Chapter 1
Developments in the Developmental Approach to Intellectual Disability
Jacob A. Burack, Natalie Russo, Cathryn Gordon Green, Oriane Landry, and Grace Iarocci
āMake for yourself a teacher, acquire for yourself a friend, and judge everyone in a positive lightā¦ā Ethics of the Fathers (Pirkei Avot, 1, 6). We dedicate this chapter in honor of Ed Zigler for all his contributions to the science and welfare of so many children, including those with intellectual disability. He is the most inspiring teacher, loyal friend, and positive influence to all who know him. As with so much of his work, his articulation of the developmental approach to intellectual disability helped humanize our understanding of a population that for too long had been underserved and kept at the fringes of society. We are especially grateful to Dante Cicchetti for inviting us to contribute this chapter, on a topic about which we are so passionate and about which he was a visionary. His leadership both in the world of science and in making the world a better place for children is an example to us all. We thank Jillian Stewart, Johanna Querengesser, Ashley Reynolds, Icoquih Badillo-Amberg, David McNeil, Eric Keskin, and Martina Tiberi as well as other members of the McGill Youth Study Team for their help in preparing the manuscript.
- DEVELOPMENTS IN THE DEVELOPMENTAL APPROACH TO INTELLECTUAL DISABILITY
- THE DIAGNOSIS OF INTELLECTUAL DISABILITY AND ITS (LACK OF) MEANINGFULNESS
- Diagnostic Criteria and Assessment
- THE ORIGINS OF THE DEVELOPMENTAL APPROACH TO THE STUDY OF INTELLECTUAL DISABILITY
- THE TWO-GROUP APPROACH AND BEYOND
- Zigler's Emphasis on Familial Intellectual Disability
- Differentiating Among Organic Etiologies: Extending Beyond the Two-Group Approach in the Quest for Increased Precision
- APPLYING DEVELOPMENTAL PRINCIPLES TO THE STUDY OF PERSONS WITH INTELLECTUAL DISABILITY: CLASSIC AND EXPANDED VERSIONS
- Zigler and the Classic Developmental Approach
- Cicchetti's Expansion of the Developmental Approach to Persons With Organic Etiologies: A Focus on Persons With Down Syndrome
- THE IMPORTANCE OF MENTAL AGE
- Considering Developmental Level
- THE STUDY OF THE āWHOLE PERSONā WITH INTELLECTUAL DISABILITY
- Social Competence
- Language Development
- The Impact of a Child With Intellectual Disability on the Family
- NEUROSCIENCE AND THE DEVELOPMENTAL APPROACH: BENEFITS AND PITFALLS IN THE APPLICATION OF CUTTING-EDGE TECHNOLOGY
- A Primer on What fMRI and ERP Measure
- Neuroscience and the Developmental Approach: A Messy Meeting of Disciplines
- CONCLUSIONS
- From Genes to Brain to Behavior in Intellectual Disability: Future Directions in Research
- Summary
- REFERENCES
Developments in the Developmental Approach to Intellectual Disability
The developmental study of intellectual disability is a long-established forerunner of developmental psychopathology with origins that predate the formal emergence of the latter discipline by decades, and yet is still in its early, and sometimes apparently regressive, stages of developmental emergence relative to other areas of work. It was largely shaped by scholars, such as Heinz Werner, Edward Zigler, and Dante Cicchetti, who were also seminal to the emergence of the scholarly discipline of developmental psychopathology, and yet it is often conceptualized as a separate unrelated entity. These complex relationships provide a lens through which we can understand the advances, and setbacks, in the study of intellectual disability, and its place in the domain of developmental psychopathology (and thereby in this volume). Within this framework, we highlight the thinking and research that led to and continue to maintain the developmental approach to intellectual disability and consider them with regard to developments in the study and understanding of intellectual disability since Hodapp and Burack's (2006) chapter in the last edition of this handbook (Cicchetti & Cohen, 2006).
As intellectual disability is essentially defined by the development of cognitive abilities and, to a considerably lesser extent, social skills that are so delayed and ultimately impaired that it only involves a small percentage of persons, it is a paradigmatic example of the construct of development at the extreme that is so essential to the field of developmental psychopathology (Burack, 1997; Cicchetti & Pogge-Hesse, 1982). In this way, intellectual disability also exemplifies Urie Bronfenbrenner's notion of an experiment of nature, which could never be replicated in an experimental setting but in this case is informative for understanding the course of typical cognitive and social development. Thus, consistent with Cicchetti's (1984) dictum that āyou can learn more about typical functioning by studying its pathology and more about its pathology by studying its typical stateā (p. 4), intellectual disability is a window into addressing issues and questions about cognitive and social development that cannot be fully answered when only considering typically developing persons (Burack, 1997; Cicchetti & Pogge-Hese, 1982; Hodapp, Burack, & Zigler, 1990). In providing the example of extreme delay, or impairment, intellectual disability would appear to allow us the opportunity to examine the integrity of the developmental system from the unique perspective of especially slowed or delayed development (Cicchetti & Beegly, 1990; Hodapp & Burack, 1990; Hodapp & Zigler, 1990). As is often the case in nature, this āslow motionā analysis of cognitive and social development allows for a particularly intense level of scrutiny that cannot be attained with events occurring at their typical speed.
The converse of Cicchetti's dictum is also particularly relevant to the study of intellectual disability as the theories and methodologies that have governed the study of development among typically developing persons have, during the past half century, transformed the way that persons with intellectual disability and their families are studied, understood, educated, and supported (for related collections, see Burack, Hodapp, Iarocci, & Zigler, 2012; Burack, Hodapp, & Zigler, 1998; Cicchetti & Beeghly, 1990; Hodapp, Burack, & Zigler, 1990). These advances are the focus of this chapter as we highlight the ongoing and evolving conceptual, methodological, and interpretive contributions of the so-called developmental approach to the study of persons with intellectual disability and the ways that they have led to a more precise and sophisticated science (Burack, Dawkins, Stewart, Flores, Iarocci, & Russo, 2012; Burack, Russo, Flores, Iarocci, & Zigler, 2012; Cicchetti & Ganiban, 1990; Hodapp, Burack, & Zigler; 1990).
The Diagnosis of Intellectual Disability and Its (Lack of) Meaningfulness
Although the diagnosis has far-reaching implications for the development and outcomes of the affected persons, intellectual disability cannot be considered at all tangible. Virtually unique among the phenomena addressed in this volume, the designation of intellectual disability is essentially based on a behavioral classification culled from scores on single measures used to operationalize each of two constructsāin this case, primarily the construct of intelligence but often also that of social adaptation. Typically, people who score in approximately the lowest 3% of the population, or two or more standard deviations below the mean, on standardized tests of intelligence and behavioral adaptation are considered to be intellectually disabled. However, the utility of this designation is compromised in two essential ways. One, the cutoff score is entirely arbitrary. Two, the low IQ, or behavioral, scores can be attained for different reasons and with different profiles as evidenced by the study of the handful of the most common of the more than 1,000 possible etiologies, each of which seems to differ considerably from the other conditions and situations associated with intellectual disability (for reviews, see Burack, 1990; Burack, Hodapp, & Zigler, 1988, 1990; Cornish & Wilding, 2010; Dykens, Hodapp, & Finucane, 2001). These group differences are especially apparent in developmental rates and trajectories as well as the profiles of relative strengths and weaknesses across the myriad of cognitive and social skills that are thought to impact intelligence and the many sub- and sub-sub-tests that make up the various different IQ tests and indexes of behavioral adaptation that are used for the diagnosis. Even given the usual within-group differences that are found in any population, the compelling and clearly demarcated group discrepancies on many aspects of functioning highlight the profound and complex developmental effects of the genesābrainābehavior relations associated with each syndrome that virtually swamp any generalized developmental effects of simply lower levels of intelligence and social adaptation (for relevant collections, see Burack et al., 1998; Burack, Iarocci, et al., 2012; Howlin, Charman, & Ghaziuddin, 2011; Tager-Flusberg, 1999).
With these pervasive group differences across virtually all aspects of being and functioning, the notion of a population of persons with intellectual disability is a mirage. Thus, the phenomenon precludes a science or study of intellectual disability per se but rather would appear to necessitate the invocation of multiple sciences of identifiable populations that differ meaningfully from each other with regard to etiology, defining features, and developmental trajectories. In this framework, both the concept and the field of intellectual disability are inherently deconstructed from the monolithic framework of a single problem and population to more precise, albeit with the consequent of increasingly complex, conceptualizations and research (Burack, Russo, et al., 2012). This demise of a single science or framework of intellectual disability would seem to come at considerable cost. Prior so-called knowledge about persons with intellectual disability as a whole needs to be forsaken, while the alternative of the imposition of multiple fine-grained fields of study based on clearly differentiated populations inevitably entails considerably more work and would seem to signal the abandonment of any sense, or even hope, of a comprehensive and cohesive field of study. Yet, when the additional work is associated with the imposition of a developmental approach that is premised on the notion of a systemic, organized, and universal system, it provides both more precise information and a unifying framework with which the various fragments of information can be grouped into a meaningful area of scholarship (Burack, 1997; Burack, Iarocci, et al., 2012; Cicchetti & Ganiban, 1990; Cicchetti & Pogge-Hesse, 1982; Karmiloff-Smith, 2009; Zigler, 1969, 1973; Zigler & Balla, 1982; Zigler & Hodapp, 1986).
Diagnostic Criteria and Assessment
In one sense, intellectual disability is relatively easily conceptualized. Across the decades and even centuries of work with persons with intellectual disability, the basic notion has been that a certain percentage of persons function at such low levels of intelligence and social adaptation that they cannot survive or function independently in society, or at least need some intensive external support to do so (e.g., Luckasson et al., 2002; AAIDD, 2010; for reviews, see Rosen, Clark, & Kivitz, 1976; Zigler & Hodapp, 1986). However, intellectual disability is also an odd and elusive behavioral classification as it involves the grouping of an extremely heterogeneous population according to amorphous concepts, arbitrary criteria, and prevailing societal values, all of which have changed often during the past century (for recent discussions, see Bertelli et al., 2014; Salvador-Carulla et al., 2011; Schalock et al., 2010; Shulman, Flores, Iarocci, & Burack, 2011).
