Reading ability and neural configurations for verbal and nonverbal information processing

Evolutionary theory suggests that lateralisation sees the execution of verbal and nonverbal information processing in opposite hemispheres to optimise performance (Rogers et al., 2004). More recently, a spectrum of laterality has been characterised by the following neural configurations: (1) a typical configuration where opposite sides of the brain process either type of information (i.e., left for language and right for perception, or the reverse), (2) a mixed configuration where both hemispheres process one type of information and a single hemisphere processes the other, (3) a bilateral configuration where both hemispheres process both types of information, or (4) a crowded configuration where both types of information are processed in a single hemisphere (Lust, Geuze, Groothuis, & Bouma, 2011). Neural configurations of verbal and nonverbal information processing have been underexplored in terms of behavioural impact on tasks which require the concurrent use of these processes, such as reading. With a prevalence of atypical configurations in poor readers already demonstrated (Illingworth & Bishop, 2009), it was predicted that atypical configurations would be most disadvantageous to possess due to a competition for resources within or across hemispheres. The behavioural impact of neural configuration was tested using functional transcranial Doppler ultrasound. Existing Word Generation and Landmark paradigms were used to measure the lateralisation of verbal and nonverbal processing in a large sample (N = 116). A battery of literacy tests measuring phonological skill and retrieval, oral expression, oral reading fluency, spelling, and handwriting was administered. The lateralisation of verbal information processing and oral reading fluency were significantly related; stronger right lateralisation was associated with faster reading. Average readers possessed typical and crowded configurations, while those with bilateral and mixed configurations displayed above-average reading. While this result was unexpected, it provides support for the view that both hemispheres of the brain play a role in the optimal performance of verbal information processing, potentially via the communication enabled by the corpus callosum (Hirnstein et al., 2008).