title: Concept-usage performance: abstraction ability, number of referents, and item familiarity.
mesh_terms: D000293:Adolescent; D002648:Child; D002657:Child Development; D003210:Concept Formation; D004495:Education of Persons with Intellectual Disabilities; D006801:Humans; D008607:Intellectual Disability; D012057:Reinforcement, Verbal; D014705:Verbal Behavior; D014706:Verbal Learning; D014796:Visual Perception