This work was supported by a grant from Shalem Fund
The objectives of the present study were to examine the developmental trajectories of crystalline and fluid intelligence and the developmental trajectories of the literal, figurative, and narrative language in adolescents (16-21) and adults (22-40) with mild and moderate non-specific intellectual disability (NSID) (N = 60, IQ = 40-70), compared to individuals with typical development (TD) (N = 60, IQ = 85-115), in the Haredi (ultra-Orthodox) sector, of the same chronological age, in light of three possible trajectories of intelligence development and cognitive ability in the population with ID (Fisher & Zeaman, 1970; Lifshitz-Vahav, 2015) : The Impaired Trajectory, the Stable Trajectory and the continuous- compensatory Trajectory.
Findings regarding crystal intelligence, literal language, and narrative language indicating an increase in grades between adolescence (16–21) and adulthood (22–40) confirm the ‘compensatory age’ theory (Lifshitz; 2020; Lifshitz-Vahav, 2015). Apparently, life experience and maturity help the population with ID in acquiring skills that were absent from the cognitive repertoire.
Another aim was to examine the contribution of the endogenous variables (chronological age, basic cognitive level, gender) and the dependent variables (crystalline and fluid intelligence) to the explanation of the explained variance of language in the two study populations.
The contribution of the fluid intelligence to the three layers of language in a population with TD on the one hand, and the contribution of chronological age and crystalline intelligence to the three layers of language in the population with ID on the other, leads to the conclusion that a population with ID relies more on crystalline intelligence that includes essentially semantic verbal associative knowledge that emerges and evolves with the rise in chronological age, whereas a population with TD relies more on the Fluid intelligence which is more closely related to the g-factor of intelligence, that includes the ability to solve abstract problems that are independent of experience, culture, and learning.
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People with intellectual developmental disabilities
Compensatory Age Theory
Shalem Fund study