Intellectual Disability

Defining Characteristics

Individuals with ID have intellectual deficits as well as deficits in adaptive functioning in the conceptual, social, and practical domains (APA, 2013).

Deficits in Intellectual Functions

  • Language development
  • Reasoning
  • Problem solving
  • Planning
  • Abstract thinking
  • Judgment
  • Academic learning
  • Learning from experience

Deficits in Adaptive Functioning

  • Failure to meet developmental and sociocultural standards for personal independence and social responsibility
  • Limited functioning in one or more daily life activities (e.g., communication, social participation, and independent living) across settings–in the home, school, work, and community).

The level of support needed for adaptive functioning (i.e., performance of basic life skills) determines the severity level for ID. According to the DSM-5 (APA, 2013), the signs and symptoms of adaptive functioning deficits across domains may include:

Conceptual Domain
  • Slow language development (children learn to talk later, if at all)
  • Slow development of pre-academic skills
  • Difficulties in academic learning (reading, writing, mathematics)
  • Difficulty understanding concepts of time and money
  • Problems with abstract thinking (concrete approach to problem solving)
  • Difficulties in executive function (i.e., planning, strategizing, priority setting, cognitive flexibility)
  • Problems with short-term memory
  • Difficulties with functional use of academic skills such as money management and time management
Social Domain
  • Limitations in language and communication skills
    • More concrete and less complex spoken language (if used), compared with peers
    • Limited vocabulary and grammatical skills
    • Receptive language that may be limited to comprehension of simple speech and gestures
    • Communication that may occur through nonspoken means only—such as gestures, signs, facial expressions, and other forms of augmentative and alternative communication (AAC)
  • Social Skills
    • Immature social judgment and decision making
    • Difficulty understanding peer social cues and social rules
    • Emotional and behavioral regulation difficulties that may adversely affect social interactions
Practical Domain
  • Requiring different levels of support for daily life activities such as
    • Personal care
    • Complex tasks (e.g., shopping, transportation, care organization, meals, money management)
    • Employment
    • Health care and legal decisions
    • Household tasks
    • Recreational skills

Communication Patterns

Individuals with ID and associated language and communication disorders may demonstrate signs and symptoms of spoken and written language disorders across the domains of phonology, morphology and syntax, semantics, and pragmatics. See spoken language disorders and written language disorders (currently under development) for information related to language comprehension and production, multiple modes of communication (e.g., AAC), and behavioral difficulties as well as social and emotional problems experienced by individuals with language disorders.

Individuals with ID are a heterogeneous group; communication abilities vary and may be nonsymbolic (e.g., gestures, vocalizations, problem behaviors) and/or symbolic (e.g., words, signs, pictures). See Communication Characteristics: Selected Populations With an Intellectual Disability for examples of typical communication patterns of individuals with ASD, cerebral palsy, Down syndrome, fetal alcohol syndrome, and Fragile X syndrome, all of which most commonly co-occur with ID.

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