The developmental approach to the study of Down syndrome: Contemporary issues in historical perspective
Tara Flanagan, Natalie Russo, Heidi Flores and Jacob Burack
The developmental approach provides an essential framework for understanding Down syndrome. Paradoxically, this framework both narrows and broadens the scope of research in the field. The narrowing involves a more fine-tuned approach to diagnosis, a more precise delineation of skill in relation to specific aetiology and developmental level, and fine-tuned matching strategies that involve comparisons on specific aspects of functioning. The broadening of the scope involves the consideration of the “whole child” in terms of personality, social, and emotional development, within the context of families, communities, and societies. This far-reaching developmental perspective revolutionised the study of intellectual disabilities with its theoretical, methodological, and interpretive innovations, while this more precise approach to the study of persons with intellectual disabilities in turn served to transform developmental theory by challenging, extending, and reconceptualising well-established developmental principles.
The current study of Down syndrome is inherently linked to the advent of the application
of the developmental approach to the study of the broader population of intellectual
disabilities. The conceptual and methodological innovations co-opted from developmental
research and applied to the study of intellectual disabilities were, paradoxically,
the catalyst for both a narrowing and a broadening of the scope of research. The
narrowing of the scope involved more definitive diagnostic criteria of different
aetiologies associated with intellectual disabilities, aetiology-specific conceptualisations
of intellectual disabilities, and the precise delineation of skill in relation to
developmental level and methods for matching by developmental level (for reviews,
1-6). The broadening of the scope involved studies in the field of
intellectual disabilities research designed to better encompass what Zigler referred
to as the "whole child"[7,8]. This
included accounting for personality, social, and emotional factors of the child,
and for the familial and larger contextual factors, all within the context of syndrome-specific
developmentally based research. Paradoxically, both the narrowing and the broadening
of the research focus within the field of intellectual disabilities were conceived
as a response to traditional views in which persons with intellectual disabilities
were considered to be a homogenous group with one or more common defects regardless
of aetiology or age (for discussions, see refs 9,10). Conceptually, at least, discussions
of strengths and weaknesses among persons with specific aetiologies at specific
ages in specific contexts now supersede monolithic pronouncements of specific deficits.
Thus, the outcome of the adoption of a developmental framework is a level of precision
of understanding of persons with intellectual disabilities that could not even be
anticipated in traditional conceptualisations.
The increased theoretical sophistication, broadened scope, and methodological precision
provided by the developmental approach serve to highlight the vastness of the endeavour
and the difficulties that are inherent to understanding persons with intellectual
disabilities. Within this context, persons with intellectual disabilities must always
be considered within the context of their aetiology and developmental level, and
in many cases with regard to social, behavioural, emotional, familial, and/or environmental
factors. And, the confluence of all these factors must be further considered with
regard to the intricacies of the ever changing real world. Thus, the increased specificity
of knowledge highlights the futility of attempts to generalise findings across the
heterogeneous group that we refer to as persons with intellectual disabilities and
clearly the notion of a single grouping or field of research under the title of
"intellectual disabilities" seems meaningless.
Yet, this is not a call of despair. Rather, the goal is to promote the vision of
research of increased precision that has its origins in 19th century
writings by pioneers of aetiological-specific research, such as Langdon Down and
William Wetherspoon Ireland, and in 20th century writings by developmental
theorists, including Heinz Werner, Edward Zigler, Dante Cicchetti, and their colleagues
who promoted the interface of developmental psychology and the study of intellectual
disabilities. This approach finds fruition in the 21st century sophistication
of experimental technology and empirical methodology in the study of genetics, brain
functioning, behaviour, social and interpersonal functioning, and emotional well-being,
as well as in the study of the relations among them. The emergence of these increasingly
precise approaches to research resonates particularly strongly with the advocates
of the more fine-tuned developmental approach with its emphasis on aetiology- and
age-specific research within the context of individuals, their families, and their
environments. Through this synergy, the key to understanding the heterogeneous group
of persons who fall under the diagnostic heading of intellectual disabilities is
a bottom up process with small but fine-tuned and precise empirical "stories"
rather than a top-down process with bigger and more general but flawed accounts.
In this article, we briefly review essential theoretical, methodological, and interpretative
contributions of the developmental approach and attempt to forge a framework for
research in the field of intellectual disabilities, as well as of Down syndrome,
and to reflect upon how the field of intellectual disabilities research has contributed
and transformed the understanding of general developmental processes.
The theoretical timeline: The developmental framework and intellectual disabilities
The study of cognitive and neuro-cognitive functions or abilities may best highlight
the contributions of the developmental approach to intellectual disabilities. These
types of functions were the singular focus in the first few decades of scientific
research on intellectual disabilities, when most empirical work in the field was
characterised by a race to identify the deficit that was the primary cause or marker
of reduced intellectual functioning. Those who undertook this frantic search emphasised
broad constructs of cognition that were considered to be essential across all domains
of cognitive functioning, including cognitive rigidity, memory processes, discrimination
learning, and attention, among many others (for a review, see
With the use of sophisticated experimental paradigms, researchers presented compelling
evidence of deficient performance in virtually all of these areas of functioning.
Each specific defect was touted as the central cause of intellectual disabilities.
Unfortunately, the studies were "fatally" flawed as researchers failed
to consider essential and obvious conceptual and methodological issues such as the
multiplicity of aetiologies associated with intellectual disabilities, the uniqueness
of each with regard to phenotypic expression, the inherent differences in developmental
level of functioning between persons with and without intellectual disabilities
of the same chronological age, and the non-cognitive factors related to life experiences
that are associated with cognitive performance. In critiquing and debunking the
various claims of the defect theorists, Zigler and colleagues (e.g., refs 6,7,8 ,12)
introduced a conceptual approach to intellectual disabilities that would be based
on classical developmental theory and would revolutionise the way people with intellectual
disabilities were viewed and studied.
The holistic but precise developmental framework
Consistent with early researchers of intellectual disabilities from the 19th (e.g.,
and 20th centuries (e.g.,
refs 15-18), Zigler proposed the 'two group
approach to intellectual disabilities' in which persons for whom the cause of intellectual
disability was familial should be conceptually differentiated from those for whom
intellectual disability could be classified as organic.
He argued that intellectual ability is characterised by a bi-modal distribution
with one mode falling as expected at an IQ of 100, and a second mode, at the tail
end of the impaired side of the normal distribution with a mode of 50. Whereas persons
with intellectual disabilities with a familial source were considered to represent
the lower end of the normal distribution of intellectual functioning, persons whose
intellectual disability had an organic basis, represented the area under the second
mode. Accordingly, Zigler proposed that these two groups were qualitatively and
quantitatively different from one another. Citing epidemiological work by Dingman
and Tarjan, he elaborated that persons
with familial, but not necessarily those with organic, causes of intellectual disability
should follow a similar developmental trajectory as typically developing persons,
albeit at a slower rate and to a lower asymptote.
The developmental story for persons with intellectual disabilities associated with
organic aetiologies was less clear. Consistent with the universal approaches of
traditional developmental theory, they were found to consistently traverse the sequences
of development for Piagetian and other cognitive tasks in the same order as was
evident among persons with intellectual disabilities with a familial source and
among typically developing children (for a review, see ref 19). However,
the organic insults were expected to be associated with structures of horizontal
development, the relationship across areas of functioning, that were different form
those of typically developing persons, so that general indicators of mental age
would not necessarily be associated with level of functioning in specific domains. Yet, even here the notion of meaningful development
was not abandoned as developmental theorists advocated for meaningful relations
across domains of functioning, even when the levels of functioning seemed discordant.
For example, Cicchetti and Pogge-Hesse argued that specific examples of organic
aetiology provide unique opportunities to expand the study of development as they
can be viewed as testing the limits of developmental organisation.
Furthermore, the slower pace of development and the discrepancies across domains
of functioning that are evident among persons with Down syndrome or other specific
aetiologies were cited as unique opportunities to examine the synchronies and asynchronies
in development and the extent to which the convergence of aspects of functioning
in typically developing persons are real or happenstance[22,23].
Accordingly, the notion of local homologies,
the relationships over time across tasks that require common underlying capacities,
was borrowed from the study of development and applied to the study of persons with
intellectual disabilities associated with organic aetiologies[5,25,26]. Within this framework, even apparently
discordant performance across domains can be considered within the context of an
organised developmental system.
The issue of developmental level
One reason that so many areas of defect were identified over the years was that
the target groups of persons with intellectual disabilities were virtually always
compared with typically developing persons matched on chronological age (see ref 9).
By definition, then, the persons with intellectual disabilities were functioning
at a lower level than those without intellectual disabilities and would be expected
to perform worse on any task that was age-appropriate and sufficiently sensitive
to differentiate between groups with considerably different levels of functioning.
Yet, despite the inevitability of the findings of group differences, the defect
theorists cited the impaired performance among the persons with intellectual disabilities
as evidence of a core deficit.
In highlighting one example of the extent to which advocates of the defect approach
misled the field, Iarocci and Burack and Burack et al., demonstrated that the notion
of attention as the core, or at least a central, defect, that was perpetuated from
the 1960s through the 1990s was based on series of articles in which matching was
exclusively based on chronological ages[9,10].
Accordingly, they argued that the findings of attention deficit would be expected
on virtually any area of functioning when chronological age matching is used. In
other words, the proponents of the attention defect theory had simply found that
"lower functioning persons were functioning at lower levels than higher functioning
persons". This, of course, is not at all surprising. Rather, based on developmental
theory, a deficit among persons with intellectual disabilities would only be important
if it was found in comparisons with typically developing persons matched on some
relevant indicator of developmental level, ranging from general measures of mental
age to more specific ones that mirror the task. A deficit in this scenario is more
likely to indicate an actual impairment because the groups are equated on developmental
level. Matching on the basis of developmental level was initiated in the 1960s in
studies of developmental disabilities, such as intellectual disabilities[7,8] and autism.
Although a few defect theorists persist in their use of chronological age matching,
by the 1990s, matching on developmental level had become a hallmark of developmental
research in the field of intellectual disabilities (e.g., refs 28,29,30).
As with many of the other areas of scholarship in the developmental approach to
intellectual disabilities, the techniques for matching by developmental level continue
to be discussed and developed, and are continuously fine-tuned (e.g., refs 28,30-33).
Among others, Loveland and Kelley and Burack et al., highlight the need to utilise
matching is linked to the development of abilities that are pertinent to the specific
function or task[28,34].
This strategy minimises the chances that differences in performance between the
groups might be an artifact of a specific relative strength or weakness displayed
by one of the groups in the area of functioning related to the experimental task
(for a related discussion, see ref 24). In order to further reduce the
risk of confounds arising from a priori group difference, Mervis and colleagues
call for rigorous statistical test criteria in the matching of groups[30,31].
With all this increased sophistication in the methodological approaches to matching,
the clear conclusion is that the complexity of the developing organism precludes
a single perfect approach to comparing across groups of persons. Rather the goal
is to simply utilise strategies that minimise the likelihood that the primary findings
are associated with obvious confounds.
In the case of yet another paradox, the discussions of matching by developmental
level allow for considerably more precise assessments of the implications of the
research findings from various experimental paradigms, but also allow for alternative
approaches. For example, Burack and colleagues argue for the use of multiple matching
measures in order to allow for the identification of the complex profiles of development
across areas of functioning[29,35].
However, this approach does not inherently provide insight about developmental changes
over time unless it is varied out across different age groups or in a longitudinal
paradigm. In an attempt to better depict the dynamic aspects of the developmental
processes, both Jarrold and Brock and Cornish, Scerif and Karmiloff-Smith eschew
matching strategies in favour of regression models that are used to chart developmental
trajectories[36,37]. This approach is reminiscent
of the early work on developmental trajectories of IQ among specific aetiological
groups, especially persons with Down syndrome (for a review, see
and is a useful reminder that the study of intellectual disabilities is inextricably
tied to developmental theory. Yet, this approach is limited by the extent to which
it useful in the complexities of the continually evolving structure in which each
domain, sub-domain, and sub-sub-domain of functioning develops at its own rate but
also in relation to each of the others. Furthermore, this approach is less useful
in the study of adulthood when developmental trajectories are limited or even flat,
but the understanding of specific aspects of functioning or patterns of functioning
is still informative for intervention. These benefits and limitations of the various
developmentally-based strategies highlight the breadth of the developmental approach
and that the choice of methodological strategies needs to be guided by the underlying
theory and research questions.
Conclusions: developmental theory and the study of intellectual disabilities
Cicchetti and Pogge-Hesse suggest that development is a dynamic process that is
not adequately captured through the simple static delineations of intact and impaired
'modules'. Rather development unfolds
over time in a complex interplay of factors that include, but are not limited to,
gene-environment relationships, critical periods for the development of specific
areas of functioning such as language, the relationship between and within different
areas of functioning, and the impact of compounding delays or differences over the
course of an organism's growth.
As the influence of the developmental approach in the study of intellectual and
other developmental disabilities increased dramatically by the end of the last century
ref 39) and into the new one,
the complexities of understanding developmental trajectories of specific aetiological
groups was emphasised conceptually[29,35,40,41] and across areas of research. For example,
both Burack, Evans, Klaiman and Iarocci, and Cornish, Scerif and Karmiloff-Smith
argued that the study of attention among persons with developmental disabilities
needs to be considered within the context of specific aetiology, specific aspect
of attentional functioning, specific developmental level, and of changes over time[9,37].
The identification of these types of intricacies of the developmental relations
across domains of functioning is central to the notion that cognitive and neurocognitive
aspects of functioning are intrinsically interrelated even if not always temporally
synchronous[42,43], and, therefore, the study
of specific aetiologies provides a effective lens for general notions of development. For example, Zelazo, Burack, Benedetto and
Frye argued that their finding that individuals with Down syndrome, who had mental
ages of approximately 5 years, tended to focus on a single state rule in theory
of mind and rule use tasks was inconsistent with claims that theory of mind is a
domain-specific psychological function but is consistent with the notion of developmental
organisation. Within this type of framework,
the unique developmental patterns evident among groups of persons with intellectual
disabilities, in general, and among those with Down syndrome, are informative about
general developmental processes and about the integrity of developmental systems
in which the organisation is challenged.
The study of persons with intellectual disabilities is a clear example of the basic
tenet of the discipline of developmental psychopathology that typical and atypical
development is essentially related and mutually informative[45,46].
Officially formalised by Zigler, the developmental approach in the study of intellectual
disabilities revolutionised research in the area by both narrowing the scope of
research to increase its precision and broadening the scope to include notions of
the whole person[7,8]. Zigler's influence continues
to resonate in current research on intellectual impairments that considers aetiology-specific
variables in conjunction with the contextual factors that impact the functioning
of a child. The evolutions and revolutions in research concerning individuals with
intellectual impairments highlight the theoretical, methodological, and interpretive
innovations that were afforded by the introduction of a developmental framework.
In turn, this fine-tuned approach to research among individuals with intellectual
impairments served a transformative function with which fundamental aspects of developmental
theory are challenged, extended, and even reconceptualised.
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The work on this manuscript was supported by an operating grant from the Social
Sciences and Humanities Research Council of Canada to J. A. Burack. The authors
thank Alexandra D'Arrisso for her work in the preparation of the manuscript.
Tara Flanagan and Heidi Flores are at McGill University, Montréal, Québec, Canada.
Natalie Russo and Jacob A Burack are at McGill University and Hôpital Rivières-des-Prairies
Correspondence to Jacob A. Burack, Department of Educational and Counselling Psychology,
McGill University, 3700 McTavish Street, Montréal, Québec H3A 1Y2 • e-mail:
Paper prepared from presentations and discussions at the Down Syndrome Research
Directions Symposium 2007, Portsmouth, UK. The symposium was hosted by Down Syndrome
Education International in association with the Anna and John J Sie Foundation,
Denver. Major sponsors also included the Down Syndrome Foundation of Orange County,
California and the National Down Syndrome Society of the USA. Information about
the symposium can be found at
Received: 6 March 2008; Accepted 13 march 2008; Published online 4 July 2008