enges.
Deficits in measured intellectual/cognitive abilities are not enough
IDD are most often considered in terms of performance on individualized measures of intelligence. Historically, the development and introduction of intelligence testing represented a major breakthrough in our ability to measure and classify IDD. But it wasn’t long before researchers and clinicians realized that normalized measures of intelligence provided only a portion of what was needed. Yet in many programs, service providers still use IQ scores to group patients into broad categories (mild, moderate, severe, and profound levels of ID). As we shall see, this view is incomplete (6, 13)
In educational settings, this IQ score shorthand is used in decision-making about classroom placement, setting performance expectations as well as designing educational programs to match academic and daily life skills training needs. Yet the validity of these predictions is often derailed by positive effects of early intervention and better management of neurodevelopmental disorders such as seizures and the negative effects of severe behavioral problems, neuropsychiatric and medical disorders (e.g., cerebral palsy or epilepsy). In addition, disruptive behaviors and the presence of unrecognized or inadequately treated mental disorders have a deleterious effect on educational performance (14). These persist into adulthood as behavioral problems that adversely affect structured employment, community independence, social activities, and residential living and produce levels of psychosocial stress on caregivers and alter the quality of life (7).
Psychodynamic-oriented clinicians use IQ scores to formulate hypotheses about their role in psychosexual, psychosocial and cognitive development. The relationship between mental age and developmental stages is a permeable one but these data do provide a system of staging strengths and vulnerabilities and clarify developmental levels of functioning. Within a psychodynamic framework, arrests and derailments of many lines of development underlie working hypotheses about the sources of challenging behaviors and how these may represent manifestations of various mental disorders. This system is less often applied and often less useful in the presence of severe IDD, cerebral palsy, epilepsy and other neurological, genetic disorders (including recognizable behavioral phenotypes) (7, 15).
In the final analysis, it is a combination of these models with behavioral and neuropsychological data that help us integrate biology, past life experiences and psychological development into our understanding of aggression, self-injurious behavior (SIB), hyperactivity and stereotypies. The increased use of attachment and separation-individuation models are providing additional insights into how an individual with IDD adapts and responds to his psychosocial environment (16). In addition, ethology, neuro-ethology and behavioral pharmacology are becoming useful tools in understanding complex social behaviors such as aggression or avoidance behaviors. This information may be as valuable as measured intellectual abilities in explaining what initiates and maintains these behaviors.
Deficits in adaptive skills are more than meets the eye
Adaptive skills represent an amalgam of abilities associated with 1) behavioral flexibility, 2) experiential learning (“plastic” intelligence), 3) problem solving, 4) coping with novel settings 5) task demands (procedural learning) and 6) mastery of skills of daily living. Social intelligence is another subset of adaptive skills that do not seem directly tied to other forms of intelligence but play a key role in all forms of skill learning (14). This relative disconnect reinforces the importance of adaptive skills in the definition of IDD.
For example, individuals with mild IDD may have sufficient adaptive skills to “disappear” into the workday world after completing school. In general, their cognitive limitations are camouflaged by good communication and reasonable adaptive skills. Yet abuse/neglect, coexisting development