigation.
EVALUATION
As a whole, the book provides an excellent overview of
current issues concerning research on SLI. For the most
part, the authors have been carrying out research on SLI
for quite a number of years, which is an extraordinary
opportunity to get first-hand knowledge of the topics that
have been debated and the answers that have been advanced
so far with regard to SLI. Another outstanding issue
regards the fact that all contributors have read each
other's articles and, thus, they refer the reader to
particular chapters where the same issues are discussed.
This contributes to maintain a coherent line and helps the
reader to situate arguments and positions within the SLI
research framework.
The book is well suited for scholars doing research on SLI
because they will get an overall picture of the field as it
stands nowadays, as well as because there are specific
proposals that suggest new lines of investigation. This is
particularly true of the section on methodological
problems, as the chapters herein included spot specific
methodological flaws that should be overcome in future
studies. Graduate students with a fair command of
linguistic theory will also find the book interesting, as
well as those acquainted with the literature on normal
language acquisition.
To conclude, I consider this volume is an outstanding
contribution not only for the answers it provides, but also
for the questions it leaves open for further research.
REFERENCES
Ingram, D. & Thompson, W. (1996) ''Early syntactic
acquisition in German: Evidence for the modal hypothesis''
Language 72: 97-120.
Karmiloff-Smith, A. (1998) ''Development itself is the key
to understanding developmental disorders''. Trends in
Cognitive Sciences 2: 389-398.
Tomasello, M. (2000) ''Do young children have adult
syntactic competence?'' Cognition 74: 209-253.
Wexler, K. (1998) ''Very early parameter setting and the
unique checking constraint: A new explanation of the
optional infinitive stage'' Lingua 106: 23-79.
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