Abstract
Reading is a complex process, drawing on a variety of brain functions in order to link symbols to words and concepts. The three major brain areas linked to reading and phonological analysis include the left temporoparietal region, the left occipitotemporal region and the inferior frontal gyrus. Decreased activation of the left posterior language system in dyslexia is well documented but there is relatively limited attention given to the role of the right hemisphere. The current study investigated differences in right and left hemisphere activation between individuals with dyslexia and non-impaired readers in lexical decision tasks (regular words, irregular words, pseudowords) during functional Magnetic Resonance Imaging (fMRI). Results revealed the expected hypo-activation in the left posterior areas in those with dyslexia but also areas of overactivation in the right hemisphere. During pseudoword decisions, for example, adults with dyslexia showed more right inferior occipital gyrus activation than controls. In general the increased activation of left-hemisphere language areas found in response to both regular and pseudowords was absent in dyslexics. Laterality indices showed that while controls showed left lateralised activation of the temporal lobe during lexical decision making, dyslexic readers showed right activation. Findings will inform theories of reading and will have implications for the design of reading interventions.
Highlights
Reading is a complex cognitive task which is acquired relatively slowly throughout childhood and requires explicit teaching and effort
Accuracy Scores were subjected to a 2 × 5 Split-Plot Analysis of Variance (ANOVA), with Group as the between-subjects factor and Task as the within-subjects factor
statistical parametric maps (SPMs) observed in participants with dyslexia for each task contrast: letter case judgment; regular word decision; irregular word decision; pseudoword decision
Summary
Reading is a complex cognitive task which is acquired relatively slowly throughout childhood and requires explicit teaching and effort. Prominent computational models of reading, such as the parallel distributed processing (PDP) group of models [3,4,5] posit that orthographic and phonological components operate cooperatively to activate lexical semantics. Regardless of language, depends on a left-lateralized network of frontal, temporoparietal, and occipitotemporal areas of the brain. The IFG is associated with articulation and is involved in phonological processing [10] Activation in this area is positively correlated with reading ability [10]. Both real words and pseudowords are processed within this left hemisphere neural network [11]
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