Reduced language processing asymmetry in non-autistic individuals with high levels of autism traits

In the normal population the left hemisphere's predominance for language processing is well established. However, in disorders such as autism atypical patterns of hemispheric lateralisation are common. Given increasing recognition of the idea that autism represents a continuum, we investigated whether the reduced/absent hemispheric asymmetry for language processing extended into the normal population at the upper end of the autism spectrum. A total of 51 participants completed the AQ questionnaire (Baron-Cohen et al., 2001), and a lateralised lexical decision task assessing identification of concrete and abstract words. Based on the clinical finding of decreased hemispheric asymmetry in people with autism, we anticipated reduced hemispheric lateralisation in non-autistic people with higher levels of autism traits. Consistent with prediction, whereas people with lower AQ scores showed a clear right visual field (left hemisphere) advantage for word/nonword discrimination, people with higher AQ scores showed equivalent performance for the left and right visual fields. Our data indicate reduced left hemisphere language dominance in people with higher levels of autism traits, just as people with a clinical diagnosis of autism show atypical lateralisation. Moreover, the data offer further support for the notion that autism is a continuum, rather than a categorical diagnosis, with atypical patterns of hemispheric asymmetry being characteristic of people at the upper end of the spectrum.