Local-global visuospatial processing in Autism Spectrum Disorders and Nonverbal Learning Disabilities: A cross-task and cross-disorder comparison

Visuospatial abilities are considered essential to our interaction with the environment and are involved in many every-day activities (Hegarty & Waller, 2005; Jansen, Wiedenbauer, & Hahn, 2010). A useful way to approach this neuropsychological domain is the global-local paradigm, according to which, people may attend an event using a global processing style, in which they consider the gestalt of a set of stimuli, or a local processing style, in which they focus on details (Forster & Dannenberg, 2010; Navon, 1977; Schooler, 2002). An abundance of research on global versus local processing has revealed preferential processing styles (with a global or local bias) in specific neurodevelopmental disorders, particularly as concerns Autism Spectrum Disorders (ASD) (Caron, Mottron, Dawson, Bertiaume, & Dawson, 2006; Kuschner, Bodner, & Minshew, 2009). Conflicting findings have often emerged in the literature (see for example Van der Hallen, Evers, Brewaeys, Van den Noortgate, & Wagemans, 2015), however, showing that participants with different developmental disorders can process both global and local information, depending on the task requirements and the cognitive domain involved, but in different and atypical ways (Dukette & Stiles, 2001). These results prevent possible generalizations and need to be further explored. Differently, global and local processing styles have never been studied in children with other neurodevelopmental disorders, such as Nonverbal Learning Disabilities (NLD), even though there is evidence to suggest that the issue could be relevant in individuals with NLD as well (Chow & Skuy, 1999). For this reason, cross-task and cross-syndrome comparisons are suggested as the best way to analyze these processing abilities and reveal similarities and differences in global and local processing styles in neurodevelopmental disorders (D’Souza, Booth, Connolly, Happe, & Karmiloff-Smith, 2016). The main aim of this PhD dissertation is to improve our understanding of the role of global and local visuospatial processing in the neuropsychological profile of specific neurodevelopmental disorders, using cross-task and cross-disorder comparisons. Children with ASD without intellectual disability (ID) or NLD were tested in terms of their performance in different domains of visuospatial skills, comparing them with each other and with children who had other neurodevelopmental disorders, such as dyslexia or Attention Deficit Hyperactivity Disorder (ADHD). The assessment focused on visuospatial processing speed, visuo-perceptual and visuo-constructive abilities, visuospatial working memory (VSWM), and their interplay with local and global processing. Based on the modified Block Design Task (BDT) paradigm (Caron et al., 2006), new tasks and stimuli have been devised in order to assess the previously mentioned visuospatial abilities, and four studies have been carried out. Study I aimed to make a cross-task comparison on global-local visuospatial processing in two groups of participants with ASD without ID – with and without a visuospatial peak (–P and –NP) – comparing them with matched typically developing (TD) individuals. The results helped us to clarify the visuospatial profile of the two groups of individuals with ASD, demonstrating the importance of taking specific factors into account (i.e. the visuospatial domains examined and the perceptual reasoning abilities). Participants with ASD-NP performed poorly in all domains, revealing weaker spatial integration abilities in the visuo-perceptual domain and a diminished sensitivity to perceptual coherence in the VSWM, while the ASD-P group used both global and local processing effectively according to the task, and a local bias only emerged in the visuo-constructive task. In agreement with D’Souza and coauthors (2016), our results support the conviction that labelling individuals with ASD as ‘local processors’ is restrictive. They may use both local and global processing styles depending on the demands of the task in hand, the visuospatial domain involved and their cognitive visuospatial functioning. Study II (Chapter 3) aimed to investigate global and local visuospatial processing in children with symptoms of NLD comparing them with children with symptoms of dyslexia and with TD controls. The results showed that children with symptoms of NLD were less accurate in visuo-constructive tasks, while children with symptoms of dyslexia were only slightly impaired in a visuo-constructive task, but clearly slower in the perceptual task. Children with symptoms of NLD were less able to benefit from different levels of coherence of the stimuli, probably as a consequence of their less flexible and efficient visuospatial processes (Mammarella, & Cornoldi, 2005). In particular, the global dominance mechanism (Navon, 1977) made it more complicated for the group with symptoms of NLD to switch from a global to a local processing, which was needed to complete the visuo-constructive task correctly. After investigating the issue of global and local visuospatial processing separately for ASD without ID and NLD, the aim of Study III (Chapter 4) was to draw a cross-disorders comparison, highlighting similarities and differences across three clinical profiles - ASD without ID, NLD and ADHD - as compared with TD controls. Our results revealed different visuospatial profiles for the groups considered, and suggested the utility of manipulating the coherence of stimuli to investigate visuospatial skills. Marked deficit in all the visuospatial domains emerged for the group with NLD, confirming that impairments in the visuospatial domain are core and distinctive symptoms of this disorder (Cornoldi, Mammarella, & Fine, 2016; Semrud-Clikeman, Walkowiak, Wilkinson, & Christopher, 2010). In addition, difficulty in integrating local configurations in a coherent whole emerged for the visuo-perceptual domain. A heterogeneous profile emerged for children with ADHD, which showed, consistently with previous studies, impairment in the visuospatial processing speed domain and in VSWM (Martinussen, Hayden, Hogg-Johnson, & Tannock, 2005; Weigard & Huang-Pollock, 2017). Moreover, these participants presented some difficulties in visuo-constructive abilities when they had to deal with global configurations, while they performed normally in visuo-perceptual task. Differently, participants with ASD performed normally in all the examined domains, using effectively both global and local visuospatial processes, with the sole exception of the visuo-constructive task in which this group showed slower response times and a diminished sensitivity to perceptual coherence (Caron et al., 2006; Shah & Frith, 1993). Finally, since individuals with NLD and those with High Functioning Autism or Asperger Syndrome (DSM-IV TR, American Psychiatric Association [APA], 2000) are often confused, Study IV (Chapter 5) included a further comparison between ASD and NLD. Visuo-constructive abilities and VSWM were investigated in a subgroup of participants with ASD without ID and without a visuospatial peak (ASD-NP) and in a group with NLD. Thus, Study IV aimed to analyze whether ASD-NP – though not representative of the ASD without ID population as a whole– shared any characteristics with the NLD group. Once again, our results differentiate the visuospatial profile of children with NLD from that of children with ASD. The former group showed an impaired performance in all the domains examined affecting both global and local levels of processing. The ASD group had a more heterogeneous profile, with normal performance in VSWM and in the drawing of a complex figure, slower response times in the segmented condition of visuoconstructive BDT and a more local and fragmented drawing style in the recall of a complex figure. Here again, local bias affected the performance of participants with ASD in tasks demanding visuoconstructive skills that specifically involved combining parts to form a single whole (Simic, Khan, & Rovet, 2013). General conclusions derived from the main findings of the four studies, and both clinical and educational implications will be thus highlighted in the final chapter of this dissertation. To conclude, investigating visuospatial abilities and global-local processing in individuals with neurodevelopmental disorders offer crucial insight for the analysis of the strengths and weaknesses of the clinical profiles examined and for their differential diagnosis. There is still space for further research on the domains of visuospatial abilities, and on the general neuropsychological functioning of children with different neurodevelopmental disorders. This dissertation was an effort to raise and clarify some points, however other questions remain open and will require further studies.