Characteristics of shifting ability in children with mild intellectual disabilities: an experimental study with a task-switching paradigm

Background: Shifting enables flexible switch between tasks or mental sets. It is a component of the executive function that plays critical roles in human behaviour control. However, shifting ability in individuals with intellectual disability (ID) has not been well clarified because of the use of intellectually demanding tasks in previous studies. The present study invented a novel shifting task with minimal intellectual demands and aimed to clarify the characteristics of shifting in adolescents with ID. Methods: Adolescents with ID (n = 21) and chronological-age-matched (n = 10) and mental-age-matched controls (n = 33) performed a novel shifting task with simple rule switching (i.e. change in direction). Analyses focused on the switch cost or the increase in the reaction time associated with rule switching. Results: Two subtypes of adolescents with ID were found with respect to the switch cost: one that lacks it and another with an increased switch cost. The lack of a switch cost was unique to the subgroup adolescents with ID and was not indicated in the control group. Conclusions: The present study indicated that shifting in adolescents with ID does not depend solely on their intellectual function and is highly heterogeneous. This finding further implies that executive functions, including shifting, must be evaluated separately from their intellectual functions.