Alterations in Global and Local Visual Processing Is Associated with Autism and Autistic Traits – a Twin Study.

Background:

Autism Spectrum Disorder (ASD) has long been suggested to be associated with altered local and global sensory processing. However, the nature of such alterations remains controversial with theories ranging from a reduced drive to integrate information into a coherent ‘gestalt’ (“weak central coherence”=WCC; Frith, 1989) to enhanced perceptual functioning in local information processing (Mottron et al., 2006) or a more detail-focused processing style (Happé, 1999) in ASD. Findings are largely contradictory, with reports of superior local processing or no differences compared to TD in high-functioning individuals with ASD (Muth et al., 2014) and no local advantage but slower global processing in more heterogeneous ASD-samples (van der Hallen, 2015).

Objectives:

In the light of these contradicting findings the current study aimed to gain more conclusive results by testing alterations in global and local visual processing in association with ASD and autistic traits for the first time in a large and well characterized sample of monozygotic (MZ) and dizygotic (DZ) twins, discordant or concordant for ASD or autistic traits. Using this approach, we implicitly controlled for a vast number of confounding factors – including family background, sex and age. Furthermore, we assessed the impact of genetic vs environmental contributions to this link by comparing MZ (100% genetically identical) and DZ twins (50% shared genes).

Methods:

134 same-sex twin pairs (N=268, 53%male, 63.5%MZ, mean age=16.5+/-5.5, 64 diagnosed with ASD) selected from the Roots of Autism and ADHD Twin Study Sweden (RATSS, Bölte et al., 2014) were included.

The Fragmented Pictures Test (FPT) was used to test the ability to construct a gestalt from incomplete visual information (global processing), measured by amount of visual information needed. The Embedded Figures Test (EFT) was used to test the ability (speed) to detect details while ignoring global information (local processing). Autistic traits were assessed with the Social Responsiveness Scale-2 (SRS). Clinical consensus diagnosis of ASD was supported by diagnostic tools, such as the Autism Diagnostic Interview – Revised (ADI-R), the Autism Diagnostic Observation Schedule Second Edition and medical history.

Conditional linear regressions were conducted to assess the within-twin pair relationships between visual tasks and ASD diagnosis/autistic traits, while controlling for general intellectual abilities using the Wechsler Intelligence Scales.

Results:

Both, ASD diagnosis (Z=2.19, p=0.028) and higher autistic traits (Z=1.97, p=0.048) were associated with the need for more visual information to construct a gestalt in the FPT. There was no difference between MZ and DZ sub-cohorts in this relationship. In contrast, speed of local processing in the EFT was only associated with autistic traits within DZ twins alone (Z=-2.15, p=.031), with twins with higher autistic traits being faster.

Conclusions:

Consistent with the WCC hypothesis, our results confirm the notion of altered global processing (need for more visual information) in ASD and individuals with high autistic traits while implicitly controlling for a large number of confounding factors. In contrast, an association between faster local processing and higher autistic traits was only seen within DZ but not MZ pairs, indicating that the latter effect is under genetic control.