Fine Motor Skills and Unsystematic Spatial Binding in the Common Region Test: Under-Inclusivity in Autism Spectrum Disorder and Over-Inclusivity in Attention-Deficit Hyperactivity Disorder

Introduction: The Common Region Test (CRT) is useful for predicting children’s visual memory as individual object-place binding predicted better object memory while objects-region coding predicted better place memory. Aim: To test children with autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD) with regards to spatial binding in the CRT. Methods: 19 children with ASD and 20 children with ADHD were gender-matched with 39 typically developing children by chronological age and with another 39 children by verbal mental age as control groups (N = 117) and tested with the CRT and Bender Gestalt test. Results: Children with ASD and ADHD showed more unsystematic coding than typically developing children. This was due to lower fine motor skills, and in children with ADHD also because of reduced verbal naming. Almost all children with ASD presented the less mature under-inclusive Type I unsystematic coding which included object-place binding, while children with ADHD showed the over-inclusive Type II unsystematic coding that was overriding the Gestalt-like properties of proximity and similarity. Conclusions: It was demonstrated that the CRT is a useful screening instrument for ASD and ADHD that shows that their spatial categorization varies in their unsystematic visuo-spatial classification due to fine motor skill deficiencies.