Developmental trajectories of hierarchical visuo-spatial processing in fragile X syndrome and ASD: Within- and cross-syndrome variability

Background/aims: Despite the advances in understanding visuo-spatial processing in developmental disorders such as ASD and fragile X syndrome (FXS), less is known about the profile of those with a comorbid diagnosis, or the role of within-disorder disparities between individuals across the ASD spectrum. Methods and procedures: Using a developmental trajectory approach, we tested 5 groups of children: Typically developing, FXS, FXS + ASD, ASD individuals who had low-moderate symptoms (HFA) and ASD individuals who had severe symptoms (LFA). Symptoms of ASD were assessed using the Childhood Autism Rating Scale: CARS and hierarchical visuo-spatial processing was assessed using the Navon task. Outcomes and results: Crucially, results differed between HFA and LFA participants. Furthermore, the pattern of results differed between those who had a diagnosis of FXS only and FXS + ASD. Poorer performance within the FXS groups and the group who are low functioning on the ASD spectrum indicated a delayed developmental rate compared to typical controls. Conclusions and implications: This study showed that diagnosis and severity of symptoms are indicative of differences in visuo-spatial processing styles. It is important that heterogeneity within FXS and ASD populations are considered in subsequent studies and look beyond diagnostic group differences. (C) 2015 Elsevier Ltd. All rights reserved.